WO2016100028A1

WO2016100028A1 - Process for producing levoglucosenone

Info

Publication number: WO2016100028A1
Application number: PCT/US2015/064653
Authority: WO
Inventors: Torren Ryan CARLSON; Joachim C. Ritter; Christina S. Stauffer
Original assignee: EI Du Pont de Nemours and Co
Current assignee: EIDP Inc
Priority date: 2014-12-16
Filing date: 2015-12-09
Publication date: 2016-06-23
Anticipated expiration: 2017-06-16

Abstract

Disclosed herein are processes for producing levoglucosenone. In one embodiment, a carbohydrate feedstock is contacted with a first solvent and a homogeneous acid at a at a first temperature between about 20 °C and about 35 °C and for a first reaction time; the solvent is then removed to obtain an acid-impregnated feedstock, which may optionally be mechanically processed; and the acid-impregnated feedstock is then contacted with a second solvent at a second temperature between about 150 °C and about 250 °C for a second reaction time sufficient to form a product mixture comprising levoglucosenone.

Description

TITLE

PROCESS FOR PRODUCING LEVOGLUCOSENONE

FIELD OF DISCLOSURE

Processes for preparing levoglucosenone from carbohydrate feedstocks are provided. The carbohydrate feedstocks can be pretreated with acid and optionally mechanically processed.

BACKGROUND

Levoglucosenone is a highly dehydrated sugar which is useful as a chemical intermediate for the production of pharmaceuticals and industrial chemicals. A reactive α,β-unsaturated carbonyl system, protected aldehyde functionality, fixed ¹C₄ conformation, and sterically hindered β-D-face make levoglucosenone a useful chiral synthon for the synthesis of biologically active compounds. Levoglucosenone can also be used as a feedstock for production of industrial chemicals such as 1 ,6-hexanediol, which is a useful intermediate in the industrial preparation of polyamides such as nylon 66. 1 ,6-Hexanediol can be converted by known methods to 1 ,6-hexamethylene diamine, a starting component in nylon production.

It is increasingly desirable to obtain industrial chemicals or their precursors from materials that are not only inexpensive but also

environmentally benign. Of particular interest are materials which can be obtained from renewable sources, that is, materials that are produced by a biological activity such as planting, farming, or harvesting. Biomass sources for such materials are becoming more attractive economically versus petroleum-based ones. As used herein, the terms "renewable" and

"biosourced" are used interchangeably.

Methods for obtaining levoglucosenone from renewable sources have been reported. For example, Shafizadeh et al. (Carbohydrate Research, 71 , 169-191 (1979)) report the pyrolytic production of levoglucosenone from acid- treated cellulose and paper. Kawamoto et al. (J. Wood Sci (2007) 53:127- 133) disclose that catalytic pyrolysis of cellulose in sulfolane containing sulfuric acid or polyphosphoric acid gave levoglucosenone, furfural, and 5- hydroxymethyl furfural. Published patent application WO 201 1 /000030 A1 discloses a method of converting particulate lignocellulosic material to produce volatile organic compounds and char; the patent application also discloses a method of converting a lignocellulosic material, such as cellulosic bleached wood pulp, into a mixture of the volatile organic liquids, 1 (S)-6,8- dioxabicyclo[3.2.1 ]oct-2-en-4-one ((-)levoglucosenone, 2-furaldehyde

(furfural) and 4-ketopentanoic acid (levulinic acid).

There is an existing need for processes to produce levoglucosenone from renewable biosources in good yield. There is an existing need for processes to produce levoglucosenone from biomass-derived starting materials, including carbohydrate feedstocks such as lignocellulose, cellulose, one or more C₆ sugars, starch, agricultural residues, forestry waste, paper, wood, or a mixture thereof.

SUMMARY

In one embodiment, a process for producing levoglucosenone is provided, the process comprising the steps:

a) contacting a carbohydrate feedstock with a first solvent and a homogeneous acid at a first temperature between about 20 °C and about 35 °C and for a first reaction time;

b) removing the first solvent to obtain an acid-impregnated feedstock; c) optionally, mechanically processing the acid-impregnated

feedstock;

d) contacting the acid-impregnated feedstock with a second solvent at a second temperature between about 150 °C and about 250 °C for a second reaction time sufficient to form a product mixture comprising

levoglucosenone.

In one embodiment, step c) is performed, and mechanically processing the acid-impregnated feedstock comprises milling, crushing, grinding, shredding, chopping, disc refining, or a combination thereof. In one embodiment, the carbohydrate feedstock comprises

lignocellulose, cellulose, one or more C_& sugars, starch, agricultural residues, forestry waste, paper, wood, or a mixture thereof. In one embodiment, the carbohydrate feedstock comprises bagasse, switchgrass, corn stover, sorghum, wood, or a mixture thereof.

In one embodiment, the first solvent comprises diethyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, acetone, acetonitrile, methanol, ethanol, isopropanol, or a mixture thereof.

In one embodiment, the homogeneous acid comprises a mineral acid. In one embodiment, the mineral acid comprises sulfuric acid, hydrochloric acid, phosphoric acid, or a mixture thereof. In one embodiment, the homogeneous acid comprises an organic acid. In one embodiment, the organic acid comprises a monocarboxylic acid, a dicarboxylic acid, and alkyl sulfonic acid, an aryl sulfonic acid, a halogenated acetic acid, a halogenated alkylsulfonic acid, a halogenated aryl sulfonic acid, or a mixture therein. In one embodiment, the homogeneous acid has a concentration in the first solvent between about 1 weight percent and about 20 weight percent, relative to the weight of the feedstock. In one embodiment, the first solvent comprises diethyl ether and the homogeneous acid comprises sulfuric acid.

In one embodiment, the second solvent comprises sulfolane, polyethylene glycol, polyethylene glycol alkyl ether, polyethylene glycol dialkyi ether, polytrimethylene glycol, or mixtures thereof.

In one embodiment, step d) further comprises adding a second acid. In one embodiment, step d) is performed at a pressure between about 0.25 kPa and about 40 kPa. In one embodiment, step d) is performed in a batch manner. In one embodiment, step d) is performed in a continuous manner. In one embodiment, the process further comprises a step of isolating at least a portion of the levoglucosenone from the product mixture. In one

embodiment, the step of isolating is by distillation. In one embodiment, the second temperature is between 200 °C and 250 °C. In one embodiment, the product mixture further comprises furfural. DETAILED DESCRIPTION

As used herein, where the indefinite article "a" or "an" is used with respect to a statement or description of the presence of a step in a process of this invention, it is to be understood, unless the statement or description explicitly provides to the contrary, that the use of such indefinite article does not limit the presence of the step in the process to one in number.

As used herein, when an amount, concentration, or other value or parameter is given as either a range, preferred range, or a list of upper preferable values and lower preferable values, this is to be understood as specifically disclosing all ranges formed from any pair of any upper range limit or preferred value and any lower range limit or preferred value, regardless of whether ranges are separately disclosed. Where a range of numerical values is recited herein, unless otherwise stated, the range is intended to include the endpoints thereof, and all integers and fractions within the range. It is not intended that the scope of the invention be limited to the specific values recited when defining a range.

As used herein, the terms "comprises," "comprising," "includes," "including," "has," "having," "contains" or "containing," or any other

variation thereof, are intended to cover a non-exclusive inclusion. For example, a composition, a mixture, process, method, article, or apparatus that comprises a list of elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such composition, mixture, process, method, article, or apparatus.

Further, unless expressly stated to the contrary, "or" refers to an inclusive or and not to an exclusive or. For example, a condition A or B is satisfied by any one of the following: A is true (or present) and B is false (or not present), A is false (or not present) and B is true (or present), and both A and B are true (or present).

As used herein, the term "about" modifying the quantity of an ingredient or reactant employed refers to variation in the numerical quantity that can occur, for example, through typical measuring and liquid handling procedures used for making concentrates or use solutions in the real world; through inadvertent error in these procedures; through

differences in the manufacture, source, or purity of the ingredients

employed to make the compositions or carry out the methods; and the like. The term "about" also encompasses amounts that differ due to different equilibrium conditions for a composition resulting from a

particular initial mixture. Whether or not modified by the term "about", the claims include equivalents to the quantities. The term "about" may mean within 10% of the reported numerical value, or for example within 5% of the reported numerical value.

As used herein, the term "carbohydrate" refers to any of a large group of organic compounds having the general formula C_m(H₂0)_n, where m and n are integers, and includes C₆ sugars, starch, and cellulose.

As used herein, the term "carbohydrate feedstock" refers to any material containing at least one carbohydrate.

As used herein, the term "biomass" refers to any cellulosic or lignocellulosic material and includes materials comprising hemicellulose, and optionally further comprising lignin, starch, oligosaccharides and/or monosaccharides.

As used herein, the term "cellulose" means a polysaccharide consisting of 1000-3000 or more glucose units in an unbranched, linear chain structure.

As used herein, the term "lignocellulosic" means comprising both lignin and cellulose. Lignocellulosic material may also comprise hemicellulose. In some embodiments, lignocellulosic material contains glucan and xylan.

As used herein, the term "hemicellulose" means a non-cellulosic polysaccharide found in lignocellulosic biomass. Hemicellulose is a branched heteropolymer consisting of different sugar monomers. It typically comprises from 500 to 3000 sugar monomeric units. As uses herein, the term "starch" refers to a carbohydrate consisting of a large number of glucose units joined by glycosidic bonds. Starch, also known as amylum, typically contains amylose and amylopectin. Examples of typical starches include corn starch, tapioca, wheat starch, rice starch, and potato starch.

As used herein, the term "sugar" includes monosaccharides, disaccharides, oligosaccharides, and anhydrosugars. Monosaccharides, or "simple sugars," are aldehyde or ketone derivatives of straight-chain polyhydroxy alcohols containing at least three carbon atoms. A pentose is a monosaccharide having five carbon atoms; examples include xylose, arabinose, lyxose, and ribose. A hexose is a monosaccharide having six carbon atoms; examples include glucose and fructose. Disaccharide molecules consist of two covalently linked monosaccharide units; examples include sucrose, lactose, and maltose. Sucrose is a disaccharide composed of the monosaccharides glucose and fructose with the molecular formula

C12H22O11. As used herein, "oligosaccharide" molecules consist of about 3 to about 20 covalently linked monosaccharide units. Anhydrosugars are molecules with an intramolecular ether formed by the elimination of water from the reaction of two hydroxyl groups of a single monosaccharide;

examples include levoglucosenone, levoglucosan, galactosan, and

mannosan. Unless indicated otherwise herein, all references to specific sugars are intended to include the D- stereoisomer, the L-stereoisomer, and mixtures of the stereoisomers.

As used herein, the term "C_n sugar" includes monosaccharides having n carbon atoms; disaccharides comprising monosaccharide units having n carbon atoms; and oligosaccharides comprising monosaccharide units having n carbon atoms. As used herein, the term "C& sugar or equivalent" includes hexoses, disaccharides comprising hexose units, oligosaccharides

comprising hexose units, and glucan. As used herein, the term "C5 sugar or equivalent" includes pentoses, disaccharides comprising pentose units, oligosaccharides comprising pentose units, and xylan. As used herein, the abbreviation "LGone" refers to levoglucosenone, also known as 1 ,6-anhydro-3,4-dideoxy- -D-pyranosen-2-one. The chemical structure of levoglucosenone is represented by Formula (I).

The chemical structure of furfural, also known as furan-2-carbaldehyde or 2-furaldehyde, is represented by Formula (II).

II

In one embodiment, a process for forming a product mixture

comprising levoglucosenone is provided, the process comprising the steps: a) contacting a carbohydrate feedstock with a first solvent and a homogeneous acid at a first temperature between about 20 °C and about 35 °C and for a first reaction time;

feedstock;

levoglucosenone.

In one embodiment, the acid-impregnated feedstock is mechanically processed before contacting with a second solvent. In one embodiment, the acid-impregnated feedstock is not mechanically processed before contacting with a second solvent. In one embodiment, the first solvent comprises diethyl ether and the homogeneous acid comprises sulfuric acid. In some

embodiments, the product mixture further comprises furfural.

To be useful for levoglucosenone production, the carbohydrate feedstock contains at least one carbohydrate, such as glucan, a C_& sugar, or an equivalent. To be useful for levoglucosenone and furfural production, the carbohydrate feedstock further contains xylan, a C5 sugar, or an equivalent. Suitable feedstocks comprising lignocellulose, cellulose, C_& sugars, starch, or mixtures thereof can be derived from biorenewable resources including biomass. Biomass may be derived from a single source, or biomass can comprise a mixture derived from more than one source; for example, biomass could comprise a mixture of corn cobs and corn stover, or a mixture of wood and leaves. Biomass includes, but is not limited to, bioenergy crops, agricultural residues, municipal solid waste, industrial solid waste, sludge from paper manufacture, yard waste, wood and forestry waste or a

combination thereof. Examples of biomass include, but are not limited to, corn grain, corn cobs, crop residues such as corn husks, corn stover, grasses, wheat, wheat straw, barley, barley straw, hay, rice straw,

switchgrass, paper (including cardboard, kraft paper, pulp, containerboard, linerboard, corrugated container board), sugar cane bagasse, sorghum, soy, components obtained from milling of grains, trees, branches, roots, leaves, wood chips, sawdust, shrubs and bushes, vegetables, fruits, flowers, and animal manure or a combination thereof. Biomass that is useful for the present process may include biomass that has a relatively high carbohydrate value, is relatively dense, and/or is relatively easy to collect, transport, store and/or handle. In one embodiment, the feedstock is ultimately derived from biomass.

In some embodiments, the carbohydrate feedstock comprises lignocellulose, cellulose, one or more C_& sugars, starch, agricultural residues, forestry waste, paper, wood, or a mixture thereof. In some embodiments, the carbohydrate feedstock comprises lignocellulose. In some embodiments, the carbohydrate feedstock comprises cellulose. In some embodiments, the carbohydrate feedstock comprises starch. In some embodiments, the carbohydrate feedstock comprises agricultural residues. In some

embodiments, the carbohydrate feedstock comprises forestry waste. In some embodiments, the feedstock comprises wood. In some embodiments, the carbohydrate feedstock comprises paper. In some embodiments, the carbohydrate feedstock comprises a C_& sugar. In some embodiments, the carbohydrate feedstock is a C_& sugar comprising glucose, levoglucosan, sucrose, fructose, or mixtures thereof. In some embodiments, the

carbohydrate feedstock comprises glucose. In some embodiments, the carbohydrate feedstock comprises levoglucosan. In some embodiments, the carbohydrate feedstock comprises sucrose.

The feedstock may be used directly as obtained from the source or may be dried to reduce the amount of moisture contained therein. In some embodiments, the feedstock has a moisture content of less than about 15 weight percent, for example less than about 10 weight percent, or for example less than about 5 weight percent.

In the first step of the process, the carbohydrate feedstock is contacted with a first solvent and a homogeneous acid at a first temperature between about 20 °C and about 35 °C for a first reaction time. The first solvent, or first solvent mixture, may serve to reduce the viscosity of the system to improve fluidity of the mixture of the feedstock, the solvent, and the acid in the reaction vessel, and / or to remove the heat of reaction and improve the performance of the process. Suitable first solvents typically have relatively low boiling points and are substantially inert under the reaction conditions of the first contacting step. Examples of suitable first solvents include low boiling ethers, low boiling ketones, low boiling nitriles, and low boiling alcohols.

In one embodiment, the first solvent comprises an ether. Ethers useful as the first solvent in the processes disclosed herein may be linear or branched, cyclic or acyclic, and may contain from two to 12 carbon atoms. Examples of useful ethers include tetrahydrofuran, tetrahydropyran, tetrahydro-2H-pyran-2-methanol, 1 ,4-dioxane, diethyl ether, dipropyl ether, dibutyl ether, dipentyl ether, and dihexyl ether.

In one embodiment, the first solvent comprises a ketone. Ketones useful as the first solvent in the processes disclosed herein may be linear or branched and may contain from two to eight carbon atoms. Examples of useful ketones include acetone and methyl ethyl ketone.

In one embodiment, the first solvent comprises a nitrile. Nitriles useful as the first solvent in the processes disclosed herein may be linear or branched and may contain from two to eight carbon atoms. Examples of useful nitriles include acetonitrile, and propionitrile.

In one embodiment, the first solvent comprises an alcohol. Alcohols useful as the first solvent in the processes disclosed herein may be linear or branched and may contain from one to eight carbon atoms. Examples of useful alcohols include methanol, ethanol, n-propanol, iso-propanol, and 2- methylpropanol.

In one embodiment, the first solvent comprises diethyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, acetone, acetonitrile, methanol, ethanol, isopropanol, or a mixture thereof. In one embodiment, the first solvent comprises diethyl ether. In one embodiment, the first solvent comprises tetrahydrofuran. In one embodiment, the first solvent comprises 2- methyltetrahydrofuran. In one embodiment, the first solvent comprises acetone. In one embodiment, the first solvent comprises acetonitrile. In one embodiment, the first solvent comprises methanol. In one embodiment, the first solvent comprises ethanol. In one embodiment, the first solvent comprises isopropanol. As used herein, the term "mixture thereof"

encompasses both mixtures within and mixtures between solvent classes, for example mixtures of ethers, and also mixtures between ethers and alcohols.

Suitable first solvents are typically available commercially from various sources, such as Sigma-Aldrich (St. Louis, MO), in various grades, many of which may be suitable for use in the processes disclosed herein. Technical grades of a solvent can contain a mixture of compounds, including the desired component and higher and lower molecular weight components or isomers.

The amount of first solvent used in the first contacting step of the process can vary, depending for example on the viscosity of the mixture of feedstock, first solvent, and acid. Typically, the solvent may be present in the first contacting step in an amount ranging from about 75 weight percent to about 98 weight percent, based on the weight of the feedstock, catalyst, and solvent. For example, the solvent may comprise from about 80 weight percent to about 98 weight percent, or from about 85 weight percent to about 98 weight percent, or from about 90 weight percent to about 98 weight percent, of the total weight. The amount of solvent may be adjusted to obtain the desired viscosity.

The homogeneous acid may comprise a mineral acid, an organic acid, or a mixture thereof. In one embodiment, the homogeneous acid is a mineral acid, and the mineral acid comprises sulfuric acid, hydrochloric acid, phosphoric acid, or a mixture thereof. In one embodiment, the homogeneous acid comprises sulfuric acid. In one embodiment, the homogeneous acid comprises hydrochloric acid. In one embodiment, the homogeneous acid comprises phosphoric acid. As used herein, the term "phosphoric acid" refers to orthophosphoric acid, H₃P0₄, and can include, unless otherwise specified, polyphosphoric acids derived from condensation of orthophosphoric acid molecules and having the general formula HO(P0₂OH)_xH, where x is the number of phosphoric units in the molecule.

In one embodiment, the homogeneous acid is an organic acid, and the organic acid comprises a monocarboxylic acid, a dicarboxylic acid, and alkyl sulfonic acid, an aryl sulfonic acid, a halogenated acetic acid, a halogenated alkylsulfonic acid, a halogenated aryl sulfonic acid, or a mixture therein.

Suitable monocarboxylic acids include formic acid and acetic acid. Suitable dicarboxylic acids include oxalic acid, malonic acid, and citric acid. An example of a suitable alkyl sulfonic acid is methane sulfonic acid. An example of a suitable aryl sulfonic acid is toluenesulfonic acid. An example of a suitable halogenated acetic acid is trifluoroacetic acid. An example of a suitable halogenated alkylsulfonic acid is trifluoromethane sulfonic acid. An example of a suitable halogenated aryl sulfonic acid is fluorobenzenesulfonic acid.

In the first contacting step, the carbohydrate feedstock is impregnated with the homogeneous acid. The concentration of the homogeneous acid in the first solvent may be selected to provide acceptable rates of

levoglucosenone production in the subsequent process step of contacting the acid-impregnated feedstock with a second solvent and heat, while minimizing unwanted side reactions. In some embodiments, the homogenous acid has a concentration in the first solvent between about 1 weight percent and about 20 weight percent, relative to the weight of the feedstock. In some

embodiments, the acid catalyst concentration in the reaction mixture is between and optionally includes any two of the following values: 1 wt%, 1 .5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 1 1 wt%, 12 wt%, 13 wt%, 14 wt%, 15 wt%, 16 wt%, 17 wt%, 18 wt%, 19 wt%, and 20 wt%. The concentration of homogenous acid employed may depend on conditions such as temperature, the specific acid used, and the feedstock. The acid may be obtained from commercial sources.

Impregnating the carbohydrate feedstock with a homogeneous acid may be performed at a first temperature between about 20 °C and about 35 °C, or for example between about 20 °C and about 30 °C. In some

embodiments, the first temperature is between and optionally includes any two of the following values: 20 °C, 21 °C, 22 °C, 23 °C, 24 °C, 25 °C, 26 °C, 27 °C, 28 °C, 29 °C, 30 °C, 31 °C, 32 °C, 33 °C, 34 °C, and 35 °C. During this impregnating step, the temperature may be kept constant or varied. Higher contacting temperatures may lead to reaction of the glucan and xylan contained in the feedstock and may be undesirable at this step in the process. Lower temperatures can also be used.

Contacting the carbohydrate feedstock with the first solvent and a homogeneous acid may be performed for a first reaction time between about 0.1 hours (h) and about 12 h, for example between about 0.1 h and about 8 h. In some embodiments, the first reaction time is between and optionally includes any two of the following values: 0.1 h, 0.2 h, 0.3 h, 0.4 h, 0.5 h, 0.6 h, 0.7 h, 0.8 h, 0.9 h, 1 h, 1 .5, 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h, 5 h, 5.5 h, 6 h, 6.5 h, 7 h, 7.5 h, 8 h, 8.5 h, 9 h, 9.5 h, 10 h, 10.5 h, 1 1 h, 1 1 .5 h, and 12 hours. The choice of first reaction time may be related to the temperature of the contacting step, the concentration of the homogeneous acid in the first solvent, and the amount of feedstock used.

Contacting the carbohydrate feedstock with the first solvent and a homogeneous acid may be performed in any suitable reactor. Optionally, the reactor may be equipped with a means, such as impellers, for agitating the feedstock, first solvent, and homogeneous acid. The contacting may be performed in a batch or continuous manner, and in a single reactor or in a series of reactors. Suitable reactor types may include, for example, continuous stirred-tank reactors.

After the contacting step, the first solvent is removed to obtain an acid- impregnated feedstock. The first solvent may be removed under reduced pressure or by filtration. Typically, the acid-impregnated feedstock can be dried before performing the next step in the process. Drying may be by air drying at room or at elevated temperature, or by heating in an oven or vacuum oven. The dry acid-impregnated feedstock may contain from about 1 to about 20 weight percent acid, for example from about 5 weight percent to about 15 weight percent, or from about 7 weight percent to about 12 weight percent, based on the weight of the feedstock.

Optionally, the acid-impregnated feedstock may be mechanically processed by applying energy to the feedstock, for example to reduce the size, increase the exposed surface area, and/or increase the availability of C6 sugars or equivalents present in the acid-impregnated feedstock for the next process step. Energy means useful for mechanically processing the acid- impregnated feedstock include, but are not limited to, milling, crushing, grinding, shredding, chopping, disc refining, ultrasound, and microwave. In some embodiments, the feedstock can have an average particle size below about 5 mm, for example below about 2 mm, before mechanical processing, and an average particle size below about 2 mm, for example below about 1 mm, after mechanical processing. The mechanical processing step may optionally be performed under an inert atmosphere, for example under nitrogen.

In the next process step, the acid-impregnated feedstock, optionally having been mechanically processed, is contacted with a second solvent. Suitable second solvents typically have boiling points in the range of 150°C to 500°C, for example in the range of 150 °C to 300 °C, and are substantially inert under the reaction conditions of this contacting step. In one

embodiment, the second solvent comprises an aprotic polar solvent, a polar polymeric material, or mixtures thereof.

In one embodiment, the second solvent comprises an aprotic solvent. Examples of suitable aprotic polar solvents include sulfolane,

dimethylformamide, N-methyl-2-pyrrolidone, and dimethyl sulfoxide. In one embodiment, the aprotic solvent comprises sulfolane. Sulfolane is also referred to as tetrahydrothiophene 1 , 1 -dioxide, or as 2,3,4,5- tetrahydrothiophene-1 , 1 -dioxide. In one embodiment, the aprotic solvent comprises dimethylformamide. In one embodiment, the aprotic solvent comprises N-methyl-2-pyrrolidone. In one embodiment, the aprotic solvent comprises dimethyl sulfoxide.

In one embodiment, the second solvent comprises a polar polymeric material. Examples of suitable polar polymer materials include polyethylene glycol, polyethylene glycol alkyl ether, polyethylene glycol dialkyl ether, polytrimethylene glycol, and mixtures thereof. In one embodiment, the second solvent comprises polyethylene glycol. In one embodiment, the second solvent comprises polyethylene glycol alkyl ether, wherein the alkyl groups are selected from methyl or ethyl. In one embodiment, the second solvent comprises polyethylene glycol monomethyl ether. In one

embodiment, the second solvent comprises polyethylene glycol monoethyl ether. In one embodiment, the second solvent comprises polyethylene glycol dialkyl ether, wherein the alkyl groups are selected from methyl or ethyl. In one embodiment, the second solvent comprises polyethylene glycol dimethyl ether. In one embodiment, the second solvent comprises polyethylene glycol diethyl ether. In one embodiment, the second solvent comprises

polytrimethylene glycol.

Suitable polyethylene glycols, polyethylene glycol alkyl ethers, polyethylene glycol dialkyl ethers, and polytrimethylene glycols have molecular weights between about 300 daltons and 10,000 daltons. In some embodiments, the number average molecular weight of the polyethylene glycols, the polyethylene glycol alkyl ethers, the polyethylene glycol dialkyl ethers, and/or the polytrimethylene glycols is between and optionally includes any two of the following values: 300 daltons, 500 daltons, 1000 daltons, 1500 daltons, 2000 daltons, 2500 daltons, 3000 daltons, 3500 daltons, 4000 daltons, 5000 daltons, 6000 daltons, 7000 daltons, 8000 daltons, 9000 daltons, and 10,000 daltons. In some embodiments, the molecular weight is between 300 daltons and 1500 daltons. In some embodiments, the molecular weight is between1000 and 10,000 daltons. In some embodiments, the molecular weight is between 500 daltons and 5000 daltons.

In some embodiments, the second solvent has a water content of about 5 weight percent or less. In some embodiments, the second solvent has a water content of about 2 weight percent or less, for example about 1 weight percent or less. In some embodiments, the second solvent is anhydrous.

The amount of second solvent used can vary, depending for example on the viscosity of the mixture of acid-impregnated feedstock and second solvent. Typically, the second solvent may be present in this contacting step in an amount ranging from about 75 weight percent to about 98 weight percent, based on the weight of the feedstock and solvent. For example, the solvent may comprise from about 80 weight percent to about 98 weight percent, or from about 85 weight percent to about 98 weight percent, or from about 90 weight percent to about 98 weight percent, of the total weight. The amount of solvent may be adjusted to obtain the desired viscosity.

In the processes disclosed herein, an acid-impregnated feedstock is contacted with a second solvent at a second temperature between about 150 °C and about 250 °C for a second reaction time sufficient to form a product mixture comprising levoglucosenone. The acid impregnated in the feedstock catalyzes conversion of the cellulose, C& sugar, starch, or mixtures thereof in the feedstock to levoglucosenone. If the feedstock also contains xylan or C5 sugars, the product mixture further comprises furfural.

Optionally, a second acid may be added to the acid-impregnated feedstock, or to the second solvent. The second acid may be the same or different from the homogeneous acid used to impregnate the feedstock. In some embodiments, the amount of the second catalyst used can be between about 1 weight percent and bout 20 weight percent (wt%), based on the weight of the feedstock. In some embodiments, the amount of the second catalyst used is between and optionally includes any two of the following values: 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 1 1 swt%, 12 wt%, 13 wt%, 14 wt%, 15 wt%, 16 wt%, 17 wt%, 18 wt%, 19 wt%, and 20 wt%, based on the weight of the acid-impregnated feedstock. The second acid may be obtained from commercial sources. If desired, a second acid may be added to increase the rate of levoglucosenone and/or furfural production. However, process economics may be improved by using a sufficient amount of homogenous acid in the step of impregnating the feedstock, so that addition of a second acid later in the process is

unnecessary.

Contacting the acid-impregnated feedstock with a second solvent may be performed at a temperature between about 150 °C and about 250 °C. In some embodiments, the second temperature is between and optionally includes any two of the following values: 150 °C, 155 °C, 160 °C, 165 °C, 170 °C, 175 °C, 180 °C, 185 °C, 190 °C, 195 °C, 200 °C, 205 °C, 210 °C, 215 °C, 220 °C, 225 °C, 230 °C, 235 °C, 240 °C, 245 °C, and 250 °C. In some embodiments, the second temperature is between about 100 °C and about 300 °C. In some embodiments, the second temperature is between about 200 °C and about 250 °C. In some embodiments, the second temperature is between about 150 °C and about 250 °C. In some embodiments, the second temperature is between about 180 °C and about 220 °C. During the contacting step, the second temperature may be kept constant or varied.

Contacting the acid-impregnated feedstock with the second solvent may be performed below atmospheric pressure, at atmospheric pressure, or above atmospheric pressure. In some embodiments, the reactor pressure is between about 0.25 kPa and about 40 kPa, and optionally includes any two of the following values: 0.25 kPa, 0.5 kPa, 1 kPa, 2 kPa, 3 kPa, 4 kPa, 5 kPa, 6 kPa, 7 kPa, 8 kPa, 9 kPa, 10 kPa, 15 kPa, 20 kPa , 25 kPa, 30 kPa, 35 kPa, and 40 kPa. In some embodiments, the pressure is between about 1 kPa and about 40 kPa, for example between about 10 kPa and about 40 kPa, or between about 20 kPa and about 40 kPa. In some embodiments, the pressure is between about 1 kPa and about 20 kPa. In some embodiments, the contacting is done under autogenous pressure. Optionally, the contacting may be performed under an inert gas such as nitrogen or argon. The choice of operating pressure may be related to the temperature of the contacting step and is often influenced by economic considerations and/or ease of operation.

An advantage of operating at a pressure below atmospheric pressure is that any water formed in this contacting step can be removed in a vapor stream. Removing the water reduces its concentration in the product mixture and thus may minimize furfural formation. In one embodiment, the step of contacting the acid-impregnated feedstock with a second solvent to form a product mixture comprising levoglucosenone is performed as a reactive distillation, wherein at least a portion of the water and at least a portion of the levoglucosenone are removed from the product mixture under reduced pressure. In one embodiment, the water content of the product mixture comprising levoglucosenone is less than about 15 weight percent. The acid-impregnated feedstock is contacted with the second solvent for a second reaction time sufficient to form a product mixture comprising levoglucosenone. Typically, the second reaction time may be between about 1 minute and about 30 min, for example between about 5 min and about 25 min. The choice of the second reaction time may be related to the

temperature of the contacting step, the concentration of the homogeneous acid contained in the impregnated feedstock, and the amount of feedstock used.

The product mixture formed during the step of contacting an acid- impregnated feedstock with a second solvent comprises levoglucosenone, and optionally furfural. The product mixture further comprises solvent and homogeneous acid. In some embodiments, the product mixture may contain from about 0.1 weight percent to about 8 weight percent levoglucosenone, for example from about 0.1 weight percent to about 6 weight percent, or from about 0.1 weight percent to about 5 weight percent, or from about 0.1 weight percent to about 3 weight percent levoglucosenone, based on the total weight of the product mixture. In some embodiment, the product mixture may further contain from about 0.01 to about 8 weight percent furfural, for example from about 0.1 to about 5 weight percent, or from about 0.2 to about 2 weight percent, based on the total weight of the product mixture. In some

embodiments, the product mixture may further comprise one or more of levoglucosan, 1 ,6-anhydro-beta-D-glucofuranose, hydroxymethylfurfural, or formaldehyde.

The processes disclosed herein may further comprise a step of isolating at least a portion of the levoglucosenone from the product mixture. The processes disclosed herein may further comprise a step of isolating at least a portion of the furfural from the product mixture. The isolating steps may be performed using techniques known in the art, for example by distillation or liquid-liquid extraction.

Contacting the acid-impregnated feedstock with a second solvent can be performed in any suitable reactor. Optionally, the reactor may be equipped with a means, such as impellers, for agitating the acid-impregnated feedstock and second solvent. The contacting may be performed in a batch, continuous, or semi-continuous manner. The contacting step may be performed in one reactor, or in a series of reactors. Suitable reactor types may include, for example, continuous stirred-tank reactors, plug flow tubular flow reactors, and slurry bubble column reactors. Reactor design is well- known and is disclosed in engineering handbooks.

The processes disclosed herein may offer several advantages over other methods for obtaining levoglucosenone. Impregnating the carbohydrate feedstock with acid, and optionally mechanically processing the impregnated material, can provide higher yield of levoglucosenone, relative to the yield obtained from untreated carbohydrate feedstock. Unlike traditional pyrolysis processes, contacting the acid-impregnated feedstock with a solvent at a temperature between about 150 °C and about 250 °C can help to control unwanted secondary reactions, minimize char formation, and minimize polymerization of reactive compounds. In addition, the continuous removal of water via distillation under reduced pressure can limit the water-catalyzed degradation of levoglucosenone to furfural and provide higher yields of levoglucosenone.

EXAMPLES

The processes described herein are illustrated in the following examples. From the above discussion and these examples, one skilled in the art can ascertain the essential characteristics of this invention, and without departing from the spirit and scope thereof, can make various changes and modifications to adapt it to various uses and conditions.

The following abbreviations are used in the examples: "LGone" means levoglucosenone, "FF" means furfural, "DMSO" means dimethylsulfoxide; "°C" means degrees Celsius; "wt%" means weight percent; "g" means gram(s); "mg" means milligram(s), "mmol" means millimole(s), "mol%" means mole percent, "M" means molar, "mg/g" means milligram(s) per gram, "h" means hour(s), "min" means minute(s); "%" means percent, "wt%" means weight percent; "ml_" means milliliter(s); "μί" means microliter(s), "pm" means micrometer(s), "mm" means millimeter(s), "m" means meter(s), "GC" means gas chromatography; "HPLC" means high pressure liquid

chromatography; "NREL" means National Renewable Energy Lab; "Temp" means temperature; "Ex" means Example, "Comp Ex" means Comparative Example.

Materials

All commercial materials were used as received unless stated otherwise. All reagents were obtained from Sigma-Aldrich (St. Louis, MO) unless stated otherwise. Levoglucosenone (90% purity) was obtained from TimTec LLC (Newark, DE). Sulfuric acid was obtained from EMD Chemicals (Gibbstown, NJ). Bagasse was obtained from DuPont (Brazil). LA bagasse was obtained from Louisiana. Switchgrass was obtained from Genera (Vonore, TN). Corn Stover was obtained from Kyle Altoff (Rochester, IN). Sorghum was obtained from Tenuta Cassana (Torre Garofoli, Italy). Wood (60% aspen/40% maple) was obtained from Fortress Paper (Canada).

Six types of biomass were selected for use as carbohydrate feedstocks for the production of levoglucosenone - two different types of bagasse, switchgrass, corn stover, sorghum, and wood. All feedstocks were dried at 105 °C for 24 hours before use. The particle size of the feedstocks as received was as follows:

• Bagasse: Retsch Milled <1 .5 mm

• Switchgrass: Hammermilled d50 ~ 1 mm

· Corn Stover: Windrowed and passed through 2.0 mm screen

• Sorghum: Banton Milled <1 .0 mm

• LA Bagasse: Banton Milled <1 .0 mm

• Wood: 60% Aspen/40% Maple, Banton Milled <1 .0 mm

Table 1 provides the composition and moisture content of each feedstock after drying. Table 1 . Carbohydrate Feedstock Compositions

"nd" means not determined Analytical Methods

The carbohydrate composition of the biomass samples was

determined according to a modified version of the standard method

NREL/TP-510-42618, as follows:

The solid to be analyzed was either air dried or dried in a vacuum oven at 80 ^°C until the moisture content was less than 20 wt%. The biomass was milled in a knife mill until it passed through a >20 mesh screen. The percent solid for each biomass was determined by drying with a halogen moisture analyzer to 105 C (Mettler Toledo), and then 300 mg (dry weight basis) of the biomass was weighed into a 100 mL glass pressure vessel (Chemglass, CG- 1880-05). 3.0 mL of 72 wt % H₂SO₄ in water was added to the solid and the mixture was mixed using a 1 /4" diameter polytetrafluoroethylene (PTFE) rod to ensure complete coverage of acid on the solid particles. The mixture was submerged in a stirred 30 ^°C water bath for 30 min. It was then briefly mixed again by vortexing the tubes between 8-10 seconds and returned to the water bath for an additional 30 min. To avoid losses, the PTFE rod remained in the mixture for this first hour. After this initial incubation period, deionized water (84 g) was added to the vessel and it was thoroughly mixed. The PTFE rod remained in the solution.

This method was modified when there was not enough biomass to complete the analysis on the scale described above. In these instances, only 50 mg of solid (dry weight basis) was added to a 15 ml_ pressure vessel (Chemglass, CG-1880-01 ) along with 0.5 ml_ of 72 wt % H₂S0₄ in

water. This was mixed thoroughly, as described above, and was then incubated at 30 ^°C for 1 h. An additional 14 mL of water was added to these small scale reactions and the contents thoroughly mixed.

A sugar recovery standard (SRS) was prepared by weighing glucose, xylose, arabinose, and DMSO (internal standard) into a bottle along with 200 g of water. 84 g of this solution was added to each of two 100 mL pressure tubes. 3 mL of 72 wt % H₂S0₄ was added to each pressure tube. A sample of each acidic SRS solution was removed before and after heating for HPLC analysis. After heating, the HPLC areas were less than before heating due to sugar degradation during the acid hydrolysis. The area ratios of each sugar were recorded and were used to calculate a unique degradation correction factor for the glucose, xylose and arabinose sugars. The correction factor was applied to the sugars detected in the unknown biomass samples being analyzed during the same experiment in an attempt to adjust for degraded sugars during the procedure.

After the 1 h incubation period at 30 ^°C and subsequent dilution with water, the pressure vessels were put into an autoclave. The autoclave was rapidly heated to a temperature of 121 -126 ^°C and held there for 60 min, after which time it cooled slowly. The samples were pulled from the autoclave after 1 .5 h. The temperature of the autoclave cooled to approximately 80 ^°C at this time. The vessels were then further cooled on ice. A weighed amount of internal standard (typically DMSO, but sometimes DMF; about 0.8000 g or 0.1000 for the smaller scale analysis) was added to the sample vessel and the mixture was shaken vigorously. The mixture was filtered to remove any remaining undissolved solids using a tared polypropylene filter funnel with a 10 micron polyethylene fritted disc (Chemglass, OP-6602). The PTFE rod was removed from the pressure tube during the filtering step. The PTFE rod was thoroughly washed over the filter. A portion of the filtrate was collected and analyzed by HPLC. The undissolved solid collected on the fritted disc was washed with copious amounts of water and was dried in a vacuum oven at 80 ^°C.

The weight of the washed and dried acid insoluble material was recorded and expressed as wt% lignin. The mole amounts of monomeric carbohydrates solubilized by the compositional analysis process and detected by the HPLC analysis were determined. The mole amounts of each were converted to weights using the molecular weights of the polymer bound sugars (i.e. 132 g / mole for xylose and arabinose as monomeric units in hemicellulose or 162 g / mole for glucose as the monomeric unit in

cellulose). These saccharides were present as polysaccharides in the native biomass, not as monomers, so their molecular weights were assumed to be 18 amu less than the monomeric molecular weight, owing to the loss of one molecule of water for each monomer in the polysaccharide chain. The detected weights of each sugar were then reported as a weight % of the dry biomass.

Levoglucosenone and furfural amounts were determined as follows.

To a weighed aliquot of the sample to be analyzed was added a standard solution of 3.5 wt% diethylene glycol diethyl ether in isopropanol. The sample was mixed thoroughly, then 1 ml_ was filtered through a 0.2 pm filter (GHP Acrodisc® 13 mm syringe filter, PALL Life Sciences, Port Washington, NY) into an auto sampler vial. GC analysis of the sample was performed with an Agilent 5890 gas chromatograph with 7673 auto sampler. The column was an Agilent RTX Stabilwax® column (30 m x 0.25 mm x 0.5 μΓη). The injector was maintained at 250 °C and the injection volume was 1 μί with a split ratio of 20: 1 . The carrier gas was helium at 1 mL/min and a FID detector at 250 °C was used. Concentrations of levoglucosenone and furfural were determined from a standard calibration curve developed for each of the analytes with diethylene glycol diethyl ether.

LGone yields were calculated based on the glucan content of each feedstock. FF yields were based on the xylan content of each feedstock to simplify calculations, although small amounts of FF were also produced from the glucan content of the biomass. Typically less than about 5% FF was observed using cellulose as feedstock under similar conditions.

Moisture analysis was performed using a halogen moisture analyzer (Mettler-Toledo).

Description of Experimental Apparatus for Contacting Feedstock with

Sulfolane to Form a Product Mixture Comprising Levoglucosenone

A 4-necked round-bottom flask (250 ml_) was equipped with each of the following items attached to one of the necks: a short path distillation apparatus, a glass solid addition tube, a glass dip-tube filled with mineral oil for internal temperature monitoring, and an adapter containing a metal tube used for nitrogen purge. A round-bottom flask was attached as a distillation receiver to the end of the condenser of the short path distillation unit to collect any volatiles that distilled over; the distillation receiver was cooled with a dry ice/acetone bath. Vacuum was introduced to the system using a diaphragm vacuum pump. House nitrogen supply was used as the nitrogen source. The vacuum and nitrogen flow were controlled with Swagelok® needle valves. The internal pot temperature and the short path distillation head temperature were monitored using digital Fluke 5211 thermocouples. The 4-necked round- bottom flask and its contents were heated with an oil bath, and aluminum foil was used to insulate the exposed sections of the apparatus which were not immersed in the oil bath.

General Procedure for Contacting Feedstock with Sulfolane to Form a

Product Mixture Comprising Levoglucosenone A weighed quantity of dry feedstock (~2.5-3 g), untreated or pretreated as described below, was loaded into a solid addition tube. A magnetic stir bar, sulfolane (100 ml_), and the appropriate amount of concentrated sulfuric acid for the desired acid loading were placed into the reaction flask. For the Comparative Examples, sufficient concentrated sulfuric acid was used to give an acid loading of 0.1 weight percent relative to the sulfolane, corresponding to about 4.6 weight percent sulfuric acid relative to the feedstock. For the Examples, no sulfuric acid was added in the step of contacting the pretreated feedstock with sulfolane and heating. The rest of the apparatus was assembled as described above.

Once fully assembled, the system was placed under a vacuum of about 13.3 kPa (~99.6 Torr). Subsurface nitrogen purging (~327 mL/min) was initiated once the vacuum had stabilized. Heating was begun once both the nitrogen and vacuum pressure were equilibrated. The internal temperature of the flask contents was monitored and upon reaching ~200 °C, the dry feedstock in the solid addition tube was dispensed into the sulfolane over about 3 minutes. The reaction mixture was subsequently heated at ~200-210 °C for a reaction time between about 5 and 25 minutes. After the desired reaction time, the product mixture was allowed to cool to room temperature.

Once cooled, the reaction mixture was filtered to separate the solids and obtain a filtrate. The solids were washed well with water and dried. Any liquid remaining in the short path condenser, which had not fully distilled over into the distillation receiver, was rinsed from the condenser with methylene chloride and collected. The filtrate, the material from the condenser, and the contents of the distillation receiver were analyzed separately by GC for levoglucosenone and furfural; the amounts were summed and reported in Table 2 as total yields of levoglucosenone and furfural. In all the Examples, the majority of the levoglucosenone was found in the filtrate and the majority of the furfural was found in the distillation receiver. Comparative Examples A through M

Production of Levoglucosenone from Untreated Feedstocks

Comparative Examples A through M demonstrated the yield of levoglucosenone and furfural obtained from various carbohydrate feedstocks which had not undergone a chemical pretreatment step before contacting with sulfolane solvent in the presence of an acid catalyst and heat. As indicated in Table 2, for each Comparative Example the untreated feedstock was subjected to the General Procedure as disclosed herein above for the reaction time indicated. In Table 2, the reaction time shown included the time for addition of the feedstock to the sulfolane solvent and for heating at ~200- 210 °C.

The results for the Comparative Examples show that all the untreated feedstocks produced levoglucosenone, with LA bagasse and wood providing the highest yields. All the untreated feedstocks also produced furfural.

Table 2. Levoglucosenone and Furfural Yields from Various Untreated

Carbohydrate Feedstocks

Examples 1 through 7

Pretreatment of Feedstocks and Their Use for Production of

Levoglucosenone

Selected carbohydrate feedstocks were pretreated before contacting with sulfolane solvent and heat. The pretreatment consisted of an acid- impregnation step followed by a mechanical processing step. The acid- impregnation step was performed by placing the carbohydrate feedstock in diethyl ether solvent containing 9 wt% H₂S0₄ (relative to the feedstock), and stirring the mixture at room temperature for 1 hour. The diethyl ether was then removed under reduced pressure. The acid-impregnated feedstock was allowed to air dry, then subjected to ball milling using 20 mm stainless steel balls as grinding media for 2 hours. The acid-impregnated, mechanically processed feedstock was then contacted with sulfolane and heated for 10 minutes following the general procedure disclosed herein above, except that no additional sulfuric acid was added to the sulfolane. Results are presented in Table 3.

Comparative Examples N through S

Comparative Examples N through S were performed according to the General Procedure above, using untreated feedstocks as indicated in Table 3. Yields of levoglucosenone and furfural are presented in Table 3.

Table 3. Levoglucosenone and Furfural Yields from Pretreated

Carbohydrate Feedstocks

Switchgrass P 29 29 2 58 49

Switchgrass 3 58 47

Corn Stover Q 19 12 4 74 57

Corn Stover 5 50 45

Bagasse R 29 15 6 29 60

Wood S 42 17 7 12 33

Average of two runs

As shown in Table 3, in several cases the acid-impregnation and mechanical processing pretreatment of a carbohydrate feedstock resulted in higher yields of levoglucosenone compared to yields from the same carbohydrate feedstock that was not pretreated in this manner. Furfural yields were also generally higher from pretreated than from corresponding untreated feedstocks. Pretreated sorghum, pretreated switchgrass, and pretreated corn stover all showed increased yields of levoglucosenone relative to the corresponding untreated material.

Examples 8, 9, and 10

Comparison of Yields from Different Pretreatments

For Examples 8, 9, and 10, switchgrass was pretreated with different methods to compare the effect of the pretreatments on the yield of

levoglucosenone.

For Example 8, switchgrass was ground using a ball mill for 2 hours (20 mm stainless steel balls), then contacted with sulfolane, about 9 wt% H₂S0₄ relative to feedstock, and heated according to the General Procedure, .

For Example 9, switchgrass was impregnated with 10 wt% H₂S0₄, relative to feedstock then contacted with sulfolane and heated according to the General Procedure, but with no additional acid in the sulfolane.

For Example 10, switchgrass was impregnated with 9 wt% H₂S0₄ relative to the feedstock and then ball milled before contacting with sulfolane and heat according to the General Procedure, but with no additional acid in the sulfolane.

Comparative Examples C and D were performed according to the General Procedure using untreated switchgrass and 4.6 wt% H₂S0₄ relative to feedstock in the sulfolane contacting step.

As shown in Table 4, a combination of both acid impregnation and ball milling produced the highest yield of LGone from switchgrass (Example 10).

Table 4. Levoglucosenone and Furfural Yields from Switchgrass with

Different Pretreatments

Claims

What is claimed is: 1 . A process comprising the steps:

b) removing the first solvent to obtain an acid-impregnated feedstock; c) optionally, mechanically processing the acid-impregnated feedstock;

levoglucosenone.

2. The process of claim 1 , wherein the carbohydrate feedstock comprises lignocellulose, cellulose, one or more C₆ sugars, starch, agricultural residues, forestry waste, paper, wood, or a mixture thereof.

3. The process of claim 1 , wherein the carbohydrate feedstock comprises bagasse, switchgrass, corn stover, sorghum, wood, or a mixture thereof.

4. The process of claim 1 , wherein the first solvent comprises diethyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, acetone, acetonitrile, methanol, ethanol, isopropanol, or a mixture thereof.

5. The process of claim 1 , wherein the homogeneous acid comprises a mineral acid.

6. The process of claim 5, wherein the mineral acid comprises sulfuric acid, hydrochloric acid, phosphoric acid, or a mixture thereof.

7. The process of claim 1 , wherein the homogeneous acid comprises an organic acid.

8. The process of claim 7, wherein the organic acid comprises a monocarboxylic acid, a dicarboxylic acid, and alkyl sulfonic acid, an aryl sulfonic acid, a halogenated acetic acid, a halogenated alkylsulfonic acid, a halogenated aryl sulfonic acid, or a mixture thereof.

9. The process of claim 1 , wherein step c) is performed, and

mechanically processing the acid-impregnated feedstock comprises milling, crushing, grinding, shredding, chopping, disc refining, or a combination thereof.

10. The process of claim 1 , wherein the homogeneous acid has a concentration in the first solvent between about 1 weight percent and about 20 weight percent, relative to the weight of the feedstock.

1 1 . The process of claim 1 , wherein the first solvent comprises diethyl ether and the homogeneous acid comprises sulfuric acid.

12. The process of claim 1 , wherein the second solvent comprises sulfolane, polyethylene glycol, polyethylene glycol alkyl ether, polyethylene glycol dialkyl ether, polytrimethylene glycol, or mixtures thereof.

13. The process of claim 1 , wherein step d) further comprises adding a second acid.

14. The process of claim 1 , wherein step d) is performed at a pressure between about 0.25 kPa and about 40 kPa.

15. The process of claim 1 , wherein step d) is performed in a batch manner.

16. The process of claim 1 , wherein step d) is performed in a continuous manner.

17. The process of claim 1 , further comprising a step of isolating at least a portion of the levoglucosenone from the product mixture.

18. The process of claim 17, wherein the step of isolating is by distillation.

19. The process of claim 1 , wherein the second temperature is between 200 °C and 250 °C.

20. The process of claim 1 , wherein the product mixture further comprises furfural.