Method for extracting light-color phenolated lignin

Abstract

The invention provides a method for rapidly extracting light-color phenolated lignin, and belongs to the field of biomass refining. The method comprises the following steps: uniformly mixing a lignocellulose raw material with a mixed solution of aromatic sulfonic acid and a phenolic compound according to a certain solid-to-liquid ratio, and carrying out ultrasonic treatment at a certain temperature; and after the treatment is completed, carrying out solid-liquid separation, pouring the obtained extracting solution into water to precipitate lignin, and washing and drying to obtain the light-color phenolated lignin. The method disclosed by the invention is simple in process, low in time consumption and high in yield, and the solvent is easy to recycle; the prepared lignin is extremely light in color and high in phenolic hydroxyl group content, retains most of aryl ether bonds, can adjust the content of phenolic hydroxyl groups and methoxyl groups in the lignin to a certain extent, and solves the problems of dark color, few functional groups and low reaction activity of the existing industrial lignin. The method can be used for producing lignin-based functional products without further color reduction and activation treatment.

Description

Technical Field

[0001] The invention belongs to the field of lignocellulose biomass refining and relates to a method for quickly extracting light-colored lignin with a high phenolic hydroxyl content from lignocellulose raw materials. Background Art

[0002] The information disclosed in this background technology section is only intended to enhance the understanding of the overall background of the invention, and should not necessarily be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to a person skilled in the art.

[0003] Lignocellulosic biomass resources are the most abundant natural renewable resources in nature, and their main chemical components are carbohydrates (cellulose, hemicellulose) and lignin. Among them, lignin has aromatic structural units and abundant functional groups such as hydroxyl and methoxy groups, which give lignin good UV resistance, antioxidant and antibacterial properties. Moreover, the various active groups in its molecular structure also make it easy to chemically modify and convert it into functional materials. It is considered to have the greatest potential to replace petroleum-based products. However, compared with cellulose and hemicellulose, lignin has not been reasonably utilized so far. For example, the pulp and paper industry that uses lignocellulosic biomass resources as raw materials prioritizes the extraction and utilization of cellulose, while lignin is mainly burned as a reaction by-product to provide energy. Moreover, during the reaction process of component separation, lignin loses a large number of aromatic ether bonds, which reduces its reactivity; in particular, the separation process inevitably introduces a variety of chromophores and auxochromes such as carbonyl, conjugated double bonds, and quinone structures, resulting in extremely dark lignin appearance, which is limited in many application areas. For example, only light-colored lignin can be used in UV protection products (such as sunscreen, special plastics), special rubber, dye dispersants, etc. Therefore, the low reactivity and dark color of industrial lignin currently seriously hinder the efficient conversion and high-value utilization of lignin.

[0004] In order to improve the utilization value of lignin, the extracted lignin has to be further activated or decolorized to obtain light-colored lignin with high reactivity, such as activation modification such as hydroxymethylation and phenolization of lignin and decolorization methods such as methanol fractionation, sulfonation modification, amination modification, and bleaching. However, these methods not only make the process cumbersome but also greatly increase the production cost. Therefore, how to directly extract high-reactivity and light-colored high-quality lignin from lignocellulose raw materials in a simple and efficient way is the key to achieving efficient and high-value utilization of lignin.

[0005] The patent (ZL 202010794458.4) discloses a method for inhibiting lignin condensation, which involves using small molecular phenolic organic substances such as cresol, phenol, and resorcinol to preferentially react with the active sites of lignin during the high-temperature separation of lignocellulosic raw materials in an acidic, alkaline or neutral cooking agent, thereby preventing the condensation reaction between lignin macromolecules. This extraction process greatly reduces the carbon-carbon bonds generated between lignin molecules and increases the yield of small molecular lignin with high reaction activity. However, the extraction method requires a high temperature, which causes most of the aromatic ether bonds in the lignin to break, and the hydroxyl groups in the lignin are easily esterified by formic acid or acetic acid. In particular, the formic acid and acetic acid used in this method are oxidizing, which will cause chromophores and auxochromes to form in the lignin structure, resulting in the obtained lignin being darker in color, hindering its application in color-limited fields such as sunscreens, dyes, active packaging materials, and light-colored resin glues. Summary of the invention

[0006] The present invention aims at the problem that the current industrial lignin is extremely dark in color, has low reactivity and is difficult to utilize, and in order to solve the deficiencies of the prior art, a method for rapidly and efficiently extracting light-colored phenolic lignin is provided. The present invention extracts by using aromatic sulfonic acid having a benzene ring structure, having a certain similarity to the structure of lignin and not having oxidizing properties, and phenolic compounds to synergistically treat lignocellulose raw materials to obtain light-colored phenolic lignin with high reactivity, providing a new mode for the efficient separation of lignin.

[0007] In order to achieve the above object, the present invention adopts the following technical solution:

[0008] The first aspect of the present invention provides a method for extracting light-colored phenolic lignin, comprising:

[0009] The lignocellulose raw material is mixed evenly with a mixed solution of aromatic sulfonic acid and phenolic compounds, and reacted under ultrasonic conditions. After the reaction is completed, the solid and liquid are separated, and the extract is collected;

[0010] The extract is poured into water to precipitate the lignin, and then washed and dried to obtain the product.

[0011] In some embodiments, the aromatic sulfonic acid is selected from at least one of benzenesulfonic acid, p-toluenesulfonic acid, and p-ethylbenzenesulfonic acid.

[0012] In some embodiments, the phenolic compound is selected from at least one of phenol, guaiacol, and syringol.

[0013] In some embodiments, in the mixed liquid medicine, the total mass fraction of the aromatic sulfonic acid and the phenolic compound is 5% to 95%, preferably, 50% to 80%.

[0014] In some embodiments, the solvent of the mixed drug solution is water.

[0015] In some embodiments, the mass ratio of the aromatic sulfonic acid to the phenolic compound is 9:1 to 2:8, preferably 8:2 to 5:5.

[0016] In some embodiments, the solid-liquid ratio of the lignocellulosic raw material to the mixed liquid medicine is 1:1-50, preferably 1:1-20.

[0017] Compared with ordinary water bath heating, ultrasonic treatment can effectively improve the yield of lignin. Therefore, in some embodiments, the ultrasonic treatment temperature is 25-100°C, preferably 50-90°C;

[0018] It should be noted that the present invention does not limit the power of ultrasonic treatment, and the process requirements can be met by simply controlling the temperature of ultrasonic treatment.

[0019] In some embodiments, the ultrasonic treatment time is 5 to 120 min, preferably, 10 to 60 min.

[0020] In some embodiments, the lignocellulosic feedstock is at least one of hardwood, softwood, or non-wood;

[0021] Preferably, the broadleaf wood is poplar and / or eucalyptus;

[0022] Preferably, the coniferous wood is pine and / or masson pine;

[0023] Preferably, the non-wood material is at least one of bamboo, bagasse, and corn stalks.

[0024] The second aspect of the present invention provides light-colored phenolic lignin prepared by the above method.

[0025] The third aspect of the present invention provides the use of the above-mentioned light-colored phenolic lignin in the preparation of UV protection products, special rubbers, dye dispersants, active packaging materials, and light-colored resin glues.

[0026] Beneficial effects of the present invention

[0027] (1) The aromatic sulfonic acid used in the present invention contains both a hydrophobic benzene ring structure and a hydrophilic sulfonic acid group. As an acidic hydrotropic solvent, it has a good selective solubilizing ability for hydrophobic lignin. With the assistance of ultrasound, it can dissolve lignin in lignocellulosic raw materials under mild conditions.

[0028] (2) As an acidic hydrotrope, aromatic sulfonic acid can easily generate protons H in aqueous solution. +, catalyzing hydrolysis to break the ester bonds, ether bonds between carbohydrates and lignin, and the aromatic ether bonds in the lignin structure, further promoting the dissolution of lignin; in particular, it can catalyze the reaction between phenolic compounds and benzene rings in lignin, increase the phenolic hydroxyl content in lignin, and increase the solubility of lignin. Therefore, the method of the present invention can quickly (less than 60 minutes) extract lignin from lignocellulosic raw materials at low temperature (less than 90°C).

[0029] (3) The aromatic sulfonic acid used in the present invention is a non-oxidizing organic strong acid. Compared with formic acid, acetic acid, etc., it will not cause lignin to be oxidized, avoid the generation of chromophores and auxochromes, and prevent the darkening of lignin. However, when aromatic sulfonic acid is used alone to extract lignin, the chromophore Hibbert ketone structure is generated in the lignin due to the breakage of the β-O-4 ether bond in the lignin structure; moreover, the Cα positive carbon ion generated by the lignin molecule in an acidic environment will condense with another lignin molecule, making it difficult to separate the lignin. Therefore, it not only affects the dissolution of lignin, but also makes the obtained lignin darker in color. The present invention uses phenolic compounds and aromatic sulfonic acids to extract lignin in a coordinated manner. The degradation and extraction process of lignin is also a process of phenolization and modification of lignin. Since the phenolic compounds are nucleophilic reagents, the para-position or ortho-position of the phenolic hydroxyl group thereof preferentially reacts with the Cα positive carbon ion, thereby preventing the condensation between lignin molecules and also avoiding the breakage of the aromatic ether bond and the formation of the chromophore group. The phenolized lignin extracted by the method of the present invention has a high yield, a high phenolic hydroxyl content, a light color, and significantly improved chemical reaction activity.

[0030] (4) The extraction process of the method of the present invention is simple, the conditions are mild, the equipment is less corrosive, the solvent is easy to recycle and reuse, the lignin yield is high, the whiteness is high, and the phenolic hydroxyl and methoxy content in the lignin can be regulated by adjusting the type of phenolic compounds (phenol does not contain methoxyl groups, guaiacol contains 1 methoxyl group, and syringol contains 2 methoxyl groups), the dosage and the extraction process conditions, which is conducive to the precise customization of the lignin structure and target performance. In addition, the method of the present invention can save the subsequent chemical modification and color reduction process of lignin, reducing production costs. DETAILED DESCRIPTION

[0031] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0032] The present invention will be further described in detail below in conjunction with specific embodiments. It should be noted that the specific embodiments are intended to explain the present invention rather than to limit it.

[0033] In the following examples, the solvent of the mixed solution is water.

[0034] The lignocellulose raw material used in this example is pine wood powder (coniferous material), and poplar wood powder (broadleaved material) and bamboo powder (non-wood) are used for parallel control experiments.

[0035] Example 1

[0036] S1. The pine wood chips were crushed into 40-60 mesh particles, and a pre-prepared 70% p-toluenesulfonic acid / phenol (the mass ratio of p-toluenesulfonic acid to phenol was 2:1) mixed solution was added at a solid-liquid ratio of 1:10, and the mixture was reacted in an ultrasonic water bath at a temperature of 70°C for 15 minutes;

[0037] S2. performing solid-liquid separation on the reactants to obtain residual pine wood particles and an extract;

[0038] S3. Under stirring conditions, the extract was slowly poured into water to precipitate the lignin, which was then allowed to stand and centrifuged, and then washed and dried to obtain light-colored phenolic lignin with a yield of 15.4% (relative to the material).

[0039] Compared with lignin extracted with p-toluenesulfonic acid alone (Comparative Example 1), the yield of the light-colored lignin is increased by 38.8%, the brightness (L) is increased from the original 35.5 to 86.1, the color difference (△E) is reduced from the original 67.1 to 19.2, the phenolic hydroxyl content is increased from the original 0.21 mmol / g to 0.40 mmol / g, and the aromatic ether bond is increased from the original 15 / 100Ar to 34 / 100Ar.

[0040] Example 2

[0041] S1. The pine wood chips were crushed into 40-60 mesh particles, and a pre-prepared 70% p-toluenesulfonic acid / phenol (the mass ratio of p-toluenesulfonic acid to phenol was 7:3) mixed solution was added at a solid-liquid ratio of 1:10, and the mixture was reacted in an ultrasonic water bath at a temperature of 70°C for 15 minutes;

[0042] S2. performing solid-liquid separation on the reactants to obtain residual pine wood particles and an extract;

[0043] S3. Under stirring conditions, slowly pour the extract into water to precipitate the lignin, let it stand, centrifuge it, and then wash and dry it to obtain light-colored phenolic lignin.

[0044] Compared with lignin extracted with p-toluenesulfonic acid alone (Comparative Example 1), the yield of the light-colored lignin increased by 73.2%, the brightness (L) increased by 91.3%, the color difference (△E) decreased by 48.2%, the phenolic hydroxyl content increased by 76.9%, and the aromatic ether bond increased by 85.2%.

[0045] Example 3

[0046] S1. The pine wood chips were crushed into 40-60 mesh particles, and a pre-prepared 70% p-toluenesulfonic acid / phenol (the mass ratio of p-toluenesulfonic acid to phenol was 2:1) mixed solution was added at a solid-liquid ratio of 1:10, and the mixture was reacted in an ultrasonic water bath at a temperature of 80°C for 15 minutes;

[0047] S2. performing solid-liquid separation on the reactants to obtain residual pine wood particles and an extract;

[0048] S3. Under stirring conditions, slowly pour the extract into water to precipitate the lignin, let it stand, centrifuge it, and then wash and dry it to obtain light-colored phenolic lignin.

[0049] Compared with lignin extracted with p-toluenesulfonic acid alone (Comparative Example 1), the yield of the light-colored lignin increased by 89.1%, the brightness (L) increased by 98.6%, the color difference (△E) decreased by 57.4%, the phenolic hydroxyl content increased by 83.3%, and the aromatic ether bond increased by 97.4%.

[0050] Example 4

[0051] S1. The pine wood chips were crushed into 40-60 mesh particles, and a pre-prepared 70% p-toluenesulfonic acid / guaiacol (the mass ratio of p-toluenesulfonic acid to guaiacol was 2:1) mixed solution was added at a solid-liquid ratio of 1:10, and the mixture was reacted in an ultrasonic water bath at a temperature of 80°C for 30 minutes;

[0052] S2. performing solid-liquid separation on the reactants to obtain residual pine wood particles and an extract;

[0053] S3. Under stirring conditions, slowly pour the extract into water to precipitate the lignin, let it stand, centrifuge it, and then wash and dry it to obtain light-colored phenolic lignin.

[0054] Compared with lignin extracted with p-toluenesulfonic acid alone (Comparative Example 1), the yield of the light-colored lignin increased by 53.9%, the brightness (L) increased by 75.6%, the color difference (△E) decreased by 42.8%, the phenolic hydroxyl content increased by 72.1%, and the aromatic ether bond increased by 65.2%.

[0055] Example 5

[0056] S1. The pine wood chips were crushed into 40-60 mesh particles, and a pre-prepared 70% p-toluenesulfonic acid / syringol (the mass ratio of p-toluenesulfonic acid to syringol was 7:3) mixed solution was added at a solid-liquid ratio of 1:10, and the mixture was reacted in an ultrasonic water bath at a temperature of 70°C for 15 minutes;

[0057] S3. Under stirring conditions, slowly pour the extract into water to precipitate the lignin, let it stand, centrifuge it, and then wash and dry it to obtain light-colored phenolic lignin.

[0058] Compared with lignin extracted with p-toluenesulfonic acid alone (Comparative Example 1), the yield of the light-colored lignin is increased by 71.4%, the brightness (L) is increased by 127.7%, the color difference (△E) is reduced by 64.6%, the phenolic hydroxyl content is increased by 76.2%, the aromatic ether bond is increased by 82.7%, and the methoxy content is increased by 227.8%.

[0059] Example 6

[0060] S1. The pine wood chips were crushed into 40-60 mesh particles, and a pre-prepared 80% benzenesulfonic acid / phenol (the mass ratio of benzenesulfonic acid to phenol was 2:1) mixed solution was added at a solid-liquid ratio of 1:10, and the mixture was reacted in an ultrasonic water bath at a temperature of 80°C for 15 minutes;

[0061] S2. performing solid-liquid separation on the reactants to obtain residual pine wood particles and an extract;

[0062] S3. Under stirring conditions, slowly pour the extract into water to precipitate the lignin, let it stand, centrifuge it, and then wash and dry it to obtain light-colored phenolic lignin.

[0063] Compared with lignin extracted with p-toluenesulfonic acid alone (Comparative Example 1), the yield of the light-colored lignin increased by 28.6%, the brightness (L) increased by 25.3%, the color difference (△E) decreased by 17.5%, the phenolic hydroxyl content increased by 34.7%, and the aromatic ether bond increased by 25.9%.

[0064] Example 7

[0065] S1. The pine wood chips were crushed into 40-60 mesh particles, and a pre-prepared 80% p-ethylbenzenesulfonic acid / phenol (the mass ratio of p-ethylbenzenesulfonic acid to phenol was 6.75:3.25) mixed solution was added at a solid-liquid ratio of 1:10, and the mixture was reacted in an ultrasonic water bath at a temperature of 80°C for 30 minutes;

[0066] S2. performing solid-liquid separation on the reactants to obtain residual pine wood particles and an extract;

[0067] S3. Under stirring conditions, slowly pour the extract into water to precipitate the lignin, let it stand, centrifuge it, and then wash and dry it to obtain light-colored phenolic lignin.

[0068] Compared with lignin extracted with p-toluenesulfonic acid alone (Comparative Example 1), the yield of the light-colored lignin increased by 18.56%, the brightness (L) increased by 59.2%, the color difference (△E) decreased by 37.3%, the phenolic hydroxyl content increased by 58.7%, and the aromatic ether bond increased by 43.8%.

[0069] Example 8

[0070] S1. The poplar wood chips were crushed into 40 mesh particles, and a pre-prepared 70% p-toluenesulfonic acid / phenol (the mass ratio of p-toluenesulfonic acid to phenol was 3:2) mixed solution was added at a solid-liquid ratio of 1:10, and the mixture was reacted in an ultrasonic water bath at a temperature of 70°C for 15 minutes;

[0071] S3. Under stirring conditions, slowly pour the extract into water to precipitate the lignin, let it stand, centrifuge it, and then wash and dry it to obtain light-colored phenolic lignin.

[0072] Compared with lignin extracted with p-toluenesulfonic acid alone (Comparative Example 1), the yield of the light-colored lignin increased by 47.7%, the brightness (L) increased by 97.0%, the color difference (△E) decreased by 61.4%, the phenolic hydroxyl content increased by 86.8%, and the aromatic ether bond increased by 73.5%.

[0073] Example 9

[0074] S1. The poplar wood chips were crushed into 40 mesh particles, and a pre-prepared 70% p-toluenesulfonic acid / syringol (the mass ratio of p-toluenesulfonic acid to syringol was 3:2) mixed solution was added at a solid-liquid ratio of 1:10, and the mixture was reacted in an ultrasonic water bath at a temperature of 80°C for 15 minutes;

[0075] S3. Under stirring conditions, slowly pour the extract into water to precipitate the lignin, let it stand, centrifuge it, and then wash and dry it to obtain light-colored phenolic lignin.

[0076] Compared with lignin extracted with p-toluenesulfonic acid alone (Comparative Example 1), the yield of the light-colored lignin is increased by 65.3%, the brightness (L) is increased by 39.9%, the color difference (△E) is reduced by 19.8%, the phenolic hydroxyl content is increased by 21.1%, the aromatic ether bond is increased by 41.5%, and the methoxy content is increased by 136.4%.

[0077] Example 10

[0078] S1. The bamboo chips were crushed into 40-60 mesh particles, and a pre-prepared 80% p-toluenesulfonic acid / phenol (the mass ratio of p-toluenesulfonic acid to phenol was 7:3) mixed solution was added at a solid-liquid ratio of 1:10, and the reaction was carried out in an ultrasonic water bath at a temperature of 80°C for 45min;

[0079] S3. Under stirring conditions, slowly pour the extract into water to precipitate the lignin, let it stand, centrifuge it, and then wash and dry it to obtain light-colored phenolic lignin.

[0080] Compared with lignin extracted with p-toluenesulfonic acid alone (Comparative Example 1), the yield of the light-colored lignin increased by 44.6%, the brightness (L) increased by 57.2%, the color difference (△E) decreased by 42.8%, the phenolic hydroxyl content increased by 69.3%, and the aromatic ether bond increased by 62.2%.

[0081] Comparative Example 1: Lignin extracted with p-toluenesulfonic acid alone

[0082] S1. The pine wood chips were crushed into 40-60 mesh particles, and a pre-prepared 70% p-toluenesulfonic acid solution was added at a solid-liquid ratio of 1:10, and the reaction was carried out in an ultrasonic water bath at a temperature of 70°C for 15 minutes;

[0083] S2. performing solid-liquid separation on the reactants to obtain residual pine wood particles and an extract;

[0084] S3. Under stirring conditions, the extract was slowly poured into water to precipitate lignin, and the mixture was allowed to stand, centrifuged, washed, and dried to obtain lignin with a yield of 11.1% (relative to the material).

[0085] The lignin has a brightness (L) of 35.5, a color difference (ΔE) of 67.1, a phenolic hydroxyl content of 0.21 mmol / g, and an aromatic ether bond of 15 / 100 Ar.

[0086] Comparative Example 2 Lignin extracted with phenol alone

[0087] S1. The pine wood chips were crushed into 40-60 mesh particles, and a pre-prepared 70% phenol solution was added at a solid-liquid ratio of 1:10, and the mixture was reacted in an ultrasonic water bath at a temperature of 70°C for 15 minutes;

[0088] S2. performing solid-liquid separation on the reactants to obtain residual pine wood particles and an extract;

[0089] S3. Under stirring conditions, the extract is slowly poured into water to precipitate the lignin, which is then allowed to stand and centrifuged, and then washed and dried to obtain lignin. The lignin yield of this method is extremely low. Due to the high freezing point of phenol, lignin separation is difficult and the feasibility is low.

[0090] From the comparison between Example 1 and Comparative Examples 1 and 2, it can be seen that the present invention effectively improves the extraction efficiency of light-colored phenolic lignin with high reactivity through the combined action of aromatic sulfonic acid and phenolic compounds.

[0091] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for extracting light-colored phenolic lignin, characterized in that: include: The lignocellulose raw material is uniformly mixed with a mixed solution of aromatic sulfonic acid and phenolic compounds, subjected to ultrasonic treatment, solid-liquid separation, and the extract is collected; The extract is poured into water to precipitate the lignin, and then washed and dried to obtain the product.

2. The method for extracting light-colored phenolic lignin according to claim 1, characterized in that: The aromatic sulfonic acid is selected from at least one of benzenesulfonic acid, p-toluenesulfonic acid and p-ethylbenzenesulfonic acid.

3. The method for extracting light-colored phenolic lignin according to claim 1, characterized in that: The phenolic compound is selected from at least one of phenol, guaiacol and syringol.

4. The method for extracting light-colored phenolic lignin according to claim 1, characterized in that: In the mixed liquid medicine, the total mass fraction of aromatic sulfonic acid and phenolic compounds is 5% to 95%, or 50% to 80%.

5. The method for extracting light-colored phenolic lignin according to claim 1, characterized in that: The mass ratio of the aromatic sulfonic acid to the phenolic compound is 9:1 to 2:8, or 8:2 to 5:

5.

6. The method for extracting light-colored phenolic lignin according to claim 1, characterized in that: The solid-liquid ratio of the lignocellulose raw material to the mixed liquid medicine is 1:1-50, or 1:1-20.

7. The method for extracting light-colored phenolic lignin according to claim 1, characterized in that: The ultrasonic treatment temperature is 25-100°C, or 50-90°C; Alternatively, the ultrasonic treatment time is 5 to 120 min, or 10 to 60 min.

8. The method for extracting light-colored phenolic lignin according to claim 1, characterized in that: The lignocellulosic raw material is at least one of hardwood, softwood or non-wood; Or, the broadleaf wood is poplar and / or eucalyptus; Or, the coniferous wood is pine and / or masson pine; Alternatively, the non-wood material is at least one of bamboo, bagasse, and corn stalks.

9. Light-colored phenolic lignin prepared by the method according to any one of claims 1 to 8.

10. Use of the light-colored phenolic lignin according to claim 9 in UV protection products, special rubbers, and dye dispersants.