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

Abstract

The present invention discloses a method for efficiently preparing 5-hydroxymethylfurfural in a temperature-controlled phase separation solvent system, and belongs to the technical field of biomass-based high-value chemical preparation. The present invention adopts a betaine hydrochloride aqueous solution and an organic solvent to construct a temperature-controlled phase separation solvent system. In the reaction system, carbohydrates can be converted into HMF without adding a catalyst, and the additional addition of a catalyst can shorten the reaction time. During the heating reaction, the betaine hydrochloride aqueous solution and the organic solvent form a two-phase system; after the reaction is completed, the room temperature is cooled for a period of time, and the betaine hydrochloride in the system is precipitated in the form of crystals. The present invention can not only catalyze the conversion of raw materials such as high-concentration fructose to obtain a high yield of 5-hydroxymethylfurfural, but also greatly improve the recovery efficiency of reagents such as catalysts and solvents, and reduce the production cost of 5-hydroxymethylfurfural. At the same time, the reaction system is environmentally friendly, has low equipment requirements, and has the ability to be applied in large-scale industrialization.

Description

Technical Field

[0001] The invention belongs to the technical field of biomass-based high-value chemical preparation, and specifically relates to a method for efficiently preparing 5-hydroxymethylfurfural in a temperature-controlled phase separation solvent system. Background Art

[0002] The efficient and low-cost preparation of biomass-based chemicals is the key to building a low-carbon and sustainable society. As an important biomass-based platform compound, the industrial preparation of 5-hydroxymethylfurfural (HMF) has attracted much attention in recent years. HMF can be prepared 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 give it unique physicochemical properties and reactivity. HMF can be converted into a series of high value-added chemicals such as 5-ethoxymethylfurfural (EMF), 2,5-dimethylfuran (DMF), 2,5-furandicarboxylic acid (FDCA), levulinic acid (LA) and so on through different chemical reactions. These compounds have important application value in the fields of biofuels, bioplastics, green solvents, and medicine. Therefore, HMF is considered to be a bridge connecting biomass refining and petrochemical refining, and is also listed as the "biomass-based platform molecule with the most development potential" by the US Department of Energy.

[0003] The aldehyde, hydroxymethyl and furan rings in HMF allow it to be derived into many high-value products, but they also make it very unstable during the preparation and separation and purification process, and it is easy to generate a large number of by-products, resulting in low yields and high costs for the final product. Developing / screening new reaction solvents and designing efficient catalytic systems are the key to improving the dehydration conversion of carbohydrates to produce HMF. In water, HMF is easily rehydrated to levulinic acid and formic acid and polymerized to produce by-products such as humus, and the selectivity of carbohydrate conversion to HMF is often low. Organic solvents have been shown to effectively increase 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 into HMF in DMSO through the solvation effect, and its yield can reach 77% (ChemSusChem, 2019, 12(10): 2211-2219). However, the separation of HMF from these solvents requires a lot of energy, which hinders their commercial application. Ionic liquids and deep eutectic solvent systems have good solubility for carbohydrates and can inhibit further hydrolysis of HMF. However, the recycling and reuse of these solvents has not been completely solved, the cost of HMF preparation is very high, and there are currently few industrial production examples.

[0004] In addition, the two-phase system, that is, the introduction of an organic extraction phase during the reaction process, can continuously extract the generated HMF from the reaction phase into the organic phase, which can inhibit the side reactions such as rehydration / decomposition / polymerization of HMF to a certain extent, thereby increasing the yield of HMF. However, the current two-phase system generally has problems such as low extraction efficiency (low HMF distribution ratio) and difficulty in recovering additives and catalysts, which seriously restricts its industrial application.

[0005] Based on the above reasons, this application is filed. Summary of the invention

[0006] In view of the problems or defects of the above-mentioned prior art, the purpose of the present invention is to provide a method for efficiently preparing 5-hydroxymethylfurfural in a temperature-controlled phase separation solvent system. The present invention introduces a temperature-controlled phase change additive (betaine hydrochloride in the present invention) into the reaction system to effectively solve the problems of substance separation, recovery and product purification in a two-phase system. At room temperature, the temperature-controlled phase change additive is insoluble in the reaction system and is easily separated from the system, thereby reducing the recovery cost of the additive and the catalyst; at the reaction temperature, the temperature-controlled phase change additive dissolves with the reaction phase and promotes the phase separation of the reaction phase and the extraction phase, so that HMF can be extracted in situ into an organic phase with a high distribution ratio, significantly improving the yield of HMF.

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

[0008] The present invention provides a method for preparing 5-hydroxymethylfurfural in a temperature-controlled phase separation solvent system, and the specific steps are as follows:

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

[0010] S2: adding a certain amount of carbohydrate to the solvent system, heating to perform a dehydration reaction, and forming layers with the betaine hydrochloride aqueous solution as a reaction phase and the organic solvent as an extraction phase;

[0011] S3: After the reaction is completed, the mixture is cooled at room temperature for a period of time, and betaine hydrochloride is precipitated in the form of crystals. The product exists in a mixed solution of an organic phase and deionized water, and 5-hydroxymethylfurfural is obtained through purification and separation.

[0012] Furthermore, in S1, different volume ratios of organic solvent and betaine hydrochloride aqueous solution 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. More preferably, it is 4:1.

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

[0014] Furthermore, in S1, the organic solvent is one or more of acetone, ethyl acetate, tetrahydrofuran, 2-methyltetrahydrofuran, and acetonitrile, preferably acetone.

[0015] Further, in S2, the concentration of the carbohydrate is the concentration of carbohydrate in the aqueous solution of betaine hydrochloride. Preferably, the concentration of the carbohydrate is 5wt%, 10wt%, 20wt%, 30wt%, 40wt%, 50wt% or 60wt%. More preferably, it is not more than 30wt%.

[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°C, preferably 90-120°C.

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

[0019] Furthermore, in S3, after the reaction is completed, a separation and purification step is also included: the reaction mixture is immediately cooled to room temperature, and is left at room temperature for a period of time until most of the betaine hydrochloride crystals are precipitated, the betaine hydrochloride and the organic phase are separated and collected respectively, and 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 may be additionally 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 sugar raw material.

[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; the acidic metal salt compound includes one or more of SnCl4, AlCl3, CrCl3, and ZnCl2.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] (1) The present invention develops a temperature-controlled phase separation solvent system composed of a betaine hydrochloride aqueous solution and an organic solvent. During the heating reaction, the betaine hydrochloride aqueous solution and the organic solvent form a two-phase system. After the reaction is completed, the betaine hydrochloride in the system is cooled to room temperature for a period of time, and the betaine hydrochloride in the system is precipitated in the form of crystals, which is convenient for recycling the betaine hydrochloride and the organic solvent. In this reaction system, 5-hydroxymethylfurfural is prepared in one pot, the process is simple, the by-products (formic acid, levulinic acid) are small, the selectivity is high, and the yield of 5-hydroxymethylfurfural can exceed 90%. This method is conducive to the efficient conversion of carbohydrates.

[0024] (2) The solvent system of the present invention does not require the addition of an additional catalyst. It has an acid catalytic function. Compared with traditional homogeneous catalyst acids (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 liquids that are harmful to the environment, and has greater prospects for industrial application. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0026] Figure 1 It is a schematic diagram of the overall reaction process of preparing 5-hydroxymethylfurfural in a temperature-controlled phase separation solvent system of 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 DESCRIPTION

[0029] The present invention provides a method for preparing 5-hydroxymethylfurfural in a temperature-controlled phase separation solvent system. A temperature-controlled phase separation solvent system is constructed by using a betaine hydrochloride aqueous solution and an organic solvent. In the reaction system, carbohydrates can be converted into HMF without adding a catalyst, and the additional addition of a catalyst can shorten the reaction time. During the heating reaction, the betaine hydrochloride aqueous solution and the organic solvent form a two-phase system; after the reaction is completed, the room temperature is cooled for a period of time, and the betaine hydrochloride in the system is precipitated in the form of crystals. Carbohydrates can be efficiently converted into 5-hydroxymethylfurfural in the solvent system, reducing side reactions, and the system can also realize the recycling of betaine hydrochloride and the organic solvent.

[0030] The method for preparing 5-hydroxymethylfurfural in a temperature-controlled phase separation solvent system of the present invention specifically comprises the following steps: S1: constructing a sugar substance dehydration reaction system, wherein the reaction system comprises a sugar raw material, betaine hydrochloride, deionized water and an organic extractant, wherein after the extractant is added at room temperature, the betaine hydrochloride is insoluble in the sugar aqueous solution, and the extractant is miscible with the sugar aqueous solution; S2: heating to carry out a dehydration reaction, wherein after heating, the betaine hydrochloride is dissolved in the reaction solution to form a reaction phase, and the extractant is phase-separated from the reaction solution, and the 5-hydroxymethylfurfural generated by the reaction can be extracted into the extractant in time; S3: cooling after the reaction is completed, and the betaine hydrochloride is precipitated from the reaction system; S4: solid-liquid separation to recover the betaine hydrochloride, and the recovered betaine hydrochloride can be directly used for the next batch reaction; and S5: distilling the extractant and deionized water to separate the 5-hydroxymethylfurfural, and the extractant and water are recycled.

[0031] The betaine hydrochloride used in the present invention can be used as a catalyst for sugar dehydration and as a temperature-controlled phase separation aid. It can promote the reaction solution and the extractant to form two phases at high temperature, and can automatically crystallize and precipitate at room temperature for easy separation and recovery. The system can not only catalyze the conversion of raw materials such as high-concentration fructose (>30 wt%) to obtain high-yield (>85%) 5-hydroxymethylfurfural, but also greatly improve the recovery efficiency of reagents such as catalysts and solvents, and reduce the production cost of 5-hydroxymethylfurfural. At the same time, the reaction system is environmentally friendly, has low equipment requirements, and has the ability to be applied in large-scale industrial applications.

[0032] The present invention is further described below in conjunction with specific implementation examples so that those skilled in the art can better understand the present invention, but the present invention is not limited to the following embodiments. It should be pointed out that based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present invention.

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

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

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

[0036] The method for preparing 5-hydroxymethylfurfural in a controllable phase separation solvent system of the present invention has the following overall reaction process: Figure 1 As shown, a certain amount of carbohydrates is dissolved in a betaine hydrochloride aqueous solution, and after acetone is added, a portion of betaine hydrochloride is precipitated; during the heating reaction process, the precipitated betaine hydrochloride is redissolved, and the betaine hydrochloride aqueous solution and acetone form a two-phase system, and the carbohydrates are dehydrated in the betaine hydrochloride aqueous solution to generate HMF, and HMF is extracted into acetone in situ to reduce the generation of by-products; after the reaction is completed, the reaction mixture is immediately cooled to room temperature and left for a period of time, and most of the betaine hydrochloride is precipitated from the solution system in the form of crystals, which is easy to separate from the system for reuse. Subsequently, an excess of acetone is added to completely precipitate the betaine hydrochloride, and then the acetone and water are removed by reduced pressure distillation to obtain 5-hydroxymethylfurfural.

[0037] Example 1 Investigating the Effect of Solvent Systems Constructed from Different Organic Solvents and Betaine Hydrochloride Aqueous Solution on the Conversion of Fructose into HMF

[0038] Weigh 0.22 g of fructose and 2 mL of 40 wt% betaine hydrochloride aqueous solution (added to a 15 mL thick-walled pressure-resistant bottle, and the fructose was dissolved by magnetic stirring; then, 6 mL of organic solvent (one of acetone, ethyl acetate, tetrahydrofuran, 2-methyltetrahydrofuran, and acetonitrile) was added thereto and mixed, and a hydrothermal reaction was carried out in an oil bath at a speed of 800 rpm and 100 ° C for 120 min. After the reaction, the reaction mixture was immediately cooled to room temperature and placed at room temperature for 2 hours. Betaine hydrochloride crystallized, the solid was separated, and the acetone organic phase was collected separately. After dilution with deionized water, the fructose conversion rate and 5-hydroxymethylfurfural yield were measured by high performance liquid chromatography. According to the experimental results, compared with other organic solvents, acetone and betaine hydrochloride aqueous solution have better fructose conversion rate and HMF yield. Therefore, the following examples are all carried out in the acetone / betaine hydrochloride system.

[0039]

[0040]

[0041] Example 2 Investigating the effect of different concentrations of betaine hydrochloride aqueous solution and acetone on the conversion of fructose into HMF

[0042] Synthesize betaine hydrochloride aqueous solutions of different concentrations. Add a certain amount of betaine hydrochloride into a beaker according to the required concentration, then add a certain amount of deionized water, place the mixture in a water bath and stir at 50 °C until the liquid is clear and no solid is present, and obtain betaine hydrochloride aqueous solutions with concentrations of 5 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, 45% wt and 50 wt%, respectively. Finally, cool the prepared betaine hydrochloride aqueous solutions to room temperature and store them in a volumetric flask to prevent water evaporation.

[0043] 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%) were weighed and added to a 15 mL thick-walled pressure bottle, and the fructose was dissolved by magnetic stirring; then, 6 mL of acetone was added to mix, and a hydrothermal reaction was carried out in an oil bath at a speed of 800 rpm and 100 °C for 120 min. After the reaction was completed, the reaction mixture was immediately cooled to room temperature and placed at room temperature for 2 hours. Betaine hydrochloride crystallized, the solid was separated, and the acetone organic phase was collected separately. After dilution with deionized water, the fructose conversion rate and 5-hydroxymethylfurfural yield were measured by high performance liquid chromatography.

[0044] As can be seen from Table 1, under the same reaction conditions, the fructose conversion rate increases with the increase of betaine hydrochloride concentration, and the HMF yield reaches a maximum value of 86.57% when the betaine hydrochloride concentration is 40 wt%. As the betaine hydrochloride concentration increases, the HMF yield decreases. This is mainly because the increase in the betaine hydrochloride concentration will increase the acidity in the reaction system, thereby increasing the fructose conversion rate. The appropriate betaine hydrochloride concentration for the subsequent reaction process is considered to be 40wt%. However, it should be noted that the betaine hydrochloride concentration must be above 20wt% to form a two-phase system with acetone under heating conditions.

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

[0046]

[0047] Example 3 Influence of the Volume Ratio of Organic Solvent to Betaine Hydrochloride Aqueous Solution on the Conversion of Fructose into HMF

[0048] 0.22 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, and the fructose was dissolved by magnetic stirring; then, different amounts of acetone (0 mL, 2 mL, 4 mL, 6 mL, 8 mL or 10 mL) were added and mixed, and a hydrothermal reaction was carried out in an oil bath at a speed of 800 rpm and 100 °C for 120 min. After the reaction, the reaction mixture was immediately cooled to room temperature and placed at room temperature for 2 hours to allow betaine hydrochloride to crystallize, the solid was separated, and the remaining mixture was diluted with deionized water. The fructose conversion rate and 5-hydroxymethylfurfural yield were measured by high performance liquid chromatography.

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

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

[0051]

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

[0053] 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 were weighed and added into a 15 mL thick-walled pressure-resistant bottle, and the fructose was dissolved 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, 8 mL of acetone was added to the mixture and the mixture was hydrothermally reacted in an oil bath at a speed of 800 rpm and 100 °C for 120 min. After the reaction, the reaction mixture was immediately cooled to room temperature and placed at room temperature for 2 hours to allow betaine hydrochloride to crystallize and precipitate, the solid was separated, and the remaining mixture was diluted with deionized water. The fructose conversion rate and 5-hydroxymethylfurfural yield were measured by high performance liquid chromatography.

[0054] It can be seen from Table 3 that under the same reaction conditions, with the increase of fructose concentration, the fructose conversion rate and HMF yield decreased accordingly; at a fructose concentration of 30wt%, the HMF yield could be maintained above 80%. When the fructose concentration increased to 60wt%, the HMF yield was 56.97%, because part of the fructose had not been converted and the high concentration of fructose increased the generation of by-products.

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

[0056]

[0057] Example 5 Investigating 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, and the fructose was dissolved by magnetic stirring to form a fructose solution with a concentration of 30 wt%; then, 8 mL of acetone was added to the mixture and the mixture was hydrothermally reacted in an oil bath at a speed of 800 rpm, a heating temperature of 90-120 °C, and a reaction time of 10-240 min. After the reaction, the reaction mixture was immediately cooled to room temperature and placed at room temperature for 2 hours to allow betaine hydrochloride to crystallize and precipitate, the solid was separated, and the remaining mixture was diluted with deionized water. The fructose conversion rate and 5-hydroxymethylfurfural yield were measured by high performance liquid chromatography.

[0059] As can be seen from Table 4, increasing the reaction temperature can accelerate the fructose conversion rate and HMF generation rate. A high HMF yield can be obtained when 30 wt% fructose is reacted at 90-120°C for 10-240 min. The HMF yield can reach 85.63% when fructose is reacted at 100°C for 180 min; the HMF yield can reach 85.69% when fructose is reacted at 110°C for 90 min; and the HMF yield can reach 86.55% when fructose is reacted at 120°C for 40 min.

[0060] Table 4 Effect of reaction temperature and reaction time on fructose conversion to HMF

[0061]

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

[0063] Weigh 2 mL of 40 wt% betaine hydrochloride aqueous solution and add it to a thick-walled pressure-resistant bottle with a volume of 15 mL. Then add different volumes of acetone to it 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 it in an oil bath, adjust the speed to 800 rpm, and heat it at 100°C for 5 min until most of the precipitated betaine hydrochloride is dissolved. Finally, the reaction mixture is immediately cooled to room temperature and placed at room temperature for 2 hours. Betaine hydrochloride crystallizes and precipitates. The solid is separated and placed in a vacuum drying oven at 80°C for 12 hours. The sample is weighed after drying, and the recovery rate of betaine hydrochloride is calculated.

[0064] from Figure 3 It can be seen that increasing the amount of acetone added and increasing the volume ratio of acetone to betaine hydrochloride aqueous solution can significantly improve the recovery rate of betaine hydrochloride. Without adding acetone, the betaine hydrochloride aqueous solution is placed at room temperature without precipitation of betaine hydrochloride crystals; when the volume ratio of acetone / betaine hydrochloride aqueous solution is 8:1, the recovery rate of betaine hydrochloride is as high as 96.4%. This shows that betaine hydrochloride can be recovered by increasing the amount of acetone used, and the solvent system can be recycled, which has important industrial application value.

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

[0066] 0.29 g or 1.15 g high fructose syrup (sugar content: 5 wt% glucose and 70 wt% fructose), 0.8 g betaine hydrochloride and a certain amount of deionized water were weighed and added to a 15 mL thick-walled pressure bottle, and dissolved by stirring to form a sugar solution with a concentration of 10 wt% or 30 wt%; then, 8 mL acetone was added to mix, and a hydrothermal reaction was carried out in an oil bath pot at a speed of 800 rpm, a heating temperature of 120 ° C, and a reaction time of 30 min. After the reaction, the reaction mixture was immediately cooled to room temperature and placed at room temperature for 2 hours. Betaine hydrochloride crystallized and precipitated, the solid was separated, and the remaining mixture was diluted with deionized water. The fructose conversion rate and 5-hydroxymethylfurfural yield were measured by high performance liquid chromatography.

[0067] 0.22 g sucrose or 0.22 g inulin (cas number 9005-80-5) and 2 mL 40 wt% betaine hydrochloride aqueous solution were weighed and added to a 15 mL thick-walled pressure-resistant bottle, and dissolved by stirring to form a sugar solution with a concentration of 10 wt%; then, 8 mL acetone was added to mix, and a hydrothermal reaction was carried out in an oil bath pot at a speed of 800 rpm, a heating temperature of 120 ° C, and a reaction time of 30 min. After the reaction, the reaction mixture was immediately cooled to room temperature and placed at room temperature for 2 hours to allow betaine hydrochloride to crystallize and precipitate, the solid was separated, and the remaining mixture was diluted with deionized water. The fructose conversion rate and 5-hydroxymethylfurfural yield were measured by high performance liquid chromatography.

[0068] It can be seen from Table 5 that under the same reaction conditions, the HMF yield is ranked from high to low as follows: high fructose syrup > inulin > sucrose. It is worth noting that after the reaction of high fructose syrup and sucrose, most of the glucose in the reaction system has not been converted, which shows that the reaction system can selectively promote the conversion of fructose to HMF, while most of the glucose can be retained, and this part of glucose can be recycled.

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

[0070]

[0071] Example 8 Investigating the Effect of Additional Addition of Acidic Catalyst on the Conversion of Carbohydrates to HMF

[0072] 0.22 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, and the fructose was dissolved by magnetic stirring; then, 8 mL of acetone was added to mix; finally, an acid catalyst (HCl, benzenesulfonic acid, Amberlyst-15 acid resin, ZnCl2) equivalent to 0.05-10% of the mass of fructose was added. The reaction bottle was heated in an oil bath at 800 rpm and 120 °C for reaction. After the reaction, the reaction mixture was immediately cooled to room temperature and placed at room temperature for 2 hours. Betaine hydrochloride crystallized, the solid was separated and the acetone organic phase was collected separately. After dilution with deionized water, the fructose conversion rate and 5-hydroxymethylfurfural yield were measured by high performance liquid chromatography. It can be seen that the introduction of an acid catalyst can accelerate the reaction.

[0073] Table 6 Conversion of different carbohydrates into HMF in 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: constructing a temperature-controlled phase separation solvent system, wherein the solvent system comprises a betaine hydrochloride aqueous solution and an organic solvent; the organic solvent is acetone; the volume ratio of the organic solvent to the betaine hydrochloride aqueous solution is 1:1-5:1; the concentration of betaine hydrochloride in the betaine hydrochloride aqueous solution is 25-40wt%; S2: adding a certain amount of carbohydrate to the solvent system, heating for dehydration reaction, and forming layers with betaine hydrochloride aqueous solution as reaction phase and organic solvent as extraction phase; the reaction temperature is 100-180°C; the reaction time is 30-180 min; the concentration of the carbohydrate is 5-40wt%; S3: After the reaction is completed, the mixture is cooled at room temperature for a period of time, and betaine hydrochloride is precipitated in the form of crystals. The product exists in a mixed solution of an organic phase and deionized water, and 5-hydroxymethylfurfural is obtained by purification and separation; 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 is immediately cooled to room temperature and left at room temperature for a period of time until most of the betaine hydrochloride crystals are precipitated, and the betaine hydrochloride and the organic phase are separated and collected respectively. The organic phase is distilled to obtain the 5-hydroxymethylfurfural; the recovered organic solvent and betaine hydrochloride are directly recycled.

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