Process for the separation of whole components of lignocellulosic biomass based on oxalic acid complex solvent system
By pretreating lignocellulose with a composite solvent system of oxalic acid, propylene carbonate, and water, the problem of low separation efficiency of lignocellulose components was solved, achieving efficient separation and degradation, and reducing costs and environmental impact.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- INST OF CHEM IND OF FOREST PROD CHINESE ACAD OF FORESTRY
- Filing Date
- 2026-04-20
- Publication Date
- 2026-07-17
AI Technical Summary
Existing technologies are difficult to efficiently separate and degrade lignocellulose, hemicellulose and lignin, and traditional pretreatment methods are energy-intensive, costly and potentially polluting to the environment.
A composite solvent system consisting of oxalic acid, propylene carbonate, and water was used to pretreat wood fiber raw materials. The efficient separation of the three major components was achieved by controlling the reaction conditions, including the optimization of the amount of propylene carbonate, the concentration of oxalic acid, and the reaction temperature.
The degradation rate of hemicellulose reached 90.3%, the degradation rate of lignin reached 87.4%, and the retention rate of cellulose reached 92.6%. Furthermore, the solvent can be recycled, reducing the cost of chemical reagents and the environmental impact.
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Figure CN122406568A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of biomass resource utilization technology, specifically relating to a method for separating all components of lignocellulosic biomass using a composite solvent system based on oxalic acid. Background Technology
[0002] Lignocellulose raw materials are abundant and widely distributed in nature, inexpensive, and renewable, making them an ideal alternative to traditional petroleum resources. They can be used to produce biomass chemicals, bio-dyes, and bio-based materials, representing a new direction for green and low-carbon industrial development and demonstrating extremely broad market prospects and application potential. Lignocellulose raw materials are mainly composed of three components: cellulose, hemicellulose, and lignin. Currently, the core objective of biomass refining technology is to achieve efficient utilization of all components of biomass raw materials, reduce production costs, and thus obtain high-value-added products. However, natural lignocellulose possesses a complex and stable anti-degradation barrier structure. This natural resistance stems from the tight binding and unique spatial structure between its components, which not only hinders the effective degradation and transformation of polysaccharide components such as cellulose and hemicellulose but also severely limits the efficient industrial utilization of biomass resources, becoming a key bottleneck restricting the high-value-added development of lignocellulose.
[0003] Pretreatment methods for wood fiber raw materials mainly fall into three categories: chemical, physical, and biological methods. Chemical methods include dilute acid treatment and alkali treatment, while physical methods include ball milling, ultrasonic treatment, and auxiliary pretreatment methods such as organic solvent treatment. Biological methods primarily utilize microorganisms and enzymes. However, traditional pretreatment technologies generally have significant drawbacks: high energy consumption, the potential environmental pollution caused by the large-scale use of chemical reagents, and the corrosiveness of these reagents increases initial investment and production costs.
[0004] In recent years, polar aprotic solvent (γ-valerol) pretreatment technology has emerged, attracting widespread attention from researchers due to its advantages such as environmental friendliness, high selectivity, low energy consumption, and low corrosiveness to equipment. Propylene carbonate, another important polar aprotic solvent, has seen limited research in the pretreatment of lignocellulose biomass. Compared to γ-valerol, propylene carbonate is produced from carbon dioxide and propylene oxide, a process that utilizes carbon dioxide as a resource, thereby reducing greenhouse gas emissions. Existing studies have used a mixture of propylene carbonate, water, and p-toluenesulfonic acid for the pretreatment of lignocellulose raw materials; however, p-toluenesulfonic acid is a strong acid with a high price, increasing pretreatment costs and limiting the widespread application of this composite system. Summary of the Invention
[0005] The technical problem solved by this invention is to provide a method for separating all components of lignocellulose biomass using a composite solvent system based on oxalic acid. This method achieves efficient separation of cellulose, hemicellulose, and lignin from lignocellulose raw materials, while achieving a degradation rate of 90.3% for hemicellulose, a degradation rate of 87.4% for lignin, and a retention rate of 92.6% for cellulose.
[0006] Technical Solution: To solve the above-mentioned technical problems, the present invention adopts the following technical solution:
[0007] A method for separating all components of lignocellulose biomass based on a composite solvent system using oxalic acid involves pretreating lignocellulose raw materials with a composite solvent system composed of propylene carbonate, water, and oxalic acid. The amount of propylene carbonate used is 60% to 90% of the volume of the composite solvent system, and the mass-to-volume ratio of oxalic acid to the composite solvent system is 0.6 to 1.2 g / mL. The degradation rate of hemicellulose is greater than 55%, the degradation rate of lignin is greater than 32%, and the retention rate of cellulose is greater than 84%.
[0008] The method for separating all components of lignocellulose biomass using the oxalic acid-based composite solvent system involves filtering to obtain liquid and solid products after pretreatment. The obtained solid products are washed with deionized water and dried to obtain cellulose-rich solid residue. The obtained liquid is allowed to stand and separate into layers. The upper aqueous phase is hemicellulose degradation products, and the lower organic phase is lignin. Water is added to the organic phase, and the lignin precipitates. The lignin is then obtained through solid-liquid separation and drying.
[0009] The method for separating all components of lignocellulose biomass using the oxalic acid-based composite solvent system involves adding the lignocellulose raw material and the composite solvent system into a reaction vessel, with a reaction temperature of 100~140 ℃, a reaction time of 20~120 min, and a stirring rate of 400 rpm.
[0010] The method for separating all components of lignocellulose biomass using the oxalic acid-based composite solvent system comprises the following steps: the amount of propylene carbonate used is 60% of the volume of the composite solvent system; the mass-to-volume ratio of oxalic acid to the composite solvent system is 1-1.2 g / mL; the reaction temperature is 140 ℃; the reaction time is 100-120 min; the degradation rate of hemicellulose is greater than 90%; the degradation rate of lignin is greater than 87%; and the retention rate of cellulose is greater than 88%.
[0011] The method for separating all components of lignocellulose biomass using the oxalic acid-based composite solvent system comprises the following steps: the amount of propylene carbonate used is 60% of the volume of the composite solvent system; the mass-to-volume ratio of oxalic acid to the composite solvent system is 1 g / mL; the reaction temperature is 140 ℃; the reaction time is 100 min; the degradation rate of hemicellulose is 90.3%; the degradation rate of lignin is 87.4%; and the retention rate of cellulose is 92.6%.
[0012] The method for separating all components of lignocellulosic biomass using an oxalic acid-based composite solvent system involves using poplar wood as the raw material, which is crushed, passed through an 80-100 mesh sieve, and dried at 105℃ for 12 hours.
[0013] The method for separating all components of lignocellulosic biomass using the oxalic acid-based composite solvent system has a ratio of lignocellulosic raw material to composite solvent system of 1 g: 10 mL.
[0014] The method for separating all components of lignocellulose biomass using the oxalic acid-based composite solvent system includes the following steps:
[0015] (1) A composite solvent system consisting of propylene carbonate, water, and oxalic acid is mixed with wood fiber raw material and placed in a closed reaction vessel; after the reaction is completed, the solid and liquid are separated after cooling to obtain liquid product and solid product;
[0016] (2) The liquid product obtained in step (1) was allowed to stand and separate into layers. The aqueous phase was the hemicellulose degradation product, and water was added to the organic phase to precipitate lignin. The lignin was obtained by separation and drying.
[0017] (3) The solid product obtained in step (1) is washed with water and dried to obtain a solid rich in cellulose;
[0018] (4) The liquid in step (2) is subjected to vacuum distillation to recover propylene carbonate, water and oxalic acid;
[0019] (5) Recycle the solvent recovered in step (4) and proceed to step (1), repeating steps (1) to (5).
[0020] The method for separating all components of lignocellulose biomass using the oxalic acid-based composite solvent system shall be repeated no more than 3 times.
[0021] Beneficial effects: Compared with the prior art, the present invention has the following advantages:
[0022] (1) This invention uses a composite solvent system composed of propylene carbonate, water, and oxalic acid as a green solvent to pretreat poplar wood, separating hemicellulose and lignin to obtain cellulose; wherein the hemicellulose is converted into pentose sugar, realizing the separation of the three major components, and the degradation efficiency of hemicellulose and lignin reaches 92.3% and 90.4% respectively, and the cellulose retention rate is 89.0%.
[0023] (2) The chemical reagents used in this invention are low cost, renewable, have little impact on the environment, and the solvents can be recycled. Attached Figure Description
[0024] Figure 1This is a diagram illustrating the effect of recycling a composite solvent system. Detailed Implementation
[0025] 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.
[0026] The raw material used in this invention is poplar wood with a particle size of 80-100 mesh. The composition of cellulose, hemicellulose, and lignin in the raw material was analyzed according to the standard NREL process. By mass, the proportions of the three elements were: cellulose 48.9%, hemicellulose 22.3%, and lignin 24.8%.
[0027] The formulas for calculating hemicellulose degradation rate, lignin degradation rate, and cellulose retention rate in the following examples and comparative examples are shown below:
[0028] Hemicellulose degradation rate = (1 - hemicellulose content in residual residue / hemicellulose content in initial raw material) × 100%;
[0029] Lignin degradation rate = (1 - lignin content of remaining residue / lignin content of initial raw material) × 100%;
[0030] Cellulose retention rate = Residual residue cellulose content / Initial raw material cellulose content × 100%.
[0031] Comparative Example 1
[0032] Six g of poplar wood powder was placed in a 100 mL high-pressure reactor, and 60 mL of a mixed solvent consisting of propylene carbonate, water, and oxalic acid was added. The propylene carbonate concentration was 20% (v / v), the oxalic acid concentration was 1% (w / v, g / mL), the reaction temperature was 140℃, and the reaction time was 100 min. After the reaction, the reactants were filtered to separate the supernatant and solid. The solid was washed with deionized water and dried to obtain a cellulose-rich sample. The supernatant was allowed to stand and separate into layers; the upper aqueous phase was the cellulose degradation product, and the lower organic phase was lignin. Water was added to the organic phase, precipitating lignin, which was then filtered and dried to obtain a lignin sample. The degradation rate of hemicellulose was 100%, the degradation rate of lignin was 19.6%, and the retention rate of cellulose was 80.4%.
[0033] Example 1
[0034] Six g of poplar wood powder was placed in a 100 mL high-pressure reactor, and 60 mL of a mixed solvent consisting of propylene carbonate, water, and oxalic acid was added. The propylene carbonate concentration was 60% (v / v), the oxalic acid concentration was 1% (w / v, g / mL), the reaction temperature was 140 ℃, and the reaction time was 100 min. After the reaction, the reactants were filtered to separate the supernatant and solid. The solid was washed with deionized water and dried to obtain a cellulose-rich sample. The supernatant was allowed to stand and separate into layers; the upper aqueous phase was the cellulose degradation product, and the lower organic phase was lignin. Water was added to the organic phase, precipitating lignin, which was then filtered and dried to obtain a lignin sample. The degradation rate of hemicellulose was 90.3%, the degradation rate of lignin was 87.4%, and the retention rate of cellulose was 92.6%.
[0035] Example 2
[0036] Six g of poplar wood powder was placed in a 100 mL high-pressure reactor, and 60 mL of a mixed solvent consisting of propylene carbonate, water, and oxalic acid was added. The propylene carbonate concentration was 90% (v / v), the oxalic acid concentration was 1% (w / v, g / mL), the reaction temperature was 140 ℃, and the reaction time was 100 min. After the reaction, the reactants were filtered to separate the supernatant and solid. The solid was washed with deionized water and dried to obtain a cellulose-rich sample. The supernatant was allowed to stand and separate into layers; the upper aqueous phase was the cellulose degradation product, and the lower organic phase was lignin. Water was added to the organic phase, precipitating lignin, which was then filtered and dried to obtain a lignin sample. The degradation rate of hemicellulose was 72.9%, the degradation rate of lignin was 39.2%, and the retention rate of cellulose was 91.4%.
[0037] Comparative Example 2
[0038] Six g of poplar wood powder was placed in a 100 mL high-pressure reactor, and 60 mL of a mixed solvent consisting of propylene carbonate, water, and oxalic acid was added. The propylene carbonate concentration was 60% (v / v), the oxalic acid concentration was 0.1% (w / v, g / mL), the reaction temperature was 140 ℃, and the reaction time was 100 min. After the reaction, the reactants were filtered to separate the supernatant and solid. The solid was washed with deionized water and dried to obtain a cellulose-rich sample. The supernatant was allowed to stand and separate into layers; the upper aqueous phase was the cellulose degradation product, and the lower organic phase was lignin. Water was added to the organic phase, precipitating lignin, which was then filtered and dried to obtain the lignin sample. The degradation rate of hemicellulose was 43.7%, the degradation rate of lignin was 20.8%, and the retention rate of cellulose was 99.6%.
[0039] Example 3
[0040] Six g of poplar wood powder was placed in a 100 mL high-pressure reactor, and 60 mL of a mixed solvent consisting of propylene carbonate, water, and oxalic acid was added. The propylene carbonate concentration was 60% (v / v), the oxalic acid concentration was 0.6% (w / v, g / mL), the reaction temperature was 140 ℃, and the reaction time was 100 min. After the reaction, the reactants were filtered to separate the supernatant and solid. The solid was washed with deionized water and dried to obtain a cellulose-rich sample. The supernatant was allowed to stand and separate into layers; the upper aqueous phase was the cellulose degradation product, and the lower organic phase was lignin. Water was added to the organic phase, precipitating lignin, which was then filtered and dried to obtain a lignin sample. The degradation rate of hemicellulose was 88.0%, the degradation rate of lignin was 77.5%, and the retention rate of cellulose was 93.4%.
[0041] Example 4
[0042] Six g of poplar wood powder was placed in a 100 mL high-pressure reactor, and 60 mL of a mixed solvent consisting of propylene carbonate, water, and oxalic acid was added. The propylene carbonate concentration was 60% (v / v), the oxalic acid concentration was 1.2% (w / v, g / mL), the reaction temperature was 140 ℃, and the reaction time was 100 min. After the reaction, the reactants were filtered to separate the supernatant and solid. The solid was washed with deionized water and dried to obtain a cellulose-rich sample. The supernatant was allowed to stand and separate into layers; the upper aqueous phase was the cellulose degradation product, and the lower organic phase was lignin. Water was added to the organic phase, precipitating lignin, which was then filtered and dried to obtain a lignin sample. The degradation rate of hemicellulose was 92.6%, the degradation rate of lignin was 89.4%, and the retention rate of cellulose was 88.0%.
[0043] Example 5
[0044] Six g of poplar wood powder was placed in a 100 mL high-pressure reactor, and 60 mL of a mixed solvent consisting of propylene carbonate, water, and oxalic acid was added. The propylene carbonate concentration was 60% (v / v), the oxalic acid concentration was 1% (w / v, g / mL), the reaction temperature was 100 ℃, and the reaction time was 100 min. After the reaction, the reactants were filtered to separate the supernatant and solid. The solid was washed with deionized water and dried to obtain a cellulose-rich sample. The supernatant was allowed to stand and separate into layers; the upper aqueous phase was the cellulose degradation product, and the lower organic phase was lignin. Water was added to the organic phase, precipitating lignin, which was then filtered and dried to obtain a lignin sample. The degradation rate of hemicellulose was 55.7%, the degradation rate of lignin was 32.3%, and the retention rate of cellulose was 88.3%.
[0045] Example 6
[0046] Six g of poplar powder was placed in a 100 mL high-pressure reactor, and 60 mL of a mixed solvent consisting of propylene carbonate, water, and oxalic acid was added. The propylene carbonate concentration was 60% (v / v), the oxalic acid concentration was 1% (w / v, g / mL), the reaction temperature was 120 ℃, and the reaction time was 100 min. After the reaction, the reactants were filtered to separate the supernatant and solid. The solid was washed with deionized water and dried to obtain a cellulose-rich sample. The supernatant was allowed to stand and separate into layers; the upper aqueous phase was the cellulose degradation product, and the lower organic phase was lignin. Water was added to the organic phase, precipitating lignin, which was then filtered and dried to obtain the lignin sample. The degradation rate of hemicellulose was 76.3%, the degradation rate of lignin was 49.7%, and the retention rate of cellulose was 84.2%.
[0047] Example 7
[0048] Six g of poplar wood powder was placed in a 100 mL high-pressure reactor, and 60 mL of a mixed solvent consisting of propylene carbonate, water, and oxalic acid was added. The propylene carbonate concentration was 60% (v / v), the oxalic acid concentration was 1% (w / v, g / mL), the reaction temperature was 140 ℃, and the reaction time was 20 min. After the reaction, the reactants were filtered to separate the supernatant and solid. The solid was washed with deionized water and dried to obtain a cellulose-rich sample. The supernatant was allowed to stand and separate into layers; the upper aqueous phase was the cellulose degradation product, and the lower organic phase was lignin. Water was added to the organic phase, precipitating lignin, which was then filtered and dried to obtain the lignin sample. The degradation rate of hemicellulose was 76.1%, the degradation rate of lignin was 55.3%, and the retention rate of cellulose was 87.2%.
[0049] Example 8
[0050] Six g of poplar wood powder was placed in a 100 mL high-pressure reactor, and 60 mL of a mixed solvent consisting of propylene carbonate, water, and oxalic acid was added. The propylene carbonate concentration was 60% (v / v), the oxalic acid concentration was 1% (w / v, g / mL), the reaction temperature was 140 ℃, and the reaction time was 60 min. After the reaction, the reactants were filtered to separate the supernatant and solid. The solid was washed with deionized water and dried to obtain a cellulose-rich sample. The supernatant was allowed to stand and separate into layers; the upper aqueous phase was the cellulose degradation product, and the lower organic phase was lignin. Water was added to the organic phase, precipitating lignin, which was then filtered and dried to obtain the lignin sample. The degradation rate of hemicellulose was 83.6%, the degradation rate of lignin was 76.7%, and the retention rate of cellulose was 96.4%.
[0051] Example 9
[0052] Six g of poplar wood powder was placed in a 100 mL high-pressure reactor, and 60 mL of a mixed solvent consisting of propylene carbonate, water, and oxalic acid was added. The propylene carbonate concentration was 60% (v / v), the oxalic acid concentration was 1% (w / v, g / mL), the reaction temperature was 140 ℃, and the reaction time was 120 min. After the reaction, the reactants were filtered to separate the supernatant and solid. The solid was washed with deionized water and dried to obtain a cellulose-rich sample. The supernatant was allowed to stand and separate into layers; the upper aqueous phase was the cellulose degradation product, and the lower organic phase was lignin. Water was added to the organic phase, precipitating lignin, which was then filtered and dried to obtain a lignin sample. The degradation rate of hemicellulose was 92.3%, the degradation rate of lignin was 90.4%, and the retention rate of cellulose was 89.0%.
[0053] Comparative Example 3
[0054] Six g of poplar wood powder was placed in a 100 mL high-pressure reactor, and 60 mL of a mixed solvent of propylene carbonate and water was added. The propylene carbonate content was 60% (v / v), the reaction temperature was 140 ℃, and the reaction time was 120 min. After the reaction, the reactants were filtered to separate the supernatant and solid. The solid was washed with deionized water and dried to obtain a cellulose-rich sample. The supernatant was allowed to stand and separate into layers. The upper aqueous phase was the cellulose degradation product, and the lower organic phase was lignin. Water was added to the organic phase, precipitating lignin. The lignin sample was obtained by filtration and drying. The degradation rate of hemicellulose was 59.0%, the degradation rate of lignin was 25.4%, and the retention rate of cellulose was 88.5%.
[0055] Comparative Example 4
[0056] Six g of poplar wood powder was placed in a 100 mL high-pressure reactor, and 60 mL of a mixed solvent consisting of water and oxalic acid was added. The oxalic acid concentration was 1% (w / v, g / mL), the reaction temperature was 140 ℃, and the reaction time was 120 min. After the reaction, the reactants were filtered to separate the supernatant and solid. The solid was washed with deionized water and dried to obtain a cellulose-rich sample. The supernatant was allowed to stand and separate into layers; the upper aqueous phase was the cellulose degradation product, and the lower organic phase was lignin. Water was added to the organic phase, precipitating lignin, which was then filtered and dried to obtain a lignin sample. The degradation rate of hemicellulose was 99.3%, the degradation rate of lignin was 30.3%, and the retention rate of cellulose was 87.6%.
[0057] Example 10
[0058] The propylene carbonate, water, and oxalic acid used in this example are the recovered solvents from Example 1. After the reaction in Example 1 was completed, the mixture was filtered, and the layers were separated to obtain an organic phase. Water was added to the organic phase, precipitating lignin. The supernatant obtained from filtration was rotary evaporated to obtain propylene carbonate and water, respectively. The amount of oxalic acid added was adjusted according to the initial pH value before the reaction in Example 1.
[0059] Six g of poplar powder was placed in a 100 mL high-pressure reactor, and 60 mL of a mixed solvent consisting of propylene carbonate, water, and oxalic acid was added. The propylene carbonate concentration was 60% (v / v). Oxalic acid was added until the pH value was the same as the initial pH value before the reaction in Example 1 (concentration 1%, w / v, g / mL). The reaction temperature was 140 °C, and the reaction time was 100 min. After the reaction, the reactants were filtered to separate the supernatant and solid. The solid was washed with deionized water and dried to obtain a cellulose-rich sample. The supernatant was allowed to stand and separate into layers; the upper aqueous phase was the cellulose degradation product, and the lower organic phase was lignin. Water was added to the organic phase, precipitating lignin, which was then filtered and dried to obtain a lignin sample. The degradation rate of hemicellulose was 91.8%, the degradation rate of lignin was 83.4%, and the retention rate of cellulose was 87.4%.
[0060] Following the same solvent recovery method, propylene carbonate and water were recovered again, oxalic acid was added, and a solvent recovery test was conducted. Figure 1 It can be seen that the solvent still showed good pretreatment effect when reused for the second and third time, and the degradation rate of hemicellulose and lignin did not decrease significantly.
[0061] 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 separating all components of lignocellulosic biomass using a composite solvent system based on oxalic acid, characterized in that, The wood fiber raw material was pretreated using a composite solvent system consisting of propylene carbonate, water and oxalic acid. The amount of propylene carbonate was 60% to 90% of the volume of the composite solvent system, and the mass-volume ratio of oxalic acid to the composite solvent system was 0.6 to 1.2 g / mL. The degradation rate of hemicellulose was greater than 55%, the degradation rate of lignin was greater than 32%, and the retention rate of cellulose was greater than 84%.
2. The method according to claim 1, characterized in that, After pretreatment, the liquid and solid products were obtained by filtration. The solid products were washed with deionized water and dried to obtain solid residue. The liquid was allowed to stand and separate into layers. The upper aqueous phase was the hemicellulose degradation product and the lower organic phase was lignin. Water was added to the organic phase, and the lignin precipitated. The lignin was then obtained by solid-liquid separation and drying.
3. The method according to claim 1, characterized in that, The wood fiber raw material and the composite solvent system are added to the reaction vessel. The reaction temperature is 100~140 ℃, the reaction time is 20~120 min, and the stirring rate is 400 rpm.
4. The method according to claim 1, characterized in that, The amount of propylene carbonate used is 60% of the volume of the composite solvent system, and the mass-volume ratio of oxalic acid to the composite solvent system is 1~1.2 g / mL; the reaction temperature is 140 ℃, and the reaction time is 100~120 min; the degradation rate of hemicellulose is greater than 90%, the degradation rate of lignin is greater than 87%, and the retention rate of cellulose is greater than 88%.
5. The method according to claim 1, characterized in that, The amount of propylene carbonate used was 60% of the volume of the composite solvent system, and the mass-volume ratio of oxalic acid to the composite solvent system was 1 g / mL; the reaction temperature was 140 ℃, and the reaction time was 100 min; the degradation rate of hemicellulose was 90.3%, the degradation rate of lignin was 87.4%, and the retention rate of cellulose was 92.6%.
6. The method according to claim 1, characterized in that, The wood fiber raw material is poplar wood, which is crushed, passed through an 80-100 mesh sieve, and dried at 105℃ for 12 hours.
7. The method according to claim 1, characterized in that, The ratio of wood fiber raw material to composite solvent system is 1g:10mL.
8. The method according to any one of claims 1 to 7, characterized in that, Includes the following steps: (1) A composite solvent system consisting of propylene carbonate, water, and oxalic acid is mixed with wood fiber raw material and placed in a closed reaction vessel; after the reaction is completed, the solid and liquid are separated after cooling to obtain liquid product and solid product; (2) The liquid product obtained in step (1) was allowed to stand and separate into layers. The aqueous phase was the hemicellulose degradation product, and water was added to the organic phase to precipitate lignin. The lignin was obtained by separation and drying. (3) The solid product obtained in step (1) is washed with water and dried to obtain a solid rich in cellulose; (4) The liquid in step (2) is subjected to vacuum distillation to recover propylene carbonate, water and oxalic acid; (5) Recycle the solvent recovered in step (4) and proceed to step (1), repeating steps (1) to (5).
9. The method according to claim 8, characterized in that, The number of iterations should not exceed 3.