Preparation method for selectively arylated lignin, and arylated lignin

Abstract

The present application relates to a preparation method for selectively arylated lignin, and arylated lignin. According to the method, lignin is extracted from natural lignin, industrial lignin or a solvent as a raw material, and an arylation reagent and lignin benzyl hydroxyl are subjected to a Friedel-Crafts alkylation reaction to realize selective synthesis of aryl-modified lignin. By utilizing the characteristic that the natural benzyl hydroxyl structure in lignin easily reacts with a nucleophilic reagent, lignin is induced to selectively react with an aromatic derivative such as phenol or phenyl ether, so as to realize directional modification of the lignin. The modification process effectively inhibits self-condensation of lignin, avoids invalid fracture of the β-O-4 aryl ether bond of the lignin under mild conditions, and realizes selective α-arylation modification. The lignin modification method improves the solubility of lignin in an organic solvent, promotes the high-value utilization of lignin, and provides important raw material support for applications such as preparation of renewable chemicals, energy substances, and renewable materials.

Description

A method for preparing selectively arylated lignin and arylated lignin Technical Field

[0001] The present invention relates to a preparation method of selectively arylated lignin and arylated 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 linked by carbon-carbon and carbon-oxygen bonds. It is the second-largest biomass resource in the plant kingdom, second only to carbohydrates in terms of reserves. High-value utilization of lignin helps reduce fossil resource consumption and environmental pollution, and promotes the bioeconomy and sustainable development. Lignin's chemical structure is complex, primarily manifested in the varying number of methoxy substituents within its structural units, with an average value ranging from 1–2. Various linkages exist between structural units, including carbon-carbon bonds (such as 5–5, β–5, and β–β) and carbon-oxygen bonds (such as β–O–4 and α–O–4). β–O–4 bonds are the most abundant type of linkage between lignin units, accounting for approximately 40–70%. Lignin's chemical complexity results in low efficiency in high-value utilization. Lignin's chemical structure can be modified through reactions such as esterification, etherification, alkylation, oxidation, and acylation, resulting in improved quality. 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 is a relatively traditional lignin alkylation modification strategy. This method originated from the phenolic resin synthesis process in which lignin is used to partially replace phenol. In this process, industrial lignin raw materials are mixed with a large amount of phenol. Under the action of a strong acid catalyst, the aromatic ether oxygen bonds in the lignin are broken, and the lignin alkyl chains are grafted with phenol groups (ACS Sustainable 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 solubility in organic solvents is significantly improved. However, due to the high phenolization reaction temperature and acid concentration, this treatment method is generally 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 severe degradation of non-lignin components (carbohydrate components), reducing 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 in the preparation of lignin-based high-value chemicals.

[0004] Summary of the Invention

[0005] The purpose of the present invention is to provide a method for selectively arylating the benzyl carbon of lignin and an arylized lignin product, thereby improving the chemical stability of lignin during separation or purification, while retaining the aryl ether bonds of lignin, and improving the reaction activity of lignin and its subsequent high-value utilization potential.

[0006] The specific technical solution of the present invention is as follows: an arylation agent, a lignin-based compound, and an acidic organic solvent are added to a high-temperature reactor in a predetermined ratio. The reaction mixture is uniformly stirred and mixed, and then heated to the reaction temperature in a sealed container. After 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 then precipitated in a reverse solvent to prepare an arylated lignin sample.

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

[0008] In the present 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, and p-toluenesulfonic acid, or a mixture of two or more thereof, or an aqueous solution of any one of or more thereof; the acidic catalyst is any one of formic acid, maleic acid, p-toluenesulfonic acid, hydrochloric acid, sulfuric acid, phosphoric acid, nitric acid, and trifluoroacetic acid, or a mixture of two or more thereof. Preferred organic solvents are 80–95 wt% formic acid aqueous solution, 85–95 wt% acetic acid aqueous solution, or 40–65 wt% maleic acid aqueous solution; and preferred acid catalysts are hydrochloric acid or sulfuric acid.

[0009] In the invention, the percentage of the lignin-based compound in 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 reagent 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 biomass raw materials 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, and the optimal reaction temperature is 100–130°C; the reaction time is 1–1440 min, the preferred reaction time is 10–300 min, and the optimal reaction time is 30–180 min.

[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 rotary evaporation under reduced pressure, 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 material and utilizes an arylating agent to undergo a Friedel-Crafts alkylation reaction with the benzyl hydroxyl group of lignin (as shown in Formula 2) to achieve the selective synthesis of arylated modified lignin. Based on the property of the naturally occurring benzyl hydroxyl structure in lignin that readily reacts with nucleophilic reagents, the present invention induces lignin to selectively react with aromatic derivatives such as phenol or phenyl ether, thereby achieving targeted modification of lignin. This modification process effectively inhibits the self-condensation of lignin, avoids the ineffective breakage of the β-O-4 aryl ether bond in lignin under mild conditions, and achieves selective α-arylation modification. This 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] Formula 2. Schematic diagram of the reaction of directed arylation of lignin (Rn is the substituent of the arylation reagent, x is the number of benzene ring substituents in the arylation reagent molecule, and R' is H or an acyl group derived from an acidic organic solvent)

[0015] This invention utilizes the chemical property of lignin, which is prone to self-condensation during chemical treatment. By adding a highly nucleophilic arylating agent, the lignin is selectively reacted with the arylating agent during the chemical treatment, thereby inhibiting the lignin's own condensation reaction. Under acidic conditions, the benzyl hydroxyl groups in lignin readily form benzyl carbocations, which react with electronegative aryl carbon groups in the lignin molecule through Friedel-Crafts alkylation and self-condensation. This reaction leads to self-crosslinking of the lignin, significantly reducing its solubility and subsequent utilization efficiency. By adding a highly nucleophilic arylating agent, the arylating agent selectively reacts with the benzyl groups in lignin under acidic organic solvents and relatively mild catalytic reaction conditions, resulting in the formation of α-arylated lignin products and effectively inhibiting the lignin's self-condensation reaction. Furthermore, after the arylating treatment, the Cα–OH groups in the lignin are replaced by Cα–Caryl groups, significantly increasing the activation energy for cleavage of the aryl ether bonds in the lignin, thus enhancing the chemical stability of the arylated lignin.

[0016] Based on the chemical reactivity of lignin, this method utilizes an arylating agent to selectively react with lignin in an acidic organic solvent to undergo a Friedel-Crafts alkylation reaction, thereby producing a targeted arylated lignin. This arylated lignin exhibits excellent organic solvent solubility and possesses a rich and tunable array of aromatic functional groups, effectively enhancing the potential for subsequent high-value utilization of lignin.

[0017] Compared with the prior art, the present invention has the following innovations and beneficial effects:

[0018] 1. Compared with existing lignin phenolization technologies, this method significantly improves the selectivity of chemical modification. By reacting lignin with an arylating agent at a relatively low temperature and in an acidic organic solvent, selective arylation of the benzylic hydroxyl groups in lignin is achieved while preserving the β–O–4 aryl ether bond structure found in native lignin. This method, which achieves selective α-arylation of lignin, is unique.

[0019] 2. Compared with existing lignin modification technologies, this method improves its universal applicability. By leveraging the high reactivity of lignin's benzyl hydroxyl groups, this modification method is applicable to a variety of arylation modification systems, effectively increasing the content of phenolic hydroxyl groups and aryl ethers in lignin, greatly expanding the potential for high-value utilization of arylation-modified lignin. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] FIG1 is a GPC chromatogram of Example 6 (arylation-modified lignin) and Comparative Example 1. DETAILED DESCRIPTION

[0021] 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.

[0022] 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 prepared by extracting lignocellulose raw materials by the following methods:

[0023] 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.

[0024] The extraction conditions of kraft lignin are as follows: the raw material is poplar wood powder (4–40 mesh), the solution is an aqueous solution containing a final concentration of 10 wt% NaOH and 3 wt% Na2S, the material-liquid mass ratio is 4:1, the cooking temperature is 160°C, and the cooking time is 3 h.

[0025] The extraction conditions of sulfite lignin are as follows: the raw material is poplar wood powder (4-40 mesh), the solution is a 4wt% NaHSO3 aqueous solution, the material-liquid mass ratio is 4:1, the cooking temperature is 140℃, and the cooking time is 6h.

[0026] The extraction conditions of lignin using acetic acid solvent are as follows: the raw material is bamboo powder (4–40 mesh), the solution is an acetic acid solution (90 wt% acetic acid, 10 wt% water content) containing a final concentration of 0.1 wt% H2SO4 acid catalyst, the material-liquid mass ratio is 10:1, the cooking temperature is 140 ° C, and the cooking time is 2 h.

[0027] The extraction conditions of ethanol solvent lignin are as follows: the raw material is bamboo powder (4–40 mesh), the solution is an ethanol solution (90wt% ethanol, 10wt% water content) containing a final concentration of 1wt% H2SO4 acid catalyst, the material-liquid mass ratio is 10:1, the cooking temperature is 160℃, and the cooking time is 4h.

[0028] Enzymatic lignin extraction conditions involved treating poplar wood flour with a planetary ball mill for 24 hours, followed by treatment with a commercial cellulase (CTec 3, 50 FPU / g wood flour) in a pH 4.8 acetic acid / sodium acetate buffer solution (20 mL / g wood flour) for 48 hours. The enzymatic hydrolysis temperature was 50°C and the shaking rate was 100 rpm. The undissolved residue was collected by filtration and purified with a 90 wt% acetic acid solution (20 mL / g residue) at room temperature. The resulting lignin was then precipitated in water (10 times the volume of the purified acetic acid solution).

[0029] Example 1

[0030] 10g of poplar wood flour (4–40 mesh), 4g of 4-propylguaiacol, and 86g of a 90wt% aqueous dioxane solution (containing 0.1wt% H2SO4) were weighed and added to a high-temperature reactor. The reactor was sealed and stirred at 500 rpm. The temperature was raised to 120°C and the reaction was continued for 30 minutes. After the reactor cooled, the reaction mixture was filtered through filter paper. The collected filtrate was concentrated to ~10mL by rotary evaporation. The concentrate was then added dropwise to 100mL of a reverse solvent (water / ethanol, 9:1, v / v), resulting in the precipitation of arylated lignin.

[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 31Quantitative determination was performed using P NMR, with TMDP as the phosphating agent. Aromatized lignin molecular weight was determined using a Shimadzu Prominence-i LC 2030 gel permeation chromatograph, with a THF solution at 0.6 mL / min as the eluent and UV detection at 280 nm. THF solubility was determined by dissolving 800 mg of arylatized lignin in 4 mL of THF. The THF solubility of the arylatized lignin was calculated by measuring the mass percentage of the THF-insoluble component relative to the total arylatized lignin at 20°C. The purity of the arylatized lignin was calculated by the difference method: purity [%] = 100% - carbohydrate content (%) - ash content (%). Carbohydrate content and ash content were determined according to NREL standard test methods (NREL / TP-510-42618 and NREL / TP-510-42622). Cellulose content and hemicellulose content correspond to the glucose and xylose contents, respectively, as determined by HPLC. The yield of cellulose pulp is the percentage of the absolute dry weight of the pulp after oven drying to the absolute dry weight of the initial lignin-based compounds.

[0032] Example 2

[0033] 10g of poplar wood flour (4–40 mesh), 4g of 4-propyl eugenol, and 86g of an 80wt% dioxane aqueous solution (containing 0.5wt% H3PO4) were weighed and added to a high-temperature reactor. The reactor was sealed and stirred at 500 rpm. The temperature was raised to 120°C and the reaction was continued for 30 minutes. After the reactor cooled, the reaction mixture was filtered through filter paper. The collected filtrate was concentrated to ~10mL by rotary evaporation. The concentrate was then added dropwise to 100mL of a reverse solvent (water / ethanol, 9:1, v / v). Aromatized lignin precipitated. Analysis and characterization of the lignin sample were performed as in Example 1.

[0034] Example 3

[0035] 10g of poplar wood flour (4–40 mesh), 4g of catechol, and 86g of a 90wt% aqueous dioxane solution (containing 1.0wt% H3PO4) were weighed and added to a high-temperature reactor. The reactor was sealed and stirred at 500 rpm. The temperature was raised to 120°C and the reaction was continued for 30 minutes. After the reactor cooled, the reaction mixture was filtered through filter paper. The collected filtrate was concentrated to ~10mL by rotary evaporation. The concentrate was then added dropwise to 100mL of a reverse solvent (water / ethanol, 9:1, v / v). Aromatized lignin precipitated. Analysis and characterization of the lignin sample were the same as in Example 1.

[0036] Example 4

[0037] 10g of poplar wood flour (4–40 mesh), 10g of phenol, and 80g of 80wt% formic acid aqueous solution were weighed and added to a high-temperature reactor. After sealing the reactor, the mixture was stirred at 500 rpm and heated to 120°C for 30 minutes. After the reactor cooled, the reaction mixture was filtered through filter paper. The collected filtrate was concentrated to ~10mL by rotary evaporation. The concentrate was then added dropwise to 100mL of reverse solvent (water / ethanol, 9:1, v / v). Aromatized lignin precipitated. Analysis and characterization of the lignin sample were the same as in Example 1.

[0038] Example 5

[0039] 10g of poplar wood flour (4–40 mesh), 4g of guaiacol, and 86g of 95wt% aqueous formic acid were weighed and added to a high-temperature reactor. After sealing the reactor, the mixture was stirred at 500 rpm and heated to 120°C for 30 minutes. After cooling, the reaction mixture was filtered through filter paper. The collected filtrate was concentrated to ~10mL by rotary evaporation. The concentrate was then added dropwise to 100mL of reverse solvent (water / ethanol, 9:1, v / v), resulting in the precipitation of arylated lignin. Analysis and characterization of the lignin samples were performed as in Example 1.

[0040] The arylated lignin prepared in this example was used to prepare an arylated lignin-based sunscreen according to the method described in (ACSSustainableChem.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 that of industrial lignin modified and purified by acetylation.

[0041] Example 6

[0042] 10g of poplar wood flour (4–40 mesh), 4g of eugenol, and 86g of 88wt% formic acid aqueous solution were weighed and added to a high-temperature reactor. After sealing the reactor, the mixture was stirred at 500 rpm and heated to 120°C for 30 minutes. After cooling, the reaction mixture was filtered through filter paper. The collected filtrate was concentrated to ~10mL by rotary evaporation. The concentrate was then added dropwise to 100mL of reverse solvent (water / ethanol, 9:1, v / v), resulting in the precipitation of arylated lignin. Analysis and characterization of the lignin sample were performed as in Example 1.

[0043] The filtrate from the reaction mixture was directly diluted with deionized water and filtered through a 0.45 μm membrane filter before being directly analyzed for water-soluble sugars using HPLC-RID. Total dissolved monosaccharides were determined by hydrolyzing the reaction filtrate in 4 wt% H₂SO₄ in an autoclave at 121°C for 1 h. Glucose and xylose were quantitatively analyzed using high-performance liquid chromatography (HPLC-RID) on an Agilent 1200 system equipped with a RID detector and a 300 mm × 7.7 mm (length (L) × internal diameter (ID)) Hi-Plex H column. The eluent was 0.01 M sulfuric acid at a flow rate of 0.6 mL min⁻¹. -1 .

[0044] Total soluble xylose content in the hydrolyzate = xylose concentration determined by HPLC × dilution factor × total volume of reaction filtrate × 0.88 / hemicellulose content in lignin-based compounds × 100%

[0045] According to the calculation method in Example 1, the yield of lignin-based compounds in the cellulose pulp obtained in Example 6 was 46.8%, the cellulose content in the cellulose pulp was 92.6%, and the residual hemicellulose content was 4.3%. The total soluble xylose content in the hydrolyzed liquid was 93%. Example 6 demonstrates that lignin aromatization promotes the efficient separation of cellulose, hemicellulose, and aromatized lignin components from lignocellulosic feedstock.

[0046] Example 7

[0047] 10g of poplar wood flour (4–40 mesh), 4g of diphenyl ether, and 86g of 80wt% aqueous acetic acid (containing 0.2wt% HCl) were weighed and added to a high-temperature reactor. The reactor was sealed and stirred at 500 rpm. The temperature was raised to 120°C and the reaction was continued for 30 minutes. After the reactor cooled, the reaction mixture was filtered through filter paper. The collected filtrate was concentrated to ~10mL by rotary evaporation. The concentrate was then added dropwise to 100mL of reverse solvent (water / ethanol, 9:1, v / v). Aromatized lignin precipitated. Analysis and characterization of the lignin sample were the same as in Example 1.

[0048] Example 8

[0049] 10g of poplar wood flour (4–40 mesh), 4g of anisole, and 86g of 90wt% aqueous acetic acid (containing 0.2wt% HCl) were weighed and added to a high-temperature reactor. After sealing the reactor, the mixture was stirred at 500 rpm and heated to 120°C for 30 minutes. After cooling, the reaction mixture was filtered through filter paper. The collected filtrate was concentrated to ~10mL by rotary evaporation. The concentrate was then added dropwise to 100mL of reverse solvent (water / ethanol, 9:1, v / v), resulting in the precipitation of arylated lignin. Analysis and characterization of the lignin samples were performed as in Example 1.

[0050] Example 9

[0051] 10g of poplar wood flour (4–40 mesh), 4g of phenylethyl ether, and 86g of 90wt% aqueous acetic acid (containing 0.2wt% HCl) were weighed and added to a high-temperature reactor. The reactor was sealed and stirred at 500 rpm. The temperature was raised to 120°C and the reaction was continued for 30 minutes. After the reactor cooled, the reaction mixture was filtered through filter paper. The collected filtrate was concentrated to ~10mL by rotary evaporation. The concentrate was then added dropwise to 100mL of reverse solvent (water / ethanol, 9:1, v / v). Aromatized lignin precipitated. Analysis and characterization of the lignin sample were the same as in Example 1.

[0052] Example 10

[0053] 10g of poplar wood flour (4–40 mesh), 4g of cresol, and 86g of 95wt% aqueous acetic acid (containing 0.2wt% HCl) were weighed and added to a high-temperature reactor. The reactor was sealed and stirred at 500 rpm. The temperature was raised to 120°C and the reaction was continued for 30 minutes. After the reactor cooled, the reaction mixture was filtered through filter paper. The collected filtrate was concentrated to ~10mL by rotary evaporation. The concentrate was then added dropwise to 100mL of reverse solvent (water / ethanol, 9:1, v / v). Aromatized lignin precipitated. Analysis and characterization of the lignin sample were the same as in Example 1.

[0054] Example 11

[0055] 5g of bamboo powder (4–40 mesh), 2g of phenol, and 93g of a 65wt% aqueous maleic acid solution were weighed and added to a high-temperature reactor. After sealing the reactor, the mixture was stirred at 500 rpm and heated to 120°C for 30 minutes. After cooling, the reaction mixture was filtered through filter paper and the filtrate was added dropwise to 300mL of deionized water. Arylated lignin precipitated. Analysis and characterization of the lignin sample were performed as in Example 1.

[0056] Example 12

[0057] 8.8g of bamboo powder (4–40 mesh), 3.52g of phenol, and 87.7g of a 60wt% aqueous maleic acid solution were weighed and added to a high-temperature reactor. After sealing the reactor, the mixture was stirred at 500 rpm and heated to 120°C for 30 minutes. After cooling, the reaction mixture was filtered through filter paper and the filtrate was added dropwise to 300mL of deionized water. Aromatized lignin precipitated. Analysis and characterization of the lignin sample were performed as in Example 1.

[0058] Example 13

[0059] 15g of bamboo powder (4–40 mesh), 6g of phenol, and 79g of a 50wt% aqueous maleic acid solution were weighed and added to a high-temperature reactor. After sealing the reactor, the mixture was stirred at 500 rpm and heated to 120°C for 30 minutes. After cooling, the reaction mixture was filtered through filter paper and the filtrate was added dropwise to 300mL of deionized water. Arylated lignin precipitated. Analysis and characterization of the lignin sample were performed as in Example 1.

[0060] Example 14

[0061] 20g of bamboo powder (4–40 mesh), 8g of phenol, and 72g of a 40wt% aqueous maleic acid solution were weighed and added to a high-temperature reactor. After sealing the reactor, the mixture was stirred at 500 rpm and heated to 120°C for 30 minutes. After cooling, the reaction mixture was filtered through filter paper and the collected filtrate was dripped into 300mL of deionized water. Aromatized lignin precipitated. Analysis and characterization of the lignin sample were the same as in Example 1.

[0062] Example 15

[0063] 24g of bamboo powder (4–40 mesh), 9.6g of phenol, and 66.4g of a 70wt% aqueous solution of p-toluenesulfonic acid were weighed and added to a high-temperature reactor. After sealing the reactor, the mixture was stirred at 500 rpm and heated to 120°C for 30 minutes. After cooling, the reaction mixture was filtered through filter paper and the filtrate was added dropwise to 300mL of deionized water. Aromatized lignin precipitated. Analysis and characterization of the lignin sample were performed as in Example 1.

[0064] Example 16

[0065] 10g of bamboo powder (4–40 mesh), 4g of phenol, and 86g of a 50wt% aqueous oxalic acid solution (containing 0.2wt% HCl) were weighed and added to a high-temperature reactor. After sealing the reactor, the mixture was stirred at 500 rpm and heated to 120°C for 30 minutes. After cooling, the reaction mixture was filtered through filter paper and the filtrate was added dropwise to 300mL of deionized water. Aromatized lignin precipitated. Analysis and characterization of the lignin sample were performed as in Example 1.

[0066] Example 17

[0067] 10g corn stalk powder (4–40 mesh), 2g phenol, and 88g 88wt% formic acid aqueous solution were weighed and added to a high-temperature reactor. The reactor was sealed and stirred at 500 rpm. The temperature was raised to 80°C and the reaction was continued for 360 minutes. After the reactor cooled, the reaction mixture was filtered through filter paper. The collected filtrate was concentrated to ~10mL by rotary evaporation. The concentrate was then added dropwise to 100mL of reverse solvent (water / ethanol, 9:1, v / v). Aromatized lignin precipitated. Analysis and characterization of the lignin sample were the same as in Example 1.

[0068] Example 18

[0069] 10g corn stalk powder (4–40 mesh), 4g phenol, and 86g 88wt% formic acid aqueous solution were weighed and added to a high-temperature reactor. After sealing the reactor, the mixture was stirred at 500 rpm and heated to 100°C for 120 minutes. After cooling, the reaction mixture was filtered through filter paper. The collected filtrate was concentrated to ~10mL by rotary evaporation. The concentrate was then added dropwise to 100mL of reverse solvent (water / ethanol, 9:1, v / v), resulting in the precipitation of arylated lignin. Analysis and characterization of the lignin samples were performed as in Example 1.

[0070] Example 19

[0071] 10g corn stalk powder (4–40 mesh), 10g phenol, and 80g 88wt% formic acid aqueous solution were weighed and added to a high-temperature reactor. After sealing the reactor, the mixture was stirred at 500 rpm and heated to 120°C for 30 minutes. After cooling, the reaction mixture was filtered through filter paper. The collected filtrate was concentrated to ~10mL by rotary evaporation. The concentrate was then added dropwise to 100mL of reverse solvent (water / ethanol, 9:1, v / v), resulting in the precipitation of arylated lignin. Analysis and characterization of the lignin samples were performed as in Example 1.

[0072] Example 20

[0073] 10g corn stalk powder (4–40 mesh), 20g phenol, and 70g 88wt% formic acid aqueous solution were weighed and added to a high-temperature reactor. After sealing the reactor, the mixture was stirred at 500 rpm and heated to 140°C for 10 minutes. After cooling, the reaction mixture was filtered through filter paper. The collected filtrate was concentrated to ~10mL by rotary evaporation. The concentrate was then added dropwise to 100mL of reverse solvent (water / ethanol, 9:1, v / v), resulting in the precipitation of arylated lignin. Analysis and characterization of the lignin samples were performed as in Example 1.

[0074] Example 21

[0075] 10g of ethanol-extracted bamboo powder lignin, 20g of phenol, and 70g of a 90wt% aqueous acetic acid solution (containing 0.2wt% HCl) were weighed and added to a high-temperature reactor. After sealing the reactor, the mixture was stirred at 500 rpm and heated to 120°C for 60 minutes. After the reactor cooled, the reaction mixture was filtered through filter paper. The collected filtrate was concentrated to ~10mL by rotary evaporation. The concentrated solution was added dropwise to 100mL of a reverse solvent (water / ethanol, 9:1, v / v), causing the arylated lignin to precipitate. Analysis and characterization of the lignin sample were the same as in Example 1.

[0076] Example 22

[0077] 20g of ethanol-extracted bamboo powder lignin, 30g of phenol, and 50g of a 90wt% aqueous acetic acid solution (containing 0.2wt% HCl) were weighed and added to a high-temperature reactor. After sealing the reactor, the mixture was stirred at 500 rpm and heated to 120°C for 60 minutes. After the reactor cooled, the reaction mixture was filtered through filter paper. The collected filtrate was concentrated to ~10mL by rotary evaporation. The concentrated solution was added dropwise to 100mL of a reverse solvent (water / ethanol, 9:1, v / v), causing the arylated lignin to precipitate. Analysis and characterization of the lignin sample were the same as in Example 1.

[0078] Example 23

[0079] 30g of ethanol-extracted bamboo powder lignin, 35g of phenol, and 35g of 90wt% aqueous acetic acid (containing 0.2wt% HCl) were weighed and added to a high-temperature reactor. After sealing the reactor, the mixture was stirred at 500 rpm and heated to 120°C for 60 minutes. After the reactor cooled, the reaction mixture was filtered through filter paper. The collected filtrate was concentrated to ~10mL by rotary evaporation. The concentrated solution was added dropwise to 100mL of reverse solvent (water / ethanol, 9:1, v / v), causing the arylated lignin to precipitate. Analysis and characterization of the lignin sample were the same as in Example 1.

[0080] Example 24

[0081] 35g of ethanol-extracted bamboo powder lignin, 10g of phenol, and 55g of a 90wt% aqueous acetic acid solution (containing 0.2wt% HCl) were weighed and added to a high-temperature reactor. After sealing the reactor, the mixture was stirred at 500 rpm and heated to 120°C for 60 minutes. After cooling, the reaction mixture was filtered through filter paper. The collected filtrate was concentrated to ~10mL by rotary evaporation. The concentrate was then added dropwise to 100mL of a reverse solvent (water / ethanol, 9:1, v / v), resulting in the precipitation of arylated lignin. Analysis and characterization of the lignin sample were performed as in Example 1.

[0082] Example 25

[0083] 10g of acetic acid-extracted bamboo powder lignin, 10g of phenol, and 80g of a 90wt% aqueous acetic acid solution (containing 0.2wt% HCl) were weighed and added to a high-temperature reactor. After sealing the reactor, the mixture was stirred at 500 rpm and heated to 130°C for 30 minutes. After the reactor cooled, the reaction mixture was filtered through filter paper. The collected filtrate was concentrated to ~10mL by rotary evaporation. The concentrated solution was added dropwise to 100mL of a reverse solvent (water / ethanol, 9:1, v / v), causing the arylated lignin to precipitate. Analysis and characterization of the lignin sample were the same as in Example 1.

[0084] Example 26

[0085] 10g of alkali lignin, 10g of catechol, and 80g of a 90wt% aqueous acetic acid solution (containing 0.2wt% HCl) were weighed and added to a high-temperature reactor. After the reactor was sealed, stirring was continued at 500 rpm, the temperature was raised to 110°C, and the reaction was allowed to proceed for 60 minutes. After the reactor cooled, the reaction mixture was filtered through filter paper, and the filtrate was concentrated to ~10mL by rotary evaporation. The concentrated solution was added dropwise to 100mL of a reverse solvent (water / ethanol, 9:1, v / v), and the arylated lignin precipitated. Analysis and characterization of the lignin sample were the same as in Example 1.

[0086] Example 27

[0087] 10g of alkali lignin, 10g of cresol, and 80g of a 90wt% aqueous acetic acid solution (containing 0.2wt% HCl) were weighed and added to a high-temperature reactor. After the reactor was sealed, stirring was continued at 500 rpm, the temperature was raised to 110°C, and the reaction was allowed to proceed for 60 minutes. After the reactor cooled, the reaction mixture was filtered through filter paper, and the filtrate was collected and concentrated to ~10mL by rotary evaporation. The concentrate was then added dropwise to 100mL of a reverse solvent (water / ethanol, 9:1, v / v), and the arylated lignin precipitated. Analysis and characterization of the lignin sample were the same as in Example 1.

[0088] Example 28

[0089] 10g of kraft lignin, 10g of cresol, and 80g of a 90wt% aqueous acetic acid solution (containing 0.2wt% HCl) were weighed and added to a high-temperature reactor. After the reactor was sealed, stirring was continued at 500 rpm, the temperature was raised to 100°C, and the reaction was carried out for 120 minutes. After the reactor cooled, the reaction mixture was filtered through filter paper, and the filtrate was collected and concentrated to ~10mL by rotary evaporation. The concentrate was added dropwise to 100mL of a reverse solvent (water / ethanol, 9:1, v / v), and the arylated lignin precipitated. Analysis and characterization of the lignin sample were the same as in Example 1.

[0090] Example 29

[0091] 10g of sulfite-processed lignin, 10g of cresol, and 80g of a 90wt% aqueous acetic acid solution (containing 0.2wt% HCl) were weighed and added to a high-temperature reactor. After sealing the reactor, the mixture was stirred at 500 rpm and heated to 90°C for 240 minutes. After the reactor cooled, the reaction mixture was filtered through filter paper. The collected filtrate was concentrated to ~10mL by rotary evaporation. The concentrate was then added dropwise to 100mL of a reverse solvent (water / ethanol, 9:1, v / v). The arylated lignin precipitated. Analysis and characterization of the lignin sample were the same as in Example 1.

[0092] Example 30

[0093] 10g of enzymatically hydrolyzed lignin, 10g of cresol, and 80g of a 90wt% aqueous acetic acid solution (containing 0.2wt% HCl) were weighed and added to a high-temperature reactor. After the reactor was sealed, stirring was continued at 500 rpm, the temperature was raised to 80°C, and the reaction was allowed to proceed for 300 minutes. After the reactor cooled, the reaction mixture was filtered through filter paper, and the collected filtrate was concentrated to ~10mL by rotary evaporation. The concentrated solution was added dropwise to 100mL of a reverse solvent (water / ethanol, 9:1, v / v), and the arylated lignin precipitated. Analysis and characterization of the lignin sample were the same as in Example 1.

[0094] Comparative Example 1

[0095] 10g of poplar wood flour (4–40 mesh) and 90g of 88wt% formic acid aqueous solution were weighed and added to a high-temperature reactor. After sealing the reactor, the mixture was stirred at 500 rpm and heated to 120°C for 30 minutes. After the reactor cooled, the reaction mixture was filtered through filter paper. The collected filtrate was concentrated to ~10mL by rotary evaporation. The concentrate was then added dropwise to 100mL of a reverse solvent (water / ethanol, 9:1, v / v), resulting in the precipitation of lignin. Analysis and characterization of the lignin sample were performed as in Example 1.

[0096] Comparative Example 2

[0097] 10g of poplar wood flour (4–40 mesh) and 90g of a 90wt% dioxane aqueous solution (containing 0.1wt% H2SO4) were weighed and added to a high-temperature reactor. After sealing the reactor, the mixture was stirred at 500 rpm and heated to 120°C for 30 minutes. After cooling, the reaction mixture was filtered through filter paper. The collected filtrate was concentrated to ~10mL by rotary evaporation. The concentrate was then added dropwise to 100mL of a reverse solvent (water / ethanol, 9:1, v / v), causing lignin to precipitate. Analysis and characterization of the lignin sample were performed as in Example 1.

[0098] Comparative Example 3

[0099] 10g of ethanol-extracted lignin and 90g of 90wt% aqueous acetic acid (containing 0.2wt% HCl) were weighed and added to a high-temperature reactor. After the reactor was sealed, the mixture was stirred at 500 rpm and heated to 120°C for 60 minutes. After the reactor cooled, the reaction mixture was filtered through filter paper. The collected filtrate was concentrated to ~10mL by rotary evaporation. The concentrated solution was added dropwise to 100mL of reverse solvent (water / ethanol, 9:1, v / v), and the lignin precipitated. Analysis and characterization of the lignin sample were the same as in Example 1.

[0100] Comparative Example 4

[0101] 10g of ethanol-extracted lignin, 20g of phenol, and 70g of ethanol (containing 0.2wt% HCl) were weighed and added to a high-temperature reactor. After sealing the reactor, the mixture was stirred at 500 rpm and heated to 120°C for 60 minutes. After the reactor cooled, the reaction mixture was filtered through filter paper. The collected filtrate was concentrated to ~10mL by rotary evaporation. The concentrate was then added dropwise to 100mL of a reverse solvent (water / ethanol, 9:1, v / v), causing the lignin to precipitate. Analysis and characterization of the lignin sample were the same as in Example 1.

[0102] Table 1. Analytical test data of lignin samples in Examples and Comparative Examples

[0103] Note: The yield of arylated lignin [wt%] is based on the initial lignin-based compound.

[0104] As can be seen from Table 1, the arylation method of the present invention is applicable to a variety of arylation reagents (including phenols and phenyl ethers) and exhibits excellent arylation effects on natural lignin, industrial lignin, and organic solvent-extracted lignin. For example, in Examples 5–6 and 8, the yields of arylated lignin were 33.8 wt%, 34.2 wt%, and 30.8 wt%, respectively, significantly higher than the yields of 19.8 wt% and 14.1 wt% in Comparative Examples 1 and 2 (no arylation reagent added). Combined with the lignin molecular weight analysis results, it was confirmed that arylated lignin effectively avoided acidic depolymerization of lignin, retaining aryl ether bonds that are unstable under acidic conditions. Compared with Comparative Example 3 (no arylation reagent added) and Comparative Example 4 (a non-preferred organic solvent), the lignin yields of Examples 21–23 were significantly improved. After arylation treatment, the molecular weight and solubility of organic solvent-extracted lignin were superior to those of the comparative samples without arylation. The above results show that the lignin arylation method improves the chemical structure characteristics and purity of lignin and promotes subsequent high-value utilization.

[0105] 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 considered as equivalent replacement methods and are included in the scope of protection 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 a biomass raw material 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, and 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 phenyl aryl ether derivatives, R4 is any one of a phenyl group, a phenol group, or 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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