Preparation method of carbon-based sulfonic acid solid acid catalyst and method for synthesizing furfural from xylose

Abstract

The present application belongs to the technical field of furfural synthesis, and particularly relates to a preparation method of a carbon-based sulfonic acid solid acid catalyst and a method for synthesizing furfural from xylose. The present application uses plasma discharge to electrically shock the surface of biomass charcoal to form defect sites. Moreover, the plasma discharge also induces water molecules and sulfonating agent molecules to ionize and dissociate to generate a large number of active species (·OH, ·H, SO3, electrons, etc.). Acidic groups such as sulfonic acid groups and hydroxyl groups are grafted on the defect sites and edges of the biomass charcoal through the interaction of SO3, ·OH and ·H free radicals. Moreover, under the protection of argon and nitrogen, the biomass charcoal structure is not seriously damaged, so that the carbon-based sulfonic acid solid acid catalyst is more firm and stable than the traditional sulfonation method, has good water and heat resistance and recyclability, and uses the carbon-based sulfonic acid solid acid catalyst to realize the conversion of xylose into furfural with high added value and high yield by using the plasma method.

Description

Technical Field

[0001] This invention belongs to the field of furfural synthesis technology, specifically relating to a method for preparing a carbon-based sulfonic acid solid acid catalyst and a method for synthesizing furfural from xylose. Background Technology

[0002] With the drastic depletion of fossil resources, the search for renewable resources that can be converted into chemical pharmaceuticals or energy alternatives has received increasing attention. Biomass is one of the most abundant renewable resources and plays a vital role in the entire energy system. Furfural (FF), also known as furanaldehyde, is an important fine chemical raw material. Furfural is chemically reactive; under acidic conditions, pentosans hydrolyze to form pentoses, which then undergo dehydration and cyclization to produce furfural. As the most important derivative of the furan ring system, furfural can be used to prepare numerous high-value-added derivatives through oxidation, condensation, and other reactions, especially furfuryl alcohol, which is the basic raw material for furan resins. Furfural is widely used in the synthetic rubber, resin, coating, pharmaceutical, and pesticide industries. The raw materials for furfural production are very diverse, mainly agricultural byproducts such as corn cobs. Therefore, the clean and efficient conversion of biomass into FF is of great significance.

[0003] Currently, furfural production still relies on traditional processes, primarily using conventional protic acids as catalysts. While carbon-based sulfonate catalysts exhibit excellent catalytic performance in biomass conversion, they are all applied to the hydrolysis of cellulose to glucose, belonging to the sugar plateau field. There are no reports on their application in the hydrolysis of hemicellulose to xylose or the catalytic production of furfural from xylose. Furthermore, the current main preparation method for carbon-based sulfonate catalysts is sulfonation, which results in catalysts with poor hydrothermal resistance and poor recyclability. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a method for preparing a carbon-based sulfonic acid solid acid catalyst and a method for synthesizing furfural from xylose. The carbon-based sulfonic acid solid acid catalyst has good hydrothermal resistance and recyclability. Using the carbon-based sulfonic acid solid acid catalyst, xylose can be converted into furfural using a plasma method with a high furfural yield.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] This invention provides a method for preparing a carbon-based sulfonic acid solid catalyst, comprising the following steps:

[0007] Under a protective gas, a first plasma discharge is performed on a mixture containing biochar and a sulfonating agent to induce a sulfonation reaction and obtain a sulfonated product; the protective gas is nitrogen and argon.

[0008] The sulfonated product was subjected to solid-liquid separation, washing, and drying in sequence to obtain a carbon-based sulfonic acid solid acid catalyst.

[0009] Preferably, the sulfonating agent is sulfuric acid.

[0010] Preferably, the concentration of the sulfuric acid is 0.5 to 1 mol / L.

[0011] Preferably, the power of the pulse power supply used for the first plasma discharge is 100-500W.

[0012] Preferably, the sulfonation reaction takes 20 to 40 minutes.

[0013] Preferably, the volume ratio of nitrogen to argon is 5-7:3-5.

[0014] This invention also provides a method for synthesizing furfural from xylose, comprising the following steps:

[0015] The feed solution, which includes xylose hydrolysate and carbon-based sulfonic acid solid acid catalyst, is subjected to a second plasma discharge to undergo an elimination reaction. The resulting reaction solution is then separated into solid and liquid components to obtain furfural and the recovered carbon-based sulfonic acid solid acid catalyst.

[0016] The carbon-based sulfonic acid solid acid catalyst is the carbon-based sulfonic acid solid acid catalyst prepared by the preparation method described in the above technical solution.

[0017] Preferably, the power of the pulse power supply used for the second plasma discharge is 100-500W.

[0018] Preferably, the elimination reaction temperature is 150–210°C; and the elimination reaction time is 40–80 min.

[0019] Preferably, the mass ratio of xylose to carbon-based sulfonic acid solid acid catalyst in the xylose hydrolysate is 1:1 to 5.

[0020] This invention provides a method for preparing a carbon-based sulfonic acid solid acid catalyst, comprising the following steps: under a protective gas, a mixture containing biochar and a sulfonating agent is subjected to a first plasma discharge to induce a sulfonation reaction, thereby obtaining a sulfonated product; the protective gas is nitrogen and argon; the sulfonated product is subjected to solid-liquid separation, washing, and drying in sequence to obtain the carbon-based sulfonic acid solid acid catalyst.

[0021] This invention utilizes plasma discharge to electrically shock the surface of biochar, creating defect sites. Furthermore, the plasma discharge induces the ionization and dissociation of water molecules and sulfonating agent molecules, generating a large number of active species (·OH, ·H, SO3, electrons, etc.). Sulfonic acid groups, hydroxyl groups, and other acidic groups are grafted onto these defect sites and edges of the biochar through the interaction of SO3, ·OH, and ·H free radicals. Moreover, under the protection of argon and nitrogen, the biochar structure is not severely damaged, making the carbon-based sulfonic acid solid catalyst more robust and stable than traditional sulfonation methods, exhibiting excellent hydrothermal resistance and recyclability.

[0022] Furthermore, this invention utilizes plasma discharge to prepare carbon-based sulfonic acid solid acid catalysts at room temperature and with low concentrations of sulfonating agent, overcoming the strict reaction conditions of high concentration sulfuric acid (18.4 mol / L) and high temperature (around 180°C) required by the traditional sulfonation method for preparing carbon-based sulfonic acid solid acid catalysts.

[0023] Furthermore, the carbon-based sulfonic acid solid acid catalyst prepared using this invention can be used to convert xylose into furfural with high added value via plasma method, and the furfural yield is high, which has high economic value. Attached Figure Description

[0024] Figure 1 This is a SEM image of the pre-sulfonated biochar in Example 1 of the present invention;

[0025] Figure 2 This is a SEM image of the sulfonated biochar in Example 1 of the present invention;

[0026] Figure 3 This is a schematic diagram of the plasma reactor used in an embodiment of the present invention;

[0027] Figure 4 The graph shows the effect of the number of times the carbon-based sulfonic acid solid acid catalyst prepared in Example 1 of this invention is reused on the synthesis of furfural from xylose. Detailed Implementation

[0028] This invention provides a method for preparing a carbon-based sulfonic acid solid catalyst, comprising the following steps:

[0029] Under a protective gas, a first plasma discharge is performed on a mixture containing biochar and a sulfonating agent to induce a sulfonation reaction and obtain a sulfonated product; the protective gas is nitrogen and argon.

[0030] The sulfonated product was subjected to solid-liquid separation, washing, and drying in sequence to obtain a carbon-based sulfonic acid solid acid catalyst.

[0031] Unless otherwise specified, the present invention does not have special requirements on the source of the raw materials used in the preparation, and commercially available products well known to those skilled in the art can be used.

[0032] In this invention, under a protective gas atmosphere, a mixture containing biochar and a sulfonating agent is subjected to a first plasma discharge to induce a sulfonation reaction, thereby obtaining a sulfonated product.

[0033] In this invention, the method for preparing biochar preferably includes the following steps: carbonizing cellulose, and then sequentially crushing, washing, and drying the resulting carbonized product to obtain biochar. In this invention, the carbonization temperature is preferably 350–450°C, more preferably 400°C; the carbonization holding time is 2–8 hours, more preferably 4–6 hours; the crushing is preferably grinding; the washing reagent is preferably deionized water; the washing is preferably washing until the resulting filtrate is colorless; the drying temperature is preferably 100–105°C, more preferably 105°C; and the drying time is preferably 10–12 hours, more preferably 10 hours.

[0034] In this invention, the particle size of the biochar is preferably 0.075-0.15 mm, more preferably 0.075-0.125 mm.

[0035] In this invention, the sulfonating agent is preferably sulfuric acid; the concentration of the sulfuric acid is preferably 0.5 to 1 mol / L, more preferably 0.7 to 1 mol / L.

[0036] The present invention does not have a special limitation on the amount of biochar and sulfonating agent used; the biochar can be impregnated with the sulfonating agent.

[0037] In this invention, the liquid phase height of the mixture containing biochar and sulfonating agent is preferably 7-11 mm, more preferably 9-10 mm.

[0038] In this invention, the mixture containing biochar and sulfonating agent is preferably obtained by mixing biochar and sulfonating agent; the distance between the top of the mixing container and the liquid phase surface of the mixture containing biochar and sulfonating agent is preferably 5-7 mm, more preferably 5 mm; the mixing is preferably carried out under stirring conditions; the stirring speed is preferably 300-600 rpm, more preferably 500 rpm; the stirring time is preferably 5-20 min, more preferably 10 min; the stirring equipment is preferably an electromagnetic stirrer.

[0039] In this invention, the protective gas is nitrogen and argon; the volume ratio of nitrogen to argon is preferably 5-7:3-5, more preferably 7:3. Argon promotes the generation of higher levels of ·H and ·OH, and the introduction of argon produces positively charged Ar... + Ar*, along with Ar*, facilitates the dissociation of nitrogen. Since nitrogen molecules rotate and vibrate at high temperatures, the addition of argon reduces physical damage to the surface of biochar by lowering the local plasma gas temperature.

[0040] In this invention, the power of the pulse power supply used for the first plasma discharge is preferably 100-500W, more preferably 400-500W, the voltage is preferably 10-30kV, more preferably 20-30kV, and the frequency is preferably 10-20kHz, more preferably 15-20kHz; the equipment used for the first plasma discharge is preferably a plasma reactor.

[0041] In this invention, the sulfonation reaction temperature is preferably room temperature; the sulfonation reaction time is preferably 20 to 40 minutes, more preferably 30 minutes.

[0042] During plasma discharge, the high electric field between the needle electrodes collidees with water molecules and sulfonating agent molecules, causing ionization and dissociation of the water molecules and sulfonating agent molecules. The resulting free electrons form a large number of active species, especially hydroxyl radicals and sulfonic acid radicals. The plasma discharge electro-electrode the surface of biochar, creating defect sites. Acidic groups such as sulfonic acid groups and hydroxyl groups are grafted onto these defect sites and edges through the interaction of SO3, ·OH and ·H radicals, thus completing sulfonation.

[0043] After obtaining the sulfonated product, the present invention sequentially performs solid-liquid separation, washing and drying on the sulfonated product to obtain a carbon-based sulfonic acid solid acid catalyst.

[0044] In this invention, the solid-liquid separation is preferably performed by filtration. The filtration process is not particularly limited; any filtration method well-known in the art can be used.

[0045] In this invention, the reagent used for washing is preferably distilled water; the temperature of the distilled water is preferably 70-80°C, more preferably 80°C; and the washing solution after washing preferably has a neutral pH value.

[0046] In this invention, the drying temperature is preferably 80-85°C, more preferably 85°C; the drying time is preferably 10-12 hours, more preferably 10 hours.

[0047] This invention also provides a method for synthesizing furfural from xylose, comprising the following steps:

[0048] The feed solution, which includes xylose hydrolysate and carbon-based sulfonic acid solid acid catalyst, is subjected to a second plasma discharge to undergo an elimination reaction. The resulting reaction solution is then separated into solid and liquid components to obtain furfural and the recovered carbon-based sulfonic acid solid acid catalyst.

[0049] The carbon-based sulfonic acid solid acid catalyst is the carbon-based sulfonic acid solid acid catalyst prepared by the preparation method described in the above technical solution.

[0050] This invention involves subjecting a feed solution comprising xylose hydrolysate and a carbon-based sulfonic acid solid catalyst to a second plasma discharge, resulting in an elimination reaction. The resulting reaction solution is then subjected to solid-liquid separation to obtain furfural and the recovered carbon-based sulfonic acid solid catalyst, respectively.

[0051] In this invention, the xylose concentration in the xylose hydrolysate is preferably 4-5.2 mg / mL, more preferably 4.5-5 mg / mL.

[0052] In this invention, the preferred method for preparing the xylose hydrolysate is as follows: bamboo powder and deionized water are mixed, hydrolyzed under a protective gas, and then the solid and liquid are separated to obtain the xylose hydrolysate. In this invention, the mass ratio of bamboo powder to deionized water is preferably 1:10–20, more preferably 1:13–15; the protective gas is preferably nitrogen; the hydrolysis pressure is preferably 3–4 MPa, more preferably 3.5 MPa; the hydrolysis temperature is preferably 180–185°C, more preferably 185°C; the holding time for hydrolysis is preferably 15–20 min, more preferably 20 min; the hydrolysis is preferably carried out under stirring conditions; the stirring rate is preferably 300–500 rpm, more preferably 400–500 rpm; the solid-liquid separation is preferably vacuum filtration; the vacuum filtration pressure is preferably 0.05–0.09 MPa, more preferably 0.06–0.08 MPa.

[0053] In this invention, the mass ratio of xylose to carbon-based sulfonic acid solid catalyst in the xylose hydrolysate is preferably 1:1 to 5, more preferably 1:2 to 3; the power of the pulse power supply used for the second plasma discharge is preferably 100 to 500 W, more preferably 400 to 500 W, the voltage is preferably 10 to 30 kV, more preferably 20 to 30 kV, and the frequency is preferably 10 to 20 kHz, more preferably 15 to 20 kHz; the temperature of the elimination reaction is preferably 150 to 210 °C, more preferably 160 to 180 °C; the time of the elimination reaction is preferably 40 to 80 min, more preferably 50 to 60 min; and the equipment used for the second plasma discharge is preferably a plasma reactor.

[0054] In this invention, the carbon-based sulfonic acid solid acid catalyst has acidic groups such as hydroxyl, carboxyl, and sulfonic acid groups on its surface, exhibiting good acidity and high selectivity, thereby converting xylose into furfural. The carbon-based sulfonic acid solid acid catalyst contains a high density of hydrophilic functional groups (phenolic hydroxyl and carboxyl groups), which can attract a large amount of water and hydrophilic molecules, thus allowing the reactants to better approach the -SO3H groups on the carbon-based sulfonic acid solid acid catalyst. The hydroxyl and oxygen free radicals can react with the OH and CH bonds of carbohydrates, promoting the conversion of xylose into furfural.

[0055] The structure of the plasma reactor used in the embodiments of the present invention is as follows: Figure 3 As shown.

[0056] In this invention, the solid-liquid separation is preferably performed by filtration; the filtration is preferably carried out using a membrane filter; the pore size of the membrane in the membrane filter is preferably 10–25 μm, more preferably 15–20 μm. This invention does not impose any particular limitation on the filtration process; any filtration method well known in the art can be used.

[0057] In this invention, the reaction solution is preferably cooled before solid-liquid separation is performed; the cooling is preferably natural cooling.

[0058] After obtaining the recovered carbon-based sulfonic acid solid acid catalyst, the present invention preferably further includes: washing and drying the recovered carbon-based sulfonic acid solid acid catalyst for reuse.

[0059] In this invention, the reagent used for washing is preferably deionized water; the number of washing cycles is preferably 3 to 6 times, more preferably 5 to 6 times.

[0060] In this invention, the drying temperature is preferably 80-85°C, more preferably 85°C; the drying time is preferably 8-10 hours, more preferably 10 hours.

[0061] In this invention, the number of times the device is reused is preferably 1 to 6 times, more preferably 4 to 6 times.

[0062] In this invention, the carbon-based sulfonic acid solid acid catalyst and the dried and recycled carbon-based sulfonic acid solid acid catalyst are placed in a sealed bag and stored in a desiccator.

[0063] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention, but they should not be construed as limiting the scope of protection of the present invention.

[0064] Examples 1-6

[0065] Cellulose was carbonized in a tube furnace at 400°C for 5 hours. After cooling, it was ground into powder with a particle size of (0.075-0.125 mm). The powder was washed with deionized water until the filtrate was colorless. The washed dark brown solid product was dried at 105°C for 10 hours to obtain biochar.

[0066] The above-mentioned biochar (Carbon) was mixed with H2SO4 solution. The distance between the top of the mixing container and the liquid surface of the resulting mixture was controlled at 5 mm. An electromagnetic stirrer was started and stirred at 500 rpm for 10 min. Before starting the pulse power supply, a cooling fan was turned on to dissipate heat. The volume ratio of nitrogen to argon was 7:3. Plasma discharge was generated in the plasma reactor. The power of the pulse power supply was 400 W, the voltage was 20 kV, and the frequency was 20 kHz. A sulfonation reaction occurred at room temperature. The sulfonation product was then filtered. The resulting solid was washed with distilled water at 80 °C until the pH of the washing liquid reached neutral. Finally, it was dried in an oven at 85 °C for 10 h to obtain a carbon-based sulfonic acid solid acid catalyst.

[0067] The specific preparation conditions for Examples 1 to 6 are shown in Table 1.

[0068] Table 1. Specific preparation conditions and sulfonic acid group density of Examples 1-6

[0069]

[0070] Comparative Example 1

[0071] The catalyst was prepared by first mixing 10g of microcrystalline cellulose (≤120 mesh) into 1L of FeCl3 solution (10mmol / L) and stirring for 5h under continuous stirring at 400rpm. Then, the water was evaporated by heating at 100℃ in a benchtop electric furnace. The remaining solid was then dried overnight in an oven at 105℃. It was then further carbonized (350℃, nitrogen protection for 1h), sulfonated with sulfuric acid (98% w / w, solid-liquid ratio 1:10, 130℃, 10h), and finally washed with hot water (80℃). The prepared magnetic carbon-based solid acid is amorphous carbon, as detailed in the prior art (QIW, LIUGF, HEC, et al. An efficient magnetic carbon-based solid acid treatment for corncobsac charity with high selectivity for xylose and enhance denzymatic digestibility[J]. Green Chemistry, 2019, 21(6):1292-304).

[0072] The synthesis of carbon-based solid acids involved placing a mixture of microcrystalline cellulose and sulfuric acid in a 100 mL PTFE-lined stainless steel high-pressure reactor at 120–200 °C. The mass ratio of microcrystalline cellulose to sulfuric acid was 1:1–20. The mixture was then heated in a muffle furnace for 4–24 h. The resulting product was filtered and treated with ethanol and hot water (80 °C) until SO4 was undetectable by BaCl2. 2-Then, it is dried overnight in a vacuum oven at 105°C. Finally, the carbon-based solid acid is ground into powder and sieved with a 120-mesh sieve. For details, see the existing technology (QI ZQ, WANGQ, LIANGCY, et al. Highly Efficient Conversion of Xylose to Furfural in a Water-MIBK System Catalyzed by Magnetic Carbon-Based Solid Acid[J]. Industrial & Engineering Chemistry Research, 2020, 59(39): 17046-56).

[0073] Application Examples 1-7

[0074] Bamboo powder and deionized water were mixed at a mass ratio of 1:15 and hydrolyzed in a high-temperature reactor at 180°C and 4MPa N2 for 20 min at a rotation speed of 400 rpm. After filtration at a pressure of 0.08 MPa, the xylose hydrolysate (xylose mass concentration of 5.2 mg / mL) was collected.

[0075] The xylose in the xylose hydrolysate and the carbon-based sulfonic acid solid acid catalyst prepared in Example 1 were added to the plasma reactor (e.g., ...) at different mass ratios. Figure 3 As shown, at room temperature, a pulse power supply (500W) was started at 500 rpm to generate plasma discharge at a voltage of 20V and a frequency of 20kHz to carry out the elimination reaction. After the plasma reactor cooled down, the reaction solution was collected and filtered using a membrane filter (membrane pore size of 20-25μm) to obtain furfural and recovered carbon-based sulfonic acid solid acid catalyst. The recovered carbon-based sulfonic acid solid acid catalyst was washed 5 times with deionized water and then dried in an oven at 80℃ for 10h. The dried recovered carbon-based sulfonic acid solid acid catalyst was then collected, placed in a sealed bag, and stored in a desiccator for use in cyclic experiments.

[0076] The specific preparation conditions for Application Examples 1 to 7 are shown in Table 2.

[0077] Table 2 shows the specific preparation conditions and furfural yields for Application Examples 1-7.

[0078]

[0079] Comparative Application Example 1

[0080] The degradation of xylose to furfural was carried out in a high-temperature reactor. The optimal reaction conditions were 0.65 g xylose, 2 g MMCSA catalyst, 190 °C, and 20 min. After being reused 5 times, the FF yield gradually decreased from 79.04% to 26.03%, indicating that the catalyst was significantly deactivated and had poor recyclability. For details, please refer to the existing technology (QIW, LIUGF, HEC, et al. An efficient magnetic carbon-based solvent treatment for corncobsac characterization with high selectivity for xylose and enhanced enzymatic digestibility[J]. Green Chemistry, 2019, 21(6): 1292-304).

[0081] Comparative Application Example 2

[0082] The reaction conditions were: 0.5 g of carbon-based solid acid catalyst, 0.25 g of corn cob, and 25 mL of deionized water. The reaction was carried out in a 100 mL thick-walled pressure bottle with a 2 cm magnetic rod on a magnetic stirrer and in an oil bath at 130 °C for 4 to 5 cycles. After the reaction was repeated, the xylose yield decreased slightly from 70.4% to 63.0%. For details, please refer to the existing technology (QIZQ, WANGQ, LIANGCY, et al. Highly Efficient Conversion of Xylose to Furfural in a Water-MIBK System Catalyzed by Magnetic Carbon-Based Solid Acid[J]. Industrial & Engineering Chemistry Research, 2020, 59(39): 17046-56).

[0083] Performance testing

[0084] Electron microscopy was performed on the biochar before and after sulfonation in Example 1. The results are as follows: Figures 1-2 As shown.

[0085] Figure 1 The image shows a scanning electron microscope (SEM) image of untreated carbon material. The sample has a complete and dense surface morphology with a small number of submicron particles and no obvious voids or cracks. This is in contrast to plasma-treated biochar. Figure 2 The sample exhibits obvious cracks, with more submicron particles around and on the surface. This demonstrates that plasma has a significant etching effect on the biochar material and creates defects on its surface, which may facilitate the grafting of acidic groups such as sulfonic acid groups, hydroxyl groups, and carboxyl groups.

[0086] Figure 4 The graph shows the effect of the number of times the carbon-based sulfonic acid solid acid catalyst prepared in Example 1 of this invention is reused on the synthesis of furfural from xylose.

[0087] Depend on Figure 4 It can be seen that after five cycles, the yield of furfural decreased from 72% to 69.5% of the carbon-based sulfonic acid solid acid catalyst prepared by the present invention, and the recovery rate was over 96%, indicating good cycling performance.

[0088] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention and not all embodiments. People can obtain other embodiments based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for synthesizing furfural from xylose, characterized in that, Includes the following steps: The feed solution, which includes xylose hydrolysate and carbon-based sulfonic acid solid acid catalyst, is subjected to a second plasma discharge to undergo an elimination reaction. The resulting reaction solution is then separated into solid and liquid components to obtain furfural and the recovered carbon-based sulfonic acid solid acid catalyst. The preparation method of the carbon-based sulfonic acid solid acid catalyst includes the following steps: Under a protective gas, a first plasma discharge is performed on a mixture containing biochar and a sulfonating agent to induce a sulfonation reaction and obtain a sulfonated product. The protective gas is nitrogen and argon; The sulfonating agent is sulfuric acid; the concentration of the sulfuric acid is 0.5~1 mol / L; The power of the pulse power supply used for the first plasma discharge is 100~500W; the sulfonation reaction time is 20~40min; the volume ratio of nitrogen to argon is 5~7:3~5; The sulfonated product was subjected to solid-liquid separation, washing and drying in sequence to obtain a carbon-based sulfonic acid solid acid catalyst. The power of the pulse power supply used for the second plasma discharge is 100~500W; The elimination reaction is carried out at a temperature of 150~210℃ and for a time of 40~80 min. The mass ratio of xylose to carbon-based sulfonic acid solid acid catalyst in the xylose hydrolysate is 1:1~5.

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