Method for preparing lignin with high hydroxyl content and low condensation degree by using moso bamboo as raw material
By treating moso bamboo with microwave-assisted alkaline eutectic solvent and enzymatic hydrolysis, lignin with high hydroxyl content and low condensation degree was prepared, which solved the problem of reduced commercial value caused by lignin condensation in the existing technology and improved the reactivity and adhesion properties of lignin.
Patent Information
- Application Number
- CN202610224533.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-02-25
- Publication Date
- 2026-05-15
AI Technical Summary
Existing methods for pretreating bamboo lignocellulose with acidic DES cannot avoid lignin condensation, which reduces its commercial value. Furthermore, existing methods lack sufficient evaluation of the effects of diols on improving the hydrolysis performance of alkaline DES and the influence of solvation parameters, thus affecting the high-value utilization of lignin.
Bamboo was pretreated under microwave radiation using 1,4-butanediol-assisted alkaline choline hydroxide eutectic solvent, combined with enzymatic hydrolysis. The molecular weight and hydroxyl content of lignin were optimized through microwave pretreatment and enzymatic hydrolysis, resulting in lignin with high hydroxyl content and low condensation degree.
The weight-average molecular weight of lignin was no higher than 1200 g/mol, the number-average molecular weight was no higher than 700 g/mol, and the total hydroxyl content was greater than 6 mmol/g. This improved the reactivity and adhesion properties of lignin and enhanced its potential as a substitute additive in the synthesis of phenol-formaldehyde resins.
Smart Images
Figure CN122037231A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of renewable energy technology, specifically relating to a method for preparing lignin with high hydroxyl content and low condensation degree using moso bamboo as raw material. Background Technology
[0002] Due to the overconsumption of fossil resources and severe environmental pollution, the exploration of environmentally friendly and renewable alternatives is receiving increasing attention. In recent decades, the biorefining of lignocellulosic biomass has been considered an ideal method. However, its high degree of inertia, including cross-linking of component tissues and cell walls, high crystallinity of cellulose, and lignification, consistently hinders the efficient conversion of biomass into renewable energy and chemicals. Cellulose is the most abundant natural polymer on Earth and is widely used as a raw material for functional applications.
[0003] Eutectic solvents (DES) have emerged as leading agents in green biocatalysis and bioconversion due to their low cost, simple synthesis, and environmental sustainability. DES consists of hydrogen bond acceptors and hydrogen bond donors, with acidic DES receiving significant attention, such as Brønsted or Lewis acidic DES, for biomass depolymerization and conversion. However, acidic DESs can donate protons to catalyze the random breaking of glycosidic bonds in xylan, leading to its hydrolysis into xylose. Xylose can then be dehydrated into furfural by Brønsted and Lewis acids, resulting in reduced yields of lignocellulose. Therefore, to maximize the yields of lignocellulose, efficient processing methods are needed to address this challenge.
[0004] However, existing methods for pretreating bamboo lignocellulose with acidic DES still cannot avoid lignin condensation, preventing its high-value utilization. Evaluations of how diols improve the hydrolytic performance of alkaline DES, particularly regarding substrate physicochemical changes and solvation parameters, are very limited. Furthermore, the effects of different solvation parameters on the pretreatment process and on substrate physicochemical changes are currently unreported in the literature.
[0005] However, lignin, as an inexpensive and renewable resource, has attracted widespread attention in the development of wood adhesives using lignin as a raw material. Phenolic hydroxyl groups are often key reaction sites, and increasing the hydroxyl content can improve the reactivity of lignin to crosslinking, degradation, and other modifications. Furthermore, low molecular weight lignin has less steric hindrance and more reaction sites, increasing its adhesive properties and making it a suitable alternative additive to phenols in the synthesis of phenol-formaldehyde resins. Therefore, activating lignin by increasing hydroxyl content or reducing molecular weight is a necessary choice to improve the performance of modified lignin products. However, due to harsh processing conditions, the dehydration and breakage of aliphatic hydroxyl groups in the lignin side chains and the condensation polymerization of lignin inevitably lead to an increase in molecular weight, reducing the commercial value of lignin. Therefore, it is essential to find a green and efficient processing method that can reduce the molecular weight of lignin and increase its hydroxyl content. Summary of the Invention
[0006] The technical problem to be solved by the present invention is to provide a method for preparing lignin with high hydroxyl content and low condensation degree using moso bamboo as raw material. By adding diol to optimize the hydrolytic performance of alkaline choline hydroxide DES on moso bamboo lignocellulase, it can also effectively deconstruct moso bamboo lignocellulose and obtain lignin with low condensation degree.
[0007] Technical Solution: To solve the above-mentioned technical problems, the present invention adopts the following technical solution:
[0008] A method for preparing lignin with high hydroxyl content and low condensation degree from moso bamboo as raw material involves using 1,4-butanediol-assisted alkaline choline hydroxide DES and microwave pretreatment of moso bamboo under microwave radiation conditions. After pretreatment, the solid and liquid are separated by centrifugation, the solid is enzymatically hydrolyzed, and the filtrate is treated to obtain lignin with high hydroxyl content and low condensation degree. The lignin has a weight-average molecular weight not exceeding 1200 g / mol, a number-average molecular weight not exceeding 700 g / mol, and a total hydroxyl content greater than 6 mmol / g. Preferably, the lignin has a weight-average molecular weight of 1138 g / mol, a number-average molecular weight of 668 g / mol, and a total hydroxyl content of 6.77 mmol / g.
[0009] The method for preparing lignin with high hydroxyl content and low condensation degree using moso bamboo as raw material has the following molar ratios in the eutectic solvent: choline hydroxide, acetamide and 1,4-butanediol: 1:1:1 to 1:1:3; and the mass ratio of moso bamboo to the eutectic solvent: 1:48 to 1:52.
[0010] The method for preparing lignin with high hydroxyl content and low condensation degree using moso bamboo as raw material includes a microwave pretreatment temperature of 125~135℃, a microwave auxiliary power of 380~420W, a heating time of 4~6min, and a holding time of 4~6min.
[0011] The method for preparing lignin with high hydroxyl content and low condensation degree using moso bamboo as raw material involves enzymatic hydrolysis with an enzyme dosage of 18-22 FPU / g dextran, a hydrolysis time of 70-74 h, a hydrolysis temperature of 48-52 °C, and a shaking speed of 140-160 rpm.
[0012] The method for preparing lignin with high hydroxyl content and low condensation degree using moso bamboo as raw material involves adding acetone aqueous solution after pretreatment, separating solid and liquid, soaking the solid residue in sodium hydroxide solution and washing until the pH is neutral, air drying, and then performing enzymatic hydrolysis treatment.
[0013] The method for preparing lignin with high hydroxyl content and low condensation degree using moso bamboo as raw material involves the following steps after centrifugation: the pH value of the filtrate is slowly adjusted using hydrochloric acid solution, and after centrifugation and washing, the precipitated lignin solid is obtained. It is then subjected to acid hydrolysis using concentrated sulfuric acid and dilute sulfuric acid, respectively. After centrifugation, acetone and water are removed from the centrifuged liquid, and the recycled eutectic solvent is obtained for recycling.
[0014] The method for preparing lignin with high hydroxyl content and low condensation degree from moso bamboo includes the following steps:
[0015] (1) Preparation of eutectic solvent: Prepare a clear and homogeneous solution by mixing choline hydroxide solution, acetamide and 1,4-butanediol solution for later use;
[0016] (2) Microwave-assisted eutectic solvent pretreatment of moso bamboo: Add eutectic solvent and moso bamboo to the microwave reactor, mix evenly, and perform microwave pretreatment;
[0017] (3) After the reaction is complete, take out the mixture and cool it. Add 50% acetone aqueous solution to the mixture and stir it evenly. Then use a vacuum filter to separate the solid and liquid components of the mixture. Soak the solid residue in 1% (w / v) sodium hydroxide solution for 4 hours. Then wash the solid residue with deionized water until the pH is neutral. Air dry the solid residue for later use.
[0018] (4) Enzymatic hydrolysis: Add 1M citrate buffer and tetracycline to the solid residue, and then carry out the enzymatic hydrolysis process;
[0019] (5) Recovery of lignin and eutectic solvent: The pH of the filtrate obtained in step (3) was slowly adjusted to 2 using 1M hydrochloric acid solution. After centrifugation and washing, the precipitated lignin sample was obtained. The solid was subjected to two-step acid hydrolysis using concentrated sulfuric acid with a mass fraction of 72% and dilute sulfuric acid with a mass fraction of 4% at 30℃ and 121℃, respectively. After centrifugation, the acetone and water were removed by rotary evaporation of the centrifuged liquid. The recovered eutectic solvent was then recycled for reuse.
[0020] The method for preparing lignin with high hydroxyl content and low condensation degree using moso bamboo as raw material involves a eutectic solvent composed of choline hydroxide, acetamide, and 1,4-butanediol in a molar ratio of 1:1:2. The eutectic solvent is prepared by placing the above substances in an 80°C water bath and reacting them with shaking at 150 rpm for 24 hours. The mass ratio of moso bamboo to the eutectic solvent is 1:50.
[0021] The method for preparing lignin with high hydroxyl content and low condensation degree using moso bamboo as raw material involves a microwave pretreatment temperature of 130℃, a microwave auxiliary power of 400W, a heating time of 5min, and a holding time of 5min.
[0022] The method for preparing lignin with high hydroxyl content and low condensation degree using moso bamboo as raw material uses Celic Tec2 cellulase for enzymatic hydrolysis, with an enzyme dosage of 20 FPU / g dextran, an enzymatic hydrolysis time of 72 h, an enzymatic hydrolysis temperature of 50 °C, and an oscillation speed of 150 rpm.
[0023] Beneficial effects: Compared with the prior art, the present invention has the following advantages:
[0024] This invention utilizes microwave-assisted choline hydroxide-acetamide-1,4-butanediol eutectic solvent pretreatment of moso bamboo. 2D-HSQC NMR spectroscopy results show that the S unit favors the formation of β-O-4 bonds. The resulting lignin has a weight-average molecular weight (M... W The molecular weight (Mn) was 1138 g / mol, the number average molecular weight (Mn) was 668 g / mol, and the total hydroxyl content of the lignin reached 6.77 mmol / g. The degree of condensation of this lignin was very low, and the total hydroxyl content was high. Attached Figure Description
[0025] Figure 1 Two-dimensional HSQC nuclear magnetic resonance spectrum of lignin prepared in Example 1;
[0026] Figure 2 Two-dimensional HSQC nuclear magnetic resonance spectrum of lignin prepared in Comparative Example 1;
[0027] Figure 3 Two-dimensional HSQC nuclear magnetic resonance spectrum of lignin prepared in Comparative Example 2;
[0028] Figure 4 Two-dimensional HSQC nuclear magnetic resonance spectrum of lignin prepared in Comparative Example 3;
[0029] Figure 5 The two-dimensional HSQC nuclear magnetic resonance spectrum of the lignin prepared in Comparative Example 4 is shown. Detailed Implementation
[0030] The present invention will be further illustrated below with reference to specific embodiments. These embodiments are implemented based on the technical solutions of the present invention, and it should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention.
[0031] Example 1
[0032] A method for improving the efficiency of cellulase hydrolysis and conversion of moso bamboo while obtaining low-condensation lignin through microwave-assisted alkaline eutectic solvent pretreatment, the specific steps of which are as follows:
[0033] (1) Preparation of eutectic solvent: Add choline hydroxide solution, acetamide and 1,4-butanediol solution to an Erlenmeyer flask in a molar ratio of 1:1:2 and place it in an 80℃ water bath and shake at 150 rpm for 24 h. After obtaining a clear and homogeneous solution, place it in a desiccator for later use.
[0034] (2) Microwave-assisted eutectic solvent pretreatment of moso bamboo: Add 100g of eutectic solvent and 2g of moso bamboo to the microwave digestion vessel, mix evenly to ensure the uniformity of the subsequent reaction, place the microwave digestion vessel in the microwave digestion instrument, heat at 130℃ with a power of 400W for 5min and maintain for 5min.
[0035] (3) After the reaction is complete, the mixture is taken out and cooled. 50% (v / v) acetone aqueous solution is added to the mixture and stirred evenly. The mixture is then separated into solid and liquid by vacuum filtration. The solid residue is soaked in 1% (w / v) sodium hydroxide solution for 4 hours. Then the solid residue is washed with deionized water until the pH is neutral. The solid residue is then air-dried for later use.
[0036] (4) Enzymatic hydrolysis: 0.5g of oven-dry solid residue was placed in an Erlenmeyer flask and 1M citrate buffer and tetracycline were added. The enzymatic hydrolysis system was 10mL and the amount of enzyme added was 20FPU / g dextran. The cellulase used for enzymatic hydrolysis was Celic Tec2 cellulase. The reaction was carried out in a water bath at a temperature of 50℃ and a shaking speed of 150rpm. After 72h of enzymatic hydrolysis, the sugar content of the enzymatic hydrolysate was analyzed by high performance liquid chromatography.
[0037] (5) Recovery of lignin and eutectic solvent: The pH of the filtrate was slowly adjusted to 2 using 1M hydrochloric acid solution. After centrifugation and washing, the precipitated lignin sample was obtained. The solid was subjected to two-step acid hydrolysis using 72% concentrated sulfuric acid and 4% dilute sulfuric acid at 30℃ and 121℃, respectively. The sugar content was determined by high performance liquid chromatography. The lignin content was determined by muffle furnace ignition and weighing method and spectrophotometry. Finally, the acetone and water were removed by rotary evaporation of the centrifuged liquid. The recovered eutectic solvent was recycled for reuse.
[0038] The results showed that the weight-average molecular weight (M) was obtained.W The lignin content was 1138 g / mol, and the total hydroxyl content of the recovered lignin was 6.77 mmol / g, which is 1.19 times higher than that of the lignin.
[0039] Comparative Example 1
[0040] A method for preparing lignin from moso bamboo includes the following steps:
[0041] (1) Place 0.5g of oven-dried bamboo sample in an Erlenmeyer flask and add 1M citrate buffer and tetracycline. The enzyme hydrolysis system is 10mL and the enzyme amount is 20FPU / g dextran. The reaction is carried out in a water bath. The reaction temperature is set at 50℃ and the shaking speed is 150rpm. After 72h of enzyme hydrolysis, the sugar content of the enzyme hydrolysate is analyzed by high performance liquid chromatography.
[0042] (2) Chemical composition analysis of the original bamboo samples: The solid was subjected to two-step acid hydrolysis using concentrated sulfuric acid with a mass fraction of 72% and dilute sulfuric acid with a mass fraction of 4% at 30℃ and 121℃, respectively. The sugar content was determined by high performance liquid chromatography, and the lignin content was determined by muffle furnace calcination and weighing method and spectrophotometry.
[0043] The results showed that the weight-average molecular weight (M) was obtained. W The lignin content was 3887 g / mol, and the total hydroxyl content of the recovered lignin was 5.66 mmol / g.
[0044] Comparative Example 2
[0045] A method for preparing lignin from moso bamboo includes the following steps:
[0046] (1) Preparation of eutectic solvent: p-toluenesulfonic acid, choline chloride and 1,3-butanediol solution were added to an Erlenmeyer flask in a molar ratio of 1:1:2 and placed in an 80℃ water bath with shaking at 150 rpm for 24 h. After obtaining a clear and homogeneous solution, it was placed in a desiccator for later use.
[0047] (2) Microwave-assisted eutectic solvent pretreatment of moso bamboo: Add 100g of eutectic solvent and 2g of moso bamboo to the microwave digestion vessel, mix evenly to ensure the uniformity of the subsequent reaction, place the microwave digestion vessel in the microwave digestion instrument, heat at 130℃ with a power of 400W for 5min and maintain for 5min.
[0048] (3) After the reaction is complete, the mixture is taken out and cooled. 50% (v / v) acetone aqueous solution is added to the mixture and stirred evenly. The mixture is then separated into solid and liquid by vacuum filtration. The solid residue is soaked in 1% (w / v) sodium hydroxide solution for 4 hours. Then the solid residue is washed with deionized water until the pH is neutral. The solid residue is then air-dried for later use.
[0049] (4) Enzymatic hydrolysis: 0.5g of oven-dry solid residue was placed in an Erlenmeyer flask and 1M citrate buffer and tetracycline were added. The enzymatic hydrolysis system was 10mL and the amount of enzyme added was 20FPU / g dextran. The reaction was carried out in a water bath at 50℃ and the shaking speed was 150rpm. After 72h of enzymatic hydrolysis, the sugar content of the hydrolysate was analyzed by high performance liquid chromatography.
[0050] (5) Recovery of lignin and eutectic solvent: The pH of the filtrate was slowly adjusted to 2 using 1M hydrochloric acid solution. After centrifugation and washing, the precipitated lignin sample was obtained. The solid was subjected to two-step acid hydrolysis using 72% concentrated sulfuric acid and 4% dilute sulfuric acid at 30℃ and 121℃, respectively. The sugar content was determined by high performance liquid chromatography. The lignin content was determined by muffle furnace ignition and weighing method and spectrophotometry. Finally, the acetone and water were removed by rotary evaporation of the centrifuged liquid. The recovered eutectic solvent was recycled for reuse.
[0051] The results showed that the weight-average molecular weight (M) was obtained. W The lignin content was 2509 g / mol, and the total hydroxyl content of the recovered lignin was 4.20 mmol / g.
[0052] Comparative Example 3
[0053] A method for preparing lignin from moso bamboo includes the following steps:
[0054] (1) Preparation of eutectic solvent: p-toluenesulfonic acid, choline chloride and 1,4-butanediol solution were added to an Erlenmeyer flask in a molar ratio of 1:1:2 and placed in an 80℃ water bath with shaking at 150 rpm for 24 h. After obtaining a clear and homogeneous solution, it was placed in a desiccator for later use.
[0055] (2) Microwave-assisted eutectic solvent pretreatment of moso bamboo: Add 100g of eutectic solvent and 2g of moso bamboo to the microwave digestion vessel, mix evenly to ensure the uniformity of the subsequent reaction, place the microwave digestion vessel in the microwave digestion instrument, heat at 130℃ with a power of 400W for 5min and maintain for 5min.
[0056] (3) After the reaction is complete, the mixture is taken out and cooled. 50% (v / v) acetone aqueous solution is added to the mixture and stirred evenly. The mixture is then separated into solid and liquid by vacuum filtration. The solid residue is soaked in 1% (w / v) sodium hydroxide solution for 4 hours. Then the solid residue is washed with deionized water until the pH is neutral. The solid residue is then air-dried for later use.
[0057] (4) Enzymatic hydrolysis: 0.5g of oven-dry solid residue was placed in an Erlenmeyer flask and 1M citrate buffer and tetracycline were added. The enzymatic hydrolysis system was 10mL and the amount of enzyme added was 20FPU / g dextran. The reaction was carried out in a water bath at 50℃ and the shaking speed was 150rpm. After 72h of enzymatic hydrolysis, the sugar content of the hydrolysate was analyzed by high performance liquid chromatography.
[0058] (5) Recovery of lignin and eutectic solvent: The pH of the filtrate was slowly adjusted to 2 using 1M hydrochloric acid solution. After centrifugation and washing, the precipitated lignin sample was obtained. The solid was subjected to two-step acid hydrolysis using 72% concentrated sulfuric acid and 4% dilute sulfuric acid at 30℃ and 121℃, respectively. The sugar content was determined by high performance liquid chromatography. The lignin content was determined by muffle furnace ignition and weighing method and spectrophotometry. Finally, the acetone and water were removed by rotary evaporation of the centrifuged liquid. The recovered eutectic solvent was recycled for reuse.
[0059] The results showed that the weight-average molecular weight (M) was obtained. W The lignin content was 1853 g / mol, and the total hydroxyl content of the recovered lignin was 4.13 mmol / g.
[0060] Comparative Example 4
[0061] A method for preparing lignin from moso bamboo includes the following steps:
[0062] (1) Preparation of eutectic solvent: Add choline hydroxide solution and acetamide in a molar ratio of 1:1 into an Erlenmeyer flask and place it in an 80℃ water bath and shake at 150 rpm for 24 h. After obtaining a clear and homogeneous solution, place it in a desiccator for later use.
[0063] (2) Microwave-assisted eutectic solvent pretreatment of moso bamboo: Add 100g of eutectic solvent and 2g of moso bamboo to the microwave digestion vessel, mix evenly to ensure the uniformity of the subsequent reaction, place the microwave digestion vessel in the microwave digestion instrument, heat at 130℃ with a power of 400W for 5min and maintain for 5min.
[0064] (3) After the reaction is complete, the mixture is taken out and cooled. 50% (v / v) acetone aqueous solution is added to the mixture and stirred evenly. The mixture is then separated into solid and liquid by vacuum filtration. The solid residue is soaked in 1% (w / v) sodium hydroxide solution for 4 hours. Then the solid residue is washed with deionized water until the pH is neutral. The solid residue is then air-dried for later use.
[0065] (4) Enzymatic hydrolysis: 0.5g of oven-dry solid residue was placed in an Erlenmeyer flask and 1M citrate buffer and tetracycline were added. The enzymatic hydrolysis system was 10mL and the amount of enzyme added was 20FPU / g dextran. The reaction was carried out in a water bath at 50℃ and the shaking speed was 150rpm. After 72h of enzymatic hydrolysis, the sugar content of the hydrolysate was analyzed by high performance liquid chromatography.
[0066] (5) Recovery of lignin and eutectic solvent: The pH of the filtrate was slowly adjusted to 2 using 1M hydrochloric acid solution. After centrifugation and washing, the precipitated lignin sample was obtained. The solid was subjected to two-step acid hydrolysis using 72% concentrated sulfuric acid and 4% dilute sulfuric acid at 30℃ and 121℃, respectively. The sugar content was determined by high performance liquid chromatography. The lignin content was determined by muffle furnace ignition and weighing method and spectrophotometry. Finally, the acetone and water were removed by rotary evaporation of the centrifuged liquid. The recovered eutectic solvent was recycled for reuse.
[0067] The results showed that the weight-average molecular weight (M) was obtained. W The lignin content was 1594 g / mol, and the total hydroxyl content of the recovered lignin was 2.48 mmol / g.
[0068] The weight-average molecular weight, number-average molecular weight, polydispersity index, aliphatic hydroxyl content, phenolic hydroxyl content, and total hydroxyl content of the lignin obtained in Examples 1 and Comparative Examples 1-4 are shown in Table 1. As can be seen from Table 1, the weight-average molecular weight (Mw) of the lignin obtained in Example 1 is 1138 g / mol, and the number-average molecular weight (Mn) is 668 g / mol, indicating a very low degree of condensation. Furthermore, the total hydroxyl content is 6.77 mmol / g, which is 1.19 times higher than that of the lignin prepared in Comparative Example 1.
[0069] Table 1. Test results of weight-average molecular weight, number-average molecular weight, polydispersity index, aliphatic hydroxyl content, phenolic hydroxyl content, and total hydroxyl content of lignin prepared in Example 1 and Comparative Examples 1-4.
[0070]
[0071] 2D-HSQC NMR spectroscopy was used to study in detail the changes in the substructure and chemical composition of lignin during DES pretreatment. The test results are as follows: Figure 1 As shown in the figure. The results show that the S unit is conducive to the formation of β-O-4 bonds. The β-O-4 content of the lignin sample in Example 1 is higher than that of untreated ground wood lignin (Comparative Example 1), which verifies that it is a low-condensation lignin. Low-condensation lignin will be beneficial for subsequent functionalization.
[0072] Table 2. Results of inter-unit bonding content of lignin prepared in Example 1 and Comparative Examples 1-4
[0073]
[0074] right Figure 1 The 2D-HSQC NMR spectra were integrated to obtain Table 2. The results in Table 2 further demonstrate that the S unit content in Example 1 is high, the β-O-4 content of the lignin sample in the pretreated solution is higher than that of the untreated ground wood lignin (Comparative Example 1), and the content of lignin linkage bonds obtained after treatment is closest to that of ground wood lignin (Comparative Example 1). The uncondensed lignin will be beneficial for subsequent functionalization.
[0075] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.
Claims
1. A method for preparing lignin with high hydroxyl content and low condensation degree from moso bamboo, characterized in that, Bamboo was pretreated by microwave radiation using a 1,4-butanediol-assisted alkaline choline hydroxide eutectic solvent. After pretreatment, the solid and liquid were separated by centrifugation, and the solid was enzymatically hydrolyzed. The filtrate was then treated to obtain lignin with high hydroxyl content and low condensation degree. The weight average molecular weight of the lignin was not higher than 1200 g / mol, the number average molecular weight was not higher than 700 g / mol, and the total hydroxyl content was greater than 6 mmol / g.
2. The method for preparing lignin with high hydroxyl content and low condensation degree from bamboo as raw material according to claim 1, characterized in that, The eutectic solvent is composed of choline hydroxide, acetamide and 1,4-butanediol in a molar ratio of 1:1:1 to 1:1:3; the mass ratio of bamboo to the eutectic solvent is 1:48 to 1:
52.
3. The method for preparing lignin with high hydroxyl content and low condensation degree from bamboo as raw material according to claim 1, characterized in that, The microwave pretreatment temperature is 125~135℃, the microwave auxiliary power is 380~420W, the heating time is 4~6min, and the holding time is 4~6min.
4. The method for preparing lignin with high hydroxyl content and low condensation degree from bamboo as raw material according to claim 1, characterized in that, The enzyme dosage for enzymatic hydrolysis is 18-22 FPU / g dextran, the hydrolysis time is 70-74 h, the hydrolysis temperature is 48-52 ℃, and the shaking speed is 140-160 rpm.
5. The method for preparing lignin with high hydroxyl content and low condensation degree from bamboo as raw material according to claim 1, characterized in that, After pretreatment, acetone aqueous solution was added to the reaction solution for solid-liquid separation. The solid residue was soaked in sodium hydroxide solution and washed until the pH was neutral. It was then air-dried and subjected to enzymatic hydrolysis.
6. The method for preparing lignin with high hydroxyl content and low condensation degree from bamboo as raw material according to claim 1, characterized in that, Treatment of the filtrate after centrifugation: The pH value of the filtrate is slowly adjusted by hydrochloric acid solution. After centrifugation and washing, the precipitated lignin solid is obtained. It is then subjected to acid hydrolysis by concentrated sulfuric acid and dilute sulfuric acid, respectively. After centrifugation, acetone and water are removed from the centrifuged liquid, and the regenerated eutectic solvent is obtained for recycling.
7. The method for preparing lignin with high hydroxyl content and low condensation degree from moso bamboo as claimed in claim 1, characterized in that, Includes the following steps: (1) Preparation of eutectic solvent: Prepare a clear and homogeneous solution by mixing choline hydroxide solution, acetamide and 1,4-butanediol solution for later use; (2) Microwave pretreatment of moso bamboo: Add eutectic solvent and moso bamboo to the microwave reactor, mix evenly, and perform microwave pretreatment; (3) After the reaction is complete, add 50% acetone aqueous solution to the mixture and stir evenly. Then, separate the solid and liquid components of the mixture. Soak the solid residue in 1% sodium hydroxide solution for 4 hours. Then wash the solid residue with deionized water until the pH is neutral. Air dry the solid residue for later use. (4) Enzymatic hydrolysis: Add 1M citrate buffer and tetracycline to the solid residue, and then carry out the enzymatic hydrolysis process; (5) Recovery of lignin and eutectic solvent: The pH of the filtrate obtained in step (3) was slowly adjusted to 2 using 1M hydrochloric acid solution. After centrifugation and washing, the precipitated lignin was obtained. The solid was subjected to two-step acid hydrolysis using 72% sulfuric acid and 4% dilute sulfuric acid at 30℃ and 121℃, respectively. After centrifugation, acetone and water were removed from the centrifuged liquid. The regenerated eutectic solvent was obtained for recycling.
8. The method for preparing lignin with high hydroxyl content and low condensation degree from bamboo as raw material according to claim 1 or 7, characterized in that, The eutectic solvent is composed of choline hydroxide, acetamide and 1,4-butanediol in a molar ratio of 1:1:
2. The eutectic solvent is prepared by placing the above substances in an 80°C water bath and shaking at 150 rpm for 24 h. The mass ratio of bamboo to the eutectic solvent is 1:
50.
9. The method for preparing lignin with high hydroxyl content and low condensation degree from bamboo as raw material according to claim 1 or 7, characterized in that, The microwave pretreatment temperature was 130℃, the microwave auxiliary power was 400W, the heating time was 5min, and the holding time was 5min.
10. The method for preparing lignin with high hydroxyl content and low condensation degree from bamboo as raw material according to claim 1 or 7, characterized in that, The cellulase used for enzymatic hydrolysis was Celic Tec2 cellulase, with an enzyme dosage of 20 FPU / g dextran, a hydrolysis time of 72 h, a hydrolysis temperature of 50 °C, and a shaking speed of 150 rpm.