A method for catalyzing the conversion of 5-hydroxymethylfurfural by chitosan using a eutectic solvent

Abstract

This invention discloses a method for the catalytic conversion of chitosan to 5-hydroxymethylfurfural using a eutectic solvent. The method involves mixing chitosan, a eutectic solvent, and a solvent to obtain a mixed solvent. The mixed solvent is placed in an oil bath at 150-190°C and reacted for 1-6 hours. Afterward, the mixture is transferred to an ice-water bath for quenching. After quenching, the reaction solution is centrifuged to obtain a supernatant containing 5-hydroxymethylfurfural. The eutectic solvent is composed of choline chloride and an organic acid in a molar ratio of 3:1 to 1:5. This invention discloses a method for the catalytic conversion of chitosan to 5-hydroxymethylfurfural using a eutectic solvent. Using renewable chitosan as raw material and a eutectic solvent composed of choline chloride and an organic acid as a catalyst, the method directly converts chitosan to 5-hydroxymethylfurfural under hydrothermal reaction conditions. This method requires less time, consumes less eutectic solvent, is simple to prepare, and has a short degradation time, providing a reference for industrial production.

Description

Technical Field

[0001] This invention relates to the field of catalytic conversion of renewable biomass, and more particularly to a method for converting chitosan to 5-hydroxymethylfurfural using a eutectic solvent. Background Technology

[0002] As my country's economy enters a new stage of high-quality development, transforming the development model and achieving high-quality development are essential, and carbon emissions are an inherent requirement. However, due to the non-renewable nature of fossil resources and their increasingly serious environmental and ecological problems, such as global warming, environmental pollution, and greenhouse gases, which are hindering sustainable socio-economic growth, developing green, economical, and renewable energy sources to replace fossil fuels has become a major direction for future development. Biomass is a renewable resource with wide availability and broad application prospects. Utilizing biomass, such as lignocellulose and chitin, to produce sustainable fuels and various value-added products has become a major force in energy conservation and emission reduction.

[0003] Chitin is the second largest biopolymer in nature after lignocellulose. It is an important component of the exoskeletons of many lower animals, such as shrimp (15%–30%) and crab (15%–20%). It is also a component of the cell membranes of lower plant fungi, such as fungi, green algae, yeast, and squid. Globally, approximately 10 billion tons of chitin are generated annually from industrial waste from fisheries and marine industries, making it an inexhaustible resource. Its deacetylated product, chitosan, possesses unique physiological activity; it is non-toxic, biodegradable, and biocompatible, and is considered one of the most promising bioactive macromolecules. Currently, 5-hydroxymethylfurfural is generally prepared from monosaccharides such as glucose and fructose. However, chitosan is a nitrogen-containing polysaccharide. This invention utilizes a eutectic solvent to directly extract 5-hydroxymethylfurfural, eliminating the step of first decomposing the polysaccharide into monosaccharides using strong acid.

[0004] Deep eutectic solvents (DESs) are low-melting-point mixed solvents composed of two or more substances in a certain proportion. They typically consist of hydrogen-bonddonors (HBDs) and hydrogen-bond acceptors (HBAs), and their melting points are significantly lower than those of any single original component. Due to their low cost, eco-friendliness, and environmental friendliness, they are considered an effective alternative to ionic liquids and are hailed as a new generation of green solvents. They possess remarkable solubility and chemical stability, making them suitable for the synthesis and separation of various compounds. In recent years, the application of deep eutectic solvents in polymer synthesis has also received widespread attention; they can be used to further overcome technical bottlenecks in biomass pretreatment, and their use as catalysts is increasingly attracting the attention of scientists.

[0005] 5-Hydroxymethylfurfural is an important furan compound. Due to its excellent chemical properties, it is widely used in medicine, chemistry, energy and other fields. It is another bio-based intermediate used in various industries or fields. It is also one of the ten most important platform chemicals listed by the U.S. Department of Energy. Its derivatives have great application prospects in fine chemicals, pharmaceuticals, biodegradable plastics and other fields.

[0006] The existing method for preparing 5-hydroxymethylfurfural involves using biorefining technology to produce it from abundant biomass resources in an acidic environment. However, due to its high cost, environmental unfriendliness, and low efficiency, it is not suitable for industrial production. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a method for the conversion of chitosan to 5-hydroxymethylfurfural using a eutectic solvent. This method utilizes renewable chitosan as a raw material and a eutectic solvent composed of choline chloride and oxalic acid as a catalyst to directly convert chitosan to 5-hydroxymethylfurfural under hydrothermal reaction conditions. This method requires less time, consumes less eutectic solvent, is simple to prepare, and has a short degradation time, providing a reference for industrial production.

[0008] To achieve the above objectives, the technical solution of the present invention is as follows: a method for catalyzing the conversion of chitosan to 5-hydroxymethylfurfural using a eutectic solvent, wherein chitosan, a eutectic solvent, and a solvent are mixed to obtain a mixed solvent; the mixed solvent is placed in an oil bath at 150-190°C, and after reacting in the oil bath for 1-6 hours, 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; wherein the eutectic solvent is composed of choline chloride and an organic acid in a molar ratio of 3:1 to 1:5.

[0009] Furthermore, the mass ratio of chitosan to eutectic solvent is 1:0.75-4.5.

[0010] Furthermore, the solvent consists of dimethyl sulfoxide and / or deionized water.

[0011] Furthermore, the eutectic solvent is prepared by the following method:

[0012] Choline chloride and organic acid were mixed evenly at 80°C to obtain a clear solution, which was then vacuum dried at 40°C for 12 hours.

[0013] Furthermore, the organic acid is selected from at least one of oxalic acid, formic acid, and L-lactic acid.

[0014] Furthermore, the supernatant containing 5-hydroxymethylfurfural was diluted to 50 mL with mobile phase, and the yield was determined by high performance liquid chromatography to be 0.57-27.5%.

[0015] Furthermore, the degree of deacetylation of the chitosan is ≥95%, and the viscosity is 100-200 mPa·s.

[0016] Furthermore, the chitosan is dried in an oven at 60°C for 48 hours before mixing.

[0017] Further, sample solutions and standard sample solutions were taken and detected by high performance liquid chromatography (HPLC). The HPLC conditions were as follows: column: Agilent Eclipse Plus C18 (5um 4.6×250mm), mobile phase: 10% methanol, column temperature: 40℃, detection wavelength: 283nm, flow rate: 0.6mL / min, injection volume: 5μL.

[0018] Further, the chitosan, eutectic solvent, and solvent are mixed evenly and then placed in a 35mL hard glass tube or Teflon tube for reaction.

[0019] In summary, the present invention has the following beneficial effects:

[0020] First, this invention utilizes a binary eutectic reaction of choline chloride and organic acid as a catalyst to convert chitosan into 5-hydroxymethylfurfural under hydrothermal reaction conditions. The use of a eutectic reaction of choline chloride and organic acid as a catalyst increases the yield of 5-hydroxymethylfurfural and overcomes the disadvantages of many organic solvents polluting the environment and expensive ionic liquids. It is stable, simple to prepare, inexpensive and environmentally friendly, and reduces environmental pollution.

[0021] Secondly, this invention utilizes chitosan, a renewable biomass resource, as a raw material and water-DMSO solution as a solvent to prepare 5-hydroxymethylfurfural under hydrothermal conditions, thus broadening the research field of effective utilization of biomass. Detailed Implementation

[0022] 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.

[0023] The method for determining the yield of 5-hydroxymethylfurfural involved in this application is as follows:

[0024] The method for detecting 5-hydroxymethylfurfural using high performance liquid chromatography (HPLC) includes the following steps:

[0025] Chromatographic column: Agilent Eclipse Plus C18 (5um 4.6×250mm), mobile phase: 10% methanol, column temperature: 40℃, detection wavelength: 283nm, flow rate: 0.6mL / min, injection volume: 5μL.

[0026] All raw materials involved in this application, except for chitosan, are commercially available and there are no special requirements.

[0027] Chitosan was purchased from Shanghai Maclean Biochemical Technology Co., Ltd., with a degree of deacetylation ≥95% and a viscosity of 100-200 mPa·s.

[0028] Example

[0029] Example 1

[0030] Choline chloride and oxalic acid were mixed evenly at a molar ratio of 1:2 at 80°C to obtain a clear solution. The clear solution was then vacuum dried at 40°C for 12 hours, sealed with sealing film, and stored in a desiccator at room temperature for later use, thus obtaining a eutectic solvent.

[0031] Place the chitosan in a 60℃ oven and dry for 48 hours for later use.

[0032] A mixed solvent consisting of chitosan (0.2000 g), DMSO (2.4000 g), deionized water (3.6000 g), and a eutectic solvent (0.1500 g) was added to a 35 mL hard glass tube, which was then immersed in a preheated oil bath at 180 °C. After reacting for 5 hours, the hard glass tube was removed from the oil bath and immediately immersed in an ice-water bath to quench the reaction. After the quenching reaction was completed, the mixture in the hard glass tube was centrifuged at 8000 r / min for 5 min. The supernatant was diluted to a 50 mL volumetric flask with ultrapure water, and the content was determined by high-performance liquid chromatography (HPLC). The yield of 5-hydroxymethylfurfural was calculated using a standard regression equation and found to be 9.09%.

[0033] Example 2

[0034] Choline chloride and formic acid were mixed evenly at a molar ratio of 1:2 at 80°C to obtain a clear solution. The clear solution was then vacuum dried at 40°C for 12 hours, sealed with sealing film, and stored in a desiccator at room temperature for later use to obtain a eutectic solvent.

[0035] Place the chitosan in a 60℃ oven and dry for 48 hours for later use.

[0036] A mixed solvent consisting of chitosan (0.2000 g), DMSO (2.4000 g), deionized water (3.6000 g), and a eutectic solvent (0.1500 g) was added to a 35 mL hard glass tube and immersed in a preheated 180°C oil bath. After reacting for 5 hours, the hard glass tube was removed from the oil bath and immediately immersed in an ice-water bath to quench the reaction. After quenching, the mixture in the hard glass tube was centrifuged at 8000 rpm for 5 minutes. The supernatant was diluted to a 50 mL volumetric flask with ultrapure water, and the content was determined by high-performance liquid chromatography (HPLC). The yield of 5-hydroxymethylfurfural was calculated using a standard regression equation and found to be 1.18%.

[0037] Example 3

[0038] Choline chloride and L-lactic acid were mixed evenly at a molar ratio of 1:2 at 80°C to obtain a clear solution. The clear solution was then vacuum dried at 40°C for 12 hours, sealed with sealing film, and stored in a desiccator at room temperature for later use, thus obtaining a eutectic solvent.

[0039] Place the chitosan in a 60℃ oven and dry for 48 hours for later use.

[0040] A mixed solvent consisting of chitosan (0.2000 g), DMSO (2.4000 g), deionized water (3.6000 g), and a eutectic solvent (0.1500 g) was added to a 35 mL hard glass tube, which was then immersed in a preheated 180°C oil bath. After reacting for 5 hours, the hard glass tube was removed from the oil bath and immediately immersed in an ice-water bath to quench the reaction. After quenching, the mixture in the hard glass tube was centrifuged at 8000 rpm for 5 minutes. The supernatant was diluted to a 50 mL volumetric flask with ultrapure water, and the content was determined by high-performance liquid chromatography (HPLC). The yield of 5-hydroxymethylfurfural was calculated to be 1.09% using a standard regression equation.

[0041] Example 4

[0042] The only difference from Example 1 is the oil bath reaction time and the oil bath temperature.

[0043] Table 1. Yield of 5-hydroxymethylfurfural in Example 4

[0044]

[0045] Example 5

[0046] The only difference from Example 1 is that the reaction time was 5 hours at a different oil bath temperature.

[0047] Table 2. Yield of 5-hydroxymethylfurfural in Example 5

[0048] Oil bath temperature (°C) Yield 150℃ 4.19％ 160℃ 4.15％ 170℃ 6.13％ 180℃ 9.09％ 190℃ 7.08％

[0049] Example 6

[0050] Choline chloride and oxalic acid were mixed evenly at a molar ratio of 1:2 at 80°C to obtain a clear solution. The clear solution was then vacuum dried at 40°C for 12 hours, sealed with sealing film, and stored in a desiccator at room temperature for later use, thus obtaining a eutectic solvent.

[0051] Place the chitosan in a 60℃ oven and dry for 48 hours for later use.

[0052] A mixed solvent consisting of chitosan (0.2000 g), deionized water (6.000 g), and a eutectic solvent (0.1500 g) without DMSO was added to a hard glass tube (35 mL). The tube was then immersed in a preheated oil bath at 180 °C and reacted for 5 hours. After quenching, the hard glass tube was removed from the oil bath and immediately immersed in an ice-water bath to quench the reaction. After quenching, the mixture in the hard glass tube was centrifuged at 8000 r / min for 5 min. The supernatant was diluted to a 50 mL volumetric flask with ultrapure water. The content of 5-hydroxymethylfurfural was determined by high-performance liquid chromatography (HPLC). The yield of 5-hydroxymethylfurfural was calculated using a standard regression equation and was 7.83%.

[0053] Example 7

[0054] The only difference from Example 6 is the use of a mixed solvent consisting of chitosan (0.2000 g), DMSO (1.2000 g), deionized water (4.8000 g), and a eutectic solvent (0.1500 g). The yield of 5-hydroxymethylfurfural was calculated using the standard regression equation and was 8.34%.

[0055] Example 8

[0056] The only difference from Example 6 is the use of a mixed solvent consisting of chitosan (0.2000 g), DMSO (3.6000 g), deionized water (2.4000 g), and a eutectic solvent (0.1500 g). The yield of 5-hydroxymethylfurfural was calculated using the standard regression equation and was 5.62%.

[0057] Example 9

[0058] The only difference from Example 6 is the use of a mixed solvent consisting of chitosan (0.2000 g), DMSO (4.8000 g), deionized water (1.2000 g), and a eutectic solvent (0.1500 g). The yield of 5-hydroxymethylfurfural was calculated using the standard regression equation and was 1.47%.

[0059] Example 10

[0060] The only difference from Example 1 is that,

[0061] Choline chloride and oxalic acid were mixed evenly at 80℃ in a molar ratio of 3:1 to obtain a clear solution. The clear solution was then vacuum dried at 40℃ for 12 hours, sealed with sealing film, and stored in a desiccator at room temperature for later use, thus obtaining a eutectic solvent.

[0062] A mixed solvent consisting of chitosan (0.2000 g), DMSO (2.4000 g), deionized water (3.6000 g), and a eutectic solvent (0.1500 g) was used. The yield of 5-hydroxymethylfurfural was calculated using a standard regression equation, and the yield was 0.64%.

[0063] Example 11

[0064] The only difference from Example 10 is that choline chloride and oxalic acid were mixed evenly at 80°C in a 2:1 molar ratio to obtain a clear solution. This clear solution was then vacuum-dried at 40°C for 12 hours, sealed with sealing film, and stored in a desiccator at room temperature for later use, yielding a eutectic solvent. The yield of 5-hydroxymethylfurfural was 1.38%.

[0065] Example 12

[0066] The difference from Example 10 is that choline chloride and oxalic acid were mixed evenly at 80°C in a 1:1 molar ratio to obtain a clear solution. This clear solution was then vacuum-dried at 40°C for 12 hours, sealed with sealing film, and stored in a desiccator at room temperature for later use, yielding a eutectic solvent. The yield of 5-hydroxymethylfurfural was 5.34%.

[0067] Example 13

[0068] The difference from Example 10 is that choline chloride and oxalic acid were mixed evenly at a molar ratio of 1:3 at 80°C to obtain a clear solution. This clear solution was then vacuum-dried at 40°C for 12 hours, sealed with sealing film, and stored in a desiccator at room temperature for later use, yielding a eutectic solvent. The yield of 5-hydroxymethylfurfural was 11.01%.

[0069] Example 14

[0070] The difference from Example 10 is that choline chloride and oxalic acid were mixed evenly at a molar ratio of 1:4 at 80°C to obtain a clear solution. This clear solution was then vacuum-dried at 40°C for 12 hours, sealed with sealing film, and stored in a desiccator at room temperature for later use, yielding a eutectic solvent. The yield of 5-hydroxymethylfurfural was 12.66%.

[0071] Example 15

[0072] The only difference from Example 10 is that choline chloride and oxalic acid were mixed evenly at a molar ratio of 1:5 at 80°C to obtain a clear solution. This clear solution was then vacuum-dried at 40°C for 12 hours, sealed with sealing film, and stored in a desiccator at room temperature for later use, yielding a eutectic solvent. The yield of 5-hydroxymethylfurfural was 10.19%.

[0073] Example 16

[0074] The only difference from Example 14 is the amount of eutectic solvent added.

[0075] Table 3. Yield of 5-hydroxymethylfurfural obtained in Example 16

[0076] Amount of eutectic solvent added (g) Yield (%) 0.1500 12.66％ 0.3000 19.58％ 0.4500 23.98％ 0.6000 26.21％ 0.7500 27.48％

[0077] As can be seen from Examples 1-3, using choline chloride and oxalic acid as a eutectic catalyst increases the yield of 5-hydroxymethylfurfural. Chitosan dehydration is an acid-catalyzed reaction. Oxalic acid is a mild weak acid. Choline chloride can form hydrogen bonds with oxalic acid, which enhances the ability of the oxalic acid carboxyl group to dissociate protons and regulates the acidity of the reaction system.

[0078] As shown in Table 1, the yield of 5-hydroxymethylfurfural can be significantly increased with the extension of reaction time, but the yield of 5-hydroxymethylfurfural decreases when the reaction time exceeds 5 hours.

[0079] As shown in Tables 1 and 2, increasing the oil bath temperature and duration improves the yield of 5-hydroxymethylfurfural (5-HMF). Increasing the reaction temperature helps increase the proportion of activated molecules, thus accelerating the reaction rate. However, when the reaction temperature exceeds 180℃ and the reaction time exceeds 5 hours, the yield of 5-HMF decreases. This decrease may be due to the self-polymerization or cross-polymerization of 5-HMF with monosaccharides, leading to the formation of humin. Furthermore, 5-HMF may undergo rehydration, generating formic acid and levulinic acid, ultimately resulting in a decrease in yield. Considering all factors, the highest yield of 5-HMF is achieved at an oil bath temperature of 180℃ and an oil bath time of 5 hours.

[0080] As shown in Examples 6-9, adding a certain amount of DMSO to the mixed solvent significantly increases the yield of 5-hydroxymethylfurfural (5-HMF). However, the yield of 5-HMF begins to decrease with increasing DMSO concentration. DMSO can directly bind hydrogen ions in the solution, promoting the dehydration and conversion of monosaccharides and improving the water molecule arrangement around sugar molecules. This effect helps improve the selectivity of the target product and reduce side reactions. However, it is important to note that water must still be present in the system to promote the hydrolysis of chitosan to glucosamine. Based on the comprehensive experimental results, the highest 5-HMF yield can be obtained when the mass fraction of DMSO in the solvent reaches 20%.

[0081] Examples 10-15 show that the ratio of hydrogen bond acceptor (HBA) to hydrogen bond donor (HBD) in the eutectic solvent affects the yield of 5-hydroxymethylfurfural (5-HMF). The acidity of the system plays a crucial role in the catalytic reaction, and in this study, the protons for catalysis are provided by HBD. To adjust the pH of the reaction system, ChCl was used as the HBA, which is achieved through hydrogen bonding with HBD. Therefore, the yield of 5-HMF is closely related to the ratio of HBD to HBA. By appropriately adjusting the ratio of HBD and HBA in the eutectic solvent, the acidity of the reaction system can be flexibly controlled, thereby accelerating the reaction rate and improving the selectivity of the target product.

[0082] As shown in Table 3, the yield of 5-hydroxymethylfurfural significantly increased with the increase of the amount of eutectic solvent added. Although eutectic catalysts can lower the activation energy and improve reaction efficiency, excessive catalyst addition can promote side reactions and may ultimately lead to a decrease in product yield.

[0083] 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; and these 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 catalyzing the conversion of 5-hydroxymethylfurfural by chitosan using a deep eutectic solvent, characterized by, Chitosan, a eutectic solvent, and a solvent are mixed to obtain a mixed solvent. The mixed solvent is placed in an oil bath at 150-190°C and reacted in the oil bath for 1-6 hours. Then, it is transferred to an ice-water bath for quenching. After the quenching reaction is completed, the reaction solution is centrifuged to obtain a supernatant containing 5-hydroxymethylfurfural. The eutectic solvent is composed of choline chloride and an organic acid in a molar ratio of 3:1 to 1:

5. The solvent is composed of dimethyl sulfoxide and deionized water. The organic acid is selected from at least one of oxalic acid, formic acid, and L-lactic acid.

2. The method for catalyzing the conversion of 5-hydroxymethylfurfural by chitosan with deep eutectic solvent according to claim 1, characterized in that, The mass ratio of chitosan to eutectic solvent is 1:0.75-4.

5.

3. The method for converting chitosan to 5-hydroxymethylfurfural using a eutectic solvent according to claim 1, characterized in that, The eutectic solvent is prepared by the following method: Choline chloride and organic acid were mixed evenly at 80°C to obtain a clear solution, which was then vacuum dried at 40°C for 12 h.

4. The method for converting chitosan to 5-hydroxymethylfurfural using a eutectic solvent 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 by high performance liquid chromatography to be 0.57-27.5%.

5. The method for converting chitosan to 5-hydroxymethylfurfural using a eutectic solvent according to claim 1, characterized in that, The chitosan has a degree of deacetylation ≥95% and a viscosity of 100-200 mpa.s.

6. The method for converting chitosan to 5-hydroxymethylfurfural using a eutectic solvent according to claim 1, characterized in that, Before mixing, the chitosan was dried in an oven at 60 °C for 48 h.

7. The method for converting chitosan to 5-hydroxymethylfurfural using a eutectic solvent 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: column: Agilent Eclipse Plus C18, 5 μm 4.6 × 250 mm; mobile phase: 10% methanol; column temperature: 40℃; detection wavelength: 283 nm; flow rate: 0.6 mL / min; injection volume: 5 μL.

8. The method for converting chitosan to 5-hydroxymethylfurfural using a eutectic solvent according to claim 1, characterized in that, After the chitosan, eutectic solvent, and solvent are mixed evenly, the mixture is placed in a 35 mL hard glass tube or Teflon tube for reaction.

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