5-hydroxymethylfurfural and preparation method thereof

Abstract

The invention discloses 5-hydroxymethylfurfural and a preparation method thereof, and belongs to the technical field of chemical engineering. The preparation method comprises the following steps: reacting a homogeneous aqueous solution containing fructose, inorganic salt and an acid catalyst in a multi-kettle series reactor to obtain the 5-hydroxymethylfurfural, the inorganic salt is selected from at least one of halogen compounds, borides, silicate, aluminate, phosphate and borate; the acidic catalyst comprises at least one of water-soluble acids. The specific inorganic salt and the specific acid catalyst are added and can play a synergistic role, the reaction is carried out under multi-kettle series connection, the backmixing degree of the reaction materials in the reactor is maximized, side reactions can be effectively controlled, black rot is avoided, the reaction production efficiency and conversion rate are effectively improved, the reaction selectivity is improved, and the method is suitable for industrial production. And the equipment maintenance and labor cost is greatly reduced.

Description

Technical Field

[0001] The present application relates to the field of chemical technology, and in particular to 5-hydroxymethylfurfural and a preparation method thereof. Background Art

[0002] 5-Hydroxymethylfurfural, as a bio-based chemical, holds significant importance in green chemistry and sustainable development. Its production and utilization help reduce dependence on non-renewable resources and promote sustainable production and consumption patterns. 5-Hydroxymethylfurfural can be used as a chemical raw material in the synthesis of many organic compounds, such as biodiesel, polymers, solvents, and chemicals. Its chemical properties make it an important precursor for the synthesis of other compounds. The production of chemicals from renewable biomass resources not only alleviates the increasingly scarce oil resources crisis but also provides a driving force for innovation in the development of new materials based on the unique structural properties of bio-based chemicals. Bio-based chemical synthesis routes using 5-Hydroxymethylfurfural (HMF) as a platform compound and subsequently converting it into other high-value-added derivatives are a promising future development direction. This series of products can be used to produce new biodegradable plastics, new polyurethanes, specialty nylons, new green solvents, and new oil additives.

[0003] The typical reaction format for the traditional production of 5-HMF (HMF) is a batch reactor. In batch reactions, production must be stopped after each reaction cycle to clean the equipment before the next batch can begin. These reactions typically require more manual intervention and downtime, potentially leading to lower production efficiency. Furthermore, batch systems often generate significant waste or become unstable during the start and end of batch production. This can lead to the formation of difficult-to-clean black rot products, which can hinder the continued progress of the reaction and reduce HMF yield. Various homogeneous and heterogeneous catalysts, including Lewis and Bronsted acids, have been developed and found to be effective for the synthesis of 5-HMF. These catalysts are widely used in the production of 5-HMF. However, due to the high reactivity of the 5-HMF produced during the reaction, these catalysts can cause it to undergo further reactions, polymerizing to form high-molecular-weight black rot products or decomposing to produce acetoacetic acid. The production of these byproducts can lead to low selectivity in the reaction, as well as corrosion and clogging of equipment, making it difficult to clean and making the reaction difficult to carry out. This significantly increases equipment maintenance and operating costs, resulting in poor economic returns. These shortcomings limit its potential industrial applications. Therefore, developing a multi-reactor tandem reaction format for HMF production has important industrial production significance and practical value. Summary of the Invention

[0004] In view of this, the present application provides a 5-hydroxymethylfurfural and a preparation method thereof, the main purpose of which is to solve the technical problems of 5-hydroxymethylfurfural having many black rot by-products, low selectivity and low yield.

[0005] In one aspect, the present application provides a method for preparing 5-hydroxymethylfurfural, comprising the following steps:

[0006] A homogeneous aqueous solution containing fructose, an inorganic salt and an acidic catalyst reacts in a multi-tank series reactor to obtain the 5-hydroxymethylfurfural.

[0007] The present application adds inorganic salts and specific acidic catalysts, and reacts in a multi-reactor series mode, with each process condition acting synergistically; wherein, multi-reactor series can effectively improve the production efficiency and conversion rate of the reaction compared to a batch reaction; and it can also avoid the problem that the side reaction of 5-hydroxymethylfurfural forms black rot, which leads to a decrease in product yield and a significant increase in equipment maintenance costs. The system for synthesizing 5-hydroxymethylfurfural used in the present application has great economic benefits, low system cost, little environmental pollution, simple operation, easy repetition, low equipment maintenance cost, and can efficiently produce high-purity 5-hydroxymethylfurfural.

[0008] Optionally, the inorganic salt is selected from at least one of halogen compounds, borides, silicates, aluminates, phosphates and borates.

[0009] Optionally, the halogen compound is selected from at least one of sodium chloride, sodium fluoride, magnesium chloride, calcium chloride, barium chloride, chromium chloride, ferric chloride, copper chloride, aluminum chloride, sodium bromide, calcium bromide and magnesium bromide.

[0010] Optionally, the boride is at least one selected from boron fluoride, magnesium boride, titanium boride, chromium boride and calcium boride.

[0011] Optionally, the silicate is selected from at least one of sodium silicate, calcium silicate, magnesium silicate and ammonium silicate.

[0012] Optionally, the aluminate is selected from at least one of sodium aluminate, calcium aluminate, magnesium aluminate and ammonium aluminate.

[0013] Optionally, the phosphate is selected from at least one of sodium phosphate, calcium phosphate, magnesium phosphate and ammonium phosphate.

[0014] Optionally, the borate is selected from at least one of sodium borate, calcium borate, magnesium borate and ammonium borate.

[0015] Optionally, the homogeneous aqueous solution containing fructose, an inorganic salt and an acidic catalyst is a mixture of fructose, an inorganic salt and water.

[0016] Optionally, the acidic catalyst comprises at least one acid soluble in water.

[0017] Optionally, the water-soluble acid is an acid that is readily soluble in water.

[0018] Optionally, the acid catalyst is selected from at least one of phosphoric acid, hydrochloric acid, sulfuric acid, boric acid and p-toluenesulfonic acid.

[0019] Optionally, the hydrochloric acid is selected from a hydrochloric acid solution with a mass concentration of 35.0 to 40.0 wt%.

[0020] Optionally, the sulfuric acid is selected from concentrated sulfuric acid with a mass concentration of 95.0 to 99.0 wt%.

[0021] Optionally, the mass ratio of the fructose, the inorganic salt, the acid catalyst and the water is 1:(0.001-2):(0.001-1):(0.5-20).

[0022] Optionally, the mass ratio of the fructose to the inorganic salt is 1:0.05-2.

[0023] Optionally, the mass ratio of fructose to inorganic salt is selected from any value of 1:0.001, 1:0.005, 1:0.01, 1:0.05, 1:0.1, 1:0.2, 1:0.5, 1:0.8, 1:1, 1:1.5, 1:1.8, 1:2, or any range between two of them.

[0024] Optionally, the mass ratio of the fructose to the acidic catalyst is 1:0.001-0.05.

[0025] Optionally, the mass ratio of fructose to acid catalyst is selected from any value of 1:0.001, 1:0.002, 1:0.005, 1:0.01, 1:0.1, 1:0.2, 1:0.5, 1:0.1, 1:0.2, 1:0.5, 1:0.8, 1:1 or any range between two of them.

[0026] Optionally, the mass ratio of the fructose to the water is 1:0.8-10.

[0027] Optionally, the mass ratio of fructose to water is selected from any value among 1:0.5, 1:0.8, 1:1, 1:2, 1:5, 1:8, 1:10, 1:12, 1:15, 1:17, 1:18, 1:20, or any range value therebetween.

[0028] Optionally, the mass ratio of the water to the inorganic salt is 1:0.05-5.

[0029] Optionally, the mass ratio of water to inorganic salt is selected from any value among 1:0.05, 1:0.10, 1:0.20, 1:0.30, 1:0.40, 1:0.50, 1:0.60, 1:0.70, 1:0.80, 1:0.90, 1:1, 1:2, 1:3, 1:4, 1:5 or any range value between two thereof.

[0030] Optionally, the amount of the acid catalyst added is 0.1 wt% to 5 wt% of the amount of fructose added.

[0031] Optionally, the amount of the acid catalyst added is the mass percentage of the fructose added amount selected from any value among 0.1wt%, 0.2wt%, 0.5wt%, 0.8wt%, 1.0wt%, 1.5wt%, 2.0wt%, 2.5wt%, 3.0wt%, 3.5wt%, 4.0wt%, 4.5wt%, 5.0wt% or any range value between two of them.

[0032] Optionally, the reaction conditions include: a reaction temperature of 60 to 180° C., and a reaction residence time of 1 to 10 hours.

[0033] Optionally, the reaction temperature is selected from any value among 60°C, 70°C, 80°C, 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 175°C, 180°C or any range between two values.

[0034] Optionally, the reaction residence time is selected from any value of 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours or 10 hours, or any range value therebetween.

[0035] Optionally, the reaction pressure is not particularly limited.

[0036] Optionally, the number of the multi-tank series reactors is 2 to 8.

[0037] Optionally, the number of the series reactors is selected from any value among 2, 3, 4, 5, 6, 7, 8, or a range between any two values.

[0038] Optionally, the method further comprises a purification step: after the reaction is completed, an extractant is added to the reaction solution to extract to obtain an upper extract, and the upper extract is subjected to reduced pressure distillation to obtain 5-hydroxymethylfurfural.

[0039] Optionally, the upper layer of ethyl acetate or dimethyl carbonate extract is subjected to reduced pressure distillation to recover the extraction solvent ethyl acetate or dimethyl carbonate, and simultaneously obtain the product 5-hydroxymethylfurfural.

[0040] Optionally, the detection method used is high performance liquid chromatography: the liquid chromatography peak area is obtained by configuring the 5-hydroxymethylfurfural content in the standard solution, and the peak area is used as the abscissa and the concentration of 5-hydroxymethylfurfural is used as the ordinate to obtain a standard curve; further, the concentration of 5-hydroxymethylfurfural in the reaction solution after the reaction can be calculated, and the yield of 5-hydroxymethylfurfural can be calculated based on the concentration.

[0041] Optionally, the extraction process includes: adding the reaction solution obtained after the reaction to an extractant for extraction operation; after standing and shaking, the solution is separated into layers, the upper layer is an organic solution phase containing 5-hydroxymethylfurfural, after separating the upper layer, ethyl acetate or dimethyl carbonate is added again to the remaining lower layer solution for extraction, and the operation is repeated multiple times.

[0042] Optionally, the volume ratio of the extractant to the reaction solution is 1 to 3:1.

[0043] Optionally, the extractant is selected from ethyl acetate and / or dimethyl carbonate.

[0044] Optionally, the extraction is performed 2 to 5 times.

[0045] Optionally, the 5-hydroxymethylfurfural yield is detected by high performance liquid chromatography, and deionized water is added to mix and constant volume during detection.

[0046] Optionally, the conditions for the reduced pressure distillation include: vacuum degree of 0.01 to 5 KPa, temperature of 30 to 60° C., and time of 0.5 to 3 hours.

[0047] Optionally, the vacuum degree is selected from any value among 0.01KPa, 0.02KPa, 0.05KPa, 0.1KPa, 0.5KPa, 1KPa, 2KPa, 3KPa, 4KPa, 4.5KPa, 5KPa, or any range between any two values.

[0048] Optionally, the temperature is selected from any value among 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C or any range between two values.

[0049] Optionally, the time is selected from any value among 0.5 hours, 0.6 hours, 0.8 hours, 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, or any range between two of them.

[0050] Optionally, the yield of 5-hydroxymethylfurfural in the preparation method is greater than 80%.

[0051] Optionally, the yield of 5-hydroxymethylfurfural in the preparation method is between 80% and 95%.

[0052] The present application provides a specific method for preparing 5-hydroxymethylfurfural, comprising:

[0053] 1) Fructose, an inorganic salt aqueous solution and a catalyst are uniformly mixed and reacted in a homogeneous state through a multi-tank series reactor. The reaction temperature is between 60 and 180° C., the reaction residence time is between 1 and 10 hours, and the number of reactors is between 2 and 8.

[0054] 2) A small amount of the reaction liquid after the reaction in step 1) is subjected to liquid chromatography analysis to determine the yield of 5-hydroxymethylfurfural, which is greater than 80%. Ethyl acetate or dimethyl carbonate is added to the reaction liquid to perform multiple extraction operations, the number of extraction operations being 2 to 5 times. After the extraction is completed, the product 5-hydroxymethylfurfural is obtained by vacuum distillation. The apparatus is connected to a water pump or an oil pump for vacuum distillation, and the system vacuum is controlled at 0.01 to 5 kPa, the vacuum distillation temperature is between 30° C. and 60° C., and the vacuum distillation operation time is between 0.5 and 3 hours.

[0055] The preparation route of the present application is to use raw materials containing fructose, inorganic salts and water, and obtain 5-hydroxymethylfurfural through a dehydration reaction under the catalytic action of an acidic catalyst. The added inorganic salts and the multi-reactor series reaction, which is different from the batch reaction, effectively inhibit the further side reactions of 5-hydroxymethylfurfural. No other impurities and black rot are generated after the reaction. After the reaction, dimethyl carbonate or ethyl acetate is used as an extractant to extract 5-hydroxymethylfurfural, and the extraction solvent and the product are recovered and separated by a reduced pressure distillation method. However, the traditional preparation process of 5-hydroxymethylfurfural is difficult to control the occurrence of its side reactions, and the generated black rot is very likely to cause equipment corrosion and blockage.

[0056] In a second aspect, the present application provides a 5-hydroxymethylfurfural, which is prepared using the above-mentioned preparation method.

[0057] Compared with the prior art, the advantages of this application include:

[0058] 1) The synergistic effect of adding specific inorganic salts and specific acid catalysts in the preparation process of 5-hydroxymethylfurfural provided in this application can effectively control the occurrence of side reactions, avoid the production of black rot, improve the selectivity of the reaction, and greatly reduce equipment maintenance and labor costs.

[0059] 2) The preparation process of the present application adopts a multi-reactor series reaction form. The reaction materials are in multiple reactors with a large degree of back mixing. The reaction stirring is uniform and controllable, which has great economic benefits, low system cost, little environmental pollution, simple operation, easy repetition, low equipment maintenance cost, and can efficiently produce high-purity 5-hydroxymethylfurfural. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] Figure 1Schematic diagram of a multi-reactor series reaction device used in the examples of this application;

[0061] Figure 2 This is the H NMR spectrum of the product synthesized in Example 1 of the present application;

[0062] Figure 3 This is the H NMR spectrum of the 5-hydroxymethylfurfural standard in this application;

[0063] Figure 4 This is the carbon NMR spectrum of the product synthesized in Example 1 of the present application;

[0064] Figure 5 This is the carbon NMR spectrum of the 5-hydroxymethylfurfural standard in this application. DETAILED DESCRIPTION

[0065] The present application will be further described below in conjunction with specific embodiments. The following description is merely a few embodiments of the present application and does not limit the present application in any form. Although the present application discloses the preferred embodiments below, it is not intended to limit the present application. Any person skilled in the art who, without departing from the scope of the technical solution of the present application, makes slight changes or modifications using the above disclosed technical content is equivalent to an equivalent implementation case and falls within the scope of the technical solution.

[0066] Unless otherwise specified, the raw materials in the examples of this application were purchased through commercial channels.

[0067] The analysis method in the examples of this application is as follows:

[0068] Carbon and hydrogen nuclear magnetic spectra were analyzed using an AVANCE II 400M liquid nuclear magnetic spectrometer produced by Bruker, and the reaction solution was dissolved in a deuterated reagent.

[0069] The high performance liquid chromatography was carried out using a model 7890A produced by Waters Corporation. The test conditions were as follows: water was used as the mobile phase, and ultraviolet-visible light and differential refractive index detectors were used.

[0070] In the examples of the present application, the yield and selectivity of 5-hydroxymethylfurfural were calculated by the following method:

[0071] Yield of 5-hydroxymethylfurfural = number of moles of 5-hydroxymethylfurfural produced / number of moles of reaction substrate added;

[0072] Selectivity of 5-hydroxymethylfurfural = number of moles of 5-hydroxymethylfurfural produced / number of moles of reaction substrate participating in the reaction.

[0073] The liquid chromatography peak area is obtained by configuring the 5-hydroxymethylfurfural content in the standard solution, and the peak area is used as the abscissa and the concentration of 5-hydroxymethylfurfural is used as the ordinate to obtain a standard curve; further, the concentration of 5-hydroxymethylfurfural in the reaction solution after the reaction can be calculated, and the yield of 5-hydroxymethylfurfural can be calculated based on the concentration.

[0074] The concentrations of concentrated sulfuric acid and hydrochloric acid used in the examples of this application are as follows:

[0075] Concentrated sulfuric acid: H SO is 98.0 wt%;

[0076] Hydrochloric acid: HCl is 37.0 wt%.

[0077] The preparation method of 5-hydroxymethylfurfural provided in the present application comprises the following steps:

[0078] a) mixing raw materials containing fructose, an inorganic salt, and an acidic catalyst into a homogeneous aqueous solution, and reacting them in a multi-reactor series reaction mode to obtain the 5-hydroxymethylfurfural, the reaction temperature being between 60° C. and 180° C., the reaction residence time being between 1 and 10 hours, and the number of series reaction reactors being 2 to 8.

[0079] b) taking a small amount of the reaction liquid after the reaction in step a) for liquid chromatography analysis to determine the yield of 5-hydroxymethylfurfural; adding ethyl acetate or dimethyl carbonate to the reaction liquid for multiple extraction operations, the number of extraction operations being 2 to 5 times; after the extraction is completed, performing a vacuum distillation operation to obtain the generated product 5-hydroxymethylfurfural, and connecting the device to a water pump or an oil pump to perform vacuum distillation, controlling the system vacuum degree to 0.01 to 5 kPa, the vacuum distillation temperature to 30 to 60° C., and the vacuum distillation operation time to 0.5 to 3 hours.

[0080] As a preferred embodiment of the above, the inorganic salt includes at least one of a halogen compound, a boride, a silicate, an aluminate, a phosphate and a borate;

[0081] The halogen compound includes at least one of sodium chloride, sodium fluoride, magnesium chloride, calcium chloride, barium chloride, chromium chloride, ferric chloride, copper chloride, aluminum chloride, sodium bromide, calcium bromide and magnesium bromide;

[0082] The boride comprises at least one of boron fluoride, magnesium boride, titanium boride, chromium boride and calcium boride;

[0083] The silicate includes at least one of sodium silicate, calcium silicate, magnesium silicate and ammonium silicate;

[0084] The aluminate includes at least one of sodium aluminate, calcium aluminate, magnesium aluminate and ammonium aluminate;

[0085] The phosphate includes at least one of sodium phosphate, calcium phosphate, magnesium phosphate, and ammonium phosphate.

[0086] The borate includes at least one of sodium borate, calcium borate, magnesium borate and ammonium borate.

[0087] The acidic catalyst includes a water-soluble acid, such as at least one of phosphoric acid, hydrochloric acid, sulfuric acid and p-toluenesulfonic acid; the water-soluble acid includes at least one of sulfuric acid and sulfonic acid.

[0088] As a preferred embodiment of the above embodiment, the mass ratio of fructose, inorganic salt, acidic catalyst and water is 1:(0.001-2):(0.001-1):(0.5-20); the mass ratio of fructose and inorganic salt is 1:0.05-2; the mass ratio of fructose and acidic catalyst is 1:0.001-0.05; and the mass ratio of fructose and water is 1:0.8-10.

[0089] Example 1

[0090] 8g of fructose, 5g of sodium chloride, and 6g of water were added to a material storage tank. 0.2g of concentrated sulfuric acid was added dropwise while stirring as a catalyst. After the raw materials were fully dissolved into a homogeneous phase, the mixture was passed through a multi-reactor reactor with four reactors in series. The temperature was raised to 100°C and the reaction residence time was 5 hours, during which the color of the reaction solution gradually deepened. After the reaction, a small amount of the reaction solution was analyzed by high-performance liquid chromatography (HPLC), which showed an 81% yield of 5-hydroxymethylfurfural with a selectivity of 95%. Dimethyl carbonate (3:1 by volume) was added to the reaction solution, and extraction was performed twice. After the extraction, the extract was connected to a water or oil pump for vacuum distillation. The system vacuum was maintained at 2 kPa, the vacuum distillation temperature was kept at 40°C, and the vacuum distillation operation time was 1.5 hours. The resulting 5-hydroxymethylfurfural had a purity of 98%.

[0091] Example 2

[0092] 8.5g of fructose, 2g of sodium silicate, and 7g of water were added to a material storage tank. 0.15g of phosphoric acid was added as a catalyst while stirring. After the raw materials were fully dissolved into a homogeneous phase, the mixture was passed through a multi-reactor series reactor with six reactors connected in series. The temperature was raised to 150°C and the reaction time was 4 hours. The color of the reaction solution gradually deepened. After the reaction, a small amount of the reaction solution was analyzed by high-performance liquid chromatography. The results showed that the yield of 5-hydroxymethylfurfural was 87% and the selectivity was 98%. Dimethyl carbonate was added to the reaction solution (the volume ratio of dimethyl carbonate to reaction solution was 2:1) and multiple extraction operations were performed. The number of extractions was 5 times. After the extraction, the extract was connected to a water pump or oil pump for vacuum distillation. The vacuum degree of the system was controlled at 3kPa, the vacuum distillation temperature was between 50°C, and the vacuum distillation operation time was between 3 hours. The purity of the obtained 5-hydroxymethylfurfural was 98%.

[0093] Examples 3 to 11

[0094] The specific ingredients, materials and reaction conditions are shown in Table 1 below. Other operations during the synthesis process are the same as in Example 1.

[0095] Table 1. Raw material composition, proportions and vacuum distillation conditions of Examples 3 to 11

[0096]

[0097]

[0098] Example 12

[0099] 5g of fructose, 10g of water, and 5g of sodium chloride were added to a material storage tank. 0.1g of hydrochloric acid was added as a catalyst while stirring. The temperature was raised to 150°C in a multi-reactor reactor with four reactors in series. The reaction was allowed to proceed for 5 hours, and the color of the reaction solution gradually deepened. After the reaction, a small amount of the reaction solution was analyzed by high-performance liquid chromatography (HPLC), which revealed an 85% yield of 5-hydroxymethylfurfural with a selectivity of 96%. Dimethyl carbonate (dimethyl carbonate:reaction solution volume ratio of 2:1) was added to the reaction solution and extracted five times. After the extraction, the extract was connected to a water or oil pump for vacuum distillation. The system vacuum was maintained at 3 kPa, the vacuum distillation temperature was kept at 55°C, and the vacuum distillation operation lasted for 3 hours. The resulting 5-hydroxymethylfurfural had a purity of 96%.

[0100] Example 13

[0101] 5g of fructose, 8g of water, and 5g of sodium chloride were added to a material storage tank. 0.1g of sulfuric acid was added as a catalyst while stirring. In a multi-reactor cascade reaction model with four reactors in series, the temperature was raised to 140°C for a residence time of 2 hours, and the reaction liquid gradually darkened in color. After the reaction, a small amount of the reaction liquid was analyzed by high-performance liquid chromatography (HPLC), revealing an 86% yield of 5-hydroxymethylfurfural with a selectivity of 98%. Dimethyl carbonate (2:1 by volume) was added to the reaction liquid and extracted five times. After the extractions were complete, the extract was connected to a water or oil pump for vacuum distillation. The vacuum was maintained at 3 kPa, the distillation temperature was kept at 50°C, and the distillation time was kept at 3 hours. The resulting 5-hydroxymethylfurfural had a purity of 98%.

[0102] Comparative Example 1

[0103] The difference between Comparative Example 1 and Example 12 is that the reaction is carried out in a single batch reactor that is not connected in series.

[0104] The specific operation includes: adding 5g of fructose, 10g of water, and 5g of sodium chloride to a batch reactor (single reactor), while stirring, adding 0.1g of hydrochloric acid as a catalyst, heating to 150°C, and reacting for 5 hours. The color of the reaction solution gradually deepens. After the reaction, a small amount of the reaction solution was taken for high-performance liquid chromatography analysis, and the results showed that the yield of 5-hydroxymethylfurfural was 73% and the selectivity was 85%. Dimethyl carbonate was added to the reaction solution (the volume ratio of dimethyl carbonate to reaction solution was 2:1) and multiple extraction operations were performed. The extraction operation was repeated 5 times. After the extraction, the extract was obtained and connected to a water pump or oil pump for vacuum distillation. The system vacuum was controlled at 4kPa, the vacuum distillation temperature was between 55°C, and the vacuum distillation operation time was between 3 hours. The purity of the obtained 5-hydroxymethylfurfural was 88%.

[0105] Comparative Example 2

[0106] The difference between Comparative Example 2 and Example 13 is that no inorganic salt is added to the reactants.

[0107] The specific operation includes adding 5g of fructose and 8g of water to a material tank, adding 0.1g of sulfuric acid as a catalyst while stirring, and heating the reaction to 140°C in a multi-reactor series reaction model with four reactors in series. The reaction residence time is 2 hours, and the color of the reaction solution gradually deepens. After the reaction, a small amount of the reaction solution is analyzed by high-performance liquid chromatography, which shows a 65% yield of 5-hydroxymethylfurfural and an 85% selectivity. Dimethyl carbonate is added to the reaction solution (the volume ratio of dimethyl carbonate to reaction solution is 2:1) and multiple extraction operations are performed. The extraction process is repeated 5 times. After the extraction is completed, the extract is connected to a water pump or oil pump for vacuum distillation. The system vacuum is maintained at 3kPa, the vacuum distillation temperature is kept at 50°C, and the vacuum distillation operation time is kept at 3 hours. The resulting 5-hydroxymethylfurfural has a purity of 88%.

[0108] Example 14 Liquid NMR Analysis

[0109] The 5-hydroxymethylfurfural prepared in Examples 1 to 13 was subjected to liquid nuclear magnetic resonance analysis. Figure 1 and Figure 3 As shown, Figure 2 and Figure 4 This is the standard spectrum of 5-hydroxymethylfurfural. Figure 1 The hydrogen nuclear magnetic resonance spectrum of 5-hydroxymethylfurfural prepared in Example 1 is as follows: Figure 1 and Figure 2 It can be seen from the comparison that the 5-hydroxymethylfurfural prepared in Example 1 has a typical standard 5-hydroxymethylfurfural hydrogen nuclear magnetic spectrum.

[0110] Figure 3The carbon nuclear magnetic resonance spectrum of 5-hydroxymethylfurfural prepared in Example 1 is as follows: Figure 3 and Figure 4 It can be seen from the comparison that the 5-hydroxymethylfurfural prepared in Example 1 has a typical standard 5-hydroxymethylfurfural carbon nuclear magnetic resonance spectrum.

[0111] The test results of 5-hydroxymethylfurfural in other examples are similar to those described above, and standard 5-hydroxymethylfurfural is obtained through this application.

[0112] After testing, the yield of 5-hydroxymethylfurfural prepared in Examples 1-13 of the present application was between 80% and 95%, the selectivity was between 93% and 98%, and the purity was between 93% and 99%.

[0113] Comparison of Example 12 and Comparative Example 1 shows that, under the same reaction conditions, Comparative Example 1 uses a batch reactor to prepare 5-hydroxymethylfurfural with a yield of 73%, a selectivity of 85%, and a purity of 88%. Example 12 uses four reactors connected in series to prepare 5-hydroxymethylfurfural with a yield of 85%, a selectivity of 96%, and a purity of 96%. This demonstrates that the present application utilizes a series of reactors to prepare 5-hydroxymethylfurfural, resulting in a stable, continuous, and efficient production process that reduces by-product generation, improves production efficiency, enhances product quality, and further increases the yield, selectivity, and purity of 5-hydroxymethylfurfural.

[0114] By comparing Example 13 and Comparative Example 2, it can be seen that, under the same reaction conditions, an inorganic salt is added to the reactants of Example 13, and the yield of the prepared 5-hydroxymethylfurfural is 86%, the selectivity is 98%, and the purity is 98%; in Comparative Example 2, no inorganic salt is added, and the yield of the prepared 5-hydroxymethylfurfural is 65%, the selectivity is 85%, and the purity is 88%; this indicates that the addition of an inorganic salt to the reactants in the present application can improve the yield and selectivity of 5-hydroxymethylfurfural.

[0115] The above descriptions are merely a few embodiments of the present application and do not constitute any form of limitation to the present application. Although the present application discloses the preferred embodiments as above, they are not intended to limit the present application. Any technical personnel familiar with the present profession, without departing from the scope of the technical solution of the present application, using the technical content disclosed above to make slight changes or modifications are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A method for preparing 5-hydroxymethylfurfural, characterized in that, The preparation method comprises the following steps: A homogeneous aqueous solution containing fructose, an inorganic salt and an acidic catalyst reacts in a multi-tank series reactor to obtain the 5-hydroxymethylfurfural.

2. A method for preparing 5-hydroxymethylfurfural according to claim 1, characterized in that, The inorganic salt is selected from at least one of halogen compounds, borides, silicates, aluminates, phosphates and borates; Preferably, the halogen compound is selected from at least one of sodium chloride, sodium fluoride, magnesium chloride, calcium chloride, barium chloride, chromium chloride, ferric chloride, copper chloride, aluminum chloride, sodium bromide, calcium bromide and magnesium bromide; Preferably, the boride is at least one selected from boron fluoride, magnesium boride, titanium boride, chromium boride and calcium boride; Preferably, the silicate is selected from at least one of sodium silicate, calcium silicate, magnesium silicate and ammonium silicate; Preferably, the aluminate is selected from at least one of sodium aluminate, calcium aluminate, magnesium aluminate and ammonium aluminate; Preferably, the phosphate is selected from at least one of sodium phosphate, calcium phosphate, magnesium phosphate and ammonium phosphate; Preferably, the borate is selected from at least one of sodium borate, calcium borate, magnesium borate and ammonium borate.

3. A method for preparing 5-hydroxymethylfurfural according to claim 1, characterized in that, The acidic catalyst includes a water-soluble acid; Preferably, the acidic catalyst is selected from at least one of phosphoric acid, hydrochloric acid, sulfuric acid, boric acid and sulfonic acid; Preferably, the hydrochloric acid is selected from a hydrochloric acid solution with a mass concentration of 35.0 to 40.0 wt%; Preferably, the sulfuric acid is selected from concentrated sulfuric acid with a mass concentration of 95.0 to 99.0 wt%.

4. A method for preparing 5-hydroxymethylfurfural according to claim 1, characterized in that, The mass ratio of the fructose, the inorganic salt, the acidic catalyst and the water is 1:(0.001-2):(0.001-1):(0.5-20); Preferably, the mass ratio of the fructose to the inorganic salt is 1:0.05-2; Preferably, the mass ratio of the fructose to the acidic catalyst is 1:0.001-0.05; Preferably, the mass ratio of the fructose to the water is 1:0.8-10.

5. A method for preparing 5-hydroxymethylfurfural according to claim 1, characterized in that, The reaction conditions include: reaction temperature of 60 to 180° C., and reaction residence time of 1 to 10 hours.

6. The method for preparing 5-hydroxymethylfurfural according to claim 1, wherein The number of the multi-tank series reactors is 2 to 8.

7. The method for preparing 5-hydroxymethylfurfural according to claim 1, wherein The method further comprises a purification step: After the reaction is completed, an extractant is added to the reaction solution to extract and obtain an upper extract. The upper extract is distilled under reduced pressure to obtain 5-hydroxymethylfurfural.

8. The method for preparing 5-hydroxymethylfurfural according to claim 7, wherein: The volume ratio of the extractant to the reaction solution is 1 to 3:1; Preferably, the extractant is selected from ethyl acetate and / or dimethyl carbonate; Preferably, the extraction is performed 2 to 5 times.

9. The method for preparing 5-hydroxymethylfurfural according to claim 7, wherein: The conditions for the reduced pressure distillation include: vacuum degree of 0.01-5 KPa, temperature of 30-60° C., and time of 0.5-3 hours.

10. A 5-hydroxymethylfurfural, characterized in that The invention is prepared by the preparation method according to any one of claims 1 to 9.

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