WO2010094697A1

WO2010094697A1 - Liquefaction of lignin with gaseous components

Info

Publication number: WO2010094697A1
Application number: PCT/EP2010/051966
Authority: WO
Inventors: Mike Kleinert
Original assignee: Bergen Teknologioverføring As
Priority date: 2009-02-17
Filing date: 2010-02-17
Publication date: 2010-08-26

Abstract

The present invention refers to a method of converting a lignin material into a liquid product and the liquid product obtainable by the method.

Description

Liquefaction of lignin with gaseous components

Description

Use of biomass for energy purposes is increasingly a focus both in research and development of alternative energy sources. The need for exploiting energy resources that are renewable, globally available and do not contribute to adverse climate effects is generally accepted (1), but the specific solutions are still in a process of development, and the list of options is still open - and expanding.

Producing renewable liquid fuels that are suitable for use in motor vehicles is perhaps the greatest challenge in the biofuel area. The quickest route to general use would be to produce a fuel that is compatible with the existing motor technology and infrastructure, which would make it faster and simpler to implement than fuels like hydrogen and electricity that require major changes at several levels of technology. Ethanol, biodiesel (FAMEs) and biogas are obvious examples of such fuels, but the amounts produced based on present day resources and technology will only cover a fraction of the total needed on a global basis (2).

For the production of renewable motor fuels (3), woody biomass is in many perspectives the preferred raw material. Natural wood is a large resource in many areas of the world and increased exploitation is sustainable. In addition, short rotation forestry may increase the available resources without competing with food production (4), thus reducing negative side-effects of change in land use or intense farming of e.g. soya, corn or sugar cane.

Ethanol production from the carbohydrate fractions of wood is already close to commercial application. However, the wood raw material also contains other components: The average composition of a Norwegian Norway spruce (Picea abies) log is 41% cellulose, 28% hemicellulose, 27% lignin and 4% resins. Thus, the use of the carbohydrate fractions leaves around one third of the material as a low-value by-product or waste. This is a significant drawback for the economy of the whole process.

For optimal use of the renewable resources it is preferable to think in terms of a bio-refinery (5,6), where the raw material coming into the refinery is completely transformed to a range of products. The product slate can then be designed to give the best possible total economy. Within this concept, the lignin and extractives that are "left over" after ethanol production should be processed to give value-added products, rather than just being burned as a process energy source. Even the 4% resins in the raw material can give a significant contribution to the total product slate if good products are obtained. In a more global context lignin, right after cellulose, has to be considered as second most prominent and abundant source of renewable and sustainable carbon.

US 3,186,923 discloses a method of increasing the yield of valuable, low- molecular weight pyrolysate products having a high oxygen content such as guaiacol, vanillin and catechol by pyrolizing natural vegetable materials such as bark, woodwaste and lignins. Pyrolysis takes place in a reactor tube, wherein commensurated bark is charged and formic acid is fed as a liquid. The reaction mixture is heated up to 450⁰C while flushing it with nitrogen. The process takes place at reduced atmospheric pressures of 20 to 100 mmHg.

AU B1 49 796/79 describes a method for hydrolising lignocellulosic material with formic acid in the presence of water at temperatures of 60-70⁰C, and ambient pressure thereby converting hemicellulose to its hydrolysis product, converting cellulose to glucose and dissolving a major portion of the lignin content. In the following, the solid residue is reacted with formic acid and hydrochloric acid thereby converting residual cellulose to glucose and converting other polysaccharides to monosaccharides. Remaining lignin residues are collected after the last step and are discarded.

FR 2 770 543 describes a method for producing cellulose, lignin, sugar and acetic acid from bark cellulose as the starting material. The starting material is mixed with formic acid and acetic acid and then heated to 5O⁰C at ambient pressure. A solid fraction, which mainly contains cellulose, is separated from the organic phase, which mainly consists of formic acid, acetic acid, monomeric sugars, solubilized polymers and lignins. The lignin fraction is not further worked up.

In this work, we have focussed on the conversion of lignin to liquids by pyrolysis/solvolysis, with the aim of obtaining liquid fuels also from this part of the raw material. The initial aim is to produce organic liquids (oils) that are compatible with petroleum products, and thus can be used as blending components in existing motor fuels. For this purpose we have selected closed system pyrolysis in a liquid reaction medium as the thermochemical conversion method, since the high oxygen content and the dominance of aromatic structures in lignins require considerable chemical transformation to give stable, petroleum-soluble liquid products. Simple classical pyrolysis technologies that only apply heating will result in conversion mainly to solid coke, just as lignin-rich material in nature would be transformed into coal, not petroleum, during natural conversion processes (7,8). The more popular processes of fast or flash pyrolysis, regardless of the applied method of heating, is primarily aimed at producing liquids. However, these bio-oils or bio-crude oils are, like the biomass they are derived from, very rich in oxygen and therefore polar and are often chemically not stable over time (9). Coke formation is expected to be higher when lignin is the raw material compared to whole wood, so the fast pyrolysis technology is overall not considered the optimal technology for thermochemical conversion in this case.

The vast majority of lignin research in terms of transportation fuel production - A - is done on hydrodeoxygenation or zeolite upgrading that utilise gaseous hydrogen and different catalysts to remove the covalently bound oxygen as water (10). Recent research has e.g. lead to patents for a "Process for catalytic conversion of lignin to liquid bio-fuels" (11).These techniques involve a two or three step procedure in which first the natural polymer is depolymerised by strong bases at elevated temperatures and subsequently the respective mono- or oligomers are hydrotreated in the presence of heavy and/or transition metals and their oxides. The products consist of alkyl phenols or alkylbenzes respectively, the former known to possess distinct octane-increasing properties.

Further, a method is known (12) for producing liquid hydrocarbons by thermochemical cracking and hydrogenating a solid starting material, wherein the solid starting material and a hydrogen donor-solvent system are reacted under conditions of non-stationary flow in a reaction rotor device with flow modulation. The hydrogen donor-solvent system consists of water and a mixture of hydrocarbon fractions with boiling temperatures in the range of 35-100 ⁰C with a circulating-postfractionating residue having a boiling temperature in the range of 450-600 ⁰C and a solidification temperature of 20 ⁰C.

Another method for converting wood or other cellulosic material into oil by reacting carbon monoxide with wood wastes in the presence of a sodium carbonate solution is described in (15).

In recent publications (16, 17), a new method of liquefying lignin to hydrogen-enriched biofuel is described.

PCT/EP2008006672 describes a method of converting a lignin material into a liquid product by treatment in a reaction medium under elevated pressure, wherein the reaction medium comprises at least one CrC₂ carboxylic acid, particularly formic acid, and/or salts, and/or esters thereof. It was an object of the present invention to provide a method of liquefying a lignin material, which can be conducted in an effective and an economical way.

Generally, the present invention refers to a liquefaction process that is capable of depolymerising the natural biopolymer lignin into a liquid product that has significantly reduced oxygen content and is therefore suitable as blending component of conventional fossile fuels in auto-motive applications. During the conversion depolymerisation and oxygen removal by formation of water takes place in a single operation, which is a major novelty as compared to presently known multi-step process yielding liquid products of comparable quality.

An aspect of the present invention involves the liquefaction of a lignin starting material, wherein a feed stream comprising gaseous components, e.g. H₂ and optionally further gaseous components such as CO, is introduced into the reaction medium.

The introduction of a feed stream comprising gaseous components may improve the energy balance of the liquefaction process in that the addition of expensive components, such as formic acid, may be reduced or even completely avoided.

Preferably, the gaseous feed stream is made up at least partially from synthesis gas, i.e. a gaseous mixture comprising CO and H₂, which may be obtained by reacting a fuel material (e.g. coal, petroleum, petroleum residues, natural gas, natural wood and biomass) with water vapour and air and/or CO₂ at elevated temperatures. In addition to H₂ and CO, the synthesis gas may comprise other gaseous products such as CO₂, methane and other hydrocarbons as well as N₂.

In some embodiments, the gaseous H₂ containing feed stream is introduced into a reaction mixture comprising lignin starting material and further reactants, which may include at least one Ci-C₂ carboxylic acid and/or salts and/or esters thereof, more preferably formic acid and/or salts and/or esters thereof. The introduction of the gaseous feed stream can help replacing, at least partially, the d-C₂ carboxylic acid, particularly the formic acid as sole source of hydrogen. Without wishing to be bound by theory, applicants assume that the carboxylic acid would serve as an "initiator" of hydrogen formation in statu nascendi and the complementary amount of required hydrogen (for the removal of oxygen from the lignin starting material by means of hydrodeoxygenation) would be provided at least partially by the gaseous hydrogen feed.

A further aspect of the present invention involves the liquefaction of a lignin starting material, wherein a feed stream comprising gaseous components as described above is introduced into the reaction medium, which further comprises at least one CrC₂ carboxylic acid, particularly formic acid, and/or salts and/or esters thereof. In this embodiment, the gaseous components may be introduced during the whole reaction period or a part thereof. Preferably, the reaction is carried out in a reaction medium comprising at least one Ci-C₂ carboxylic acid, particularly formic acid, and/or salts and/or esters thereof, wherein the gaseous components, e.g. H₂ and optionally further gaseous components such as CO, are introduced during the course of the reaction, e.g. after 1-6 h, when the reaction temperature has reached a predetermined value.

A further aspect of the present invention involves the liquefaction of a lignin starting material under conditions involving the adjustment of a predetermined substantially constant reaction temperature and a pressure profile, i.e. a varying pressure over the course of the reaction. In this embodiment, the reaction temperature is maintained substantially constant after an initial the heating period. The pressure within the reactor is, however, varied over the reaction time. Preferably, the pressure is increased over the reaction time. This temperature/pressure control leads to an increased yield and/or quality of reaction products either with or without the addition of gaseous feed streams. The adjustment of a substantially constant temperature and a varying pressure profile over the course of the reaction allows an excellent operating control of the gas composition in the reaction medium by taking into account the ongoing chemical reactions such as water-gas-shift reaction (H₂O + CO <→ CO₂ + H₂), steam reforming (CH₄ + H₂O <→ CO + 3H₂) and Boudouard reaction (CO + CO₂ <→ 2CO).

Preferably, the method of the invention comprises a slow pyrolysis or solvolysis process that converts a multi-phase system of a liquid/gaseous reaction medium and of solid lignin, which stems from e.g. ethanol production from lignocellulosic biomass (wood) or waste streams from pulp and paper industry, both biomass streams in which the desired carbohydrate fraction like cellulose etc. is removed, into a two-phase system comprising a liquid aqueous phase and a liquid bio-oil (product) phase. The phases can easily be separated. No or very little solid by-product (char) is formed, which, however, is always the case in presently known slow pyrolysis processes. Yields of product oils are preferably about at least 50-90% or higher on a mass basis from solid lignin to liquid bio-oil. Stirring of the reaction mixture during the whole reaction period or a part thereof is advantageous.

The bipolarity and the amount of covalently bound oxygen in the liquid product is significantly reduced, making the liquid product highly compatible with fossile fuels.

Preferably, in the invention heating rates in the range of 0.1-50°C/min, preferably 1-30°C/min, more preferably 1-20°C/min and residence times of a couple minutes to some hours are used.

A first aspect of the present invention provides a method of converting a lignin material into a liquid product, comprising the steps:

(a) providing a lignin starting material,

(b) subjecting said starting material to a treatment in a reaction medium under elevated pressure comprising H₂ and optionally further gaseous components such as CO, wherein said starting material is converted to a liquid product, and

(c) obtaining the liquid product from the reaction medium.

In this aspect, a gaseous feed stream comprising H₂ and optionally further gaseous components such as CO, preferably in the form of a synthesis gas, is introduced into the reaction medium comprising the lignin starting materials. In addition to the gaseous components, the reaction medium may comprise other components, particularly at least one C_rC₂ carboxylic acid and/or salts and/or esters thereof, at least one alcohol and/or water, an alkylating agent and/or an inorganic salt and/or a catalyst. In some embodiments, the reaction medium is free from Ci_-2 carboxylic acids, salts and esters thereof and contains an alcohol, particularly ethanol.

A further aspect of the present invention provides a method of converting a lignin material into a liquid product, comprising the steps:

(a) providing a lignin starting material,

(b) subjecting said starting material to a treatment in a reaction medium under elevated pressure comprising:

(i) H₂ and optionally further gaseous components such as CO, (ii) optionally at least one CrC₂ carboxylic acid, and/or salts and/or esters thereof, (iii) optionally at least one alcohol and/or water,

(iv) optionally an alkylating agent, and (v) optionally an inorganic salt and/or a catalyst, wherein said starting material is converted to a liquid product, and

(c) obtaining the liquid product from the reaction medium.

In this aspect, the lignin starting material is subjected to a treatment under elevated pressure in the presence of a reaction medium comprising H₂, optionally component (ii) and optionally components (iii), (iv) and/or (v) as described above. The gaseous component (i) may be introduced at the beginning of the reaction and/or may be introduced during the course of the reaction, e.g. after 1-6 h, when the predetermined reaction temperature has been reached after an initial heating step. The introduction of gaseous components into the reaction mixture may occur continuously over a predetermined period of time and/or batchwise.

Still a further aspect of the present invention provides a method of converting a ligning material into a liquid product comprising the steps:

(a) providing a lignin starting material,

(b) subjecting said starting material to a treatment in a reaction medium under elevated pressure, wherein the reaction mixture is heated to a predetermined temperature and kept substantially constant during the course of the reaction and wherein the pressure of the reaction mixture is varied during the course of the reaction, wherein said starting material is converted to a liquid product, and

(c) obtaining the liquid product from the reaction medium.

In this aspect, the gaseous component (i) may be absent or introduced at the beginning or during the course of the reaction, e.g. after having reached the predetermined substantially constant reaction temperature. In some embodiments, the reaction medium preferably comprises components (ii) and optionally components (iii), (iv), and/or (v) as described above. In other embodiments, component (ii) may be absent, if gaseous component (i) is present. The term "substantially constant" means a temperature variation of ± 10°C, more preferably ± 5°C during the course of the reaction. The pressure variation preferably comprises an increase of the pressure during the course of the reaction, e.g. an increase of 50-200 bar, preferably of 100-150 bar. For example, an initial reaction pressure of 250-300 bar may increase to a reaction pressure of 350-450 bar during the course of the reaction. As used herein, "lignin" and "lignin material" are used interchangeably and refer to a biomass material which is an amorphous three-dimensional energy- rich phenolic biopolymer. Lignin is typically deposited in nearly all vascular plants and provides rigidity and strength to their cell walls. The lignin polymeric structure is composed primarily of three phenylpropanoid building units interconnected by etheric and carbon-to-carbon linkages. Non-limiting examples of lignin material can include agricultural lignin, wood lignin, lignin derived from municipal wast, Kraft lignin, organosolve lignin, and combinations thereof. Preferably, the solid lignin starting material is selected from wood lignin or products derived therefrom such as processed steam explosion material, hydrolysis lignin or lignosulfonate from pulp and paper industries and combinations thereof. Examples of lignins which may be used in the present invention are shown in Table 1.

Table 1 : Lignin starting materials and their chemical composition.

C H O H/C H/O C/O

Different industrial or scientific lignin samples [%] [%] [%] mol. mol. mol.

Organosolv (commercial) 65 5.7 28.7 1.04 3.15 3.02

Hydrolytic (commercial) 63 5.7 30 1.08 3.02 2.80

Alkali (commercial) 59 5.6 33.5 1.13 2.65 2.35 milled wood lignin 58 5.1 36.2 1.05 2.24 2.13

Organosolv (commercial, Aldrich) 66.3 5.3 27.9 0.95 3.02 3.17

DP510 (commercial, Borregaard) 42.0 4.6 47.1 1.31 1.55 1.19

DP511, dry (Borregaard) 47.6 4.3 47.2 1.07 1.44 1.34

Aspen milled wood lignin (scientific, KTH) 58.7 5.9 35.3 1.2 2.65 2.22

Spruce milled wood lignin (scientific, KTH) 59.2 6 34.6 1.21 2.75 2.28

Spruce lignin (scientific, KTH) 61.2 5.8 31.7 1.13 2.9 2.57

Birch lignin (scientific, KTH) 54.1 5.5 38 1.21 2.3 1.90

Aspen lignin (scientific, KTH) 59.2 5.7 33.2 1.15 1.15 1.82

Lignin from EtOH plant, (scientific, Lund) 55.2 6 38.6 1.3 2.47 1.90

Lignin from EtOH plant, (scientific, College 31.3

Bergen) 63.3 4.7 3 0.88 2.38 2.69

Lignin from EtOH plant, wa. (commercial,

SEKAB) 54.8 6.1 39.0 1.32 2.75 1.87

Lignin from EtOH plant, e. (commercial, SEKAB) 58.8 6.0 34.4 1.21 2.47 2.28

In the method of the present invention, the lignin material preferably comprises less than 50% by weight, more preferably less than 30% by weight and most preferably less than 15% by weight of cellulosic material.

The method of the present invention is preferably carried out in a single step. This means that the conversion of the lignin material to the liquid product is carried out in a single reaction, preferably without an interruption, e.g. an intermediate cooling step or separation step.

The reaction may be carried out in the absence of any added catalyst, e.g. any metal-containing catalyst. In other embodiments, the reaction may be carried out in the presence of catalysts, particularly hydrogenation catalysts. Examples of catalysts are SiO₂-based catalysts such as zeolites, metal (oxide) catalysts, e.g. transition metal (oxide), e.g. Va and/or Ni (oxide) catalysts or iron, e.g. iron (III) salts. Standard hydrogenation catalysts such as Pd/C are particularly well suited.

The treatment according to the invention may be carried out at elevated temperatures. The reaction temperature is usually from 200-500 °C, preferably from 300-450 ⁰C, more preferably from 320-420 ⁰C, and most preferably from 350-400 ⁰C. The reaction is carried out as a slow pyrolysis process, wherein the heating of the reaction mixture occurs preferably with a rate of about 1 -30 °C/min. The reaction pressure is usually from 50-1000 bar, preferably 100-500 bar, more preferably from 100-250 bar. In another embodiment, the preferred pressure range is from 250-400 bar. The reaction time is preferably from 2 h to 100 h, more preferably from 10 h to 24 h. The weight ratio of lignin starting material to reaction medium is preferably from about 1 :1 to about 1 :12, more preferably from about 1 :2 to about 1 :10.

The reaction medium preferably comprises (i) H₂ and optionally further gaseous components such as CO and further components, e.g. (ii) at least one d-C₂ carboxylic acid and/or salts and/or esters thereof, (iii) optionally at least one alcohol and/or water, (iv) optionally an alkylating agent and (v) optionally an inorganic salt and/or a catalyst. In some embodiments, the reaction medium is free from component (ii).

The reaction medium preferably comprises at least 1 %, preferably 10-90% by weight of component (i). Further, the medium preferably comprises at least 1%, preferably 10 to 90% by weight of component (ii) (if component (ii) is present), 0 to 60% by weight of component (iii), 0 to 50% by weight of component (iv) and 0 to 10% by weight of component (v).

In a preferred embodiment component (iii) is present in an amount of from 2 to 60% by weight, more preferably of from 5 to 60% by weight. A preferred example of component (iii) is ethanol.

Component (i) of the reaction medium comprises H₂, preferably in an amount of at least 1 % by weight, more preferably between 5-10% by weight, and optionally other gaseous components such as CO in an amount of preferably 5-10% by weight.

Component (ii) of the reaction medium comprises at least one CrC₂ carboxylic acid, e.g. formic acid and/or acetic acid and/or salts and/or esters thereof. Preferably, component (ii) of the reaction medium comprises formic acid, and/or alkali salts, e.g. lithium, sodium and/or potassium salts, and/or esters, e.g. CrC₃ alcohol esters thereof. More particularly, the reaction medium comprises at least 20%, preferably at least 30%, more preferably at least 60% by weight formic acid, and/or alkali salts, e.g. lithium, sodium and/or potassium salts, and/or esters, e.g. Ci-C₃ alcohol esters thereof. In some embodiments, however, component (ii) may be absent.

Formic acid may be produced by conventional means or by means of hydrothermal conversion of carbohydrate biomass at mild temperatures (13). Alternatively, formic acid may be produced from carbon dioxide in situ (14).

Further, the reaction medium optionally comprises as component (iii) at least one alcohol, e.g. an aliphatic alcohol, preferably at least one d-C₅ alcohol, more preferably at least one CrC₃ alcohol and/or water. The preferred C1-C3 alcohol may be selected from methanol, ethanol, n-propanol, isopropanol or mixtures thereof. Especially preferred is ethanol. The proportion of water in component (iii) is preferably less than 10 % by volume. In a preferred embodiment component (iii) is a technical grade alcohol, e.g. an aliphatic alcohol, preferably at least one C1-5 alcohol, more preferably at least one C1-3 alcohol, comprising less than 10%, preferably less than 8%, even more preferably less than 5% by volume of water.

Further, the reaction medium optionally comprises as component (iv) an alkylating agent. The alkylating agent may be selected from dimethyl carbonate (DMC), tetramethylammonium hydroxide (TMAH) and/or combinations thereof.

Furthermore, the reaction medium may optionally comprise as component (v) an inorganic salt and/or a catalyst. The inorganic salt may be selected from NaCI, NaHCO₃, MgSO₄, FeSO₄, FeCI₃, FeBr₃, AICI₃, AIBr₃ and/or combinations thereof.

After the reaction has taken place, the reaction mixture preferably comprises two liquid phases, an organic phase containing the desired product and an aqueous phase. Further, small amounts of solid products, e.g. char and/or coke as well as gaseous reaction products may be present. The desired liquid organic product may be separated from the aqueous phase by conventional methods, e.g. in a separatory funnel or by decanting. If desired, the aqueous phase may be extracted with a hydrophobic organic solvent in order to obtain organic products present in the aqueous layer. Moreover, component (iii) which is present in both, the aqueous and the oily product phase, can be isolated and recycled, e.g. by destination, in order to reduce the overall demand of these compounds. The product obtainable by the method of the present invention comprises preferably, e.g. 50% by weight or more alkyl or polyalkyl phenols having a molecular weight in the range of 100-250 Da, more preferably in the range of 100-200 Da. Main product classes are aliphatic, both linear and branched hydrocarbons of up to ten carbon atoms and phenols with one or more Ci-₃ substituents, but no methoxy groups are incorporated.

The amount of polyphenol^ compounds in the product is less than 5% by weight (based on a total amount of product), more preferably less than 3% by weight and even more preferably less than 1 % by weight.

The term "polyphenol^ compounds" as used herein refers to aromatic or heteroaromatic compounds having at least two phenolic hydroxy groups per molecule. Examples for polyphenol^ compounds include tannins, flavonoids and catechols.

The above described product composition shows markedly increased C/O and H/C molar ratios compared to the lignin source used (cf. Table 1), which result in an improved energy content relative to the starting material and which make them readily miscible with conventional fuels.

The elemental composition of the liquid product is: 60 to 85% C, preferably 70-85% C, 6.5 to 15% H₁ preferably 10-15% H, 2 to 25% O, preferably 2-7% O, and 0 to 1.0% S.

In another embodiment, the elemental composition of the liquid product is: 70 to 85% C, preferably 80-85% C, 7 to 15% H, preferably 10-15% H₁ 2 to 20% O, preferably 2-7% O, and 0 to 1.0% S. The molar ratios of the main elements H, C and O are preferably: H/C: 1.3 to 2.2, preferably 1.6-2.2, H/O: 10 to 45, preferably 30-45, and C/O: 5 to 30, preferably 20 to 30.

The yield of liquid product in the method of the present invention is preferably at least 80% by weight, more preferably at least 90% by weight, most preferably at least 95% by weight, based on the weight of the lignin starting material. The amount of solid product, e.g. char and/or coke, is preferably less than 20% by weight, more preferably less than 10% by weight, most preferably less than 5% by weight, based on the weight of the lignin starting material.

The aqueous phase obtained after the reaction may comprise from 0-60 wt- %, preferably from 0-50 wt.-%, more preferably from 0-40 wt.-% and most preferably from 3-40 wt.-% of optionally substituted phenols based on the total amount of the aqueous phase.

The phenolic compounds may be readily extracted out of the aqueous phase by known solvents, such as dichloromethane or toluene, and can be added to the obtained product to increase yield. The phenols are partly deprotonated and dissolved in water as phenolates. A large proportion of these phenolic ions can be re-protonated by adjustment of a suitably low pH of the aqueous phase. The generated phenols immediately congregate in high concentration in a small amount of a suitable organic solvent without the requirement of laborious extraction or destination. Another beneficial effect is the generation of an aqueous phase with sharply reduced concentration of environmentally problematic dissolved phenols which makes further scavenging obsolete.

If desired, combustible gases formed during the conversion, e.g. hydrogen carbon monoxide, methane, ethane and/or propane or mixtures thereof may be used for the heating in treatment step (b). Furthermore, the obtained liquid product may be employed to substitute at least a part of the optional alcohol in component (iii), in order to significantly reduce the need of additional alcohols in the process.

The present invention further refers to a liquid product obtainable from lignin material wherein the elemental composition of the liquid product is: 60 to 85% C, preferably 70-85% C, 6.5 to 15% H₁ preferably 10-15% H, 2 to 25% O, preferably 2-7% O, and 0 to 1.0% S.

In another embodiment, the elemental composition of the liquid product is: 70 to 85% C, preferably 80-85% C, 7 to 15% H, preferably 10-15% H₁ 2 to 20% O₁ preferably 2-7% O, and 0 to 1.0% S.

The molar ratios of the main elements H, C and O are preferably: H/C: 1.3 to 2.2, preferably 1.6-2.2, H/O: 10 to 45, preferably 30-45, and C/O: 5 to 30, preferably 20 to 30.

The lignin product obtainable according to the method of the present invention may be used as an addition to fuel, particularly for fuel for vehicles or as raw material for upgrading into petroleum-compatible fuels and other refining products, or as monomeric phenolic building blocks for the manufacture of organic polymers such as bio-plastics or resins. Figure Legends

Figure 1. Positive and negative ESI-MS spectra of two typical bio-oils of the invention

Figure 2. ¹³C NMR in chloroform-of (77.2 ppm) of a typical bio-oil.

Example

Experimental part

Lignin material (5 g), a solvent mixture of component (ii) and (iii) (5 ml formic acid and 50 ml ethanol) are placed in a high pressure reactor (75 ml non- stirred pressure vessel, Parr Instruments, Series 4740). After sealing the reactor the gas volume above the liquid reaction mixture is evacuated by means of reduced pressure and rinsed with hydrogen. This procedure is repeated once and finally the gas pressure above the liquid is adjusted to 50 bar. The closed reactor is placed in an oven that can be electrically heated and might contain some fan to maintain better heat transfer by the hot air. Alternatively, the reactor can be placed in a bath of a hot medium (salt, sand etc.).

The reactor is heated from room temperature to 380 ⁰C and maintained at that temperature for 14 hours. After that reaction time the reaction vessel is taken out of the heat source and allowed to cool to ambient temperature which might also be done more rapidly by immersing into or rinsing with cold water. After cooling the reactor is opened and gases are trapped.

A representative gas analysis showed that at the above stated conditions a mixture of ca. 14% methane, 20% ethane, 14% carbon dioxide and 11% carbon monoxide is formed and accompanied by 20% (excess) hydrogen.

After opening the reactor the two phases are separated in a separatory funnel or by simple decanting. The crude reaction mixture contains a brownish top-layer that comprises the organic phase, the crude product-oil, and a clear, colourless aqueous phase that contains some phenol and phenol alkylates. To increase the yield of obtained organic products the aqueous layer can be extracted with any hydrophobic organic solvent, e. g. dichloromethane and/or toluene which is done at a reduced acidity of pH 2-3 in order to obtain phenols instead of phenolates in the aqueous medium. The low viscous, brownish oil is obtained with a yield of about 85% by weight and shows an elemental composition and molecular rations as follows:

77.83% C, 9.2% H₁ 12.2% O; H/C 1.41 , H/O 11.99, C/O 8.50. The amount of formed coke is less than 7% (340 mg).

Slightly varied reaction conditions provide bio-oils with properties indicated below. They have in common a distinctly enhanced H/C ratio and are significantly lower in oxygen as compared by previous art of lignin liquefaction.

C H O H/C H/O C/O

[%] [%] [%] mol. mol. mol.

76.8 13.5 8.9 1.9 20.0 10.0

80.7 9.0 10.1 1.3 14.1 10.6

82.0 10.3 7.3 1.5 22.4 14.9

82.3 12.4 5.2 1.6 30.0 19.0

83.0 11.0 5.6 1.5 30.7 20.0

82.0 10.3 7.3 1.5 22.4 14.9

Product composition

The formed bio-oils that are derived from the biopolymer lignin (up to 5000 Da) show a certain mass distribution. By means of MALDI-Tof and ESI-MS the largest masses appear to be in the range of less than 700 Da (16). The more detailed GC/MS analysis shows, however, that these masses make up just a minor fraction of the product, with monomeric lignin units of alkyl or polyalkyl phenols (100-200 Da) being the major product fraction (see Fig. 1). To a small degree Fischer-Tropsch-type of products could also be determined, but these also represent a minor product fraction.

Proton and carbon nuclear magnetic resonance spectroscopy (¹H and ¹³C- NMR) of a typical oil obtained by the invention are shown in Figure 2: A substantial portion of the carbons were located below 40 ppm thus belonging to carbons without any oxygen attachment; a result in good agreement with the ¹H NMR. In the ¹³C NMR spectrum, major signals were found in the aromatic region with the highest concentration centered about 130 ppm, indicating alkyl-substituted aromatic (and olefinic) structures. Furthermore, the signal cluster at -150 ppm showed the presence of phenolic structures. Minor carboxyl and carbonyl signals (>160 ppm) were also present in the spectrum. From the spectrum, it was obvious that the mixture of compounds present in the bio-oil was of low molecular mass origin since the spectral width of the individual signals was small and in the order of 2-5 Hz. Furthermore, the signal at ~56 ppm, typical of lignin-derived methoxyl groups, was completely absent, demonstrating that a comprehensive chemical modification of all aromatic structures takes place in the pyrolysis reaction.

List of References

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Claims

1. A method of converting a lignin material into a liquid product, comprising the steps:

(a) providing a lignin starting material,

(b) subjecting said starting material to a treatment in a reaction medium under elevated pressure comprising H≥ and optionally further gaseous components, wherein said starting material is converted to a liquid product, and

(c) obtaining the liquid product from the reaction medium.

2. The method of claim 1 , wherein the lignin material comprises less than 50% by weight, preferably less than 30% by weight, of cellulosic material.

3. The method of claim 1 or 2, which is carried out in a single step.

4. The method of any one of claims 1-3, which is carried out in the absence of any added catalyst.

5. The method of any one of claims 1-4, wherein the reaction temperature is from 200-500°C.

6. The method of any one of claims 1-5, wherein the reaction mixture is heated with a rate of about 1 to 3O⁰CVm in.

7. The method of any one of claims 1-6, wherein the reaction pressure is from 50 to 1000 bar.

8. The method of any one of claims 1-7, wherein the reaction time is from 2 h to 24 h.

9. The method of any one of claims 1 -8, wherein the weight ratio of Iignin material to reaction medium is from about 1 :1 to about 1 :12.

10. The method of any one of claims 1 -9, wherein the reaction medium further comprises at least one d-₂ carboxylic acid and/or salts and/or esters thereof, at least one alcohol and/or water, alkylating agent, and/or and inorganic salt.

11. The method of any one of claims 1-10, wherein the reaction medium further comprises formic acid, and/or alkali salts, e.g. lithium, sodium and/or potassium salts, and/or esters, e.g. CrC₃ alcohol esters thereof.

12. The method of claim 11 , wherein the reaction medium further comprises at least 1%, preferably at least 10% by weight formic acid, and/or alkali salts, e.g. lithium, sodium and/or potassium salts, and/or esters, e.g. CrC₃ alcohol esters thereof.

13. The method of any one of claims 1 -12, wherein the reaction medium further comprises an alkylating agent selected from dimethyl carbonate (DMC), tetramethylammonium hydroxide (TMAH) and combinations thereof.

14. The method of any one of claims 1 -13, wherein the reaction medium further comprises an inorganic salt selected from NaCI, NaHCO₃, MgSO₄, FeSO₄, FeCI₃, FeBr₃, AICI₃, AIBr₃ and combinations thereof.

15. The method of any one of claims 1 -3 and 5-14, wherein the reaction medium further comprises a catalyst, particularly a hydrogenation catalyst, wherein the catalyst is preferably selected from Pd/C and/or SiO₂-based catalysts such as zeolites, metal (oxide) catalysts, e.g. transition metal (oxide), e.g. Va and/or Ni (oxide) catalysts.

16. The method of any one of claims 1-15, wherein the elemental compo- sition of the liquid product is: 65 to 85% C, preferably 70 to 85% C, 6.5 to 15% H, preferably 10 to 15% H, 2 to 25% O, preferably 2 to 7% O, and 0 to 1.0% S.

17. The method of any one of claims 1-16, wherein the liquid product has a molar ratio:

H/C: 1.3 to 2.2, preferably 1.6 to 2.2, H/O: 10 to 45, preferably 30 to 45, and C/O: 5 to 30, preferably 20 to 30.

18. The method of any one of claims 1-17, wherein the yield of liquid product is 50-90% by weight based on the weight of the lignin starting material.

19. The method of any one of claims 1-18, wherein the amount of solid product, e.g. char and/or coke, is less than 20% by weight, preferably less than 10% by weight based on the weight of the lignin starting material.

20. The method of any one of claims 1-19, wherein gases formed during the conversion are used for heating in treatment step (b).

21. A method of converting a lignin material into a liquid product, comprising the steps: (a) providing a lignin starting material,

(i) H2 and optionally further gaseous components,

(ii) optionally at least one CrC₂ carboxylic acid, and/or salts and/or esters thereof,

(iii) optionally at least one alcohol and/or water,

(iv) optionally an alkylating agent, and (v) optionally an inorganic salt and/or a catalyst, wherein said starting material is converted to a liquid product, and (c) obtaining the liquid product from the reaction medium.

22. The method of claim 21, wherein component (i) is present at the beginning of the reaction and/or is added during the course of the reaction.

23. The method of claim 21 or 22 comprising the features of at least one of claims 2-20.

24. A method of converting a ligning material into a liquid product comprising the steps:

(a) providing a lignin starting material,

(b) subjecting said starting material to a treatment in a reaction medium under elevated pressure, wherein the reaction mixture is heated to a predetermined temperature and kept substantially constant during the course of the reaction and wherein the pressure of the reaction mixture is varied during the course of the reaction, wherein said starting material is converted to a liquid product, and (c) obtaining the liquid product from the reaction medium.

25. The method of claim 24 comprising the features of at least one of claims 1-23.