Method for preparing 5-hydroxymethylfurfural from chitosan catalyzed by organic weak acid-ionic liquid

Abstract

The application discloses a method for preparing 5-hydroxymethylfurfural by catalyzing chitosan with an organic weak acid-ionic liquid, which comprises the following steps: taking chitosan as raw material, taking an organic weak acid-imidazole-based ionic liquid as catalyst, taking dimethyl sulfoxide aqueous solution as solvent, and obtaining 5-hydroxymethylfurfural through hydrothermal reaction; the organic weak acid-imidazole-based ionic liquid is composed of an organic weak acid and an imidazole-based ionic liquid, the organic weak acid is a main catalyst, and the imidazole-based ionic liquid is an auxiliary catalyst; the dimethyl sulfoxide aqueous solution is composed of dimethyl sulfoxide and deionized water. The method for preparing 5-hydroxymethylfurfural by catalyzing chitosan with an organic weak acid-ionic liquid, which utilizes a catalytic system with an organic weak acid as catalyst and an imidazole-based ionic liquid as auxiliary catalyst, and directly converts chitosan into 5-hydroxymethylfurfural through hydrothermal reaction. The method needs less ionic liquid, has low system viscosity, is simple to operate, and has short degradation time, and is very suitable for industrial production of 5-hydroxymethylfurfural.

Description

Technical Field

[0001] This invention relates to the field of biomass conversion technology, and in particular to a method for preparing 5-hydroxymethylfurfural from chitosan using organic weak acid-ionic liquid catalysis. Background Technology

[0002] Fossil fuels are the material foundation for social stability and economic development. However, the Earth's fossil resources are finite and non-renewable. Over-exploitation and irrational use by humans have led to global environmental problems and resource crises. With the continuous progress and development of the global economy, resource shortages and environmental pollution will become even more severe. Therefore, finding renewable and environmentally friendly alternative energy sources has become a global challenge. Widely available biomass is the most likely renewable resource to replace fossil fuels. It is estimated that the Earth produces 200 billion tons of biomass annually, equivalent to ten times the current global annual energy consumption; however, only 5% of biomass resources are currently utilized by humans. Therefore, the full development and utilization of biomass resources is of great significance for alleviating resource shortages and protecting the environment.

[0003] Chitin and chitosan are ubiquitous biomass found in nature, possessing excellent biocompatibility, biodegradability, antibacterial properties, and hygroscopicity, making them widely applicable in medicine, agriculture, cosmetics, and water treatment. Chitin and chitosan are the most abundant natural nitrogen-containing polysaccharides on Earth, found in the shells of arthropods such as shrimp and crabs, as well as in the cell walls of fungi and certain algae. Approximately 10 billion tons of chitin biomass are generated annually in waste from global fisheries and marine industries. Therefore, as an important nitrogen source for Earth and marine life, fully utilizing chitin biomass is crucial for the effective development of marine resources, addressing increasingly serious environmental problems, and alleviating resource shortages, becoming an important direction for the future development of the chemical raw materials and energy industries.

[0004] Biomass-based platform molecules refer to a series of organic compounds prepared from natural, renewable biomass through conversion and widely used. As a link between renewable biomass resources and fine chemicals, biomass-based platform molecules are of great significance in the utilization of biological resources and have attracted increasing attention from researchers. Currently, biomass can be degraded into various biomass-based platform molecules. Among them, 5-HMF is one of the important biomass platform compounds released by the U.S. Department of Energy and can be directly obtained from various biomass sources. 5-HMF molecules contain active groups such as aldehydes and hydroxyl groups, and can undergo reactions such as hydrogenation, oxidative dehydrogenation, esterification, halogenation, polymerization, and hydrolysis to further convert them into other fine chemicals. It plays a crucial role in the preparation of important materials such as polymers, pharmaceuticals, resins, plastics, and fuel additives.

[0005] Currently, mainstream industrial production processes for furfural typically use sulfuric acid as a catalyst, but this leads to a series of problems such as equipment corrosion, separation difficulties, and wastewater treatment. While transition metal salts can lower the activation energy required for the reaction, thereby improving reactant conversion and target product selectivity, they cause heavy metal pollution, which is inconsistent with the trend of green development. With increasing attention to the environmental impact of chemical production, the requirements for green and sustainable production are also becoming more stringent. Therefore, developing green, simple, efficient, and low-cost methods, and finding more efficient solvents and catalysts to fully dissolve biomass and promote its conversion, to achieve the preparation of the high-value-added platform compound 5-HMF from biomass, has significant research and production value.

[0006] To address the challenge of converting biomass into platform compounds, researchers have focused on finding greener, more environmentally friendly, and cheaper catalytic systems. Natural organic acids, such as oxalic acid and tartaric acid, have relatively mild acidity, are less corrosive to equipment, and are available from lignocellulose. They offer several advantages, including biodegradability, non-toxicity, and ease of post-reaction handling, making them ideal green catalysts. However, organic acids exhibit weak dissociation in water or organic solvents, resulting in generally low catalytic dehydration efficiency. Higher acid concentrations or co-application with other catalysts are typically required to achieve conversion rates comparable to inorganic acids. The acidity of the catalyst can affect the hydrolysis rate; while high acid concentrations accelerate chitosan dehydration, they can also lead to further hydrolysis of 5-hydroxymethylfurfural into levulinic acid, increasing the probability of humin formation.

[0007] Therefore, exploring a method to enhance the dissociation ability of organic acids, especially to effectively adjust their acidity in solvents, is of great significance for achieving the green, stable and efficient conversion of carbohydrates into platform compounds. Summary of the Invention

[0008] To address the problems of high system viscosity and poor selectivity of 5-hydroxymethylfurfural (5-HMF) due to byproduct formation in existing technologies, this invention aims to provide a method for preparing 5-hydroxymethylfurfural (5-HMF) from chitosan using an organic weak acid-ionic liquid catalysis system. This method utilizes an organic weak acid as a catalyst and an imidazole-based ionic liquid as a co-catalyst to directly convert chitosan into 5-HMF via a hydrothermal reaction. This method requires less ionic liquid, has low system viscosity, is simple to operate, and has a short degradation time, making it highly suitable for industrial production of 5-HMF.

[0009] To achieve the above objectives, the technical solution of the present invention is: a method for preparing 5-hydroxymethylfurfural from chitosan using an organic weak acid-ionic liquid catalyst, wherein chitosan is used as raw material, an organic weak acid-imidazolium ionic liquid is used as catalyst, dimethyl sulfoxide aqueous solution is used as solvent, the reaction temperature is 180℃, the reaction time is 5h, and 5-hydroxymethylfurfural is obtained.

[0010] The organic weak acid-imidazolium ionic liquid is composed of an organic weak acid and an imidazolium ionic liquid, wherein the organic weak acid is the main catalyst and the imidazolium ionic liquid is the co-catalyst.

[0011] The dimethyl sulfoxide aqueous solution is composed of dimethyl sulfoxide and deionized water.

[0012] Furthermore, it includes the following steps:

[0013] A mixture of chitosan, an organic weak acid, dimethyl sulfoxide, dimethyl sulfoxide and imidazole ionic liquid was prepared. The mixture was placed in an oil bath at 180°C for 5 hours. After the reaction was completed, the mixture was transferred to an ice-water bath for quenching. After the quenching reaction was completed, the reaction solution was centrifuged to obtain a supernatant containing 5-hydroxymethylfurfural.

[0014] Furthermore, the mass ratio of the organic weak acid to the imidazole ionic liquid is 0.7:1.2.

[0015] Furthermore, the mass ratio of dimethyl sulfoxide to deionized water is 2:3.

[0016] Furthermore, the organic weak acid is selected from at least one of oxalic acid, formic acid, citric acid, succinic acid, malonic acid, and acetic acid.

[0017] Further, the imidazole ionic liquid is selected from at least one of 1-allyl-3-methylimidazolium bromide, 1-ethyl-3-methylimidazolium bromide, 1-allyl-3-methylimidazolium chloride, 1-ethyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium chloride, and 1-ethyl-3-methylimidazolium acetate.

[0018] Furthermore, the supernatant containing 5-hydroxymethylfurfural was diluted to 50 mL with the mobile phase, and its yield was determined by high performance liquid chromatography.

[0019] Furthermore, the sample solution and standard sample solution were taken and detected by high performance liquid chromatography (HPLC). The HPLC conditions were as follows: a C18HD 5μm 250×4.6mm column, an ultraviolet detector, an ultraviolet detection wavelength of 283nm, a mobile phase of CH3OH / H2O = 10 / 90 (volume ratio), a mobile phase flow rate of 0.70mL / min, and an injection volume of 5μL.

[0020] In summary, the present invention has the following beneficial effects:

[0021] This invention presents a novel method for the efficient conversion of chitosan to 5-hydroxymethylfurfural, using chitosan as a raw material, a mixed solution of water and dimethyl sulfoxide (DMSO) as a solvent, a weak organic acid as a catalyst, and an imidazole ionic liquid as a co-catalyst. This method is simple to operate, easy to implement, and yields good product yields.

[0022] The method of this invention requires less ionic liquid, has low system viscosity, is simple to operate, and has a short degradation time, making it very suitable for the industrial production of 5-hydroxymethylfurfural. Furthermore, this invention uses inexpensive and readily available ionic liquids, such as choline chloride and 1-butyl-3-methylimidazolium chloride, which can promote the dissociation of organic acids, stabilize organic acids, and are relatively inexpensive. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] The method for determining the yield of 5-hydroxymethylfurfural involved in this application is as follows:

[0025] A method for detecting 5-hydroxymethylfurfural (HMF) using high-performance liquid chromatography (HPLC) includes the following steps: Accurately weigh 0.2000 g of 5-HMF standard (purity >99%) using an electronic balance, add 50 mL of mobile phase (methanol / water, volume ratio 10 / 90) for dilution to prepare a 4.0 mg / mL standard solution. This solution is then sequentially diluted with the mobile phase to prepare 5-HMF standard solutions with concentrations of 0.1, 0.2, 0.3, 0.4, 0.5, and 0.6 mg / mL. After filtration through a 0.22 μm microporous membrane, the solution is detected by HPLC. The concentration is calculated based on the peak area, and a standard curve is constructed. The 5-HMF sample solution is also filtered through a microporous membrane and detected by HPLC; its concentration is calculated using the standard curve. All raw materials used in this application are commercially available and have no special requirements.

[0026] Example 1

[0027] The specific method for preparing 5-hydroxymethylfurfural from chitosan using organic weak acid-ionic liquid catalysis is as follows:

[0028] Mix 2.4 g of DMSO and 3.6 g of deionized water thoroughly to obtain a dimethyl sulfoxide aqueous solution;

[0029] A mixed solvent consisting of chitosan (0.2 g), dimethyl sulfoxide aqueous solution (6 g), 1-butyl-3-methylimidazolium chloride (1.2 g), and an organic weak acid (0.1 g) was added to a 35 mL thick-walled pressure-resistant bottle. The bottle was immersed in an oil bath preheated to 180 °C and reacted for 3 hours. The bottle was then removed and immediately placed in an ice-water bath to stop the reaction. The mixture was centrifuged at 8000 rpm for 5 minutes at 25 °C using a benchtop centrifuge. The supernatant was transferred to a 50 mL volumetric flask, diluted to volume, and the peak area and concentration of the target product were determined by high-performance liquid chromatography (HPLC). The yield of 5-hydroxymethylfurfural was calculated using a standard regression equation.

[0030] To investigate the effect of weak organic acids on the yield of 5-hydroxymethylfurfural, the weak organic acids in Example 1 were screened as follows:

[0031] Table 1. Yields of 5-hydroxymethylfurfural in Examples 1.1-1.5

[0032] Example Example 1.1 Example 1.2 Example 1.3 Example 1.4 Example 1.5 Example 1.5 organic weak acids oxalic acid Formic acid Citric acid Succinic acid glacial acetic acid malonic acid Yield (%) 9.18 4.47 1.99 1.6 0.06 0.1

[0033] As shown in Table 1, the acidity of the catalyst can also affect the hydrolysis rate and thus the catalytic yield. The synergistic effect of oxalic acid and ionic liquid can significantly improve the catalytic activity; the catalytic activity of adding oxalic acid alone or adding ionic liquid alone is significantly weaker than the effect of the synergistic effect of the two.

[0034] Example 2

[0035] The specific method for preparing 5-hydroxymethylfurfural from chitosan using organic weak acid-ionic liquid catalysis is as follows:

[0036] Mix 2.4 g of DMSO and 3.6 g of deionized water thoroughly to obtain a dimethyl sulfoxide aqueous solution;

[0037] A mixed solvent consisting of chitosan (0.2 g), dimethyl sulfoxide aqueous solution (6 g), imidazole ionic liquid (1.2 g), and oxalic acid (0.1 g) was added to a 35 mL thick-walled pressure-resistant bottle. The bottle was immersed in an oil bath preheated to 180 °C and reacted for 3 hours. The bottle was then removed and immediately placed in an ice-water bath to stop the reaction. The mixture was centrifuged at 8000 rpm for 5 minutes at 25 °C using a benchtop centrifuge. The supernatant was transferred to a 50 mL volumetric flask, diluted to volume, and the peak area and concentration of the target product were determined by high-performance liquid chromatography (HPLC). The yield of 5-hydroxymethylfurfural was calculated using a standard regression equation.

[0038] To investigate the effect of imidazole ionic liquids on the yield of 5-hydroxymethylfurfural, the imidazole ionic liquids in Example 1 were screened as follows:

[0039] Table 2. Yield of 5-hydroxymethylfurfural in Example 2.2

[0040] Example Imidazole ionic liquids Yield (%) Example 2.1 1-Allyl-3-methylimidazolium bromide 8.23 Example 2.2 1-Ethyl-3-methylimidazolium bromide 6.41 Example 2.3 1-Allyl-3-methylimidazolium chloride 6.04 Example 2.4 1-Ethyl-3-methylimidazolium chloride 4.89 Example 2.5 1-Butyl-3-methylimidazolium chloride 9.18 Example 2.6 1-Ethyl-3-methylimidazolium acetate 0

[0041] As can be seen from Table 2, the results for 1-ethyl-3-methylimidazolium acetate are not surprising, because the reaction is carried out under acid catalysis. The acetate anion of 1-ethyl-3-methylimidazolium acetate neutralizes the acid and acidity in the reaction mixture, resulting in low selectivity for 5-hydroxymethylfurfural.

[0042] As shown in Tables 1 and 2, the synergistic effect of oxalic acid and 1-butyl-3-methylimidazolium chloride significantly improves the yield of 5-hydroxymethylfurfural, mainly because it regulates the acidity of oxalic acid, promotes its dissociation and release of hydrogen ions, thereby enhancing its catalytic performance. The H+ released by the self-dissociation of oxalic acid... + The catalytic dehydration performance is relatively poor. Upon addition of 1-butyl-3-methylimidazolium chloride, the chloride anion in the chloride acts as a strongly electronegative group, interacting with the hydrogen ions of the hydroxyl group in oxalic acid through hydrogen bonding. Due to the electron-withdrawing effect of the chloride group, the electron density cloud of the oxygen atom on the hydroxyl group decreases, thereby weakening the OH bond. Furthermore, the interaction between the anions and cations of 1-butyl-3-methylimidazolium chloride also weakens the OH bond, making it easier for the hydrogen in the carboxyl group to dissociate as hydrogen ions.

[0043] Example 3

[0044] The only difference from Example 1 is that the oil bath temperature is different, the reaction time is different, and the organic acid is oxalic acid.

[0045] Table 3. Yield of 5-hydroxymethylfurfural in Example 3

[0046]

[0047] Table 3 shows that increasing the oil bath temperature and duration improves the yield of 5-hydroxymethylfurfural (5-HMF). However, when the oil bath time exceeds 5 hours, the yield tends to decrease. This decrease may be due to the reaction of 5-HMF with monosaccharides, leading to the formation of humin. Furthermore, 5-HMF can be further converted to produce byproducts such as formic acid and levulinic acid.

[0048] The reason why the yield of 5-hydroxymethylfurfural (5-HMF) obtained in Example 1 (3.44% yield after 3 hours of oil bath at 180°C) differs from the yield of 9.18% obtained in Example 2 (9.18% yield after 3 hours of oil bath at 180°C) is explained as follows: The experiments in Examples 1 and 2 were preliminary experiments, and the oil bath used was not the same as that used in the single-factor experiments. Differences in instrument temperature may affect the yield. All single-factor experiments in Example 3 of this application were conducted in the same oil bath, ensuring the accuracy of the data!

[0049] Example 4

[0050] The specific method for preparing 5-hydroxymethylfurfural from chitosan using organic weak acid-ionic liquid catalysis is as follows:

[0051] Mix 2.4 g of DMSO and 3.6 g of deionized water thoroughly to obtain a dimethyl sulfoxide aqueous solution;

[0052] A mixed solvent consisting of chitosan (0.2 g), dimethyl sulfoxide aqueous solution (6 g), 1-butyl-3-methylimidazolium chloride (1.2 g), and oxalic acid (0.1 g) was added to a 35 mL thick-walled pressure-resistant bottle. The bottle was immersed in an oil bath preheated to a certain temperature. After reacting for 5 hours, the bottle was removed and immediately placed in an ice-water bath to stop the reaction. The mixture was centrifuged at 8000 rpm for 5 minutes at 25 °C using a benchtop centrifuge. The supernatant was transferred to a 50 mL volumetric flask, diluted to volume, and the peak area and concentration of the target product were determined by high-performance liquid chromatography (HPLC). The yield of 5-hydroxymethylfurfural was calculated using a standard regression equation.

[0053] To investigate the effect of oil bath temperature on the yield of 5-hydroxymethylfurfural, the oil bath temperature in Example 4 was screened as follows:

[0054] Table 4. Yield of 5-hydroxymethylfurfural in Example 4

[0055] oil bath temperature 150℃ 160℃ 170℃ 180℃ Yield (%) 0.14 0.74 5.36 9.02

[0056] Table 4 shows that under oil bath conditions of 5 hours, the yield of 5-hydroxymethylfurfural increased as the reaction temperature increased from 150℃ to 190℃, indicating that the reaction accelerated at higher temperatures. The yields reached 0.14%, 0.74%, 5.36%, and 9.02% at 150℃, 160℃, 170℃, and 180℃, respectively. Further increases in temperature may lead to the dissociation of oxalic acid, affecting the yield of 5-hydroxymethylfurfural.

[0057] Example 5

[0058] The specific method for preparing 5-hydroxymethylfurfural from chitosan using organic weak acid-ionic liquid catalysis is as follows:

[0059] Mix DMSO and deionized water thoroughly to obtain a dimethyl sulfoxide aqueous solution.

[0060] A mixed solvent consisting of chitosan (0.2 g), dimethyl sulfoxide aqueous solution (6 g), 1-butyl-3-methylimidazolium chloride (1.2 g), and oxalic acid (0.1 g) was added to a 35 mL thick-walled pressure-resistant bottle. The bottle was immersed in an oil bath preheated to a certain temperature. After reacting for 5 hours, the bottle was removed and immediately placed in an ice-water bath to stop the reaction. The mixture was centrifuged at 8000 rpm for 5 minutes at 25 °C using a benchtop centrifuge. The supernatant was transferred to a 50 mL volumetric flask, diluted to volume, and the peak area and concentration of the target product were determined by high-performance liquid chromatography (HPLC). The yield of 5-hydroxymethylfurfural was calculated using a standard regression equation.

[0061] To investigate the effect of the composition of the dimethyl sulfoxide aqueous solution on the yield of 5-hydroxymethylfurfural, the dimethyl sulfoxide aqueous solution in Example 5 was screened as follows:

[0062] Table 5. Yield of 5-hydroxymethylfurfural in Example 5

[0063] DMSO(g) Deionized water (g) Yield (%) 0 6 6.53 1.2 4.8 8.89 2.4 3.6 9.02 3.6 2.4 7.88 4.8 1.2 2.4 6 0 0

[0064] As shown in Table 5, DMSO is the key solvent for the hydrothermal conversion of chitosan to 5-hydroxymethylfurfural. With the addition of DMSO, the yield of 5-hydroxymethylfurfural first increases and then decreases. DMSO can combine with hydrogen ions in the system, promote the hydrolysis of monosaccharides, inhibit the formation of by-products, and thus improve the yield of the target product.

[0065] Example 6

[0066] The only difference from Example 1 is the amount of 1-butyl-3-methylimidazolium chloride used.

[0067] Table 6. Yield of 5-hydroxymethylfurfural in Example 6

[0068] 0wt% 10wt% 20wt% 30wt% 40wt% Yield (%) 6.57 7.61 9.02 7.88 5.88

[0069] In Table 6, the mass percentages are the mass ratios of 1-butyl-3-methylimidazolium chloride and dimethyl sulfoxide aqueous solution.

[0070] As shown in Table 6, the yield of 5-hydroxymethylfurfural increased significantly with the change in the amount of 1-butyl-3-methylimidazolium chloride. The addition of 1-butyl-3-methylimidazolium chloride has a positive effect on the preparation of 5-hydroxymethylfurfural, improving the solubility of chitosan in DMSO aqueous solution, increasing the proton-donating ability of oxalic acid, and effectively regulating the acidity of the system. Although 1-butyl-3-methylimidazolium chloride can increase the reaction rate and reduce the activation energy, excessive addition will promote the occurrence of side reactions and reduce the catalytic efficiency.

[0071] Example 7

[0072] The only difference from Example 1 is the amount of oxalic acid used.

[0073] Table 7 Yield of 5-hydroxymethylfurfural in Example 7

[0074] Oxalic acid (g) 0.1 0.2 0.3 0.4 0.5 Yield (%) 9.32 19.32 24.42 24.08 26.85 Oxalic acid (g) 0.6 0.7 0.8 Yield (%) 27.96 29.07 29.24

[0075] As shown in Table 7, the yield of 5-hydroxymethylfurfural increases with the change in oxalic acid dosage and then gradually stabilizes. The acidity of the system plays a crucial role in the catalytic reaction. The hydrogen protons that play a catalytic role are mainly provided by oxalic acid. 1-Butyl-3-methylimidazolium chloride can interact with the OH group of oxalic acid, promoting hydrogen dissociation and improving the selectivity of the target product.

[0076] Example 8

[0077] The only difference from Example 2 is that no organic acid is added.

[0078] When only ionic liquids are added without adding organic acids, the catalytic activity of the system is not strong, and the catalytic effect on 5-hydroxymethylfurfural is relatively weak.

[0079] Comparative Example

[0080] Comparative Example 1

[0081] The only difference between Example 2 and Example 8 is that no weak organic acid was added. The standard regression equation showed that 5-hydroxymethylfurfural had almost no yield without the addition of the weak organic acid.

[0082] Comparative Example 2

[0083] The only difference from Example 1 is that no imidazole ionic liquid was added.

[0084] Table 8. Yield of 5-hydroxymethylfurfural in Comparative Example 2

[0085] organic weak acids oxalic acid Formic acid Citric acid Succinic acid malonic acid acetic acid Yield (%) 2.59 0.97 0.38 0.07 0 0

[0086] As can be seen from Tables 1 and 8, the yield of 5-hydroxymethylfurfural was higher after the addition of the ionic liquid compared to the yield without it. The ionic liquid acts as a co-catalyst in the catalytic system and can adjust the acidity of the system.

[0087] As can be seen from Examples 1-8 and Comparative Examples 1-2, ionic liquids enhance the dissociation ability of oxalic acid by adjusting the acidity of the organic acid catalyst. This promotes the dehydration of chitosan to 5-hydroxymethylfurfural (HMF), and DMSO aqueous solution can suppress the generation of byproducts in the catalytic system, thus improving the accessibility of 5-HMF.

[0088] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing 5-hydroxymethylfurfural from chitosan using an organic weak acid-ionic liquid catalysis, characterized in that, Using chitosan as raw material, an organic weak acid-imidazolium ionic liquid as a catalyst, and a dimethyl sulfoxide aqueous solution as a solvent, the reaction temperature was 180℃ and the reaction time was 5 h to obtain 5-hydroxymethylfurfural. The organic weak acid-imidazolium ionic liquid is composed of an organic weak acid and an imidazolium ionic liquid, wherein the organic weak acid is the main catalyst and is oxalic acid, and the imidazolium ionic liquid is the co-catalyst and is 1-butyl-3-methylimidazolium chloride. The mass ratio of the organic weak acid to the imidazolium ionic liquid is 0.7:1.

2. The dimethyl sulfoxide aqueous solution is composed of dimethyl sulfoxide and deionized water, and the mass ratio of dimethyl sulfoxide to deionized water is 2:

3.

2. The method for preparing 5-hydroxymethylfurfural from chitosan using an organic weak acid-ionic liquid catalysis according to claim 1, characterized in that, The process includes the following steps: a mixture of chitosan, an organic weak acid, dimethyl sulfoxide, dimethyl sulfoxide and imidazole ionic liquid is prepared. The mixture is placed in an oil bath at 180°C and reacted for 5 hours. Then, it is transferred to an ice-water bath for quenching reaction. After the quenching reaction is completed, the reaction solution is centrifuged to obtain a supernatant containing 5-hydroxymethylfurfural.

3. The method for preparing 5-hydroxymethylfurfural from chitosan using an organic weak acid-ionic liquid catalysis according to claim 1, characterized in that, The supernatant containing 5-hydroxymethylfurfural was diluted to 50 mL with mobile phase, and the yield was determined to be 29.07% by high performance liquid chromatography.

4. The method for preparing 5-hydroxymethylfurfural from chitosan using an organic weak acid-ionic liquid catalysis according to claim 1, characterized in that, Sample solutions and standard sample solutions were taken and detected by high performance liquid chromatography (HPLC). The HPLC conditions were as follows: a C18HD 5μm 250×4.6mm column, a UV detector, a UV detection wavelength of 283nm, a mobile phase CH3OH / H2O volume ratio of 10 / 90, a mobile phase flow rate of 0.70mL / min, and an injection volume of 5μL.

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