Preparation method of oxidized lignin based on lignin priority strategy

Abstract

The application discloses a preparation method of oxidized lignin based on a lignin priority strategy. The method uses biomass as raw material, an imidazole type polyacid site ionic liquid as a catalyst, and a mixed solution of an organic solvent and water as a solvent, and is heated to 80-140 DEG C under the condition of 0.1-1.5 MPa oxygen pressure for 1-5 hours; and the obtained mixture is separated to obtain oxidized lignin solid. The application combines the two processes of biomass grading and lignin oxidation modification, avoids repeated solid-liquid separation and lignin precipitation operations, simplifies the operation process, and saves the operation cost.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lignocellulose pretreatment, and particularly relates to a preparation method of lignin preferential oxidation type lignin. BACKGROUND

[0002] At present, biomass is mainly used for pulping and papermaking, and for preparing bio-based chemicals such as bioethanol, sugar and lactic acid through fermentation. In the bio-refining process, due to its stubborn structure, it is necessary to pretreat it to remove the lignin component which plays a protective and preventive role, aiming to improve the quality of paper or obtain the maximum sugar yield in the fermentation process. In addition, in addition to being used as a surfactant, water reducing agent and dispersant, lignin, as one of the few renewable aromatic polymers, can also replace the petroleum-based route to prepare aromatic compounds. However, the pretreatment of biomass needs to use strong acid and strong base, which causes the breakage of natural ether bonds in the molecular structure of lignin and the irreversible formation of high-stability C-C bonds, which leads to the characteristics of complex lignin structure, poor solubility and high chemical bond dissociation energy. Therefore, under the premise of not affecting the subsequent utilization of cellulose, the development of a new type of biomass delignification process, i.e. lignin preferential strategy, has attracted widespread attention.

[0003] The lignin preferential strategy is an important way to realize the utilization of whole components of biomass. This strategy refers to preventing re-aggregation reaction through catalysis or group protection chemical means in the process of biomass delignification. It is not equivalent to the high value of lignin single component, but refers to the sustainable utilization of whole components of biomass. At present, the lignin preferential strategy mainly includes: ① coupling reduction reaction in the process of lignin organic solvent extraction to convert and consume carbon positive cation or free radical intermediates to prevent the irreversible formation of C-C bonds; ② in the process of acid / alkali catalyzed delignification, using dihydric alcohol to capture and convert unstable aldehyde intermediates, or through aldehyde reagent to cyclize C α -OH and Cγ-OH to avoid the generation of benzyl cation; ③ using the good solubility of ionic liquid to biomass and the controllable chemical and physical properties to realize the extraction and separation of lignin. Compared with the first two pretreatment methods, the main and widely emphasized advantage of ionic liquid pretreatment process is that it can make the cellulose part of lignocellulose de-crystallize, while destroying the lignin and hemicellulose network.

[0004] For example, Rodriguez et al. (H. Rodriguez, M. Francisco, M. Rahman, N. Sun, R. D. Rogers. Biphasic liquid mixtures of ionic liquids and polyethylene glycols. Physical Chemistry Chemical Physics, 2009, 11(46), 10916-10922.) used polyethylene glycol and ionic liquid binary solvent (PEG-2000 and [C2mim]Cl) with high thermal stability to separate the mixture of cellulose and lignin. It was found that the ionic liquid phase included cellulose and lignin, while only lignin was in the PEG phase; Xu et al. (J. K. Xu, L. Dai, Y. Gui, L. Yuan, C. T. Zhang, Y. Lei. Synergistic benefits from a lignin-first biorefinery of poplar via coupling acesulfamate ionic liquid followed by mild alkaline extraction. Bioresource Technology, 2020, 303:122.) first used a food additive type ionic liquid to dissolve biomass, and then combined with alkaline method to separate lignin. The results showed that the lignin removal rate reached 70.7%, and the subsequent cellulose bioconversion rate increased from 15.4% to 90.5%. But this method includes two processes of ionic liquid dissolving biomass and alkaline separating lignin, the process is complicated, and the amount of ionic liquid used as solvent is large.

[0005] It is well known that lignin is a rigid, hyperbranched biological macromolecule composed of three different types of phenylpropane units, which contains a large number of active functional groups such as -OH, -COOH, CH3O-, etc. Therefore, lignin can be combined and grafted with other materials to prepare new materials through electrostatic interaction, hydrogen bonding and covalent interaction, etc. In addition, the oxidation modification of lignin can introduce more active -OH groups and more negative charges, which improves its reactivity and dispersibility. For example, Kalliola et al. (A. Kalliola, T. Vehmas, T. T. Tamminen. Alkali-O2 oxidized lignin-a bio-based concrete plasticizer. Industrial Crops and Products, 2015, 74: 150-157) used alkali catalytic oxidation to modify lignin, and the oxidized lignin showed more superior plasticizing performance than sodium lignosulfonate in cement paste, mortar and concrete, etc. Mattinen et al. (M. L. Mattinena, J. J. Valle-Delgado, T. Leskinen, T. Anttila, G. Riviere, M. Sipponen, A. Paananen, K. Lintinen, M. Kostiainen, M. Enzymatically and chemically oxidized lignin nanoparticles for biomaterial applications. Enzyme and Microbial Technology, 2018, 111: 48-56.) used hydrogen peroxide as an oxidant to prepare colloidal lignin nanoparticles by alkali catalytic oxidation under ultrasonic conditions. The material showed excellent stability in tetrahydrofuran organic solvent, which had great application potential in the fields of pharmaceuticals, food and cosmetics. However, both of these two methods are to prepare oxidized lignin by alkali catalysis using industrial lignin as raw material, which is equivalent to extracting lignin and then oxidizing it. The process is complex and significantly increases the cost of preparation. SUMMARY

[0006] The present application aims to provide a preparation method of high-quality oxidized lignin based on lignin priority strategy with one-pot method, which has simple process, can avoid repeated solid-liquid separation and lignin precipitation operations, and has lower preparation cost.

[0007] The present application is realized by the following technical solutions:

[0008] A preparation method of oxidized lignin based on lignin priority strategy, which uses biomass as raw material, imidazole-type polyacid site ionic liquid as catalyst, and a mixture of organic solvent and water as solvent, and is heated to 80-140℃ under oxygen pressure of 0.1-1.5MPa for 1-5 hours; the obtained mixture is separated to obtain oxidized lignin solid.

[0009] Preferably, the imidazole-type ionic liquid is [HIm][HSO4], [C3H6SO3HIm][H2PO4], [C3H6SO3HIm][Cl], [C3H6SO3HIm][HSO4], [C3H6SO3HIm][FeCl4], [C3H6SO3HIm][ZnCl3], [C3H6SO3HIm][CoCl3], [C3H6SO3HIm][CuCl3], [C3H6SO3HIm][MnCl3] or [C3H6SO3HIm][AlCl4] or a combination of two or more thereof.

[0010] Preferably, the [C3H6SO3HIm][H2PO4], [C3H6SO3HIm][Cl] or [C3H6SO3HIm][HSO4] is prepared by dissolving imidazole in acetonitrile or acetone solvent, adding equal molar amount of 1,3-propane sultone, refluxing; the mixture obtained after reaction is filtered, washed and dried to obtain white solid intermediate; then, the intermediate is dissolved in water, and equal molar amount of H2SO4, H3PO4 or HCl solution is added, and the reaction is carried out at 40-60°C for 5-10h; the solvent is removed, and the product is washed and dried.

[0011] The [HIm][HSO4] is prepared by reacting equal molar amount of imidazole with sulfuric acid at 40-60°C for 5-10h.

[0012] The [C3H6SO3HIm][FeCl4], [C3H6SO3HIm][ZnCl3], [C3H6SO3HIm][CoCl3], [C3H6SO3HIm][CuCl3], [C3H6SO3HIm][MnCl3] or [C3H6SO3HIm][AlCl4] is prepared by dissolving imidazole in acetonitrile or acetone solvent, adding equal molar amount of 1,3-propane sultone, refluxing; the mixture obtained after reaction is filtered, washed and dried to obtain white solid intermediate; then, the intermediate is dissolved in water, and equal molar amount of FeCl3, ZnCl2, CoCl2, CuCl2, MnCl2 or AlCl3 aqueous solution is added, and the reaction is carried out at room temperature for 5-10h; the solvent is removed, and the product is washed and dried.

[0013] Preferably, the refluxing is carried out at 60-120°C for 6-12h.

[0014] The solvent is removed by rotary evaporation.

[0015] The drying is vacuum drying, and the drying is carried out at 80-120°C for 8-16h.

[0016] The imidazole is dissolved in acetonitrile or acetone, and the mass-volume ratio of imidazole to acetonitrile or acetone is (1-5):50, in units of gram and milliliter, respectively.

[0017] The mass-volume ratio of the intermediate to water is (1-5):20, in units of gram and milliliter, respectively.

[0018] Preferably, the biomass is one or more of bagasse, corn cob, miscanthus, poplar, bamboo and corn stalk.

[0019] Preferably, the organic solvent is one of methanol, ethanol, n-propanol, formic acid and acetic acid; and the reaction is carried out in a stainless steel reactor with an inner liner.

[0020] Preferably, the volume fraction of the organic solvent in the mixed solution is 50-90%.

[0021] Preferably, the mass-volume ratio of the biomass to the mixed solution is (1-3):30, in units of gram and milliliter, respectively; and the molar mass ratio of the catalyst to the biomass is (0.37-2.22):2, in units of mmol and g, respectively.

[0022] Preferably, the separation is a solid-liquid separation of the reaction mixture by suction filtration, precipitation of the filtrate with water, standing, and then solid-liquid separation by normal-pressure suction filtration.

[0023] Preferably, the standing time is 24-48h; and the amount of water added for precipitation is 2-4 times the amount of the filtrate.

[0024] Compared with the prior art, the present application has the following advantages:

[0025] The present application utilizes the characteristics of acidic ionic liquid that has both catalytic hydrolysis and oxidation functions, and uses it to catalyze the oxidation pretreatment of delignification of biomass, selectively breaks the lignin-polysaccharide linkage in bagasse biomass and oxidizes the Cα benzyl alcohol in the lignin molecule, realizes one-pot in-situ separation and oxidation modification of lignin, and develops a new lignin priority strategy and technology. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 Fig. 4 is an infrared spectrum of oxidized lignin in Example 3 of the present application.

[0027] Figure 2 Fig. 4 is an infrared spectrum of oxidized lignin in Example 3 of the present application.

[0028] Figure 3 Fig. 4 is an infrared spectrum of oxidized lignin in Example 3 of the present application.

[0029] Figure 4 Effect of different pretreatment time on delignification process in the present application embodiment 16-19.

[0030] Figure 5 Infrared spectrogram of bagasse, oxidized lignin and residue in the present application embodiment 18.

[0031] Figure 6 SEM diagram of residue and oxidized lignin and bagasse in the present application embodiment 18.

[0032] Figure 7 Effect of different solvents on delignification process in the present application embodiment 20-23.

[0033] Figure 8 Effect of different oxygen pressure on delignification process in the present application embodiment 24-26.

[0034] Figure 9 GC-MS diagram of oxidized lignin depolymerization product in the present application embodiment 27.

[0035] Figure 10 MS diagram of 4-ethyl phenol of oxidized lignin depolymerization product in the present application embodiment 27. DETAILED DESCRIPTION

[0036] In order to better understand the technical features of the present application, the present application will be further described below in combination with the drawings and embodiments, but the scope of the present application claimed is not limited to this.

[0037] In view of the problems of the prior art that the preparation process of oxidized lignin is complex, separation is difficult, and the preparation cost is high, and most of them need to use strong acid and strong base and high temperature and high pressure and other harsh conditions, and the industrial lignin obtained by most of the prior art is difficult to convert and utilize due to the formation of a large number of stable C-C bonds; the present application utilizes the catalytic effect of biomass in acidic imidazole type multi-acid site ionic liquid to break the chemical bonds connecting the three main components of biomass (lignin, cellulose and hemicellulose), mainly obtaining lignin and cellulose, and hemicellulose is hydrolyzed into monosaccharides or oligosaccharides, and under a pure oxygen atmosphere, further oxidation forms oxidized lignin and cellulose.

[0038] The present application has the characteristics that the imidazole type multi-acid site ionic liquid has the functions of catalytic hydrolysis and oxidation, and has good thermal stability, and has the characteristics of multi-acid sites, which significantly enhances the catalytic activity, selectively catalyzes the breakage of lignin-polysaccharide bonds of lignocellulose and the oxidation of hydroxyl groups on the α-C of lignin molecules, and has a significant advantage, and further realizes one-pot separation and preparation of oxidized modified lignin.

[0039] The yield of the oxidized lignin is up to 17.1 wt.%, and the recovery rate of the cellulose residue is 57.3 wt.%. The yield of the depolymerized monophenol obtained from the oxidized lignin is 245.0 mg g -1 , which are both much higher than those of alkali lignin and sodium lignosulfonate, and the selectivity of 4-ethylphenol is 35.4%. The main monophenol products are 4-ethylphenol, 4-ethyl-2-methoxyphenol, 2-methoxy-4-propylphenol, 2.6-dimethoxy-4-ethylphenol and 2.6-dimethoxy-4-propylphenol. Among them, the proportions of H, G and S unit products are 38.1%, 33.4% and 28.5%, respectively. The oxidized lignin obtained in the application has great potential application value in the fields of concrete plasticization (cement dispersant), heavy metal removal of sewage, preparation of aromatic chemicals and medical biomaterials, etc.

[0040] The quality performance of the oxidized lignin in the application is mainly the depolymerization performance, which is realized by the following operation. First, 100 mg of lignin, 50 mg of Pd / C catalyst (5 wt%) and 10 mL of ethanol-water mixed solvent (8:2, v / v) are placed in a reaction kettle, 1.0 MPa of argon is filled, and the reaction is carried out at 230℃ for 3 h. After the reaction is completed, solid-liquid separation is carried out by suction filtration, the filtrate is added with an internal standard for constant volume gas chromatography analysis, the liquid after constant volume is added to deionized water to regenerate lignin, and then solid-liquid separation is carried out again, and the regenerated lignin is washed and dried to obtain the regenerated lignin, which is used for structure characterization and conversion rate calculation.

[0041] The calculation formulae of the fiber residue rate and the yield of the oxidized lignin in the application are shown as formulae (1-1) and (1-2).

[0042]

[0043] wherein m, m OL and m RE are the mass of bagasse, oxidized lignin and fiber residue, g; Y OL and Y RE are the yield of oxidized lignin and fiber residue.

[0044] It should be noted that the catalyst of the present application, although disclosed less, can also be purchased, and the [C3H6SO3HIm][H2PO4], [C3H6SO3HIm][Cl] or [C3H6SO3HIm][HSO4] of the present application is preferably prepared by the following method: imidazole is dissolved in acetonitrile or acetone solvent, and equimolar amount of 1,3-propanesultone is added, and refluxed; after reaction, the obtained mixture is filtered, washed and dried to obtain white solid intermediate; then, the intermediate is dissolved in water, and equimolar amount of H2SO4, H3PO4 or HCl solution is added, and reacted at 40-60℃ for 5-10h; the solvent is removed, and washed and dried.

[0045] The [C3H6SO3HIm][FeCl4], [C3H6SO3HIm][ZnCl3], [C3H6SO3HIm][CoCl3], [C3H6SO3HIm][CuCl3], [C3H6SO3HIm][MnCl3] and [C3H6SO3HIm][AlCl4] of the present application are preferably prepared by the following method: imidazole is dissolved in acetonitrile or acetone solvent, and equimolar amount of 1,3-propanesultone is added, and refluxed; after reaction, the obtained mixture is filtered, washed and dried to obtain white solid intermediate; then, the intermediate is dissolved in water, and equimolar amount of FeCl3, ZnCl2, CoCl2, CuCl2, MnCl2 or AlCl3 aqueous solution is added, and reacted at room temperature for 5-10h; the solvent is removed, and washed and dried;

[0046] Based on the preparation method of the above [C3H6SO3HIm][H2PO4], [C3H6SO3HIm][Cl], [C3H6SO3HIm][HSO4] and the preparation method of the above [C3H6SO3HIm][FeCl4], [C3H6SO3HIm][ZnCl3], [C3H6SO3HIm][CoCl3], [C3H6SO3HIm][CuCl3], [C3H6SO3HIm][MnCl3] or [C3H6SO3HIm][AlCl4], it is further preferred that the temperature of the reflux reaction is 60-120℃ and the time is 6-12h; the removal of the solvent is carried out by rotary evaporation; the drying is vacuum drying, the drying temperature is 80-120℃, and the drying time is 8-16h; the imidazole is dissolved in acetonitrile or acetone, and the mass-volume ratio of imidazole to acetonitrile or acetone is (1-5):50; the mass-volume ratio of the intermediate to water is (1-5):20.

[0047] The biomass raw material used in the examples is crushed by a plant crusher. The reaction is carried out in a stainless steel reaction kettle with lining.

[0048] The biomass in the present application can be selected from various options, and the biomass in the prior art can basically achieve the purpose of the present application, and preferably one or more of bagasse, corn cob, miscanthus, poplar, bamboo and corn stalk. The organic solvent can be selected according to the solubility, and preferably one of methanol, ethanol, n-propanol, formic acid and acetic acid; the volume fraction of the organic solvent in the mixed solution can be selected according to the solubility requirement, and preferably the volume fraction of the organic solvent in the mixed solution is 50-90%. The amount of biomass, solvent and catalyst can be selected according to the purpose of the present application; preferably, in units of grams and milliliters, the mass-volume ratio of biomass to mixed solution is (1-3):30; in units of mmol and g, the molar mass ratio of catalyst to biomass is (0.37-2.22):2.

[0049] The classification of the present application is to separate the reaction mixture by solid-liquid separation through filtration, take the filtrate, precipitate with water, stand, and then separate the two phases by filtration under normal pressure.

[0050] It should be noted that in the oxygen pressure of the present application, 0.1 MPa refers to one standard atmospheric pressure. The oxidizing agent molecular oxygen in the present application is a green oxidizing agent.

[0051] Example 1: Preparation of [C3H6SO3HIm][HSO4] ionic liquid

[0052] Dissolve 0.1 mol of imidazole and 0.1 mol of 1.3-propane sultone in acetonitrile, and react at 60℃ for 8h to form quaternary ammonium salt intermediate [C3H6SO3][Im]; then, dissolve 0.01 mol of [C3H6SO3][Im] in 50 mL of water, and slowly add an equal amount of dilute solution containing sulfuric acid or hydrochloric acid or phosphoric acid, and react at 50℃ for 5h. After removing the water by rotary evaporation, dry at 80℃ under vacuum for 24h to obtain the target ionic liquid [C3H6SO3HIm][HSO4].

[0053] Example 2: Preparation of [C3H6SO3HIm][FeCl4] ionic liquid

[0054] Dissolve 0.1 mol of imidazole and 0.1 mol of 1.3-propane sultone in acetonitrile, and react at 60℃ for 8h to form quaternary ammonium salt intermediate [C3H6SO3][Im]; then, dissolve 0.01 mol of [C3H6SO3][Im] in 50 mL of water, and slowly add an equal amount of dilute solution containing sulfuric acid or hydrochloric acid or phosphoric acid, and react at 50℃ for 5h. After removing the water by rotary evaporation, dry at 80℃ under vacuum for 24h to obtain the target ionic liquid [C3H6SO3HIm][HSO4].

[0055] Example 3: A preparation method of oxidized lignin based on lignin priority strategy

[0056] The extraction of oxidized lignin comprises the following steps:

[0057] 2 g of bagasse, 1.84 mmol of [C3H6SO3HIm][HSO4] acidic ionic liquid and 30 mL of n-propanol-water binary solvent (80:20, v / v) were placed in a 100 mL reaction kettle, and after replacing the air with oxygen, the reaction kettle was pressurized to 1.0 MPa, and then heated to 80°C by electricity, and reacted for 4 h.

[0058] After the reaction was completed, the solid-liquid two-phase separation was realized by means of suction filtration, and the obtained filtrate was added to 3 times of deionized water to precipitate the oxidized lignin, and then left overnight;

[0059] After standing overnight, the solid-liquid two-phase separation was realized again by means of suction filtration at normal pressure, and the obtained lignin solid was washed with 100 mL of deionized water for 3 times, and then dried and ground, and finally the oxidized lignin solid was obtained.

[0060] It was tested that the lignin yield obtained in this embodiment reached 7.6 wt.%, while retaining 81.0 wt.% of the residue rate, and the test results are shown in the following table: Figure 1 .

[0061] Example 4: A preparation method of oxidized lignin based on lignin priority strategy

[0062] The difference between this embodiment and Example 3 is that:

[0063] 2 g of bagasse, 1.84 mmol of [C3H6SO3HIm][HSO4] acidic ionic liquid and 30 mL of n-propanol-water binary solvent (80:20, v / v) were placed in a 100 mL reaction kettle, and after replacing the air with oxygen, the reaction kettle was pressurized to 1.0 MPa, and then heated to 100°C by electricity, and reacted for 4 h.

[0064] The lignin yield obtained in this embodiment reached 16.6 wt.%, while retaining 57.3 wt.% of the residue rate, and the results are shown in the following table: Figure 1 .

[0065] Example 5: A preparation method of oxidized lignin based on lignin priority strategy

[0066] The difference between this embodiment and Example 3 is that:

[0067] 2 g of bagasse, 1.84 mmol of [C3H6SO3HIm][HSO4] acidic ionic liquid and 30 mL of n-propanol-water binary solvent (80:20, v / v) were placed in a 100 mL reaction kettle, and after replacing the air with oxygen, the reaction kettle was pressurized to 1.0 MPa, and then heated to 120°C by electricity, and reacted for 4 h.

[0068] The lignin yield of this example reached 13.8wt.%, while the residue rate remained 43.5wt.%, and the results are shown in the following table: Figure 1 .

[0069] Example 6: A preparation method of oxidized lignin based on lignin priority strategy

[0070] The difference between this example and example 3 is that:

[0071] 2g of bagasse, 1.84mmol of [C3H6SO3HIm] [HSO4] acidic ionic liquid and 30mL of n-propanol-water binary solvent (80:20, v / v) were placed in a 100mL reaction kettle, and after replacing the air with oxygen, the reaction kettle was pressurized to 1.0MPa, and then heated to 140℃ by electricity, and reacted for 4h.

[0072] The lignin yield of this example reached 14.6wt.%, while the residue rate remained 37.2wt.%, and the results are shown in the following table: Figure 1 .

[0073] Figure 2 and 3 are respectively the FT-IR spectra of the oxidized lignin, residue and bagasse in examples 3-6 of the present application and the two-dimensional heteronuclear single quantum coherence spectrum (2D HSQC NMR) of the oxidized lignin. It can be seen from Figure 2 that in the lignin sample, the absorption at 1600, 1516 and 1466cm -1 belongs to the stretching vibration peak of aromatic ring skeleton, and the absorption intensity is greatly enhanced compared with the bagasse, which indicates that the lignin is effectively separated from the bagasse, and there is no absorption in the residue, which indicates that the lignin is completely separated. The absorption peak at 1708cm -1 belongs to the conjugated C=O, and its intensity is enhanced with the increase of temperature, which indicates that the aryl C α -OH unit is oxidized. There is no obvious characteristic absorption peak belonging to carbohydrates at 893cm -1 , which indicates that the lignin contains less carbohydrate impurities. At the same time, the characteristic peaks of the three basic structural units of lignin are also observed in the spectrum of the lignin sample. For example, 1165cm -1 is the H structural unit, 1273, 1226 and 835cm -1 belong to the G structural unit, and 1332 and 1132cm -1 are the S structural unit. In addition, the vibration peak of -OH at 3448cm -1 is found in the spectrum of the lignin sample, and its intensity is weakened with the increase of temperature, which indicates that the side chain -OH is oxidized. Figure 3In the present study, the spectrum was divided into three regions, including the aliphatic region, the oxygen-containing aliphatic region and the aromatic region. In the aliphatic region, there were certain amount of aromatic ring α-CH, β-CH2 and γ-CH3. In the oxygen-containing aliphatic region, there were a large number of three structural unit linkages of lignin molecules, such as methoxyl, β-O-4, β'-O-4, α-O-4, β-β and β-5. In the aromatic region, there were basic structural units such as ferulic acid salt (FA), p-hydroxyphenyl (H), guaiacyl (G) and syringyl (S). In addition, with the increase of pretreatment temperature, the C α The characteristic signal of -H was also obviously weakened, which was mainly due to the oxidation of H-C α -OH in the lignin molecule into ketone.

[0074] Example 7: A preparation method of oxidized lignin based on lignin priority strategy

[0075] The difference between this example and Example 3 is that:

[0076] 2 g of sugarcane bagasse, 1.00 mmol of [C3H6SO3HIm][FeCl4] acidic ionic liquid and 30 mL of ethanol-water binary solvent (80:20, v / v) were placed in a 100 mL reaction kettle, and after replacing the air with oxygen, the reaction kettle was pressurized to 0.5 MPa, and then heated to 100°C by electricity, and reacted for 3 h.

[0077] The lignin yield obtained in this example reached 8.0 wt.%, while the residue rate remained at 67.8 wt.%.

[0078] Example 8: A preparation method of oxidized lignin based on lignin priority strategy

[0079] The difference between this example and Example 3 is that:

[0080] 2 g of sugarcane bagasse, 0.50 mmol of [C3H6SO3HIm][HSO4] and 0.50 mmol of [C3H6SO3HIm][FeCl4] mixed acidic ionic liquid and 30 mL of ethanol-water binary solvent (80:20, v / v) were placed in a 100 mL reaction kettle, and after replacing the air with oxygen, the reaction kettle was pressurized to 0.5 MPa, and then heated to 100°C by electricity, and reacted for 3 h.

[0081] The lignin yield obtained in this example reached 9.0 wt.%, while the residue rate remained at 68.0 wt.%.

[0082] Example 9: A preparation method of oxidized lignin based on lignin priority strategy

[0083] The difference between this example and Example 3 is that:

[0084] 2 g bamboo, 0.50 mmol [C3H6SO3HIm][HSO4] and 0.50 mmol [C3H6SO3HIm][FeCl4] mixed acidic ionic liquid and 30 mL ethanol-water binary solvent (80:20, v / v) in a 100 mL reactor, and after replacing the air with oxygen, the reactor was pressurized to 0.5 MPa, heated to 120°C by electricity, and reacted for 4 h.

[0085] The lignin yield obtained in this example reached 13.4 wt.%, while retaining 55.3 wt.% of the residue rate.

[0086] Example 10: A preparation method of oxidative lignin based on lignin priority strategy

[0087] The difference between this example and Example 3 is that:

[0088] 2 g bamboo, 0.50 mmol [C3H6SO3HIm][HSO4] and 0.50 mmol [C3H6SO3HIm][FeCl4] mixed acidic ionic liquid and 30 mL ethanol-water binary solvent (80:20, v / v) in a 100 mL reactor, and after replacing the air with oxygen, the reactor was pressurized to 0.5 MPa, heated to 120°C by electricity, and reacted for 4 h.

[0089] The lignin yield obtained in this example reached 9.9 wt.%, while retaining 57.4 wt.% of the residue rate.

[0090] Example 11: A preparation method of oxidative lignin based on lignin priority strategy

[0091] The difference between this example and Example 3 is that:

[0092] 2 g bamboo, 0.50 mmol [C3H6SO3HIm][HSO4] and 0.50 mmol [C3H6SO3HIm][FeCl4] mixed acidic ionic liquid and 30 mL ethanol-water binary solvent (80:20, v / v) in a 100 mL reactor, and after replacing the air with oxygen, the reactor was pressurized to 0.5 MPa, heated to 120°C by electricity, and reacted for 4 h.

[0093] The lignin yield obtained in this example reached 9.9 wt.%, while retaining 57.4 wt.% of the residue rate.

[0094] Example 12: A preparation method of oxidative lignin based on lignin priority strategy

[0095] The difference between this example and Example 3 is that:

[0096] 2 g of bagasse, 1.84 mmol of [C3H6SO3HIm][HSO4] acidic ionic liquid and 30 mL of formic acid-water binary solvent (80:20, v / v) were placed in a 100 mL autoclave, and after replacing the air with oxygen, the autoclave was pressurized to 1.0 MPa, and then heated to 100°C by electricity, and reacted for 4 h.

[0097] The lignin yield obtained in this example reached 4.3 wt.%, while the residue rate remained 46.7 wt.%.

[0098] Example 13: A preparation method of oxidized lignin based on lignin priority strategy

[0099] The difference between this example and Example 3 is that:

[0100] 2 g of bagasse, 1.84 mmol of [HIm][HSO4] acidic ionic liquid and 30 mL of n-propanol-water binary solvent (80:20, v / v) were placed in a 100 mL autoclave, and after replacing the air with oxygen, the autoclave was pressurized to 1.0 MPa, and then heated to 100°C by electricity, and reacted for 4 h.

[0101] The lignin yield obtained in this example reached 3.0 wt.%, while the residue rate remained 83.5 wt.%.

[0102] Example 14: A preparation method of oxidized lignin based on lignin priority strategy

[0103] The difference between this example and Example 3 is that:

[0104] 2 g of bagasse, 1.84 mmol of [C3H6SO3HIm][H2PO4] acidic ionic liquid and 30 mL of n-propanol-water binary solvent (80:20, v / v) were placed in a 100 mL autoclave, and after replacing the air with oxygen, the autoclave was pressurized to 1.0 MPa, and then heated to 100°C by electricity, and reacted for 4 h.

[0105] The lignin yield obtained in this example reached 3.0 wt.%, while the residue rate remained 89.9 wt.%.

[0106] Example 15: A preparation method of oxidized lignin based on lignin priority strategy

[0107] The difference between this example and Example 3 is that:

[0108] 2 g of bagasse, 1.84 mmol of [C3H6SO3HIm][HSO4] acidic ionic liquid and 30 mL of n-propanol-water binary solvent (80:20, v / v) were placed in a 100 mL autoclave, and the autoclave was pressurized to 1.0 MPa after replacing air with oxygen. The reaction was carried out at 100°C for 1 h by electric heating.

[0109] The lignin yield obtained in this example reached 6.6 wt.%, while the residue rate remained 77.5 wt.%, and the results are shown in the attached table.

[0110] Example 16: A preparation method of oxidized lignin based on lignin priority strategy

[0111] The difference between this example and Example 3 is that:

[0112] 2 g of bagasse, 1.84 mmol of [C3H6SO3HIm][HSO4] acidic ionic liquid and 30 mL of n-propanol-water binary solvent (80:20, v / v) were placed in a 100 mL autoclave, and the autoclave was pressurized to 1.0 MPa after replacing air with oxygen. The reaction was carried out at 100°C for 1 h by electric heating.

[0113] The lignin yield obtained in this example reached 6.6 wt.%, while the residue rate remained 77.5 wt.%, and the results are shown in the attached table. Figure 4 .

[0114] Example 17: A preparation method of oxidized lignin based on lignin priority strategy

[0115] The difference between this example and Example 3 is that:

[0116] 2 g of bagasse, 1.84 mmol of [C3H6SO3HIm][HSO4] acidic ionic liquid and 30 mL of n-propanol-water binary solvent (80:20, v / v) were placed in a 100 mL autoclave, and the autoclave was pressurized to 1.0 MPa after replacing air with oxygen. The reaction was carried out at 100°C for 1 h by electric heating.

[0117] The lignin yield obtained in this example reached 6.6 wt.%, while the residue rate remained 77.5 wt.%, and the results are shown in the attached table. Figure 4 .

[0118] Example 18: A preparation method of oxidized lignin based on lignin priority strategy

[0119] The difference between this example and Example 3 is that:

[0120] 2g of bagasse, 1.84mmol of [C3H6SO3HIm][HSO4] acidic ionic liquid and 30mL of n-propanol-water binary solvent (80:20, v / v) were placed in a 100mL reactor. After replacing the air with oxygen, the reactor was pressurized to 1.0MPa and electrically heated to 100℃ for 3h.

[0121] The lignin yield obtained in this embodiment reached 17.1 wt.%, while retaining a residue rate of 57.3 wt.%, as shown in the appendix. Figure 4 .

[0122] Appendix Figure 5 and 6 The images shown are the infrared spectra and SEM images of the residue, oxidized lignin, and bagasse from Example 18 of this invention. Figure 5 In the middle, the infrared spectrum of the residue is at 1368, 1062 and 890 cm⁻¹. -1 Distinct characteristic peaks appeared, attributed to the CH and CO groups of cellulose, as well as the -COC absorption peaks on the pyran ring and glycosidic bond. (The remaining text appears to be incomplete and requires further context.) Figure 6 In the initial reaction, bagasse had a smooth and full surface, but after the reaction, the surface became rough, loose, and bubbly. This is mainly because most of the hemicellulose and lignin were dissolved and converted into soluble substances. The separated lignin had a non-crystalline surface with a particle size of less than 500 nm. Meanwhile, the residue-based carbon material (calcined at 800℃ under a nitrogen atmosphere for 2 hours) exhibited a layered structure and macroporous structure similar to graphene, with most pores having a diameter of approximately 50 nm. This is primarily because the main component of the residue is cellulose, which is easily oxidized during the delignin treatment, and oxygen-containing groups are lost during high-temperature calcination, resulting in a large number of macropores.

[0123] Example 19: A method for preparing oxidized lignin based on a lignin-preferred strategy

[0124] The difference between this embodiment and Embodiment 3 is that:

[0125] 2g of bagasse, 1.84mmol of [C3H6SO3HIm][HSO4] acidic ionic liquid and 30mL of n-propanol-water binary solvent (80:20, v / v) were placed in a 100mL reactor. After replacing the air with oxygen, the reactor was pressurized to 1.0MPa and electrically heated to 100℃ for 5h.

[0126] The lignin yield obtained in this embodiment reached 15.4 wt.%, while retaining a residue rate of 56.9 wt.%, as shown in the appendix. Figure 4 .

[0127] Example 20: A method for preparing oxidized lignin based on a lignin-preferred strategy

[0128] The difference between this embodiment and embodiment 3 is that:

[0129] 2 g of bagasse, 1.84 mmol of [C3H6SO3HIm][HSO4] acidic ionic liquid and 30 mL of n-propanol solvent were placed in a 100 mL reaction kettle, and after replacing the air with oxygen, the reaction kettle was pressurized to 1.0 MPa, and then heated to 100°C by electricity, and reacted for 4 h.

[0130] The lignin yield obtained in this embodiment reached 10.0 wt.%, while retaining a residue rate of 54.5 wt.%, and the results are shown in the attached table 1. Figure 7 .

[0131] Embodiment 21: A preparation method of oxidized lignin based on a lignin priority strategy

[0132] The difference between this embodiment and embodiment 3 is that:

[0133] 2 g of bagasse, 1.84 mmol of [C3H6SO3HIm][HSO4] acidic ionic liquid and 30 mL of n-propanol-water binary solvent (90:10, v / v) were placed in a 100 mL reaction kettle, and after replacing the air with oxygen, the reaction kettle was pressurized to 1.0 MPa, and then heated to 100°C by electricity, and reacted for 4 h.

[0134] The lignin yield obtained in this embodiment reached 13.6 wt.%, while retaining a residue rate of 58.5 wt.%, and the results are shown in the attached table 1. Figure 7 .

[0135] Embodiment 22: A preparation method of oxidized lignin based on a lignin priority strategy

[0136] The difference between this embodiment and embodiment 3 is that:

[0137] 2 g of bagasse, 1.84 mmol of [C3H6SO3HIm][HSO4] acidic ionic liquid and 30 mL of n-propanol-water binary solvent (60:40, v / v) were placed in a 100 mL reaction kettle, and after replacing the air with oxygen, the reaction kettle was pressurized to 1.0 MPa, and then heated to 100°C by electricity, and reacted for 4 h.

[0138] The lignin yield obtained in this embodiment reached 10.8 wt.%, while retaining a residue rate of 55.5 wt.%, and the results are shown in the attached table 1. Figure 7 .

[0139] Embodiment 23: A preparation method of oxidized lignin based on a lignin priority strategy

[0140] The difference between this embodiment and embodiment 3 is that:

[0141] 2 g of bagasse, 1.84 mmol of [C3H6SO3HIm][HSO4] acidic ionic liquid and 30 mL of n-propanol-water binary solvent (80:20, v / v) were placed in a 100 mL autoclave, and the autoclave was pressurized to 0.1 MPa after replacing air with oxygen, and then the temperature was raised to 100°C by electric heating, and the reaction was carried out for 4 h.

[0142] The lignin yield obtained in this example reached 10.1 wt.%, while the residue rate reached 63.0 wt.%, and the results are shown in the following table: Figure 7 .

[0143] Example 24: A preparation method of oxidized lignin based on the lignin priority strategy

[0144] The difference between this example and Example 3 is that:

[0145] 2 g of bagasse, 1.84 mmol of [C3H6SO3HIm][HSO4] acidic ionic liquid and 30 mL of n-propanol-water binary solvent (80:20, v / v) were placed in a 100 mL autoclave, and the autoclave was pressurized to 0.1 MPa after replacing air with oxygen, and then the temperature was raised to 100°C by electric heating, and the reaction was carried out for 4 h.

[0146] The lignin yield obtained in this example reached 10.1 wt.%, while the residue rate reached 63.0 wt.%, and the results are shown in the following table: Figure 8 .

[0147] Example 25: A preparation method of oxidized lignin based on the lignin priority strategy

[0148] The difference between this example and Example 3 is that:

[0149] 2 g of bagasse, 1.84 mmol of [C3H6SO3HIm][HSO4] acidic ionic liquid and 30 mL of n-propanol-water binary solvent (80:20, v / v) were placed in a 100 mL autoclave, and the autoclave was pressurized to 0.1 MPa after replacing air with oxygen, and then the temperature was raised to 100°C by electric heating, and the reaction was carried out for 4 h.

[0150] The lignin yield obtained in this example reached 10.1 wt.%, while the residue rate reached 63.0 wt.%, and the results are shown in the following table: Figure 8 .

[0151] Example 26: A preparation method of oxidized lignin based on the lignin priority strategy

[0152] The difference between this example and Example 3 is that:

[0153] 2 g of bagasse, 1.84 mmol of [C3H6SO3HIm][HSO4] acidic ionic liquid and 30 mL of n-propanol-water binary solvent (80:20, v / v) were placed in a 100 mL autoclave, and after replacing the air with oxygen, the autoclave was pressurized to 1.5 MPa, heated to 100°C by electricity, and reacted for 4 h.

[0154] The lignin yield obtained in this example reached 15.5 wt.%, while the residual rate remained at 55.2 wt.%, and the results are shown in the attached Figure 8 .

[0155] Example 27: Study on the depolymerization performance of the obtained oxidized lignin

[0156] In order to evaluate the depolymerization performance of the separated oxidized lignin, the present application uses it as a raw material for the preparation of high value-added aromatic chemicals in the alcoholysis process, and the specific steps are as follows: first, 100 mg of oxidized lignin, 50 mg of Pd / C (5 wt%, purchased from Shanghai Aldrin Reagent Co., Ltd.) and 10 mL of ethanol-water mixed solvent (8:2, v / v) are placed in a 100 mL autoclave, 1.0 MPa of argon is filled, and the reaction is carried out at 230°C for 3 h; after the reaction is completed, the solid-liquid separation is carried out by suction filtration, the filtrate is added with an internal standard for constant volume gas chromatography analysis, the constant volume liquid is added to a certain amount of deionized water to regenerate lignin, and after the solid-liquid separation, washing and drying, regenerated lignin is obtained and used for structure characterization and conversion rate calculation. The calculation formulas of monophenol yield and lignin conversion rate are shown in formulas (1-3), (1-4) and (1-5):

[0157]

[0158] wherein f i , Y i and A i are the correction factor, yield and peak area of product i, respectively; Y is the total monophenol yield; M, M relig and M OL represent the mass of internal standard solution, regenerated lignin and oxidized lignin, respectively (g); W and A are the mass concentration and peak area of the internal standard; C OL is the conversion rate of oxidized lignin.

[0159] In this example, the lignin conversion rate is 82.8%, the total phenol yield is 245.0 mg g -1 , the 4-ethylphenol yield is 86.7 mg g -1 , and the selectivity is 35.4%.

[0160] The results are shown in the attached Figure 9The GC spectrum of the volatile products of oxidized lignin depolymerization in this Example 27. As can be seen from the figure, the main products of oxidized lignin depolymerization are 4-ethylphenol, 4-ethyl-2-methoxyphenol, 2-methoxy-4-propylphenol, 2.6-dimethoxy-4-ethylphenol and 2.6-dimethoxy-4-propylphenol. Among them, the product of H, G and S unit accounts for 38.1, 33.4 and 28.5% respectively, which shows that the H unit of the oxidized lignin is easy to be depolymerized, followed by the G unit, and finally the S unit. Figure 10 The mass spectrum (MS) of the main product 4-ethylphenol obtained by depolymerization of oxidized lignin in this Example 27. As shown in the figure, the maximum mass-to-charge ratio (m / z) of the product is 122, which corresponds to the relative molecular mass of 4-ethylphenol (122). In addition, compared with the Agilent NIST MS Search 2.4 database, it is determined that the product is 4-ethylphenol.

[0161] Comparative Example 1: Performance comparison of industrial lignin depolymerization

[0162] Take 100 mg of alkali lignin (Kraft lignin), 50 mg of Pd / C catalyst (5 wt.%) and 10 mL of ethanol-water mixed solvent (8:2, v / v) into a high-pressure reaction kettle, replace the air in the reaction kettle with argon for 3 times, and then pressurize to 1.0 MPa (argon). At a speed of 600 rpm, heat the reaction kettle to 230°C at a rate of 5°C / min, and keep for 4 h.

[0163] The lignin conversion rate obtained in this comparative example is 62.5%, and the total yield of phenols is 26.3 mg g -1 .

[0164] Comparative Example 2: Study on the performance of the obtained oxidized lignin depolymerization

[0165] The difference between this comparative example and Comparative Example 1 is:

[0166] Take 100 mg of sodium lignosulphonate, 50 mg of Pd / C catalyst (5 wt.%) and 10 mL of ethanol-water mixed solvent (8:2, v / v) into a high-pressure reaction kettle, replace the air in the reaction kettle with argon for 3 times, and then pressurize to 1.0 MPa (argon). At a speed of 600 rpm, heat the reaction kettle to 230°C at a rate of 5°C / min, and keep for 4 h. The total yield of phenols obtained in this comparative example is 44.0 mg g -1 .

[0167] As can be seen from the above examples, the present application introduces an oxidation reaction into the process of biomass delignification, i.e., the functional ionic liquid is used to selectively break the lignin-polysaccharide connection in the bagasse biomass and oxidize the C α The benzyl alcohol realizes one-pot in-situ oxidation and separation of lignin, realizes a new lignin preferential strategy. The obtained oxidized lignin has a yield of 3.0-17.1 wt.%, and the recovery rate of the cellulose residue is 46.7-89.9 wt.%. Under the same depolymerization conditions, the yield of monophenol obtained by depolymerization of the oxidized lignin in Example 7 is 245.0 mg g -1 , which is much higher than the yields of monophenol obtained by depolymerization of the two industrial lignins, alkali lignin and sodium lignosulfonate (26.3 and 44.0 mg g -1 ), both of which are much higher than the two industrial lignins, alkali lignin and sodium lignosulfonate, and the selectivity of 4-ethylphenol is as high as 35.4%. The main monophenol products are 4-ethylphenol, 4-ethyl-2-methoxyphenol, 2-methoxy-4-propylphenol, 2.6-dimethoxy-4-ethylphenol and 2.6-dimethoxy-4-propylphenol. These monophenol products are all high-value-added chemicals. Among them, 4-ethylphenol is widely used in food additives, cosmetics, pharmaceuticals and other fields. At the same time, the obtained oxidized modified lignin has a large number of active groups such as -OH and more negative charges introduced, so it can not only be used as a cement dispersant, a sewage heavy metal removal agent and for preparing aromatic chemicals, but also as a biomaterial for application in the fields of pharmaceuticals, food and cosmetics. Therefore, the oxidized lignin has great potential economic value.

[0168] The embodiments of the present application are not limited by the above examples, and any changes, substitutions, combinations made without departing from the spirit and principles of the present application shall be equivalent replacement modes, and all are included in the protection scope of the present application.

Claims

1. A method for preparing oxidized lignin based on a lignin-preferred strategy, characterized in that, Using biomass as raw material, imidazole-type polyacid site ionic liquid as catalyst, and a mixture of organic solvent and water as solvent, the reaction is carried out at 80-140℃ for 1-5 hours under an oxygen pressure of 0.1-1.5 MPa; the resulting mixture is separated to obtain oxidized lignin solid. The imidazole-type polyacid site ionic liquid is [HIm][HSO4], [C3H6SO3HIm][H2PO4], [C3H6SO3HIm][Cl], [C3H6SO3HIm][HSO4], [C3H6SO3HIm][FeCl4], [C3H6SO3HIm][ZnCl3], [C3H6SO3HIm][CoCl3], [C3H6SO3HIm][CuCl3], [C3H6SO3HIm][MnCl3], or [C3H6SO3HIm][AlCl4].

2. The method for preparing oxidized lignin based on a lignin-preferential strategy according to claim 1, characterized in that, The [C3H6SO3HIm][H2PO4], [C3H6SO3HIm][Cl], or [C3H6SO3HIm][HSO4] are prepared by the following method: imidazole is dissolved in acetonitrile or acetone, and an equimolar amount of 1,3-propylsulfonate lactone is added, and the mixture is refluxed; the resulting mixture is filtered, washed, and dried to obtain an intermediate; subsequently, the intermediate is dissolved in water, and an equimolar amount of H2SO4, H3PO4, or HCl solution is added, and the mixture is reacted at 40-60 °C for 5-10 h; the solvent is removed, and the mixture is washed and dried; The [HIm][HSO4] was obtained by reacting an equimolar amount of imidazole with sulfuric acid at 40-60 °C for 5-10 h. The [C3H6SO3HIm][FeCl4], [C3H6SO3HIm][ZnCl3], [C3H6SO3HIm][CoCl3], [C3H6SO3HIm][CuCl3], [C3H6SO3HIm][MnCl3], or [C3H6SO3HIm][AlCl4] are prepared by the following method: imidazole is dissolved in acetonitrile or acetone solvent, and an equimolar amount of 1,3-propylsulfonate lactone is added, and the mixture is refluxed; the resulting mixture is filtered, washed, and dried to obtain an intermediate; subsequently, the intermediate is dissolved in water, and an equimolar amount of aqueous solutions of FeCl3, ZnCl2, CoCl2, CuCl2, MnCl2, or AlCl3 is added, and the mixture is reacted at room temperature for 5-10 h; the solvent is removed, the mixture is washed, and dried.

3. The method for preparing oxidized lignin based on a lignin-preferential strategy according to claim 2, characterized in that, The reflux reaction is carried out at a temperature of 60-120 °C for 6-12 h. The solvent removal is performed by rotary evaporation; The drying process is vacuum drying, with a drying temperature of 80-120 ℃ and a drying time of 8-16 h. The imidazole is dissolved in acetonitrile or acetone, with the mass-to-volume ratio of imidazole to acetonitrile or acetone being (1-5):50, expressed in grams and milliliters, respectively. The intermediate and water are expressed in grams and milliliters, respectively, with a mass-to-volume ratio of (1-5):

20.

4. The method for preparing oxidized lignin based on a lignin-preferential strategy according to claim 1, characterized in that, The biomass mentioned is one or more of the following: bagasse, corn cob, miscanthus, poplar wood, bamboo, and corn stalks.

5. The method for preparing oxidized lignin based on a lignin-preferential strategy according to claim 1, characterized in that, The organic solvent is one of methanol, ethanol, n-propanol, formic acid, and acetic acid; the reaction is carried out in a lined stainless steel reactor.

6. The method for preparing oxidized lignin based on a lignin-preferential strategy according to claim 1, characterized in that, The organic solvent accounts for 50-90% of the volume fraction of the mixture.

7. The method for preparing oxidized lignin based on a lignin-preferential strategy according to claim 1, 4, 5, or 6, characterized in that, The mass-to-volume ratio of biomass to mixed liquid is (1-3):30, expressed in grams and milliliters, respectively; the molar mass ratio of catalyst to biomass is (0.37-2.22):2, expressed in mmol and g, respectively.

8. The method for preparing oxidized lignin based on a lignin-preferential strategy according to claim 1, characterized in that, The separation involves first separating the solid and liquid phases of the mixture obtained from the reaction by vacuum filtration, then adding water to the filtrate to precipitate it, allowing it to stand, and finally using atmospheric pressure vacuum filtration to achieve solid-liquid two-phase separation.

9. The method for preparing oxidized lignin based on a lignin-preferential strategy according to claim 8, characterized in that, The settling time is 24-48 hours; the amount of water added for precipitation is 2-4 times that of the filtrate.

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