EP2850152A1 - Mechanism for production of biobased products from plant lignin - Google Patents

Mechanism for production of biobased products from plant lignin

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Publication number
EP2850152A1
EP2850152A1 EP13729124.1A EP13729124A EP2850152A1 EP 2850152 A1 EP2850152 A1 EP 2850152A1 EP 13729124 A EP13729124 A EP 13729124A EP 2850152 A1 EP2850152 A1 EP 2850152A1
Authority
EP
European Patent Office
Prior art keywords
lignin
biomass
caustic
oxidative processing
oxidative
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP13729124.1A
Other languages
German (de)
French (fr)
Inventor
John Peterson
Premaladha PODDUTOORI
Vladimir ROMAKH
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Vertichem Corp
Original Assignee
Vertichem Corp
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Filing date
Publication date
Application filed by Vertichem Corp filed Critical Vertichem Corp
Publication of EP2850152A1 publication Critical patent/EP2850152A1/en
Withdrawn legal-status Critical Current

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08H—DERIVATIVES OF NATURAL MACROMOLECULAR COMPOUNDS
    • C08H6/00—Macromolecular compounds derived from lignin, e.g. tannins, humic acids
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10G—CRACKING HYDROCARBON OILS; PRODUCTION OF LIQUID HYDROCARBON MIXTURES, e.g. BY DESTRUCTIVE HYDROGENATION, OLIGOMERISATION, POLYMERISATION; RECOVERY OF HYDROCARBON OILS FROM OIL-SHALE, OIL-SAND, OR GASES; REFINING MIXTURES MAINLY CONSISTING OF HYDROCARBONS; REFORMING OF NAPHTHA; MINERAL WAXES
    • C10G1/00—Production of liquid hydrocarbon mixtures from oil-shale, oil-sand, or non-melting solid carbonaceous or similar materials, e.g. wood, coal
    • C10G1/08—Production of liquid hydrocarbon mixtures from oil-shale, oil-sand, or non-melting solid carbonaceous or similar materials, e.g. wood, coal with moving catalysts
    • C10G1/086—Characterised by the catalyst used
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10G—CRACKING HYDROCARBON OILS; PRODUCTION OF LIQUID HYDROCARBON MIXTURES, e.g. BY DESTRUCTIVE HYDROGENATION, OLIGOMERISATION, POLYMERISATION; RECOVERY OF HYDROCARBON OILS FROM OIL-SHALE, OIL-SAND, OR GASES; REFINING MIXTURES MAINLY CONSISTING OF HYDROCARBONS; REFORMING OF NAPHTHA; MINERAL WAXES
    • C10G2300/00—Aspects relating to hydrocarbon processing covered by groups C10G1/00 - C10G99/00
    • C10G2300/10—Feedstock materials
    • C10G2300/1011—Biomass
    • C10G2300/1014—Biomass of vegetal origin
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P30/00—Technologies relating to oil refining and petrochemical industry
    • Y02P30/20—Technologies relating to oil refining and petrochemical industry using bio-feedstock

Definitions

  • the present invention is directed generally to a method of production of biobased chemicals from lignin sources, including waste lignin.
  • a method for production may be provided by oxidative processing in the presence of caustic.
  • a method of selectively producing biobased chemicals from lignin sources is also described herein.
  • biomass can be a potentially inexhaustible, domestic, natural resource for the production of energy, transportation fuels, and chemicals.
  • the advantage in use of biomass for such purposes is magnified during an oil crisis, a surge in oil prices, or political unrest within oil producing regions of the world.
  • Biomass includes plant and wood biomass, including agricultural biomass. Biomass can be employed as a sustainable source of energy and is a valuable alternative to fossil fuels. More specifically, the biorefining of biomass into derivative products typically produced from petroleum can help to stop the depletion of petroleum, or at least reduce the current demand and dependence. Biomass can become a key resource for chemical production in much of the world. Biomass, unlike petroleum, is renewable. Biomass can provide sustainable substitutes for petrochemically derived feedstocks used in existing markets.
  • Biomass is made up primarily of cellulose, hemicellulose, and lignin. These components, if economically separated from one another, can provide vital sources of chemicals normally derived from petrochemicals. The use of biomass can also be beneficial with agricultural and/or woody plants that are sparsely used and plant wastes that currently have little or no use. Biomass can provide valuable chemicals and reduce dependence on coal, gas, and fossil fuels, in addition to boosting local and worldwide economies.
  • OrganoSolvTM and Alcell ® processes which are used to efficiently remove the lignin from the other components under mild conditions, kraft pulping, sulfite pulping, pyrolysis, steam explosion, ammonia fiber explosion, dilute acid hydrolysis, alkaline hydrolysis, alkaline oxidative treatment, and enzymatic treatment.
  • Kraft pulping is by far the dominant chemical pulping practiced in the world. However, often the removal of lignin from plant biomass can be a costly process, and some research efforts are now aimed at designing plants that either deposit less lignin or produce lignins that are more amenable to chemical degradation in order to avoid separating the biomass components.
  • Lignin which can comprise about 15% to about 30% of the organic matrix of woody and agricultural biomass, is the most abundant source of aromatic chemicals outside of crude oil. Lignin can be used in developing technologies that transform plant biomass into value-added aromatic chemicals.
  • Lignin has a complex, polymeric structure whose exact structure is unknown.
  • This large group of aromatic polymers in lignin may be a result from the oxidative combinatorial linking of the 4-hydroxyphenyl propanoid building blocks provided by nature.
  • the aromatic portion of these building blocks is composed of 4-hydroxyphenyl, guaiacyl (4-hydroxy-3- methoxyphenyl), and syringyl (4-hydroxyl-3,5-dimethoxyphenyl) units. These units may be abbreviated as H,G, and S, respectively.
  • the lignin itself may also vary in the ratio of these units depending on its source.
  • lignin can be a source of aromatic chemicals outside of the conventional sources of petroleum and coal.
  • Lignin may be obtained from wood and/or agricultural sources as fresh biomass. This wood and/or agricultural lignin may be waste lignin or recovered lignin from these sources. Lignin can also be obtained from multiple sources that utilize plant material, including pulp and paper mills and the sugar cane milling industries. It is also a major by-product in the cellulosic biomass-to-ethanol process. Often, these sources of lignin may be considered waste products where there can be an associated cost to dispose of the lignin instead of alternative methods where this lignin can provide value-added materials.
  • lignin-rich black liquor is burnt in a recovery boiler to recover the spent alkali and to generate heat and power for mill operations.
  • Some of the lignin in black liquor could be precipitated and used for value-added applications, especially since a production bottleneck may exist from the thermal capacity of the recovery boiler.
  • the present invention provides methods of production of biobased chemicals from lignin sources, including waste lignin, in which the end products may be selectively chosen.
  • the present invention may also provide control over lignin bond fragmentation in the selective production of the biobased chemicals.
  • it is an object of the present invention to provide a method for biorefining comprising the steps of providing lignin biomass; treating the lignin biomass using an oxidative process in the presence of caustic; and producing at least one product of from the lignin biomass.
  • the lignin biomass comprises at least one lignin building block of p-coumaryl alcohol, coniferyl alcohol, and sinapyl alcohol.
  • Another object of the present invention is that the lignin biomass is provided from at least one biomass of plant biomass, woody plant biomass, agricultural plant biomass, and cultivated plant biomass.
  • Still another object of the present invention is that the lignin biomass is provided from at least one biomass of fresh plant biomass, recovered plant biomass, pulp and paper mill biomass, cellulosic ethanol refinery biomass, sugar cane mill biomass, commercial plant biomass fractionator biomass, and lignin residues biomass.
  • lignin biomass is provided from kraft pulp mill lignin, sulfite pulp mill lignin, soda pulp mill lignin, cellulosic ethanol refinery lignin, and commercial biomass fractionator lignin.
  • lignin biomass is provided from lignin residue lignin.
  • One object of the present invention is that lignin biomass is provided from waste lignin.
  • waste lignin is provided from at least one waste lignin of recovered biomass, kraft pulp mill waste lignin, sulfite pulp mill waste lignin, soda pulp mill waste lignin, cellulosic ethanol refinery waste lignin, commercial biomass fractionator waste lignin, and sugar cane mill waste lignin.
  • Still another object of the present invention is that oxidative processing in the presence of caustic of lignin biomass is provided by at least one caustic of lithium hydroxide, sodium hydroxide, potassium hydroxide, cesium hydroxide, magnesium hydroxide, barium hydroxide, calcium hydroxide, and carbonates and/or oxides of Group I and Group II metals of the Periodic Table.
  • Still yet another object of the present invention is that oxidative processing in the presence of caustic of lignin biomass is conducted in solvent comprising at least one solvent of water, ethanol, propanol, isopropanol, acetonitrile, and ionic liquids.
  • Yet another object of the present invention is that the oxidative processing in said presence of caustic of lignin biomass is performed at a reaction temperature of about 50 °C to about 300 °C.
  • Still yet another object of the present invention is that the oxidative processing in said presence of caustic of lignin biomass is performed at a reaction temperature of about 100 °C to about 200 °C.
  • Another object of the present invention is that the oxidative processing in the presence of caustic selectively cleaves the ⁇ - ⁇ carbon-carbon bond of a p-coumaryl alcohol, coniferyl alcohol, and/or sinapyl alcohol building block of the lignin biomass.
  • Still another object of the present invention is that the oxidative processing in the presence of caustic provides a caustic-induced carbon-carbon bond fragmentation of the lignin biomass.
  • Yet another object of the present invention is that oxidative processing in the presence of caustic comprises oxidation of a product of the caustic-induced carbon-carbon bond fragmentation of the lignin biomass.
  • Still yet another object of the present invention is that oxidative processing in the presence of caustic provides a caustic-induced carbon-oxygen bond fragmentation of the lignin biomass.
  • oxidative processing in the presence of caustic comprises oxidation of a product of the caustic-induced carbon-oxygen bond fragmentation of the lignin biomass.
  • oxidative processing in the presence of caustic comprises oxidation of a phenolate anion of the lignin biomass.
  • Yet another object of the present invention is that oxidative processing in the presence of caustic provides at least one biobased product which retains about 77% of the structural carbon atoms of the lignin biomass.
  • Still yet another object of the present invention is that oxidative processing in the presence of caustic of lignin biomass is provided from at least one process of batch processing and flow processing.
  • Another object of the present invention is that oxidative processing in the presence of caustic of lignin biomass is provided by at least one process of catalytic oxidative processing and stoichiometric oxidative processing.
  • Still another object of the present invention is that catalytic oxidative processing is provided from at least one catalyst of a metal salt, a metal complex, and an elemental metal.
  • Another object of the present invention is that the catalyst of the catalytic oxidative processing is homogeneous. [0039] Another object of the present invention is that the catalyst of the catalytic oxidative processing is heterogeneous.
  • Another object of the present invention is that the catalyst of the catalytic oxidative processing is supported on an inert solid matrix.
  • Yet another object of the present invention is that oxidative processing in the presence of caustic is provided through catalyst chelation to said phenolate anion of said lignin biomass.
  • Still another object of the present invention is that an oxidant in the
  • stoichiometric oxidative processing comprises an organic nitro compound.
  • Yet another object of the present invention is that the organic nitro compound is a polymer.
  • At least one biobased product from the lignin biomass comprises at least one biobased product of aryl aldehydes and aryl carboxylic acids.
  • At least one biobased product from the lignin biomass comprises at least two biobased products of aryl aldehydes and aryl carboxylic acids.
  • aryl aldehydes and aryl carboxylic acids comprise at least one chemical of commodity chemicals, fine chemicals, and specialty chemicals.
  • aryl aldehydes comprise at least one chemical of 4-hydroxybenzaldehyde, vanillin, and syringaldehyde.
  • aryl carboxylic acids comprise at least one chemical of general molecular structure:
  • Ri is selected from among hydrogen and methoxy.
  • aryl carboxylic acids comprise one chemical of general molecular structure: wherein Ri and R 2 are selected from among hydrogen and methoxy.
  • Still yet another object of the present invention is that aryl carboxylic acids comprise at least one chemical of general molecular structure:
  • R 1; R 2 , and R 3 are selected from among hydrogen and methoxy.
  • Another object of the present invention is that the p-coumaryl alcohol, coniferyl alcohol, and sinapyl alcohol ratio of the lignin biomass regulates the biobased product of lignin biomass provided by oxidative processing in the presence of caustic.
  • Yet another object of the present invention is that it provides a method for biorefining, comprising the steps of: providing lignin biomass comprising at least one biomass of woody plant biomass, agricultural plant biomass, cultivated plant biomass, kraft pulping biomass, sulfite pulping biomass, soda pulping biomass, cellulosic ethanol refinery biomass, sugar cane mill biomass, lignin residue biomass, and waste biomass; treating the lignin biomass by oxidative processing in the presence of caustic; treating the lignin biomass by oxidative processing in the presence of caustic wherein a caustic-induced carbon-carbon bond fragmentation of the lignin biomass occurs; treating the lignin biomass by the oxidative processing in the presence of caustic wherein oxidation of a product of the caustic-induced carbon-carbon bond fragmentation of the lignin biomass occurs; treating the lignin biomass by the oxidative processing in the presence of caustic wherein a caustic-induced carbon-oxygen bond fragment
  • Another object of the present invention is that the product distribution from the process described herein parallels the H:G:S ratio of the lignin itself.
  • Figure 2 schematically illustrates one aspect of the present invention.
  • Figure 4 schematically illustrates one aspect of the present invention.
  • Figure 5 is a flow diagram schematically illustrating another aspect of the present invention.
  • Figure 9 schematically illustrates one aspect of the present invention.
  • Figure 10 schematically illustrates one aspect of the present invention.
  • Figure 13 schematically illustrates one aspect of the present invention.
  • Figure 14 schematically illustrates one aspect of the present invention.
  • Figure 15 schematically illustrates one aspect of the present invention.
  • Figure 16 schematically illustrates one aspect of the present invention.
  • Figure 17 schematically illustrates one aspect of the present invention.
  • Figure 18 schematically illustrates one aspect of the present invention.
  • FIGURE 1 provides a schematic overview where lignin 16 may be provided from various sources.
  • the sources for the lignin 16 may include fresh plant biomass 2, recovered biomass 4, commercial biomass fractionators 6, pulp and paper mills 8, cellulosic ethanol refineries 10, sugar can mills 12, and/or lignin residue biomass 14.
  • Lignin 16 may be a structurally complex, polymeric substance made up of 4- hydroxyphenyl propanoid building blocks containing 4-hydroxyphenyl (abbreviated as H), guaiacyl (4-hydroxy-3-methoxyphenyl) (abbreviated as G), and syringyl (4-hydroxy-3,5- dimethoxyphenyll) units (abbreviated as S).
  • H 4-hydroxyphenyl
  • G guaiacyl
  • S syringyl
  • S syringyl
  • the abundance of each of these units within the lignin 16 may change somewhat between individual plant species for woody lignin, namely lignin content for hardwoods and softwoods, as well as for agricultural sources and both cultivated and uncultivated plants. This difference in the units based on the species for the lignin 16 can control, or at least predict, the amounts and types of chemical products that may be produced within the process described herein.
  • fresh plant biomass 2 may be utilized as a lignin source.
  • Fresh plant biomass 2 may be considered to be biomass from agricultural plants, woody plants, and/or other plant biomass sources.
  • Fresh plant biomass 2 may also include cultivated plant biomass.
  • Fresh plant biomass 2 may be used where it may be grown specifically for this application, which may include, but is not limited to, switchgrass, miscanthus, hybrid eucalyptus trees, and hybrid poplar trees. Some fresh plant biomass 2 not specifically grown for this application may include agricultural or tree harvesting surplus.
  • the lignin 16 can be separated from the other components like cellulose, hemicellulose, and other extractives. After the lignin 16 is separated, it may be added to the process described herein.
  • Sources of recovered biomass 4 may include several biomass waste products.
  • the recovered biomass 4 can include woody biomass like wood chips, sawdust, and/or recovered wood, and/or agricultural plant biomass like wheat straw, rice straw corn stover and/or other agricultural products typically left to rot in the field. Additionally, other plant biomass may also include lawn and tree maintenance byproducts.
  • Another potential source of lignin 16 from recovered biomass 4 may include sugar cane milling. Sugar cane milling may provide lignin 16 since bagasse, or sugarcane waste fiber, can be generated. Bagasse is the name given to the discarded husks of the sugarcane plant after they have been pressed to extract the juices which are refined to make sugar.
  • Recovered biomass 4 may also include other waste products, including at least one waste lignin of sulfite pulping mill waste lignin, kraft pulping mill waste lignin, soda pulping mill waste lignin, and sugar cane mill waste lignin.
  • Both the fresh plant biomass 2 and the recovered biomass 4 may be treated to provide lignin 16 using any of the methods described in U.S. utility applications: A METHOD FOR PRODUCING BIOBASED CHEMICALS FROM PLANT BIOMASS (U.S. Application Number 13/292,222 filed November 9, 2011), A METHOD FOR PRODUCING BIOBASED CHEMICALS FROM WOODY BIOMASS (U.S. Application No. 13/292,437 filed November 9, 2011), A METHOD FOR PRODUCING BIOBASED CHEMICALS FROM
  • Another source of lignin 16 may be commercial biomass fractionators 6.
  • These commercial biomass fractionators 6 can be a thermal and/or mechanical processor which directly inputs raw biomass such as fresh plant biomass 2, woodchips and crop waste and produces multiple component streams, which may include sugars, cellulose, hemicellulose, and lignin 16.
  • One example of a commercial biomass fractionator 6 may be Vertichem Corporation.
  • Pulp and paper mills 8 may also contribute to the lignin 16 from kraft pulping, sulfite pulping, and soda pulping.
  • Lignin 16 can be removed during paper processing in a pulp and paper mills 8, where it is typically viewed as an undesirable component of biomass that requires both energy and chemicals to remove it during the pulping operation.
  • These pulp and paper mills 8 may generally recover the lignin 16 as a by-product of the pulping process and may use it as boiler fuel. This removal of lignin 16 may be done by a chemical removal, with or without mechanical means.
  • Some chemical methods of lignin 16 removal from pulp and paper mills 8 may be kraft pulping, sulfite pulping, and soda pulping.
  • the more dominant chemical pulping technique employed can be kraft processing, which employs high pHs by using considerable amounts of aqueous sodium hydroxide and sodium sulfide at high temperatures to degrade cellulosic biomass into cellulose, hemicellulose, and lignin 16 in a stepwise process.
  • black liquor can be burnt in a recovery boiler to recover the spent alkali and to generate heat and power for mill operations.
  • some of the lignin 16 in black liquor can be precipitated and used for value-added applications where these exist. This conversion to value-added applications may be particularly attractive for a kraft pulping mill where a production bottleneck exists due to the thermal capacity of the recovery boiler.
  • This process may provide kraft lignin.
  • the soda pulp mill may also provide another chemical pulping process where caustic soda can be used to produce pulp. Although it is an old method, it can be effective in separating pulp from wood and grasses.
  • Another source of lignin 16 may also be cellulosic ethanol refineries 10. With the cellulosic ethanol refineries 10, they may produce lignin 16 and other by-products in the cellulosic biomass-to-ethanol process, which can also be used to produce energy required for the ethanol production process. Cellulosic ethanol refineries 10 produce ethanol fuel.
  • the cellulosic ethanol can be made from plant materials like switchgrass, miscanthus, wheat stalks, corn stover, and woody biomass.
  • Cellulosic ethanol refineries 10 may use the OrganoSolvTM process or the Alcell ® process to obtain lignin 16.
  • OrganoSolvTM lignin may be obtained by treatment of fresh plant biomass 2 or bagasse, the fibrous residue that remains after plant material may be treated with various organic solvents.
  • the OrganoSolvTM process may produce separate streams of cellulose, hemicelluloses, and lignin 16. It can be considered environmentally friendly because it may not use the sulfides, sulfites, and harsh conditions used in the kraft or lignosulfonate pulping processes, but it can have a higher cost because of the solvent recovery in this process.
  • Some processes that may be used to separate the biomass to obtain lignin 16 can include any of the methods described in U.S. utility applications: A METHOD FOR PRODUCING BIOBASED CHEMICALS FROM PLANT BIOMASS (U.S. Application Number 13/292,222 filed
  • Another process to obtain lignin 16 that may be used at cellulosic ethanol refineries 10 may include acidic hydrolysis and/or enzymatic reactions.
  • the lignin 16 recovered from the cellulosic ethanol refineries 10 may be used as boiler fuel. Additionally, the lignin 16 recovered from the cellulosic ethanol refineries 10 may undergo a pretreatment prior to entry into the process(es) described herein. The purpose of this lignin pretreatment may be to remove unwanted impurities from the lignin 16 and may include a series of steps to further separate lignin 16 from the other components of biomass such as cellulose and hemicellulose as well as the fats, oils, resins, pitches, waxes, other extractables that may be present in the biomass, or the salts, enzymes, and cellular debris that may be contaminating the lignin from biomass processing.
  • a lignin pretreatment process is described in detail in A
  • sugar cane mills 12 may also provide lignin 16 used in the process described herein.
  • Sugar cane mill mill 12 biomass can include bagasse by-product from sugar cane processing to produce sugar. Bagasse, the fibrous matter that remains after sugarcane or sorghum stalks are crushed to extract their juice, may often be used as a primary fuel source for sugar mills. The bagasse may be burned, producing a sufficient heat energy to supply all the needs of typical sugar cane mills 12. However, there may be an excess of bagasse when the energy supply to the sugar cane mills 12 has been provided.
  • Lignin residue biomass 14 can include lignin residue caustic solution by-product or recovered solid depolymerized lignin residue from tiered biobased chemical and biofuel production described in A METHOD FOR PRODUCING BIOBASED CHEMICALS FROM PLANT LIGNIN (U.S. Application Number 13/453,422 filed April 23, 2012).
  • lignin 16 may be used within the process described to create value-added product(s). Producing these chemicals may provide a reduction in the costs associated with waste disposal of lignin 16 and a means to generate Nincome from biobased chemical production. Besides waste product sources of lignin 16 for the recovered biomass 4, lignin 16 waste from the lignin 16 processing may also provide a source for producing energy.
  • This waste may include recovered plant biomass waste lignin, kraft pulp mill waste lignin, sulfite pulp mill waste lignin, soda pulp mill waste lignin, cellulosic ethanol refinery waste lignin, sugar cane mill waste lignin, and commercial biomass fractionators waste lignin.
  • the waste product of the lignin biomass may be less than 30% of the lignin weight. It may also be less than 20% of the lignin weight. It may also be less than 10% of the lignin weight.
  • These waste products, although reduced, may be used to produce energy which utilizes the waste product, providing value to the process. This energy production may be heat and/or power.
  • FIGURE 2 provides some of the chemical building blocks of lignin 16.
  • Lignin 16 constitutes one of the three major components of lignocellulosic biomass, of which the other two major components are cellulose and hemicellulose.
  • the polymeric structure of lignin 16 can be very complex and a complete structure elucidation of any single lignin is still unknown.
  • the building block compositions of lignin, the extent of polymerization, and the abundance of lignin alter from plant species to plant species. The H:G:S ratio of lignin may then be used
  • a suitable feedstock i.e., a specific plant species, and/or a biomass treatment method, and/or blend of different lignin types
  • This composition may therefore provide control of the composition of the biobased product(s) from lignin 16.
  • the abundance of lignin in plants generally may decrease from softwoods to hardwoods, and also may decrease from hardwoods to grasses.
  • lignin structure can be impacted by the treatment process used to separate lignin from the other components of biomass.
  • Lignin 16 can be an amorphous polymer made up of three phenyl propanoid building blocks shown in Figure 2. These building blocks may differ in the degree of oxygen substitution on the phenyl ring, or in the degree of methoxy substitution on the phenyl ring. In nature, lignin can impart strength and rigidity to the plant by extensive cross linking with polymeric hemicellulose and/or cellulose. [0098] Most plant lignin 16 types may be comprised of all three building blocks shown in Figure 2. Depending on the species of plant, the ratio of these three building blocks may vary. The composition of lignin may frequently be stated in terms of its 4-hydroxyphenyl (H), guaiacyl (G), and sinapyl (S) content.
  • H 4-hydroxyphenyl
  • G guaiacyl
  • S sinapyl
  • aromatic systems can correspond, respectively, to the p- coumaryl alcohol, coniferyl alcohol, and sinapyl alcohol building blocks of lignin.
  • the p- coumaryl alcohol building block may correspond to the p-hydroxyphenyl (H) make-up of lignin. Grassy plants like wheat straw and corn stover may tend to have the highest H contents.
  • Two H- derived oxidation products of lignin may include 4-hydroxybenzaldehyde and 4-hydroxybenzoic acid.
  • the coniferyl alcohol building block may correspond to the guaiacyl (G) make-up of lignin.
  • Two G-derived oxidation products of lignin may include vanillin and vanillic acid.
  • the sinapyl alcohol building block may correspond to the sinapyl (S) make-up of lignin.
  • hardwoods have high S contents, which can often be over 50% where the balance may be comprised predominantly of G. Some examples of hardwoods may include willow and oak.
  • Two S -derived products may include syringaldehyde and syringic acid.
  • Table A may provide normalized H:G:S ratios found in certain lignin 16 by selective ⁇ - ⁇ cleavage lignin oxidative depolymerization cleavage of the C9 phenyl propanoid building blocks (the ⁇ - ⁇ cleavage is described further in Figure 4):
  • FIGURE 3 provides some common linkages and abundances in certain woody softwood and hardwood plants. The chart provides estimates as to the abundance of a particular linkage within some specific species. Although numbers have been provided, these numbers may vary due to other factors which may include but are not limited to lignin treatment, growth rate of the plant, region where growth of the plant occurs, and/or genetic differences of the plant.
  • linkages of these softwoods and hardwoods there may be at least 8 different linkages which may be commonly found. These linkages may include: ⁇ - ⁇ -4, 5-5, ⁇ - 5, 4-0-5, ⁇ -1, ⁇ - ⁇ , spirodienone, and dibenzodioxocin. The abundance of these linkages may be measured by their prevalence per 100 C9 units.
  • the predominant linkage structure in lignin may be a ⁇ - ⁇ -4 linkage. This linkage may account for about 45% to about 60% or more of all linkages in woody lignin. In other types of plant lignin, this number may vary. For example, this linkage may reach about 80% or more in corn stover lignin.
  • the linkage designation of ⁇ - ⁇ -4 can refer to a carbon- oxygen bond between the ⁇ -carbon, which is the central carbon of the propyl side chain of one building block, with the 4-hydroxy group on the phenyl ring of a second lignin phenyl propanoid building block.
  • a ⁇ - ⁇ -4 linkage may occur between and among H, G, and S building blocks.
  • the 5-5 linkage type can refer to a carbon-carbon bond between C-5 positions of two phenyl rings of two different phenyl propanoid building blocks. This linkage type may be common in some softwoods, but may not be as prevalent in some hardwoods. A 5-5 linkage may occur between and among H and G building blocks. A S building block may not enter into a 5-5 linkage because the C-5 position of S is occupied by a methoxy group and prevents this linkage.
  • the ⁇ -5 linkage may also be found in both softwoods and hardwoods.
  • the ⁇ -5 linkage can refer to a carbon-carbon bond between the ⁇ -carbon position of one building block and C-5 position of the phenyl ring of a second building block.
  • a ⁇ -5 linkage may occur between and among H, G, and S building blocks, although the building block comprising the C-5 linkage position may not be S because the C-5 position of S is occupied by a methoxy group and prevents this linkage.
  • the 4-0-5 linkage may be another linkage found in certain woody plants.
  • the 4-0-5 linkage can refer to an ether linkage, which can comprise an oxygen-carbon bond, between a 4-hydroxyphenyl group of one building block with the C-5 position on a phenyl ring of a second building block.
  • a 4-0-5 linkage may occur between and among H, G, and S building blocks, although the building block comprising the C-5 linkage position may not be S because the C-5 position of S is occupied by a methoxy group and prevents this linkage.
  • Another linkage may also include a ⁇ -l linkage.
  • the ⁇ -l linkage can occur through a carbon-carbon bond between the ⁇ -carbon of one building block and position 1 of another phenyl ring.
  • a ⁇ -l linkage may occur between and among H, G, and S building blocks.
  • Yet another linkage may include a ⁇ - ⁇ linkage.
  • a ⁇ - ⁇ linkage can be a carbon- carbon bond between the ⁇ positions of two building blocks, generally leading to a fused bis- furan system. This linkage may occur between any of the three building blocks. This linkage may occur between and among H, G, and S building blocks.
  • Some other linkages may be the spirodienone and dibenzodioxocin linkages.
  • the spirodienone and dibenzodioxocin linkages can be multifunctional linkages. These linkage types, however, may not be seen across all lignin types.
  • the spirodienone linkage may occur with any of the three building blocks, whereas the dibenzodioxocin linkage may only occur with p-coumaryl alcohol and coniferyl alcohol building blocks since the 5-methoxy group of sinapyl alcohol prevents its formation.
  • the spirodienone linkage may occur between and among any of the three building blocks, shereas the biobenzodioxocin linkage may only occur with H or G because the C-5 position of S is occupied by a methoxy group and prevents this linkage.
  • those linkages in Figure 3 may be commonly found linkages in certain woody plants. They are, however, not an exhaustive list of all linkages found. Further, not all linkages can be seen in every lignin type, and the ratio of these linkages may change between different plant species and between different lignin pretreatments even within the same plant species.
  • FIGURE 4 depicts some carbon-carbon and carbon-oxygen bond cleavage strategies for the production of biobased chemicals and/or biofuelsfor the most structurally common ⁇ - ⁇ -4 linkage.
  • Different types of lignin 16 may also have different linkages between the building blocks to make-up the polymeric structure. Determining the quantity of certain linkage types from the lignin 16 source may selectively allow for the production of certain end- products. Especially in the design of an efficient biobased chemical production process, the cleavage of the structural linkages of lignin 16 may be selected such that specific products may be produced.
  • the most common phenyl propanoid linkage type for lignin 16 may be ⁇ - ⁇ -4, which can account for typically about 50% or more of all linkages in lignin 16.
  • the ⁇ - ⁇ -4 linkage can refer to a bond between the ⁇ carbon, which can be the central carbon of the propyl side chain, and the 4-hydroxy group on the aryl ring of a second lignin building block.
  • Other linkages may frequently occur in ligninl6, including 5-5, ⁇ -5, 4-0-5, ⁇ -1, ⁇ - ⁇ , spirodienone and dibenzodioxocin.
  • the ⁇ - ⁇ cleavage which can yield a C8 fragment (phenyl ring with a C2 side chain) and a CI alkyl fragment.
  • the ⁇ - ⁇ cleavage which may yield a C7 fragment (phenyl ring with a CI side chain) and a CI and/or C2 alkyl fragment.
  • the l- ⁇ cleavage which can yield a C6 fragment (phenyl ring) and a CI, C2, and/or C3 alkyl fragment.
  • a few specific examples of biobased chemicals listed in A METHOD FOR PRODUCING BIOBASED CHEMICALS FROM PLANT LIGNIN may include, but are not limited to, certain chemicals.
  • the type of each carbon-carbon cleavage may result in a specified chemical being produced.
  • the chemicals formed may include, but are not limited to, ethylbenzene, styrene, ethylcyclohexane, ethylcyclohexene, 4- hydroxystyrene, 3-methoxy-4-hydroxystyrene, 3,5-dimethoxy-4-hydroxystyrene, 4-ethylphenol, 2-methoxy-4-ethylphenol, 2,6-dimethoxy-4-ethylphenol, l-(4-hydroxyphenyl)ethanone, l-(4- hydroxy-3-methoxyphenyl)ethanone, l-(4-hydroxy-3,5-dimethoxy)ethanone, (4- hydroxyphenyl) acetaldehyde, (4-hydroxy- 3 -methoxyphenyl) acetaldehyde, (4-hydroxy-3 , 5 - dimethoxyphenyl)acetaldehyde
  • the chemicals formed may include, but are not limited to, toluene, methylcyclohexane, methylcyclohexene, 4-methylphenol, 2- methoxy-4-methylphenol, 2,6-dimethoxy-4-methylphenol, , 4-hydroxybenzaldehyde, vanillin, syringaldehyde, 4-hydroxybenzoic acid, vanillic acid, syringic acid, acetic acid, glycolic acid, glyoxylic acid, oxalic acid, and/or formic acid.
  • benzene, phenol, guaiacol, 2,6-dimethoxyphenol , cyclohexane, cyclohexene, propanoic acid, lactic acid, malonic acid, acetic acid, glycolic acid, glyoxylic acid oxalic acid, and/or formic acid may result.
  • multiple carbon-oxygen bond cleavage strategies may also exist since oxygen atom may be present at the a, and/or ⁇ , and/or ⁇ carbons of the propyl side chain, as well as at the 3, and/or 4, and/or 5 positions of the phenyl ring.
  • Figure 4 depicts a ⁇ - ⁇ -4 cleavage since the ⁇ - ⁇ -4 linkage may be the most prevalent linkage structural connection in lignin.
  • a ⁇ - ⁇ -4 cleavage may yield two C9 phenyl propanoids, each with a phenyl ring and a C3 side chain. Additionally carbon-oxygen bond cleavage may occur at the a and ⁇ position of the side chain and at oxygen positions on the phenyl ring.
  • FIGURE 5 provides a method for biobased chemical and/or biofuel production from lignin 16.
  • the products from the lignin biomass may comprise at least one product of biobased chemicalsand lignin residues. At least one of said products from said lignin biomass may also comprise at least two products of biobased chemicalsand lignin residues.
  • the biobased chemicals may comprise at least one chemical of commodity chemicals, fine chemicals, and specialty chemicals.
  • This method may be provided from a type of chemically-induced process, namely ⁇ - ⁇ -lignin oxidative depolymerisation. These chemically-induced processes may occur at a reaction temperature of about 50 °C to about 300 °C, or performed at a reaction temperature of about 100 °C to about 200 °C.
  • lignin 16 Several different methods may be used in the depolymerization of lignin 16. These options may include gasification, pyrolysis, hydrogenolysis, oxidative depolymerization, and/or hydrolysis. Although the methods provided above may allow for depolymerization of lignin 16, some of these methods may provide more selective cracking of the bonds within the lignin 16, allowing for particular chemicals to be produced. Some of these methods may also be more efficient than others. The method may be chosen such that certain biobased chemical(s) may be produced.
  • the gasification of lignin may be one method for depolymerizing lignin.
  • Gasification may degrade the carbocyclic backbone of lignin into low molecular weight gaseous CI products such as hydrogen, carbon monoxide, carbon dioxide and/or methane.
  • gaseous CI products such as hydrogen, carbon monoxide, carbon dioxide and/or methane.
  • these gases may have to be subsequently converted back into aromatic and/or aliphatic compounds by multistep, complex secondary processes.
  • gasification can be used in the production of biobased chemicals, the complex nature of this process may reduce its efficiency when compared to other potential processes.
  • thermolysis may be a pyrolytic procedure performed at temperatures of about 200 °C to about 900 °C and in the absence of air so the lignin structure may be fragmented into smaller molecular weight units without significant combustion into carbon dioxide.
  • the product distribution of thermolysis can be influenced by lignin feedstock type, the heating rate, the final depolymerization temperature, and/or additives.
  • the primary gaseous products of lignin thermolysis may be carbon monoxide, carbon dioxide, and/or methane.
  • the liquid oil fraction may consist of methanol, acetone, acetaldehyde, mono-lignols, and/or mono-phenols and poly- substituted phenols. While the complex composition of the bio-oil can presents the potential for production of chemicals from lignin, the economic separation of pure compounds from this mixture may be a significant economic challenge.
  • thermolysis may provide a considerable amount of water from the dehydration of lignin, many of the volatile products may be water soluble, which can involve an additional step to remove the volatile product(s) from the waste water to prevent environmental pollution.
  • a third method for depolymerizing lignin may be hydrogenolysis, which occurs when pyrolysis occurs in the presence of hydrogen or a hydrogen-donating liquid.
  • Catalysts and solvents may be employed to speed up the depoymerization reaction and may increase the yield of bio-oil.
  • Solvents may include water, ethanol, propanol, isopropanol, acetonitrile, and/or ionic liquids.
  • Typical reaction temperatures for hydrogenolysis may be about 300 °C to about 600 °C, which are lower than the temperatures used in lignin thermolysis.
  • Lignin hydrogenolysis tends to afford a higher net conversion, a higher yield of mono-phenols, and less char formation relative to thermolysis.
  • the obtained bio-oil consists of a mixture of monomeric, dimeric and oligomeric phenolic products.
  • Using hydrogenolysis may provide considerable amounts of the dimeric and/or oligomeric phenolic products, potentially reducing the yield of biobased chemical products.
  • Oxidative depolymerization in the presence of caustic can also be another method for the depolymerization of lignin 16.
  • a mild ⁇ - ⁇ lignin oxidative depolymerisation reaction 18 and/or an extensive ⁇ - ⁇ lignin oxidative depolymerisation reaction 20 may provide an efficient means for lignin 16 depolymerization. These processes break the lignin 16 polymer down into smaller fragments and specific biobased chemicals.
  • Selective ⁇ - ⁇ lignin oxidative depolymerisation may provide entry to at least one chemical of aryl aldehydes 22 and/or aryl carboxylic acids 24.
  • Oxidative lignin depolymerisation may be preferentially conducted in the presence of caustic.
  • caustic may be that the lignin may have a higher solubility under alkaline conditions (high pH).
  • Another benefit of the use of caustic in oxidative lignin depolymerisation may be that it may induce cleavage of certain carbon-oxygen bonds within lignin, and most notably the ⁇ - ⁇ -4 linkage.
  • Yet another benefit of the use of caustic in oxidative lignin depolymerisation may be that it may induce a breaking of certain carbon-carbon bonds within lignin.
  • ⁇ - ⁇ -4 and other cleavages of the lignin backbone may occur along with an ⁇ - ⁇ lignin oxidative depolymerisation.
  • Such caustic-induced lignin cleavage may proceed prior to, in concert with, or subsequent to an ⁇ - ⁇ lignin oxidative depolymerisation.
  • These caustic-induced cleavages may also be conducted as a separate processing step of an ⁇ - ⁇ lignin oxidative depolymerisation.
  • These caustic-induced cleavages may take place within the same reactor as an ⁇ - ⁇ lignin oxidative depolymerisation, or they may be conducted in a separate reactor.
  • Oxidative lignin depolymerisation may utilize metal catalysis.
  • the catalyst for these reactions may be a homogeneous species, or a heterogeneous species, or a mixed metal system, or a metal system supported on an inert solid matrix.
  • the metal catalyst may include, but is not limited to, various salts and complexes of the Periodic Table Group 3 through Group 12 transitions metals, and/or lanthanides, and/or actinides, as well as mixed metal systems thereof.
  • the oxidant for such reactions may be air, oxygen, hydrogen peroxide, organic peroxide, or an organic nitro compound.
  • the reaction processing can be conducted as a batch or flow operation.
  • Aryl aldehydes 22 may be the primary product group of a mild ⁇ - ⁇ lignin oxidative depolymerisation reaction 18.
  • aryl aldehydes 22 that may be produced include at least one chemical of 4-hydroxybenzaldehyde, vanillin and syringaldehyde. These aldehydes may be formed by ⁇ - ⁇ lignin oxidative cleavage of the phenyl propanoid building blocks making up the ⁇ - ⁇ -4, and/or ⁇ -5, and/or ⁇ -l, and/or ⁇ - ⁇ , and/or spirodienone, and/or dibenzodioxocin linkages in lignin.
  • the product yield from such a reaction may be from about 5 weight percent to about 50 weight percent or higher relative to the dried lignin weight.
  • the aryl aldehyde 22 product mix from a mild ⁇ - ⁇ lignin oxidative depolymerisation reaction 18 may generally reflect the H:G:S ratio of the lignin 16, and can be controlled in part by the selection lignin 16 feedstock (i.e., the plant species and/or biomass treatment method). Alternatively, a blend of lignin feedstock may be used to control the product distribution to the desired H:G:S ratio.
  • a lignin 16 of high G content may provide higher levels of vanillin and/or vanillic acid than a lignin 16 of lower G content.
  • lignin 16 highest in H or S content may respectively provide aryl aldehydes 22 (i.e., 4-hydroxybenzaldehyde and 4-hydrobenzoic acid for H, syringaldehyde and syringic acid for S, respectively) corresponding to H or S phenyl ring substitution patterns.
  • aryl aldehydes 22 i.e., 4-hydroxybenzaldehyde and 4-hydrobenzoic acid for H, syringaldehyde and syringic acid for S, respectively
  • Over-oxidation of the formed aryl aldehydes 22 product(s), even under conditions of a mild ⁇ - ⁇ lignin oxidative depolymerisation reaction 18, may lead to certain aryl carboxylic acids 24, and more specifically to at least one chemical of 4-hydroxybenzoic acid, vanillic acid, and syringic acid.
  • Aryl carboxylic acids 24 may be the primary products of extensive ⁇ - ⁇ lignin oxidative depolymerisation reaction 20.
  • the product yield from such a reaction may be from about 25 weight percent to about 100 weight percent relative to the dried lignin weight. More preferably, the product yield may be from about 50 weight percent to about 100 weight percent.
  • the oxidant or catalyst used in an extensive ⁇ - ⁇ lignin oxidative depolymerisation reaction 20 may be a stronger oxidant (i.e., a higher redox potential) than that used in a mild ⁇ - ⁇ lignin oxidative depolymerisation reaction 18.
  • the product mixture of the aryl carboxylic acids 24 may reflect the H:G:S ratio of the Lignin 16, and may be controlled by lignin 16 feedstock selection (i.e., the plant species and/or biomass treatment). Alternatively, a blend of lignin feedstock can be used to control the H:G:S product distribution.
  • the major aryl carboxylic acids 24 products that may be formed by the an extensive ⁇ - ⁇ lignin oxidative depolymerisation reaction 20 are shown in Figure 6.
  • the prevalent products of such an oxidation may be at least one chemical of 4-hydroxybenzoic acid, vanillic acid, and syringic acid.
  • depolymerisation in the presence of caustic may be so advantageous in the preparation of these products is that it may provide the C-7 carbocyclic structure of these products directly, while maximizing utilization of the available carbon atoms that may be provided through nature in lignin, and while minimizing by-products from other lignin cleavage modes that may complicate product quality.
  • selective ⁇ - ⁇ lignin oxidative depolymerisation may provide for an efficient use of the lignin' s carbon utilization.
  • depolymerisation reaction 18 and/or an extensive ⁇ - ⁇ lignin oxidative depolymerisation reaction 20 can range from more than about 90% to less than about 10% of the original amount of lignin 16 entering the process. It may also range from about 50% to about 10% of the original amount of lignin 16 entering the process.
  • Lignin residue can be sent (a) for heat and power generation, and/or (b) for recycling for further use as lignin 16, and/or (c) transformed into tiered biobased chemicals and biofuels as described in A METHOD FOR PRODUCING BIOBASED
  • FIGURE 6 illustrates the aryl carboxylic acids 24 that may be produced by an extensive ⁇ - ⁇ lignin oxidative depolymerisation reaction 20.
  • Figure 7 depicts the extensive ⁇ - ⁇ lignin oxidative lignin depolymerization reaction 20 where aryl carboxylic acids 24 may be the primary products.
  • At least one chemical of 4-hydroxybenzoic acid, vanillic acid, and syringic acid may be formed by ⁇ - ⁇ oxidative cleavage of the phenyl propanoid making up the ⁇ - ⁇ -4, and/or ⁇ -5, and/or ⁇ -l, and/or ⁇ - ⁇ , and/or spirodienone, and/or dibenzodioxocin linkages of lignin.
  • At least one chemical of compounds 4 and 5 may be formed by an extensive ⁇ - ⁇ lignin oxidative depolymerisation reaction 20 of the phenyl propanoid making up a ⁇ -5 linkage.
  • an extensive ⁇ - ⁇ lignin oxidative depolymerisation reaction 20 of the dibenzodioxocin and 5-5 linkages can occur, chemical(s) of compounds 6, 7, and/or 8 may be formed.
  • an extensive ⁇ - ⁇ lignin oxidative depolymerisation reaction 32 of the 4-0-5 linkage may occur at least one chemical of compounds 9-13 as shown in Figure 6 may arise.
  • the abundances of the products shown in Figure 6 may parallel the H:G:S ratio of the lignin 16 and can be influenced by the lignin 16 feedstock (i.e., the plant species) and/or lignin 16 pre-treatment method.
  • the feedstock may be blended with different lignin 16 types to adjust the H:G:S ratio of the lignin 16 and achieve a desired product ratio.
  • FIGURE 7 provides lignin model compounds for mechanistic studies of selective ⁇ - ⁇ lignin oxidative depolymerization in the presence of caustic. Under caustic and oxidative conditions, other investigators have suggested that lignin may undergo a number of potential reactions selected from among, but not limited to:
  • the selective oxidation of lignin to aryl aldehydes 22 and aryl carboxylic acids 24 may be minimally 2-electron and 4-electron oxidative transformations, respectively. Since this process may affect an ⁇ - ⁇ bond cleavage of the phenyl propanoid building block, additional oxidations to the other cleavage segment may potentially occur in parallel to formation of the of aryl aldehydes 22 and/or aryl carboxylic acids 24, which may result in nominally a 4-electron oxidation process.
  • the oxidant for such reactions may be air, oxygen, hydrogen peroxide, organic peroxide, an organic nitro compound, or mixtures thereof.
  • aryl aldehydes 22 may require the use of a mild transitional metal oxidant in order to prevent over oxidation of the aryl aldehydes 22 into aryl carboxylic acids 24.
  • metal systems selected from at least one metal of vanadium, chromium, manganese, iron, cobalt, nickel, and copper may be effective oxidants of lignin.
  • Model 1 may mimic a ⁇ - ⁇ -4 linkage structure in lignin wherein the phenyl ring has a guaiacyl (G) substitution pattern. As such, Model 1 may be open to all the reaction pathways described above. The aryl aldehyde that may be expected from Model 1 is vanillin.
  • Model 2 The lignin model compound labeled as Model 2 may be patterned similarly to that of Model 1, with exception that the ⁇ -hydroxy group is capped as a methyl ether. As such, Model 2 may be open to all of the reaction pathways described above with the exception of the mechanistic pathway involving an oxidation of a ⁇ -hydroxy group followed by a retroaldol reaction to give the aryl aldehyde. If Model 2 should undergo oxidation to give an aryl aldehyde, the product may be vanillin.
  • Model 3 The lignin model compound labeled as Model 3 may also be patterned similarly to that of Model 1, with exception that Model 3 has a meta-phenol substitution pattern and Model 1 the phenol group which is para-oriented with respect to the propyl chain. As such, Model 3 may be open to all of the reaction pathways described above with exception of the mechanistic pathway described as an oxidation of a para-phenolate ring followed by a carbon- carbon bond fragmentation to form an aryl aldehyde.
  • Model 3 may undergo a similar oxidation to Model 1, the aryl aldehyde product of Model 3 may be 3- hydroxybenzaldehyde.
  • Model 4 The lignin model compound labeled as Model 4 can differ from that of Model 1 in that an ethyl group may be substituted in place of the ⁇ -guaiacyl group. As such, Model 4 may not be prone to a ⁇ - ⁇ -4 cleavage in the presence of caustic as is possible with Model 1. Therefore, if either ⁇ - ⁇ -4 cleavage and/or a ⁇ -hydroxy oxidation is on a critical mechanistic path to the aryl aldehydes, Model 4 may not afford vanillin upon oxidation.
  • the epoxides labeled as Model 5 can be potential model compound intermediates of the types of lignin fragment structures that may be formed upon a caustic- induced ⁇ - ⁇ -4 cleavage of lignin.
  • the neighboring a-hydroxy and/or ⁇ -hydroxy group may undergo proton exchange with the caustic.
  • the resulting lignin alkoxide may then promote an intramolecular nucleophilic displacement of the ⁇ -guaiacyl group.
  • These epoxides may be in equilibrium with each other through a Payne rearrangement.
  • Model 5 can provide yet another probe into the importance of ⁇ - ⁇ -4 cleavage in lignin oxidation under caustic conditions. If Model 5 should undergo oxidation to give an aryl aldehyde, the product may be vanillin.
  • FIGURE 8 provides a general reaction for the oxidation of the lignin model compounds, specifically Models 1-4, to aryl aldehydes and aryl acids.
  • Experimental results for the Lignin Model 1-3 reactions are provided in Tables 1-3 below. Additionally, the caustic- induced fragmentation of Model 3 may be more fully explained in Figure 9.
  • Table 4 may provide a comparison of the product distributions from Model 1, 2, and 3 reactions, whereas Table 5 may illustrate data for a competitive oxidation of Models 1 and 3.
  • Table 6 can provide the experimental results for the Lignin Model 4 reactions, and described below and more fully in conjunction with Figure 11. Highlights of these results can be summarized below each respective table.
  • chromatographic peak may provide further structural identity information. Mole % conversions or masses for each product may then be calculated from the chromatographic peak areas.
  • Model 1 results may be found in Table 1 (below). Entries 1-3 indicate that cleavage of a guaiacol group from Model 1 may occur to a significant extent even in the absence of catalyst. Notably, a higher concentration of caustic may not further enhance this reaction. This cleavage may be analogous to that of a caustic-induced depolymerisation of lignin. The net effect of such caustic-induced reaction may be a ⁇ - ⁇ -4 cleavage, although the reaction mechanism may not be discerned from these experiments. Only small amounts of vanillin and vanillic acid may be observed in the absence of catalyst with Model 1, the small amounts of which is formed may be the result of oxidation by the oxygen present in the reaction atmosphere.
  • Entries 4-6 indicate that the presence of iron(II) catalysis alone, and/or iron(III) through oxidation of iron(II) by oxygen, may have a minimal effect on vanillin production. Again, larger amounts of guaiacol and only small amounts of vanillin and vanillic acid may be observed in these reactions. The slight increase in product amounts in entries 5 and 6 may be a result of an extended reaction time or higher caustic concentration. Entries 7-9 may reflect the dramatic influence of copper(II) catalysis in the mild ⁇ - ⁇ lignin oxidative depolymerisation reaction 18 of lignin 16.
  • the low oxidation potential of copper(II) may induce a selective ⁇ - ⁇ cleavage of phenyl propanoid structure of Model 1 and can release vanillin as the product.
  • Separate experiments may demonstrate the oxidation of vanillin into vanillic acid in the presence of copper(II) catalysis.
  • the slightly higher levels of vanillic acid in entries 8 and 11 at longer reaction times may be the result of further oxidation of the vanillin product.
  • the longer reaction time of entry 8 may also provide a somewhat higher product yield of vanillin.
  • the level of guaiacol in entries 7-9 may rise proportionally to the amount of vanillin produced relative to the background experiments in entries 1-3.
  • Entries 10-11 may indicate an incremental increase in vanillin product yield when copper(II) catalysis is coupled with that of iron(II/III).
  • the high selectivity for ⁇ - ⁇ cleavage of phenyl propanoic! structure of Model 1 may be preserved with this mixed catalyst system.
  • the longer reaction time of entry 8 may also provide a somewhat higher product yield.
  • the level of guaiacol in entries 7 and 8 may raise proportional to the amount of vanillin produced relative to the background experiments in entries 1-3.
  • nitrobenzene can be a well-established oxidant for lignin 16.
  • Entry 12 can demonstrate that nitrobenzene oxidation of Model 1 may provide vanillin.
  • the yields for this reaction may be modest relative to copper(II) and/or copper(II)/iron(II,III) catalysis.
  • some findings of the Model 1 study may be:
  • lignin Model 1 may serve as a viable model compound for selective oxidation of lignin to aryl aldehydes 22;
  • caustic-induced ⁇ - ⁇ -4 cleavage of guaiacol may proceed prior to or simultaneous with oxidation of the substrate;
  • a small amount of lignin oxidation may occur with molecular oxygen in the absence of any catalyst
  • copper(II) may be an effective catalyst to induce ⁇ - ⁇ carbon-carbon bond cleavage in lignin phenyl propanoids
  • iron(II/III) alone may be a poor catalyst for lignin oxidation, but when
  • VAN Vanillin
  • VAN Acid Vanillic Acid
  • GUA Guaiacol
  • Model 2 results may show that the experimental result in entry 1 for Model 2 can reflect a dramatic inhibition of caustic-induced guaiacol cleavage relative to Model 1, entries 1-3, Table I.
  • the ⁇ -hydroxy group may be capped as a methyl ether.
  • entry 2 for Model 2 may suggest the presence of iron(II) catalysis alone, and/or iron(III) through oxidation of iron(II) by oxygen, may have a minimal direct role upon vanillin production and/or ⁇ - ⁇ -4 cleavage.
  • Entries 3 and 4 for Model 2 wherein copper(II) catalysis can support an increase in amount of vanillin and guaiacol relative to entry 1 may be analogous to the results observed for Model 1 with exception that the amount of vanillin produced from Model 2 may be about 25% of that from Model 1.
  • Model 2 The lower aqueous solubility of Model 2 relative to Model 1 may be causing at least some of this differential; however, complete solubilisation of Model 2 can be achieved at a substrate concentration of 50 mg (entries 5 and 6) without significant improvement in vanillin yield even at higher catalyst loadings.
  • the study may indicate about 1: 1 ratios of vanillin to guaiacol with Model 4, if not slightly more vanillin than guaiacol, whereas with Model 1 the amount of guaiacol produced nearly always exceeded that of vanillin. This result may be consistent with a faster rate of caustic-induced ⁇ - ⁇ -4 cleavage in Model 1 relative to Model 2.
  • some findings of the Model 2 study may be:
  • capping of the ⁇ -hydroxy group of the phenyl propanoid may dramatically retard the rate of caustic-induced ⁇ - ⁇ -4 cleavage relative to Model 1;
  • a caustic-induced ⁇ - ⁇ -4 cleavage of guaiacol may proceed by more than one reaction pathway;
  • a small amount of lignin oxidation may occur with molecular oxygen in the absence of a catalyst
  • copper(II) may be an effective catalyst to induce ⁇ - ⁇ carbon-carbon bond cleavage in lignin phenyl propanoids
  • Model 3 results in Table 3 may show that 3-hydroxybenzaldehyde may be produced instead of vanillin because of the meta substitution pattern of the phenyl ring.
  • Model 3 may produce very little guaiacol. Indeed, the low yields of caustic-induced guaiacol cleavage from Model 3 may approximate those of Model 2 even though the propyl side chain substitution of Model 3 may be identical to that of Model 1. Therefore, this difference in reactivity of Model 3 and Model 1 may be associated with the phenyl ring substitution pattern.
  • Model 3 the phenolic group may be meta-oriented with respect to the propyl chain, whereas in Model 1 it may be para-oriented.
  • the resonance stabilized phenolate anion of Model 1 may conjugate to the C-l phenyl carbon adjacent to the propyl side chain, whereas in Model 3 the phenolate anion may be cross conjugated to the side chain. Entry 1 in Table 3 therefore may suggest the importance of a para- substituted phenolate anion to the ⁇ - ⁇ -4 cleavage mechanism.
  • This product may be produced by thermally-induced, hemolytic radical fragmentation of the ⁇ carbon-oxygen bond releasing a guaiacyl radical and a secondary alkyl radical.
  • the analogous compound may not be detected with either Model 1 or Model 2, which may suggest a new mechanistic pathway as hypothesized in Figure 9.
  • a mass spectrum for this product is provided in Figure 10.
  • iron(II/III) catalysis alone may have little effect on aryl aldehyde production (entry 2).
  • Entries 3 and 3 can reflect the data for copper(II) and copper(II)/iron(II/III) catalysis.
  • aryl aldehyde i.e., 3- hydroxybenzaldehyde
  • the yields of aryl aldehyde may be significantly diminished relative to the equivalent oxidations of Models 1 and 2.
  • a slight improvement in aryl aldehyde yield can be observed with the mixed catalyst system.
  • the para-phenolate of Models 1 and 2 may play an important role in oxidation.
  • the para-phenolate, or a para- phenolate radical may be resonance conjugated to the propyl side chain, whereas in Model 3 the system may be cross conjugated with the propyl side chain.
  • some findings of the Model 3 study may be:
  • a para-phenolate or para-phenolate radical may be an important component of lignin caustic-induced depolymerisation and/or oxidation;
  • Model 3 may be the least reactive model substrate of Models 1-3; 3. copper(II) may be an effective catalyst to induce ⁇ - ⁇ carbon-carbon bond cleavage in lignin phenyl propanoids; and/or
  • iron(II/III) alone may be a poor catalyst for lignin oxidation, but when
  • 3-HBA 3-Hydroxybenzaldehyde
  • 3-HPDiol l-(3-Hydroxyphenyl)-l,3-propanediol
  • GUA Guaiacol
  • Tables 4 and 5 are also provided to show the comparison of the product distributions from Model 1, 2, and 3 reactions and illustrate data for a competitive oxidation of Models 1 and 3, respectively.
  • a comparison of the entries may demonstrate the change in reactivity between these substrates. Capping the ⁇ -hydroxy group as a methyl ether in Model 2, may reduce its reactivity relative to that of Model 1.
  • Model 3 describes the reaction in which the phenol group occupies a meta position with respect to the propyl side chain.
  • entry 3 may reveal a change in the mechanism of caustic-induced fragmentation of Model 3 relative to that of Models 1 and 2 as evidenced in the commitment formation of 3-HPDiol in proportional amounts to that of GUA.
  • entries 1, 2 and 3 may demonstrate that a ⁇ -hydroxy group and a para-phenol group are both important to caustic-induced lignin depolymerisation. With both Models 2 and 3, the amount of guaiacyl (GUA) formed may be about 10-fold less than that of Model 1.
  • Entries 4, 5, and 6 may demonstrate that iron(II/III) alone are not an effective catalyst for lignin oxidation.
  • Entries 7, 8 and 9 may demonstrate the importance of copper(II) catalysis for selective oxidative cleavage of the lignin ⁇ - ⁇ carbon-carbon bond during aryl aldehyde and/or aryl carboxylic acid formation. Copper(II) alone may be an effective catalyst for this reaction.
  • Entries 10, 11, and 12 may illustrate the beneficial effect of a combination copper(II)/iron(II,III) catalyst system.
  • Entries 4, 5 and 6 may reveal iron(II,III) alone has little effect, the role of iron(II,III) in the combination catalyst is likely to promote the oxidation of copper(I) back to copper(II) by iron(III) per the following set of equations and favourable redox potentials:
  • VAN Vanillin
  • VAN Acid Vanillic Acid
  • 3-HBA 3-Hydroxybenzaldehyde
  • 3- HPDiol l-(3-Hydroxyphenyl)-l,3-propanediol
  • GUA Guaiacol
  • Oxidation of the para-substituted phenol of Model 1 may yield a radical that is resonance stabilized with position- 1 of the phenyl ring.
  • the meta-substituted phenol orientation of Model 3 on the other hand may not yield the same resonance stabilized radical of Model 1 due to cross conjugation.
  • GUA production may be greatly reduced with Model 3 relative to Model 1 (entries 1 and 2, and entries 4 and 5), a result which may suggest a change in the primary caustic-induced cleavage mechanisms between these substrates.
  • a comparison of entries 3 and 6, wherein the reaction contained equal amounts of the two Model substrates may illustrate the preferential oxidation of a para-substituted phenol relative to a meta- substituted phenol. Neither reaction may lead to any detectable 3-HBA. The 3-HBA may only be observed when Model 3 is the only substrate present in the oxidation reaction.
  • VAN Vanillin
  • VAN Acid Vanillic Acid
  • 3-HBA 3-Hydroxybenzaldehyde
  • 3- HPDiol l-(3-Hydroxyphenyl)-l,3-propanediol
  • GUA Guaiacol
  • Model 4 results are shown in Table 6.
  • guaiacol may not be a possible reaction product because R 3 is an ethyl group. As a result, ⁇ - ⁇ -4 cleavage may not occur.
  • the product may be 4- (l-butenyl)guaiacol (BGUA), entry 1.
  • BGUA 4- (l-butenyl)guaiacol
  • the reaction pathway to this product can be depicted in Figure 11.
  • An 1H NMR spectra for the entry 1 reaction mixture under argon is shown in Figure 12.
  • the mass spectrum for the product is provided in Figure 13.
  • a more detailed explanation of plausible mechanistic pathways to form this product are described in Figure 14.
  • Model 4 caustic-induced fragmentation may occur using argon at about 130 °C. This fragmentation is slower at lower temperatures.
  • Entry 2 demonstrates that stoichiometric amounts of copper(II) catalysis may not alone be enough to convert BGUA into vanillin.
  • entry 3 Upon introduction of air alone (entry 3) or air/iron(II/III) (entry 4), a small amount of vanillin can be produced from Model 4, although the amount of BGUA may remain comparable to that of entries 1 and 2.
  • the levels of BGUA in the product composition may be reduced relative to that in entries 1 and 2.
  • an additional amount of vanillin can be formed, suggesting that oxidation of BGUA leads to vanillin.
  • depolymerisation pathways may be at play for this oxidation to occur.
  • VAN Vanillin
  • BGUA 4-(l-Butenyl)guaiacol
  • FIGURE 9 provides a potential mechanism for a caustic-induced fragmentation of lignin Model 3.
  • a reaction product of Model 3 may be l-(3-hydroxyphenyl)-l,3-propanediol (3-HPDiol), and at first appearance looks like it may be a reduction product of Model 3.
  • reaction is conducted in an oxidizing environment (air, and/or catalyst/air) and this product is formed in all examples.
  • FIGURE 10 provides a mass spectrum of the post trimethylsilyl-derivatized 1- (3-hydroxyphenyl)-l,3-propanediol product.
  • the parent ion at 240 mass units may correspond to the mono-trimethylsilyl product.
  • the relatively stronger ions at 166 mass units and 73 mass units, respectively, may correspond to a fragmentation of the 240 mass ion (i.e. 166 mass units may be trimethylsilylphenol and 73 mass units may be the propyl side chain as
  • FIGURE 11 provides a caustic-induced fragmentation and oxidative cleavage of lignin Model 4.
  • Model 4 may be a lignin model substrate in which ⁇ - ⁇ -4 cleavage may not occur since the ⁇ -position of Model 4 can be occupied by an ethyl group (carbon-carbon bond) instead of a phenolic group of another lignin phenyl propanoid building block (carbon-oxygen bond).
  • Model 4 may provide a two-fold insight as to whether: (i) ⁇ - ⁇ -4 cleavage may be a prerequisite to selective ⁇ - ⁇ oxidation of lignin during aromatic aldehyde 20 and/or aromatic carboxylic acid 22 production, and/or (ii) other caustic-induced fragmentation reactions may be occurring in the course of this oxidation reaction.
  • the first step of phenyl propanoid oxidative depolymerization may be a caustic- induced elimination of water from the polymeric molecule, and more specifically, by elimination of water from the ⁇ -hydrogen atom and the a-hydroxy group of the phenyl propanoid side chain. Tarabanko et al suggested this elimination reaction may be a reversible process. If such a reversible elimination/addition process may occur as the first step, the Model 4 substrate may incorporate a deuterium atom at the ⁇ -position. Furthermore, such deuterium atom incorporation may be observable by NMR spectroscopy.
  • Model 4 the predominant process when Model 4 is treated with caustic in the absence of air or catalyst may be illustrated.
  • a caustic-induced reaction may be conducted under argon, no deuterium incorporation may be detected at the ⁇ -position of Model 4 by NMR spectroscopy. Therefore, these experiments may provide a mechanistic pathway, and may teach away from the prior art from Tarabanko et al.
  • a major new product may be formed when Model 4 was treated with caustic in the absence of air or copper(II) catalyst.
  • the 1H NMR spectroscopy and GC-MS analysis of the crude reaction product may support a product arising from a novel and unexpected ⁇ - ⁇ carbon-carbon bond fragmentation.
  • That product may be l-(4-hydroxy-3-methoxyphenyl)-l-butene (BGUA).
  • BGUA l-(4-hydroxy-3-methoxyphenyl)-l-butene
  • Figures 12 and 13 The 1H NMR spectrum and gas chromato graph/mass spectrum of this reaction product are provided in Figures 12 and 13, respectively.
  • Figure 12 may clearly depict the olefinic and ethyl group resonances for BGUA at 6.29, 6.11, 2.12, 1.08 ppm.
  • the mass spectrum of Figure 13 can be consistent with the expected mass (250 mass units) of a post-reaction derivatized trimethylsilyl-BGUA.
  • oxidation of this crude reaction product may contain residual amounts of Model 4 along with 1- (4-hydroxy-3-methoxyphenyl)-l-butene by introduction of a copper(II) catalyst and air into the vessel provided vanillin. Concomitant with the formation of vanillin may be a reduction in the level of l-(4-hydroxy-3-methoxyphenyl)-l-butene.
  • prior art from Tarabanko et al. had reported the oxidation of eugenol to provide vanillin, although these authors never connected the oxidation of eugenol with an unusual caustic-induced fragmentation of a phenyl propanoid in lignin.
  • Eugenol can be structurally similar to l-(4-hydroxy-3-methoxyphenyl)-l-butene, except that the side chain of eugenol may contain one fewer carbon atoms. Vanillin may also be the major product when catalyst and air are introduced into the vessel at the beginning of the reaction. Fourthly, the conversion of Model 4 into vanillin may be dependent upon oxygen. When a reaction conducted in the presence of argon rather than air with a molar ratio of copper(II) catalyst to substrate, the l-(4-hydroxy-3-methoxyphenyl)-l-butene intermediate may not be converted into vanillin.
  • a ⁇ - ⁇ -4 elimination may not be the only pathway for lignin oxidation to aryl aldehydes 20. Further, caustic-induced lignin depolymerisation may proceed by at least one reaction mechanism of ⁇ - ⁇ carbon-carbon bond fragmentation. Also, the
  • intermediate products of a caustic-induced ⁇ - ⁇ carbon-carbon bond fragmentation of lignin may be oxidized to vanillin in a second step to product aryl aldehydes 20.
  • stoichiometric amounts of a catalyst alone may be insufficient to achieve such oxidation.
  • the reaction may require the presence of an added oxidant such as air or oxygen.
  • FIGURE 12 provides an NMR spectrum of a product mixture from a caustic- induced fragmentation of Model 4, which is described in Figures 8 and 11.
  • FIGURE 13 provides a mass spectrum of be 4-(l-butenyl)guaiacol (BGUA), from a caustic-induced fragmentation of Model 4, which is described in Figures 8 and 11.
  • BGUA 4-(l-butenyl)guaiacol
  • FIGURE 14 provides two plausible mechanistic pathways for a caustic-induced ⁇ - ⁇ fragmentation of a lignin phenyl propanoid.
  • Pathways 1 and 2 may differ in the number of steps involved in the fragmentation.
  • Pathway 1 may be a concerted fragmentation whereas Pathway 2 may be a two-step fragmentation mechanism.
  • Either pathway may, in principle, be reversible, although the extent of such reverse reactions is unknown. Thermodynamic and entropic effects may drive the free energy of this fragmentation.
  • the net result of either pathway may be the formation of a 4-hydroxystyrene intermediate, formaldehyde, and water.
  • the electronic -rich nature of the 4-hydroxystyrene intermediate may allow for susceptibility to oxidation.
  • pathway 1 a proton exchange of the ⁇ -hydroxy group with caustic may set up a concerted fragmentation of the resulting ⁇ -alkoxide anion. In the course of the fragmentation process, the caustic may be regenerated.
  • pathway 2 a proton exchange of the phenolic hydroxyl group with caustic may produce a phenolate anion.
  • the ejection of hydroxide anion from the a-carbon may then provide a para-quinone methide intermediate.
  • a subsequent retro- Aldol reaction of the para-quinone methide may serve to achieve a ⁇ - ⁇ fragmentation of a lignin phenyl propanoid.
  • FIGURE 15 provides the mechanism for the oxidation of Model 5 in the presence of caustic. Experimental results for this reaction are provided in Table 7 below.
  • Model 5 may be converted into vanillin in the presence of air and/or air and catalysis.
  • Five products can be detected in this reaction: vanillin (VAN), vanillic acid (VAN Acid), 3,4- dihydro-3-hydroxyguaiacol (3,4-DHGUA), acetovanillone (Ac VAN), and 4-(l- hydroxyethyl)guaiacol) 4-HeGUA.
  • VAN vanillin
  • VAN Acid vanillic acid
  • 3,4-DHGUA 3,4- dihydro-3-hydroxyguaiacol
  • acetovanillone Ac VAN
  • 4-(l- hydroxyethyl)guaiacol) 4-HeGUA 4-HeGUA.
  • VAN vanillin
  • VAN Acid vanillic acid
  • 3,4-DHGUA 3,4- dihydro-3-hydroxyguaiacol
  • Ac VAN acetovanillone
  • Both products may amount to net reduction products.
  • the formation of such products may be the result of base-catalyzed Cannizzaro and related reactions.
  • the structural assignment of 3,4- DHGUA can be considered as tentative based on the mass spectral data shown in Figure 16.
  • the mass of 228 and fragmentations at 213 may be consistent with a post trimethylsilyl-derivatized 3,4-DHGUA.
  • the results obtained herein may point to at least one other possible mechanism for ⁇ - ⁇ -4 cleavage in lignin: intramolecular displacement which may produce an epoxide of which Model 5 mirrors. This mechanistic hypothesis may be further described in Figure 17.
  • VAN Vanillin
  • VAN Acid Vanillic Acid
  • 3,4-DHGUA 3,4-Dihydro-3- hydrox guaiacol
  • AcVan Acetovanillone
  • 4-HeGUA 4-(l-Hydroxyethyl)guaiacol
  • FIGURE 16 provides the mass spectrum of 3,4-DHGUA, which is described in Figures 8 and 15.
  • FIGURE 17 provides some alternate mechanistic pathways for caustic-induced ⁇ - ⁇ -4 cleavage of the phenyl propanoid in lignin wherein secondary products may be produced.
  • at least one other mechanism of lignin cleavage other than ⁇ - ⁇ fragmentation may be occurring in the presence of caustic. This can be evidenced by the formation of guaiacol in caustic reactions of Lignin Models 1, 2, and 3 in the absence of catalyst. If the ⁇ - ⁇ fragmentation were the sole pathway, guaiacol may not necessarily be liberated as a product until post oxidation.
  • Models 1, 2, and 3 the reactions described herein may produce guaiacol. These pathways may include:
  • a phenolate anion assisted opening of the benzylic epoxide ring to product a triol which may then subsequently suffer a caustic-induced ⁇ - ⁇ fragmentation or oxidation to vanillin.
  • Lignin Model 1 any of these pathways may be viable and the production of guaiacol in the control experiments of entries 1 and 2, Table 1 (seen in Figure 8), support the hypothesis.
  • Lignin Model 2 at least one of these ⁇ - ⁇ -4 cleavage pathways may be inhibited since the ⁇ -hydroxy group of Model 2 may be capped by a methoxy group. This may be consistent with the experimental observation of a dramatically reduced yield of guaiacol in entry 1, Table 2 (seen in Figure 8) for Model 2 relative to that for Model 1.
  • Lignin Model 2 may therefore provide experimental evidence for the viability of a proton exchange of the ⁇ -hydroxy group with caustic, followed by intramolecular displacement of guaiacol to produce an epoxide intermediate.
  • Lignin Model 3 may also contain the same propyl side chain substitution pattern as Model 1. Although it may be expected to yield guaiacol in proportional yields to that of the control experiments of Model 1, the meta-phenolate anion of Model 3 may alter the path of these reactions too and vary the yield with respect to Model 1. Instead, homolytic cleavage may be a minor pathway with Model 3. The absence of the guaiacol group in Model 4 may preclude the viability of ⁇ - ⁇ -4 cleavage pathway. As noted in Figure 9, ⁇ - ⁇ fragmentation is the major pathway of caustic-induced reaction with Model 4.
  • Prior art has provided a crystal structure of a vanillin - copper(II) complex.
  • the copper(II) ion is chelated between the phenoxide and methoxy oxygen atoms of two vanillin molecules.
  • the catalyst i.e. Cu 2+
  • Single electron transfer from the electron-rich phenolate ring may then afford a phenoxy radical and a copper(I) species.
  • This radical can be resonance stabilized with conjugation extending to the 1 -position of the phenyl ring, which may be adjacent to the propyl (R) group.
  • the radical can suffer different outcomes, including but not limited to fragmentation, dimerization, hydrogen atom abstraction, etc. to provide the products seen in these reactions.
  • Copper(I) may be oxidized by oxygen or by a co-catalyst iron(III). The overall process may thus be catalytic in the metal species and driven by oxygen as the oxidant.
  • Example 1 Synthesis of Compound 1 [4-0-(tert-Butyldimethylsilyl)vanillin]: To a 250-mL, round-bottomed flask, was added vanillin (10.00 g, 65.72 mmol), ieri-butyldimethylsilyl chloride (11.88 g, 78.84 mmol), imidazole (11.18 g, 164.25 mmol), and dry N,N-dimethylformamide (130 mL) under nitrogen atmosphere, and the reaction stirred at room temperature overnight. The next morning, water was added to quench the reaction and the mixture extracted with
  • Example 2 Synthesis of Compound 2 [Methyl 2-(Methoxy)phenoxyacetate]: To a 250-mL, two-necked, round-bottomed flask equipped with a reflux condenser was added potassium carbonate (20.71 g, 149.84 mmol), acetonitrile (130 mL), methyl bromoacetate (22.92 g, 149.84 mmol), and guaiacol (12.40 g, 99.89 mmol). The reaction was placed under nitrogen atmosphere and refluxed for 2.5 hours. After cooling to room temperature the mixture was filtered.
  • Example 4 Synthesis of Lignin Model 1: To a 250-mL, round-bottomed flask under nitrogen atmosphere were added anhydrous tetrahydrofuran (100 mL), compound 3 (5.00 g, 10.80 mmol), and lithium aluminum hydride (0.82 g, 21.62 mmol). The mixture was stirred at room temperature for 3 hours before cooling to 0 °C and quenching the reaction with a saturated aqueous solution of Rochelle's salt (sodium potassium tartrate). This mixture was then stirred overnight. The product was extracted with ethyl acetate. The combined organic phases were dried of sodium sulfate and concentrated under reduced pressure to give the crude product.
  • anhydrous tetrahydrofuran 100 mL
  • compound 3 5.00 g, 10.80 mmol
  • lithium aluminum hydride 0.82 g, 21.62 mmol
  • Example 7 Synthesis of Lignin Model 2: To a 250-mL, round-bottomed flask under a nitrogen atmosphere was added dry N,N-dimethylformamide (120 mL), compound 5 (9.32 g, 16.98 mmol), and sodium hydride (0.82 g, 34.00 mmol). The mixture was stirred for 15 minutes to generate the sodium alkoxide. To this mixture iodomethane (4.83 g, 34.00 mmol) was added and the stirring continued overnight. After cooling the reaction to 0 °C, glacial acetic acid (25 mL) was added followed by water (100 mL). The product was extracted with ethyl acetate, and the combined organic layers were dried over sodium sulfate and concentrated under reduced pressure to give the crude product. Crude yield: 87%.
  • Example 8 Synthesis of Compound 6 [3-Benzoylbenzaldehyde]: To a 250-mL two-necked, round-bottomed flask equipped with a reflux condenser was added potassium carbonate (17.00 g, 123.00 mmol), acetonitrile (150 mL), benzoyl chloride (23.02 g, 163.76 mmol), and 3- hydroxybenzaldehyde (10.00 g, 81.89 mmol) under nitrogen atmosphere. The reaction was refluxed overnight, and allowed to cool to ambient temperature. The resulting mixture was filtered. The filtrate was washed with a saturated aqueous sodium bicarbonate solution and extracted with dichloromethane.
  • Example 10 Synthesis Lignin Model 3: To a 250-mL, round-bottomed flask under nitrogen was added anhydrous tetrahydrofuran (100 mL), compound 7 (12.03 g, 28.49 mmol), and lithium aluminum hydride (4.33 g, 114.97 mmol). The reaction was stirred for 3 hours before the mixture was cooled to 0 °C and quenched with a saturated aqueous solution of Rochelle salt (sodium potassium tartrate). This mixture was stirred overnight and extracted with ethyl acetate. The combined organic layers were dried over sodium sulfate and concentrated under reduced pressure.
  • anhydrous tetrahydrofuran 100 mL
  • compound 7 (12.03 g, 28.49 mmol
  • lithium aluminum hydride 4.33 g, 114.97 mmol
  • Example 12 - Synthesis of Lignin Model 4 To a 250-mL, round-bottomed flask under nitrogen was added anhydrous tetrahydrofuran (100 mL), compound 8 (13.79 g, 37.42 mmol), and lithium aluminum hydride (2.84 g, 74.84 mmol). The reaction was stirred for 3 hours before cooling to 0 °C and quenching with a saturated aqueous solution of Rochelle salt (sodium potassium tartrate). This mixture was stirred overnight and extracted with ethyl acetate. The combined organic phases were dried sodium sulfate and concentrated under reduced pressure. The crude material was purified by silica gel column chromatography using ethyl
  • Example 14 Synthesis of 10 [l-(4-hydroxy-3-methoxyphenyl)-2-propen-l-ol]: To a 250- mL, round-bottomed flask under nitrogen atmosphere was added anhydrous tetrahydrofuran (50 mL), a 1.0 M solution of tetrabutylammonium fluoride in tetrahydrofuran (15.46 g, 59.13 mmol), and compound 9 (8.72 g, 29.56 mmol). The reaction was stirred for 1 hour before water was added to quench the reaction. The mixture was extracted with ethyl acetate. The combined organic layers were dried over sodium sulfate and concentrated under reduced pressure.
  • Example 15 Synthesis of Lignin Model 5.
  • dichloromethane 150 mL
  • compound 10 5.59 g, 31.02 mmol
  • the solution was cooled to 0 °C before portion wise addition of meta-chloroperoxybenzoic acid (20.00 g, 115.89 mmol).
  • the reaction was then allowed to warm to ambient temperature and was stirred overnight.
  • the reaction was quenched by addition of a 10% sodium thiosulphate solution.
  • the organic phase was washed with saturated aqueous sodium bicarbonate solution, and the aqueous phases re-extracted with dichloromethane.
  • Example 16 General Procedure for Oxidation of Lignin Models in the Presence of Caustic: To a 100-mL, thick-walled, glass pressure tube is charged 6 mL of aqueous sodium hydroxide (100 mg caustic equivalent) and the appropriate model compound. The mixture is magnetically stirred to affect a solution. The indicated concentration of catalyst is then added, the vessel capped under and air atmosphere, and placed into a pre-heated oil bath at 130 °C. The reaction was magnetically stirred for the indicated reaction time at 130 °C. The vessel contents are then allowed to cool, neutralized to pH ⁇ 2with 10% sulfuric acid solution at ambient temperature, and the products extracted with methyl ieri-butyl ether. The product composition (free product and derivatization with N,0-bis(trimethylsilyl)trifluoroacetamide using pyridine as promoter) was analyzed by gas chromatography-mass spectroscopy.
  • aqueous sodium hydroxide 100 mg caustic equivalent

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Abstract

The present invention is directed generally to a method of production of biobased chemicals from lignin sources, including waste lignin. This method may allow for selectively producing biobased chemicals from lignin sources using certain processing methods. The methods for production of these biobased chemicals may be provided by oxidative processing in the presence of a caustic. Further, the oxidative processing, including catalytic oxidative processing and stoichiometric oxidative processing, may also be used. The present invention may also provide control over lignin bond fragmentation in the selective production of the biobased chemicals.

Description

MECHANISM FOR PRODUCTION OF BIOBASED
PRODUCTS FROM PLANT LIGNIN
This application claims priority from U.S. Serial No. 61/646,475, entitled MECHANISM FOR PRODUCTION OF BIOBASED PRODUCTS FROM PLANT LIGNIN, filed May 14, 2012, which is incorporated herein by reference.
I. Background of the Invention
A. Field of Invention
[0001] The present invention is directed generally to a method of production of biobased chemicals from lignin sources, including waste lignin. A method for production may be provided by oxidative processing in the presence of caustic. A method of selectively producing biobased chemicals from lignin sources is also described herein.
B. Description of the Related Art
[0002] The world currently faces depletion of fossil fuels while demands for these fuels are ever increasing. Petrochemicals provide an energy source and a component of the majority of raw materials used in many industries. In fact, approximately 95% of all chemicals manufactured today are derived from petroleum. However, this heavy reliance upon fossil fuels is creating harm to the environment. The burning of these fossil fuels has led to the pollution of air, water and land, as well as global warming and climate changes. Through the use of fossil fuels, the environment has been harmed, perhaps irreparably, in an effort to meet the nearly insatiable demand for energy and manufactured products. Fossil fuels are a finite natural resource. With the depletion of readily available oil reserves across the globe, the supply chain has shifted to more complex and environmentally risky production technologies. A reduction and conservation of fossil fuels is clearly needed. Some alternatives to fossil fuels, like solar power, wind power, geothermal power, hydropower, and nuclear power, are used to a degree. However, a more efficient use of renewable resources is always being sought.
[0003] As a stable and independent alternative to fossil fuels, biomass can be a potentially inexhaustible, domestic, natural resource for the production of energy, transportation fuels, and chemicals. The advantage in use of biomass for such purposes is magnified during an oil crisis, a surge in oil prices, or political unrest within oil producing regions of the world. Biomass includes plant and wood biomass, including agricultural biomass. Biomass can be employed as a sustainable source of energy and is a valuable alternative to fossil fuels. More specifically, the biorefining of biomass into derivative products typically produced from petroleum can help to stop the depletion of petroleum, or at least reduce the current demand and dependence. Biomass can become a key resource for chemical production in much of the world. Biomass, unlike petroleum, is renewable. Biomass can provide sustainable substitutes for petrochemically derived feedstocks used in existing markets.
[0004] Biomass is made up primarily of cellulose, hemicellulose, and lignin. These components, if economically separated from one another, can provide vital sources of chemicals normally derived from petrochemicals. The use of biomass can also be beneficial with agricultural and/or woody plants that are sparsely used and plant wastes that currently have little or no use. Biomass can provide valuable chemicals and reduce dependence on coal, gas, and fossil fuels, in addition to boosting local and worldwide economies.
[0005] In processes separating biomass, several options are available: the
OrganoSolv™ and Alcell® processes which are used to efficiently remove the lignin from the other components under mild conditions, kraft pulping, sulfite pulping, pyrolysis, steam explosion, ammonia fiber explosion, dilute acid hydrolysis, alkaline hydrolysis, alkaline oxidative treatment, and enzymatic treatment. Kraft pulping is by far the dominant chemical pulping practiced in the world. However, often the removal of lignin from plant biomass can be a costly process, and some research efforts are now aimed at designing plants that either deposit less lignin or produce lignins that are more amenable to chemical degradation in order to avoid separating the biomass components.
[0006] Although the cellulosic fraction of biomass has garnered substantial attention recently as a feedstock for ethanol biofuel and other basic chemicals, the intrinsic value of the lignin continues to be largely overlooked. Lignin, which can comprise about 15% to about 30% of the organic matrix of woody and agricultural biomass, is the most abundant source of aromatic chemicals outside of crude oil. Lignin can be used in developing technologies that transform plant biomass into value-added aromatic chemicals.
[0007] Lignin has a complex, polymeric structure whose exact structure is unknown. This large group of aromatic polymers in lignin may be a result from the oxidative combinatorial linking of the 4-hydroxyphenyl propanoid building blocks provided by nature. The aromatic portion of these building blocks is composed of 4-hydroxyphenyl, guaiacyl (4-hydroxy-3- methoxyphenyl), and syringyl (4-hydroxyl-3,5-dimethoxyphenyl) units. These units may be abbreviated as H,G, and S, respectively. The lignin itself may also vary in the ratio of these units depending on its source.
[0008] Because of its make-up, lignin can be a source of aromatic chemicals outside of the conventional sources of petroleum and coal. Lignin may be obtained from wood and/or agricultural sources as fresh biomass. This wood and/or agricultural lignin may be waste lignin or recovered lignin from these sources. Lignin can also be obtained from multiple sources that utilize plant material, including pulp and paper mills and the sugar cane milling industries. It is also a major by-product in the cellulosic biomass-to-ethanol process. Often, these sources of lignin may be considered waste products where there can be an associated cost to dispose of the lignin instead of alternative methods where this lignin can provide value-added materials.
[0009] Another source of lignin is the black liquor produced from kraft pulp mills. In the kraft pulping process, lignin-rich black liquor is burnt in a recovery boiler to recover the spent alkali and to generate heat and power for mill operations. Some of the lignin in black liquor could be precipitated and used for value-added applications, especially since a production bottleneck may exist from the thermal capacity of the recovery boiler.
[0010] The present invention provides methods of production of biobased chemicals from lignin sources, including waste lignin, in which the end products may be selectively chosen. The present invention may also provide control over lignin bond fragmentation in the selective production of the biobased chemicals.
II. Summary of the Invention
[0011] Accordingly, it is an object of the present invention to provide a method for biorefining comprising the steps of providing lignin biomass; treating the lignin biomass using an oxidative process in the presence of caustic; and producing at least one product of from the lignin biomass.
[0012] One object of the present invention is that the lignin biomass comprises at least one lignin building block of p-coumaryl alcohol, coniferyl alcohol, and sinapyl alcohol.
[0013] Another object of the present invention is that the lignin biomass is provided from at least one biomass of plant biomass, woody plant biomass, agricultural plant biomass, and cultivated plant biomass.
[0014] Still another object of the present invention is that the lignin biomass is provided from at least one biomass of fresh plant biomass, recovered plant biomass, pulp and paper mill biomass, cellulosic ethanol refinery biomass, sugar cane mill biomass, commercial plant biomass fractionator biomass, and lignin residues biomass.
[0015] Yet another object of the present invention is that lignin biomass is provided from kraft pulp mill lignin, sulfite pulp mill lignin, soda pulp mill lignin, cellulosic ethanol refinery lignin, and commercial biomass fractionator lignin. [0016] Still yet another object of the present invention is that lignin biomass is provided from lignin residue lignin.
[0017] One object of the present invention is that lignin biomass is provided from waste lignin.
[0018] Another object of the present invention is that waste lignin is provided from at least one waste lignin of recovered biomass, kraft pulp mill waste lignin, sulfite pulp mill waste lignin, soda pulp mill waste lignin, cellulosic ethanol refinery waste lignin, commercial biomass fractionator waste lignin, and sugar cane mill waste lignin.
[0019] Still another object of the present invention is that oxidative processing in the presence of caustic of lignin biomass is provided by at least one caustic of lithium hydroxide, sodium hydroxide, potassium hydroxide, cesium hydroxide, magnesium hydroxide, barium hydroxide, calcium hydroxide, and carbonates and/or oxides of Group I and Group II metals of the Periodic Table.
[0020] Yet another object of the present invention is that oxidative processing in the presence of caustic of lignin biomass is performed with an oxidant selected from at least one oxidant of air, oxygen, hydrogen peroxide, and organic peroxide.
[0021] Still yet another object of the present invention is that oxidative processing in the presence of caustic of lignin biomass is conducted in solvent comprising at least one solvent of water, ethanol, propanol, isopropanol, acetonitrile, and ionic liquids.
[0022] Another object of the present invention is that the oxidative processing in the presence of caustic of lignin biomass is carried out at a reaction pH of about 10 to about 14. [0023] Still another object of the present invention is that the oxidative processing in the presence of caustic of lignin biomass is carried out at a reaction pH of about 12 to about 14.
[0024] Yet another object of the present invention is that the oxidative processing in said presence of caustic of lignin biomass is performed at a reaction temperature of about 50 °C to about 300 °C.
[0025] Still yet another object of the present invention is that the oxidative processing in said presence of caustic of lignin biomass is performed at a reaction temperature of about 100 °C to about 200 °C.
[0026] Another object of the present invention is that the oxidative processing in the presence of caustic selectively cleaves the α-β carbon-carbon bond of a p-coumaryl alcohol, coniferyl alcohol, and/or sinapyl alcohol building block of the lignin biomass.
[0027] Still another object of the present invention is that the oxidative processing in the presence of caustic provides a caustic-induced carbon-carbon bond fragmentation of the lignin biomass.
[0028] Yet another object of the present invention is that oxidative processing in the presence of caustic comprises oxidation of a product of the caustic-induced carbon-carbon bond fragmentation of the lignin biomass.
[0029] Still yet another object of the present invention is that oxidative processing in the presence of caustic provides a caustic-induced carbon-oxygen bond fragmentation of the lignin biomass.
[0030] Another object of the present invention is that oxidative processing in the presence of caustic comprises oxidation of a product of the caustic-induced carbon-oxygen bond fragmentation of the lignin biomass. [0031] Still another object of the present invention is that oxidative processing in the presence of caustic comprises oxidation of a phenolate anion of the lignin biomass.
[0032] Yet another object of the present invention is that oxidative processing in the presence of caustic provides at least one biobased product which retains about 77% of the structural carbon atoms of the lignin biomass.
[0033] Still yet another object of the present invention is that oxidative processing in the presence of caustic of lignin biomass is provided from at least one process of batch processing and flow processing.
[0034] Another object of the present invention is that oxidative processing in the presence of caustic of lignin biomass is provided by at least one process of catalytic oxidative processing and stoichiometric oxidative processing.
[0035] Still another object of the present invention is that catalytic oxidative processing is provided from at least one catalyst of a metal salt, a metal complex, and an elemental metal.
[0036] Yet another object of the present invention is that the catalyst of the catalytic oxidative processing is provided from at least one catalyst of Group 3 through Group 12 transitional elements of the Periodic Table.
[0037] Still yet another object of the present invention is that the catalyst of the catalytic oxidative processing is provided from at least one of the Group 3 through Group 12 transitional elements of the Periodic Table of vanadium, chromium, manganese, iron, cobalt, nickel, and copper.
[0038] Another object of the present invention is that the catalyst of the catalytic oxidative processing is homogeneous. [0039] Another object of the present invention is that the catalyst of the catalytic oxidative processing is heterogeneous.
[0040] Another object of the present invention is that the catalyst of the catalytic oxidative processing is supported on an inert solid matrix.
[0041] Yet another object of the present invention is that oxidative processing in the presence of caustic is provided through catalyst chelation to said phenolate anion of said lignin biomass.
[0042] Still another object of the present invention is that an oxidant in the
stoichiometric oxidative processing comprises an organic nitro compound.
[0043] Yet another object of the present invention is that the organic nitro compound is a polymer.
[0044] Still yet another object of the present invention is that at least one biobased product from the lignin biomass comprises at least one biobased product of aryl aldehydes and aryl carboxylic acids.
[0045] Another object of the present invention is that at least one biobased product from the lignin biomass comprises at least two biobased products of aryl aldehydes and aryl carboxylic acids.
[0046] Still another object of the present invention is that aryl aldehydes and aryl carboxylic acids comprise at least one chemical of commodity chemicals, fine chemicals, and specialty chemicals. [0047] Yet another object of the present invention is that aryl aldehydes comprise at least one chemical of 4-hydroxybenzaldehyde, vanillin, and syringaldehyde.
[0048] Still yet another object of the present invention is that aryl carboxylic acids comprise at least one chemical of 4-hydroxybenzoic acid, vanillic acid, and syringic acid.
[0049] Another object of the present invention is that aryl carboxylic acids comprise at least one chemical of general molecular structure:
wherein Ri and R2 are selected from among hydrogen and methoxy.
[0050] Still another object of the present invention is that aryl carboxylic acids comprise at least one chemical of general molecular structure:
wherein Ri is selected from among hydrogen and methoxy.
[0051] Yet another object of the present invention is that aryl carboxylic acids comprise one chemical of general molecular structure: wherein Ri and R2 are selected from among hydrogen and methoxy.
[0052] Still yet another object of the present invention is that aryl carboxylic acids comprise at least one chemical of general molecular structure:
wherein R1; R2, and R3 are selected from among hydrogen and methoxy.
[0053] Another object of the present invention is that the p-coumaryl alcohol, coniferyl alcohol, and sinapyl alcohol ratio of the lignin biomass regulates the biobased product of lignin biomass provided by oxidative processing in the presence of caustic.
[0054] Still another object of the present invention is that the p-coumaryl alcohol, coniferyl alcohol, and sinapyl alcohol ratio of at least two lignin biomasses regulates the biobased product of lignin biomass provided by oxidative processing in the presence of caustic.
[0055] Yet another object of the present invention is that it provides a method for biorefining, comprising the steps of: providing lignin biomass comprising at least one biomass of woody plant biomass, agricultural plant biomass, cultivated plant biomass, kraft pulping biomass, sulfite pulping biomass, soda pulping biomass, cellulosic ethanol refinery biomass, sugar cane mill biomass, lignin residue biomass, and waste biomass; treating the lignin biomass by oxidative processing in the presence of caustic; treating the lignin biomass by oxidative processing in the presence of caustic wherein a caustic-induced carbon-carbon bond fragmentation of the lignin biomass occurs; treating the lignin biomass by the oxidative processing in the presence of caustic wherein oxidation of a product of the caustic-induced carbon-carbon bond fragmentation of the lignin biomass occurs; treating the lignin biomass by the oxidative processing in the presence of caustic wherein a caustic-induced carbon-oxygen bond fragmentation of the lignin biomass occurs; treating the lignin biomass by the oxidative processing in the presence of caustic wherein oxidation of a product of the caustic-induced carbon-oxygen bond fragmentation of the lignin biomass occurs; treating the lignin biomass by the oxidative processing in the presence of caustic wherein oxidation of a phenolate anion of the lignin biomass occurs; conducting the oxidative processing of the lignin biomass in the presence of caustic to selectively provide at least one biobased product which retains about 77% of the structural carbon atoms of the lignin biomass; treating the lignin biomass by the oxidative processing in the presence of caustic by at least one process of stoichiometric oxidative processing and catalytic oxidative processing; and producing at least one biobased product from the lignin biomass comprising at least one chemical of aryl aldehydes and aryl carboxylic acids; wherein selective production of the biobased product of the lignin biomass occurs.
[0056] Another object of the present invention is that the product distribution from the process described herein parallels the H:G:S ratio of the lignin itself.
[0057] Still another object of the present invention is that the selection of the lignin source can therefore allow for the prediction of a certain product ratio.
[0058] Further, another object of the present invention can be to provide a method for biorefining that is easy to implement and use.
[0059] Still other benefits and advantages of the invention will become apparent to those skilled in the art to which it pertains upon a reading and understanding of the following detailed specification. III. Brief Description of the Drawings
[0060] The invention may take physical form in certain parts and arrangement of parts, a preferred embodiment of which will be described in this specification and illustrated in the accompanying drawings which form a part hereof and wherein:
[0061] Figure 1 is a diagram schematically illustrating lignin sources in the resent invention.
[0062] Figure 2 schematically illustrates one aspect of the present invention.
[0063] Figure 3 schematically illustrates one aspect of the present invention.
[0064] Figure 4 schematically illustrates one aspect of the present invention.
[0065] Figure 5 is a flow diagram schematically illustrating another aspect of the present invention.
[0066] Figure 6 schematically illustrates one aspect of the present invention.
[0067] Figure 7 schematically illustrates one aspect of the present invention.
[0068] Figure 8 schematically illustrates one aspect of the present invention.
[0069] Figure 9 schematically illustrates one aspect of the present invention.
[0070] Figure 10 schematically illustrates one aspect of the present invention.
[0071] Figure 11 schematically illustrates one aspect of the present invention. [0072] Figure 12 schematically illustrates one aspect of the present invention.
[0073] Figure 13 schematically illustrates one aspect of the present invention.
[0074] Figure 14 schematically illustrates one aspect of the present invention.
[0075] Figure 15 schematically illustrates one aspect of the present invention.
[0076] Figure 16 schematically illustrates one aspect of the present invention.
[0077] Figure 17 schematically illustrates one aspect of the present invention.
[0078] Figure 18 schematically illustrates one aspect of the present invention.
IV. Detailed Description of the Invention
[0079] Referring now to the drawings wherein the showings are for purposes of illustrating embodiments of the invention only and not for purposes of limiting the same.
[0080] FIGURE 1 provides a schematic overview where lignin 16 may be provided from various sources. The sources for the lignin 16 may include fresh plant biomass 2, recovered biomass 4, commercial biomass fractionators 6, pulp and paper mills 8, cellulosic ethanol refineries 10, sugar can mills 12, and/or lignin residue biomass 14.
[0081] Lignin 16 may be the most abundant source of aromatic chemicals outside of crude oil and coal. Lignin 16 can be used in developing technologies that transform various sources of biomass and lignin 16 waste into value-added aromatic chemicals. The sources of lignin 16 may include at least one biomass of plant biomass, woody plant biomass, agricultural plant biomass, and cultivated plant biomass. The sources of lignin 16 may include fresh plant biomass 2, recovered biomass 4, commercial biomass fractionators 6, pulp and paper mills 8, cellulosic ethanol refineries 10, sugar can mills 12, and/or lignin residue biomass 14. Although these sources of lignin 16 can be used, these sources of lignin 16 are not limited to only those listed herein. No matter the origin of the lignin 16, any different sources of lignin 16 may be used within the process described herein.
[0082] Lignin 16 may be a structurally complex, polymeric substance made up of 4- hydroxyphenyl propanoid building blocks containing 4-hydroxyphenyl (abbreviated as H), guaiacyl (4-hydroxy-3-methoxyphenyl) (abbreviated as G), and syringyl (4-hydroxy-3,5- dimethoxyphenyll) units (abbreviated as S). The abundance of each of these units within the lignin 16 may change somewhat between individual plant species for woody lignin, namely lignin content for hardwoods and softwoods, as well as for agricultural sources and both cultivated and uncultivated plants. This difference in the units based on the species for the lignin 16 can control, or at least predict, the amounts and types of chemical products that may be produced within the process described herein.
[0083] To begin the process described herein, fresh plant biomass 2 may be utilized as a lignin source. Fresh plant biomass 2 may be considered to be biomass from agricultural plants, woody plants, and/or other plant biomass sources. Fresh plant biomass 2 may also include cultivated plant biomass. Fresh plant biomass 2 may be used where it may be grown specifically for this application, which may include, but is not limited to, switchgrass, miscanthus, hybrid eucalyptus trees, and hybrid poplar trees. Some fresh plant biomass 2 not specifically grown for this application may include agricultural or tree harvesting surplus. Where fresh plant biomass 2 is used, the lignin 16 can be separated from the other components like cellulose, hemicellulose, and other extractives. After the lignin 16 is separated, it may be added to the process described herein.
[0084] Sources of recovered biomass 4 may include several biomass waste products. The recovered biomass 4 can include woody biomass like wood chips, sawdust, and/or recovered wood, and/or agricultural plant biomass like wheat straw, rice straw corn stover and/or other agricultural products typically left to rot in the field. Additionally, other plant biomass may also include lawn and tree maintenance byproducts. Another potential source of lignin 16 from recovered biomass 4 may include sugar cane milling. Sugar cane milling may provide lignin 16 since bagasse, or sugarcane waste fiber, can be generated. Bagasse is the name given to the discarded husks of the sugarcane plant after they have been pressed to extract the juices which are refined to make sugar. This agricultural waste can be very plentiful and may otherwise be burnt or discarded in the sugar cane milling process. Recovered biomass 4 may also include other waste products, including at least one waste lignin of sulfite pulping mill waste lignin, kraft pulping mill waste lignin, soda pulping mill waste lignin, and sugar cane mill waste lignin.
[0085] Both the fresh plant biomass 2 and the recovered biomass 4 may be treated to provide lignin 16 using any of the methods described in U.S. utility applications: A METHOD FOR PRODUCING BIOBASED CHEMICALS FROM PLANT BIOMASS (U.S. Application Number 13/292,222 filed November 9, 2011), A METHOD FOR PRODUCING BIOBASED CHEMICALS FROM WOODY BIOMASS (U.S. Application No. 13/292,437 filed November 9, 2011), A METHOD FOR PRODUCING BIOBASED CHEMICALS FROM
AGRICULTURAL BIOMASS (U.S. Application No. 13/292,531 filed November 9, 2011), and A METHOD FOR PRODUCING BIOBASED CHEMICALS FROM CULTIVATED PLANT BIOMASS (U.S. Application No. 13/292,632 filed November 9, 2011).
[0086] Another source of lignin 16 may be commercial biomass fractionators 6. These commercial biomass fractionators 6 can be a thermal and/or mechanical processor which directly inputs raw biomass such as fresh plant biomass 2, woodchips and crop waste and produces multiple component streams, which may include sugars, cellulose, hemicellulose, and lignin 16. One example of a commercial biomass fractionator 6 may be Vertichem Corporation. Some of these component streams may include lignin 16 streams to produce useful products such as aryl aldehydes, aryl carboxylic acids, aryl esters, aryl ketones, aryl alcohols, aliphatic carboxylic acids, phenols, alkyl phenols, alkenylphenols, benzene, toluene, xylene (collectively, benzene, toluene, and xylene are often referred to as "BTX"), mesitylenes, biaryls, aryl alkanes, aryl alkenes, alkanes, alkenes, cycloalkanes, cycloalkenes, alkyl esters, and performance chemicals. Within the process, the biomass may be treated to yield a highly pure cellulose fraction. Several different methods may be used for the separation, including pH, temperature, and pressure adjustments. A reaction involving enzymes may also be used. Other methods of fractionation may include chemical, mechanical, and biological methods. For instance, the biomass fractionator may separate the cellulose out by hot water treatments, hot alkaline treatments, and/or an alkaline oxidation step. Although the commercial biomass fractionators 6 may provide useful biobased products, they may also produce or leave behind other solids comprising of lignin 16. Instead of becoming a waste product, these lignin 16 solids may be used within the process described herein.
[0087] Pulp and paper mills 8 may also contribute to the lignin 16 from kraft pulping, sulfite pulping, and soda pulping. Lignin 16 can be removed during paper processing in a pulp and paper mills 8, where it is typically viewed as an undesirable component of biomass that requires both energy and chemicals to remove it during the pulping operation. These pulp and paper mills 8 may generally recover the lignin 16 as a by-product of the pulping process and may use it as boiler fuel. This removal of lignin 16 may be done by a chemical removal, with or without mechanical means. Some chemical methods of lignin 16 removal from pulp and paper mills 8 may be kraft pulping, sulfite pulping, and soda pulping.
[0088] The more dominant chemical pulping technique employed can be kraft processing, which employs high pHs by using considerable amounts of aqueous sodium hydroxide and sodium sulfide at high temperatures to degrade cellulosic biomass into cellulose, hemicellulose, and lignin 16 in a stepwise process. In the kraft process, black liquor can be burnt in a recovery boiler to recover the spent alkali and to generate heat and power for mill operations. However, some of the lignin 16 in black liquor can be precipitated and used for value-added applications where these exist. This conversion to value-added applications may be particularly attractive for a kraft pulping mill where a production bottleneck exists due to the thermal capacity of the recovery boiler. This process may provide kraft lignin.
[0089] The sulfite processing yielding lignosulfonates can also be relatively common in the pulp and paper industry. The sulfite process may be conducted between about pH 2 to about pH 12 using sulfite with a counterion. This counterion may be either calcium or magnesium. The product may be soluble in water as well as some highly polar organics and amines.
[0090] The soda pulp mill may also provide another chemical pulping process where caustic soda can be used to produce pulp. Although it is an old method, it can be effective in separating pulp from wood and grasses.
[0091] Another source of lignin 16 may also be cellulosic ethanol refineries 10. With the cellulosic ethanol refineries 10, they may produce lignin 16 and other by-products in the cellulosic biomass-to-ethanol process, which can also be used to produce energy required for the ethanol production process. Cellulosic ethanol refineries 10 produce ethanol fuel. The cellulosic ethanol can be made from plant materials like switchgrass, miscanthus, wheat stalks, corn stover, and woody biomass.
[0092] Cellulosic ethanol refineries 10 may use the OrganoSolv™ process or the Alcell® process to obtain lignin 16. OrganoSolv™ lignin may be obtained by treatment of fresh plant biomass 2 or bagasse, the fibrous residue that remains after plant material may be treated with various organic solvents. The OrganoSolv™ process may produce separate streams of cellulose, hemicelluloses, and lignin 16. It can be considered environmentally friendly because it may not use the sulfides, sulfites, and harsh conditions used in the kraft or lignosulfonate pulping processes, but it can have a higher cost because of the solvent recovery in this process. Some processes that may be used to separate the biomass to obtain lignin 16 can include any of the methods described in U.S. utility applications: A METHOD FOR PRODUCING BIOBASED CHEMICALS FROM PLANT BIOMASS (U.S. Application Number 13/292,222 filed
November 9, 2011), A METHOD FOR PRODUCING BIOBASED CHEMICALS FROM WOODY BIOMASS (U.S. Application No. 13/292,437 filed November 9, 2011), A METHOD FOR PRODUCING BIOBASED CHEMICALS FROM AGRICULTURAL BIOMASS (U.S. Application No. 13/292,531 filed November 9, 2011), and A METHOD FOR PRODUCING BIOBASED CHEMICALS FROM CULTIVATED PLANT BIOMASS (U.S. Application No. 13/292,632 filed November 9, 2011). Another process to obtain lignin 16 that may be used at cellulosic ethanol refineries 10 may include acidic hydrolysis and/or enzymatic reactions.
Typically, the lignin 16 recovered from the cellulosic ethanol refineries 10 may be used as boiler fuel. Additionally, the lignin 16 recovered from the cellulosic ethanol refineries 10 may undergo a pretreatment prior to entry into the process(es) described herein. The purpose of this lignin pretreatment may be to remove unwanted impurities from the lignin 16 and may include a series of steps to further separate lignin 16 from the other components of biomass such as cellulose and hemicellulose as well as the fats, oils, resins, pitches, waxes, other extractables that may be present in the biomass, or the salts, enzymes, and cellular debris that may be contaminating the lignin from biomass processing. A lignin pretreatment process is described in detail in A
METHOD FOR PRODUCING BIOBASED CHEMICALS FROM PLANT BIOMASS (U.S. Application Number 13/292,222 filed November 9, 2011).
[0093] Besides the other sources for lignin 16, sugar cane mills 12 may also provide lignin 16 used in the process described herein. Sugar cane mill mill 12 biomass can include bagasse by-product from sugar cane processing to produce sugar. Bagasse, the fibrous matter that remains after sugarcane or sorghum stalks are crushed to extract their juice, may often be used as a primary fuel source for sugar mills. The bagasse may be burned, producing a sufficient heat energy to supply all the needs of typical sugar cane mills 12. However, there may be an excess of bagasse when the energy supply to the sugar cane mills 12 has been provided.
[0094] Yet another source of lignin 16 may be lignin residue biomass 14. Lignin residue biomass 14 can include lignin residue caustic solution by-product or recovered solid depolymerized lignin residue from tiered biobased chemical and biofuel production described in A METHOD FOR PRODUCING BIOBASED CHEMICALS FROM PLANT LIGNIN (U.S. Application Number 13/453,422 filed April 23, 2012).
[0095] Although several sources for lignin are presented herein, those sources for lignin are not limited to those listed. Any lignin 16 provided may be used within the process described to create value-added product(s). Producing these chemicals may provide a reduction in the costs associated with waste disposal of lignin 16 and a means to generate Nincome from biobased chemical production. Besides waste product sources of lignin 16 for the recovered biomass 4, lignin 16 waste from the lignin 16 processing may also provide a source for producing energy. This waste may include recovered plant biomass waste lignin, kraft pulp mill waste lignin, sulfite pulp mill waste lignin, soda pulp mill waste lignin, cellulosic ethanol refinery waste lignin, sugar cane mill waste lignin, and commercial biomass fractionators waste lignin. In this reduction of waste for the process described herein, the waste product of the lignin biomass may be less than 30% of the lignin weight. It may also be less than 20% of the lignin weight. It may also be less than 10% of the lignin weight. These waste products, although reduced, may be used to produce energy which utilizes the waste product, providing value to the process. This energy production may be heat and/or power.
[0096] FIGURE 2 provides some of the chemical building blocks of lignin 16. Lignin 16 constitutes one of the three major components of lignocellulosic biomass, of which the other two major components are cellulose and hemicellulose. The polymeric structure of lignin 16 can be very complex and a complete structure elucidation of any single lignin is still unknown. The building block compositions of lignin, the extent of polymerization, and the abundance of lignin alter from plant species to plant species. The H:G:S ratio of lignin may then be used
advantageously in the selection of a suitable feedstock (i.e., a specific plant species, and/or a biomass treatment method, and/or blend of different lignin types) for the production of a specific biobased product and/or to achieve a certain ratio of specific biobased products. This composition may therefore provide control of the composition of the biobased product(s) from lignin 16. The abundance of lignin in plants generally may decrease from softwoods to hardwoods, and also may decrease from hardwoods to grasses. Moreover, lignin structure can be impacted by the treatment process used to separate lignin from the other components of biomass.
[0097] Lignin 16 can be an amorphous polymer made up of three phenyl propanoid building blocks shown in Figure 2. These building blocks may differ in the degree of oxygen substitution on the phenyl ring, or in the degree of methoxy substitution on the phenyl ring. In nature, lignin can impart strength and rigidity to the plant by extensive cross linking with polymeric hemicellulose and/or cellulose. [0098] Most plant lignin 16 types may be comprised of all three building blocks shown in Figure 2. Depending on the species of plant, the ratio of these three building blocks may vary. The composition of lignin may frequently be stated in terms of its 4-hydroxyphenyl (H), guaiacyl (G), and sinapyl (S) content. These aromatic systems can correspond, respectively, to the p- coumaryl alcohol, coniferyl alcohol, and sinapyl alcohol building blocks of lignin. First, the p- coumaryl alcohol building block may correspond to the p-hydroxyphenyl (H) make-up of lignin. Grassy plants like wheat straw and corn stover may tend to have the highest H contents. Two H- derived oxidation products of lignin may include 4-hydroxybenzaldehyde and 4-hydroxybenzoic acid. Second, the coniferyl alcohol building block may correspond to the guaiacyl (G) make-up of lignin. Softwoods like spruce and pine, in general, may tend to have the highest G content, often in excess of about 80% of the plant lignin. Two G-derived oxidation products of lignin may include vanillin and vanillic acid. Third, the sinapyl alcohol building block may correspond to the sinapyl (S) make-up of lignin. Typically, hardwoods have high S contents, which can often be over 50% where the balance may be comprised predominantly of G. Some examples of hardwoods may include willow and oak. Two S -derived products may include syringaldehyde and syringic acid. The values provided below in Table A may provide normalized H:G:S ratios found in certain lignin 16 by selective α-β cleavage lignin oxidative depolymerization cleavage of the C9 phenyl propanoid building blocks (the α-β cleavage is described further in Figure 4):
Table A: H:G:S Normalized Percentage Ratios of Various Plant Lignins
10 Poplar ND 37 63
Softwoods
11 Softwood Kraft 8 85 7
12 Black Spruce 7 84 7
Agricultural
13 Wheat Straw, milled only 53 40 7
14 Wheat Straw, alkaline treatment 27 63 10
15 Wheat Straw, acid treatment 45 46 9
16 Rice Straw 33 46 21
17 Corn Stover 40 31 7
* ND = Not detected and/or not reported
Based on the lignin provided, the product distribution may parallel the H:G:S ratio. Selection of the lignin source may therefore allow for the prediction of a certain product ratio. For example, if high levels of G-derived products are desired, then a lignin composition of high G content may be preferred. These high-level of G-derived products may be obtained from either a specific lignin, which may include a specific plant species or biomass pretreatment method, that may provide a lignin of high G content and/or a blend of different lignin forms such that the blend has the desired G content.
[0099] Besides the different H:G:S ratios from the different species, there may also be a difference in the H:G:S ratio after the biomass pretreatment method, even within the same plant species species (see Table A wheat straw entries 13-15). For these different plant species and also lignin obtained from different biomass pretreatment methods, many different chemical linkages may occur between the three building blocks. Some of these common linkages may be seen in Figure 3.
[0100] No matter the lignin 16 source or type of treatment, the polymeric structure of lignin may be complex and a complete structure for any single lignin is unknown. Further, samples of lignin obtained from a single lignin source may also differ in its polymeric structure, providing variable building block compositions even within the same sample. [0101] FIGURE 3 provides some common linkages and abundances in certain woody softwood and hardwood plants. The chart provides estimates as to the abundance of a particular linkage within some specific species. Although numbers have been provided, these numbers may vary due to other factors which may include but are not limited to lignin treatment, growth rate of the plant, region where growth of the plant occurs, and/or genetic differences of the plant.
[0102] For the lignin linkages of these softwoods and hardwoods, there may be at least 8 different linkages which may be commonly found. These linkages may include: β-Ο-4, 5-5, β- 5, 4-0-5, β-1, β-β, spirodienone, and dibenzodioxocin. The abundance of these linkages may be measured by their prevalence per 100 C9 units.
[0103] The predominant linkage structure in lignin may be a β-Ο-4 linkage. This linkage may account for about 45% to about 60% or more of all linkages in woody lignin. In other types of plant lignin, this number may vary. For example, this linkage may reach about 80% or more in corn stover lignin. The linkage designation of β-Ο-4 can refer to a carbon- oxygen bond between the β-carbon, which is the central carbon of the propyl side chain of one building block, with the 4-hydroxy group on the phenyl ring of a second lignin phenyl propanoid building block. A β-Ο-4 linkage may occur between and among H, G, and S building blocks.
[0104] Another notable linkage may be the 5-5 linkage. The 5-5 linkage type can refer to a carbon-carbon bond between C-5 positions of two phenyl rings of two different phenyl propanoid building blocks. This linkage type may be common in some softwoods, but may not be as prevalent in some hardwoods. A 5-5 linkage may occur between and among H and G building blocks. A S building block may not enter into a 5-5 linkage because the C-5 position of S is occupied by a methoxy group and prevents this linkage.
[0105] The β-5 linkage may also be found in both softwoods and hardwoods. The β-5 linkage can refer to a carbon-carbon bond between the β-carbon position of one building block and C-5 position of the phenyl ring of a second building block. A β-5 linkage may occur between and among H, G, and S building blocks, although the building block comprising the C-5 linkage position may not be S because the C-5 position of S is occupied by a methoxy group and prevents this linkage.
[0106] The 4-0-5 linkage may be another linkage found in certain woody plants. The 4-0-5 linkage can refer to an ether linkage, which can comprise an oxygen-carbon bond, between a 4-hydroxyphenyl group of one building block with the C-5 position on a phenyl ring of a second building block. A 4-0-5 linkage may occur between and among H, G, and S building blocks, although the building block comprising the C-5 linkage position may not be S because the C-5 position of S is occupied by a methoxy group and prevents this linkage.
[0107] Another linkage may also include a β-l linkage. The β-l linkage can occur through a carbon-carbon bond between the β-carbon of one building block and position 1 of another phenyl ring. A β-l linkage may occur between and among H, G, and S building blocks.
[0108] Yet another linkage may include a β-β linkage. A β-β linkage can be a carbon- carbon bond between the β positions of two building blocks, generally leading to a fused bis- furan system. This linkage may occur between any of the three building blocks. This linkage may occur between and among H, G, and S building blocks.
[0109] Some other linkages, although not as common or prevalent as some of the aforementioned linkages, may be the spirodienone and dibenzodioxocin linkages. The spirodienone and dibenzodioxocin linkages can be multifunctional linkages. These linkage types, however, may not be seen across all lignin types. The spirodienone linkage may occur with any of the three building blocks, whereas the dibenzodioxocin linkage may only occur with p-coumaryl alcohol and coniferyl alcohol building blocks since the 5-methoxy group of sinapyl alcohol prevents its formation. The spirodienone linkage may occur between and among any of the three building blocks, shereas the biobenzodioxocin linkage may only occur with H or G because the C-5 position of S is occupied by a methoxy group and prevents this linkage. [0110] To note, those linkages in Figure 3 may be commonly found linkages in certain woody plants. They are, however, not an exhaustive list of all linkages found. Further, not all linkages can be seen in every lignin type, and the ratio of these linkages may change between different plant species and between different lignin pretreatments even within the same plant species.
[0111] FIGURE 4 depicts some carbon-carbon and carbon-oxygen bond cleavage strategies for the production of biobased chemicals and/or biofuelsfor the most structurally common β-Ο-4 linkage. Different types of lignin 16 may also have different linkages between the building blocks to make-up the polymeric structure. Determining the quantity of certain linkage types from the lignin 16 source may selectively allow for the production of certain end- products. Especially in the design of an efficient biobased chemical production process, the cleavage of the structural linkages of lignin 16 may be selected such that specific products may be produced.
[0112] The most common phenyl propanoid linkage type for lignin 16 may be β-Ο-4, which can account for typically about 50% or more of all linkages in lignin 16. The β-Ο-4 linkage can refer to a bond between the β carbon, which can be the central carbon of the propyl side chain, and the 4-hydroxy group on the aryl ring of a second lignin building block. Other linkages may frequently occur in ligninl6, including 5-5, β-5, 4-0-5, β-1, β-β, spirodienone and dibenzodioxocin. However, not all linkages may be seen in every lignin 16 type, and the ratio of these linkages can change between the different lignins 16. The four potential carbon-carbon bond cleavages of a C9 phenyl propanoid backbone shown in Figure 4 are:
1. No carbon-carbon cleavage, which may leave a C9 fragment (phenyl ring with a C3 side chain).
2. The β-γ cleavage, which can yield a C8 fragment (phenyl ring with a C2 side chain) and a CI alkyl fragment.
3. The α-β cleavage, which may yield a C7 fragment (phenyl ring with a CI side chain) and a CI and/or C2 alkyl fragment. 4. The l-α cleavage, which can yield a C6 fragment (phenyl ring) and a CI, C2, and/or C3 alkyl fragment.
[0113] A few specific examples of biobased chemicals listed in A METHOD FOR PRODUCING BIOBASED CHEMICALS FROM PLANT LIGNIN (U.S. Application Number 13/453,422 filed April 23, 2012) may include, but are not limited to, certain chemicals. In particular, the type of each carbon-carbon cleavage may result in a specified chemical being produced. For no carbon-carbon cleavage, the resulting chemicals may include, but are not limited to, propylbenzene, 1 -phenyl- 1-propene, l-phenyl-2-propene, propylcyclohexane, propylcyclohexene, eugenol, isoeugenol, syringeugenol, iso-syringeugonol, propylcyclohexane, 4-propylphenol, 2-methoxy-4-propylphenol, 2,6-dimethoxy-4-hydroxyphenol, 3-(4- hydroxyphenyl)propionic acid, 3-(4-hydroxy-3-methoxyphenyl)propionic acid, 3-(4-hydroxy- 3,5-dimethoxyphenyl)propionic acid, 3-(4-hydroxyphenyl)propionaldehyde, 3-(4-hydroxy-3- methoxyphenyl)propionaldehyde, 3-(4-hydroxy-3,5-dimethoxyphenyl)propionaldehyde, 4- hydroxycinnamic acid, 4-hydroxy-3-methoxycinnamic acid, and/or 4-hydroxy-3,5- dimethoxycinnamic acid. For a β-γ carbon-carbon cleavage, the chemicals formed may include, but are not limited to, ethylbenzene, styrene, ethylcyclohexane, ethylcyclohexene, 4- hydroxystyrene, 3-methoxy-4-hydroxystyrene, 3,5-dimethoxy-4-hydroxystyrene, 4-ethylphenol, 2-methoxy-4-ethylphenol, 2,6-dimethoxy-4-ethylphenol, l-(4-hydroxyphenyl)ethanone, l-(4- hydroxy-3-methoxyphenyl)ethanone, l-(4-hydroxy-3,5-dimethoxy)ethanone, (4- hydroxyphenyl) acetaldehyde, (4-hydroxy- 3 -methoxyphenyl) acetaldehyde, (4-hydroxy-3 , 5 - dimethoxyphenyl)acetaldehyde, (4-hydroxyphenyl) acetic acid, homovanillic acid, homosyringic acid, and/or formic acid. For an α-β carbon-carboncleavage, the chemicals formed may include, but are not limited to, toluene, methylcyclohexane, methylcyclohexene, 4-methylphenol, 2- methoxy-4-methylphenol, 2,6-dimethoxy-4-methylphenol, , 4-hydroxybenzaldehyde, vanillin, syringaldehyde, 4-hydroxybenzoic acid, vanillic acid, syringic acid, acetic acid, glycolic acid, glyoxylic acid, oxalic acid, and/or formic acid. With an 1-a carbon-carbon cleavage, benzene, phenol, guaiacol, 2,6-dimethoxyphenol , cyclohexane, cyclohexene, propanoic acid, lactic acid, malonic acid, acetic acid, glycolic acid, glyoxylic acid oxalic acid, and/or formic acid may result. [0114] Likewise, multiple carbon-oxygen bond cleavage strategies may also exist since oxygen atom may be present at the a, and/or β, and/or γ carbons of the propyl side chain, as well as at the 3, and/or 4, and/or 5 positions of the phenyl ring. For instance, Figure 4 depicts a β-Ο-4 cleavage since the β-Ο-4 linkage may be the most prevalent linkage structural connection in lignin. A β-Ο-4 cleavage may yield two C9 phenyl propanoids, each with a phenyl ring and a C3 side chain. Additionally carbon-oxygen bond cleavage may occur at the a and γ position of the side chain and at oxygen positions on the phenyl ring.
[0115] FIGURE 5 provides a method for biobased chemical and/or biofuel production from lignin 16. The products from the lignin biomass may comprise at least one product of biobased chemicalsand lignin residues. At least one of said products from said lignin biomass may also comprise at least two products of biobased chemicalsand lignin residues. The biobased chemicals may comprise at least one chemical of commodity chemicals, fine chemicals, and specialty chemicals. This method may be provided from a type of chemically-induced process, namely α-β-lignin oxidative depolymerisation. These chemically-induced processes may occur at a reaction temperature of about 50 °C to about 300 °C, or performed at a reaction temperature of about 100 °C to about 200 °C. Further, the chemical-induced processing can induced by caustic, including, at least one caustic of lithium hydroxide, sodium hydroxide, potassium hydroxide, cesium hydroxide, magnesium hydroxide, barium hydroxide, calcium hydroxide, and carbonates and oxides of Group I and Group II metals of the Periodic Table. In Figure 4, lignin 16 may be first subjected to a mild α-β lignin oxidative depolymerisation reaction 18 and extensive α-β lignin oxidative depolymerisation reaction 20. These lignin oxidative
depolymerization steps, whether mild or extensive, can break the lignin 16 polymer down into smaller fragments and specific biobased chemicals.
[0116] Several different methods may be used in the depolymerization of lignin 16. These options may include gasification, pyrolysis, hydrogenolysis, oxidative depolymerization, and/or hydrolysis. Although the methods provided above may allow for depolymerization of lignin 16, some of these methods may provide more selective cracking of the bonds within the lignin 16, allowing for particular chemicals to be produced. Some of these methods may also be more efficient than others. The method may be chosen such that certain biobased chemical(s) may be produced.
[0117] The gasification of lignin may be one method for depolymerizing lignin.
Gasification may degrade the carbocyclic backbone of lignin into low molecular weight gaseous CI products such as hydrogen, carbon monoxide, carbon dioxide and/or methane. In order to produce biobased chemicals in this manner, these gases may have to be subsequently converted back into aromatic and/or aliphatic compounds by multistep, complex secondary processes. Although gasification can be used in the production of biobased chemicals, the complex nature of this process may reduce its efficiency when compared to other potential processes.
[0118] Yet another method for lignin depolymerization can be pyrolysis. Pyrolysis may convert lignin into gases, liquid oil (also known as bio-oil), and/or tar and char. One type of pyrolysis, thermolysis, may be a pyrolytic procedure performed at temperatures of about 200 °C to about 900 °C and in the absence of air so the lignin structure may be fragmented into smaller molecular weight units without significant combustion into carbon dioxide. The product distribution of thermolysis can be influenced by lignin feedstock type, the heating rate, the final depolymerization temperature, and/or additives. The primary gaseous products of lignin thermolysis may be carbon monoxide, carbon dioxide, and/or methane. The liquid oil fraction may consist of methanol, acetone, acetaldehyde, mono-lignols, and/or mono-phenols and poly- substituted phenols. While the complex composition of the bio-oil can presents the potential for production of chemicals from lignin, the economic separation of pure compounds from this mixture may be a significant economic challenge. Although thermolysis may provide a considerable amount of water from the dehydration of lignin, many of the volatile products may be water soluble, which can involve an additional step to remove the volatile product(s) from the waste water to prevent environmental pollution. Additionally, certain amounts of tar and char in the reactor may be formed in the reactor, requiring yet another step involving a cleaning of the reactor. [0119] A third method for depolymerizing lignin may be hydrogenolysis, which occurs when pyrolysis occurs in the presence of hydrogen or a hydrogen-donating liquid. Catalysts and solvents may be employed to speed up the depoymerization reaction and may increase the yield of bio-oil. Solvents may include water, ethanol, propanol, isopropanol, acetonitrile, and/or ionic liquids. Typical reaction temperatures for hydrogenolysis may be about 300 °C to about 600 °C, which are lower than the temperatures used in lignin thermolysis. Lignin hydrogenolysis tends to afford a higher net conversion, a higher yield of mono-phenols, and less char formation relative to thermolysis. Depending upon the catalyst and hydrogen source, the obtained bio-oil consists of a mixture of monomeric, dimeric and oligomeric phenolic products. Using hydrogenolysis may provide considerable amounts of the dimeric and/or oligomeric phenolic products, potentially reducing the yield of biobased chemical products.
[0120] Oxidative depolymerization in the presence of caustic can also be another method for the depolymerization of lignin 16. A mild α-β lignin oxidative depolymerisation reaction 18 and/or an extensive α-β lignin oxidative depolymerisation reaction 20 may provide an efficient means for lignin 16 depolymerization. These processes break the lignin 16 polymer down into smaller fragments and specific biobased chemicals. Selective α-β lignin oxidative depolymerisation may provide entry to at least one chemical of aryl aldehydes 22 and/or aryl carboxylic acids 24.
[0121] Oxidative lignin depolymerisation (mild or extensive) may be preferentially conducted in the presence of caustic. One benefit of the use of caustic may be that the lignin may have a higher solubility under alkaline conditions (high pH). Another benefit of the use of caustic in oxidative lignin depolymerisation may be that it may induce cleavage of certain carbon-oxygen bonds within lignin, and most notably the β-Ο-4 linkage. Yet another benefit of the use of caustic in oxidative lignin depolymerisation may be that it may induce a breaking of certain carbon-carbon bonds within lignin. The caustic for oxidative lignin depolymerisation may be provided by at least one caustic of lithium hydroxide, sodium hydroxide, potassium hydroxide, cesium hydroxide, magnesium hydroxide, barium hydroxide, and calcium hydroxide. In another embodiment of the invention, oxides and carbonate salts of Group I and II metals may be employed as the caustic for oxidative lignin depolymerisation. In yet another embodiment of the inventions, the pH of the lignin-caustic solution may be about 10 to about 14. In still another embodiment of the invention, the pH of the lignin-caustic solution may be about 12 to about 14. Particularly when this reaction is performed in the presence of caustic, β-Ο-4 and other cleavages of the lignin backbone may occur along with an α-β lignin oxidative depolymerisation. Such caustic-induced lignin cleavage may proceed prior to, in concert with, or subsequent to an α-β lignin oxidative depolymerisation. These caustic-induced cleavages may also be conducted as a separate processing step of an α-β lignin oxidative depolymerisation. These caustic-induced cleavages may take place within the same reactor as an α-β lignin oxidative depolymerisation, or they may be conducted in a separate reactor.
[0122] Oxidative lignin depolymerisation (mild or extensive) may utilize metal catalysis. The catalyst for these reactions may be a homogeneous species, or a heterogeneous species, or a mixed metal system, or a metal system supported on an inert solid matrix. The metal catalyst may include, but is not limited to, various salts and complexes of the Periodic Table Group 3 through Group 12 transitions metals, and/or lanthanides, and/or actinides, as well as mixed metal systems thereof. The oxidant for such reactions may be air, oxygen, hydrogen peroxide, organic peroxide, or an organic nitro compound. The reaction processing can be conducted as a batch or flow operation. The solvent system for this reaction may be aqueous, alcoholic, organic, ionic liquid based, or mixtures thereof. The reaction may be performed at a temperature from about 50 °C to about 300 °C. More preferably, the reaction may be conducted at a temperature of about 100 °C to about 200 °C.
[0123] Aryl aldehydes 22 may be the primary product group of a mild α-β lignin oxidative depolymerisation reaction 18. Specific examples of aryl aldehydes 22 that may be produced include at least one chemical of 4-hydroxybenzaldehyde, vanillin and syringaldehyde. These aldehydes may be formed by α-β lignin oxidative cleavage of the phenyl propanoid building blocks making up the β-Ο-4, and/or β-5, and/or β-l, and/or β-β, and/or spirodienone, and/or dibenzodioxocin linkages in lignin. The product yield from such a reaction may be from about 5 weight percent to about 50 weight percent or higher relative to the dried lignin weight. [0124] The aryl aldehyde 22 product mix from a mild α-β lignin oxidative depolymerisation reaction 18 may generally reflect the H:G:S ratio of the lignin 16, and can be controlled in part by the selection lignin 16 feedstock (i.e., the plant species and/or biomass treatment method). Alternatively, a blend of lignin feedstock may be used to control the product distribution to the desired H:G:S ratio. As an example, a lignin 16 of high G content may provide higher levels of vanillin and/or vanillic acid than a lignin 16 of lower G content.
Similarly, that lignin 16 highest in H or S content may respectively provide aryl aldehydes 22 (i.e., 4-hydroxybenzaldehyde and 4-hydrobenzoic acid for H, syringaldehyde and syringic acid for S, respectively) corresponding to H or S phenyl ring substitution patterns. Over-oxidation of the formed aryl aldehydes 22 product(s), even under conditions of a mild α-β lignin oxidative depolymerisation reaction 18, may lead to certain aryl carboxylic acids 24, and more specifically to at least one chemical of 4-hydroxybenzoic acid, vanillic acid, and syringic acid.
[0125] Aryl carboxylic acids 24 may be the primary products of extensive α-β lignin oxidative depolymerisation reaction 20. The product yield from such a reaction may be from about 25 weight percent to about 100 weight percent relative to the dried lignin weight. More preferably, the product yield may be from about 50 weight percent to about 100 weight percent. The oxidant or catalyst used in an extensive α-β lignin oxidative depolymerisation reaction 20 may be a stronger oxidant (i.e., a higher redox potential) than that used in a mild α-β lignin oxidative depolymerisation reaction 18. The product mixture of the aryl carboxylic acids 24 may reflect the H:G:S ratio of the Lignin 16, and may be controlled by lignin 16 feedstock selection (i.e., the plant species and/or biomass treatment). Alternatively, a blend of lignin feedstock can be used to control the H:G:S product distribution. The major aryl carboxylic acids 24 products that may be formed by the an extensive α-β lignin oxidative depolymerisation reaction 20 are shown in Figure 6. The prevalent products of such an oxidation may be at least one chemical of 4-hydroxybenzoic acid, vanillic acid, and syringic acid.
[0126] Selective α-β lignin oxidative depolymerisation in the presence of caustic may have important commercial implications for transformations of lignin into valuable biobased products that consist of at least one chemical of aryl aldehydes, aryl benzoic acids, 4- methylphenols, toluene, xylene, and mesitylene. Such transformations may involve a subsequent hydroprocessing of the oxidation products (i.e., the aryl aldehydes 22 and/or aryl carboxylic acids 24) into other biobased products per U.S. Utility application No. 13/470,398, METHOD FOR SELECTIVE PRODUCTION OF BIOBASED CHEMICALS AND BIOFUELS FROM PLANT LIGNIN, filed May 14, 2012. The reason why selective α-β lignin oxidative
depolymerisation in the presence of caustic may be so advantageous in the preparation of these products is that it may provide the C-7 carbocyclic structure of these products directly, while maximizing utilization of the available carbon atoms that may be provided through nature in lignin, and while minimizing by-products from other lignin cleavage modes that may complicate product quality. Overall, selective α-β lignin oxidative depolymerisation may provide for an efficient use of the lignin' s carbon utilization. These processes may afford lignin biobased chemicals, and depending upon the extent of the mild α-β lignin oxidative depolymerisation reaction 18 and/or an extensive α-β lignin oxidative depolymerisation reaction 20, a certain amount of a recoverable lignin residue.
[0127] The amount of lignin residue from the mild α-β lignin oxidative
depolymerisation reaction 18 and/or an extensive α-β lignin oxidative depolymerisation reaction 20 can range from more than about 90% to less than about 10% of the original amount of lignin 16 entering the process. It may also range from about 50% to about 10% of the original amount of lignin 16 entering the process. Lignin residue can be sent (a) for heat and power generation, and/or (b) for recycling for further use as lignin 16, and/or (c) transformed into tiered biobased chemicals and biofuels as described in A METHOD FOR PRODUCING BIOBASED
CHEMICALS FROM PLANT LIGNIN (U.S. Application Number 13/453,422 filed April 23, 2012).
[0128] FIGURE 6 illustrates the aryl carboxylic acids 24 that may be produced by an extensive α-β lignin oxidative depolymerisation reaction 20. Figure 7 depicts the extensive α-β lignin oxidative lignin depolymerization reaction 20 where aryl carboxylic acids 24 may be the primary products. In the extensive α-β lignin oxidative lignin depolymerization reaction 20, which may yield a C7 fragment (phenyl ring with a CI side chain) and a CI and/or C2 alkyl fragment, at least one chemical of 4-hydroxybenzoic acid, vanillic acid, and syringic acid may be formed by α-β oxidative cleavage of the phenyl propanoid making up the β-Ο-4, and/or β-5, and/or β-l, and/or β-β, and/or spirodienone, and/or dibenzodioxocin linkages of lignin.
[0129] At least one chemical of compounds 4 and 5 may be formed by an extensive α-β lignin oxidative depolymerisation reaction 20 of the phenyl propanoid making up a β-5 linkage. When an extensive α-β lignin oxidative depolymerisation reaction 20 of the dibenzodioxocin and 5-5 linkages can occur, chemical(s) of compounds 6, 7, and/or 8 may be formed. When an extensive α-β lignin oxidative depolymerisation reaction 32 of the 4-0-5 linkage may occur at least one chemical of compounds 9-13 as shown in Figure 6 may arise.
[0130] Besides compounds 4 and/or 5, the remainder of the compounds shown in Figure 6 may be minor components of an extensive α-β lignin oxidative depolymerisation reaction 20.
[0131] Further, the abundances of the products shown in Figure 6 may parallel the H:G:S ratio of the lignin 16 and can be influenced by the lignin 16 feedstock (i.e., the plant species) and/or lignin 16 pre-treatment method. Alternatively, the feedstock may be blended with different lignin 16 types to adjust the H:G:S ratio of the lignin 16 and achieve a desired product ratio.
[0132] FIGURE 7 provides lignin model compounds for mechanistic studies of selective α-β lignin oxidative depolymerization in the presence of caustic. Under caustic and oxidative conditions, other investigators have suggested that lignin may undergo a number of potential reactions selected from among, but not limited to:
1. An oxidation of a para-phenolate ring followed by a carbon-carbon bond fragmentation to form aryl aldehydes 20 and/or aryl carboxylic acids 24;
2. An oxidation of an a-hydroxy group followed by oxidative split to give the aryl aldehydes 20 and/or aryl carboxylic acids 24; 3. An oxidation of a β-hydroxy group followed by oxidative split to give the aryl aldehydes 20 and/or aryl carboxylic acids 24;
4. An oxidation of a γ-hydroxy group followed by a retroaldol reaction to give the aryl aldehydes 20 and/or aryl carboxylic acids 24; and
5. Caustic-induced nucleophilic breakage of various carbon-oxygen bonds such as a β-Ο-4 linkage as well as loss of water from the molecule through an elimination mechanism of the β-hydrogen and the a-hydroxy group.
[0133] The selective oxidation of lignin to aryl aldehydes 22 and aryl carboxylic acids 24 may be minimally 2-electron and 4-electron oxidative transformations, respectively. Since this process may affect an α-β bond cleavage of the phenyl propanoid building block, additional oxidations to the other cleavage segment may potentially occur in parallel to formation of the of aryl aldehydes 22 and/or aryl carboxylic acids 24, which may result in nominally a 4-electron oxidation process.
[0134] Various metal salts and metal complexes of the Periodic Table Group 3 through Group 12 transitional metals, mixed metal systems of the Periodic Table Group 3 through Group 12 transitional metals, and various metal salts and metal complexes capable of achieving one- electron oxidations may be useful as catalysts for selective α-β lignin oxidative
depolymerisation. The oxidant for such reactions may be air, oxygen, hydrogen peroxide, organic peroxide, an organic nitro compound, or mixtures thereof.
[0135] The preparation of aryl aldehydes 22, in particular, may require the use of a mild transitional metal oxidant in order to prevent over oxidation of the aryl aldehydes 22 into aryl carboxylic acids 24. In this light, metal systems selected from at least one metal of vanadium, chromium, manganese, iron, cobalt, nickel, and copper may be effective oxidants of lignin.
[0136] An understanding of the reaction mechanism for lignin oxidation under caustic conditions may offer the possibility of designing even more selective catalysts for this reaction. Although described in this figure, the lignin model compounds are described further in Figure 8. These model compounds may provide an opportunity to probe the mechanism of selective α-β lignin oxidation.
[0137] The lignin model compound labeled as Model 1 may mimic a β-Ο-4 linkage structure in lignin wherein the phenyl ring has a guaiacyl (G) substitution pattern. As such, Model 1 may be open to all the reaction pathways described above. The aryl aldehyde that may be expected from Model 1 is vanillin.
[0138] The lignin model compound labeled as Model 2 may be patterned similarly to that of Model 1, with exception that the γ-hydroxy group is capped as a methyl ether. As such, Model 2 may be open to all of the reaction pathways described above with the exception of the mechanistic pathway involving an oxidation of a γ-hydroxy group followed by a retroaldol reaction to give the aryl aldehyde. If Model 2 should undergo oxidation to give an aryl aldehyde, the product may be vanillin.
[0139] The lignin model compound labeled as Model 3 may also be patterned similarly to that of Model 1, with exception that Model 3 has a meta-phenol substitution pattern and Model 1 the phenol group which is para-oriented with respect to the propyl chain. As such, Model 3 may be open to all of the reaction pathways described above with exception of the mechanistic pathway described as an oxidation of a para-phenolate ring followed by a carbon- carbon bond fragmentation to form an aryl aldehyde. The reason for this exception may be that upon a single electron oxidation of Model 3, the resonance forms of the meta-phenol radical may be cross conjugated to the propyl side chain, whereas in Model 1 the phenol radical can be conjugated to C-l aryl position immediately adjacent to the propyl side chain. If Model 3 may undergo a similar oxidation to Model 1, the aryl aldehyde product of Model 3 may be 3- hydroxybenzaldehyde.
[0140] The lignin model compound labeled as Model 4 can differ from that of Model 1 in that an ethyl group may be substituted in place of the β-guaiacyl group. As such, Model 4 may not be prone to a β-Ο-4 cleavage in the presence of caustic as is possible with Model 1. Therefore, if either β-Ο-4 cleavage and/or a β-hydroxy oxidation is on a critical mechanistic path to the aryl aldehydes, Model 4 may not afford vanillin upon oxidation.
[0141] Lastly, the epoxides labeled as Model 5 can be potential model compound intermediates of the types of lignin fragment structures that may be formed upon a caustic- induced β-Ο-4 cleavage of lignin. In this instance, the neighboring a-hydroxy and/or γ-hydroxy group may undergo proton exchange with the caustic. The resulting lignin alkoxide may then promote an intramolecular nucleophilic displacement of the β-guaiacyl group. These epoxides may be in equilibrium with each other through a Payne rearrangement. Ring opening of either epoxide with caustic may then produce a triol analog of Model 1 in which the β-guaiacyl group may be replaced by a β-hydroxy group. As such, Model 5 can provide yet another probe into the importance of β-Ο-4 cleavage in lignin oxidation under caustic conditions. If Model 5 should undergo oxidation to give an aryl aldehyde, the product may be vanillin.
[0142] FIGURE 8 provides a general reaction for the oxidation of the lignin model compounds, specifically Models 1-4, to aryl aldehydes and aryl acids. Experimental results for the Lignin Model 1-3 reactions are provided in Tables 1-3 below. Additionally, the caustic- induced fragmentation of Model 3 may be more fully explained in Figure 9. Table 4 may provide a comparison of the product distributions from Model 1, 2, and 3 reactions, whereas Table 5 may illustrate data for a competitive oxidation of Models 1 and 3. Table 6 can provide the experimental results for the Lignin Model 4 reactions, and described below and more fully in conjunction with Figure 11. Highlights of these results can be summarized below each respective table.
[0143] With respect to the tables provided below, all reactions were conducted in 100- mL, glass pressure tubes in the presence of about 1 bar of air as the oxidant as more fully described in Example 15. The model substrate may be dissolved in aqueous sodium hydroxide solution. The catalyst may be added to this solution at the indicated mole % concentration relative to the substrate lignin model compound. The contents of the sealed vessel may be then heated at 130 °C for the indicated reaction time. The reaction work-up may consist of neutralization to about pH 2 with dilute sulfuric acid, extraction of the organic products with methyl tert-butyl ether, and an analysis of the product mixture by gas chromatography. Product identities may then be established by matching chromatographic peak retention times relative to those peaks of authentic standards. In addition, mass spectroscopic analysis of the
chromatographic peak may provide further structural identity information. Mole % conversions or masses for each product may then be calculated from the chromatographic peak areas.
[0144] Model 1 results may be found in Table 1 (below). Entries 1-3 indicate that cleavage of a guaiacol group from Model 1 may occur to a significant extent even in the absence of catalyst. Notably, a higher concentration of caustic may not further enhance this reaction. This cleavage may be analogous to that of a caustic-induced depolymerisation of lignin. The net effect of such caustic-induced reaction may be a β-Ο-4 cleavage, although the reaction mechanism may not be discerned from these experiments. Only small amounts of vanillin and vanillic acid may be observed in the absence of catalyst with Model 1, the small amounts of which is formed may be the result of oxidation by the oxygen present in the reaction atmosphere. Entries 4-6 indicate that the presence of iron(II) catalysis alone, and/or iron(III) through oxidation of iron(II) by oxygen, may have a minimal effect on vanillin production. Again, larger amounts of guaiacol and only small amounts of vanillin and vanillic acid may be observed in these reactions. The slight increase in product amounts in entries 5 and 6 may be a result of an extended reaction time or higher caustic concentration. Entries 7-9 may reflect the dramatic influence of copper(II) catalysis in the mild α-β lignin oxidative depolymerisation reaction 18 of lignin 16. The low oxidation potential of copper(II) may induce a selective α-β cleavage of phenyl propanoid structure of Model 1 and can release vanillin as the product. Separate experiments may demonstrate the oxidation of vanillin into vanillic acid in the presence of copper(II) catalysis. Thus the slightly higher levels of vanillic acid in entries 8 and 11 at longer reaction times may be the result of further oxidation of the vanillin product. The longer reaction time of entry 8 may also provide a somewhat higher product yield of vanillin. The level of guaiacol in entries 7-9 may rise proportionally to the amount of vanillin produced relative to the background experiments in entries 1-3. Entries 10-11 may indicate an incremental increase in vanillin product yield when copper(II) catalysis is coupled with that of iron(II/III). The high selectivity for α-β cleavage of phenyl propanoic! structure of Model 1 may be preserved with this mixed catalyst system. The longer reaction time of entry 8 may also provide a somewhat higher product yield. Once again, the level of guaiacol in entries 7 and 8 may raise proportional to the amount of vanillin produced relative to the background experiments in entries 1-3. For entry 12, nitrobenzene can be a well-established oxidant for lignin 16. Entry 12 can demonstrate that nitrobenzene oxidation of Model 1 may provide vanillin. The yields for this reaction, however, may be modest relative to copper(II) and/or copper(II)/iron(II,III) catalysis. For the mechanism, some findings of the Model 1 study may be:
1. lignin Model 1 may serve as a viable model compound for selective oxidation of lignin to aryl aldehydes 22;
2. caustic-induced β-Ο-4 cleavage of guaiacol may proceed prior to or simultaneous with oxidation of the substrate;
3. a small amount of lignin oxidation may occur with molecular oxygen in the absence of any catalyst;
4. copper(II) may be an effective catalyst to induce α-β carbon-carbon bond cleavage in lignin phenyl propanoids; and/or
5. iron(II/III) alone may be a poor catalyst for lignin oxidation, but when
combined with copper(II) may provide superior yields of vanillin relative to that of copper(II) alone.
TABLE 1. OXIDATION STUDIES OF LIGNIN MODEL 1 IN PRESENCE OF CAUSTIC
8 — 6 100 100 2 20.3 0.86 23.5
13.5 + 0.1 + 16.0 +
9 — 6 100 400 1
2.0 0.0 2.5
19.0 + 0.4 + 21.4 +
10 6 6 100 100 1
1.0 0.0 2.4
11 6 6 100 100 2 26.3 0.7 24.9
3.8 + 0.5 + 7.0 +
12 Nitrobenzene, 200 mol % 100 400 1
0.3 0.1 0.5
* VAN = Vanillin; VAN Acid = Vanillic Acid; GUA = Guaiacol
[0145] Model 2 results (see Table 2 below) may show that the experimental result in entry 1 for Model 2 can reflect a dramatic inhibition of caustic-induced guaiacol cleavage relative to Model 1, entries 1-3, Table I. In Model 2, the γ-hydroxy group may be capped as a methyl ether. There may be about an 8-fold reduction in the amount of guaiacol formed with Model 2 relative to Model 1 under otherwise identical experimental conditions. This may suggest that the free γ-hydroxy group in the phenyl propanoid is important to a caustic-induced depolymerisation of lignin by β-Ο-4 cleavage. As with Model 1, entry 2 for Model 2 may suggest the presence of iron(II) catalysis alone, and/or iron(III) through oxidation of iron(II) by oxygen, may have a minimal direct role upon vanillin production and/or β-Ο-4 cleavage. Entries 3 and 4 for Model 2 wherein copper(II) catalysis can support an increase in amount of vanillin and guaiacol relative to entry 1 may be analogous to the results observed for Model 1 with exception that the amount of vanillin produced from Model 2 may be about 25% of that from Model 1. The lower aqueous solubility of Model 2 relative to Model 1 may be causing at least some of this differential; however, complete solubilisation of Model 2 can be achieved at a substrate concentration of 50 mg (entries 5 and 6) without significant improvement in vanillin yield even at higher catalyst loadings. Moreover, the study may indicate about 1: 1 ratios of vanillin to guaiacol with Model 4, if not slightly more vanillin than guaiacol, whereas with Model 1 the amount of guaiacol produced nearly always exceeded that of vanillin. This result may be consistent with a faster rate of caustic-induced β-Ο-4 cleavage in Model 1 relative to Model 2. For the mechanism, some findings of the Model 2 study may be:
1. capping of the γ-hydroxy group of the phenyl propanoid may dramatically retard the rate of caustic-induced β-Ο-4 cleavage relative to Model 1; 2. a caustic-induced β-Ο-4 cleavage of guaiacol may proceed by more than one reaction pathway;
3. a small amount of lignin oxidation may occur with molecular oxygen in the absence of a catalyst;
4. copper(II) may be an effective catalyst to induce α-β carbon-carbon bond cleavage in lignin phenyl propanoids;
5. iron(II/III) alone may be a poor catalyst for lignin oxidation, but when
combined with copper(II) may provide yields of vanillin that are superior to that of copper(II) alone; and/or
6. the total amount of vanillin produced from Model 2 may be reduced to about 25% of that of Model 1. This result may indicate that some form of lignin depolymerisation may generally take place prior to oxidation, and that the absence of a free γ-hydroxy group may inhibit a major lignin
depolymerisation pathway.
TABLE 2. OXIDATION STUDIES OF LIGNIN MODEL 2 IN PRESENCE OF CAUSTIC
* VAN = Vanillin; VAN Acid = Vanillic Acid; GUA = Guaiacol [0146] Model 3 results in Table 3 may show that 3-hydroxybenzaldehyde may be produced instead of vanillin because of the meta substitution pattern of the phenyl ring. In the presence or absence of added catalyst (entries 1-4), Model 3 may produce very little guaiacol. Indeed, the low yields of caustic-induced guaiacol cleavage from Model 3 may approximate those of Model 2 even though the propyl side chain substitution of Model 3 may be identical to that of Model 1. Therefore, this difference in reactivity of Model 3 and Model 1 may be associated with the phenyl ring substitution pattern. In Model 3, the phenolic group may be meta-oriented with respect to the propyl chain, whereas in Model 1 it may be para-oriented. As a result, the resonance stabilized phenolate anion of Model 1 may conjugate to the C-l phenyl carbon adjacent to the propyl side chain, whereas in Model 3 the phenolate anion may be cross conjugated to the side chain. Entry 1 in Table 3 therefore may suggest the importance of a para- substituted phenolate anion to the β-Ο-4 cleavage mechanism. Additionally, there may be the 1- (3-hydroxyphenyl)-l,3-propanediol (3-HPDiol) fragmentation product that is co-produced with the Model 3 substrate. This product may be produced by thermally-induced, hemolytic radical fragmentation of the β carbon-oxygen bond releasing a guaiacyl radical and a secondary alkyl radical. The analogous compound may not be detected with either Model 1 or Model 2, which may suggest a new mechanistic pathway as hypothesized in Figure 9. A mass spectrum for this product is provided in Figure 10. As seen with Models 1 and 2, iron(II/III) catalysis alone may have little effect on aryl aldehyde production (entry 2). Entries 3 and 3 can reflect the data for copper(II) and copper(II)/iron(II/III) catalysis. Notably, the yields of aryl aldehyde (i.e., 3- hydroxybenzaldehyde) may be significantly diminished relative to the equivalent oxidations of Models 1 and 2. As before, a slight improvement in aryl aldehyde yield can be observed with the mixed catalyst system. These observations can also suggest the para-phenolate of Models 1 and 2 may play an important role in oxidation. As noted above, the para-phenolate, or a para- phenolate radical, may be resonance conjugated to the propyl side chain, whereas in Model 3 the system may be cross conjugated with the propyl side chain. For the mechanism, some findings of the Model 3 study may be:
1. a para-phenolate or para-phenolate radical, may be an important component of lignin caustic-induced depolymerisation and/or oxidation;
2. Model 3 may be the least reactive model substrate of Models 1-3; 3. copper(II) may be an effective catalyst to induce α-β carbon-carbon bond cleavage in lignin phenyl propanoids; and/or
4. iron(II/III) alone may be a poor catalyst for lignin oxidation, but when
combined with copper(II) may provide yields of vanillin that are superior to that of copper(II) alone.
TABLE 3. OXIDATION STUDIES OF LIGNIN MODEL 3 IN PRESENCE OF CAUSTIC
* 3-HBA = 3-Hydroxybenzaldehyde; 3-HPDiol = l-(3-Hydroxyphenyl)-l,3-propanediol; GUA = Guaiacol
[0147] Tables 4 and 5 are also provided to show the comparison of the product distributions from Model 1, 2, and 3 reactions and illustrate data for a competitive oxidation of Models 1 and 3, respectively. A comparison of the entries may demonstrate the change in reactivity between these substrates. Capping the γ-hydroxy group as a methyl ether in Model 2, may reduce its reactivity relative to that of Model 1. Model 3 describes the reaction in which the phenol group occupies a meta position with respect to the propyl side chain. Moreover, entry 3 may reveal a change in the mechanism of caustic-induced fragmentation of Model 3 relative to that of Models 1 and 2 as evidenced in the commitment formation of 3-HPDiol in proportional amounts to that of GUA. A comparison of entries 1, 2 and 3 may demonstrate that a γ-hydroxy group and a para-phenol group are both important to caustic-induced lignin depolymerisation. With both Models 2 and 3, the amount of guaiacyl (GUA) formed may be about 10-fold less than that of Model 1. Entries 4, 5, and 6 may demonstrate that iron(II/III) alone are not an effective catalyst for lignin oxidation. Entries 7, 8 and 9 may demonstrate the importance of copper(II) catalysis for selective oxidative cleavage of the lignin α-β carbon-carbon bond during aryl aldehyde and/or aryl carboxylic acid formation. Copper(II) alone may be an effective catalyst for this reaction. Entries 10, 11, and 12, may illustrate the beneficial effect of a combination copper(II)/iron(II,III) catalyst system. In all cases there may be an increase in the amount of aryl aldehyde produced in these reaction when iron(II/III) is added to the catalyst system relative to the parallel entries 7, 8, and 9. However, since Entries 4, 5 and 6 may reveal iron(II,III) alone has little effect, the role of iron(II,III) in the combination catalyst is likely to promote the oxidation of copper(I) back to copper(II) by iron(III) per the following set of equations and favourable redox potentials:
Reaction Redox Potential
Fe3+aq + e " -» Fe2+aq E = +0.77 V
Cu+aq Cu2+aq + e- E = -0.15 V
Fei+aq + Cu+aq 4Fe2+aq + Cu2+aq E = +0.62 V
TABLE 4. OXIDATION LIGNIN MODELS 1 - 3 IN PRESENCE OF CAUSTIC;
COMPARISON OF RESULTS
* VAN = Vanillin; VAN Acid = Vanillic Acid; 3-HBA = 3-Hydroxybenzaldehyde; 3- HPDiol = l-(3-Hydroxyphenyl)-l,3-propanediol; GUA = Guaiacol
With respect to Table 5, a comparison of entries 1 and 2, and entries 4 and 5, may reveal the dramatic difference in reactivity of these two model substrates. Oxidation to produce the aryl aldehyde (i.e., 3-hydroxybenzaldehyde (3-HBA)) may be greatly diminished with Model 3 supporting the importance of the para-substituted phenol moiety to facile lignin oxidation.
Oxidation of the para-substituted phenol of Model 1 may yield a radical that is resonance stabilized with position- 1 of the phenyl ring. The meta-substituted phenol orientation of Model 3 on the other hand may not yield the same resonance stabilized radical of Model 1 due to cross conjugation. Moreover, GUA production may be greatly reduced with Model 3 relative to Model 1 (entries 1 and 2, and entries 4 and 5), a result which may suggest a change in the primary caustic-induced cleavage mechanisms between these substrates. A comparison of entries 3 and 6, wherein the reaction contained equal amounts of the two Model substrates, may illustrate the preferential oxidation of a para-substituted phenol relative to a meta- substituted phenol. Neither reaction may lead to any detectable 3-HBA. The 3-HBA may only be observed when Model 3 is the only substrate present in the oxidation reaction.
TABLE 5. COMPETITIVE OXIDATION STUDIES OF LIGNIN MODELS 1 AND 3 IN
PRESENCE OF CAUSTIC
* VAN = Vanillin; VAN Acid = Vanillic Acid; 3-HBA = 3-Hydroxybenzaldehyde; 3- HPDiol = l-(3-Hydroxyphenyl)-l,3-propanediol; GUA = Guaiacol
[0148] Model 4 results are shown in Table 6. In Model 4, guaiacol may not be a possible reaction product because R3 is an ethyl group. As a result, β-Ο-4 cleavage may not occur. Of interest herein is the observation of a novel caustic-induced fragmentation product that may shed light on other reaction pathways for lignin depolymerisation. The product may be 4- (l-butenyl)guaiacol (BGUA), entry 1. The reaction pathway to this product can be depicted in Figure 11. An 1H NMR spectra for the entry 1 reaction mixture under argon is shown in Figure 12. The mass spectrum for the product is provided in Figure 13. A more detailed explanation of plausible mechanistic pathways to form this product are described in Figure 14. Optionally, Model 4 caustic-induced fragmentation may occur using argon at about 130 °C. This fragmentation is slower at lower temperatures.
[0149] The experiment in Entry 1 was conducted under an argon atmosphere and as such may be a non-oxidizing environment. In this reaction, no vanillin may be produced;
however, a 44.5 mole % yield of BGUA may be observed. Entry 2 demonstrates that stoichiometric amounts of copper(II) catalysis may not alone be enough to convert BGUA into vanillin. Upon introduction of air alone (entry 3) or air/iron(II/III) (entry 4), a small amount of vanillin can be produced from Model 4, although the amount of BGUA may remain comparable to that of entries 1 and 2. In the presence of copper(II) or copper(II)/iron(II/III), the levels of BGUA in the product composition may be reduced relative to that in entries 1 and 2. Moreover, an additional amount of vanillin can be formed, suggesting that oxidation of BGUA leads to vanillin. In the prior art from Tarabanko, eugenol (1 less carbon atom in the side chain than BGUA) was oxidized to vanillin. However, the incremental amount of vanillin produced in these experiments may not explain completely the decrease in BGUA levels. This decrease may be due to copper(II) complexing to BGUA and/or Model 4 and leading to other radical coupling by-products that may not be detected by the analytical method. The production of vanillin from Model 4, entries 5-6, however, may provide the first experimental evidence that β-Ο-4 cleavage may not necessarily be a prerequisite to lignin phenyl propanoid oxidation even though Model 2 suggests some form of lignin depolymerisation may be beneficial. Therefore, other
depolymerisation pathways may be at play for this oxidation to occur.
TABLE 6. OXIDATION STUDIES OF LIGNIN MODEL 4 IN PRESENCE OF CAUSTIC
6.2 + 3.2 +
5 — 6 Air 75 100 1
0.7 1.1
7.0 + 2.2 +
6 6 6 Air 75 100 1
0.6 0.1
* VAN = Vanillin; BGUA = 4-(l-Butenyl)guaiacol
[0150] FIGURE 9 provides a potential mechanism for a caustic-induced fragmentation of lignin Model 3. A reaction product of Model 3 may be l-(3-hydroxyphenyl)-l,3-propanediol (3-HPDiol), and at first appearance looks like it may be a reduction product of Model 3.
However, the reaction is conducted in an oxidizing environment (air, and/or catalyst/air) and this product is formed in all examples.
[0151] Homolytic fragmentation of Model 3 may offer another mode of β-Ο-4 cleavage. Homolytic fragmentation may provide a resonance stabilized phenoxy radical and a secondary radical. Recombination of these radicals may reform Model 3. A recombination of two secondary radicals may produce a CI 8 product that may not be detected by the GC analysis method. Additionally, hydrogen radical scavenging from solvent or other OH groups present in the reaction may lead to the fragmentation products. Since only small amounts of both products may be formed, homolytic fragmentation of lignin may only be a minor pathway in β-Ο-4 cleavage.
[0152] FIGURE 10 provides a mass spectrum of the post trimethylsilyl-derivatized 1- (3-hydroxyphenyl)-l,3-propanediol product. The parent ion at 240 mass units may correspond to the mono-trimethylsilyl product. The relatively stronger ions at 166 mass units and 73 mass units, respectively, may correspond to a fragmentation of the 240 mass ion (i.e. 166 mass units may be trimethylsilylphenol and 73 mass units may be the propyl side chain as
C(0)CH2CH2OH).
[0153] FIGURE 11 provides a caustic-induced fragmentation and oxidative cleavage of lignin Model 4. Model 4 may be a lignin model substrate in which β-Ο-4 cleavage may not occur since the β-position of Model 4 can be occupied by an ethyl group (carbon-carbon bond) instead of a phenolic group of another lignin phenyl propanoid building block (carbon-oxygen bond). Model 4 may provide a two-fold insight as to whether: (i) β-Ο-4 cleavage may be a prerequisite to selective α-β oxidation of lignin during aromatic aldehyde 20 and/or aromatic carboxylic acid 22 production, and/or (ii) other caustic-induced fragmentation reactions may be occurring in the course of this oxidation reaction.
[0154] The first step of phenyl propanoid oxidative depolymerization may be a caustic- induced elimination of water from the polymeric molecule, and more specifically, by elimination of water from the β-hydrogen atom and the a-hydroxy group of the phenyl propanoid side chain. Tarabanko et al suggested this elimination reaction may be a reversible process. If such a reversible elimination/addition process may occur as the first step, the Model 4 substrate may incorporate a deuterium atom at the β-position. Furthermore, such deuterium atom incorporation may be observable by NMR spectroscopy.
[0155] For Figure 11, the predominant process when Model 4 is treated with caustic in the absence of air or catalyst may be illustrated. First, when a caustic-induced reaction may be conducted under argon, no deuterium incorporation may be detected at the β-position of Model 4 by NMR spectroscopy. Therefore, these experiments may provide a mechanistic pathway, and may teach away from the prior art from Tarabanko et al. Secondly, a major new product may be formed when Model 4 was treated with caustic in the absence of air or copper(II) catalyst. The 1H NMR spectroscopy and GC-MS analysis of the crude reaction product may support a product arising from a novel and unexpected β-γ carbon-carbon bond fragmentation. That product may be l-(4-hydroxy-3-methoxyphenyl)-l-butene (BGUA). The 1H NMR spectrum and gas chromato graph/mass spectrum of this reaction product are provided in Figures 12 and 13, respectively. Figure 12 may clearly depict the olefinic and ethyl group resonances for BGUA at 6.29, 6.11, 2.12, 1.08 ppm. Similarly, the mass spectrum of Figure 13 can be consistent with the expected mass (250 mass units) of a post-reaction derivatized trimethylsilyl-BGUA. Thirdly, oxidation of this crude reaction product may contain residual amounts of Model 4 along with 1- (4-hydroxy-3-methoxyphenyl)-l-butene by introduction of a copper(II) catalyst and air into the vessel provided vanillin. Concomitant with the formation of vanillin may be a reduction in the level of l-(4-hydroxy-3-methoxyphenyl)-l-butene. Previously, prior art from Tarabanko et al. had reported the oxidation of eugenol to provide vanillin, although these authors never connected the oxidation of eugenol with an unusual caustic-induced fragmentation of a phenyl propanoid in lignin. Eugenol can be structurally similar to l-(4-hydroxy-3-methoxyphenyl)-l-butene, except that the side chain of eugenol may contain one fewer carbon atoms. Vanillin may also be the major product when catalyst and air are introduced into the vessel at the beginning of the reaction. Fourthly, the conversion of Model 4 into vanillin may be dependent upon oxygen. When a reaction conducted in the presence of argon rather than air with a molar ratio of copper(II) catalyst to substrate, the l-(4-hydroxy-3-methoxyphenyl)-l-butene intermediate may not be converted into vanillin.
[0156] With Model 4, a β-Ο-4 elimination may not be the only pathway for lignin oxidation to aryl aldehydes 20. Further, caustic-induced lignin depolymerisation may proceed by at least one reaction mechanism of β-γ carbon-carbon bond fragmentation. Also, the
intermediate products of a caustic-induced β-γ carbon-carbon bond fragmentation of lignin may be oxidized to vanillin in a second step to product aryl aldehydes 20. Last, stoichiometric amounts of a catalyst alone may be insufficient to achieve such oxidation. The reaction may require the presence of an added oxidant such as air or oxygen.
[0157] FIGURE 12 provides an NMR spectrum of a product mixture from a caustic- induced fragmentation of Model 4, which is described in Figures 8 and 11.
[0158] FIGURE 13 provides a mass spectrum of be 4-(l-butenyl)guaiacol (BGUA), from a caustic-induced fragmentation of Model 4, which is described in Figures 8 and 11.
[0159] FIGURE 14 provides two plausible mechanistic pathways for a caustic-induced β-γ fragmentation of a lignin phenyl propanoid. Pathways 1 and 2 may differ in the number of steps involved in the fragmentation. Pathway 1 may be a concerted fragmentation whereas Pathway 2 may be a two-step fragmentation mechanism. Either pathway may, in principle, be reversible, although the extent of such reverse reactions is unknown. Thermodynamic and entropic effects may drive the free energy of this fragmentation. The net result of either pathway may be the formation of a 4-hydroxystyrene intermediate, formaldehyde, and water. The electronic -rich nature of the 4-hydroxystyrene intermediate may allow for susceptibility to oxidation.
[0160] In pathway 1, a proton exchange of the γ-hydroxy group with caustic may set up a concerted fragmentation of the resulting γ-alkoxide anion. In the course of the fragmentation process, the caustic may be regenerated. In pathway 2, a proton exchange of the phenolic hydroxyl group with caustic may produce a phenolate anion. The ejection of hydroxide anion from the a-carbon may then provide a para-quinone methide intermediate. A subsequent retro- Aldol reaction of the para-quinone methide may serve to achieve a β-γ fragmentation of a lignin phenyl propanoid.
[0161] The experiments described herein may not point to either fragmentation pathway specifically, but experimental results with Model 4 in particular can support that such fragmentation may be occurring in selective α-β lignin oxidative depolymerisation to produce aryl aldehydes 22 in the presence of caustic. Neither fragmentation pathway may necessarily result in the immediate production of guaiacol, although guaiacol may be formed upon oxidative cleavage of the α-β bond of the 4-hydroxystyrene intermediate. Therefore, at least one other mechanistic pathway can be occurring to produce guaiacol when the catalyst is absent from the reaction containing caustic.
[0162] FIGURE 15 provides the mechanism for the oxidation of Model 5 in the presence of caustic. Experimental results for this reaction are provided in Table 7 below.
Notably, Model 5 may be converted into vanillin in the presence of air and/or air and catalysis. Five products can be detected in this reaction: vanillin (VAN), vanillic acid (VAN Acid), 3,4- dihydro-3-hydroxyguaiacol (3,4-DHGUA), acetovanillone (Ac VAN), and 4-(l- hydroxyethyl)guaiacol) 4-HeGUA. Of these, at least VAN, VAN Acid and Ac VAN may be routinely seen in lignin 16 oxidations in the presence of caustic. [0163] The fragmentation of Model 5 to 3,4-DHGUA and 4-HeGUA may provide insight on competitive processes occurring during lignin oxidation under oxidative conditions. Both products may amount to net reduction products. The formation of such products may be the result of base-catalyzed Cannizzaro and related reactions. The structural assignment of 3,4- DHGUA can be considered as tentative based on the mass spectral data shown in Figure 16. The mass of 228 and fragmentations at 213 (loss of methyl) may be consistent with a post trimethylsilyl-derivatized 3,4-DHGUA. The results obtained herein may point to at least one other possible mechanism for β-Ο-4 cleavage in lignin: intramolecular displacement which may produce an epoxide of which Model 5 mirrors. This mechanistic hypothesis may be further described in Figure 17.
Table 7. OXIDATION STUDIES OF LIGNIN MODEL 5 IN THE PRESENCE OF
CAUSTIC
* VAN = Vanillin; VAN Acid = Vanillic Acid; 3,4-DHGUA = 3,4-Dihydro-3- hydrox guaiacol; AcVan = Acetovanillone; 4-HeGUA = 4-(l-Hydroxyethyl)guaiacol
[0164] FIGURE 16 provides the mass spectrum of 3,4-DHGUA, which is described in Figures 8 and 15.
[0165] FIGURE 17 provides some alternate mechanistic pathways for caustic-induced β-Ο-4 cleavage of the phenyl propanoid in lignin wherein secondary products may be produced. As discussed in the previous figures, at least one other mechanism of lignin cleavage other than β-γ fragmentation may be occurring in the presence of caustic. This can be evidenced by the formation of guaiacol in caustic reactions of Lignin Models 1, 2, and 3 in the absence of catalyst. If the β-γ fragmentation were the sole pathway, guaiacol may not necessarily be liberated as a product until post oxidation. [0166] With Models 1, 2, and 3, the reactions described herein may produce guaiacol. These pathways may include:
1. S 2 nucleophilic displacement of guaiacol in Models 1-3 by direct displacement of hydroxide for guaiacolate anion.
2. Proton exchange of the γ-hydroxy group with caustic, followed by intramolecular displacement of guaiacolate anion to produce an epoxide intermediate similar to Model 5.
3. Proton exchange of the a-hydroxy group with caustic, followed by intramolecular displacement of guaiacolate anion to produce an epoxide intermediate similar to Model 5.
4. Interconversion of these two epoxides in caustic media by Payne rearrangement resulting in a scrambling of the original stereochemistry at the β-guaiacol position.
5. Caustic-induced ring opening of either epoxide to produce a triol, which may then subsequently suffer a caustic-induced β-γ fragmentation or oxidation to vanillin.
6. Alternatively, a phenolate anion assisted opening of the benzylic epoxide ring to product a triol, which may then subsequently suffer a caustic-induced β-γ fragmentation or oxidation to vanillin.
[0167] With Lignin Model 1, any of these pathways may be viable and the production of guaiacol in the control experiments of entries 1 and 2, Table 1 (seen in Figure 8), support the hypothesis. In Lignin Model 2, at least one of these β-Ο-4 cleavage pathways may be inhibited since the γ-hydroxy group of Model 2 may be capped by a methoxy group. This may be consistent with the experimental observation of a dramatically reduced yield of guaiacol in entry 1, Table 2 (seen in Figure 8) for Model 2 relative to that for Model 1. Lignin Model 2 may therefore provide experimental evidence for the viability of a proton exchange of the γ-hydroxy group with caustic, followed by intramolecular displacement of guaiacol to produce an epoxide intermediate.
[0168] Lignin Model 3 may also contain the same propyl side chain substitution pattern as Model 1. Although it may be expected to yield guaiacol in proportional yields to that of the control experiments of Model 1, the meta-phenolate anion of Model 3 may alter the path of these reactions too and vary the yield with respect to Model 1. Instead, homolytic cleavage may be a minor pathway with Model 3. The absence of the guaiacol group in Model 4 may preclude the viability of β-Ο-4 cleavage pathway. As noted in Figure 9, β-γ fragmentation is the major pathway of caustic-induced reaction with Model 4.
[0169] FIGURE 18 provides the copper(II) chelate assisted oxidation of lignin. The combined results of Tables 1-5 (provided in Figure 8) may show the participation of a para- phenoxide anion in the copper(II)-mediated oxidation process. As such, there may be superior yields of vanillin for Model 1 relative to that of 3-HBA from Model 3. Further, there can be 4- fold greater yields of vanillin from Model 2 relative to that of 3-HBA from Model 3.
Additionally, there may be no significant effect with iron(II,III) catalysis alone. A homogenous catalyst, as seen in Figure 7, may be used.
[0170] Prior art has provided a crystal structure of a vanillin - copper(II) complex. In this crystal structure, the copper(II) ion is chelated between the phenoxide and methoxy oxygen atoms of two vanillin molecules. Based on this prior art, a mechanism may exist wherein the catalyst (i.e. Cu2+) complexes to the phenoxide of the Model substrates herein, and similarly other lignin phenyl propanoid building blocks. Single electron transfer from the electron-rich phenolate ring may then afford a phenoxy radical and a copper(I) species. This radical can be resonance stabilized with conjugation extending to the 1 -position of the phenyl ring, which may be adjacent to the propyl (R) group. The radical can suffer different outcomes, including but not limited to fragmentation, dimerization, hydrogen atom abstraction, etc. to provide the products seen in these reactions. Copper(I) may be oxidized by oxygen or by a co-catalyst iron(III). The overall process may thus be catalytic in the metal species and driven by oxygen as the oxidant. [0171] Further, several examples are provided below that provide various aspects of the invention described herein:
Example 1 - Synthesis of Compound 1 [4-0-(tert-Butyldimethylsilyl)vanillin]: To a 250-mL, round-bottomed flask, was added vanillin (10.00 g, 65.72 mmol), ieri-butyldimethylsilyl chloride (11.88 g, 78.84 mmol), imidazole (11.18 g, 164.25 mmol), and dry N,N-dimethylformamide (130 mL) under nitrogen atmosphere, and the reaction stirred at room temperature overnight. The next morning, water was added to quench the reaction and the mixture extracted with
dichloromethane. The combined organic layers were dried over sodium sulfate and concentrated under reduced pressure. The crude product was purified by silica gel column chromatography using ethyl acetate/hexanes (1 :9) as the eluent. Yield: 74%. 1H NMR (400 MHz, CDC13) δ 9.75 (s, 1H), 7.20-7.40 (2H), 6.80-6.90 (d, J= 5.6 Hz, 1H), 3.77 (s, 3H), 0.91 (s, 9H), 0.09 (s, 6H).
Example 2 - Synthesis of Compound 2 [Methyl 2-(Methoxy)phenoxyacetate]: To a 250-mL, two-necked, round-bottomed flask equipped with a reflux condenser was added potassium carbonate (20.71 g, 149.84 mmol), acetonitrile (130 mL), methyl bromoacetate (22.92 g, 149.84 mmol), and guaiacol (12.40 g, 99.89 mmol). The reaction was placed under nitrogen atmosphere and refluxed for 2.5 hours. After cooling to room temperature the mixture was filtered. The filtrate was evaporated to give pale yellow oil, which was purified by silica gel column chromatography using ethyl acetate/hexanes (1 :4) as the eluent. Yield: 81%. 1H NMR (400 MHz, CDC13) δ 6.75-7.05 (m, 4H), 4.68 (s, 2H), 3.87 (s, 3H), 3.78 (s, 3H).
Example 3 - Synthesis of Compound 3 [Aldol Condensation Product of Compounds 1 and
2]: To a 250-mL, two-necked, round-bottomed flask under nitrogen was added anhydrous tetrahydrofuran (60 mL) and N,N-diisopropylamine (5.70 g, 56.30 mmol). This solution was cooled to -78 °C and a 2.5 M solution of /i-butyl lithium in anhydrous tetrahydrofuran (3.61 g, 56.30 mmol) added slowly and stirred for 30 minutes to generate lithium /V,/V-diisopropylamide. A solution of compound 2 (8.83 g, 45.04 mmol) in anhydrous tetrahydrofuran (30 mL) was added dropwise to the lithium /V,/V-diisopropylamide solution and stirred for 15 minutes, followed by drop wise addition of compound 1 (10.00 g, 37.54 mmol) dissolved in anhydrous tetrahydrofuran (30 mL) over a period of 5 minutes. The reaction mixture was then stirred for 3 hours, quenched at -78 °C with a saturated aqueous ammonium chloride solution (150 mL), and allowed to warm to room temperature. The organic layer was washed with water, and the aqueous phase extracted with ethyl acetate. The combined organic phases were dried over sodium sulfate and concentrated under reduced pressure to give the crude product. Crude yield: 91%. 1H NMR (400 MHz, CDC13) δ 6.77-7.05 (m, 7H), 5.11 (t, 1H), 4.68 (m, 1H), 3.83 (s, 3H), 3.78 (s, 3H), 3.63 (s, 3H), 3.52 (m, 1H), 0.96 (s, 9H), 0.12 (s, 6H).
Example 4 - Synthesis of Lignin Model 1: To a 250-mL, round-bottomed flask under nitrogen atmosphere were added anhydrous tetrahydrofuran (100 mL), compound 3 (5.00 g, 10.80 mmol), and lithium aluminum hydride (0.82 g, 21.62 mmol). The mixture was stirred at room temperature for 3 hours before cooling to 0 °C and quenching the reaction with a saturated aqueous solution of Rochelle's salt (sodium potassium tartrate). This mixture was then stirred overnight. The product was extracted with ethyl acetate. The combined organic phases were dried of sodium sulfate and concentrated under reduced pressure to give the crude product.
Crude yield: 89%.
To the above crude product under nitrogen atmosphere was added anhydrous tetrahydrofuran (50 mL) and a 1.0 M solution of tetrabutylammonium fluoride in tetrahydrofuran (4.81 g, 18.41 mmol). The reaction was stirred at room temperature for 1 hour. Water was added to quench the reaction and the mixture extracted with ethyl acetate. The combined organic layers were dried over sodium sulfate and concentrated under reduced pressure. The crude material was purified by silica gel column chromatography using ethyl acetate/hexanes (1:4 followed by 3:2) as the eluent. Yield: 68%. 1H NMR (400 MHz, CDC13) δ 6.75- 7.10 (m, 7H), 5.62 (s, 1H), 4.95 (m, 1H), 4.13 (m, 1H), 3.85 (m, 7H), 3.60-3.70 (m, 1H), 3.49 (m, 1H), 2.75 (m, 1H). 13C NMR (100 MHz, CDC13) 151.77, 147.05, 146.82, 145.28, 132.00, 124.41, 121.83, 121.17, 119.21, 114.47, 112.35, 108.84, 87.59, 72.92, 60.92, 56.08. HREI-MS+: observed m/z = 320.1272; theoretical m/z = 320.1260. Example 5 - Synthesis of Compound 4 [Bis-(fert-Butyldimethylsilyl Ether of Compound 3]:
To a 250-mL, round-bottomed flask under nitrogen atmosphere was added acetonitrile (150 mL), compound 3 (10.19 g, 22.02 mmol), ie/ -butyldimethylsilyl chloride (6.63 g, 43.99 mmol), and l,8-diazabicyclo[5.4.0]undec-7-ene (6.71 g, 44.05 mmol). The reaction mixture was stirred overnight at room temperature before quenching with water. The organic phase was washed with saturated aqueous sodium bicarbonate solution, and the combined aqueous phases extracted with ethyl acetate. The combined organic layers were then dried over sodium sulfate and concentrated under reduced pressure. The crude material was purified by silica gel column chromatography using ethyl acetate/hexanes (1:4 followed by 3:2) as eluent. Yield: 93%. 1H NMR (400 MHz, CDC13) δ 6.60-7.02 (m, 6H), 6.44-6.38 (d, J = 8. 8 Hz, 1H), 4.96 (d, J = 8 Hz, 1H), 4.40 (d, J = 8 Hz, 1H), 3.75 (s, 6H), 3.68 (s, 3H), 0.97 (s, 9H), 0.81 (s, 9H), 0.11 (s, 6H), - 0.00 (s, 3H), -0.21 (s, 3H).
Example 6 - Synthesis of Compound 5 [Ester Reduction Product of Compound 4]: To a
250-mL, round-bottomed flask under a nitrogen atmosphere was added anhydrous
tetrahydrofuran (100 mL), compound 4 (11.77 g, 20.40 mmol), and lithium aluminum hydride (1.55 g, 40.79 mmol). The mixture was stirred at room temperature for 3 hours before cooling to 0 °C and quenching the reaction with a saturated aqueous solution of Rochelle salt (sodium potassium tartrate). This mixture was stirred overnight and extracted with ethyl acetate. The combined organic layers were dried over sodium sulfate and concentrated under reduced pressure to give the crude product. Crude yield: 83%. 1H NMR (400 MHz, CDC13) δ 6.70-7.15 (m, 7H), 4.95 (m, 1H), 4.12 (m, 1H), 3.85 (s, 3H), 3.75 (s, 3H), 3.72 (m, 3H), 0.97 (s, 9H), 0.89 (s, 3H), 0.84 (s, 6H), 0.13 (s, 6H), 0.075 (s, 3H), -0.007 (s, 3H).
Example 7 - Synthesis of Lignin Model 2: To a 250-mL, round-bottomed flask under a nitrogen atmosphere was added dry N,N-dimethylformamide (120 mL), compound 5 (9.32 g, 16.98 mmol), and sodium hydride (0.82 g, 34.00 mmol). The mixture was stirred for 15 minutes to generate the sodium alkoxide. To this mixture iodomethane (4.83 g, 34.00 mmol) was added and the stirring continued overnight. After cooling the reaction to 0 °C, glacial acetic acid (25 mL) was added followed by water (100 mL). The product was extracted with ethyl acetate, and the combined organic layers were dried over sodium sulfate and concentrated under reduced pressure to give the crude product. Crude yield: 87%.
To the above crude product under nitrogen atmosphere was added anhydrous tetrahydrofuran (80 mL) and a 1.0 M solution of tetrabutylammonium fluoride in tetrahydrofuran (11.04 g, 42.20 mmol). The reaction was stirred at room temperature for 1 hour before water was added to quench the reaction. This mixture was extracted with ethyl acetate, and the combined organic layers dried over sodium sulfate and concentrated under reduced pressure. The crude product was purified by silica gel column chromatography using ethyl acetate/hexanes (1:4 followed by 3:2) as the eluent. Yield: 68%. 1H NMR (400 MHz, CDC13) δ 6.80- 7.15 (m, 7H), 4.98 (m, 1H), 4.15 (m, 1H), 3.85 (m, 9H), 3.65 (m, 1H), 3.49 (m, 1H), 2.75 (m, 1H). 13C NMR (100 MHz, CDC13) 151.78, 149.18, 148.62, 147.05, 132.63, 132.10, 124.42, 121.82, 121.20, 120.10, 118.57, 112.33, 111.16, 110.10, 109.34, 89.70, 87.61, 74.50, 72.84, 61.10, 60.93, 56.08.
Example 8 - Synthesis of Compound 6 [3-Benzoylbenzaldehyde]: To a 250-mL two-necked, round-bottomed flask equipped with a reflux condenser was added potassium carbonate (17.00 g, 123.00 mmol), acetonitrile (150 mL), benzoyl chloride (23.02 g, 163.76 mmol), and 3- hydroxybenzaldehyde (10.00 g, 81.89 mmol) under nitrogen atmosphere. The reaction was refluxed overnight, and allowed to cool to ambient temperature. The resulting mixture was filtered. The filtrate was washed with a saturated aqueous sodium bicarbonate solution and extracted with dichloromethane. The combined organic layers were dried over sodium sulfate and concentrated under reduced pressure. The crude material was purified by silica gel column chromatography using ethyl acetate/hexanes (1:4) as the eluent. Yield: 81%. 1H NMR (400 MHz, CDC13) δ 10.05 (s, 1H), 8.10- 8.25 (m, 2H) 7.40-7.85 (m, 7H).
Example 9 - Synthesis of Compound 7 [Aldol Condensation Product of Compounds 2 and
6]: To a 250-mL, two-necked, round-bottomed flask under nitrogen was added anhydrous tetrahydrofuran (60 mL) and /V,/V-diisopropylamine (5.70 g, 56.30 mmol). The resulting solution was cooled to -78 °C and a 2.5 M solution of /i-butyl lithium in tetrahydrofuran (3.61 g, 56.30 mmol) was added slowly and stirred for 30 minutes to generate lithium /V,/V-diisopropylamide. A solution of compound 2 (8.83 g, 45.04 mmol) in anhydrous tetrahydrofuran (30 mL) was added drop wise to the lithium N,N-diisopropylamide solution and stirred for 15 minutes to generate the enolate, followed by the drop wise addition of compound 6 (8.49 g, 37.54 mmol) in an anhydrous tetrahydrofuran (30 mL) solution over a period of 5 minutes. The reaction mixture was stirred for 3 hours, then quenched at -78 °C with a saturated aqueous solution of ammonium chloride (150 mL), and allowed to warm to room temperature. The organic layer was separated, and the aqueous layer was extracted with ethyl acetate. The combined organic layers were washed with water, dried over sodium sulfate and concentrated under reduced pressure to give the crude product. Crude yield: 76%. 1H NMR (400 MHz, CDC13) δ 8.18 (m, 2H), 6.80-7.80 (m, 11H), 5.25 (m, 1H), 4.76 (d, J = 4.8 Hz, 1H), 4.55 (m, 1H), 3.84 (s, 3H), 3.67 (s, 3H), 3.50 (m, 1H).
Example 10 - Synthesis Lignin Model 3: To a 250-mL, round-bottomed flask under nitrogen was added anhydrous tetrahydrofuran (100 mL), compound 7 (12.03 g, 28.49 mmol), and lithium aluminum hydride (4.33 g, 114.97 mmol). The reaction was stirred for 3 hours before the mixture was cooled to 0 °C and quenched with a saturated aqueous solution of Rochelle salt (sodium potassium tartrate). This mixture was stirred overnight and extracted with ethyl acetate. The combined organic layers were dried over sodium sulfate and concentrated under reduced pressure. The crude material was purified by silica gel column chromatography using ethyl acetate/hexanes (1:4) as the eluent. Yield: 89%. 1H NMR (400 MHz, CDC13) δ 6.60-7.20 (m, 8H), 4.96 (m, 1H), 4.15 (m, 1H), 4.08 (m, 1H), 3.90 (m, 1H), 3.80 (s, 3H), 3.15 (m, 1H). 13C NMR (100 MHz, CDC13) 156.40, 151.50, 141.70, 129.89, 124.32, 121.89, 120.74, 118.31, 115.09, 113.26, 112.45, 86.61, 72.93, 60.73, 56.07.
Example 11 - Synthesis of 8 [Aldol Condensation Product of Compound 1 and Methyl Butyrate]: To a 250-mL, two-necked, round-bottomed flask under nitrogen was added anhydrous tetrahydrofuran (60 mL) and N,N-diisopropylamine (5.70 g, 56.30 mmol). The resulting solution was cooled to -78 °C and a 2.5 M solution of rc-butyl lithium in tetrahydrofuran (3.61 g, 56.30 mmol) was added slowly and stirred for 30 minutes to generate lithium N,N- diisopropylamide. A solution of methyl butyrate (4.59 g, 45.04 mmol) in anhydrous tetrahydrofuran (30 mL) was added dropwise to the lithium N,N-diisopropylamide solution and stirred for 15 minutes, followed by the dropwise addition of a solution of compound 1 (10.00 g, 37.54 mmol) in anhydrous tetrahydrofuran (30 mL) over a period of 5 minutes. The reaction mixture was stirred for 3 hours, then quenched at -78 °C with a saturated aqueous solution of ammonium chloride (150 mL) and allowed to warm to room temperature. The organic layer was separated, and the aqueous layer was extracted with ethyl acetate. The combined organic phases were washed with water, dried over sodium sulfate and concentrated under reduced pressure to give the crude product. Crude yield: 100%. 1H NMR (400 MHz, CDC13) δ (enantiomeric mixture) 6.65-6.90 (m, 6H), 4.85 (m, 1H), 4.70 (m, 1H), 3.79 (s, 6H), 3.70 (s, 4H), 3.55 (s, 2H), 2.68 (m, 4H), 1.78 (m, 2H), 1.55 (m,lH), 1.25 (m, 1H), 0.96 (s, 18H), 0.85 (m, 6H), 0.12 (s,126H).
Example 12 - Synthesis of Lignin Model 4: To a 250-mL, round-bottomed flask under nitrogen was added anhydrous tetrahydrofuran (100 mL), compound 8 (13.79 g, 37.42 mmol), and lithium aluminum hydride (2.84 g, 74.84 mmol). The reaction was stirred for 3 hours before cooling to 0 °C and quenching with a saturated aqueous solution of Rochelle salt (sodium potassium tartrate). This mixture was stirred overnight and extracted with ethyl acetate. The combined organic phases were dried sodium sulfate and concentrated under reduced pressure. The crude material was purified by silica gel column chromatography using ethyl
acetate/hexanes (1:4 followed by 3:2) as the eluent. Yield: 30%. (enantiomeric mixture) 1H NMR (400 MHz, CDC13) δ 6.60-6.90 (m, 6H), 6.14 (bs, 2H), 4.81 (bs, 1H), 4.50 (m, 1H), 3.79 (s, 6H), 3.62 (s, 4H), 1.74 (m, 2H), 1.20 (m, 4H), 0.80 (m, 6H). 13C NMR (100 MHz, CDC13) 146.72, 146.00, 145.19, 145.00, 135.62,134.90, 119.67, 119.08, 114.08, 108.81, 79.33, 64.66, 63.58, 55.96, 48.20, 48.05, 21.08, 18.08, 11.96, 11.66.
Example 13 - Synthesis of 9 [l-4-tert-butyldimethylsiloxyl-3-methoxyphenyl-2-propen-l-ol]:
To a 250-mL, two-necked, round-bottomed flask under nitrogen was added anhydrous tetrahydrofuran (80 mL) and compound 1 (8.19 g, 30.74 mmol). The vessel contents were cooled to -78 °C, and a 1.0 M solution of vinylmagnesium bromide in tetrahydrofuran (36.88 mL, 36.88 mmol) was added slowly. The reaction was stirred for 2 hours while the cooling bath was allowed to slowly warm to 0 °C. The reaction mixture was quenched at 0 °C with a saturated aqueous solution of ammonium chloride (100 mL). The organic layer was separated. The aqueous layer was extracted with ethyl acetate, and the combined organic layers washed with brine, dried over sodium sulfate and concentrated under reduced pressure to give the crude product. Crude yield: 96%. 1H NMR (400 MHz, CDC13) δ 6.70-6.90 (m, 3H), 6.02 (m, 1H), 5.57 (s, 1H), 5.34 (m, 1H), 5.17 (m, 1H) 3.88 (s, 3H), 3.79 (s, 1H), 0.97 (s, 9H), 0.12 (s, 6H).
Example 14 - Synthesis of 10 [l-(4-hydroxy-3-methoxyphenyl)-2-propen-l-ol]: To a 250- mL, round-bottomed flask under nitrogen atmosphere was added anhydrous tetrahydrofuran (50 mL), a 1.0 M solution of tetrabutylammonium fluoride in tetrahydrofuran (15.46 g, 59.13 mmol), and compound 9 (8.72 g, 29.56 mmol). The reaction was stirred for 1 hour before water was added to quench the reaction. The mixture was extracted with ethyl acetate. The combined organic layers were dried over sodium sulfate and concentrated under reduced pressure. The crude material was purified by silica gel column chromatography using ethyl acetate/hexanes (1:4 followed by 3:2) as the eluent. Yield: 51%. 1H NMR (400 MHz, CDC13) δ 6.70-6.95 (m, 3H), 6.02 (m, 1H), 5.58 (s, 1H), 5.34 (m, 1H), 5.17 (m, 1H) 3.88 (s, 3H), 1.87 (s, 1H)..
Example 15 - Synthesis of Lignin Model 5. To a 250-mL, two-necked, round-bottomed flask under nitrogen was added dichloromethane (150 mL) and compound 10 (5.59 g, 31.02 mmol). The solution was cooled to 0 °C before portion wise addition of meta-chloroperoxybenzoic acid (20.00 g, 115.89 mmol). The reaction was then allowed to warm to ambient temperature and was stirred overnight. The reaction was quenched by addition of a 10% sodium thiosulphate solution. The organic phase was washed with saturated aqueous sodium bicarbonate solution, and the aqueous phases re-extracted with dichloromethane. The combined organic layers were dried over sodium sulfate and concentrated under reduced pressure. The crude material was purified by silica gel column chromatography using ethyl acetate/hexanes (1;4 followed by to 3:2) as the eluent. Yield: 6%. 1H NMR (400 MHz, CDC13) δ 6.75-7.00 (m, 3H), 5.65 (bs, 1H), 4.85 (d, J = 2 Hz, 1H), 4.40 (d, J = 3.2 Hz, 1H), 3.90 (m, 3H), 3.20 (m 1H), 2.80-3.00 (m, 3H). Example 16 - General Procedure for Oxidation of Lignin Models in the Presence of Caustic: To a 100-mL, thick-walled, glass pressure tube is charged 6 mL of aqueous sodium hydroxide (100 mg caustic equivalent) and the appropriate model compound. The mixture is magnetically stirred to affect a solution. The indicated concentration of catalyst is then added, the vessel capped under and air atmosphere, and placed into a pre-heated oil bath at 130 °C. The reaction was magnetically stirred for the indicated reaction time at 130 °C. The vessel contents are then allowed to cool, neutralized to pH < 2with 10% sulfuric acid solution at ambient temperature, and the products extracted with methyl ieri-butyl ether. The product composition (free product and derivatization with N,0-bis(trimethylsilyl)trifluoroacetamide using pyridine as promoter) was analyzed by gas chromatography-mass spectroscopy.
[0172] The embodiments have been described, hereinabove. It will be apparent to those skilled in the art that the above methods and apparatuses may incorporate changes and modifications without departing from the general scope of this invention. It is intended to include all such modifications and alterations in so far as they come within the scope of the appended claims or the equivalents thereof.
Having thus described the invention, it is now claimed:

Claims

A method for biorefining, comprising the steps of:
providing lignin biomass;
treating said lignin biomass by oxidative processing in the presence of caustic; and producing at least one biobased product from said lignin biomass.
The method of claim 1, wherein said lignin biomass comprises at least one lignin building block of p-coumaryl alcohol, coniferyl alcohol, and sinapyl alcohol.
The method of claim 1, wherein said lignin biomass is provided from at least one biomass of plant biomass, woody plant biomass, agricultural plant biomass, and cultivated plant biomass.
The method of claim 1, wherein said lignin biomass is provided from at least one biomass of fresh plant biomass, recovered plant biomass, pulp and paper mill biomass, cellulosic ethanol refinery biomass, sugar cane mill biomass, commercial biomass fractionator biomass, and lignin residue biomass.
The method of claim 1, wherein said lignin biomass is provided from kraft pulp mill lignin.
The method of claim 1, wherein said lignin biomass is provided from sulfite pulp mill lignin.
The method of claim 1, wherein said lignin biomass is provided from soda pulp mill lignin.
The method of claim 1, wherein said lignin biomass is provided from cellulosic ethanol refinery lignin.
9. The method of claim 1, wherein said lignin biomass is provided from commercial plant biomass fractionator lignin.
10. The method of claim 1, wherein said lignin biomass is provided from lignin residue lignin.
11. The method of claim 1, wherein said lignin biomass is provided from waste lignin.
12. The method of claim 11, wherein said waste lignin is provided from at least one waste lignin of recovered biomass, kraft pulp mill waste lignin, sulfite pulp mill waste lignin, soda pulp mill waste lignin, cellulosic ethanol refinery waste lignin, commercial plant biomass fractionator waste lignin, and sugar cane mill waste lignin.
13. The method of claim 1, wherein said oxidative processing in said presence of caustic is provided by at least one caustic of lithium hydroxide, sodium hydroxide, potassium hydroxide, cesium hydroxide, magnesium hydroxide, barium hydroxide, calcium hydroxide, and carbonates and oxides of Group I and Group II metals of the Periodic Table.
14. The method of claim 1, wherein said oxidative processing in said presence of caustic is performed with an oxidant selected from at least one oxidant of air, oxygen, hydrogen peroxide, hydrogen peroxide, and organic peroxide.
15. The method of claim 14 wherein said oxidative processing of said lignin biomass in the presence of caustic is performed with an oxidant selected from at least one oxidant of air and oxygen.
16. The method of claim 1, wherein said oxidative processing in said presence of caustic is conducted in solvent comprising at least one solvent of water, ethanol, propanol, isopropanol, acetonitrile, and ionic liquids.
17. The method of claim 1, wherein said oxidative processing in said presence of caustic is carried out at a reaction pH of about 10 to about 14.
18. The method of claim 1, wherein said oxidative processing of said lignin biomass in said presence of caustic is carried out at a reaction pH of about 12 to about 14.
19. The method of claim 1, wherein said oxidative processing in said presence of caustic is performed at a reaction temperature of about 50 °C to about 300 °C.
20. The method of claim 1, wherein said oxidative processing in said presence of caustic is performed at a reaction temperature of about 100 °C to about 200 °C.
21. The method of claim 1, wherein said oxidative processing in said presence of caustic selectively cleaves the α-β carbon-carbon bond of a p-coumaryl alcohol, coniferyl alcohol, and/or sinapyl alcohol building block of said lignin biomass.
22. The method of claim 1, wherein said oxidative processing in said presence of caustic provides a caustic-induced carbon-carbon bond fragmentation of said lignin biomass.
23. The method of claim 22, wherein said oxidative processing in said presence of caustic comprises oxidation of a product of said caustic-induced carbon-carbon bond fragmentation of said lignin biomass.
24. The method of claim 1, wherein said oxidative processing in said presence of caustic provides a caustic-induced carbon-oxygen bond fragmentation of said lignin biomass.
25. The method of claim 24, wherein said oxidative processing in said presence of caustic comprises oxidation of a product of said caustic-induced carbon-oxygen bond fragmentation of said lignin biomass.
26. The method of claim 1, wherein said oxidative processing in said presence of caustic comprises oxidation of a phenolate anion of said lignin biomass.
27. The method of claim 26, wherein said oxidative processing in the presence of caustic is provided through catalyst chelation to said phenolate anion of said lignin biomass.
28. The method of claim 1, wherein said oxidative processing in said presence of caustic provides at least one biobased product which retains about 77% of the structural carbon atoms of said lignin biomass.
29. The method of claim 1, wherein said oxidative processing in said presence of caustic is provided from at least one process of batch processing and flow processing.
30. The method of claim 1, wherein said oxidative processing in said presence of caustic is provided by at least one process of catalytic oxidative processing and
stoichiometric oxidative processing.
31. The method of claim 30 wherein said catalytic oxidative processing is provided from at least one catalyst of a metal salt, a metal complex, and an elemental metal.
32. The method of claim 31 wherein said catalyst of said catalytic oxidative processing is provided from at least one catalyst of Group 3 through Group 12 transitional elements of the Periodic Table.
33. The method of claim 32 wherein said catalyst of said catalytic oxidative processing is provided from at least one said Group 3 through Group 12 transitional elements of the Periodic Table of vanadium, chromium, manganese, iron, cobalt, nickel, and copper.
34. The method of claim 31 wherein said catalyst of said catalytic oxidative processing is homogeneous.
35. The method of claim 31 wherein said catalyst of said catalytic oxidative processing is heterogeneous.
36. The method of claim 31 wherein said catalyst of said catalytic oxidative processing is supported on an inert solid matrix.
37. The method of claim 30, wherein an oxidant in said stoichiometric oxidative
processing is provided by an organic nitro compound.
38. The method of claim 37, wherein said organic nitro compound is a polymer.
39. The method of claim 1, wherein said at least one biobased product from said lignin biomass comprises at least one biobased product of aryl aldehydes and aryl carboxylic acids.
40. The method of claim 1, wherein said at least one biobased product from said lignin biomass comprises at least two biobased products of aryl aldehydes and aryl carboxylic acids.
41. The method of claim 39, wherein said aryl aldehydes and said aryl carboxylic acids comprise at least one chemical of commodity chemicals, fine chemicals, and specialty chemicals.
42. The method of claim 39, wherein said aryl aldehydes comprise at least one chemical of 4-hydroxybenzaldehyde, vanillin, and syringaldehyde.
43. The method of claim 39, wherein said aryl carboxylic acids comprise at least one chemical of 4-hydroxybenzoic acid, vanillic acid, and syringic acid.
44. The method of claim 39, wherein said aryl carboxylic acids comprise at least one chemical of general molecular structure: wherein R and R2 are selected from among hydrogen and methoxy.
The method of claim 39, wherein said aryl carboxylic acids comprise at least one chemical of general molecular structure:
wherein R is selected from among hydrogen and methoxy.
46. The method of claim 39, wherein said aryl carboxylic acids comprise at least one chemical of general molecular structure:
wherein R and R2 are selected from among hydrogen and methoxy.
The method of claim 39, wherein said aryl carboxylic acids comprise at least one chemical of general molecular structure: wherein R1; R2, and R3 are selected from among hydrogen and methoxy.
48. The method of claim 2, wherein said p-coumaryl alcohol, said coniferyl alcohol, and said sinapyl alcohol ratio of said lignin biomass regulates the biobased product provided by oxidative processing of said lignin biomass in the presence of caustic.
49. The method of claim 48, wherein said p-coumaryl alcohol, said coniferyl alcohol, and said sinapyl alcohol ratio of at least two lignin biomasses regulates the biobased product provided by oxidative processing of said lignin biomass in said presence of caustic.
50. A method for biorefining, comprising the steps of:
providing lignin biomass comprising at least one biomass of woody plant biomass, agricultural plant biomass, cultivated plant biomass, kraft pulping biomass, sulfite pulping biomass, soda pulping biomass, cellulosic ethanol refinery biomass, sugar cane mill biomass, lignin residue biomass, and waste biomass;
treating said lignin biomass by oxidative processing in the presence of caustic
treating said lignin biomas by oxidative processing in the presence of caustic wherein a caustic-induced carbon-carbon bond fragmentation of said lignin biomass occurs;
treating said lignin biomass by said oxidative processing in the presence of caustic wherein oxidation of a product of said caustic-induced carbon-carbon bond fragmentation of said lignin biomass occurs; treating said lignin biomass by said oxidative processing in the presence of caustic wherein a caustic-induced carbon-oxygen bond fragmentation of said lignin biomass occurs;
treating said lignin biomass by said oxidative processing in the presence of caustic wherein oxidation of a product of said caustic-induced carbon-oxygen bond fragmentation of said lignin biomass occurs;
treating said lignin biomass by said oxidative processing in the presence of caustic wherein oxidation of a phenolate anion of said lignin biomass occurs; treating said lignin biomass by said oxidative processing in the presence of caustic by at least one process of stoichiometric oxidative processing and catalytic oxidative processing;
conducting said oxidative processing of said lignin biomass in the presence of caustic to selectively provide at least one biobased product which retains about 77% of the structural carbon atoms of said lignin biomass; and
producing at least one biobased product from said lignin biomass comprising at least one chemical of aryl aldehydes and aryl carboxylic acids; wherein selective production of said biobased product of said lignin biomass occurs.
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