Method for forming low-condensation lignin in acidic pretreatment process
By adding the hydroxyl-containing green additive mannitol during the acid pretreatment process, the lignin structure is stabilized and its condensation reaction is inhibited, the problem of lignin self-condensation in an acidic environment is solved, and the separation efficiency and application prospects of lignin are improved.
Patent Information
- Application Number
- CN202510155278.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-02-12
- Publication Date
- 2025-05-13
AI Technical Summary
During the acid pretreatment process, lignin is prone to self-condensation reaction, which limits the monomer yield and separation efficiency after lignin decomposition, and affects the accessibility of biological enzymatic treatment.
By adding the hydroxyl-containing green additive mannitol during the acid pretreatment process, the lignin structure is stabilized and its hydrophilicity is improved, thereby inhibiting the condensation reaction of lignin.
It has achieved effective inhibition of lignin self-condensation reaction on the basis of ensuring high dissolution efficiency of lignin, improved the high-quality conversion efficiency of lignin, and improved its application prospects.
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Figure CN119978427A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to the technical field of high-value utilization of wood fiber biomass, in particular to a method for forming low-condensation lignin in an acid pretreatment process. Background Art
[0002] The acidic catalytic system of wood fiber provides good value for the comprehensive utilization of biomass. However, the repolymerization of lignin in an acidic environment will have an adverse effect on the high-value conversion of lignin.
[0003] The main means is to effectively disassemble wood fiber biomass macromolecules (cellulose, hemicellulose and lignin) by using effective biomass pretreatment technology (acid, alkali, organic solvent, organic acid, deep eutectic solvent (DES) and ionic liquid (ILs), etc.). Among the main biomass macromolecules, lignin is a natural high molecular polymer with a variety of functional group structures, which is conducive to chemical modification and can be used to prepare a variety of energy chemicals. The comprehensive utilization of lignin is of great help to the development of a low-carbon economy. However, in the process of pretreatment reaction, due to the formation of carbon cations, the lignin separation and dissolution process is usually accompanied by inevitable self-condensation (CC bond condensation), which greatly limits the monomer yield and separation efficiency after lignin decomposition, especially the deposition of condensed structure lignin on the surface of wood fiber, which affects the accessibility of biological enzymatic hydrolysis. However, as a common functional group, hydroxyl can effectively improve the hydrophilicity of organic compounds. At the same time, whether there is a stable interaction between hydroxyl and lignin structure in theory, the inhibition of carbon cation formation cannot be ignored, which needs further study. Therefore, it is very necessary to effectively inhibit the self-condensation reaction of lignin on the basis of ensuring high lignin dissolution efficiency, so as to find out the key factors affecting the lignin condensation phenomenon and then establish a method for regulating the lignin condensation reaction. This will help improve the high-quality conversion efficiency of lignin and enhance the broad application prospects of lignin.
[0004] Therefore, finding a method to prepare low-condensation lignin is the current key research direction. Summary of the invention
[0005] In order to solve the above technical problems existing in the prior art, the present invention provides a method for forming low-condensation lignin during acid pretreatment.
[0006] A method for forming low-condensation lignin during an acid pretreatment process comprises the following steps:
[0007] (1) Air-dry the cleaned wood;
[0008] (2) taking the absolutely dry sawdust of step (1), soaking it in distilled water and adding green additives, and then placing it in a high-temperature and high-pressure reactor for reaction; separating the hydrolysis product and the remaining solid after the reaction, filtering to remove insoluble particles, and refrigerating the hydrolyzate; washing the remaining solid residue with distilled water until it is neutral, and then air-drying it for storage;
[0009] Taking the clarified hydrolyzate obtained in step (2), determining the contents of glucose and xylose in the hydrolyzate by ion chromatography, determining the content of lignin by ultraviolet spectroscopy, and calculating that the separation yield of hemicellulose is 74.51%-83.63%, the separation yield of lignin is 7.2%-12.5%, and the separation yield of cellulose is 13.1%-18.2%;
[0010] (3) The remaining solid residue obtained in step (2) is ball-milled using a zirconia ball mill; then, the ball-milled sample is placed in dioxane / water, stirred at 35° C., and treated in the dark for 30 hours; after treatment, the mixture is filtered, and the process is performed three times; the collected filtrate is freeze-dried to obtain crude lignin; the obtained crude lignin is added to acetic acid / water, and then the solution is poured into water and stirred, the suspension is centrifuged, the obtained lignin is added to ethanol / 1,2-dichloroethane and mixed, and then precipitated in ether; after precipitation in ether, the mixture is centrifuged, the induced lignin is washed with petroleum ether, and the collected sample is freeze-dried.
[0011] The lignin sample obtained in step (3) was dissolved in 400 μL of a mixed solution of anhydrous pyridine and deuterated chloroform (1.6 / 1, v / v). Then, N-hydroxy-5-norbornene-2,3-diimide (7.3 mg ml -1 ) and chromium(III) acetylacetonate (3.6 mg mL -1 ) was added to the mixed solution as an internal standard and relaxation agent; then 100 μL of phosphating agent (2-chloro-4,4,5,5-tetramethyl-1,3,2-dioxaphosphine-tetramethyl-1,3,2-dioxaphosphine, TMDP) was added; the above solution was added to a 5mm NMR tube and reacted for 5 minutes. The hydroxyl content of lignin increased by 57.4% after adding the green additive.
[0012] Take 40 mg of the lignin sample obtained in step (3) and dissolve it in 0.5 mL of DMSO-d6 solution. Transfer the solution to a 5 mm diameter NMR tube. The β-O-4 bond content of the lignin after adding the green additive was determined to be 53 / 100 aromatic units. Up to 47.12% of the β-O-4 bonds were retained.
[0013] Furthermore, the wood in step (1) is poplar.
[0014] Furthermore, the wood in step (1) is air-dried and then placed in a sealed bag for storage to balance moisture for future use.
[0015] Furthermore, the green additive is the hydroxyl-containing green additive mannitol.
[0016] Furthermore, the reaction conditions of step (2) are as follows: solid-liquid ratio is 1:10 (g:ml), in 5% H 2 SO 4 The concentration and reaction temperature are 120℃-160℃ and the reaction time is 30min-60min.
[0017] Furthermore, the filtration in step (2) is performed using a 0.45 μm organic filter membrane.
[0018] Furthermore, the ball milling in step (3) is performed at a speed of 1000 rap / min for 96 hours, with positive and negative pressures applied every 30 minutes.
[0019] Furthermore, in the step (3), the specific ratio of dioxane to water is 9 / 1, v / v, and the mixture is stirred at 35° C. and treated in the dark for 30 hours.
[0020] Furthermore, the step (3) is specifically to add the obtained crude lignin to acetic acid / water (9 / 1, v / v), then pour the solution into water and stir for 40 minutes, centrifuge the suspension at 12000 rpm for 8 minutes, add the obtained lignin to ethanol / 1,2-dichloroethane (1 / 2, v / v) and mix for 1 hour, and then precipitate in 150 mL of ether.
[0021] Furthermore, in step (3), after precipitation in ether and centrifugation at 12000 rpm for 8 min, the induced lignin is washed three times with petroleum ether, and the collected samples are freeze-dried.
[0022] Compared with the prior art, the technical effects created by the present invention are embodied in:
[0023] (1) The present invention is a method for preparing low-condensation lignin, which utilizes the technology of adding hydroxyl-containing green additives during acid pretreatment to achieve a stabilizing effect on the lignin structure, and utilizes the pretreatment method to promote the effective separation of hemicellulose while preventing the condensation reaction of lignin by improving the hydrophilicity of lignin to obtain low-condensation lignin. The hydroxyl groups in the low-condensation lignin structure are generally suitable for the synthesis of new materials.
[0024] (2) The interaction between hydroxyl-containing green additives and lignin can reduce the condensation phenomenon of lignin. Especially in the initial stage of the reaction, the interaction between hydroxyl-containing green additives and lignin cannot be ignored. The scheme of the present invention is aimed at the problem of lignin degradation and repolymerization in an acidic pretreatment environment. By introducing green additives to stabilize the lignin structure, the degradation and repolymerization of lignin during acidic pretreatment are inhibited. The law between the structure of green additives and the anti-condensation phenomenon of lignin is revealed, that is, the strong hydrogen bonding effect and obvious π-π conjugation phenomenon between green additives and the α-hydroxyl group of the lignin branched structure are closely related to the reduction of lignin condensation phenomenon.
[0025] (3) The present invention provides a new insight into the fundamental mechanism of the hydroxyl-containing green additive-assisted pretreatment process, opening up new opportunities for realizing valuable aromatic products from lignin and promoting the industrial economic viability of lignocellulosic biomass. BRIEF DESCRIPTION OF THE DRAWINGS
[0026] Figure 1 It is a reaction schematic diagram of the present invention. DETAILED DESCRIPTION
[0027] The technical solution of the present invention is further defined below in conjunction with specific implementation methods, but the scope of protection required is not limited to the description.
[0028] Example 1
[0029] The present invention provides a method for preparing low-condensation lignin. The present invention utilizes the technology of adding hydroxyl-containing green additives during acid pretreatment to achieve a stabilizing effect on the lignin structure, and utilizes the pretreatment method to improve the hydrophilicity of lignin to prevent the condensation reaction of lignin to obtain low-condensation lignin while promoting the separation efficiency of hemicellulose.
[0030] The specific implementation process is:
[0031] (1) The washed poplar wood needs to be air-dried. After being air-dried, the poplar wood is stored in a sealed bag to balance the moisture for future use.
[0032] (2) Take 20 g of the dry mass of poplar wood chips obtained in step (1), soak them in 200 mL of distilled water and add the green additive mannitol, then put them into a high-temperature and high-pressure reactor with a solid-liquid ratio of 1:10 (g:ml) and heat them in 5% H 2 SO 4 The concentration was 1.5 and the reaction temperature was 120°C for 30 min. After the reaction, the hydrolyzate and the remaining solid were separated, and the insoluble particles were removed by filtration with a 0.45 μm organic filter membrane. The hydrolyzate was refrigerated at 3°C. The remaining solid residue was washed with distilled water until neutral and then air-dried for storage.
[0033] (3) Taking the clarified hydrolyzate obtained in step (2), determining the contents of glucose and xylose in the hydrolyzate by ion chromatography, and determining the content of lignin by ultraviolet spectroscopy, the separation yield of hemicellulose is calculated to be 54.51%-63.63%, the separation yield of lignin is 4.2%-8.5%, and the separation yield of cellulose is 13.1%-18.2%.
[0034] (4) Take the remaining solid residue obtained in step (2) and take 30g of wood powder. Use a zirconia ball mill to ball mill for 96h at a speed of 1000rap / min. Perform positive and negative pressure every 30min. Then, 25g of the ball-milled sample is stirred at 35°C in 500mL of dioxane / water (9 / 1, v / v) and treated in the dark for 30h. After treatment, the mixture is filtered, and the process is performed three times. The collected filtrate is freeze-dried to obtain crude lignin. The obtained lignin is added to 40mL of acetic acid / water (9 / 1, v / v), and then the solution is poured into 400mL of water and stirred for 40min. The suspension is centrifuged at 12000rpm for 8min, and the obtained lignin is added to 10mL of ethanol / 1,2-dichloroethane (1 / 2, v / v) and mixed for 1h, and then precipitated in 150mL of ether. After centrifugation at 12000 rpm for 8 min, the induced lignin was washed three times with 80 mL of petroleum ether, and the collected samples were freeze-dried.
[0035] (5) Take 15 mg of the lignin sample obtained in step (4) and dissolve it in 400 μL of a mixed solution of anhydrous pyridine and deuterated chloroform (1.6 / 1, v / v). Then, add N-hydroxy-5-norbornene-2,3-diimide (7.3 mg ml -1 ) and chromium(III) acetylacetonate (3.6 mg mL -1 ) was added to the mixed solution as an internal standard and relaxation agent. Then 100 μL of phosphating agent (2-chloro-4,4,5,5-tetramethyl-1,3,2-dioxophosphine-tetramethyl-1,3,2-dioxophosphine, TMDP) was added. The above solution was added to a 5 mm NMR tube and reacted for 5 minutes. It was determined that the hydroxyl content of lignin increased by 17.4% after adding the green additive mannitol.
[0036] (6) Take 40 mg of the lignin sample obtained in step (4) and dissolve it in 0.5 mL of DMSO-d6 solution. Transfer the solution to a 5 mm diameter NMR tube. The β-O-4 bond content of the lignin after adding the green additive mannitol was measured to be 33 / 100 aromatic units. Up to 27.12% of the β-O-4 bonds were retained.
[0037] Example 2
[0038] The present invention provides a method for preparing low-condensation lignin. The present invention utilizes the technology of adding hydroxyl-containing green additives during acid pretreatment to achieve a stabilizing effect on the lignin structure, and utilizes the pretreatment method to improve the hydrophilicity of lignin to prevent the condensation reaction of lignin to obtain low-condensation lignin while promoting the separation efficiency of hemicellulose.
[0039] The specific implementation process is:
[0040] (1) The washed poplar wood needs to be air-dried. After being air-dried, the poplar wood is stored in a sealed bag to balance the moisture for future use.
[0041] (2) Take 20 g of the dry mass of poplar wood chips obtained in step (1), soak them in 200 mL of distilled water and add the green additive mannitol, then put them into a high-temperature and high-pressure reactor with a solid-liquid ratio of 1:10 (g:ml) and heat them in 5% H 2 SO 4 The concentration was 1000 μg / mL and the reaction temperature was 140°C for 40 min. After the reaction, the hydrolyzate and the remaining solid were separated and filtered with a 0.45 μm organic filter membrane to remove insoluble particles. The hydrolyzate was refrigerated at 3°C. The remaining solid residue was washed with distilled water until neutral and then air-dried for storage.
[0042] (3) Taking the clarified hydrolyzate obtained in step (2), determining the contents of glucose and xylose in the hydrolyzate by ion chromatography, and determining the content of lignin by ultraviolet spectroscopy, the separation yield of hemicellulose is calculated to be 64.51%-73.63%, the separation yield of lignin is 5.2%-9.5%, and the separation yield of cellulose is 15.1%-19.2%.
[0043] (4) Take the remaining solid residue obtained in step (2) and take 30g of wood powder. Use a zirconia ball mill to ball mill for 96h at a speed of 1000rap / min. Perform positive and negative pressure every 30min. Then, 25g of the ball-milled sample is stirred at 35°C in 500mL of dioxane / water (9 / 1, v / v) and treated in the dark for 30h. After treatment, the mixture is filtered, and the process is performed three times. The collected filtrate is freeze-dried to obtain crude lignin. The obtained lignin is added to 40mL of acetic acid / water (9 / 1, v / v), and then the solution is poured into 400mL of water and stirred for 40min. The suspension is centrifuged at 12000rpm for 8min, and the obtained lignin is added to 10mL of ethanol / 1,2-dichloroethane (1 / 2, v / v) and mixed for 1h, and then precipitated in 150mL of ether. After centrifugation at 12000 rpm for 8 min, the induced lignin was washed three times with 80 mL of petroleum ether, and the collected samples were freeze-dried.
[0044] (5) Take 15 mg of the lignin sample obtained in step (4) and dissolve it in 400 μL of a mixed solution of anhydrous pyridine and deuterated chloroform (1.6 / 1, v / v). Then, add N-hydroxy-5-norbornene-2,3-diimide (7.3 mg ml -1 ) and chromium(III) acetylacetonate (3.6 mg mL -1 ) was added to the mixed solution as an internal standard and relaxation agent. Then 100 μL of phosphating agent (2-chloro-4,4,5,5-tetramethyl-1,3,2-dioxophosphine-tetramethyl-1,3,2-dioxophosphine, TMDP) was added. The above solution was added to a 5 mm NMR tube and reacted for 5 minutes. It was determined that the hydroxyl content of lignin increased by 27.4% after adding the green additive mannitol.
[0045] (6) Take 40 mg of the lignin sample obtained in step (4) and dissolve it in 0.5 mL of DMSO-d6 solution. Transfer the solution to a 5 mm diameter NMR tube. The β-O-4 bond content of the lignin after adding the green additive mannitol was measured to be 43 / 100 aromatic units. Up to 37.12% of the β-O-4 bonds were retained.
[0046] Example 3
[0047] The present invention provides a method for preparing low-condensation lignin. The present invention utilizes the technology of adding a hydroxyl-containing green additive mannitol during an acidic pretreatment process to achieve a stabilizing effect on the lignin structure. The pretreatment method is used to improve the hydrophilicity of lignin to prevent the condensation reaction of lignin to obtain low-condensation lignin while promoting the separation efficiency of hemicellulose.
[0048] The specific implementation process is:
[0049] (1) The washed poplar wood needs to be air-dried. After being air-dried, the poplar wood is stored in a sealed bag to balance the moisture for future use.
[0050] (2) Take 20 g of the dry mass of poplar wood chips obtained in step (1), soak them in 200 mL of distilled water and add the green additive mannitol, then put them into a high-temperature and high-pressure reactor with a solid-liquid ratio of 1:10 (g:ml) and heat them in 5% H 2 SO 4 The concentration and reaction temperature are 120℃-160℃ for 30min-60min. After the reaction, the hydrolyzate and the remaining solid are separated, and the insoluble particles are removed by filtration with a 0.45μm organic filter membrane. The hydrolyzate is refrigerated at 3℃. The remaining solid residue is washed with distilled water until it is neutral and then air-dried for storage.
[0051] (3) Taking the clarified hydrolyzate obtained in step (2), determining the contents of glucose and xylose in the hydrolyzate by ion chromatography, and determining the content of lignin by ultraviolet spectroscopy, the separation yield of hemicellulose is calculated to be 74.51%-83.63%, the separation yield of lignin is 7.2%-12.5%, and the separation yield of cellulose is 13.1%-18.2%.
[0052] (4) Take the remaining solid residue obtained in step (2) and take 30g of wood powder. Use a zirconia ball mill to ball mill for 96h at a speed of 1000rap / min. Perform positive and negative pressure every 30min. Then, 25g of the ball-milled sample is stirred at 35°C in 500mL of dioxane / water (9 / 1, v / v) and treated in the dark for 30h. After treatment, the mixture is filtered, and the process is performed three times. The collected filtrate is freeze-dried to obtain crude lignin. The obtained lignin is added to 40mL of acetic acid / water (9 / 1, v / v), and then the solution is poured into 400mL of water and stirred for 40min. The suspension is centrifuged at 12000rpm for 8min, and the obtained lignin is added to 10mL of ethanol / 1,2-dichloroethane (1 / 2, v / v) and mixed for 1h, and then precipitated in 150mL of ether. After centrifugation at 12000 rpm for 8 min, the induced lignin was washed three times with 80 mL of petroleum ether, and the collected samples were freeze-dried.
[0053] (5) Take 15 mg of the lignin sample obtained in step (4) and dissolve it in 400 μL of a mixed solution of anhydrous pyridine and deuterated chloroform (1.6 / 1, v / v). Then, add N-hydroxy-5-norbornene-2,3-diimide (7.3 mg ml -1 ) and chromium(III) acetylacetonate (3.6 mg mL -1 ) was added to the mixed solution as an internal standard and relaxation agent. Then 100 μL of phosphating agent (2-chloro-4,4,5,5-tetramethyl-1,3,2-dioxophosphine-tetramethyl-1,3,2-dioxophosphine, TMDP) was added. The above solution was added to a 5 mm NMR tube and reacted for 5 minutes. It was determined that the hydroxyl content of lignin increased by 57.4% after adding the green additive mannitol.
[0054] (6) Take 40 mg of the lignin sample obtained in step (4) and dissolve it in 0.5 mL of DMSO-d6 solution. Transfer the solution to a 5 mm diameter NMR tube. The β-O-4 bond content of the lignin after adding the green additive mannitol was measured to be 53 / 100 aromatic units. Up to 47.12% of the β-O-4 bonds were retained.
[0055] Finally, it should be pointed out that the above embodiments are only representative examples of the present invention. Obviously, the technical solution of the present invention is not limited to the above embodiments, and there are many variations. All variations that can be directly derived or associated with the content disclosed by ordinary technicians in this field should be considered as the protection scope of the present invention.
Claims
1. A method for forming low-condensation lignin during acid pretreatment, characterized in that: The steps include: (1) Air-dry the cleaned wood; (2) taking the absolutely dry sawdust of step (1), soaking it in distilled water with the green additive mannitol, and then placing it in a high-temperature and high-pressure reactor for reaction; separating the hydrolyzate and the remaining solid after the reaction, filtering to remove insoluble particles, and refrigerating the hydrolyzate; washing the remaining solid residue with distilled water until it is neutral, and then air-drying it for storage; (3) The remaining solid residue obtained in step (2) is ball-milled using a zirconia ball mill; then, the ball-milled sample is placed in dioxane / water, stirred at 35° C., and treated in the dark for 30 hours; after treatment, the mixture is filtered, and the process is performed three times; the collected filtrate is freeze-dried to obtain crude lignin; the obtained crude lignin is added to acetic acid / water, and then the solution is poured into water and stirred, the suspension is centrifuged, the obtained lignin is added to ethanol / 1,2-dichloroethane and mixed, and then precipitated in ether; after precipitation in ether, the mixture is centrifuged, the induced lignin is washed with petroleum ether, and the collected sample is freeze-dried.
2. The method for forming low-condensation lignin in an acid pretreatment process according to claim 1, characterized in that: The wood in step (1) is poplar.
3. The method for forming low-condensation lignin in an acidic pretreatment process according to claim 1, characterized in that: The wood in step (1) is air-dried and then placed in a sealed bag for storage to balance moisture for future use.
4. The method for forming low-condensation lignin in an acidic pretreatment process according to claim 1, characterized in that: The green additive is mannitol, a hydroxyl-containing green additive.
5. The method for forming low-condensation lignin in an acidic pretreatment process according to claim 1, characterized in that: The reaction conditions of step (2) are as follows: solid-liquid ratio is 1:10 (g:ml), the reaction is carried out at a H2SO4 concentration of 5% and a reaction temperature of 120°C-160°C for 30min-60min.
6. The method for forming low-condensation lignin in an acidic pretreatment process according to claim 1, characterized in that: The filtration in step (2) is performed using a 0.45 μm organic filter membrane.
7. The method for forming low-condensation lignin in an acidic pretreatment process according to claim 1, characterized in that: The ball milling in step (3) is performed at a speed of 1000 rap / min for 96 hours, with positive and negative pressures applied every 30 minutes.
8. The method for forming low-condensation lignin in an acidic pretreatment process according to claim 1, characterized in that: In the step (3), the ratio of dioxane to water is 9 / 1, v / v, and the mixture is stirred at 35° C. and treated in the dark for 30 hours.
9. The method for forming low-condensation lignin in an acidic pretreatment process according to claim 1, characterized in that: The step (3) specifically comprises adding the obtained crude lignin to acetic acid / water (9 / 1, v / v), then pouring the solution into water and stirring for 40 minutes, centrifuging the suspension at 12000 rpm for 8 minutes, adding the obtained lignin to ethanol / 1,2-dichloroethane (1 / 2, v / v) and mixing for 1 hour, and then precipitating in 150 mL of ether.
10. The method for forming low-condensation lignin in an acidic pretreatment process according to claim 1, characterized in that: In the step (3), after precipitation in ether, the mixture was centrifuged at 12000 rpm for 8 min, and the induced lignin was washed three times with petroleum ether, and the collected samples were freeze-dried.