Method for preparing 5-hydroxymethylfurfural in temperature-controlled phase separation solvent system

Abstract

The present invention belongs to the technical field of biomass-based high-value chemical preparation. Disclosed is a method for efficiently preparing 5-hydroxymethylfurfural in a temperature-controlled phase separation solvent system. In the present invention, a betaine hydrochloride aqueous solution and an organic solvent are used to construct a temperature-controlled phase separation solvent system, a carbohydrate in the reaction system can be converted into HMF without adding a catalyst, and the reaction time can be shortened by additionally adding a catalyst. During the heating reaction process, the betaine hydrochloride aqueous solution and the organic solvent form a two-phase system; and after the reaction is finished, cooling is performed at room temperature for a period of time, and betaine hydrochloride in the system is precipitated in a crystal form. The present invention can not only catalyze the conversion of raw materials, such as high-concentration fructose (>30 wt%), to prepare high-yield (>85%) 5-hydroxymethylfurfural, but also greatly improves the recovery efficiency of reagents, such as the catalyst and the solvent, and reduces the production cost of 5-hydroxymethylfurfural. In addition, the reaction system is environmentally friendly, has low requirements for devices, and has the capability for large-scale industrial application.

Description

A method for preparing 5-hydroxymethylfurfural in a temperature-controlled phase separation solvent system Technical Field

[0001] This invention belongs to the field of biomass-based high-value chemical preparation technology, specifically relating to a method for efficiently preparing 5-hydroxymethylfurfural in a temperature-controlled phase separation solvent system. Background Technology

[0002] The efficient and low-cost preparation of biomass-based chemicals is key to building a low-carbon and sustainable society. 5-Hydroxymethylfurfural (HMF), as an important biomass-based platform compound, has attracted significant attention for its industrial preparation in recent years. HMF can be produced from carbohydrates such as cellulose, glucose, and fructose through hydrolysis, isomerization, and dehydration reactions. The aldehyde group, hydroxymethyl group, and furan ring in its molecular structure endow it with unique physicochemical properties and reactivity. HMF can be converted into a series of high-value-added chemicals through various chemical reactions, such as 5-ethoxymethylfurfural (EMF), 2,5-dimethylfuran (DMF), 2,5-furandicarboxylic acid (FDCA), and levulinic acid (LA). These compounds have significant application value in biofuels, bioplastics, green solvents, and pharmaceuticals. Therefore, HMF is considered a bridge connecting biomass refining and petrochemical refining, and has been listed by the U.S. Department of Energy as one of the "most promising biomass-based platform molecules."

[0003] The aldehyde, hydroxymethyl, and furan rings in HMF enable the derivatization of numerous high-value products, but also make it highly unstable during preparation and purification, easily generating a large number of byproducts, resulting in low product yields and high costs. Developing / screening novel reaction solvents and designing efficient catalytic systems are key to improving the dehydration conversion of carbohydrates to HMF. In water, HMF readily rehydrates to synthesize levulinic acid and formic acid, and polymerizes to generate byproducts such as humic substances, often resulting in low selectivity for carbohydrate conversion to HMF. Organic solvents have been shown to effectively improve the yield of HMF, among which the polar aprotic solvent dimethyl sulfoxide (DMSO) is widely used as a reaction medium in the preparation of HMF from carbohydrates. In the absence of additional catalysts, fructose can be efficiently converted to HMF in DMSO through solvation, achieving a yield of up to 77% (ChemSusChem, 2019, 12(10): 2211-2219). However, separating HMF from these solvents requires a large amount of energy, hindering their commercial application. Ionic liquids and eutectic solvent systems exhibit excellent solubility for carbohydrates and can inhibit further hydrolysis of HMF. However, the recycling and reuse of these solvents has not been fully resolved, and the preparation cost of HMF is very high, resulting in few industrial-scale production examples.

[0004] Furthermore, biphase systems, which introduce an organic extraction phase during the reaction, allow the generated HMF to be continuously extracted from the reaction phase into the organic phase. This can, to some extent, suppress side reactions such as HMF rehydration, decomposition, and polymerization, thereby improving the yield of HMF. However, current biphase systems generally suffer from low extraction efficiency (low HMF distribution ratio) and difficulties in recovering additives and catalysts, which severely restrict their industrial application.

[0005] Based on the above reasons, this application is hereby submitted. Summary of the Invention

[0006] To address the problems or deficiencies of the existing technology, the present invention aims to provide a method for the efficient preparation of 5-hydroxymethylfurfural (HMF) in a temperature-controlled phase-separation solvent system. The present invention introduces a temperature-controlled phase change aid (betaine hydrochloride in this invention) into the reaction system, which effectively solves the problems of substance separation, recovery, and product purification in a two-phase system. At room temperature, the temperature-controlled phase change aid is insoluble in the reaction system and can be easily separated from the system, reducing the recovery cost of the aid and catalyst. At the reaction temperature, the temperature-controlled phase change aid dissolves in the reaction phase and promotes phase separation between the reaction phase and the extraction phase, enabling HMF to be extracted in situ into an organic phase with a high partition ratio, significantly improving the yield of HMF.

[0007] To achieve the above objectives, the technical solution of the present invention is as follows:

[0008] This invention provides a method for preparing 5-hydroxymethylfurfural in a temperature-controlled phase-separated solvent system, the specific steps of which are as follows:

[0009] S1: Construct a temperature-controlled phase separation solvent system, wherein the solvent system includes an aqueous solution of betaine hydrochloride and an organic solvent;

[0010] S2: A certain amount of carbohydrate is added to the solvent system and heated to carry out a dehydration reaction. The betaine hydrochloride aqueous solution is used as the reaction phase and the organic solvent is used as the extraction phase to form a layer.

[0011] S3: After the reaction is completed, the product is cooled at room temperature for a period of time. Betaine hydrochloride precipitates in crystal form. The product is present in a mixed solution of organic phase and deionized water. After purification and separation, 5-hydroxymethylfurfural is obtained.

[0012] Further, in S1, organic solvents and betaine hydrochloride aqueous solutions with different volume ratios are used to construct a controllable phase separation solvent system. The volume ratio of the organic solvent to the betaine hydrochloride aqueous solution is 0.5:1 to 8:1. Preferably, in S1, the volume ratio of the organic solvent to the betaine hydrochloride aqueous solution is 1:1, 2:1, 3:1, 4:1, or 5:1. A more preferred ratio is 4:1.

[0013] Further, in S1, the concentration of betaine hydrochloride in the aqueous solution is 5-50 wt%, preferably 40 wt%.

[0014] Further, in S1, the organic solvent is one or more selected from acetone, ethyl acetate, tetrahydrofuran, 2-methyltetrahydrofuran, and acetonitrile. Acetone is preferred.

[0015] Further, in S2, the concentration of the carbohydrate is the carbohydrate concentration in the betaine hydrochloride aqueous solution. Preferably, the concentration of the carbohydrate is 5 wt%, 10 wt%, 20 wt%, 30 wt%, 40 wt%, 50 wt%, or 60 wt%. More preferably, it is no more than 30 wt%.

[0016] Furthermore, in S2, the carbohydrate is selected from any one of fructose, high fructose syrup, sucrose, and inulin.

[0017] Furthermore, in S2, the reaction temperature is 60~180℃, preferably 90~120℃.

[0018] Furthermore, in S2, the reaction time is 5 to 360 minutes, preferably 10 to 240 minutes.

[0019] Furthermore, in step S3, after the reaction is completed, a separation and purification step is also included: the reaction mixture is immediately cooled to room temperature and left at room temperature for a period of time until most of the betaine hydrochloride crystallizes out; the betaine hydrochloride and the organic phase are separated and collected separately; the organic phase is distilled to obtain the 5-hydroxymethylfurfural; the recovered organic solvent and betaine hydrochloride can be directly recycled.

[0020] Furthermore, an acidic catalyst can be added to the reaction system of the present invention to accelerate the reaction; the acidic catalyst is selected from one or more of inorganic acids, organic acids, acidic ion exchange resins, and acidic metal salt compounds; preferably, the mass of the acidic catalyst is 0.05 to 10% of the total mass of the carbohydrate raw materials.

[0021] Preferably, the inorganic acid includes one or more of sulfuric acid, hydrochloric acid, and phosphoric acid; the organic acid includes one or more of sulfonic acid, trichloroacetic acid, and acetic acid; the acidic ion exchange resin includes one or more of sulfonic acid-based cation exchange resin and carboxylic acid-based cation exchange resin; and the acidic metal salt compound includes one or more of SnCl4, AlCl3, CrCl3, and ZnCl2.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] (1) This invention develops a temperature-controlled phase separation solvent system constructed from an aqueous solution of betaine hydrochloride and an organic solvent. During the heating reaction, the aqueous solution of betaine hydrochloride and the organic solvent form a two-phase system. After the reaction is completed, the system is cooled to room temperature for a period of time, and the betaine hydrochloride in the system precipitates in crystal form, which facilitates the recovery and recycling of betaine hydrochloride and organic solvent. In this reaction system, 5-hydroxymethylfurfural can be prepared in a one-pot process. The process is simple, with few byproducts (formic acid, levulinic acid), high selectivity, and a 5-hydroxymethylfurfural yield exceeding 90%. This method is beneficial for the efficient conversion of carbohydrates.

[0024] (2) The solvent system of the present invention does not require the addition of an additional catalyst, and it has its own acid catalytic function. Compared with traditional homogeneous catalysts (such as sulfuric acid, hydrochloric acid, phosphoric acid, metal salts, etc.), it reduces the generation of by-products, equipment corrosion and the discharge of waste liquid that is harmful to the environment, and has greater prospects for industrial application. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 is a schematic diagram of the overall reaction process for preparing 5-hydroxymethylfurfural in a temperature-controlled phase separation solvent system according to the present invention.

[0027] Figure 2. Schematic diagram of fructose dehydration process in betaine hydrochloride / acetone reaction system;

[0028] Figure 3. Comparison of the effects of different volume ratios of acetone / betaine hydrochloride solution systems on the recovery rate of betaine hydrochloride. Detailed Implementation

[0029] This invention provides a method for preparing 5-hydroxymethylfurfural (HMF) in a temperature-controlled phase-separated solvent system. A temperature-controlled phase-separated solvent system is constructed using an aqueous solution of betaine hydrochloride and an organic solvent. In this reaction system, carbohydrates can be converted to HMF without the addition of a catalyst; the addition of a catalyst can shorten the reaction time. During the heating reaction, the aqueous solution of betaine hydrochloride and the organic solvent form a two-phase system. After the reaction, cooling to room temperature for a period of time causes the betaine hydrochloride in the system to precipitate in crystal form. Carbohydrates can be efficiently converted to 5-hydroxymethylfurfural in this solvent system, reducing side reactions. This system also allows for the recycling of betaine hydrochloride and the organic solvent.

[0030] This invention discloses a method for preparing 5-hydroxymethylfurfural in a temperature-controlled phase separation solvent system, specifically comprising the following steps: S1: Constructing a dehydration reaction system for carbohydrates, the reaction system comprising carbohydrate raw materials, betaine hydrochloride, deionized water, and an organic extractant. After adding the extractant at room temperature, betaine hydrochloride is insoluble in the sugar aqueous solution, while the extractant is miscible with the sugar aqueous solution; S2: Heating to carry out the dehydration reaction, after heating, betaine hydrochloride dissolves in the reaction solution to form the reaction phase, while the extractant separates from the reaction solution, and the 5-hydroxymethylfurfural generated in the reaction can be extracted into the extractant in a timely manner; S3: After the reaction is completed, cooling is performed, and betaine hydrochloride precipitates from the reaction system; S4: Solid-liquid separation is performed to recover betaine hydrochloride, and the recovered betaine hydrochloride can be directly used in the next batch of reaction; S5: Distillation of the extractant and deionized water is performed to separate 5-hydroxymethylfurfural, and the extractant and water are recycled.

[0031] The betaine hydrochloride used in this invention can serve as both a catalyst for sugar dehydration and a temperature-controlled phase separation aid. At high temperatures, it promotes the formation of two phases between the reaction solution and the extractant, while at room temperature, it automatically crystallizes out for easy separation and recovery. This system not only catalyzes the conversion of high-concentration fructose (>30 wt%) and other raw materials to produce high-yield (>85%) 5-hydroxymethylfurfural, but also significantly improves the recovery efficiency of catalysts, solvents, and other reagents, reducing the production cost of 5-hydroxymethylfurfural. Furthermore, this reaction system is environmentally friendly, requires minimal equipment, and is suitable for large-scale industrial application.

[0032] The present invention will be further described below with reference to specific implementation examples to enable those skilled in the art to better understand the invention. However, the invention is not limited to the following embodiments. It should be noted that all other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0033] Unless otherwise specified, all reagents and materials used in the following examples are commercially available. For example, the fructose used in the following examples of the present invention has the chemical formula C6H. 12 O6, with a molecular weight of 180.15 and CAS number 7660-25-5. The betaine hydrochloride used in the following examples has the molecular formula C5H. 12 ClNO2 has a molecular weight of 153.61 and a CAS number of 590-46-5.

[0034] The detection method for 5-hydroxymethylfurfural in the following embodiments of the present invention is: high performance liquid chromatography.

[0035] The specific test conditions were as follows: the mobile phase used was 5 mM dilute sulfuric acid solution, the flow rate was 0.6 mL / min, the chromatographic column was HPX-87H, the test temperature was 40 ℃, and the injection volume was 10 μL.

[0036] This invention discloses a method for preparing 5-hydroxymethylfurfural (HMF) in a controllable phase separation solvent system. The overall reaction process is shown in Figure 1. A certain amount of carbohydrates dissolves in an aqueous solution of betaine hydrochloride. After the addition of acetone, some of the betaine hydrochloride precipitates. During the heating reaction, the precipitated betaine hydrochloride redissolves, forming a two-phase system with the betaine hydrochloride aqueous solution and acetone. The carbohydrates dehydrate in the betaine hydrochloride aqueous solution to generate HMF, which is then extracted in situ into acetone, reducing byproduct formation. After the reaction is complete, the reaction mixture is immediately cooled to room temperature and left to stand for a period of time. Most of the betaine hydrochloride precipitates from the solution system in crystalline form, making it easy to separate and reuse. Subsequently, excess acetone is added to completely precipitate the betaine hydrochloride. Acetone and water are then removed by vacuum distillation to obtain 5-hydroxymethylfurfural.

[0037] Example 1 investigated the effect of solvent systems constructed from different organic solvents and betaine hydrochloride aqueous solutions on the conversion of fructose to HMF.

[0038] Weigh 0.22 g of fructose and 2 mL of 40 wt% betaine hydrochloride aqueous solution (add to a 15 mL thick-walled pressure-resistant bottle, and dissolve the fructose by magnetic stirring); then add 6 mL of organic solvent (one of acetone, ethyl acetate, tetrahydrofuran, 2-methyltetrahydrofuran, or acetonitrile) and mix. Conduct a hydrothermal reaction in an oil bath at 800 rpm and 100 °C for 120 min. After the reaction is complete, immediately cool the reaction mixture to room temperature and allow it to stand at room temperature for 2 hours. Betaine hydrochloride crystallizes out. Separate the solid and collect the acetone organic phase separately. After dilution with deionized water, the fructose conversion rate and 5-hydroxymethylfurfural (HMF) yield are determined by high-performance liquid chromatography (HPLC). Based on the experimental results, acetone and betaine hydrochloride aqueous solution have better fructose conversion rate and HMF yield compared to other organic solvents. Therefore, the following examples are all conducted in an acetone / betaine hydrochloride system.

[0039]

[0040]

[0041] Example 2 investigated the effect of solvent systems constructed from different concentrations of betaine hydrochloride aqueous solution and acetone on the conversion of fructose to HMF.

[0042] Aqueous solutions of betaine hydrochloride at different concentrations were synthesized. A certain amount of betaine hydrochloride was added to a beaker according to the desired concentration, followed by a certain amount of deionized water. The mixture was placed in a water bath and stirred at 50 °C until the liquid became clear and free of solids, yielding aqueous solutions of betaine hydrochloride with concentrations of 5 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, 45 wt%, and 50 wt%. Finally, the prepared aqueous solutions of betaine hydrochloride were cooled to room temperature and stored in volumetric flasks to prevent water evaporation.

[0043] Weigh 0.22 g of fructose and 2 mL of betaine hydrochloride aqueous solution (concentration of 5 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, 45 wt%, or 50 wt%) and add them to a 15 mL thick-walled pressure-resistant bottle. Dissolve the fructose by magnetic stirring. Then, add 6 mL of acetone and mix. Conduct a hydrothermal reaction in an oil bath at 800 rpm and 100 °C for 120 min. After the reaction is complete, immediately cool the reaction mixture to room temperature and let it stand at room temperature for 2 hours. Betaine hydrochloride crystallizes out. Separate the solid and collect the acetone organic phase separately. After diluting with deionized water, determine the fructose conversion rate and the yield of 5-hydroxymethylfurfural using high-performance liquid chromatography.

[0044] As shown in Table 1, under the same reaction conditions, the fructose conversion rate increases with increasing betaine hydrochloride concentration. The HMF yield reaches its maximum of 86.57% at a betaine hydrochloride concentration of 40 wt%. The HMF yield decreases with further increases in betaine hydrochloride concentration. This is mainly because increasing the betaine hydrochloride concentration enhances the acidity of the reaction system, thereby increasing the fructose conversion rate. A suitable betaine hydrochloride concentration of 40 wt% is considered for subsequent reaction processes. However, it should be noted that a betaine hydrochloride concentration above 20 wt% is required to form a biphase system with acetone under heating conditions.

[0045] Table 1. Effects of different concentrations of betaine hydrochloride aqueous solution on fructose conversion to HMF

[0046]

[0047] Example 3 investigated the effect of the volume ratio of organic solvent to betaine hydrochloride aqueous solution on the conversion of fructose to HMF.

[0048] Weigh 0.22 g of fructose and 2 mL of 40 wt% betaine hydrochloride aqueous solution and add them to a 15 mL thick-walled pressure-resistant bottle. Dissolve the fructose by magnetic stirring. Then, add different amounts of acetone (0 mL, 2 mL, 4 mL, 6 mL, 8 mL, or 10 mL) and mix. Conduct a hydrothermal reaction in an oil bath at 800 rpm and 100 °C for 120 min. After the reaction is complete, immediately cool the reaction mixture to room temperature and let it stand at room temperature for 2 hours. Betaine hydrochloride crystallizes out. Separate the solid, dilute the remaining mixture with deionized water, and determine the fructose conversion rate and 5-hydroxymethylfurfural yield using high-performance liquid chromatography.

[0049] As shown in Table 2, when acetone is added to a fixed 2 mL of betaine hydrochloride aqueous solution, the fructose conversion rate and HMF yield increase with the increase of the added amount. A high HMF yield of 89.44% can be obtained when the volume ratio of acetone to betaine aqueous solution is 8:2. Further increasing the amount of acetone does not significantly improve the HMF yield. Therefore, a solvent system with a volume ratio of acetone to betaine aqueous solution of 8:2 will be used in the following examples.

[0050] Table 2 Effect of acetone dosage on fructose-to-HMF conversion.

[0051]

[0052] Example 4 investigated the effect of substrate concentration on fructose conversion to HMF.

[0053] Weigh out a certain amount of fructose (0.11 g, 0.22 g, 0.50 g, 0.86 g, 1.33 g, 2.00 g, or 3.00 g) and 2 mL of 40 wt% betaine hydrochloride aqueous solution, and add them to a 15 mL thick-walled pressure-resistant bottle. Dissolve the fructose by magnetic stirring to form fructose solutions of different concentrations (5 wt%, 10 wt%, 20 wt%, 30 wt%, 40 wt%, 50 wt%, or 60 wt%). Then, add 8 mL of acetone and mix. Conduct a hydrothermal reaction in an oil bath at 800 rpm and 100 °C for 120 min. After the reaction is complete, immediately cool the reaction mixture to room temperature and let it stand at room temperature for 2 hours. Betaine hydrochloride crystallizes out. Separate the solid, dilute the remaining mixture with deionized water, and determine the fructose conversion rate and 5-hydroxymethylfurfural yield using high-performance liquid chromatography.

[0054] As shown in Table 3, under the same reaction conditions, the fructose conversion rate and HMF yield decreased with the increase of fructose concentration. At a fructose concentration of 30 wt%, the HMF yield could be maintained above 80%. When the fructose concentration increased to 60 wt%, the HMF yield was 56.97%, because some fructose had not been converted and the high fructose concentration increased the generation of by-products.

[0055] Table 3 Effect of substrate concentration on fructose conversion to HMF

[0056]

[0057] Example 5 investigated the effects of reaction temperature and reaction time on the conversion of fructose to HMF.

[0058] 0.86 g of fructose and 2 mL of 40 wt% betaine hydrochloride aqueous solution were weighed and added to a 15 mL thick-walled pressure-resistant bottle. The fructose was dissolved by magnetic stirring to form a 30 wt% fructose solution. Then, 8 mL of acetone was added and mixed. The mixture was then subjected to a hydrothermal reaction in an oil bath at 800 rpm and a temperature of 90–120 °C for 10–240 min. After the reaction was completed, the reaction mixture was immediately cooled to room temperature and left at room temperature for 2 hours. Betaine hydrochloride crystallized out. The solid was separated, and the remaining mixture was diluted with deionized water. The fructose conversion rate and the yield of 5-hydroxymethylfurfural were determined by high-performance liquid chromatography.

[0059] Table 4 shows that increasing the reaction temperature accelerates the fructose conversion rate and HMF formation rate. High HMF yields can be obtained for 30 wt% fructose reacting at 90–120℃ for 10–240 min. The HMF yield reaches 85.63% when fructose reacts at 100℃ for 180 min; 85.69% when fructose reacts at 110℃ for 90 min; and 86.55% when fructose reacts at 120℃ for 40 min.

[0060] Table 4. Effects of reaction temperature and reaction time on the conversion of fructose to HMF

[0061]

[0062] Example 6 investigated the effect of acetone dosage on the recovery rate of betaine hydrochloride.

[0063] Weigh 2 mL of a 40 wt% betaine hydrochloride aqueous solution and add it to a 15 mL thick-walled pressure-resistant bottle. Then, add different volumes of acetone to form acetone / betaine hydrochloride solution systems with different volume ratios (0 / 1, 1 / 1, 2 / 1, 3 / 1, 4 / 1, 5 / 1, 6 / 1, 7 / 1, or 8 / 1). Subsequently, heat in an oil bath at 100°C for 5 min at 800 rpm until some of the precipitated betaine hydrochloride dissolves. Finally, immediately cool the reaction mixture to room temperature and allow it to stand at room temperature for 2 hours to allow betaine hydrochloride to crystallize. Separate the solid and place it in a vacuum drying oven at 80°C for 12 hours. Weigh the dried sample and calculate the recovery rate of betaine hydrochloride.

[0064] As shown in Figure 3, increasing the amount of acetone added and raising the volume ratio of acetone to betaine hydrochloride aqueous solution can significantly improve the recovery rate of betaine hydrochloride. Without the addition of acetone, no betaine hydrochloride crystals precipitate when the betaine hydrochloride aqueous solution is left at room temperature; when the volume ratio of acetone to betaine hydrochloride aqueous solution is 8:1, the recovery rate of betaine hydrochloride reaches as high as 96.4%. This indicates that betaine hydrochloride can be recovered by increasing the amount of acetone used, achieving the recycling of the solvent system, which has significant industrial application value.

[0065] Example 7: Conversion of different carbohydrates into HMF in an acetone / betaine hydrochloride solvent system

[0066] Weigh 0.29 g or 1.15 g of high-fructose corn syrup (sugar content: 5 wt% glucose and 70 wt% fructose), 0.8 g of betaine hydrochloride, and a certain amount of deionized water into a 15 mL thick-walled pressure-resistant bottle. Dissolve the solution by stirring to form a sugar solution with a concentration of 10 wt% or 30 wt%. Then, add 8 mL of acetone and mix. Conduct a hydrothermal reaction in an oil bath at 800 rpm and 120 °C for 30 min. After the reaction is complete, immediately cool the reaction mixture to room temperature and let it stand at room temperature for 2 hours. Betaine hydrochloride crystallizes out. Separate the solid, dilute the remaining mixture with deionized water, and determine the fructose conversion rate and 5-hydroxymethylfurfural yield using high-performance liquid chromatography.

[0067] Weigh 0.22 g of sucrose or 0.22 g of inulin (CAS No. 9005-80-5) and 2 mL of 40 wt% betaine hydrochloride aqueous solution into a 15 mL thick-walled pressure-resistant bottle. Dissolve the solution by stirring to form a 10 wt% sugar solution. Then, add 8 mL of acetone and mix. Conduct a hydrothermal reaction in an oil bath at 800 rpm and 120 °C for 30 min. After the reaction is complete, immediately cool the reaction mixture to room temperature and let it stand at room temperature for 2 hours. Betaine hydrochloride crystallizes out. Separate the solid, dilute the remaining mixture with deionized water, and determine the fructose conversion rate and 5-hydroxymethylfurfural yield using high-performance liquid chromatography.

[0068] As shown in Table 5, under the same reaction conditions, the yield of HMF, from highest to lowest, is: high fructose syrup > inulin > sucrose. It is noteworthy that after the reaction of high fructose syrup and sucrose, a large portion of glucose remains unconverted in the reaction system. This indicates that the reaction system can selectively promote the conversion of fructose into HMF, while retaining most of the glucose, which can be recycled.

[0069] Table 5. Conversion of different carbohydrates into HMF in the acetone / betaine hydrochloride solvent system.

[0070]

[0071] Example 8 investigates the effect of adding an additional acidic catalyst on the conversion of carbohydrates to HMF.

[0072] 0.22 g of fructose and 2 mL of a 40 wt% aqueous solution of betaine hydrochloride were weighed and added to a 15 mL thick-walled pressure-resistant bottle. The fructose was dissolved by magnetic stirring. Then, 8 mL of acetone was added and mixed. Finally, an acidic catalyst (one of HCl, benzenesulfonic acid, Amberlyst-15 acidic resin, or ZnCl2) equivalent to 0.05–10% of the fructose mass was added. The reaction flask was heated in an oil bath at 120 °C at 800 rpm. After the reaction was completed, the reaction mixture was immediately cooled to room temperature and left at room temperature for 2 hours. Betaine hydrochloride crystallized out. The solid was separated, and the acetone organic phase was collected separately. After dilution with deionized water, the fructose conversion rate and the yield of 5-hydroxymethylfurfural were determined by high-performance liquid chromatography. It can be seen that the introduction of an acidic catalyst can accelerate the reaction.

[0073] Table 6. Conversion of different carbohydrates into HMF in the acetone / betaine hydrochloride solvent system.

[0074] .

Claims

1. A method for preparing 5-hydroxymethylfurfural in a temperature-controlled phase separation solvent system, characterized in that: The specific steps are as follows: S1: Construct a temperature-controlled phase separation solvent system, wherein the solvent system comprises an aqueous solution of betaine hydrochloride and an organic solvent; the organic solvent is acetone; the volume ratio of the organic solvent to the aqueous solution of betaine hydrochloride is 1:1 to 5:1; the concentration of betaine hydrochloride in the aqueous solution of betaine hydrochloride is 25 to 40 wt%. S2: A certain amount of carbohydrate is added to the solvent system, and a dehydration reaction is carried out by heating. A betaine hydrochloride aqueous solution is used as the reaction phase, and the organic solvent is used as the extraction phase to form separate layers. The reaction temperature is 100~180℃; the reaction time is 30~180 min; and the concentration of the carbohydrate is 5~40 wt%. S3: After the reaction is completed, the mixture is cooled at room temperature for a period of time. Betaine hydrochloride precipitates in crystal form. The product is present in a mixed solution of organic phase and deionized water. After purification and separation, 5-hydroxymethylfurfural is obtained. In S2, the carbohydrate is selected from any one of fructose, high fructose syrup, and inulin.

2. The method according to claim 1, characterized in that: The reaction mixture was immediately cooled to room temperature and left at room temperature for a period of time until most of the betaine hydrochloride crystallized out. The betaine hydrochloride and the organic phase were separated and collected separately. The organic phase was distilled to obtain the 5-hydroxymethylfurfural. The recovered organic solvent and betaine hydrochloride were directly recycled.

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