阅读说明：本技术 一种提高生物质的木质素分级分离和解聚的方法及其应用 (Method for improving lignin fractionation and depolymerization of biomass and application thereof ) 是由 董澄宇 吕绍元 杨智淳 谢灏贤 默罕默德·凯鲁·伊斯拉姆 于 2020-11-06 设计创作，主要内容包括：本发明属于生物质应用技术领域,公开一种提高生物质的木质素分级分离和解聚的方法及其应用。该方法是将处理的生物质用预处理溶液在120～173℃蒸煮,以酸作为催化剂,预处理溶液包括有机溶剂和水；有机溶剂为C2-C5及含有两个以上羟基的有机溶剂,得到含有纤维素和木质素的生物质和含有木质素的预处理溶液；然后将该预处理溶液分离,洗涤合并含有木质素的预处理液,再将其与水混合,经沉淀、过滤和干燥处理,制得木质素；将木质素、有机溶剂和解聚催化剂混合,在保护气氛下,在180～250℃进行催化解聚反应,得到木质素单体。该方法提高了木质素的解聚性和单酚化合物的产率,木质素单体具有较多的β-O-4键和较少的缩合酚基。(The invention belongs to the technical field of biomass application, and discloses a method for improving lignin fractionation and depolymerization of biomass and application thereof. The method comprises the steps of cooking a treated biomass at 120-173 ℃ by using a pretreatment solution, wherein the pretreatment solution comprises an organic solvent and water and takes an acid as a catalyst; the organic solvent is C2-C5 and the organic solvent containing more than two hydroxyl groups, so that biomass containing cellulose and lignin and a pretreatment solution containing the lignin are obtained; separating the pretreatment solution, washing and combining the pretreatment solution containing lignin, mixing the pretreatment solution with water, and performing precipitation, filtration and drying treatment to obtain lignin; mixing lignin, an organic solvent and a depolymerization catalyst, and carrying out catalytic depolymerization reaction at 180-250 ℃ in a protective atmosphere to obtain a lignin monomer. The method improves lignin depolymerization property and monophenol compound yield, and lignin monomer has more beta-O-4 bonds and less condensed phenol groups.)

1. A method for improving lignin fractionation and depolymerization of biomass is characterized by comprising the following specific steps:

s1, processing biomass containing lignocellulose into small size through chopping, chipping, peeling, grinding or grinding, and then washing to obtain biomass;

s2, cooking the biomass obtained in the step S1 at 120-173 ℃ by using an acid as a catalyst to obtain a biomass containing cellulose and lignin and a pretreatment solution containing lignin; the pretreatment solution is an organic solvent and water; the organic solvent is more than one of C2-C5, an organic solvent containing more than two hydroxyl groups and an organic solution containing ether bonds or ketone groups;

s3, separating the biomass containing the cellulose and the lignin from the pretreatment solution containing the lignin, washing the biomass containing the cellulose and the lignin by using the pretreatment solution with the same concentration at the temperature of 60-80 ℃, combining the pretreatment solution containing the lignin, mixing the combined pretreatment solution containing the lignin with water, and performing precipitation, filtration and drying treatment to obtain the lignin;

and S4, mixing the obtained lignin, an organic solvent and a depolymerization catalyst, heating to 180-250 ℃ in a protective atmosphere, stirring for catalytic depolymerization reaction, and cooling to room temperature to obtain lignin monomers, namely syringyl propane and syringyl propanol.

2. The method for improving lignin fractionation and depolymerization of biomass according to claim 1, wherein said biomass containing lignocellulose in step S1 is at least one selected from wood chips, bark, plant litter, rice straw, stalks, rice hulls, flax chips, wheat straw, fruit shells, wheat husks, and bagasse.

3. The method for improving lignin fractionation and depolymerization of biomass according to claim 1, wherein said acid is organic acid or/and inorganic acid in a concentration of 1 to 200mmol/L in step S2, and said acid is a pretreatment solution in a mass concentration of 0.01 to 2 wt.%; the mass ratio of the organic solvent to the water is (13-17): (3-7).

4. The method for improving lignin fractionation and depolymerization of biomass according to claim 1, wherein said C2-C5 and organic solvent containing two or more hydroxyl groups in step S2 are diols or triols; the organic solution containing ether bonds is diethylene glycol ether, and the organic solution containing ketone groups is dihydroxyacetone; the organic acid is more than one of formic acid, acetic acid, oxalic acid, maleic acid, benzoic acid or methanesulfonic acid; the inorganic acid is more than one of hydrochloric acid, sulfuric acid or phosphoric acid.

5. The method for improving lignin fractionation and depolymerization of biomass according to claim 4, wherein said diol is one or more of ethylene glycol, 1, 2-propanediol, 1, 3-butanediol, 1, 4-butanediol, 1, 2-butanediol, 1, 5-pentanediol, 1, 4-pentanediol, 1, 3-pentanediol, or 1, 2-pentanediol; the trihydric alcohol is glycerol, 1,3, 5-pentanetriol, 2,3, 4-pentanetriol, 1,2, 5-pentanetriol, 1,2, 4-pentanetriol and 2,3, 4-pentanetriol.

6. The method for improving lignin fractionation and depolymerization of biomass according to claim 1, wherein the ratio of mass of biomass to volume of pretreatment solution in step S2 is 1000 g: (0.1-50) L.

7. The method for improving lignin fractionation and depolymerization of biomass according to claim 1, wherein said lignin-containing pretreatment liquid and water of step S3 are in a volume ratio of 1: (3-10).

8. The method for improving lignin fractionation and depolymerization of biomass according to claim 1, wherein said organic solvent in step S4 is one or more of ethanol, isopropanol, and acetone; the depolymerization catalyst is Ru/C, Ni/C, Ni/Al₂O₃、Ni/SiO₂-Al₂O₃、Ru/Al₂O₃、Ru/SiO₂、Ru/ZrO₂Or Ru/SiO₂-Al₂O₃One or more of (1); the protective atmosphere is nitrogen or argon; the mass ratio of the lignin to the volume of the organic solvent to the depolymerization catalyst is (0.02-0.2) g: 20mL of: 1g of a compound; the time of the catalytic depolymerization reaction is 2-10 h.

9. A monolignol, wherein the monolignol is syringyl propane and syringyl propanol, and is prepared by the method for improving lignin fractionation and depolymerization of biomass according to any one of claims 1 to 8.

10. The use of the monolignol of claim 9 in the chemical or pharmaceutical field.

Technical Field

The invention belongs to the technical field of biomass application, and particularly relates to a method for improving lignin fractionation and depolymerization of biomass and application thereof.

Background

Lignocellulosic biomass is a valuable resource for the production of biofuels and functional chemicals. The cellulose biomass mainly comprises cellulose, hemicellulose and lignin, and chemical components of the cellulose biomass are greatly different among different plant species and are distributed in different positions of plants. Wherein cellulose is a linear polymer of glucose interconnected by 1, 4-glycosidic linkages, the polymer being arranged as ordered fibers having crystalline and amorphous regions. Hemicellulose is a matrix in plant cell walls, a branched polymer composed mainly of pentoses (e.g., xylose and arabinose) and hexoses (e.g., glucose, mannose, and galactose). Lignin is a three-dimensional aromatic biopolymer, and lignocellulose is structurally strong, resistant to physical, chemical and biological degradation, and provides physical strength to plant cell walls. Sources of biomass material from agricultural and municipal activities may be composed of different plant species (i.e., herbs, shrubs, hardwoods, and softwoods) and/or different parts of the plant.

Sugar-based biorefinery technologies are widely adopted for their high economic efficiency and potential for environmental friendliness in the production of biofuels and biochemicals. In this process, lignocellulosic biomass is enzymatically digested to sugars, which are then converted to the desired product by fermentation or chemical catalytic processes. Unlike cellulose and hemicellulose, lignin is composed mainly of aromatic subunits, is nearly non-biodegradable, and therefore cannot be used as a carbon source for fermentation. With the recent social interest in "green chemistry" and "environmentally friendly chemistry", lignin has been reconsidered as a valuable chemical.

A common method of utilizing lignocellulosic materials is to separate the major components of the material. Degradation reactions typically occur during the separation process, particularly where lignin and/or hemicellulose are involved, resulting in a low value product. The C-C bond formed in the degradation is repolymerization or condensation. Since the repolymerization generally results in degradation products having high molecular weights, solid products such as humus and industrial lignin are formed. The C-C bonds formed are more difficult to cleave than the original ether bonds in the lignocellulosic components. The degradation reaction is due to the presence of unstable compounds under the reaction conditions. Such unstable compounds typically carry C ═ O or C ═ C functional groups, such as xylose, glucose, furfural, hydroxymethylfurfural, coniferyl alcohol, sinapyl alcohol, phenolic compounds with C2-aldehyde substituents, and hubert ketone, and the like. C ═ O and/or C ═ C unstable compounds can be converted to stable compounds by hydrogenation or the like.

A particular method of fractionation of lignocellulose, as disclosed in US20160024712a1 and US20090176286a1, is to extract lignin and hemicellulose from lignocellulosic material at high temperatures (120-280 ℃) using a water-soluble organic solvent (e.g. ethanol) in combination with water and/or acid. The cellulose fraction is obtained as a solid residue which can be used in commercial pulp applications. A major portion of the hemicellulose is converted to sugars and/or degradation products. While the lignin fraction undergoes degradation reactions, the dissolved lignin is separated from the dissolved hemicellulose-derived products by precipitation. However, lignin is difficult to convert to low molecular weight products (such as monomeric phenols) based on its degradation properties.

WO2017178513a1 discloses a method for fractionating lignocellulosic material using a mixture of water and organic solvent, such as water and formaldehyde, to stabilize soluble products and prevent degradation. The obtained lignin has a solid high molecular weight product of chemically bonded aldehydes and can be recovered from the liquor by precipitation. There is also a need to convert lignin to lower molecular weight products, such as monomeric phenols. The yields of monophenolic products obtained are close to the theoretical maximum based on aldehyde stabilization, the absolute values of which differ between different plant types (Shuai, Science,2016, 329-) 333; Lan, Angewandte Chemie International Edition,2018, 1356-. During the aldehyde solvent assisted fractionation of lignocellulose, hemicellulose is converted to furfural and stable sugars, the structure of the latter depending on the structure of the aldehyde. In the case of formaldehyde, formylated sugars, such as diformylxylose (WO2017178513a1), can be obtained, and the cellulose obtained will contain a solid product of chemically bonded aldehydes. WO2015009145a1 discloses a method for fractionating biomass to reduce processing costs, increase delignification, reduce side reactions, in particular hemicellulose degradation, with the aim of improving cellulose hydrolysis and increasing the naturalness of the resulting lignin. The method is used for carrying out fractionation on the lignocellulose biomass in a treatment solution at the temperature of lower than 170 ℃. Due to the high degree of delignification (> 80%) only in low boiling solvents (ethanol/water, v/v 60/40) at a temperature of 140 ℃. Ethanol is a low boiling solvent, however, which requires high specification reactors to scale up the process.

In addition to the above methods, the lignocellulosic material may be isolated by treating the biomass in an organic solvent or in a water-miscible solvent in the presence of a transition metal catalyst. The method can fractionate lignocellulose and catalytically convert soluble lignin into stable compounds. EP2891748a1 discloses the catalytic fractionation of lignocellulosic materials using a mixture of water and a secondary alcohol (e.g. isopropanol) at 170-240 ℃ in the absence of hydrogen and in the presence of a nickel catalyst. Since secondary alcohols are used as hydrogen donors, lignin can be converted into a solid form containing hemicellulose and cellulose in addition to being catalytically converted into low molecular weight lignin oil (EP2891748A 1; Ferrini and Rinaldi, Angewandte Chemie International Edition, 2014, 8634-. Part of the solvent is converted to the corresponding aldehyde/ketone, e.g. isopropanol is converted to acetone. Lignin oils are rich in a variety of compounds including 4- (3-hydroxy-propyl) -healing lignans, 4- (3-hydroxy-propyl) -eugenol, 4-n-propyl-healing lignans, 4-n-propyl-eugenol, and cyclohexanol. In this process, the dissolved hemicellulose sugars are unstable due to the degradation of the soluble sugars. (Rinaldi ACS Sustainable chem.Eng.2018,6, 13408-13419).

US20170152278a1 discloses the catalytic fractionation of lignocellulosic materials using water and water miscible alcohols (e.g. mixtures of methanol and ethanol) at 160-190 ℃. The process uses a palladium-based catalyst in the absence of hydrogen to convert and stabilize the extracted lignin. Lignin is catalytically converted to low molecular weight lignin oil, which contains a large number of phenolic molecules, mainly 4- (2-propenyl) guaiacol and 4- (2-propenyl) eugenol (US20170152278A1, Galkin and Samec, ChemSusChem,2014, 2154-. Cellulose is recovered in the form of carbohydrate pulp. Depending on the processing intensity of the process, part of the hemicellulose remains as a polymer in the pulp and another part of the hemicellulose is dissolved and degraded (Galkin, ChemSusChem,2016, 3280-3287; Kumaniaev, Green Chemistry,2017, 5767-5771) and thus serves as a hydrogen donor for the process. Solvent purification is required after the reaction to remove sugar-derived degradation products from the lignin product oil, which requires additional solvents beyond the reaction solvent.

Van den Bosch et al disclose catalytic fractionation of lignocellulosic material in methanol at 250 ℃ in the presence of hydrogen and a Ru/C catalyst (Energy)&Environmental Science,2015, 1748-. In which process lignin is catalytically converted into low molecular weight lignin oil (<1500g·mol^-1) Containing a large amount of phenolic monomers (50% by weight with respect to the initial lignin), mainly 4-n-propylguaiacol and 4-n-propylguaiacol. However, after hydrogenolysis, it is also necessary to separate the solids/solids, i.e. to separate the solid heterogeneous metal catalyst from the solid cellulose and hemicellulose residues (polysaccharide fraction). Such separation is impractical on an industrial scale due to catalyst recovery and deactivation problems and their incompatibility with the leading edge biorefinery strategies. Furthermore, harsh hydrogenolysis conditions often result in the loss of hemicellulose and cellulose or their conversion to sugar alcohols.

Another catalytic fractionation process of lignocellulosic material is the so-called hydrolytic hydrogenation. Liu et al (ACS Sustainable Chemistry & Engineering,2017, 5940-. Both cellulose and hemicellulose are solubilized and catalytically converted to polyols, such as sorbitol and xylitol, which can result in the loss of polysaccharides in sugar-based biorefineries. The lignin undergoes degradation reactions and is recovered as water-insoluble solids.

Li et al (Energy)&Environmental Science,2012,6383-6390) discloses one-pot catalytic hydrocracking of lignocellulosic material. The lignocellulosic material is produced from tungsten carbide (W)₂C) The catalyst and pressurized hydrogen were treated in water at 245 ℃. In this process the biomass is dissolved, as opposed to the previously described "catalytic fractionation" of cellulose which is recovered in solid form. In one-pot catalytic hydrocracking, both the cellulose and hemicellulose fractions are catalytically converted to polyols, including ethylene glycol, 1, 2-propanediol and 1, 2-butanediol. Lignin is catalytically converted to a mixture of low molecular weight products, rich in monophenolic compounds, such as 4- (3-hydroxy-propyl) -guaiacol, 4- (3-hydroxy-propyl) -eugenol, 4-n-propylguaiacol, 4-n-propyleugenol. This requires work-up of the product, for example separation of phenolic compounds from the polyols by liquid-liquid extraction, which can lead to loss of polysaccharide in sugar based biorefineries.

W2020002361A1 discloses catalytic lignocellulosic biorefineries of phenols, polyols and cellulose using a mixture of an alcohol solvent and water (e.g. n-butanol/water) at 160-200 ℃ at 10-30 bar. The cellulose remains in the solid residue, which is recovered as a slurry upon filtration. This process can fractionate out sugar and lignin monomers in a biphasic system. Lignin is catalytically converted into a low molecular weight product mixture and is enriched in monophenolic compounds with high selectivity to 4- (3-hydroxypropyl) -guaiacol, 4- (3-hydroxypropyl) -eugenol and the like. In practice, separating cellulose and lignin does not require a high energy consumption, but the process requires a high energy input and most of the energy is wasted on cellulose decomposition. Therefore, the energy efficiency of the one-pot biorefinery is low.

In summary, if the lignin is extracted before hydrogenolysis or catalytic depolymerization, many of the above problems can be avoided and the biomass can be treated separately with low energy consumptionSaccharide and lignin fractions and continuous treatment of the dissolved lignin with a heterogeneous catalyst under flow conditions. The biorefinery fractionation or pretreatment process uses water and organic solvents (such as alcohols, tetrahydrofuran or gamma-valerolactone, ionic liquids) as the pretreatment, and high temperature and/or inexpensive inorganic acids (such as H) as the process₂SO₄And HCl) is a catalyst, which helps remove lignin from cellulose and hemicellulose. At present a large amount of lignin is derived from the process using these techniques. However, both acid and/or high temperature may cause irreversible condensation of the lignin during its extraction, which greatly affects its further extraction. In particular, the lignin ether linkage is cleaved during extraction and subsequently a highly stable C-C bond is formed. This mechanism is believed to involve the formation of highly reactive carbenium ions at the alpha position of lignin and reaction with the negatively charged positions of the methoxy groups on the lignin aromatic rings.

Although increasing environmental pressures are driving the shift from petrochemical refinery production to bio refinery production, the production of biofuels and useful products from biomass in an economical and sustainable manner involves many challenges. Biorefinery processes remain conceptual to a large extent and commercial exploitation in real life is limited. It is known that biorefinery processes require optimization of pretreatment conditions for different biomass species, which means that a single treatment system cannot efficiently perform a biorefinery process for a range of biomass materials (e.g., hardwood, softwood, straw, wheat straw, bagasse) or mixed biomass (e.g., a mixture of different wood species, a mixture of softwood and hardwood). Therefore, there is an urgent need to enhance the biorefinery process for treating lignocellulosic material, such as (i) fractionating cellulose-rich solid material and lignin-rich product stream; (ii) biorefinery processes use low toxicity solvents, low energy consumption (e.g., use of moderate temperatures), and low cost (and low specification reactors); (iii) the extracted lignin produces mono-phenolic compounds, di-phenolic compounds and small oligo-phenolic compounds; in addition, easy product isolation and controlled product selectivity are also desirable features. More importantly, the monophenolic compounds are highly selective for 4- (3-hydroxy-propyl) -guaiacol and 4- (3-hydroxy-propyl) -eugenol. The high selectivity to 4- (3-hydroxy-propyl) -guaiacol and 4- (3-hydroxy-propyl) -eugenol is defined herein as obtaining a monomer product of more than 80% by weight. Thus, there is a need for improved processes for biorefining lignin.

Disclosure of Invention

In order to overcome the disadvantages and shortcomings of the prior art, the present invention is primarily directed to a method for improving lignin fractionation and depolymerization of biomass.

It is another object of the present invention to provide monolignols, i.e., syringyl propane and syringyl propanol, produced by the above-described methods for enhancing lignin fractionation and depolymerization of biomass.

It is a further object of the present invention to provide the use of the monolignol described above.

The purpose of the invention is realized by the following technical scheme:

a method for improving lignin fractionation and depolymerization of biomass comprises the following specific steps:

s1, processing biomass containing lignocellulose into small size through chopping, chipping, peeling, grinding or grinding, and then washing to obtain biomass;

s2, cooking the biomass obtained in the step S1 at 120-173 ℃ by using the pretreatment solution, and obtaining biomass containing cellulose and lignin and the pretreatment solution containing the lignin by using acid as a catalyst; the pretreatment solution is an organic solvent and water; the organic solvent is more than one of C2-C5, an organic solvent containing more than two hydroxyl groups and an organic solution containing ether bonds or ketone groups;

s3, separating the biomass containing the cellulose and the lignin from the pretreatment solution containing the lignin, washing the biomass containing the cellulose and the lignin by using the pretreatment solution with the same concentration at the temperature of 60-80 ℃, combining the pretreatment solution containing the lignin, mixing the combined pretreatment solution containing the lignin with water, and performing precipitation, filtration and drying treatment to obtain the lignin;

and S4, mixing the obtained lignin, an organic solvent and a depolymerization catalyst, heating to 180-250 ℃ in a protective atmosphere, stirring for catalytic depolymerization reaction, and cooling to room temperature to obtain lignin monomers, namely syringyl propane and syringyl propanol.

Preferably, the biomass containing lignocellulose in step S1 is at least one of wood chips, bark, plant litter, rice straw, stalks, rice hulls, flax scraps, wheat straw, fruit shells, wheat hulls, bagasse, hardwood, and softwood.

Preferably, the acid in the step S2 is an organic acid or/and an inorganic acid, and the concentration of the acid is 1-200 mmol/L. The mass concentration of the acid serving as the pretreatment solution is 0.01-2 wt.%; the mass ratio of the organic solvent to the water is (13-17): (3-7).

Preferably, the C2-C5 and the organic solvent containing more than two hydroxyl groups are dihydric alcohol or trihydric alcohol; the organic solution containing ether bonds is diethylene glycol ether, and the organic solution containing ketone groups is dihydroxyacetone; the organic acid is more than one of formic acid, acetic acid, oxalic acid, maleic acid, benzoic acid or methanesulfonic acid; the inorganic acid is more than one of hydrochloric acid, sulfuric acid or phosphoric acid.

More preferably, the dihydric alcohol is one or more of ethylene glycol, 1, 2-propylene glycol, 1, 3-butylene glycol, 1, 4-butylene glycol, 1, 2-butylene glycol, 1, 5-pentanediol, 1, 4-pentanediol, 1, 3-pentanediol, or 1, 2-pentanediol; the trihydric alcohol is glycerol, 1,3, 5-pentanetriol, 2,3, 4-pentanetriol, 1,2, 5-pentanetriol, 1,2, 4-pentanetriol and 2,3, 4-pentanetriol.

Preferably, the ratio of the mass of the biomass to the volume of the pretreatment solution in step S2 is 1000 g: (0.1-50) L.

Preferably, the volume ratio of the pretreatment solution containing lignin and water in the step S3 is 1: (3-10).

Preferably, the organic solvent in step S4 is one or more of ethanol, isopropanol, and acetone; the depolymerization catalyst is Ru/C, Ni/C, Ni/Al₂O₃、Ni/SiO₂-Al₂O₃、Ru/Al₂O₃、Ru/SiO₂、Ru/ZrO₂Or Ru/SiO₂-Al₂O₃One or more of (1); the protective atmosphere is nitrogen or argon; the mass ratio of the lignin to the volume of the organic solvent to the depolymerization catalyst is (0.02-0.2) g: 20mL of: 1g of a compound; the time of the catalytic depolymerization reaction is 2-10 h.

The depolymerization catalyst may also be selected from transition metals such as palladium, platinum, rhodium, molybdenum, tungsten, and the like. The carrier of the catalyst can be SiO₂，Al₂O₃，ZrO₂Or activated carbon, the catalyst may be pre-activated prior to use, for example by removal of oxygen or oxides using a reducing agent.

The lignin monomer is syringyl propane and syringyl propanol, and is prepared by the method for improving the lignin fractionation and depolymerization of biomass.

The lignin monomer is applied to the chemical industry or the medical field.

The method for efficiently producing the lignin monomer under the conditions of low temperature and low pressure adopts the pretreatment solution and the acid catalysis treatment method, can effectively dissolve a large amount of lignin from a large amount of different lignocellulose-containing biomasses at 100-165 ℃, is used for treating the lignocellulose-containing biomass from various sources, including mixing biomass wastes of different species, and becomes a highly desirable biomass refining process. The method can convert yard and woody waste into liquid fuels in a cost-effective manner. Meets the requirements of the field on biological refining process, and can be used in an economic mode and on a commercial scale.

Conventional biomass processing methods are typically directed to specific biomass and require complex optimization processes to process different biomass types, such as wood from different species of trees. The invention aims at non-specific biomass, and lignin of various types of biomass can be effectively dissolved by adopting the combination of the polyhydroxy solvent and the acid of the pretreatment solution, so that complex raw materials can be effectively treated, and the method can be suitable for any types of biomass. Such as lignocellulosic biomass including forestry residues, agricultural residues, yard waste, animal and human waste (e.g., biodegradable municipal waste). It may also be a herbaceous biomass such as grass, straw, wheat straw, husks (rice hulls, wheat hulls), bagasse, hardwood, softwood and/or combinations of these materials. Prior to the pretreatment step, the untreated biomass may be washed and/or reduced in size. For example, it is processed by chopping, chipping, peeling, grinding or milling.

In an exemplary embodiment, lignocellulosic biomass is treated with at least one polyhydroxyl solvent in the presence of at least one acid in a pretreatment reactor (e.g., a vessel made of steel, glass, or plastic) to separate the biomass and lignin into a cellulose-rich product stream and a lignin-rich product stream (liquid). The polyhydroxy solvent pretreatment can be advantageously carried out at a temperature of 100 to 165 ℃, preferably 120 to 150 ℃, and in one embodiment, the polyhydroxy solvent pretreatment is carried out at a temperature of 100 to 120 ℃ and at atmospheric pressure (the pressure inside the reactor is not higher than the pressure of the external environment). The low-temperature organic solvent can effectively separate lignin and cellulose at 100-165 ℃. Generally, the condensation degree of lignin increases with the increase of temperature, and the lignin is more difficult to separate. The duration of the pretreatment of the polyhydroxyl solvent to effect fractionation can be carried out over a wide range of times. The duration of the polyhydroxy solvent pretreatment step is generally 30 to 250min, preferably 40 to 150min, and more preferably 60 to 120 min.

The organic solvent in the pretreatment solution is C2-C5, contains at least two or more hydroxyl functional groups and optionally contains one or more of ether bonds or ketone groups, and is preferably selected from dihydric alcohol, trihydric alcohol and polyhydric alcohol. The dihydric alcohol is preferably ethylene glycol, 1, 2-propylene glycol, 1, 3-butylene glycol, 1, 4-butylene glycol, more preferably 1, 4-butylene glycol; the trihydric alcohols are preferably glycerol, 1,3, 5-pentanetriol, 2,3, 4-pentanetriol, 1,2, 5-pentanetriol, 1,2, 4-pentanetriol, 2,3, 4-pentanetriol.

In a preferred embodiment, the pretreatment solution includes an acid catalyst. Generally, when a glycol is used during the pretreatment, an acid is required to adjust the pH to 0.5 to 7, preferably 1.5 to 3. The concentration of the acid in the pretreatment solution is 1-200 mmol/L, preferably 15-100 mmol/L. An acid amount of 200mmol/L in the pretreatment solution above the upper limit may result in more side reactions, thereby increasing the formation of impurities. While an acid of 1mmol/L below the lower limit reduces the degree of fractionation and delignification achieved by the process. Acid catalysts including organic or inorganic acids may be used in the pretreatment step. The pKa value of the acid is preferably 4.5, more preferably 3 or less, and most preferably 1 or less. Wherein the organic acid is formic acid, acetic acid, oxalic acid, maleic acid, benzoic acid, phosphoric acid or methanesulfonic acid (such as aluminum triflate, aluminum copper triflate, lanthanum triflate, nickel triflate), the inorganic acid is hydrochloric acid, sulfuric acid, lewis acid ferric chloride and combinations thereof, and most preferably sulfuric acid is used as the acid catalyst.

In one embodiment, 1 kg of dry biomass is mixed with 0.1 to 50L of pretreatment solution, preferably 1.0 to 10L, and a suspension of biomass, pretreatment solution and acid catalyst is obtained. The optimum ratio of the amounts of pretreatment liquid to biomass depends on the type of biomass, and for economic reasons the liquid-solid weight ratio (L/S) of the glycol pretreated biomass is as low as possible, preferably L/S.ltoreq. 7/1. Hydrolysis reactions occur in the presence of water in the pretreatment solution when the network structure of the biomass is destroyed by the glycol. This is due to hydrolysis occurring on the covalent bond linking the lignin and hemicellulose. Preferably, the pretreatment solution contains 1 to 10 wt% of water. The pretreated lignocellulosic biomass is separated into a cellulose-rich product stream and a lignin-rich product stream (liquid) by any separation method known to those skilled in the art, but is not limited to pressing, filtration, settling or centrifugation. The pretreatment of the lignocellulosic biomass with the polyhydroxyl solvent and the acid results in a cellulose-rich extract containing less impurities, while the lignin-rich liquor contains a higher content of lignin.

The present invention has higher yields and efficiencies than prior methods without the use of stringent pretreatment conditions (less lignin degradation and condensation). The biorefinery system of the present invention allows the individual steps of biomass treatment (pretreatment, hydrolysis and fermentation) to be carried out in a single reactor, thereby reducing the number of operating units, even without the need for separate units. Conventional biomass processing methods typically require the use of a pressure vessel made of a material that withstands high temperatures and pressures, such as carbon steel or stainless steel or similar alloys. Because ethanol has a high vapor pressure at 120-170 ℃, a high specification pressure vessel (typically made of stainless steel with thickened walls) is required for ethanol pretreatment and Kishimoto pulping processes. Another example is the acid/base treatment of biomass, which is carried out at 170 ℃ and high pressure (>600 kPa). Due to the harsh biomass processing conditions, the diols of the present invention typically have higher boiling points (e.g., 230 ℃ for 1,4-BDO) and lower vapor pressures than water and ethanol used in conventional pretreatment processes. FIG. 1 is a graph of vapor pressures at different temperatures for a conventional pretreatment solvent of the prior art. As can be seen from fig. 1, the vapor pressure of 1,4-BDO at 120 ℃ is about 8KPa (compared to about 20KPa for water and about 30KPa for ethanol), and thus, glycol/acid pretreatment can be performed using a low specification reactor, such as a reactor made of serum bottle, plastic, glass or stainless steel in a simple laboratory environment. It can also be carried out in a commercial fermentor (e.g., with 5mm 316 SS). The tank body is only 1-5 mm thick, preferably 3-5 mm thick, and more preferably 3-4 mm thick, and can also be used in the pre-treatment step disclosed currently. It follows that a batch reactor model becomes feasible in a biorefinery, allowing batch processing of biomass. A first generation biorefinery (using food or starchy feedstocks for biofuel production) can be easily upgraded to a second generation biorefinery (using forestry and agricultural residues as feedstocks) without the need to convert the cooking unit to a high pressure vessel (>300 kPa). Thus, the use of glycol/acid pretreatment reduces the number of operational components in the biomass processing system, thereby reducing overall cost.

The invention also employs pre-extraction and enzymatic hydrolysis of a cellulose-rich product stream (pulp). Enzymatic hydrolysis is accomplished by the enzymatic hydrolysis of cellulose to glucose by an enzyme or combination of enzymes capable of hydrolyzing cellulose, referred to as hydrolases, preferably cellulase. Hydrolysis of cellulose is also known as cellulose hydrolysis. The process may use any cellulase enzyme for the enzymatic hydrolysis. Suitable cellulases are endo-cellulases (cleaving cellulose at an internal position), exo-cellulases (cleaving cellulose at more external positions to produce cellobiose or cellotetraose), beta-glucosidases (cellobiase, cleaving the exo-cellulase product into glucose units). Less preferred other cellulases, such as oxidative cellulases and cellulose phosphorylases, preferably a combination of cellulases is used, in particular a combination of an endocellulase, an exocellulase and a beta-glucosidase. In an embodiment, although most of the hemicellulose has been completely dissolved in the pretreatment solution, the hemicellulose remaining after the polyhydroxy solvent pretreatment may be decomposed using hemicellulase (e.g., xylanase, arabinanase, mannanase, etc.) to decompose. In an exemplary embodiment of the invention, the conversion of glucose for enzymatic hydrolysis during saccharification and fermentation of a cellulose-rich product stream resulting from glycol and acid pretreatment is > 90%. Alternatively, the cellulose-rich product stream may be subjected to disc milling or grinding (with additional water and pH adjustment) prior to the enzymatic hydrolysis. Disc milling or grinding produces shorter cellulose fibers, which facilitates the saccharification and fermentation process. Optionally, water is added to adjust the pH to a pH of 2 to 7, preferably 4 to 6, more preferably at a pH of 4.8 prior to the saccharification and fermentation process.

When biomass is treated by conventional pretreatment methods under complicated pretreatment conditions (e.g., highly acidic or high temperature), a large amount of lignin precipitates and condensates are generated. The lignin precipitates and condensates contain most of the cellulose and cannot be extracted from the biomass, rendering it non-enzymatically digestible and reducing glucose conversion. The glycol and acid pretreatment method overcomes the problem of not being able to effectively dissolve lignin, thereby maintaining the stability and depolymerizability of the lignin dissolved in the liquid.

Glycol and acid pretreatment methods improve the overall yield of lignin extraction from lignocellulosic biomass. The extraction rate of lignin by the conventional method is about 80%, and the lignin can be effectively dissolved by the pretreatment of the dihydric alcohol and the acid, the extraction rate of the lignin can reach more than 90%, and the lignin has high depolymerization performance. Thus, by using a diol and acid pre-treatment at appropriate temperatures, higher quality and higher lignin extraction can be obtained. In addition, the obtained lignin has more β -O-4 bonds and less condensed phenolic groups, which improves the depolymerization of lignin and the yield of monophenol compounds. Since the extracted lignin has new hydroxyl groups, the solubility and depolymerization properties of the dissolved lignin are significantly increased, thereby increasing the yield of lignin monophenolic compounds, which is useful for the preparation of valuable products in the biomedical and chemical fields.

The high depolymerization of the extracted lignin and the high yield of monophenolic compounds of the present invention are demonstrated by a process for producing phenolic compounds comprising mixing a lignin feedstock with a) water and an alcohol, b) a catalyst comprising ruthenium, and c) nitrogen and subjecting them to a temperature of at least 250 ℃. The method includes externally supplying nitrogen at a partial pressure of 10bar or more at room temperature, or externally supplying nitrogen at a partial pressure of 10 to 30bar at room temperature. Comprising subjecting the following raw materials to a temperature of at least 250 ℃, A) a catalyst comprising ruthenium, water and alcohol, nitrogen and lignin extracted by pretreatment with 170 ℃ ethanol in the raw material medium, and B) a catalyst comprising ruthenium, water and alcohol, nitrogen and lignin extracted by pretreatment with 120 ℃ ethanol, C) a catalyst comprising ruthenium, water and alcohol, nitrogen and lignin extracted by pretreatment with 170 ℃ diol, nitrogen and D) a catalyst comprising ruthenium, water and alcohol, nitrogen and lignin extracted by pretreatment with 120 ℃ diol. Wherein more of the phenol compounds in the mixture, less than 80 wt% of the mono-phenol compounds (syringyl propane and syringyl propanol) have the following structural formula:

compared with the prior art, the invention has the following beneficial effects:

1. the present invention is a process for fractionating lignocellulosic biomass into a cellulose-rich product stream (pulp) and a lignin-rich product stream (liquor), comprising organosolv treatment of the optional biomass with a polyhydroxyl solvent. The mono-alcohol solvent such as ethanol has higher reactivity to structural components of biomass, and side reactions do not occur because the poly-hydroxyl solvent can reduce the side reactions.

2. The process of the present invention provides a product fluid of higher purity, which is economically desirable in view of maximizing the value of the effective biomass, and also makes the subsequent cellulose pulp enzymatic digestion more efficient.

3. The process of the present invention uses an integrated solid lignocellulosic feedstock well that is species independent and can selectively extract lignin and cellulose (separation rates of over 90%) while keeping the cellulose solid.

4. The method of the invention can prepare lignin fluid and cellulose fluid from lignocellulose material, the hydrolysis rate of the cellulose can reach more than 90 percent, and the method is beneficial to refining the downstream glycosyl biology.

5. The invention can control the selectivity of monophenol compounds, and the content of guaiacol and eugenol compounds in the catalytic depolymerization products can reach more than 90 percent.

6. The pretreatment reaction in the biological refining method can be carried out at a lower temperature (120 ℃), the energy consumption (for example, moderate temperature) can be reduced by using a high-boiling-point organic solvent, and the method is simple and has low cost.

7. The lignin obtained by the method has more beta-O-4 bonds and less condensed phenolic groups, and the depolymerization performance of the lignin and the yield of the monophenol compounds are improved. Since the extracted lignin has new hydroxyl groups, the solubility and depolymerization properties of the dissolved lignin are significantly increased, thereby increasing the yield of lignin monophenolic compounds, which is useful for the preparation of valuable products in the biomedical and chemical fields.

Drawings

FIG. 1 shows the pressures of different organic solvents at different temperatures in the prior art.

FIG. 2 is a graph of the cellulose and lignin content of substrates under different pretreatment conditions of examples 1-10 and comparative examples 1-8.

FIG. 3 is a two-dimensional heteronuclear single quantum correlation spectrum of lignin extracted under different pretreatment conditions in examples 1-10 and comparative examples 1-8.

FIG. 4 is a graph showing the functional group contents of lignin extracted under different pretreatment conditions in examples 1 to 10 and comparative examples 1 to 8.

FIG. 5 is a graph showing the enzymatic hydrolysis efficiency of cellulose after different pretreatments in examples 1 to 10 and comparative examples 1 to 8.

FIG. 6 shows the contents of compounds obtained after catalytic depolymerization of lignin extracted under different pretreatment conditions in examples 10 and 11 and comparative examples 6 and 9, under Ru/C catalyst.

Detailed Description

The following examples are presented to further illustrate the present invention and should not be construed as limiting the invention. Unless otherwise specified, the technical means used in the examples are conventional means well known to those skilled in the art. Reagents, methods and apparatus used in the present invention are conventional in the art unless otherwise indicated.

Eucalyptus chips used in the examples of the invention were provided by the rey forestry bureau, guangdong province. Pretreatment solvents and other chemicals were purchased from J & K Acros Organics. Commercial cellulase Cellic Ctec2 was supplied by Novozymes Investment Co.Ltd. and Pronase was supplied by Sigma Chemical Company, USA.

Examples 1 to 5

1. Pretreatment of eucalyptus powder: the eucalyptus pieces are prepared into eucalyptus powder, the eucalyptus powder is added into a pretreatment liquid (a mixed solution of dihydric alcohol and water), sulfuric acid is used as a catalyst, and a rotary digester (Xiyangtongda light industry equipment limited company) is adopted to pretreat the eucalyptus powder. Wherein the dihydric alcohol is Ethylene Glycol (EG), 1, 2-propylene glycol (1,2-PG), 1, 3-propylene glycol (1,3-PG), 1, 3-butanediol (1,3-BDO), 1, 4-butanediol (1, 4-BDO).

50g of eucalyptus wood powder, 20mmol/L of sulfuric acid and pretreatment solution (the volume ratio of dihydric alcohol to water is 65%: 35%), and the mass ratio of liquid (sulfuric acid to dihydric alcohol) to solid (7: 1 and mixing. The digester is heated to 167-173 ℃ at a rate of 3 ℃/min for pretreatment and held at that temperature for 60min, the specific experimental conditions for examples 1-5 are shown in table 1.

TABLE 1 acid concentration, glycol in pretreatment solution and solvent ratio in examples 1-5

2. The pretreated substrate (solid biomass, containing cellulose and a small amount of lignin) and the pretreatment liquid containing a large amount of lignin were separated with nylon cloth. The solid biomass was washed 3 times (75 mL each) with the same concentration of warm (60 ℃) pretreatment solution (mixed solution of glycol and water). And then, the volume ratio of the combined pretreatment liquid containing the lignin to water is 1: 3 mixing, precipitating, filtering and drying to obtain the lignin.

Examples 6 to 10

1. Pretreatment of eucalyptus powder: the eucalyptus powder is added into a pretreatment solution (a mixed solution of dihydric alcohol and water), sulfuric acid is used as a catalyst, and a rotary digester (Xianyangtong light industry equipment Co., Ltd.) is adopted for pretreatment of the eucalyptus powder. Wherein the dihydric alcohol is Ethylene Glycol (EG), 1, 2-propylene glycol (1,2-PG), 1, 3-propylene glycol (1,3-PG), 1, 3-butanediol (1,3-BDO), 1, 4-butanediol (1, 4-BDO).

50g of eucalyptus wood powder, 25mmol/L of sulfuric acid and pretreatment solution (the volume ratio of dihydric alcohol to water is 85%: 15%), and the mass ratio of liquid (sulfuric acid to dihydric alcohol) to solid (7): 1 and mixing. The digester is heated to 167-173 ℃ at a rate of 3 ℃/min for pretreatment and held at that temperature for 60min, with the specific experimental conditions for examples 6-10 shown in table 2.

TABLE 2 acid concentrations, glycols in pretreatment solutions and solvent ratios thereof in examples 6-10

2. The pretreated substrate (solid biomass, containing cellulose and a small amount of lignin) and the pretreatment solution containing a large amount of lignin were separated with a nylon cloth. The solid biomass was washed 3 times (75 mL each) with the same concentration of warm (60 ℃) pretreatment solution (mixed solution of glycol and water). And then, the volume ratio of the combined pretreatment liquid containing the lignin to water is 1: 3 mixing, precipitating, filtering and drying to obtain the lignin.

Example 11

The difference from example 10 is that: the acid concentration is 150mmol/L, the pretreatment temperature is 120 ℃, and the pretreatment time is 240 min.

Comparative examples 1 to 4

The eucalyptus powder is added into a pretreatment solution (a mixed solution of monohydric alcohol and water), sulfuric acid is used as a catalyst, and a rotary digester (Xianyangtong light industrial equipment Co., Ltd.) is adopted for pretreatment of the eucalyptus powder. Wherein the monohydric alcohol is methanol (MeOH), ethanol (EtOH), 2-propanol (2-ProOH), 2-butanol (2-BuOH)).

50g of eucalyptus wood powder, 20mmol/L of sulfuric acid and a pretreatment solution (65% to 35% by volume of monohydric alcohol and water) are mixed in a liquid (sulfuric acid and monohydric alcohol) solid-to-mass ratio of 7: 1 and mixing. The digester is heated to 167-173 ℃ at a rate of 3 ℃/min and held at that temperature for 60min, the specific experimental conditions for comparative examples 1-4 are shown in table 3.

TABLE 3 monohydric alcohol and solvent ratios in the acid concentration pretreatment solutions of comparative examples 1-4

Comparative examples 5 to 8

The eucalyptus powder is added into a pretreatment solution (a mixed solution of monohydric alcohol and water), sulfuric acid is used as a catalyst, and a rotary digester (Xianyangtong light industrial equipment Co., Ltd.) is adopted for pretreatment of the eucalyptus powder. Wherein the monohydric alcohol is methanol (MeOH), ethanol (EtOH), 2-propanol (2-ProOH), 2-butanol (2-BuOH)).

50g of eucalyptus wood powder, 25mmol/L of sulfuric acid and a pretreatment solution (85% by volume of monohydric alcohol and water: 15%) in a liquid (sulfuric acid and monohydric alcohol) solid-to-mass ratio of 7: 1 and mixing. The digester was heated to 167-173 ℃ at a rate of 3 ℃/min and held at that temperature for 60min, the specific experimental conditions for comparative examples 5-8 are shown in table 4.

TABLE 4 acid concentration, monohydric alcohol in pretreatment solution, and solvent ratio in comparative examples 5-8

Comparative example 9

The difference from example 6 is that: the acid concentration is 150mmol/L, the pretreatment temperature is 120 ℃, and the pretreatment time is 240 min.

Test example 1 chemical composition analysis of eucalyptus

The chemical composition of the pre-treated eucalyptus wood was analyzed according to the standard procedures of the national renewable energy laboratory (NERL). The hydrolyzed monomeric sugar units were quantified by high performance liquid chromatography (HPLC, Shimadzu) equipped with a CHO-782Transgenomic column and the acid-insoluble lignin content was calculated gravimetrically.

FIG. 2 is a graph of the cellulose and lignin content of the substrates under different pretreatment conditions in examples 1-10 and comparative examples 1-8. As can be seen from FIG. 2, the dissolution levels of lignin under two pretreatment conditions, comparative examples 1-4 were pretreated with 20mM acid and 65% monohydric alcohol in the pretreatment solution, and examples 1-5 were pretreated with 25mM acid and 85% dihydric alcohol in the pretreatment solution, while the components of the original eucalyptus wood (42% cellulose, 21% hemicellulose and 25% lignin). As shown in fig. 2, in eucalyptus wood treated with methanol, ethanol, 2-propanol and 2-butanol (i.e., comparative examples 1-8), there were a large amount of lignin residues in the pretreated substrate due to the condensation effect. Whereas the hemicellulose is completely removed during the pretreatment. The large amount of lignin remaining in the substrate affects the production rate of bioethanol in downstream processes. In the eucalyptus wood treated with the dihydric alcohol (examples 1 to 10), the residual amount of lignin in the substrate was significantly reduced, and the extraction rate of lignin was significantly improved. As shown in FIG. 2, the lignin content in the substrate was reduced from 25% to 4.3-6%. The results show that in the case of 20mmol/L acid and 25mmol/L acid, the lignin is separated/dissolved in more amount in the glycol than in the monohydric alcohols (methanol, ethanol, 2-propanol and 2-butanol). When the acid and mono/di-alcohol concentrations are increased in the pretreatment conditions, the amount of lignin separated/dissolved in the glycol increases significantly. The residual lignin content after pretreatment with 2-propanol and 2-butanol (25mM acid, 85%) was increased by 20% over that obtained when methanol (25mM acid, 85%) was used as the pretreatment solution. The residual lignin content after pretreatment with dihydric alcohol (such as ethylene glycol, 1, 2-propylene glycol, 1, 3-butylene glycol, and 1, 4-butylene glycol) is below 6%, and the extraction rate of lignin is above 90%. Even though lignin changes its chemical properties after pretreatment, it is still soluble in glycols. Table 5 shows the lignin content and the extraction yield of eucalyptus wood in examples 1 to 10 and comparative examples 1 to 8. As can be seen from table 5, the lignin extraction rate after the monohydric alcohol pretreatment is lower than that of the dihydric alcohol, and is more susceptible to the concentration of the acid.

TABLE 5 Lignin content and extraction yield in Eucalyptus in examples 1-10 and comparative examples 1-8

Test example 2 chemical composition analysis of other Biomass

The analysis of the various substrate components before and after pretreatment was carried out according to the standard procedure of the national renewable energy laboratory (NERL). The substrate under test was pretreated with (i) 85% ethanol in the pretreatment solution or (ii) 85% 1, 4-butanediol in the pretreatment solution. Using 25mmol/L H in two pretreatments₂SO₄Treating at 170 deg.C for 60 min. In table 6 it is indicated that in all tested substrates, including pine, rice hull and mixed wood (pine (softwood) and eucalyptus (hardwood) combinations), pretreatment with 1, 4-butanediol achieved more than 85% lignin extraction from wood within 1 h.

Despite the use of experimental conditions below 170 ℃, the extraction yield of lignin (yield of lignin) achieved by the present method is still higher than that of lignin using other prior pretreatment techniques such as ethanol (extraction yield of lignin is higher than that of ethanol pretreated with the method of the present invention in table 5). As can be seen from tables 5 and 6, the lignin extraction rate of the 1, 4-butanediol pretreatment was 87 to 94%, the lignin extraction rate of the ethanol pretreatment was 70 to 84%, the lignin extraction rate of the 1, 4-butanediol pretreatment was higher than that of the ethanol pretreatment, and the influence of the concentration of the acid in the pretreatment on the 1, 4-butanediol pretreatment method was lower than that of ethanol, because the side reaction was prevented by the diol pretreatment. The results show that glycol pretreatment allows for assignment of non-biomass species and simultaneous treatment of multiple different lignocellulosic biomasses without tedious optimization or substrate selection/purification based on different lignocellulosic biomasses. The ethanol pretreatment can be obviously different under different pretreatment intensities.

TABLE 6 Lignin content in different substrates and lignin extraction yield after pretreatment thereof

Table 7 shows the lignin content of different substrates and their wood extraction yield after pretreatment. Comparing the ratio of pine to eucalyptus in the pretreatment solution (i)85% ethanol or (ii) a lignin content of 85% 1, 4-butanediol in the pretreatment solution before and after pretreatment. (i) And (ii) both mixed 150mmol/L H₂SO₄And pretreated at 120 ℃ for 240 min. By pretreating the virgin substrate, lignin removal from cork can be achieved within 4 hours at temperatures below 120 ℃>70% removal of lignin from hardwood>80 percent. This relatively low temperature pretreatment step may allow for the option of a low-profile reactor for energy and chemical production, thereby reducing the cost-effective challenges faced by biorefineries known in the art.

TABLE 7 Lignin content of different substrates and their lignin extraction yield after pretreatment

Test example 3 physicochemical Properties of Mono/Di-Alcohol extracted Lignin

And (3) analyzing by adopting Nuclear Magnetic Resonance (NMR) to obtain a two-dimensional heteronuclear single quantum correlation spectrum (2D HSQC) so as to compare the molecular scale structures of the lignin sample pretreated by the ethanol and the 1, 4-butanediol. The pretreated lignin (labeled EtOH-S and 1,4-BDO-S) was prepared and purified as described in Meng et al (Meng, X.et al, ACS Sustainable Chemistry & Engineering,2017.5 (9): p 8004-. Two-dimensional heteronuclear single quantum correlation spectroscopy was performed using a JEOL ECZR 500MHz spectrometer equipped with a 5mm ROYAL probe. A representative 2D HSQC NMR spectrum of lignin after pretreatment with ethanol and 1, 4-butanediol is shown in fig. 3. Fig. 3 is a two-dimensional heteronuclear single quantum correlation spectrum of lignin extracted under different pretreatment conditions in example 10 and comparative example 6. Wherein, fig. 3(a) and (a ') are two-dimensional heteronuclear single quantum correlation spectra of lignin extracted in comparative example 6, and fig. 3(b) and (b') are two-dimensional heteronuclear single quantum correlation spectra of lignin extracted in example 10. Wherein, the G series is Guaiacryl, and the B series is beta-beta. As can be seen from FIG. 3, in the aliphatic region of the 2D HSQC NMR spectrum, β -O-4, β -5 and β - β are the main unit linkages in the lignin sample (a' in FIG. 3). In contrast, a unique signal (corresponding label G5) was found in the 2D HSQC spectra of residual lignin and soluble lignin after pretreatment with 1, 4-butanediol and acid, indicating the presence of 1, 4-butanediol related functional groups in the alpha position of the beta-O-4 bond. Studies have shown that to quantify hydroxyl groups in lignin samples, each sample was phosphorylated with 2-chloro-4, 4,5, 5-tetramethyl-1, 3, 2-dioxaphospholane (TMDP) in pyridine/deuterated chloroform (v/v ═ 1.6/1.0). Quantitative 31PNMR spectra were obtained on a JEOL ECZR 500MHz spectrometer using an inverse gated decoupled pulse sequence, 90 ° pulsing, 25s pulse delay and 32 scans. All chemical shifts in the literature are relative to an internal standard of 145 ppm. The quantitative calculation of hydroxyl groups was based on the amount of hydroxyl groups of the internal standard, and the results of 31PNMR analysis are shown in FIG. 4, where FIG. 4 is the functional group content of lignin extracted under different pretreatment conditions in examples 1-10 and comparative examples 1-8. Wherein, a is examples 1 to 5 and comparative examples 1 to 4; b are examples 6-10 and comparative examples 5-8. As can be seen from fig. 4, the amount of phenolic hydroxyl groups of lignin in eucalyptus wood after pretreatment with glycol and acid is about 20% higher than the amount of phenolic hydroxyl groups of lignin after pretreatment with methanol or ethanol (the preferred index of structural integrity). And contain relatively high amounts of aliphatic OH groups after pretreatment with the glycol, indicating that the alpha position of beta-O-4 has been converted to an ether linkage (i.e., a functional group with which the ether linkage is associated with the glycol). The weight average molecular weight (Mw) and number average molecular weight (Mn) of the lignin samples were determined by Gel Permeation Chromatography (GPC) as previously described. (O.ringer et al. journal of Chromatography A,2006,1102, 154-. Table 8 shows the molecular weight and polydispersity index of the soluble lignin in examples 1-10 and comparative examples 1-8. It shows the molecular weight of the lignin samples in examples 1-10 and comparative examples 1-8 as determined by GPC. The Mw and Mn of lignin in eucalyptus wood after glycol pretreatment is greater than the Mw and Mn of lignin after monohydric alcohol pretreatment, meaning that the molecular weight of lignin extracted from glycol pretreatment is higher than that of monohydric alcohol.

TABLE 8 molecular weight and polydispersity index of soluble lignin in examples 1-10 and comparative examples 1-8

Test example 4 enzymatic hydrolysis

Enzymatic hydrolysis was performed in acetate buffer (50mmol/L, pH 4.8) at 2% (w/v) solid load, enzyme load 7.5FPU/g dextran in 500mL erlenmeyer flask. The mixture was incubated at 50 ℃ and 150rpm for 72h in a rotary shaker. 1ml of the supernatant was collected at 3, 6, 9, 24, 48, 72 hours for sugar analysis. FIG. 5 is a graph showing the enzymatic hydrolysis efficiency of cellulose after different pretreatments in examples 1 to 10 and comparative examples 1 to 8. As can be seen from fig. 5, under the pretreatment condition of the acid concentration of 20mM, the cellulose content in the eucalyptus wood pretreated with 65% methanol or ethanol was increased to 90% or more due to the removal of lignin and hemicellulose from the eucalyptus wood, whereas when the acid concentration was increased to 25mM, the cellulose content in the eucalyptus wood pretreated with 85% methanol or ethanol was decreased to 80% or less. When the pretreatment conditions were changed to 25mM and 85% 2-propanol or 2-butanol pretreatment, the cellulose content in eucalyptus wood decreased to below 40%. However, this phenomenon was not observed in the pretreatment with glycol. The results found that the conversion of cellulose exceeded 90% at both strengths of pretreatment, indicating that cellulose-rich extracts pretreated with glycols showed high enzymatic digestibility, regardless of pretreatment conditions, compared to extracts pretreated with other known organic solvents. Thus, the glycol pretreatment method is highly adaptable and can be used with minimal optimization. In order to increase the monomer yield of the present invention, a reaction gas (e.g., hydrogen) may be introduced to further increase the monomer yield.

Test example 5 catalytic depolymerization of glycol pretreated lignin

And mixing the obtained lignin, an organic solvent and a depolymerization catalyst, heating to 180-250 ℃ in a protective atmosphere, stirring for catalytic depolymerization reaction, and cooling to room temperature to obtain lignin monomers, namely syringyl propane and syringyl propanol. Specifically, 0.2g of the lignin obtained in examples 1-10, 20mL of ethanol and 10mg of Ru/C catalyst (5 wt%) were charged to a 50mL Parr reactor (5512 bench reactor, T316 stainless steel, Parr Instruments, IL). And replacing the air in the reactor with nitrogen for 3-5 times, and then filling the nitrogen, wherein the partial pressure of the nitrogen is 10 bar. The reaction was stirred at 250rpm for 5h while warming to 250 ℃ over 30 min. After completion of the catalytic depolymerization reaction, the reactor was cooled to room temperature with an external compressed air stream and the resulting lignin monomer-containing liquid sample was quantitatively analyzed by gas chromatography.

The monolignol obtained from the above reaction was analyzed by directly sampling 1mL of the resulting solution and adding 100. mu.L of an internal standard (8mg decane dissolved in 5mL 1, 4-dioxane). The solution was analyzed by Agilent 7890B GC equipped with an HP5 column (30 m.times.0.32 mm) and a Flame Ionization Detector (FID) (ca. 1.1 mL). The temperature program starts from 40 ℃, keeps for 3min, and then raises the temperature to 100 ℃ at 30 ℃/min; then the temperature is raised to 300 ℃ at 40 ℃/min and kept for 5 min. The monolignol peaks in the GC-FID chromatogram were detected using GC-MS equipped with an Agilent 7890B series GC and an Agilent 5977A series mass spectrometer of HP5-MS capillary column under the same operating conditions.

The catalytic depolymerization of lignin samples pretreated with ethanol or 1, 4-butanediol produces two major phenolic products, syringyl propane and syringyl propanol. FIG. 6 shows the content of compounds after catalytic depolymerization of lignin extracted under different pretreatment conditions in examples 10 and 11 and comparative examples 6 and 9 under Ru/C catalyst. As can be seen from fig. 6, the selectivity of syringyl propane and syringyl propanol exceeded 91% in all cases. The results show that the Ru/C catalyst has high selectivity for depolymerization of organosolv lignin macromolecules compared to other multi-metal catalysts that form mixtures of aromatic and cyclohexyl compounds. Compared with lignin pretreated by ethanol, the yield of syringyl propane and syringyl propanol after lignin depolymerization pretreated by 1, 4-butanediol is obviously improved. The yield of syringyl propane and syringyl propanol depolymerized with lignin pretreated with ethanol at 120 deg.c (comparative example 9) was 6%, and the highest yield of syringyl propane and syringyl propanol after depolymerization with lignin pretreated with 1, 4-butanediol at 120 deg.c (example 11) was 14%. The results demonstrate that the 1, 4-butanediol pretreatment method of the present invention significantly improves the depolymerization yield of lignin, indicating that the yield is more improved at a pretreatment temperature of 120 ℃. This is because the alkoxy group in 1, 4-butanediol can undergo nucleophilic addition reaction with the reactive C.alpha.benzyl carbenium ion during the pretreatment of 1, 4-butanediol, thereby minimizing the cleavage of ether linkages. While the unreacted alkoxy groups of 1, 4-butanediol bonded to the alpha position of lignin (i.e. the hydroxyl groups in 1, 4-butanediol) increase the amount of aliphatic OH on lignin. In contrast, the OH on lignin was reduced after ethanol pretreatment. Because the aliphatic hydroxyl groups on the lignin are positively correlated with the solubility of the lignin. Thus, pretreatment with 1, 4-butanediol increases the solubility of lignin without significant destruction of ether linkages (. beta. -O-4). The beta-O-4 ether bond is prevented from cracking in the glycol pretreatment process, thereby improving the yield of the lignin monomer.

The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other changes, modifications, substitutions, combinations and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and all such changes, modifications, substitutions, combinations and simplifications are intended to be included in the scope of the present invention.