Method for preparing 5-hydroxymethylfurfural by dehydration of mixed sugars in a deep eutectic solvent

Abstract

The application aims to provide a method for preparing 5-hydroxymethylfurfural by mixing and dehydrating sugars in a eutectic solvent, and specifically comprises the following steps: S1: constructing a eutectic system, wherein the eutectic system comprises glucose, fructose and choline chloride; S2: adding a catalyst and an extractant, and heating to perform a dehydration reaction, wherein the extractant is layered with the eutectic system; and S3: separating 5-hydroxymethylfurfural after the reaction is completed. The method forms a high-concentration sugar-containing eutectic system by mixing glucose, fructose and choline chloride, and efficiently prepares 5-hydroxymethylfurfural after screening various reaction conditions, so that the yield of HMF can be improved, the loss conversion of glucose can be reduced, and the side reaction can be reduced.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of chemical industry, and particularly discloses a method for preparing 5-hydroxymethylfurfural by dehydrating mixed sugars in a deep eutectic solvent. BACKGROUND

[0002] Biomass-based chemicals are important support for building a low-carbon chemical industry, and 5-hydroxymethylfurfural is a biomass-based platform compound with wide application prospects, which can be used to produce other high-value-added biomass-based chemicals, materials and liquid fuels. It is known that, due to the fact that fructose is prone to exist in a furan configuration, the reaction conditions for preparing 5-hydroxymethylfurfural by catalytic dehydration of fructose are relatively mild, high in efficiency and good in selectivity. However, the cost of preparing 5-hydroxymethylfurfural from fructose is relatively high due to the high price of fructose, which to a large extent limits the large-scale application of 5-hydroxymethylfurfural in the downstream segment. Cheaper and more readily available glucose is a more ideal raw material for producing 5-hydroxymethylfurfural, but due to the fact that glucose is more prone to exist in a pyran configuration in a solvent, the reaction conditions for preparing 5-hydroxymethylfurfural by directly acid-catalyzed dehydration of glucose are relatively harsh, the reaction concentration is low, the selectivity is relatively low, and there are more side reactions. For example, glucose or fructose and choline chloride are mixed to form a deep eutectic solvent (with a monosaccharide concentration of 20wt%) in a mass ratio of 1:4, acetonitrile is used as an extractant, the solid acid dosage is 50% (relative to the monosaccharide), the reaction is carried out at 100℃ for 4h, the yield of 5-hydroxymethylfurfural prepared by dehydration of fructose is 91.3%, and the yield of 5-hydroxymethylfurfural prepared by dehydration of glucose is only 60.1% (Industrial Crops and Products, 2023, 194: 116354). When other conditions are the same, the yield of 5-hydroxymethylfurfural prepared by catalyzing sucrose (sucrose is formed by dehydration of one molecule of glucose and one molecule of fructose, and the glucose / fructose ratio is 1:1) is up to 68%, and the sucrose is completely converted (at 120℃ for 2h). When SnCl4·5H2O is used as a catalyst, glucose, choline chloride and water are mixed to form a deep eutectic solvent (with a monosaccharide concentration of 6wt%) in a mass ratio of 0.1:1:0.5, methyl isobutyl ketone is used as an extractant, the catalyst mass is 5% (relative to the glucose), the reaction is carried out at 130℃ for 2h, and the yield of HMF prepared by dehydration of glucose is 64.3% (ChemSusChem, 2022, 15(13): e202101889). When other conditions are the same, the yield of HMF prepared by catalyzing sucrose (sucrose is completely converted) is up to 71.9% (at 130℃ for 2h).

[0003] Therefore, when the eutectic system is composed of fructose and choline chloride, the yield of 5-hydroxymethylfurfural can reach more than 90% by regulating the acid catalyst and reaction conditions. There is no report on directly preparing 5-hydroxymethylfurfural by mixing sugar (such as glucose and fructose) and choline chloride to form a eutectic system. However, there is a report on using sucrose as a raw material in the above-mentioned literature. Sucrose is first hydrolyzed into one molecule of fructose and one molecule of glucose, and then dehydrated to produce 5-hydroxymethylfurfural. The yield of 5-hydroxymethylfurfural prepared by conversion in the eutectic system composed of sucrose is usually less than 75%, and due to the high reaction temperature, all the sugar substances such as sucrose are completely converted.

[0004] Glucose can be isomerized to fructose under the action of enzymes or chemical catalysts. Due to the chemical equilibrium of isomerization reaction, the selectivity of glucose isomerization to fructose is usually about 50%. Therefore, a mixture of glucose and fructose is obtained after isomerization reaction. It is a tedious and energy-consuming process to completely separate and purify glucose and fructose from the above-mentioned mixed sugar product. Directly using the above-mentioned mixed sugar (fructose- glucose syrup or high-fructose syrup) to prepare 5-hydroxymethylfurfural with an acid catalyst usually causes a large amount of glucose component to be converted into byproducts, resulting in waste of raw materials. There is a significant difference in the kinetic rate of acid-catalyzed dehydration reaction between glucose and fructose. The reaction energy barrier required for the conversion of glucose is much higher than that of fructose, that is, the acid-catalyzed dehydration of fructose to prepare 5-hydroxymethylfurfural can be regulated at a lower reaction temperature, while the conversion loss of glucose is minimized. In addition, glucose and fructose with multiple hydroxyl functional groups can act as hydrogen bond donors and can form strong hydrogen bond interactions with hydrogen bond acceptors such as choline chloride to form a eutectic system. The hydrogen bond network in the eutectic system can stabilize glucose, and at the same time can inhibit the activity of the hydroxyl group in the 5-hydroxymethylfurfural product of fructose dehydration, reducing the occurrence of 5-hydroxymethylfurfural side reactions. Therefore, it has very important application value to develop a catalytic process based on the eutectic solvent system which can selectively convert fructose in mixed sugar to 5-hydroxymethylfurfural with less glucose loss. SUMMARY

[0005] The present application aims to provide a method for preparing 5-hydroxymethylfurfural by dehydration of mixed sugar in a eutectic solvent. By constructing a high-concentration sugar-containing eutectic system containing glucose, fructose and choline chloride, and screening various reaction conditions, 5-hydroxymethylfurfural can be efficiently prepared, side reactions can be reduced, and glucose loss can be reduced and the yield of HMF can be improved.

[0006] To achieve the above-mentioned purpose, the technical solutions of the present application are as follows:

[0007] In one aspect, the present application provides a method for preparing 5-hydroxymethylfurfural by dehydration of mixed sugar in a eutectic solvent, the specific steps are as follows:

[0008] S1: constructing a eutectic system, wherein the eutectic system comprises glucose, fructose and choline chloride;

[0009] S2: adding a catalyst and an extractant, and heating to perform a dehydration reaction, wherein the extractant is layered with the eutectic system;

[0010] S3: separating 5-hydroxymethylfurfural after the reaction is completed.

[0011] Further, in S1, the mass ratio of glucose, fructose and choline chloride is (0.5-1):(1-0.5):(2-8). Preferably, in S1, the mass ratio of glucose, fructose and choline chloride is 1:1:2, 1:1:3, 1:1:4, 1:1:5, 1:1:6, 1:1:7 or 1:1:8.

[0012] Further, in S1, the specific process is that the glucose, fructose and choline chloride are mixed and heated to prepare the eutectic system. Preferably, in S1, the glucose, fructose and choline chloride are mixed and heated at 40-50℃ to prepare the eutectic system.

[0013] Further, in S2, the catalyst is an acidic catalyst, and the acidic catalyst is selected from one or more of acidic ion exchange resin, metal salt and inorganic acid.

[0014] Preferably, the acidic ion exchange resin comprises at least one of carboxylic acid group cation exchange resin and sulfonic acid group cation exchange resin, and the type of the acidic ion exchange resin is selected from one or more of Amberlyst 15, CS650 and D113. Preferably, the metal salt is selected from one or more of SnCl4·5H2O, NiCl2·6H2O and CrCl3·6H2O. Preferably, the inorganic acid is selected from one or more of sulfuric acid, hydrochloric acid, nitric acid and phosphoric acid. Preferably, the mass of the catalyst is 0.05-10% of the total mass of the mixed glucose and fructose. Preferably, the mass of the catalyst is 0.05-0.1%, 1%-10% or 5%-10% of the total mass of the mixed glucose and fructose. Preferably, the mass of the catalyst is 0.05, 0.1%, 0.5%, 1%, 2%, 5%, 6%, 8%, 9% or 10% of the total mass of the mixed glucose and fructose.

[0015] Further, in S2, water needs to be added. Preferably, the mass of the water is 0-150% of the total mass of the mixed glucose and fructose. Preferably, the mass of the water is 10-100%, 20-50% or 25% of the total mass of the mixed glucose and fructose.

[0016] Further, in S2, the extractant is capable of dissolving the 5-hydroxymethylfurfural, and the extractant is selected from one or more of methyl isobutyl ketone, ethyl acetate, acetonitrile, γ-valerolactone, tetrahydrofuran, and methyl tetrahydrofuran. Further, the volume of the extractant is 20-40 times the total mass of the glucose and fructose mixture. The extractant is capable of dissolving the 5-hydroxymethylfurfural, and as the reaction proceeds, the 5-hydroxymethylfurfural is continuously dissolved in the extractant, promoting the selective conversion of fructose in the eutectic system.

[0017] Further, in S2, the heating temperature is 50-90°C, and the reaction time is 1-4h. Further, in S2, the heating temperature is 50, 60, 70, 80, or 90°C, and the reaction time is 1, 2, 3, or 4h.

[0018] Further, in S3, the separation refers to adding water to dilute the reaction system, and the choline chloride and the remaining glucose are dissolved in water under stirring to obtain a mixture of choline chloride, glucose, and water. Further, in S3, the mass of the water is 2-10 times the total mass of the glucose and fructose mixture. Further, in S3, the mass of the water is 4-6 times the total mass of the glucose and fructose mixture.

[0019] Further, before S1, the method further comprises a step of isomerizing glucose to obtain a mixture of glucose and fructose.

[0020] Further, after S3, the method further comprises S4: isomerizing the mixture of choline chloride, glucose, and water to obtain a mixture of glucose and fructose.

[0021] Advantages

[0022] The present application provides a method for preparing 5-hydroxymethylfurfural by dehydrating a mixed sugar in a eutectic solvent. A mixed sugar containing glucose and fructose is combined with choline chloride to form a eutectic solvent to obtain a high-concentration sugar-containing system. An acid catalyst and an organic extraction solvent are added to the eutectic system, and under heating conditions, the fructose in the mixed sugar is selectively dehydrated to prepare 5-hydroxymethylfurfural, while the glucose is as little converted as possible. After the reaction is completed, water is added to dilute the eutectic system, promoting the transfer of 5-hydroxymethylfurfural to the organic extraction phase.

[0023] In the construction of the eutectic system, by selectively controlling the mass ratio of glucose, fructose, and choline chloride, the reaction temperature, the water content of the system, the reaction time, the mass of the catalyst, the type of the catalyst, the organic extraction agent, and the amount of the extraction agent, etc., the appropriate proportion that can reduce the loss of glucose and reduce the side reactions is found, and the reaction conditions that can improve the yield of HMF are also found. Specifically, the following advantages are achieved:

[0024] (1) By constructing a eutectic system of glucose, fructose and choline chloride, the glucose and 5-hydroxymethylfurfural are stabilized by hydrogen bonding network structure, and the selective preparation of 5-hydroxymethylfurfural from fructose is realized, with a yield of more than 90%, a glucose loss of less than 10%, and avoidance of the complicated and energy-consuming separation and purification process of glucose and fructose.

[0025] (2) Before the reaction, the added extractant forms a phase separation with the eutectic system, so that part of the product 5-hydroxymethylfurfural can be transferred to the extractant in real time during the reaction, realizing the extraction during the reaction, and minimizing the condensation or degradation of 5-hydroxymethylfurfural in the eutectic system due to the acidic condition, which can significantly improve the yield.

[0026] (3) After the reaction is completed, water is added to dilute and destroy the eutectic system of glucose, fructose and choline chloride, and choline chloride and glucose are dissolved in water to form a salt solution containing choline chloride, which promotes the further transfer of the remaining 5-hydroxymethylfurfural to the organic extractant, and most of the 5-hydroxymethylfurfural can be extracted and separated in a single extraction, which can reduce the use of extractant and the number of extraction stages.

[0027] (4) Choline chloride is a biologically friendly substance, and after the separation of 5-hydroxymethylfurfural, the remaining choline chloride and glucose are further dissolved in water to form an aqueous solution which can be subjected to enzymatic or chemical catalytic reaction to further isomerize the unreacted glucose into fructose and glucose, and further prepare 5-hydroxymethylfurfural, realizing low waste discharge, being conducive to industrial production, and reducing environmental pollution.

[0028] (5) The glucose in the eutectic system can be further recycled and utilized, reducing waste and environmental pollution.

[0029] (6) The method of the present application can avoid the high-energy separation and purification process of mixed sugar after isomerization of glucose, realize the selective dehydration of fructose in mixed sugar to prepare 5-hydroxymethylfurfural, and control the loss of glucose, which has good application prospect.

[0030] The present application will be further described below in conjunction with specific examples. These examples are only used to illustrate the present application and not to limit the scope of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 Schematic diagram of recycling glucose after preparing 5-hydroxymethylfurfural from mixed sugar by selective conversion of fructose. DETAILED DESCRIPTION

[0032] The present application will be further described below in conjunction with specific examples. These examples are only used to illustrate the present application and not to limit the scope of the present application.

[0033] After the catalytic reaction, the eutectic system was diluted with water, and the contents of glucose and fructose in the water phase were detected by high performance liquid chromatography, and the content of 5-hydroxymethylfurfural in the organic extraction phase was detected by gas chromatography. The conversion rate of glucose and fructose and the yield of 5-hydroxymethylfurfural were calculated according to the following formula:

[0034]

[0035] Examples 1-5 investigated the effect of reaction temperature on the conversion of mixed sugar to HMF in the eutectic system

[0036] 0.5 g of glucose, 0.5 g of fructose and 1.0 g of choline chloride (ChCl) were mixed in a round-bottom flask and heated at 40°C to obtain a transparent eutectic system. Then 0.05 g of macroporous strong acid resin Amberlyst 15 and 20 mL of methyl isobutyl ketone (MIBK) were added. The flask was connected to a condenser to recover the volatile methyl isobutyl ketone, and then heated to 50°C, 60°C, 70°C, 80°C and 90°C respectively under stirring for 4 h. After the reaction, 4 g of deionized water was added to dilute the lower eutectic system, and the product 5-hydroxymethylfurfural (HMF) was separated by extraction under stirring. The contents of glucose and fructose in the water phase were determined by high performance liquid chromatography, and the conversion rate of sugar was calculated. The content of 5-hydroxymethylfurfural in the organic extraction phase was determined by gas chromatography, and its yield was calculated. The results are shown in Table 1 Examples 1-5.

[0037] Table 1 Effect of reaction temperature on the conversion of mixed sugar to HMF in the eutectic system

[0038]

[0039]

[0040] As shown in Table 1, the conversion rates of glucose and fructose both increased with increasing reaction temperature, but the yield of HMF decreased significantly when the reaction temperature continued to increase to 90°C. This is mainly due to the possible increase in side reactions of sugar and HMF at higher temperatures. Therefore, a suitable temperature of 80°C is considered for the subsequent reaction process.

[0041] Examples 6-10 investigated the effect of choline chloride ratio on the conversion of mixed sugar to HMF in the eutectic system

[0042] The 0.5 g glucose, 0.5 g fructose, 0.5 g, 1.0 g, 2.0 g, 3.0 g and 4.0 g choline chloride (ChCl) were mixed in a round bottom flask and heated at 40 °C to obtain a transparent eutectic system, then 0.05 g macroporous strong acid resin Amberlyst 15, 0.25 g deionized water and 20 mL methyl isobutyl ketone (MIBK) were added, the flask was connected to a condenser to condense and recover the volatile methyl isobutyl ketone, then heated to 80 °C under stirring for 4 h. After the reaction was completed, 4 g deionized water was added to dilute the lower eutectic system, and the product 5-hydroxymethylfurfural (HMF) was separated by fully extracting under stirring. The glucose and fructose contents in the aqueous phase were determined by high performance liquid chromatography, and the sugar conversion rate was calculated; the content of 5-hydroxymethylfurfural in the organic extraction phase was determined by gas chromatography, and the yield was calculated, and the related results are listed in Table 2 of Examples 6-10.

[0043] Table 2 Influence of choline chloride ratio on mixed sugar conversion to HMF in eutectic system

[0044]

[0045] Example 7 in Table 2 and Example 4 in Table 1 were compared, and the water content was increased by 25%, which significantly inhibited the conversion of glucose, but the yield of HMF also decreased significantly. As shown in Table 2, when water was added to the system, the ChCl ratio in the eutectic system was increased to 8, the glucose conversion rate was further inhibited, and the HMF yield could be increased to nearly 80%. This is mainly due to the strengthening of the hydrogen bond network of the eutectic system (DES system) after increasing the amount of choline chloride, which strengthens the interaction between glucose and choline chloride, reduces the consumption of glucose, and also promotes the selective conversion of fructose. However, it should be noted that it will be difficult to form a eutectic system by continuously increasing the content of ChCl.

[0046] Examples 11-13 investigated the influence of reaction time on the conversion of mixed sugar to HMF in the eutectic system

[0047] A mixture of 0.5 g glucose, 0.5 g fructose and 4.0 g choline chloride (ChCl) was heated to 40 °C to obtain a transparent deep eutectic solvent (DES). Then, 0.05 g Amberlyst 15 (denoted as A-15 in Table 3), 0.25 g deionized water and 20 mL methyl isobutyl ketone (MIBK) were added into the flask. The flask was connected to a condenser to recover the volatile MIBK. The mixture was heated to 80 °C and stirred for 1 h, 2 h and 3 h, respectively. After the reaction, 4 g deionized water was added to dilute the lower DES. The product 5-hydroxymethylfurfural (HMF) was extracted from the mixture. The glucose and fructose contents in the aqueous phase were determined by high performance liquid chromatography (HPLC), and the sugar conversion was calculated. The HMF content in the organic phase was determined by gas chromatography (GC), and the HMF yield was calculated. The results are shown in Table 3 (Examples 11-13).

[0048] Examples 14-16: Effect of catalyst mass on the conversion of mixed sugars to HMF in the deep eutectic solvent

[0049] A mixture of 0.5 g glucose, 0.5 g fructose and 4.0 g choline chloride (ChCl) was heated to 40 °C to obtain a transparent deep eutectic solvent (DES). Then, 0.05 g Amberlyst 15 (denoted as A-15 in Table 3), 0.25 g deionized water and 20 mL methyl isobutyl ketone (MIBK) were added into the flask. The flask was connected to a condenser to recover the volatile MIBK. The mixture was heated to 80 °C and stirred for 1 h, 2 h and 3 h, respectively. After the reaction, 4 g deionized water was added to dilute the lower DES. The product 5-hydroxymethylfurfural (HMF) was extracted from the mixture. The glucose and fructose contents in the aqueous phase were determined by high performance liquid chromatography (HPLC), and the sugar conversion was calculated. The HMF content in the organic phase was determined by gas chromatography (GC), and the HMF yield was calculated. The results are shown in Table 3 (Examples 11-13).

[0050] Table 3: Effect of reaction time and catalyst mass on the conversion of mixed sugars to HMF in the deep eutectic solvent

[0051]

[0052]

[0053] The results of Examples 11-13 in Table 3 and Example 10 in Table 2 show that as the reaction time increases from 1 h to 4 h, the glucose conversion increases from 18.89% to 31.88%, while the HMF yield increases first and then decreases, and the highest HMF yield of 84.11% is obtained when the reaction time is 2 h. The above results show that prolonging the reaction time will lead to continuous conversion of glucose, while more side reactions of the product HMF will occur, resulting in a decrease in selectivity and yield.

[0054] The results of Examples 12, 14-16 in Table 3 show that as the mass of the acidic resin catalyst increases from 1% to 10%, the glucose conversion increases from 5.10% to 40.20%, and the fructose conversion also increases from 76.91% to 99.99%; then the HMF yield reaches 84.11% when the mass of the acidic resin catalyst is 5%, and the HMF yield slightly decreases when the mass of the catalyst continues to increase. The above results show that increasing the mass of the acidic resin catalyst will lead to continuous conversion of glucose and fructose, and the yield of the product HMF will also increase significantly, but too high a catalyst mass will also lead to side reactions of HMF, resulting in a decrease in yield.

[0055] Examples 17-21 investigate the effect of water content on the conversion of mixed sugars to HMF in the eutectic system

[0056] 0.5 g of glucose, 0.5 g of fructose, and 4.0 g of choline chloride (ChCl) were added to a round-bottom flask and mixed, then heated at 40°C to obtain a transparent eutectic system, then 0.05 g of macroporous strong acid resin Amberlyst 15, deionized water (0 g, 0.5 g, 0.75 g, 1 g, and 1.5 g), and 20 mL of methyl isobutyl ketone (MIBK) were added. The flask was connected to a condenser to condense the volatile methyl isobutyl ketone, then heated to 80°C under stirring for 2 h. After the reaction was completed, 4 g of deionized water was added to dilute the lower eutectic system, and the product 5-hydroxymethylfurfural (HMF) was separated by extraction under stirring. The glucose and fructose contents in the aqueous phase were determined by high-performance liquid chromatography, and the sugar conversion was calculated; the content of 5-hydroxymethylfurfural in the organic extraction phase was determined by gas chromatography, and the yield was calculated, and the related results are listed in Table 4 Examples 17-21.

[0057] Table 4 Effect of water content on the conversion of mixed sugars to HMF in the eutectic system

[0058]

[0059]

[0060] The results of Example 12 in Table 3 and Examples 17-21 in Table 4 show that as the water content of the system increases from 0% to 150%, the glucose conversion rate is first inhibited, and when the water content reaches 50%, the glucose conversion rate is reduced to within 20%, and when the water content continues to increase to 150%, the glucose conversion rate is further reduced to 6.69%. However, it should be noted that at this time, the fructose conversion rate and the HMF yield are reduced to 42.25% and 27.91%, respectively. The above results show that increasing the water content of the system can sequentially inhibit the conversion of glucose and fructose, and inhibiting the conversion of glucose is the effect desired to be achieved by the present application, but when the water content is too high, both the fructose conversion rate and the HMF yield are significantly reduced, so controlling the water content of the system is very important for the selective dehydration of fructose in the mixed sugar in the deep eutectic system to prepare HMF.

[0061] Examples 22-26 investigate the effect of extractant on the conversion of mixed sugar to HMF in the deep eutectic system

[0062] 0.5 g of glucose, 0.5 g of fructose, and 4.0 g of choline chloride (ChCl) were added to a round-bottom flask and mixed, then heated at 40°C to obtain a transparent deep eutectic system, then 0.05 g of macroporous strong acid resin Amberlyst 15, 0.25 g of deionized water, and 20 mL of organic extractant were added, the flask was connected to a condenser to condense and recover the volatile methyl isobutyl ketone, then heated to 80°C under stirring for 2 h. After the reaction was completed, 4 g of deionized water was added to dilute the lower deep eutectic system, and the product 5-hydroxymethylfurfural (HMF) was separated by extraction under stirring. The glucose and fructose contents in the aqueous phase were determined by high-performance liquid chromatography, and the sugar conversion rate was calculated; the content of 5-hydroxymethylfurfural in the organic extractant was determined by gas chromatography, and the yield was calculated, and the related results are listed in Table 5 Examples 22-26.

[0063] Table 5 Effect of extractant on the conversion of mixed sugar to HMF in the deep eutectic system

[0064]

[0065]

[0066] The results of Example 12 in Table 3 and Examples 22-26 in Table 5 show that when different organic extractants are used, the glucose conversion rate can be controlled within 30%, and the HMF yield is between 65% and 84%, and the HMF yield is the highest when methyl isobutyl ketone is used as the organic extractant.

[0067] Examples 27-28 investigate the amount of organic extractant methyl isobutyl ketone MIBK

[0068] The 0.5 g glucose, 0.5 g fructose and 4.0 g choline chloride (ChCl) were mixed in a round bottom flask and heated at 40 °C to obtain a transparent deep eutectic solvent, then 0.05 g macroporous strong acid cation exchange resin Amberlyst 15, 0.25 g deionized water and methyl isobutyl ketone (MIBK, 30 mL and 40 mL) were added. The flask was connected to a condenser to condense and recover the volatile methyl isobutyl ketone, then heated to 80 °C under stirring for 2 h. After the reaction was completed, 4 g deionized water was added to dilute the lower eutectic system, and the product 5-hydroxymethylfurfural (HMF) was separated by extraction under stirring. The glucose and fructose contents in the aqueous phase were determined by high performance liquid chromatography, and the sugar conversion rate was calculated; the content of 5-hydroxymethylfurfural in the organic extract phase was determined by gas chromatography, and the yield was calculated. The results are shown in Table 5, Examples 27-28.

[0069] The results of Examples 12 in Table 3 and Examples 27-28 in Table 5 show that when the amount of organic extractant methyl isobutyl ketone MIBK is increased, the conversion rate of glucose can gradually decrease to 13.78%, and the yield of HMF increases to 89.13%.

[0070] Example 29 investigates the effect of reducing the amount of acid resin

[0071] The 0.5 g glucose, 0.5 g fructose and 4.0 g choline chloride (ChCl) were mixed in a round bottom flask and heated at 40 °C to obtain a transparent deep eutectic solvent, then 0.05 g macroporous strong acid cation exchange resin Amberlyst 15, 0.25 g deionized water and methyl isobutyl ketone (MIBK, 30 mL and 40 mL) were added. The flask was connected to a condenser to condense and recover the volatile methyl isobutyl ketone, then heated to 80 °C under stirring for 2 h. After the reaction was completed, 4 g deionized water was added to dilute the lower eutectic system, and the product 5-hydroxymethylfurfural (HMF) was separated by extraction under stirring. The glucose and fructose contents in the aqueous phase were determined by high performance liquid chromatography, and the sugar conversion rate was calculated; the content of 5-hydroxymethylfurfural in the organic extract phase was determined by gas chromatography, and the yield was calculated. The results are shown in Table 5, Examples 27-28.

[0072] The results of Example 29 in Table 5 show that by reducing the amount of acid resin, the conversion rate of glucose can be further reduced to 7.54%, and the yield of HMF increases to 93.45%.

[0073] Examples 30-31 investigate the effect of acid catalyst on the conversion of mixed sugars to HMF in the deep eutectic system

[0074] Example 29 0.5 g glucose, 0.5 g fructose and 4.0 g choline chloride (ChCl) were mixed in a round bottom flask and heated at 40 °C to obtain a transparent deep eutectic solvent. Then 0.02 g of macroporous strong acid resin Amberlyst 15, 0.25 g deionized water and 40 mL organic extractant were added. The flask was connected to a condenser to recover the volatile methyl isobutyl ketone. The reaction was then heated to 80 °C under stirring for 2 h. After the reaction, 4 g deionized water was added to dilute the deep eutectic solvent. The product 5-hydroxymethylfurfural (HMF) was separated by extraction under stirring. The glucose and fructose contents in the aqueous phase were determined by high performance liquid chromatography (HPLC) and the sugar conversion was calculated. The HMF content in the organic extractant was determined by gas chromatography (GC) and the HMF yield was calculated. The results are shown in Table 6, Example 29.

[0075] Table 6. Effect of acid catalysts on the conversion of mixed sugars to HMF in deep eutectic solvents

[0076]

[0077]

[0078] The results in Table 5, Example 29 and Table 6, Examples 30-31 show that the glucose conversion can be controlled within 20% and the HMF yield is above 70% when comparing different types of macroporous acid resin catalysts. The HMF yield is the highest and the glucose conversion is the lowest when using Amberlyst 15 as the catalyst.

[0079] Examples 32-34

[0080] Example 32 0.5 g glucose, 0.5 g fructose and 4.0 g choline chloride (ChCl) were mixed in a round bottom flask and heated at 40 °C to obtain a transparent deep eutectic solvent. Then 0.25 g deionized water and 40 mL organic extractant were added. SnCl4-5H2O (5 wt%), NiCl2-6H2O (5 wt%) or CrCl3-6H2O (10 wt%) was added to the deep eutectic solvent. The flask was connected to a condenser to recover the volatile methyl isobutyl ketone. The reaction was then heated to 80 °C under stirring for 2 h. After the reaction, 4 g deionized water was added to dilute the deep eutectic solvent. The product 5-hydroxymethylfurfural (HMF) was separated by extraction under stirring. The glucose and fructose contents in the aqueous phase were determined by high performance liquid chromatography (HPLC) and the sugar conversion was calculated. The HMF content in the organic extractant was determined by gas chromatography (GC) and the HMF yield was calculated. The results are shown in Table 6, Examples 32-34.

[0081] The results in Table 6, Examples 32-34 show that the glucose conversion is above 30% and the HMF yield is around 80% when comparing different types of chloride salts as catalysts.

[0082] Examples 35-38

[0083] After mixing 0.5 g glucose, 0.5 g fructose and 4.0 g choline chloride (ChCl) in a round bottom flask, a transparent deep eutectic solvent was obtained by heating at 40℃, then 0.25 g deionized water and 40 mL organic extractant were added, followed by sulfuric acid (0.05 wt%), nitric acid (0.05 wt%), hydrochloric acid (0.05 wt%) or phosphoric acid (0.1 wt%), the flask was connected to a condenser to condense the volatile methyl isobutyl ketone, then the reaction was carried out at 80℃ for 2 h under stirring. After the reaction was completed, 4 g deionized water was added to dilute the lower eutectic system, and the product 5-hydroxymethylfurfural (HMF) was separated by fully extracting under stirring. The glucose and fructose contents in the aqueous phase were determined by high performance liquid chromatography, and the sugar conversion rate was calculated; the content of 5-hydroxymethylfurfural in the organic extraction phase was determined by gas chromatography, and the yield was calculated, and the related results are shown in Table 6 Examples 35-38.

[0084] The results of Examples 35-38 in Table 6 show that the conversion rate of glucose can be controlled within 30% and the yield of HMF is about 80% by comparing different inorganic acids as catalysts.

[0085] The present application provides a method for preparing 5-hydroxymethylfurfural by dehydration of mixed sugar in a deep eutectic solvent system. The hydrogen bond network structure in the deep eutectic solvent system can stabilize glucose and 5-hydroxymethylfurfural, thereby realizing the selective dehydration of fructose in mixed sugar to prepare 5-hydroxymethylfurfural with a yield of more than 90% and a glucose loss of less than 10%, avoiding the complicated and energy-consuming separation and purification of glucose and fructose.

[0086] In the present application, a certain amount of water is added after the completion of the dehydration reaction to dilute and destroy the deep eutectic system, and the obtained choline chloride aqueous solution can promote the transfer of 5-hydroxymethylfurfural to the organic extraction phase, so that most of the 5-hydroxymethylfurfural can be extracted and separated by single extraction, thereby reducing the use of extraction agent and extraction stages.

[0087] In addition, since choline chloride is a biologically friendly substance, the remaining choline chloride aqueous solution can continue to isomerize the unreacted glucose to fructose by enzyme catalysis or chemical catalysis, and further prepare 5-hydroxymethylfurfural.

[0088] The reagents used in the present application can be purchased from the market or can be prepared by the method described in the present application.

[0089] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A process for the preparation of 5-hydroxymethylfurfural, characterized in that, Specifically comprising the following steps: S1: mixing glucose, fructose and choline chloride, and heating at 40-50℃ to construct a eutectic system; S2: adding a catalyst, water and an extractant methyl isobutyl ketone, heating to 80℃ for 1-2 h of dehydration reaction, the extractant being layered with the eutectic system; S3: separating 5-hydroxymethylfurfural after the reaction; In S1, the mass ratio of glucose, fructose and choline chloride is 1:1:8; the mass of the catalyst is 2-5% of the total mass of the mixed glucose and fructose; the catalyst is at least one of Amberlyst 15, CS650 and D113, and the mass of the water is 25-50% of the total mass of the mixed glucose and fructose.

2. The method of claim 1, wherein, The mass of the catalyst is 2% of the total mass of the mixed glucose and fructose.

3. The method of claim 1, wherein, In S2, the mass of the water is 25% of the total mass of the mixed glucose and fructose.

4. The method of claim 1, wherein, In S2, the volume of the extractant is 20-40 times of the total mass of the mixed glucose and fructose.

5. The method of claim 1, wherein, In S2, the reaction time of heating is 2 h.

6. The method of claim 1, wherein, In S3, the separation refers to adding water to the reaction system, stirring and extracting to dissolve choline chloride and the remaining glucose in water to obtain a mixture of choline chloride, glucose and water.

7. The method of claim 6, wherein, In S3, the mass of the water is 2-10 times of the total mass of the mixed glucose and fructose.

8. The method of claim 1, wherein, Before S1, there is also a step of isomerizing glucose to obtain a mixture of glucose and fructose.

9. The method of claim 1, wherein, After S3, there is also S4: isomerizing the mixture of choline chloride, glucose and water to obtain a mixture of glucose and fructose.

Images