Preparation method of selective arylated lignin and arylated lignin

Abstract

The invention discloses a preparation method of selective arylated lignin and the arylated lignin. According to the method, natural lignin or lignin extracted by a solvent is taken as a raw material, an arylation reagent and lignin benzyl hydroxyl are subjected to Friedel-Crafts alkylation reaction, and the arylation modified lignin is selectively synthesized. Based on the characteristic that a natural benzyl hydroxyl structure in lignin is easy to react with a nucleophilic reagent, lignin is induced to selectively react with aromatic derivatives such as phenol and phenyl ether, and oriented modification of lignin is realized. The modification process effectively inhibits self-condensation of lignin, avoids invalid breakage of beta-O-4 aryl ether bonds of lignin under mild conditions, and realizes selective alpha-arylation modification. According to the lignin modification method, the solubility of the lignin in an organic solvent is improved, high-value utilization of the lignin is promoted, and an important raw material support is provided for application of preparing renewable chemicals, energy substances, renewable materials and the like.

Description

Technical Field

[0001] The invention relates to a preparation method of selective aryl lignin and aryl lignin, and in particular to a high-value utilization technology of lignin and a lignin functional modification technology and product. Background Art

[0002] Lignin is an amorphous polymer composed of phenylpropane units connected by carbon-carbon bonds and carbon-oxygen bonds. It is the second largest biomass resource in the plant kingdom after carbohydrates. High-value utilization of lignin will help reduce the consumption of fossil resources and environmental pollution, and promote the process of bio-economy and sustainable development. The chemical structure of lignin is complex, mainly reflected in: the number of methoxy substituents in the structural units is different, with an average value between 1-2; there are various connection forms between structural units, including carbon-carbon bond connection (such as 5-5, β-5 and β-β, etc.) and carbon-oxygen bond connection (such as β-O-4 and α-O-4, etc.). Among them, β-O-4 bond connection is the most abundant connection mode between lignin units, accounting for about 40-70%. The complexity of lignin in chemical structure leads to its low efficiency in high-value utilization. The chemical structure of lignin can be modified by esterification, etherification, alkylation, oxidation, acylation and other reactions to achieve the effect of modification and quality improvement. Through chemical modification, the proportion of specific chemical functional groups in lignin polymers can be increased, the chemical stability of lignin can be improved, and the impurity content can be reduced, thereby improving the efficiency of high-value application of lignin components.

[0003] Lignin phenolization modification is a more traditional lignin alkylation modification strategy, which originated from the phenolic resin synthesis process using lignin to partially replace phenol. Among them, the industrial lignin raw material is mixed with a large amount of phenol. Under the action of a strong acid catalyst, the aromatic ether oxygen bond in the lignin is broken, and the lignin alkyl chain is grafted with a phenol group (ACSSustainable Chem. Eng., 2018, 6, 5504-5512; Chem. Eng. J., 2023, 453, 139770; CN112661920 A). After lignin phenolization treatment, the molecular weight is significantly reduced and the organic solvent solubility is significantly improved. However, due to the high phenolization reaction temperature and acid concentration, this treatment method is usually only applicable to industrial lignin whose lignin structure has undergone severe condensation. For raw materials that retain a large amount of natural lignin structure (such as lignocellulose and organic solvent extracted lignin), this treatment method causes serious degradation of non-lignin components (carbohydrate components), which reduces the overall utilization efficiency of the raw materials. In addition, during the phenolization process, lignin is significantly depolymerized. Although the low molecular weight phenolized lignin product can be used for the synthesis of phenolic resin, the potential for subsequent catalytic conversion is greatly reduced, making it difficult to use for the preparation of lignin-based high-value chemicals. Summary of the invention

[0004] The purpose of the present invention is to provide a method for selectively arylating the benzyl carbon of lignin and an aryl lignin product, so as to improve the chemical stability of lignin during separation or purification, while retaining the aromatic ether bonds of lignin, thereby improving the reaction activity of lignin and the potential for subsequent high-value utilization.

[0005] Technical Solution

[0006] The specific technical scheme of the present invention is: an arylation agent, a lignin-based compound, and an acidic organic solvent are added to a high-temperature reactor in a certain proportion. The reaction mixture is uniformly stirred and mixed, and then heated to the reaction temperature under closed conditions. After reaching the set reaction time, the reactor is cooled, the reaction mixture is filtered through filter paper and the filtrate is collected. The filtrate is concentrated by vacuum distillation and precipitated in a reverse solvent to prepare an arylation-modified lignin sample.

[0007] In the invention, the arylating agent is any one of phenol, phenol derivatives, phenylalkyl ethers, phenylalkyl ether derivatives, phenylaryl ethers, phenylaryl ether derivatives, or a mixture of two or more thereof having an aromatic ring structure. Preferred arylating agents are phenol, guaiacol, syringol, 4-propylguaiacol, 4-propylsyringol, catechol, anisole, diphenyl ether, phenethyl ether, and cresol.

[0008] In the invention, the organic solvent is any one of dioxane, dimethylformamide, dimethylacetamide, dimethyl sulfoxide, tetrahydrofuran, formic acid, acetic acid, propionic acid, butyric acid, oxalic acid, lactic acid, fumaric acid, maleic acid, p-toluenesulfonic acid, or a mixture of two or more thereof, or an aqueous solution of any one or more thereof; the acid catalyst is any one of formic acid, maleic acid, p-toluenesulfonic acid, hydrochloric acid, sulfuric acid, phosphoric acid, nitric acid, trifluoroacetic acid, or a mixture of two or more thereof. The preferred organic solvent is 80-95wt% formic acid aqueous solution, 85-95wt% acetic acid aqueous solution, 40-65wt% maleic acid aqueous solution; the preferred acid catalyst is hydrochloric acid and sulfuric acid.

[0009] In the invention, the percentage of the lignin-based compound to the total mass of the material before the arylation reaction is 0.1-35wt%, and the preferred mass percentage is 5%-20%; the ratio of the mass of the arylation agent to the mass of the lignin-based compound is 0.1:1-10:1, the preferred mass ratio is 0.2:1-2:1, and the more preferred mass ratio is 0.4:1-1:1; the mass fraction of the acidic catalyst in the acidic organic solvent is 0.02-5wt%, wherein the preferred mass fraction ratio of the acidic catalyst is 0.05-2wt%, and the more preferred mass fraction ratio is 0.1-1wt%.

[0010] In the present invention, the lignin-based compound is any one of a biomass raw material containing lignin (wood powder, bamboo powder, straw powder, etc.), industrial lignin (alkali lignin, sulfate lignin, sulfite lignin, enzymatic lignin), and organic solvent extracted lignin (ethanol extracted lignin, acetic acid extracted lignin), or a mixture of two or more thereof.

[0011] In the invention, the temperature of the arylation reaction is 60-160°C, the preferred arylation temperature is 80-140°C, the optimal reaction temperature is 100-130°C, the reaction time is 1-1440min, the preferred reaction time is 10-300min, and the optimal reaction time is 30-180min.

[0012] In the present invention, the mixture after the arylation reaction is filtered through filter paper to remove insoluble impurities, the volatile solvent in the filtrate is removed by reduced pressure rotary evaporation, and then the remaining arylation reagent is removed by precipitation with a reverse solvent (the volume fraction of ethanol in the ethanol aqueous solution is 0%-20%), and the arylated lignin precipitate is collected.

[0013] The present invention uses natural lignin or industrial lignin as raw materials, utilizes an arylating agent to react with the benzyl hydroxyl group of lignin to undergo a Friedel-Crafts alkylation reaction (as shown in Formula 2), and realizes the selective synthesis of aryl-modified lignin. Based on the characteristic that the benzyl hydroxyl structure naturally present in lignin is easily reactive with nucleophilic reagents, the present invention induces lignin to selectively react with aromatic derivatives such as phenol and phenyl ether to realize the directional modification of lignin. The modification process effectively inhibits the self-condensation of lignin, avoids the ineffective breakage of the β-O-4 aromatic ether bond of lignin under mild conditions, and realizes the selective α-arylization modification. The lignin modification method improves the solubility of lignin in organic solvents, promotes the high-value utilization of lignin, and provides important raw material support for the preparation of renewable chemicals, energy substances, and renewable materials.

[0014]

[0015] Formula 2. Schematic diagram of the reaction of oriented arylation of lignin (R n is the substituent of the arylating agent, x is the number of substituents of the benzene ring in the arylating agent molecule, and R' is H or an acyl group derived from an organic acid solvent) The mechanism of the present invention is:

[0016] The present invention utilizes the chemical property that lignin is prone to self-condensation reaction during chemical treatment, and by adding an arylating agent with strong nucleophilicity, the lignin is selectively reacted with the arylating agent during the chemical treatment, and the condensation reaction of the lignin itself is inhibited. Among them, the benzyl hydroxyl group of lignin is easy to form a benzyl carbon cation under acidic conditions, and can undergo a Friedel-Crafts alkylation self-condensation reaction with the electronegative aromatic carbon in the lignin molecule. This reaction causes the lignin to self-crosslink, greatly reducing the solubility and subsequent utilization efficiency of the lignin. The present invention adds an arylating agent with strong nucleophilicity, and under acidic organic solvents and relatively mild catalytic reaction conditions, the arylating agent is selectively reacted with the lignin benzyl group to undergo a Friedel-Crafts alkylation reaction, and the α-arylation product of lignin is directionally generated, and the self-condensation reaction of lignin is effectively inhibited. At the same time, after the arylization treatment, the C in the lignin α –OH is C α –C aryl Substitution greatly increases the activation energy of cleavage of the aryl ether bonds in lignin, making the arylated lignin exhibit higher chemical stability.

[0017] Based on the chemical reactivity of lignin, the present invention uses an arylation agent to selectively react with lignin in an acidic organic solvent to produce a Friedel-Crafts alkylation reaction to prepare arylated lignin. The arylated lignin has excellent organic solvent solubility and rich and adjustable aromatic functional groups, which can effectively improve the subsequent high-value utilization potential of lignin.

[0018] Compared with the prior art, the present invention has the following innovations and beneficial effects:

[0019] 1. Compared with the existing lignin phenolization technology, the selectivity of chemical modification is significantly improved in this method. By reacting the arylation agent with lignin under low temperature and acidic organic solvent conditions, the selective arylation of the benzyl hydroxyl group of lignin can be achieved while retaining the β-O-4 aromatic ether bond structure in natural lignin. This method achieves selective α-arylation of lignin and is original.

[0020] 2. Compared with the existing lignin modification technology, this method improves the universality of the modification method. Taking advantage of the high reactivity of the benzyl hydroxyl group of lignin, this modification method is suitable for a variety of arylation modifications, which can effectively increase the content of phenolic hydroxyl and aryl ether in lignin, greatly expanding the high-value utilization potential of arylation-modified lignin. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The GPC chromatograms of Example 6 (aromatic modified lignin) and Comparative Example 1 are shown. DETAILED DESCRIPTION

[0022] In order to further elaborate and illustrate the present invention, several specific implementation cases are listed below, but the present invention is not limited to the following embodiments.

[0023] The lignin-based compounds in the following embodiments include lignocellulose (one or a mixture of two or more of poplar wood powder, bamboo powder, and corn stalk powder as raw materials), or are extracted and prepared from lignocellulose raw materials by the following methods:

[0024] The extraction conditions of alkali lignin are as follows: the raw material is poplar wood powder (4-40 mesh), the solution is a 15wt% NaOH aqueous solution, the material-liquid mass ratio is 5:1, the cooking temperature is 180℃, and the cooking time is 4h.

[0025] The extraction conditions of kraft lignin were as follows: the raw material was poplar wood powder (4–40 mesh), and the solution contained a final concentration of 10 wt% NaOH and 3 wt% Na 2 S aqueous solution, material-liquid mass ratio 4:1, cooking temperature 160℃, cooking for 3h.

[0026] The extraction conditions of sulfite lignin were as follows: the raw material was poplar wood powder (4–40 mesh), and the solution was 4 wt% NaHSO 3 The mass ratio of material to liquid is 4:1, the cooking temperature is 140℃, and the cooking time is 6h.

[0027] The extraction conditions of lignin by acetic acid solvent were as follows: the raw material was bamboo powder (4–40 mesh), the solution contained a final concentration of 0.1 wt% H 2 SO 4 The acetic acid solution of the acid catalyst (90wt% acetic acid, 10wt% water content) had a material-liquid mass ratio of 10:1, a cooking temperature of 140°C, and a cooking time of 2h.

[0028] The extraction conditions of ethanol solvent lignin were as follows: the raw material was bamboo powder (4–40 mesh), the solution contained a final concentration of 1 wt% H 2 SO 4 Ethanol solution of acid catalyst (90wt% ethanol, 10wt% water content), material-liquid mass ratio 10:1, cooking temperature 160℃, cooking for 4h.

[0029] The extraction conditions of enzymatic lignin are as follows: after treating poplar wood powder with a planetary ball mill for 24 hours, commercial cellulase (CTec 3, 50 FPU / g wood powder) was used in a pH 4.8 acetic acid / sodium acetate buffer solution (20 mL / g wood powder) for 48 hours, the enzymatic hydrolysis temperature was 50°C, and the shaking rate was 100 rpm. The undissolved residue was collected by filtration, purified with a 90 wt% acetic acid solution (20 mL / g residue) at room temperature, and the obtained lignin was precipitated in water (10 times the volume of the purified acetic acid solution).

[0030] Example 1. Weigh 10 g of poplar wood powder (4-40 mesh), 4 g of 4-propylguaiacol, 86 g of 90 wt% dioxane aqueous solution (containing 0.1 wt% H 2 SO 4 ), add to the high temperature reactor. After the reactor is sealed, start stirring at 500 rpm, heat to 120°C, and react for 30 minutes. After the reactor is cooled, the reaction mixture is filtered through filter paper, the filtrate is collected and concentrated to ~10mL by rotary evaporation, and the concentrated solution is dropped into 100mL of reverse solvent (water / ethanol, 9:1, v / v), and the arylated lignin is precipitated.

[0031] The arylated lignin was collected after filtration through filter paper, dried in an oven at 60°C, and weighed. The yield of arylated lignin was the percentage of the absolute dry weight of arylated lignin to the absolute dry weight of the initial lignin-based compound. The phenolic hydroxyl content was determined by 31 P NMR nuclear magnetic quantitative determination, TMDP is selected as the phosphating agent. The molecular weight test of arylated lignin uses Shimadzu Prominence-i LC 2030 gel permeation chromatography, the eluent is 0.6mL / min THF solution, and the UV signal detection wavelength is 280nm. THF solubility test is carried out by dissolving 800mg arylated lignin in 4mL THF, and calculating the THF solubility of arylated lignin by measuring the mass percentage of THF insoluble components in the total arylated lignin under 20°C. The purity of arylated lignin is calculated by the difference method, where purity [%] = 100% - carbohydrate content % - ash content %. Wherein, carbohydrate content and ash content are determined by NREL standard test methods (NREL / TP-510-42618 and NREL / TP-510-42622).

[0032] Example 2. Weigh 10 g of poplar wood powder (4-40 mesh), 4 g of 4-propyl syringol, 86 g of 80 wt% dioxane aqueous solution (containing 0.5 wt% H 3 PO 4 ), add to the high temperature reactor. After the reactor is sealed, start stirring at 500 rpm, heat to 120°C, react for 30 minutes, and after the reactor is cooled, filter the reaction mixture through filter paper, collect the filtrate and concentrate it to ~10mL by rotary evaporation, drop the concentrated solution into 100mL reverse solvent (water / ethanol, 9:1, v / v), and the arylated lignin will precipitate. The analysis and characterization of the lignin sample are the same as in Example 1.

[0033] Example 3. Weigh 10 g of poplar wood powder (4-40 mesh), 4 g of catechol, 86 g of 90 wt% dioxane aqueous solution (containing 1.0 wt% H 3 PO 4), add to the high temperature reactor. After the reactor is sealed, start stirring at 500 rpm, heat to 120°C, react for 30 minutes, and after the reactor is cooled, the reaction mixture is filtered through filter paper, the filtrate is collected and concentrated to 10 mL by rotary evaporation, and the concentrated solution is dropped into 100 mL of reverse solvent (water / ethanol, 9:1, v / v), and the arylated lignin is precipitated. The analysis and characterization of the lignin sample are the same as in Example 1.

[0034] Example 4. Weigh 10g of poplar wood powder (4-40 mesh), 10g of phenol, and 80g of 80wt% formic acid aqueous solution and add them to a high-temperature reactor. After the reactor is sealed, stir at a constant speed of 500 rpm, heat to 120°C, and react for 30 minutes. After the reactor is cooled, the reaction mixture is filtered through filter paper, and the filtrate is collected and concentrated to ~10mL by rotary evaporation. The concentrated solution is dripped into 100mL of reverse solvent (water / ethanol, 9:1, v / v), and the arylated lignin is precipitated. The analysis and characterization of the lignin sample are the same as in Example 1.

[0035] Example 5. Weigh 10g of poplar wood powder (4-40 mesh), 4g of guaiacol, and 86g of 95wt% formic acid aqueous solution and add them to a high-temperature reactor. After the reactor is sealed, stir at a constant speed of 500 rpm, heat to 120°C, and react for 30 minutes. After the reactor is cooled, the reaction mixture is filtered through filter paper, and the filtrate is collected and concentrated to ~10mL by rotary evaporation. The concentrated solution is dripped into 100mL of reverse solvent (water / ethanol, 9:1, v / v), and the arylated lignin is precipitated. The analysis and characterization of the lignin sample are the same as in Example 1.

[0036] The arylated lignin prepared in this embodiment was used to prepare an arylated lignin-based sunscreen according to the method described in (ACS Sustainable Chem. Eng. 2018, 6, 12532-12540). When the amount of arylated lignin added was 1%-10%, the sunscreen lotion had good uniformity; when the amount of arylated lignin added was 2%, the SPF value was 42.1, which was better than the acetylated modified and purified industrial lignin.

[0037] Example 6. Weigh 10g of poplar wood powder (4-40 mesh), 4g of eugenol, and 86g of 88wt% formic acid aqueous solution and add them to a high-temperature reactor. After the reactor is sealed, stir at a constant speed of 500 rpm, heat to 120°C, and react for 30 minutes. After the reactor is cooled, the reaction mixture is filtered through filter paper, and the filtrate is collected and concentrated to ~10mL by rotary evaporation. The concentrated solution is dripped into 100mL of reverse solvent (water / ethanol, 9:1, v / v), and the arylated lignin is precipitated. The analysis and characterization of the lignin sample are the same as in Example 1.

[0038] Example 7. Weigh 10g of poplar wood powder (4-40 mesh), 4g of diphenyl ether, and 86g of 80wt% acetic acid aqueous solution (containing 0.2wt% HCl) and add them to a high-temperature reactor. After the reactor is sealed, stir at 500 rpm, heat to 120°C, and react for 30 minutes. After the reactor is cooled, the reaction mixture is filtered through filter paper, and the filtrate is collected and concentrated to ~10mL by rotary evaporation. The concentrated solution is dripped into 100mL of reverse solvent (water / ethanol, 9:1, v / v), and the arylated lignin is precipitated. The analysis and characterization of the lignin sample are the same as in Example 1.

[0039] Example 8. Weigh 10g of poplar wood powder (4-40 mesh), 4g of anisole, and 86g of 90wt% acetic acid aqueous solution (containing 0.2wt% HCl) and add them to a high-temperature reactor. After the reactor is sealed, stir at a constant speed of 500 rpm, heat to 120°C, and react for 30 minutes. After the reactor is cooled, the reaction mixture is filtered through filter paper, and the filtrate is collected and concentrated to ~10mL by rotary evaporation. The concentrated solution is dripped into 100mL of reverse solvent (water / ethanol, 9:1, v / v), and the arylated lignin is precipitated. The analysis and characterization of the lignin sample are the same as in Example 1.

[0040] Example 9. Weigh 10g of poplar wood powder (4-40 mesh), 4g of phenethyl ether, and 86g of 90wt% acetic acid aqueous solution (containing 0.2wt% HCl) and add them to a high-temperature reactor. After the reactor is sealed, stir at 500 rpm, heat to 120°C, and react for 30 minutes. After the reactor is cooled, the reaction mixture is filtered through filter paper, and the filtrate is collected and concentrated to ~10mL by rotary evaporation. The concentrated solution is dripped into 100mL of reverse solvent (water / ethanol, 9:1, v / v), and the arylated lignin is precipitated. The analysis and characterization of the lignin sample are the same as in Example 1.

[0041] Example 10. Weigh 10g of poplar wood powder (4-40 mesh), 4g of cresol, and 86g of 95wt% acetic acid aqueous solution (containing 0.2wt% HCl) and add them to a high-temperature reactor. After the reactor is sealed, stir at 500 rpm, heat to 120°C, and react for 30 minutes. After the reactor is cooled, the reaction mixture is filtered through filter paper, and the filtrate is collected and concentrated to ~10mL by rotary evaporation. The concentrated solution is dripped into 100mL of reverse solvent (water / ethanol, 9:1, v / v), and the arylated lignin is precipitated. The analysis and characterization of the lignin sample are the same as in Example 1.

[0042] Example 11. Weigh 5g of bamboo powder (4-40 mesh), 2g of phenol, and 93g of 65wt% maleic acid aqueous solution and add them to a high-temperature reactor. After the reactor is sealed, stir at a constant speed of 500 rpm, heat to 120°C, and react for 30 minutes. After the reactor is cooled, the reaction mixture is filtered through filter paper, and the filtrate is collected and dripped into 300mL of deionized water, and the arylated lignin is precipitated. The analysis and characterization of the lignin sample are the same as in Example 1.

[0043] Example 12. Weigh 8.8g bamboo powder (4-40 mesh), 3.52g phenol, and 87.68g 60wt% maleic acid aqueous solution and add them to a high-temperature reactor. After the reactor is sealed, stir at a constant speed of 500 rpm, heat to 120°C, and react for 30 minutes. After the reactor is cooled, the reaction mixture is filtered through filter paper, and the filtrate is collected and dripped into 300mL deionized water, and the arylated lignin is precipitated. The analysis and characterization of the lignin sample are the same as in Example 1.

[0044] Example 13. Weigh 15g of bamboo powder (4-40 mesh), 6g of phenol, and 79g of 50wt% maleic acid aqueous solution and add them to a high-temperature reactor. After the reactor is sealed, stir at a constant speed of 500 rpm, heat to 120°C, and react for 30 minutes. After the reactor is cooled, the reaction mixture is filtered through filter paper, and the filtrate is collected and dripped into 300mL of deionized water, and the arylated lignin is precipitated. The analysis and characterization of the lignin sample are the same as in Example 1.

[0045] Example 14. Weigh 20g of bamboo powder (4-40 mesh), 8g of phenol, and 72g of 40wt% maleic acid aqueous solution and add them to a high-temperature reactor. After the reactor is sealed, stir at a constant speed of 500 rpm, heat to 120°C, and react for 30 minutes. After the reactor is cooled, the reaction mixture is filtered through filter paper, and the filtrate is collected and dripped into 300mL of deionized water, and the arylated lignin is precipitated. The analysis and characterization of the lignin sample are the same as in Example 1.

[0046] Example 15. Weigh 24g of bamboo powder (4-40 mesh), 9.6g of phenol, and 66.4g of 70wt% p-toluenesulfonic acid aqueous solution and add them to a high-temperature reactor. After the reactor is sealed, stir at a constant speed of 500 rpm, heat to 120°C, and react for 30 minutes. After the reactor is cooled, the reaction mixture is filtered through filter paper, and the filtrate is collected and dripped into 300mL of deionized water, and the arylated lignin is precipitated. The analysis and characterization of the lignin sample are the same as in Example 1.

[0047] Example 16. Weigh 10g bamboo powder (4-40 mesh), 4g phenol, and 86g 50wt% oxalic acid aqueous solution (containing 0.2wt% HCl) and add them to a high-temperature reactor. After the reactor is sealed, stir at 500 rpm, heat to 120°C, and react for 30min. After the reactor is cooled, the reaction mixture is filtered through filter paper, and the filtrate is collected and dripped into 300mL deionized water, and the arylated lignin is precipitated. The analysis and characterization of the lignin sample are the same as in Example 1.

[0048] Example 17. Weigh 10g corn stalk powder (4-40 mesh), 2g phenol, and 88g 88wt% formic acid aqueous solution and add them to a high-temperature reactor. After the reactor is sealed, stir at a constant speed of 500 rpm, heat to 80°C, and react for 360min. After the reactor is cooled, the reaction mixture is filtered through filter paper, and the filtrate is collected and concentrated to ~10mL by rotary evaporation. The concentrated solution is dripped into 100mL of reverse solvent (water / ethanol, 9:1, v / v), and the arylated lignin is precipitated. The analysis and characterization of the lignin sample are the same as in Example 1.

[0049] Example 18. Weigh 10g corn stalk powder (4-40 mesh), 4g phenol, and 86g 88wt% formic acid aqueous solution and add them to a high-temperature reactor. After the reactor is sealed, stir at a constant speed of 500 rpm, heat to 100°C, and react for 120min. After the reactor is cooled, the reaction mixture is filtered through filter paper, and the filtrate is collected and concentrated to ~10mL by rotary evaporation. The concentrated solution is dripped into 100mL of reverse solvent (water / ethanol, 9:1, v / v), and the arylated lignin is precipitated. The analysis and characterization of the lignin sample are the same as in Example 1.

[0050] Example 19. Weigh 10g corn stalk powder (4-40 mesh), 10g phenol, and 80g 88wt% formic acid aqueous solution and add them to a high-temperature reactor. After the reactor is sealed, stir at a constant speed of 500 rpm, heat to 120°C, and react for 30 minutes. After the reactor is cooled, the reaction mixture is filtered through filter paper, and the filtrate is collected and concentrated to ~10mL by rotary evaporation. The concentrated solution is dripped into 100mL of reverse solvent (water / ethanol, 9:1, v / v), and the arylated lignin is precipitated. The analysis and characterization of the lignin sample are the same as in Example 1.

[0051] Example 20. Weigh 10g corn stalk powder (4-40 mesh), 20g phenol, and 70g 88wt% formic acid aqueous solution and add them to a high-temperature reactor. After the reactor is sealed, stir at a constant speed of 500 rpm, heat to 140°C, and react for 10 minutes. After the reactor is cooled, the reaction mixture is filtered through filter paper, and the filtrate is collected and concentrated to ~10mL by rotary evaporation. The concentrated solution is dripped into 100mL of reverse solvent (water / ethanol, 9:1, v / v), and the arylated lignin is precipitated. The analysis and characterization of the lignin sample are the same as in Example 1.

[0052] Example 21. Weigh 10g of ethanol-extracted bamboo powder lignin, 20g of phenol, and 70g of 90wt% acetic acid aqueous solution (containing 0.2wt% HCl) and add them to a high-temperature reactor. After the reactor is sealed, stir at a constant speed of 500 rpm, heat to 120°C, and react for 60min. After the reactor is cooled, the reaction mixture is filtered through filter paper, and the filtrate is collected and concentrated to ~10mL by rotary evaporation. The concentrated solution is dripped into 100mL of reverse solvent (water / ethanol, 9:1, v / v), and the arylated lignin is precipitated. The analysis and characterization of the lignin sample are the same as in Example 1.

[0053] Example 22. Weigh 20g of ethanol-extracted bamboo powder lignin, 30g of phenol, and 50g of 90wt% acetic acid aqueous solution (containing 0.2wt% HCl) and add them to a high-temperature reactor. After the reactor is sealed, stir at 500 rpm, heat to 120°C, and react for 60min. After the reactor is cooled, the reaction mixture is filtered through filter paper, and the filtrate is collected and concentrated to ~10mL by rotary evaporation. The concentrated solution is dripped into 100mL of reverse solvent (water / ethanol, 9:1, v / v), and the arylated lignin is precipitated. The analysis and characterization of the lignin sample are the same as in Example 1.

[0054] Example 23. Weigh 30g of ethanol-extracted bamboo powder lignin, 35g of phenol, and 35g of 90wt% acetic acid aqueous solution (containing 0.2wt% HCl) and add them to a high-temperature reactor. After the reactor is sealed, stir at a constant speed of 500 rpm, heat to 120°C, and react for 60min. After the reactor is cooled, the reaction mixture is filtered through filter paper, and the filtrate is collected and concentrated to ~10mL by rotary evaporation. The concentrated solution is dripped into 100mL of reverse solvent (water / ethanol, 9:1, v / v), and the arylated lignin is precipitated. The analysis and characterization of the lignin sample are the same as in Example 1.

[0055] Example 24. Weigh 35g of ethanol-extracted bamboo powder lignin, 10g of phenol, and 55g of 90wt% acetic acid aqueous solution (containing 0.2wt% HCl) and add them to a high-temperature reactor. After the reactor is sealed, stir at a constant speed of 500 rpm, heat to 120°C, and react for 60min. After the reactor is cooled, the reaction mixture is filtered through filter paper, and the filtrate is collected and concentrated to ~10mL by rotary evaporation. The concentrated solution is dripped into 100mL of reverse solvent (water / ethanol, 9:1, v / v), and the arylated lignin is precipitated. The analysis and characterization of the lignin sample are the same as in Example 1.

[0056] Example 25. Weigh 10g of acetic acid to extract bamboo powder lignin, 10g of phenol, and 80g of 90wt% acetic acid aqueous solution (containing 0.2wt% HCl) and add them to a high-temperature reactor. After the reactor is sealed, stir at a constant speed of 500 rpm, heat to 130°C, and react for 30 minutes. After the reactor is cooled, the reaction mixture is filtered through filter paper, and the filtrate is collected and concentrated to ~10mL by rotary evaporation. The concentrated solution is dripped into 100mL of reverse solvent (water / ethanol, 9:1, v / v), and the arylated lignin is precipitated. The analysis and characterization of the lignin sample are the same as in Example 1.

[0057] Example 26. Weigh 10g of alkali lignin, 10g of catechol, and 80g of 90wt% acetic acid aqueous solution (containing 0.2wt% HCl) and add them to a high-temperature reactor. After the reactor is sealed, stir at 500 rpm, heat to 110°C, and react for 60 minutes. After the reactor is cooled, the reaction mixture is filtered through filter paper, and the filtrate is collected and concentrated to ~10mL by rotary evaporation. The concentrated solution is dripped into 100mL of reverse solvent (water / ethanol, 9:1, v / v), and the arylated lignin is precipitated. The analysis and characterization of the lignin sample are the same as in Example 1.

[0058] Example 27. Weigh 10g of alkali lignin, 10g of cresol, and 80g of 90wt% acetic acid aqueous solution (containing 0.2wt% HCl) and add them to a high-temperature reactor. After the reactor is sealed, stir at a constant speed of 500 rpm, heat to 110°C, and react for 60 minutes. After the reactor is cooled, the reaction mixture is filtered through filter paper, and the filtrate is collected and concentrated to ~10mL by rotary evaporation. The concentrated solution is dripped into 100mL of reverse solvent (water / ethanol, 9:1, v / v), and the arylated lignin is precipitated. The analysis and characterization of the lignin sample are the same as in Example 1.

[0059] Example 28. Weigh 10g of kraft lignin, 10g of cresol, and 80g of 90wt% acetic acid aqueous solution (containing 0.2wt% HCl) and add them to a high-temperature reactor. After the reactor is sealed, stir at 500 rpm, heat to 100°C, and react for 120min. After the reactor is cooled, the reaction mixture is filtered through filter paper, and the filtrate is collected and concentrated to ~10mL by rotary evaporation. The concentrated solution is dripped into 100mL of reverse solvent (water / ethanol, 9:1, v / v), and the arylated lignin is precipitated. The analysis and characterization of the lignin sample are the same as in Example 1.

[0060] Example 29. Weigh 10g of sulfite lignin, 10g of cresol, and 80g of 90wt% acetic acid aqueous solution (containing 0.2wt% HCl) and add them to a high-temperature reactor. After the reactor is sealed, stir at 500 rpm, heat to 90°C, and react for 240min. After the reactor is cooled, the reaction mixture is filtered through filter paper, and the filtrate is collected and concentrated to ~10mL by rotary evaporation. The concentrated solution is dripped into 100mL of reverse solvent (water / ethanol, 9:1, v / v), and the arylated lignin is precipitated. The analysis and characterization of the lignin sample are the same as in Example 1.

[0061] Example 30. Weigh 10g of enzymatic lignin, 10g of cresol, and 80g of 90wt% acetic acid aqueous solution (containing 0.2wt% HCl) and add them to a high-temperature reactor. After the reactor is sealed, stir at a constant speed of 500 rpm, heat to 80°C, and react for 300min. After the reactor is cooled, the reaction mixture is filtered through filter paper, and the filtrate is collected and concentrated to ~10mL by rotary evaporation. The concentrated solution is dripped into 100mL of reverse solvent (water / ethanol, 9:1, v / v), and the arylated lignin is precipitated. The analysis and characterization of the lignin sample are the same as in Example 1.

[0062] Comparative Example 1. Weigh 10g of poplar wood powder (4-40 mesh) and 90g of 88wt% formic acid aqueous solution and add them to a high-temperature reactor. After the reactor is sealed, stir at a constant speed of 500 rpm, heat to 120°C, and react for 30 minutes. After the reactor is cooled, the reaction mixture is filtered through filter paper, and the filtrate is collected and concentrated to ~10mL by rotary evaporation. The concentrated solution is dripped into 100mL of reverse solvent (water / ethanol, 9:1, v / v), and lignin is precipitated. The analysis and characterization of the lignin sample are the same as in Example 1.

[0063] Comparative Example 2. Weigh 10 g of poplar wood powder (4-40 mesh), 90 g of 90 wt% dioxane aqueous solution (containing 0.1 wt% H 2 SO 4), add to the high temperature reactor. After the reactor is sealed, start stirring at 500 rpm, heat to 120°C, react for 30 minutes, and after the reactor is cooled, the reaction mixture is filtered through filter paper, the filtrate is collected and concentrated to ~10mL by rotary evaporation, and the concentrated solution is dripped into 100mL of reverse solvent (water / ethanol, 9:1, v / v), and lignin is precipitated. The analysis and characterization of the lignin sample are the same as in Example 1.

[0064] Comparative Example 3. Weigh 10g of ethanol-extracted lignin and 90g of 90wt% acetic acid aqueous solution (containing 0.2wt% HCl) and add them to a high-temperature reactor. After the reactor is sealed, stir at a constant speed of 500 rpm, heat to 120°C, and react for 60min. After the reactor is cooled, the reaction mixture is filtered through filter paper, and the filtrate is collected and concentrated to ~10mL by rotary evaporation. The concentrated solution is dripped into 100mL of reverse solvent (water / ethanol, 9:1, v / v), and lignin is precipitated. The analysis and characterization of the lignin sample are the same as in Example 1.

[0065] Comparative Example 4. Weigh 10g of ethanol-extracted lignin, 20g of phenol, and 70g of ethanol (containing 0.2wt% HCl) and add them to a high-temperature reactor. After the reactor is sealed, stir at a constant speed of 500 rpm, heat to 120°C, and react for 60min. After the reactor is cooled, the reaction mixture is filtered through filter paper, and the filtrate is collected and concentrated to ~10mL by rotary evaporation. The concentrated solution is dripped into 100mL of reverse solvent (water / ethanol, 9:1, v / v), and lignin is precipitated. The analysis and characterization of the lignin sample are the same as in Example 1.

[0066] Table 1. Analytical test data of lignin samples in Examples and Comparative Examples

[0067]

[0068]

[0069] Note: Aromatized lignin yield [wt%] is based on the initial lignin-based compound.

[0070] As can be seen from Table 1, the arylation method of the present invention is applicable to a variety of arylation agents (including phenols and phenyl ethers), and has a good arylation effect on natural lignin and organic solvent extracted lignin. For example, in Examples 5-6 and 8, the yields of arylated lignin were 33.8wt%, 34.2wt% and 30.8wt%, respectively, which were significantly higher than the lignin yields of Comparative Examples 1 and 2 (without the addition of arylation agents) (19.8wt% and 14.1wt%). At the same time, combined with the results of lignin molecular weight analysis, it can be confirmed that arylated lignin effectively avoids the acidic depolymerization of lignin and retains the aromatic ether bonds that are unstable under acidic conditions. Compared with Comparative Example 3 (without the addition of arylation agents) and Comparative Example 4 (non-preferred organic solvent), the lignin yield of Examples 21-23 is significantly improved. After arylation treatment of organic solvent extracted lignin, the molecular weight and solubility of lignin are better than those of comparative samples without arylation reaction. The above results indicate that the lignin aromatization method improves the chemical structure characteristics and purity of lignin and promotes its subsequent high-value utilization.

[0071] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the basic principles of the chemical reactions involved in the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A method for selective aromatization of lignin, characterized in that: In an acidic organic solvent, an arylation agent is used to react with the benzyl hydroxyl group in the lignin-based compound to undergo an arylation reaction, thereby achieving directional modification of lignin and preparing an arylated lignin product; The arylating agent is any one of phenol, phenol derivatives, phenylalkyl ether, phenylalkyl ether derivatives, phenylaryl ether, and phenylaryl ether derivatives having an aromatic ring structure, or a mixture of two or more thereof.

2. The method according to claim 1, characterized in that: The organic solvent is an organic reagent or an aqueous solution of an organic reagent, the organic reagent is any one of dioxane, tetrahydrofuran, formic acid, acetic acid, propionic acid, butyric acid, oxalic acid, lactic acid, fumaric acid, maleic acid, and p-toluenesulfonic acid, or a mixture of two or more thereof, the aqueous solution of the organic reagent is any one of the organic reagents or a mixture of two or more thereof, and the mass content of water in the organic solvent is 0-60wt% (preferably the mass content of water is 5-40wt%, and more preferably the mass content of water is 10-20wt%); The acid catalyst is any one of formic acid, maleic acid, p-toluenesulfonic acid, hydrochloric acid, sulfuric acid, phosphoric acid, and trifluoroacetic acid, or a mixture of two or more thereof. The mass fraction of the acid catalyst in the acidic organic solvent is 0.02-5wt%, wherein the preferred mass fraction of the acid catalyst is 0.05-2wt%, and more preferably 0.1-1wt%.

3. The method according to claim 1, characterized in that The lignin-based compound is any one or a mixture of two or more of biomass raw materials containing lignin (one or more of wood powder, bamboo powder, straw powder, etc.), industrial lignin (one or more of alkali lignin, sulfate lignin, sulfite lignin, enzymatic lignin, etc.), and organic solvent extracted lignin (one or more of ethanol extracted lignin, acetic acid extracted lignin, etc.).

4. The method according to claim 1, characterized in that: The arylation reaction temperature is 60–160°C, the optimal arylation temperature is 80–140°C, the more optimal reaction temperature is 100–130°C, the reaction time is 1–1440 min, the more optimal reaction time is 10–300 min, and the more optimal reaction time is 30–180 min.

5. The method according to claim 1, characterized in that: The substituent R1 of the benzene ring in phenol and phenol derivatives is any one of an alkyl group (the number of carbon atoms of the alkyl group is 1-10), a phenolic hydroxyl group, and a methoxy group, or a mixture of two or more thereof, and the value of x is 0-4 (number); in phenyl alkyl ether derivatives, R2 is an alkyl group (the number of carbon atoms of the alkyl group is 1-10), and R3 is any one of an alkyl group (the number of carbon atoms of the alkyl group is 1-10), a phenolic hydroxyl group, and a methoxy group, or a mixture of two or more thereof, and the value of x (number) is 0-4; In the phenyl aryl ether derivative, R4 is any one of a phenyl group, a phenol group or an anisole group; 6. The method according to claim 1, characterized in that: The total materials before the arylation reaction include lignin-based compounds, arylation agents and acidic organic solvents, wherein the mass fraction of the lignin-based compounds is 0.1-35wt%, the preferred mass percentage is 5%-20%, and the more preferred mass percentage is 8%-16%; the ratio of the mass of the arylation agent to the mass of the lignin-based compound is 0.1:1-10:1, the preferred mass ratio is 0.2:1-2:1, and the more preferred mass ratio is 0.4:1-1:

1.

7. The method according to claim 1, characterized in that: The mixture after the arylation reaction is filtered, the solvent evaporated and the reverse solvent precipitated to obtain the arylated lignin product. The specific process is as follows: The insoluble impurities other than lignin are removed by physical filtration, part of the reaction solvent is removed by volatilizing the solvent, the remaining arylation reagent is removed by precipitation by adding a reverse solvent (water or ethanol aqueous solution, the volume fraction of ethanol in the reverse solvent is 0%-20%), and the arylated lignin precipitate is collected.

8. The arylated lignin product prepared by the method according to any one of claims 1 to 7.

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