A method for lignin depolymerisation and product thereof

Abstract

According to an example aspect of the present invention, there is provided a method for depolymerizing lignin comprising the steps of: providing a composition comprising lignin that has been separated from cellulose, adding a solution comprising an organic solvent and water in a ratio ranging from 1:10 to 10:1 to the composition comprising lignin to form a reaction solution, heating the reaction solution to a temperature of at least 200°C for at least 1 hour.

Description

A METHOD FOR LIGNIN DEPOLYMERISATION AND PRODUCT THEREOFFIELD

[0001] The present invention belongs to the field methods for lignin depolymerisation.BACKGROUND

[0002] Lignocellulose, the natural composite of cellulose, hemicellulose and lignin, is the most abundant form of biomass. Nowadays, cellulose and hemicellulose are utilized in the second-generation (2G) bioethanol industries to produce bioethanol, remaining enzymatic hydrolysis lignin (EHL) as a low-value byproduct. For every litre of 2G bioethanol, there is extracted as a solid waste about 0.5-1.5 kg of EHL as a solid waste. Nowadays, EHL is mostly burned for energy recovery. As a renewable resource of aromatic molecules, EHL is an ideal feedstock for the sustainable production of commercial aromatic chemicals and fuels. If EHL can be more efficiently utilized, the energy efficiency and profit of the 2G bioethanol production process could be improved.

[0003] Lignin pyrolysis is a method that produce lignin oil, but most of lignin are converted into char and gas. Catalytic lignin solvolysis achieve complete lignin liquefaction, but the catalysts used are prone to deactivation due to the absorption of large lignin fragments and char formation.

[0004] Non-catalytic lignin solvolysis is less expensive and complex than catalytic lignin solvolysis. Nevertheless, serious condensation reaction will occur in non-catalytic lignin solvolysis, resulting in large yield of char. Different solvents, including methanol, ethanol, THF, iso-propanol, n-butanol and their mixtures, and reaction conditions, including reaction temperature, reaction time and initial hydrogen pressure, have been examined previously [1-10], Nevertheless, to our best knowledge, there is no reported results that achieve complete lignin liquefaction without char formation via non-catalytic lignin solvolysis. Hence, there is a need to explore new methods for achieving complete lignin liquefaction via non-catalytic processes.SUMMARY OF THE INVENTION

[0005] The invention is defined by the features of the independent claims. Some specific embodiments are defined in the dependent claims.

[0006] According to a first aspect of the present invention, there is provided a method for depolymerizing lignin. The method comprises the steps of: providing a composition comprising lignin that has been separated from cellulose, adding a solution comprising an organic solvent and water in a ratio ranging from 1 :10 to 10:1 to the composition comprising lignin to form a reaction solution, and heating the reaction solution to a temperature of at least 200 °C for at least 1 hour.

[0007] According to a second aspect of the present invention, there is provided a product obtainable with the method according to the first aspect of the invention.

[0008] According to a third aspect of the invention there is provided use of the product according to the second aspect of the invention in or as a biofuel.

[0009] According to a fourth aspect of the invention there is provided use of the product according to the second aspect of the invention as a feedstock for synthesis of polymer.

[0010] Advantages

[0011] One advantage of the present disclosure is that it discloses a method where lignin, such as hydrolysed lignin or lignin containing waste from pulping process, may be transformed to lignin-oil that is rich in phenols.

[0012] Another advantage is than the method disclosed herein does not depend on use of a catalyst, thus making the method disclosed here in less expensive and less complex than catalytic processes.

[0013] Another advantage is that lignin-oil may be formed without producing excess amounts of char, even without char formation.

[0014] One advantage of the method disclosed herein is that the method allows transformation of solid waste formed for example in 2G bioethanol production or in organosolv process to lignin-oil, which can be further upgraded to chemicals and / or fuel.

[0015] Another advantage of the present disclosure is that it provides a product comprising high concentration of monomeric compounds, such as phenols, aromatic compounds and cyclic alkenes. Such product may be utilized for example in biofuel or in polymer synthesis.

[0016] Further advantage of the present disclosure is that the heating value of the product is higher than the heating value of lignin provided to the method.BRIEF DESCRIPTION OF THE DRAWINGS

[0017] FIGURE 1 illustrates liquefaction degree of EHL and total monomer yield obtained in EG-ethanol mixtures

[0018] FIGURE 2 illustrates yields of total monomers obtained in pure EG and EG- primary alcohol mixtures.

[0019] FIGURE 3 illustrates phenolic monomers detected in the product.

[0020] FIGURE 4 illustrates liquefaction degree of EHL obtained in pure alcohol and alcohol-water mixtures (isopropanol-water achieves 100% EHL liquefaction degree).

[0021] FIGURE 5 illustrates EHL liquefaction in methanol, ethanol, isopropanol, and their mixture with H2O.

[0022] FIGURE 6 illustrates EHL liquefaction in isopropanol-H2O (in ratio 3:2) at different temperatures.

[0023] FIGURE 7 illustrates EHL liquefaction in isopropanol-H2O (in ratio 3:2) with different amounts of EHL.

[0024] FIGURE 8 illustrates EHL liquefaction in ethyl acetate, tetrahydrofuran, dioxane and their mixture with H2O.

[0025] FIGURE 9 illustrates monomers detected in EHL liquefaction in isopropanol- H2O (in ratio 3:2) solvent.

[0026] FIGURE 10 illustrates monomers detected in upgrading of products obtained in isopropanol-FEO (in ratio 3:2).

[0027] FIGURE 11 illustrates EHL liquefaction in C5, H2O or C5-H2O mixture with Raney Ni catalyst under H2.

[0028] FIGURE 12 illustrates monomer yield obtained from EHL liquefaction in C5, H2O or C5-H2O mixture with Raney Ni catalyst under H2.

[0029] FIGURE 13 illustrates monomers detected in C5 phase.

[0030] FIGURE 14 illustrates monomers detected in H2O phase.

[0031] FIGURE 15 illustrates HSQC-NMR spectra of EHL and products in ethanol phase.

[0032] FIGURE 16 illustrates ' H-NMR spectra of EHL and products in ethanol phase.

[0033] FIGURE 17 illustrates the products obtained from upgrading of lignin oligomers in ethanol with WO3 catalyst.

[0034] FIGURE 18 illustrates EHL liquefaction in C5, H2O and C5-H2O mixture with Raney Ni catalyst under N2.

[0035] FIGURE 19 illustrates monomers detected in C5 phase.

[0036] FIGURE 20 illustrates monomers detected in H2O phase.

[0037] FIGURE 21 illustrates monomer yields obtained in C5, H2O and C5-H2O mixture with Raney Ni catalyst under N2.

[0038] FIGURE 22 illustrates yields of monomers in C5 phase before and after upgrading.

[0039] FIGURE 23 illustrates monomers detected after the upgrading of products in C5 phase.

[0040] FIGURE 24 illustrates yields of monomers in H2O phase before and after upgrading.

[0041] FIGURE 25 illustrates monomers detected after the upgrading of products in H2O phase.EMBODIMENTS

[0042] In the present context, the term “lignin” is generally understood as a heterogenous macromolecule of plant origin. Lignin may be generally defined as an amorphous three-dimensional polymer, which is mainly and naturally composed of phenolic building blocks. The exact chemical composition of lignin varies from species to species. Traditionally lignin is considered to be formed from oxidative coupling of p- coumaryl alcohol, conifer alcohol and sinapyl alcohol.

[0043] As used herein, the term “lignin-derived compounds” may refer to any compound of smaller molecular weight than the natural lignin polymer, including small molecules, i.e. low molecular weight compounds, and that has been obtained from lignin through breakage of chemical bonds. Lignin-derived compound may be a (macromolecule, which corresponds to or is derived from a (monomeric) building block of natural lignin or is a homo- or heterodimer of such (monomeric) building blocks. Examples of lignin-derived compounds include aromatic compounds, such as phenols, small molecular weight fragments and oligomeric and monomeric lignin moieties, such as p- coumaryl alcohol, conifer alcohol, sinapyl alcohol, vanillin, syringaldehyde, coniferyl aldehyde, vanillic acid, and / or syringic acid. The monomeric lignin moieties may form dimeric or oligomeric compounds of varied lengths. Typically, lignin derived compounds are a highly heterogeneous assembly of monomeric and oligomeric phenolic structures. The structures may contain functional groups such as carboxylic, aldehyde, ketone, ester, ether, and hydroxyl and methoxy groups.

[0044] As used herein the term “monomers” or “monomer products” refers to small molecular weight products that have monomeric structures. Such monomers are produced from lignin with the method disclosed herein. Monomers may include for example cycloalkanes, such as cyclohexane, methylcyclohexane ethylcyclohexane and propylcyclohexane, arenes, such as benzene, toluene, ethylbenzene and propylbenzene, and phenols, such as phenol, methylphenol, ethylphenol, and propylphenol.

[0045] As used herein the term “oligomer” or “oligomeric” refers to compounds comprising two or more monomers. The monomers comprised in an oligomer may be the same or differ from each other. For example, oligomer may comprise compounds with two or more benzene rings. The structures may contain functional groups such as carboxylic, aldehyde, ketone, ester, ether, and hydroxyl and methoxy groups.

[0046] As used herein the term “lignin-oil” refers to a bio-oil comprising depolymerized lignin that is in liquefied. Lignin-oil may include monomeric, dimeric and / or oligomeric lignin-derived compounds. Lignin oil is rich in alcohols and phenolics, and can be further upgraded to biofuels.

[0047] As used here in, the term “liquefied lignin” refers to lignin being inseparable from solution by filtration. The term “liquefaction degree” refers to the amount of lignin being liquefied from the total lignin provided to the reaction.

[0048] As used herein the term “weight-average molecular weight” refers to the ordinary arithmetic mean of the molecular weights of the individual constituents in the composition. It is determined as the sum of the weight of all molecules within a composition divided by the total number of molecules that are present in that composition.

[0049] The present invention describes a method for depolymerizing lignin. The method comprises the steps of providing a composition comprising lignin, adding a solution comprising an organic solvent and water to the composition comprising lignin to form a reaction solution, heating the reaction solution to a temperature of at least 200 °C for at least 1 hour. It has been surprisingly found that addition of water to the reaction solution improves depolymerizing of lignin so that lignin depolymerization and / or liquefaction may be performed even without using a catalyst. The method disclosed herein may even reach 100 % liquefaction of lignin without any char formation.

[0050] The solution added to the composition comprising lignin comprises water and at least one organic solvent. In some embodiments, the organic solvent may be a non-polar solvent. For example, the organic solvent may be selected from alkenes, or from non-polar aromatic solvents, such as benzene, alkylbenzene, polycyclic aromatic hydrocarbons, or combinations thereof. Alkenes include straight chain alkanes, cycloalkanes, or combinations thereof, for example butanes, pentanes and hexanes. In some examples, the non-polar solvent may be selected from ethyl acetate, tetrahydrofuran, dioxane, orcombinations thereof. In other embodiments, the organic solvent may be selected from polar solvents, such as alcohols or other oxygen-containing organic compounds, such as ethers, esters, acids, ketones, phenolics, or combinations thereof. Alcohols include for example primary alcohols, such as methanol, ethanol, and isopropanol, as well as other alcohols such as cyclohexanol, benzyl alcohol and glycols. Glycols include for example ethylene glycol and propylene glycol. In some embodiments, the organic solvent is selected from an alcohol, such as methanol, ethanol, isopropanol, ethylene glycol, propylene glycol, or combinations thereof, from oxygenated organic compounds, such as ethyl acetate, tetrahydrofuran, dioxane, acetone or combinations thereof, or from a nonpolar hydrocarbon, such as alkenes, arenes or combinations thereof, or from mixtures obtained from petroleum refining, such as gasoline, diesel, or jet fuel. The alcohol solvents include monohydric and polyhydric alcohols with carbon number lower than 8.

[0051] In some embodiments, the solution comprises the organic solvent and water in a ratio ranging from 10:1 to 1 :10, such as from 5:1 to 1 :5, or from 1 :4 to 4:1, or from 3:2 to 2:3. It has been observed, that solvent and water ratio ranging from 3:2 to 2:3 may be especially advantageous. As demonstrated in the examples below, such ratio of water and organic solvent enables even complete liquefaction of lignin. Liquefaction of lignin herein refers to lignin not be separatable from the solution by filtration. For example, the organic solvent may be selected from methanol, ethanol, isopropanol or combinations thereof, and the solution may comprise the organic solvent and water in a ratio ranging from 5:1 to 1 :5.

[0052] In some embodiments, the composition comprising lignin may comprise lignin that has been separated from cellulose and / or hemicellulose. Examples of materials comprising lignin include Kraft lignin, hydrolysed lignin, or organosolv lignin. Preferably, the composition comprising lignin is waste material produced in processing of lignocellulosic material. Processing of lignocellulosic material may include for example ethanol biorefinery process (2g bioethanol production), or from pulp making process, such as from organosolv biorefinery process, or black liquor from kraft pulping process or from sulfite pulping process. In some examples, the composition comprising lignin may be derived from dissolving dry lignin in a suitable solvent. Such dry lignin may be obtained for example from a lignin extraction process, for example black liquor treatment with an acid and CO2 to precipitate, or from a biorefinery process. For example, for every liter of 2G bioethanol production, about 0.5 -1.5 kg of enzymatically hydrolysed lignin is producedas solid waste. Such lignin can be upgraded with the herein disclosed metho to lignin-oil, which can further be upgraded to chemicals and fuels.

[0053] In some embodiments, the concentration of lignin in the reaction solution may be in the range of 0.01 to 10 g / mL, such as 0.01-5g / ml, 0.01-3g / mL, 0.01-1.0 g / mL or 0.01-0.5g / mL. For example, complete liquefaction of lignin may be achieved when the concentration of lignin is up to 2 g / mL and the solvent comprises isopropanol and water in ratio 3:2. The temperature during the reaction in such embodiments may be in the range of 220 to 250 °C. It has been observed that having lignin concentration below 1 g / mL may be advantageous in some embodiments, because at such concentrations char formation is not observed.

[0054] In some embodiments, the heating is performed under an inert atmosphere or an atmosphere consisting of inert gas and hydrogen gas. Inert gas may be for example nitrogen gas or argon gas. An inert atmosphere may be advantageous for lignin depolymerisation because having an atmosphere comprising air may lead to lignin combustion at high temperatures.

[0055] The formed reaction solution is then heated. In some embodiments, the reaction solution is heated for 1 to 24 hours, such as for 1 to 6 hours.

[0056] The temperature during the heating is at least 200 °C, such as at least 250 °C. The temperature during the heating may range from 200 to 4000C, such as from 200 to 3500C or from 200 to 3000C. As demonstrated in example 6, increasing temperature improves liquefaction of lignin in solution. Temperatures above 2000C can provide even completely liquefied lignin.

[0057] In some embodiments, the pressure at the beginning of the heating step ranges from 0 to 300 bar, such as from 0 to 200 bar. In some examples, the pressure relates to the pressure of provided hydrogen gas.

[0058] In some embodiments, the heating of the reaction solution is performed in absence of a catalyst. It has been discovered that the condition as disclosed are sufficient even for complete liquefaction of lignin and thus no catalyst is required in the process. However, a catalyst may be further added to the reaction solution is some embodiments. In some embodiments, the organic solvent may be a non-polar solvent and the heating stepmay be performed in the presence of a catalyst, such as a metal catalyst. Suitable catalysts include for example metal catalysts such as a transition metal catalyst. In some examples, the catalyst may comprise a metal selected from group VIIIB of the periodic table. For example, the catalyst may comprise a metal selected from Ni, Co, Cd, Pd, Pt, Rh, or Ru. Addition of catalyst may be especially advantageous when the organic solvent of the solution is water immiscible.

[0059] In some examples, the reaction solution may be stirred during the heating step. Speed of stirring may range from 0 to 1000 rpm. Stirring may be advantageous especially when water immiscible organic solvent is used in the solution.

[0060] The product obtained after the heating step comprises lignin-oil. After the heating step, the reaction solution may be in some examples extracted to separate the lignin-oil from the solution. Extraction may be performed for example with water and / or a non-polar solvent, such as ethyl acetate or dichloromethane. Lignin-oil may be obtained after extraction by evaporating the non-polar solvent.

[0061] In some embodiments, the method further comprises a second step, which herein is in some cases referred to as upgrading of lignin-oil. The second step comprises after the heating step: adding a catalyst to the reaction solution, and heating the reaction solution to a temperature of at least 200 °C for at least 1 hour under an inert atmosphere or under an atmosphere consisting of at least one inert gas and hydrogen gas.

[0062] In some embodiments, the catalyst may be a metal catalyst, such as a transition metal catalyst. In some examples, the catalyst may comprise a metal selected from group VIIIB of the periodic table or the catalyst may be a metal oxide, metal sulphide, metal carbide or a metal nitride comprising a metal selected from groups VB, VIB or VIIB of the periodic table. Group VIIIB of the periodic table refers to the grouping of elements according to CAS group numbering. Group VIIIB of the periodic table consists of groups 8, 9 and 10 according to IUPAC group numbering. The metal selected from group VIIIB may be for example Ru, Co, Rh, Pd, Ni or Pt. The groups VB, VIB or VIIB of the periodic table refer to the grouping of elements according to CAS group numbering. Groups VB, VIB or VIIB correspond to groups 5, 6 and 7 according to the IUPAC group numbering, respectively. Metal selected from groups VB, VIB or VIIB of the periodic table may be for example Nb, V, W, Mo, Re, or Ti. In some embodiments the metal catalyst may comprise aluminium. The metal catalyst may comprise a metal selected from Ni, Co, Cd, Pd, Pt, Rh,Ru, Nb, V, W, Mo, Re, Ti, or Al. The catalyst may be for example a metal oxide, a metal sulfide, a metal carbide, or a metal nitride. The metal catalyst may be in some embodiments be supported on a catalyst support, such as activated carbon supports, alumina supports or silica supports.

[0063] The temperature during the second heating step is at least 200 °C, such as at least 250 °C. The temperature during the second heating step may range from 200 to 4000C, such as from 200 to 3500C or from 200 to 3000C.

[0064] In some embodiments, the reaction solution is separated into water phase and organic solvent phase prior to addition of the catalyst. Such separation may be especially advantageous if the organic solvent in the reaction solution is water immiscible, such as a non-polar solvent. Separation may be performed for example by extraction. Either or both of the separated fractions may be subjected to the second step of the method. For example, if the solution added to the composition comprising lignin consisted of water and a polar solvent, such as an alcohol, no separation step is needed but the catalyst may be added directly to the reaction solution after the first heating step. If the solution comprised a water immiscible organic solvent, such as non-polar solvent, the reaction solution may be separated after the heating step to water fraction and non-polar solvent fraction. After the separation, a catalyst may be added to both fractions followed by the second heating step.

[0065] The first heating step does not in all cases result in clear solution but solid material or liquid having higher viscosity than the reaction solution (referred to herein as viscous liquid) may remain in the reaction solution. Higher viscosity than the reaction solution refers to dynamic viscosity being over 50 mPa*s at 25 °C. In some embodiments, the solid material or liquid having higher viscosity than the reaction solution remaining in the reaction solution after the first heating step is separated and dissolved in a solvent prior to addition of the catalyst. Such solid material or viscous liquid typically comprises large oligomeric lignin fragments. The solid material or viscous liquid may be separated from the reaction solution after the heating step, for example by filtration, and dissolved in a solvent, such as oxygen containing organic solvent like ethanol, ethyl acetate, tetrahydro furan or acetone. The so formed solution may then be subjected to the second step of the method as disclosed herein. Separating and dissolving the solid material or viscous liquid may further improve the yield of lignin-oil.

[0066] The second heating step with the catalyst may further depolymerize the provided lignin. The weight-average molecular weight of the product may decrease during the second step. Typically, the amount of monomeric lignin-derived compounds increases during the second step. For example, during the second heating reaction the total amount of monomers may increase by 25 %, or by 50 %, or by 75 %.

[0067] During the second heating step, phenols may undergo hydrodeoxygenation, resulting in their conversion into arenes and alkanes. Hydrodeoxygenation refers to hydrogenolytic reaction in which the removal of the oxygen atom from the reactant occurs in the presence of hydrogen. Hydrogen may be in some embodiments provided as hydrogen gas to the reaction. In other embodiments, reactions of the organic solvent, such as alcohol and water may provide hydrogen, eliminating the need for external H2 introduction.

[0068] Another aspect of the invention is a product obtainable with the herein described method. The product comprises monomeric compounds derived from lignin. Such monomeric compounds include for example phenols, aromatics, and cyclic alkenes. The product may in some embodiments comprise oligomeric compounds derived from lignin. Examples of compounds comprised in the product include para-ethyl and vinyl- substituted phenols, guaiacol, ketone-substituted guaiacol and / or syringol, 4-propenyl syringol, and esters derived from ferulic acid and / or p-coumaric acid. Other examples of compounds that may be comprised in the product include alkanes; cycloalkanes, such as cyclohexane, methylcyclohexane, ethylcyclohexane, and propylcyclohexane; arenes, such as benzene, toluene, ethylbenzene, and propylbenzene; and alkylphenols, such as phenol, methylphenol, ethylphenol, and propylphenol. The exact ratio, amount and identity of the monomers depends on the used solution and reaction conditions.

[0069] Typically, the weight-average molecular weight of the product is much smaller than the weight-average molecular weight of the material comprising lignin. For example, the weight-average molecular weight may be below 1000 g / mol, such as below 900 g / mol. After the second heating step with the catalyst, the weight-average molecular weight may be further reduced, for example to below 500 g / mol or below 300 g / mol.

[0070] In some embodiments, the product may comprise at least 80 wt-%, such as at least 90 wt-% or at least 95 wt-% of depolymerized lignin.

[0071] Typically, the oxygen content of the product is lower than the oxygen content of the composition comprising lignin. However, the heating value of the product is higher than the heating value of the provided composition comprising lignin.

[0072] Another aspect of the disclosure is the use of the product obtainable by the method disclosed herein in or as a biofuel.

[0073] Another aspect of the disclosure is use of the product obtainable with the herein disclosed method as a feedstock for synthesis of polymers. For example, phenolic products produced with the herein disclosed method may be used as a substitute for the production of Bisphenol-A epoxy resin.

[0074] The particularity of the herein disclosed method is that no catalyst is needed and no char is produced to achieve complete liquefaction of lignin, such as enzymatically hydrolysed lignin (EHL). In a preferred embodiment, EG (ethylene glycol), primary alcohol (i.e., methanol, ethanol, and isopropanol) and H2O as well as their mixture are used as solvent for EHL non-catalytic solvolysis. The liquid product obtained with the method disclosed herein is rich in phenolic monomers which can be used for production of aromatic chemicals and fuels. With our method, the waste produced in 2 G biorefinery can be utilized to produce biofuels, and the energy efficiency and profit of the 2 G biorefinery will thus be improved.

[0075] The method can be employed in lignin upgrading process to produce ligninbased chemicals and fuels. The method may comprise the non-catalytic solvolysis step, using mixed alcohols as the solvents and mostly focuses on EHL from 2 G biorefinery technology, but also does not exclude other types of lignin, such as Kraft lignin and organosolv lignin. With this method, EHL is completely depolymerized by solvent without char formation, yielding lignin oils rich in phenolic monomers.

[0076] In some examples, EHL is depolymerized in solvent, such as in alcohol solvent, at N2 or H2 atmosphere in the temperature range of 200-300 °C. After the reaction, the liquid product is lignin oil with solvent. For separation of lignin-oil and solvent, the liquid products may be extracted with water and ethyl acetate, and lignin oil is obtained after evaporation of ethyl acetate.

[0077] The alcohol solvents may include ethylene glycol, primary alcohol (i.e., methanol, ethanol, and isopropanol), water, and their mixtures.

[0078] The mass concentration of EHL may be in the range of 0.01-0.05 g / ml, or in the range of 0.01-1 g / mL.

[0079] The reaction temperature may be in the range of 200-300 °C.

[0080] Reaction atmosphere may be H2, inert gas (e.g., N2 or Ar) and the initial pressure may be in the range of 0-200 bar.

[0081] Reaction time may be in the range of l-24h, such as 1-6 h.

[0082] The stirring speed during the reaction may be in the range of 0-1000 rpm;

[0083] The lignin-oil can be preserved in original solvent or separated through extraction with water and ethyl acetate.Examples

[0084] Example 1

[0085] The reaction is carried out in a 10 ml batch reactor. Enzymatically hydrolysed lignin (EHL, 0.1 g) and solvent (6 mL) were loaded into the reactor. After six purges with nitrogen, the sealed reactor was heated to the 280 °C with the stirring fixed at 600 rpm for 6 h. After the reaction, the reaction mixture is filtrated to separate the liquid product and solid residue. The liquid product was quickly injected into the Agilent 7890-5973 GC-MS system and the Agilent 7890 GC equipped with FID for qualitative and quantitative analysis. Anisole is used as the internal standard for the quantitative analysis of products. The conversion and product yield of model compound conversion were calculated with the equation: Total monomer yield =The total weight of monomer products / The weight of the initial EHL added into the reactor

[0086] Figure 1. shows the results of 0.1 g EHL solvolysis in 6 mL ethylene glycol (EG)-ethanol mixed solvents with different volume ratio. Both the liquefaction degree and the yield of total monomers gradually increase with the increase of the amount of EG. Complete EHL liquefaction achieves in 1.5 mL EG-4.5 mL ethanol and 2.0 mL EG-4.0 mL ethanol. The highest total monomer yield, i.e., 12.2 wt%, is achieved in 2.0 mL EG-4.0 mL ethanol.

[0087] It is to be understood that the embodiments of the invention disclosed are not limited to the particular structures, process steps, or materials disclosed herein, but areextended to equivalents thereof as would be recognized by those ordinarily skilled in the relevant arts. It should also be understood that terminology employed herein is used for the purpose of describing particular embodiments only and is not intended to be limiting.

[0088] Example 2

[0089] The reaction is carried out in a 10 ml batch reactor. EHL (0.5 g) and solvent (6 mL) were loaded into the reactor. After purging with nitrogen, the sealed reactor was then heated to the 320 °C. Other parameters are the same as with example one.

[0090] Pure EG and EG-primary alcohol mixtures (v / v, 2 mL / 4 mL), including EG- methanol, EG-ethanol, EG-isopropanol, all achieved complete EHL liquefaction. As shown in Figure 2 pure EG gives the lower total monomer yield than mixed solvents, and the highest total monomer yield, i.e., 11.8 wt% was obtained in EG-isopropanol mixture. The monomers detected in EG-isopropanol are phenolics, and their structures are shown in Figure 3.

[0091] Example 3

[0092] The reaction is carried out in a 50 ml batch reactor. EHL (0.5 g) and solvent (30 mL) were loaded into the reactor. After purging with nitrogen, the sealed reactor was then heated to the 240 °C. Other parameters are same with embodiment one.

[0093] Primary alcohols (i.e., methanol, ethanol, and isopropanol) and alcohol-water mixtures (v / v, 20 mL / 10 mL) were used as solvent, and the EHL liquefaction degree are shown in Figure 4. The liquefaction degrees obtained by methanol and ethanol are similar, but higher than that by isopropanol. However, all of these pure alcohols cannot achieve complete EHL liquefaction. When the mixtures of alcohol and water are used as solvent, the liquefaction degrees are significantly improved. The liquefaction degree obtained by methanol-water mixture and ethanol-water mixture are 93.7 % and 95.3 %, respectively, and the isopropanol-water mixture achieves complete EHL liquefaction.

[0094] Example 4.

[0095] The liquefaction of 1 g of EHL in 50 mL of solvent was carried out in a 100 mL batch reactor under N2 atmosphere at 250 °C for 3 h. Following the reaction, the resultant product underwent filtration to separate solid and liquid products. The liquefaction degree was calculated with equation: liquefaction degree (wt%) = (1 -weight of the solid product / weight of added EHL)* 100

[0096] Figure 5 shows the EHL liquefaction degree in pure alcohol (methanol, ethanol or isopropanol) and alcohol-H2O mixtures. The addition of H2O into methanol or ethanol improves EHL liquefaction degree. When the volume ratio of alcohol to H2O is fixed at 3 / 2, the mixture of isopropanol and H2O achieves complete EHL liquefaction, while the liquefaction degrees obtained in ethanol-H2O and methanol-H2O are 95.8 wt% and 94.6 wt%, respectively. The effect of the volume ratio of isopropanol to H2O was also examined. High liquefaction degrees of EHL are achieved when the volume ratios of isopropanol to H2O are 3 / 2 and 2 / 3. The liquefaction degrees of EHL obtained in isopropanol-H2O (ratio 2 / 3) is 97.7 wt%, slightly lower than that obtained in isopropanol- H2O (ratio 3 / 2). In isopropanol-H2O with volume ratios of 1 / 4 and 4 / 1, the liquefaction degree of EHL is 84.9 and 87.3 wt%, respectively.

[0097] Example 6

[0098] The liquefaction of 1 g EHL in 50 ml isopropanol-H2O (in ratio 3:2) was carried out as in example 4 but the temperature during the reaction is altered. As shown in Figure 6, the EHL liquefaction degree increases with the increase of the reaction temperature. The EHL liquefaction degree reaches 100 wt% in isopropanol-H2O (3:2) at 200 °C and 250 °C.

[0099] Example 7

[0100] The effect of the amount of EHL on its liquefaction degree in 50 mL isopropanolTLO (in ratio 3:2) was examined at 200 and 250 °C (Figure 7). At 200 °C, 1.5 g EHL is completely liquefied in 50 mL isopropanol-H2O (in ratio 3:2), with the liquefaction degree significantly decreasing as the amount of EHL is further increased. Nevertheless, at 250 °C, isopropanol-H2O (in ratio 3:2) achieves complete liquefaction of 2 g EHL, and the EHL liquefaction degree is 90.3 wt% with 3 g EHL.

[0101] Example 8

[0102] The liquefaction of EHL was investigated in ethyl acetate (EA), tetrahydrofuran (THF), dioxane, and their mixtures with water. The reactions were conducted at 260 °C under air atmosphere for 6 h, using 0.1 g of EHL in 5 mL of solvent. The liquefaction degrees in EA, THF, and dioxane are 59.7%, 78.4%, and 94.6%, respectively (Figure 8). The addition of water significantly enhances the liquefaction degree. Specifically, the liquefaction degree reached 94.6 wt% in EA-H2O (3:2) solvent, and reached 100.0 wt-% in both THF-H2O (3:2) and dioxanc-FLO (3:2) solvents.

[0103] Example 9.

[0104] Following EHL liquefaction, the liquid products were extracted with 50 mL of dichloromethane. Subsequently, the monomers present in the dichloromethane extract were both qualitatively and quantitatively analyzed using a Shimadzu GC-MS (QP2010SE with Optic 4) and an Agilent 7890 GC-FID, respectively. Quantification was achieved using n-dodecane as the internal standard. The carbon yield of total monomers was determined using the equation: total yield of monomers = (carbon mass of total monomers / carbon mass of EHL put into reaction)* 100

[0105] Figure 9 illustrates the monomers identified in reaction of 1 g EHL in 50 mL isopropanol-H2O (in ratio 3 / 2) at 250 °C. These monomers comprise para-ethyl and vinyl- substituted phenols, guaiacol, ketone-substituted guaiacol and syringol, 4-propenyl syringol, as well as esters derived from ferulic and p-coumaric acids. Comparable products were obtained in other alcohol-water, ester- water, and ether- water mixtures. The total yield of monomers obtained in isopropanol-H2O (in ratio 3 / 2) is 4.2%.

[0106] The weight-average molecular weight (Mw) of both the original EHL and the resulting liquid products obtained in isopropanol-H2O (in ratio 3 / 2) was determined utilizing an Agilent HPLC system equipped with Phenogel columns (5 pm - 5 nm and 100 nm) and a UV detector set at 280 nm. Tetrahydrofuran served as the eluent at a flow rate of 1.0 ml min / -l. Notably, the Mw of the liquid product obtained in isopropanol was 894 g / mol, significantly lower than that of the original EHL (4333 g / mol). Moreover, this value further decreased to 759 g / mol in the presence of isopropanol-H2O (in ratio 3:2). This indicates that the addition of H2O into isopropanol promotes EHL depolymerization.

[0107] Example 10

[0108] The liquid product obtained from the solvolysis of 1 g of EHL in 50 mL isopropanol-H2O (in ratio 3:2) at 250 °C underwent further upgrading using Raney Ni at 320 °C under a N2 atmosphere. In this reaction, reforming reactions of isopropanol-H2O provided hydrogen for the upgrading process, eliminating the need for external H2 introduction.

[0109] Figure 10 illustrates the monomers identified in the upgraded product. The total yield of identified monomers reached 45.6 %, with a selectivity of 35.1 % forcycloalkanes (including cyclohexane, methylcyclohexane, ethylcyclohexane, and propylcyclohexane), 51.6 % for arenes (including benzene, toluene, ethylbenzene, and propylbenzene), and 13.3 % for alkylphenols (including phenol, methylphenol, ethylphenol, and propylphenol). Throughout the upgrading process, the remaining large lignin fragments undergo further depolymerization. The molecular weight of the lignin oil decreased from 759 g / mol before upgrading to 283 g / mol after product upgrading.

[0110] Example 11

[0111] The liquefaction of 3 g of EHL in a mixture of 15 mL pentane (C5) and 15 mL H2O, with 1 g of Raney Ni catalyst, was conducted in a 100 mL batch reactor at 300 °C under 2 MPa H2 for 6 h. After completion of the reaction, the resulting product underwent filtration to separate liquid products from solid residue. The solid residue was then washed with ethanol to dissolve large lignin fragments, remaining char and used catalyst. The yield of char was calculated with the equation:Char yield (%) = ((weight of solid residue after washing with ethanol-weight of catalyst) / weight of added EHL)* 100The liquefaction degree was calculated with the equation:Liquefaction degree (wt%) = 100 - char yield

[0112] Eigure 11 illustrates the result of liquefying 3 g of EHL in a mixture of 15 mL C5 and 15 mL H2O under 2 MPa H2 with 1 g of Raney Ni. When using 30 mL of C5, the liquefaction degree is only 55.0 wt%. Employing 30 mL of H2O raises the liquefaction degree to 95.2 wt%. Interestingly, in a 15 mL C5 and 15 mL H2O mixture, the liquefaction degree reaches 100.0 wt%.

[0113] The monomer products in the C5 and H2O phases underwent qualitative and quantitative analysis using Shimadzu GC-MS (QP2010SE with Optic 4) and Agilent 7890 GC-EID, respectively. Prior to analysis, the product in the H2O phase was extracted with dichloromethane (30 mL). n-Dodecane and anisole served as internal standards for quantifying products in the C5 and H2O phases, respectively. The total carbon yield of monomers was determined using the equation:Yield of monomers (%) = (carbon mass of monomers / carbon mass of EHL put into the reaction)* 100%

[0114] The total monomer yields obtained from pure C5, pure H2O, and the C5-H2Omixture are depicted in Figure 12. In the mixture of 15 mL C5 and 15 mL H2O, the total monomer yield is 16.6%. The products consist of alkanes, arenes, and phenolics, with yields of 1.9%, 4.2%, and 10.6%, respectively. In the pentane phase, both arenes and phenolics are detected (Figure 13), while in the H2O phase, only phenolics are detected (Figure 14). Monomers obtained in 30 mL H2O exclusively contain phenolics, with a total yield of 3.0%. Conversely, monomers obtained in 30 mL C5 include alkanes, aromatics, and phenolics, with a total yield of 9.4% (5.7% phenolics, 2.0% aromatics, 1.7% alkanes), which is lower than that obtained in the mixture of 15 mL pentane and 15 mL H2O.

[0115] The Mw of the products obtained from the mixture of 15 mL C5 and 15 mL H2O were determined through GPC analysis. The Mw of products in the pentane, H2O, and ethanol phases are 229.6, 292.9, and 551.8 g / mol, respectively. Notably, the products in the ethanol phase consist of large lignin fragments, whose structures were analyzed using HSQC-NMR (Figure 15) and 1H-NMR (Figure 16). Interestingly, these products lack P-O- 4 linkages and exhibit reduced methoxy group content but increased phenolic hydroxyl group content compared to the original EHL. Therefore, the products in ethanol phase have the potential to be used as a substitute of phenol for the production of phenol formaldehyde resin.

[0116] Example 12

[0117] Lignin oligomers were obtained from lignin depolymerization in water- alkane using the method disclosed in example 11. 1 g lignin oligomers was dissolved in 50 ml ethanol, and then the mixture was pumped into a fixed bed reactor. WO3 supported on AI2O3 was used as a catalyst for oligomers upgrading at 300 °C under N2 atmosphere. After the reaction, phenolics with several ethyl and methyl substituent groups on their benzene rings are detected as the product (Figure 17). The total yield of these was 20.3 wt %.

[0118] Example 13

[0119] Liquefaction of 0.25 g of EHL in 25 mL C5 and 25 ml H2O with 0.25 g Raney Ni as a catalyst was carried out in a 100 mL batch reactor at 300 °C under 0 MPa N2 for 6 h. Following the reaction, the resultant product underwent filtration to separate liquid products from solid residue. The solid residue was also washed with ethanol to dissolve large lignin fragments, remaining char and used catalyst form the solid residue. The yield of char was calculated with equation:Char yield (%) = ((weight of solid residue after washing with ethanol-weight ofcatalyst) / weight of added EHL)* 100The liquefaction degree was calculated with the equation:Liquefaction degree (wt%) = 100 - char yield

[0120] Figure 18 depicts the results of liquefying 0.25 g of EHL with 0.25 g Raney Ni under 0 MPa N2 in 50 mL C5, H2O and C5-H2O mixture. Unlike the reaction under H2, no product is solubilized in the ethanol phase, suggesting the absence of ethanol-soluble lignin fragments in this reaction. Both C5-H2O mixture and pure H2O solvent achieve higher EHL liquefaction degrees compared to pure pentane. Specifically, the EHL liquefaction degree in pure C5 is 47.8 wt%, while in pure H2O, it reaches 89.6 wt%. In the case of 15 mL C5-35 mL H2O, the EHL liquefaction degree mirrors that obtained in pure H2O, while 35 mL C5-15 mL H2O and 25 mL C5-25 mL H2O achieve higher EHL liquefaction degrees, which are 94.7 and 95.3 wt%, respectively.

[0121] Unlike the reaction under H2, the reaction under N2 yields only arenes and phenols, with no formation of alkanes. Aromatics and phenolics are detected in the pentane phase (Figure 19), while only phenolics are detected in the H2O phase (Figure 20).

[0122] Figure 21 illustrates the total monomer yields produced in these reactions. In pure C5, the total yield is 13.4 %, comprising 6.03 % arenes and 7.38 % phenols. In pure H2O, the total yield is 7.4 %, including 3.6 % arenes and 3.8 % phenols. The total yields in C5-H2O solvent range from 18.0 to 23.0 %. Increasing the amount of H2O from 15 to 35 mL in the C5-H2O solvent leads to an increase in the yield of arenes from 11.1 % to 13.3 % and a decrease in the yield of phenols from 11.7 % to 5.7 %.

[0123] Example 14

[0124] The upgrading of products in the C5 phase, obtained from the liquefaction of 3 g EHL in a mixture of 15 mL C5 and 15 mL H2O under H2 with a 1 g Raney Ni catalyst, was conducted in a 50 mL batch reactor. The process employed 0.1 g Ru / C as a catalyst and operated at 240 °C under 4 MPa H2. The upgrading of products in the H2O phase obtained from the same reaction was carried out in the same reactor using 0.1 g Raney Ni catalyst at 320 °C under 1 MPa H2. Following the reaction, the product in the H2O phase was extracted with dichloromethane (30 mL). To quantify products in the C5 and H2O phases, n-dodecane and anisole were used as internal standards, respectively. The total carbon yield of monomers was determined using the equation:

[0125] Yield of monomers (%) = (carbon mass of monomers / carbon mass of 3 g EHL)* 100%

[0126] The comparison of monomer yields in the C5 phase before and after upgrading is illustrated in Figure 22. During the upgrading process, the lignin fragments are further depolymerized, resulting in increase of total monomer yield from 10 % before upgrading to 16 % after upgrading. Moreover, during upgrading, the hydrogenation of benzene rings in phenols occurs, leading to the formation of alcohols. Subsequently, these alcohols undergo hydrodeoxygenation to produce alkanes as final products, as depicted in Figure 23. Specifically, the yields of alkanes and alcohols obtained after upgrading are 10.9% and 5.5% wt%, respectively.

[0127] Figure 24 compares the yields of monomers in the H2O phase before and after upgrading. Similar to the C5 phase, the total monomer yield in the H2O phase also improves from 3.0% before upgrading to 3.8% after upgrading. During the upgrading process, phenols undergo hydrodeoxygenation, resulting in their conversion into arenes and alkanes, as shown in Figure 25. The components in the upgraded products comprise 2.3% of phenols, 1.1% of arenes, and 0.5% of alkanes.

[0128] Unless otherwise stated, properties that have been experimentally measured or determined herein have been measured or determined at room temperature. Unless otherwise indicated, room temperature is 25 °C.

[0129] Unless otherwise stated herein or clear from the context, any percentages referred to herein are expressed as percent by weight based on a total weight of the respective composition.

[0130] As used herein, unless otherwise indicated, the term “average molecular weight” refers to a weight average molecular weight (also abbreviated “MW” or “Mw”).

[0131] The viscosity can be measured with a viscometer, such as a Brookfield or Cole-Parmer viscometer, which rotates a disc or cylinder in a fluid sample and measures the torque needed to overcome the viscous resistance to the induced movement. The rotation can be at any desired rate, such as from 1 to 30 rpm, preferably at 5 rpm, and preferably with the material being measured being at 25 °C.

[0132] Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the presentinvention. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment.

[0133] As used herein, a plurality of items, structural elements, compositional elements, and / or materials may be presented in a common list for convenience. However, these lists should be construed as though each member of the list is individually identified as a separate and unique member. Thus, no individual member of such list should be construed as a de facto equivalent of any other member of the same list solely based on their presentation in a common group without indications to the contrary. In addition, various embodiments and example of the present invention may be referred to herein along with alternatives for the various components thereof. It is understood that such embodiments, examples, and alternatives are not to be construed as de facto equivalents of one another, but are to be considered as separate and autonomous representations of the present invention.

[0134] Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided, such as examples of lengths, widths, shapes, etc., to provide a thorough understanding of embodiments of the invention. One skilled in the relevant art will recognize, however, that the invention can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the invention.

[0135] The verbs “to comprise” and “to include” are used in this document as open limitations that neither exclude nor require the existence of also un-recited features. The features recited in depending claims are mutually freely combinable unless otherwise explicitly stated. Furthermore, it is to be understood that the use of "a" or "an", i.e. a singular form, throughout this document does not exclude a plurality.ACRONYMS LISTEHL enzymatically hydrolysed ligninEG ethylene glycolCITATION LISTNon Patent Literature1. Chemosphere, 93 (2013) 1755-17642. Energy Fuels, 28 (2014) 6429-6437 3. Bioresource Technology, 165 (2014) 319-3224. Energy Fuels, 31 (2017) 10842-108495. Energy Fuels, 31 (2017) 7223-72336. Sustainable Energy Fuels, 1 (2017) 2006-20157. ACS Sustainable Chem. Eng., 8 (2019) 1023-1030 8. Sustainable Energy Fuels, 4 (2020) 6212-62269. Energy Fuels, 24 (2010) 4659-466710. Polym. Degrad, and Stabil., 97 (2012) 839-848

Claims

CLAIMS:

1. Method for depolymerizing lignin comprising the steps of:- providing a composition comprising lignin that has been separated from cellulose,- adding a solution comprising an organic solvent and water in a ratio ranging from 1:10 to 10:1 to the composition comprising lignin to form a reaction solution,- heating the reaction solution to a temperature of at least 200 °C for at least 1 hour.

2. The method according to claim 1, wherein the organic solvent is selected from an alcohol, such as methanol, ethanol, isopropanol, ethylene glycol, propylene glycol, or combinations thereof; from oxygenated organic compounds, such as ethyl acetate, tetrahydrofuran, dioxane, acetone or combinations thereof; or from a non-polar hydrocarbon, such as alkenes, arenes or combinations thereof; or from mixtures obtained from petroleum refining, such as gasoline, diesel, or jet fuel.

3. The method according to claim 1 or 2, wherein the solution comprises the organic solvent and water in a ratio ranging from 5:1 to 1 :5, such as from 3 :2 to 2:3.

4. The method according to any of the preceding claims, wherein the composition comprising lignin is obtained from ethanol biorefinery process, from pulp making process, such as from organosolv biorefinery process, kraft pulping process or sulfite pulping process, or from enzymatic or chemical hydrolysis process of lignocellulosic material.

5. The method according to any of the preceding claims, wherein the concentration of lignin in the reaction solution is in the range of 0.01-10.0 g / mL, such as in the range of 0.01-3.0 g / mL or in the range of 0.01-1.0 g / mL.

6. The method according to any of the preceding claims, wherein the heating is performed under an inert atmosphere or under an atmosphere consisting of inert gas and hydrogen gas.

7. The method according to any of the preceding claims, wherein the reaction solution is heated for 1 to 24 hours, for example 1 to 6 hours.

8. The method according to any of the preceding claims, wherein the pressure at the beginning of the heating step ranges from 0 to 300 bar.

9. The method according to any of the preceding claims, wherein the heating of the reaction solution is performed in the absence of a catalyst.

10. The method according to any of the claims 1-8, wherein the organic solvent is a nonpolar solvent and the heating step is performed in the presence of a catalyst, such as a metal catalyst.

11. The method according to any of the claims 1- 9, wherein the organic solvent is selected from methanol, ethanol, isopropanol or combinations thereof, and the solution comprises the organic solvent and water in a ratio ranging from 5:1 to 1 :5.

12. The method according to any of the preceding claims, wherein the reaction solution is heated to at least 250 °C.

13. The method according to any of the preceding claims, further comprising after the heating step:- adding a catalyst to the reaction solution,- heating the reaction solution to a temperature of at least 200 °C for at least 1 hour under an inert atmosphere or under an atmosphere consisting of inert gas and / or hydrogen gas.

14. The method according to claim 13, wherein the catalyst comprises a metal, such as a transition metal.

15. The method according to claim 13, wherein the catalyst comprises a metal selected from group VIIIB of the periodic table or the catalyst is a metal oxide, metal sulfide, metal carbide or a metal nitride comprising a metal selected from groups VB, VIB or VIIB of the periodic table.

16. The method according to any of the claims 13-15, wherein the reaction solution is separated into water phase and organic solvent phase prior to addition of the catalyst.

17. The method according to any of the claims 13-16, wherein solid material or liquid having higher viscosity than the reaction solution remaining in the reaction solution after the first heating step is separated and dissolved in a solvent prior to addition of the catalyst.

18. The method according to any of the claims 13-17, wherein the reaction solution is heated to at less 250 °C.

19. Product obtainable with the method according to any of the preceding claims.

20. The product according to claim 19, wherein the weight-average molecular weight of the product is below 1000 g / mol, such as below 500 g / mol.

21. Use of the product according to claim 19 or 20 in or as a biofuel.

22. Use of the product according to claim 19 or 20 as a feedstock for synthesis of polymer.

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