A method for preparing highly chemically reactive lignin

Abstract

This invention provides a method for preparing highly chemically reactive lignin, belonging to the field of biomass refining. The method includes: S1. Mixing lignocellulosic raw materials with an aromatic phenol solution containing a ferric chloride catalyst at a certain solid-liquid ratio, and reacting fully at a certain temperature and pH value; S2. After the reaction is complete, separating the solid and liquid phases to obtain an extract; S3. Concentrating, purifying, and drying the extract to obtain highly chemically reactive lignin. Compared with existing technologies, this invention utilizes biomass raw materials to directly obtain highly chemically reactive lignin through a one-step separation process. The process is simple and solves the problems of low chemical reactivity and low functional group content in existing industrial lignin, allowing it to be used in the production of lignin-based products without further activation.

Description

Technical Field

[0001] This invention belongs to the field of biomass refining, and specifically provides a method for preparing highly chemically reactive lignin. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] Lignocellulosic biomass feedstocks mainly consist of three components: cellulose, hemicellulose, and lignin, and are among the most abundant renewable resources on Earth. Lignin is one of the most abundant polymers in nature, containing a large number of aromatic compounds. It is generally considered an underutilized byproduct of pulp and paper production or second-generation ethanol plants, primarily used as an energy source for boilers. However, with technological advancements and the rapid development of the bioeconomy, how to more effectively separate lignin from lignocellulosic feedstocks and further utilize it to prepare high-value biomaterials, biochemicals, and biofuels is an urgent issue to be addressed.

[0004] Lignin with different functional groups (carboxyl, hydroxyl, amino, sulfonic acid, etc.) can have its chemical reactivity greatly enhanced. Depending on the functional groups, it can be used to prepare lignin-based materials with different functionalities, which is the primary pathway for the high-value utilization of lignin. However, currently, lignin obtained through the separation of wood fiber raw materials typically contains only small amounts of carboxyl and hydroxyl groups. To obtain lignin with abundant specific functional groups, chemical modification of the lignin is necessary. Therefore, lignin with low chemical reactivity has become a bottleneck restricting the high-quality utilization of lignin.

[0005] Lignin requires a series of complex chemical reactions to be separated from biomass feedstocks, mainly involving the breaking of ether bonds and the formation of new carbon-carbon bonds. The inventor's previous patent CN111958730A disclosed a method for inhibiting lignin condensation, but its phenolic modification efficiency still needs improvement. Summary of the Invention

[0006] To address the problem of low lignin activity and difficulty in its utilization, this invention provides a method for preparing highly chemically reactive lignin with significantly increased phenolic hydroxyl content. In this invention, an acidic solution system containing aromatic phenols and a ferric chloride catalyst allows ferric ions to form a ligand complex with the aromatic phenols. This complex, acting as a highly active nucleophilic aromatic group, reacts with intermediates in the lignin degradation and removal process. During this process, the strongly nucleophilic aromatic phenol complex replaces the dissolved lignin fragments to react with the active intermediates of the lignin molecule, generating new carbon-carbon bonds and obtaining in-situ phenolically modified lignin, resulting in a lignin product with a high phenolic hydroxyl content and a low relative molecular mass.

[0007] The reaction system of this invention achieves good lignin removal efficiency and has strong raw material adaptability, including both wood and non-wood raw materials.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides a method for preparing highly chemically reactive lignin, comprising:

[0010] The lignocellulose raw material is mixed with an aromatic phenol solution containing ferric chloride and reacted at a certain temperature and pH value. After the reaction is completed, the solid and liquid are separated to obtain the extract.

[0011] The extract was concentrated, purified, and dried to obtain highly chemically reactive lignin.

[0012] This invention starts from the very beginning of lignin production. While the ether bonds in lignin break, aromatic phenols replace the degraded lignin molecular fragments, thereby generating carbon-carbon bonds with the lignin. As the lignin degrades and dissolves, aromatic phenols are grafted onto it, significantly increasing the content of phenolic hydroxyl groups in the lignin structure and yielding highly active lignin. This addresses the problem of low lignin activity at its source, providing a new model for the high-value utilization of lignin.

[0013] In some embodiments, the solid-liquid ratio of the wood fiber raw material to the aromatic phenol solution containing ferric chloride catalyst is 1:1-50, preferably 1:(5-20), and particularly preferably 1:(5-15).

[0014] In some embodiments, the aromatic phenol solution containing the ferric chloride catalyst has an aromatic phenol mass fraction of 0.1%-80%, preferably 1%-30%, and particularly preferably 1%-15%.

[0015] In some embodiments, the mass fraction of ferric chloride in the aromatic phenol solution containing the ferric chloride catalyst is 0.1-10%.

[0016] In some embodiments, the aromatic phenol is one or a combination of diphenols and polyphenols.

[0017] In some embodiments, the aromatic phenol is selected from at least one of catechol, resorcinol, pyrogallol, and phlorogallol.

[0018] In some embodiments, the reaction temperature is 80-200°C, preferably 100-180°C, and particularly preferably 120-150°C.

[0019] In some embodiments, the reaction time is 1-500 min, preferably 30-180 min, and particularly preferably 60-120 min.

[0020] In some embodiments, the reaction pH is 0.1-3, preferably 0.5-2, and particularly preferably 1-1.5.

[0021] It should be noted that this application does not impose any specific limitations on the purification method for lignin. Any lignin purification method known to those skilled in the art can be used to concentrate and purify the lignin to obtain highly chemically reactive lignin. For example, after evaporating and concentrating the extract, the concentrate can be purified and dried using tetrahydrofuran and diethyl ether to obtain a highly chemically reactive product.

[0022] In some embodiments, the wood fiber raw material is any one of broadleaf wood, coniferous wood, or non-wood. Broadleaf wood, such as poplar, eucalyptus, pine, bamboo, etc., is preferred.

[0023] In a second aspect, the present invention provides a highly chemically reactive lignin prepared by the above-described method.

[0024] A third aspect of the present invention provides the use of the above-described highly chemically reactive lignin in the preparation of biomaterials, biochemicals, or biofuels.

[0025] Beneficial effects of the present invention

[0026] (1) The multi-component reaction in the cooking process of this invention allows the lignin in the wood fiber raw material to be degraded and de-ligninized while being grafted and modified by aromatic phenols. The one-step separation process directly obtains highly chemically reactive lignin with a high content of phenolic hydroxyl groups.

[0027] (2) The phenolic hydroxyl content in the highly chemically reactive lignin obtained by this invention is relatively high, and the reactivity is significantly improved, which is conducive to the comprehensive, effective and high-value utilization of lignocellulose biomass.

[0028] (3) The preparation process of this invention is simple, the solvent is easy to recycle and reuse, and there is no secondary pollution.

[0029] (4) In the acidic solution system containing aromatic phenols and ferric chloride catalyst, ferric ions will form ligand complexes with aromatic phenols. These complexes, as active nucleophilic aromatic groups, will react with intermediates in the lignin degradation and removal process. During this process, the strongly nucleophilic aromatic phenol complexes replace the dissolved lignin fragments to react with the active intermediates of the lignin molecule, generating new carbon-carbon bonds, obtaining in-situ phenolically modified lignin, and yielding lignin products with high phenolic hydroxyl content and low relative molecular mass.

[0030] The reaction system of this invention achieves good lignin removal efficiency and has strong raw material adaptability, including both wood and non-wood raw materials. Detailed Implementation

[0031] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0032] The present invention will be further described in detail below with reference to specific embodiments. It should be noted that the specific embodiments are explanations of the present invention and not limitations thereof.

[0033] Unless otherwise specified, the content of each ingredient used below is a percentage by mass.

[0034] In this embodiment, poplar wood powder was used as the lignocellulose raw material, and pine wood powder and bamboo powder were used for parallel control experiments. The yield of lignin was determined by gravimetric method, and the removal rate was calculated accordingly. The content of phenolic hydroxyl groups in lignin was determined by nuclear magnetic resonance phosphorus spectroscopy.

[0035] Example 1

[0036] S1. Mix poplar powder with water at a mass-to-volume ratio of 1:10 (g / mL), adjust the pH to 1, and keep the mixture at 130℃ for 90 min to obtain the extract and residual solid cellulose.

[0037] S2. The extract was concentrated by rotary evaporation at 40°C. The concentrate was dissolved in tetrahydrofuran, and insoluble matter was removed by centrifugation. The supernatant was further concentrated by vacuum rotary evaporation. The obtained concentrate was added dropwise to diethyl ether for precipitation. The precipitate solid was obtained by centrifugation and was purified lignin.

[0038] The lignin removal rate was 5.32%. The phenolic hydroxyl content of the sample was determined, and the phenolic hydroxyl content of the highly chemically reactive lignin was found to be 2.30 mmol / g.

[0039] Example 2

[0040] S1. Poplar powder was mixed with the cooking liquid at a mass-to-volume ratio of 1:10 (g / mL), the pH was adjusted to 1, and ferric chloride was added at 1% (mass fraction of the solution). The mixture was kept at 130℃ for 90 min to obtain the extract and residual solid cellulose. The cooking liquid was a mixture of water and catechol at a volume ratio of 20:1.

[0041] S2. The extract was concentrated by rotary evaporation at 40°C. The concentrate was dissolved in tetrahydrofuran, and insoluble matter was removed by centrifugation. The supernatant was further concentrated by vacuum rotary evaporation. The obtained concentrate was added dropwise to diethyl ether for precipitation. The precipitate solid was obtained by centrifugation and was purified to obtain a highly chemically reactive solid.

[0042] The lignin removal rate was 9.05%. The phenolic hydroxyl content of the sample was determined, and the phenolic hydroxyl content of the highly chemically reactive lignin was found to be 5.12 mmol / g.

[0043] Example 3

[0044] S1. Poplar wood powder was mixed with the cooking liquid at a mass-to-volume ratio of 1:10 (g / mL), the pH was adjusted to 1, and ferric chloride was added at 1% (mass fraction of the solution). The mixture was kept at 130℃ for 90 min to obtain the extract and residual solid cellulose. The cooking liquid was a mixture of water and catechol at a volume ratio of 10:1.

[0045] S2. The extract was concentrated by rotary evaporation at 40°C. The concentrate was dissolved in tetrahydrofuran, and insoluble matter was removed by centrifugation. The supernatant was further concentrated by vacuum rotary evaporation. The obtained concentrate was added dropwise to diethyl ether for precipitation. The precipitate solid was obtained by centrifugation and was purified to obtain a highly chemically reactive solid.

[0046] The lignin removal rate was 15.25%. The phenolic hydroxyl content of the sample was determined, and the phenolic hydroxyl content of the highly chemically reactive lignin was found to be 8.20 mmol / g.

[0047] Example 4

[0048] S1. Poplar wood powder was mixed with the cooking liquid at a mass-to-volume ratio of 1:10 (g / mL), the pH was adjusted to 1, and ferric chloride was added at 1% (mass fraction of the solution). The mixture was kept at 130℃ for 90 min to obtain the extract and residual solid cellulose. The cooking liquid was a mixture of water and resorcinol at a volume ratio of 10:1.

[0049] S2. The extract was concentrated by rotary evaporation at 40°C. The concentrate was dissolved in tetrahydrofuran, and insoluble matter was removed by centrifugation. The supernatant was further concentrated by vacuum rotary evaporation. The obtained concentrate was added dropwise to diethyl ether for precipitation. The precipitate solid was obtained by centrifugation and was purified to obtain a highly chemically reactive solid.

[0050] The lignin removal rate was 20.45%. The phenolic hydroxyl content of the sample was determined, and the phenolic hydroxyl content of the highly chemically reactive lignin was found to be 10.30 mmol / g.

[0051] Example 5

[0052] S1. Poplar wood powder was mixed with the cooking liquid at a mass-to-volume ratio of 1:10 (g / mL), the pH was adjusted to 1, and ferric chloride was added at 1% (mass fraction of the solution). The mixture was kept at 130℃ for 90 min to obtain the extract and residual solid cellulose. The cooking liquid was a mixture of water and phloroglucinol at a volume ratio of 10:1.

[0053] S2. The extract was concentrated by rotary evaporation at 40°C. The concentrate was dissolved in tetrahydrofuran, and insoluble matter was removed by centrifugation. The supernatant was further concentrated by vacuum rotary evaporation. The obtained concentrate was added dropwise to diethyl ether for precipitation. The precipitate solid was obtained by centrifugation and was purified to obtain a highly chemically reactive solid.

[0054] The lignin removal rate was as high as 19.32%. The phenolic hydroxyl content of the sample was determined, and the phenolic hydroxyl content of the highly chemically reactive lignin was found to be 12.20 mmol / g.

[0055] Example 6

[0056] The steps are the same as in Implementation Case 5, except that no ferric chloride catalyst is added.

[0057] The lignin removal rate was 6.43%. The phenolic hydroxyl content of the sample was determined, and the phenolic hydroxyl content of the highly chemically reactive lignin was found to be 4.36 mmol / g.

[0058] As can be seen from Examples 5 and 6, compared with simply using aromatic phenols as cooking agents, the strongly nucleophilic aromatic phenol complex formed by trivalent iron ions and aromatic phenols can better phenolicly modify lignin, resulting in lignin products with higher phenolic hydroxyl content.

[0059] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing highly chemically reactive lignin, characterized in that, include: The wood fiber raw material is mixed with an aromatic phenol solution containing ferric chloride catalyst and reacted at a certain temperature and pH value. After the reaction is completed, the solid and liquid are separated to obtain the extract. The extract was concentrated, purified, and dried to obtain highly chemically reactive lignin. The aromatic phenol is selected from at least one of catechol, resorcinol, pyrogallol, and phlorogallol; The lignin in the wood fiber raw material is grafted with aromatic phenols to obtain in-situ phenolically modified lignin.

2. The method for preparing highly chemically reactive lignin as described in claim 1, characterized in that, The solid-liquid ratio of the wood fiber raw material to the aromatic phenol solution containing ferric chloride catalyst is 1:1-50.

3. The method for preparing highly chemically reactive lignin as described in claim 1, characterized in that, The aromatic phenol solution containing ferric chloride catalyst has an aromatic phenol mass fraction of 0.1%-80%.

4. The method for preparing highly chemically reactive lignin as described in claim 1, characterized in that, In the aromatic phenol solution containing ferric chloride catalyst, the mass fraction of ferric chloride is 0.1-10%.

5. The method for preparing highly chemically reactive lignin as described in claim 1, characterized in that, The reaction temperature is 80-200℃; Alternatively, the reaction time is 1-500 min; Alternatively, the reaction pH value is 0.1-3.

6. The method for preparing highly chemically reactive lignin as described in claim 1, characterized in that, The wood fiber raw material is any one of broadleaf wood, coniferous wood, or non-wood.

7. The highly chemically reactive lignin prepared by the method according to any one of claims 1-6.

8. The application of the highly chemically reactive lignin according to claim 7 in the preparation of biomaterials.

9. The application of the highly chemically reactive lignin according to claim 7 in the preparation of biochemicals.

10. The application of the highly chemically reactive lignin according to claim 7 in the preparation of biofuels.