A method for preparing 5-hydroxymethylfurfural by using sweet sorghum juice

Abstract

This invention discloses a method for preparing 5-hydroxymethylfurfural (5-HMF) using inexpensive sweet sorghum juice. Using sweet sorghum juice as raw material, in a water / acetone solvent system, and utilizing acids and / or Lewis acids as catalysts, the mixed reaction system is heated and reacted. After purification, extraction, and vacuum distillation, the 5-HMF is obtained. The sweet sorghum juice used in this invention is rich in sucrose, glucose, and fructose, and is characterized by high yield, low cost, and ease of production. The preparation of 5-HMF using sweet sorghum juice in a green acetone / water solvent system is a method with good potential for industrial application. Furthermore, this invention uses HCl as a catalyst, ensuring complete conversion of sucrose and fructose in the sweet sorghum juice, while retaining more than 85% of glucose. Based on the fructose conversion rate, the 5-HMF yield can reach over 90%. Using AlCl3 as a catalyst, sucrose, glucose, and fructose in the sweet sorghum juice can be completely converted, and based on the total sugar conversion rate, the 5-HMF yield can reach 70%.

Description

Technical Field

[0001] This invention belongs to the field of biomass energy chemical preparation technology, specifically relating to a method for preparing 5-hydroxymethylfurfural using sweet sorghum juice. Background Technology

[0002] 5-Hydroxymethylfurfural (HMF) is an important biomass-based platform compound obtained through the highly selective hydrolysis of fructose. It can be used as a raw material to derive a series of high-value-added compounds, such as 2,5-furandicarboxylic acid, 2,5-dimethylfuran, 2,5-dimethyltetrahydrofuran, and ethoxyethylfurfural. Although there is considerable research on the preparation of HMF, its high production cost limits most studies to laboratory-scale operations, making large-scale production difficult. The cost of raw materials is a significant factor restricting the production cost of HMF. With the market price of fructose continuously rising, finding a cheaper and more abundant carbohydrate source to replace fructose and reduce the production cost of HMF is imperative.

[0003] Sweet sorghum (Sorghum bicolor (L.) Moench) is a highly efficient C4 energy crop, characterized by its large biomass, high stem sugar content, strong stress resistance, and high water and nitrogen use efficiency, making it suitable for widespread cultivation on marginal lands. Sweet sorghum juice contains abundant soluble sugars (such as sucrose, glucose, and fructose), as well as small amounts of inorganic salts and organic acids. Compared to sugarcane, sweet sorghum juice has a higher content of reducing sugars (glucose and fructose) and a lower content of non-reducing sugars (sucrose). The yield of sweet sorghum juice can reach 20,000 liters per hectare. Utilizing sweet sorghum juice as a catalytic conversion feedstock to prepare the more valuable platform compound 5-hydroxymethylfurfural is highly attractive.

[0004] Sweet sorghum juice contains abundant soluble sugars, such as sucrose, glucose, and fructose, forming a mixed sugar system. In this system, different carbohydrates are converted to 5-hydroxymethylfurfural (HMF) via different pathways, increasing the complexity of the reaction system and placing higher demands on operating conditions. Sucrose is a disaccharide that first requires hydrolysis under acidic catalysts to produce glucose and fructose. The conversion of glucose to HMF generally involves two steps: glucose isomerization to fructose, followed by fructose dehydration to HMF. Studies have shown that Lewis acids primarily control the isomerization step, while Brønsted acids mainly drive the dehydration process. Therefore, in the preparation of 5-hydroxymethylfurfural from sweet sorghum juice, it is crucial to comprehensively evaluate the reaction pathways of individual sugars and identify the key rate-limiting steps. It is necessary to develop an economical and efficient process for preparing HMF from sweet sorghum juice.

[0005] Generally, solid acid catalysts are easier to separate and reuse, making them superior to homogeneous catalysts. However, under hydrothermal reaction conditions, humic substances inevitably form during the dehydration of sugars to prepare HMF. These humic substances deposit on the catalyst surface, reducing or deactivating the catalyst. Therefore, from the perspective of industrial HMF production, inexpensive and efficient homogeneous acid catalytic systems are also attractive. Conventional homogeneous catalysts include mineral acids (HCl, H2SO4, H3PO4, etc.), organic acids (formic acid, acetic acid, etc.), and salts containing transition metals (ZnCl2, AlCl3, CrCl3, SnCl4, etc.). Among these, AlCl3, due to its low cost and low toxicity, can be used to prepare HMF from glucose by adjusting different amounts of AlCl3 and Brønsted acids (e.g., HCl), achieving HMF yields exceeding 40% in both batch and continuous flow reaction systems. A suitable solvent can effectively suppress side reactions and reduce the cost of separation and purification. Water, with its environmentally friendly and inexpensive properties, is considered an ideal solvent in chemical catalysis; however, few studies have used water alone as a reaction solvent for HMF preparation. Because dehydration is the primary reaction in the conversion of carbohydrates to HMF, pure aqueous solvents are unfavorable for the forward reaction, making it difficult to obtain high HMF yields. Furthermore, due to the reactive nature of HMF, it readily hydrates in high-temperature aqueous environments to form byproducts such as levulinic acid and formic acid, severely impacting the selectivity and yield of HMF. Polar aprotic solvents can effectively improve the yield of HMF, with dimethyl sulfoxide (DMSO) being widely used in research. Without the addition of a catalyst, fructose can be efficiently converted to HMF in DMSO through a solvation effect, achieving a yield of up to 77%. Water is considered an ideal green solvent for chemical catalysis due to its environmental friendliness and ease of availability; however, the sugar dehydration used for HMF production is typically nonselective in aqueous systems. Solvents such as dimethyl sulfoxide (DMSO) can greatly reduce the formation of humic substances by protecting hexoses and products from degradation, thereby increasing the selectivity of HMF. However, DMSO has a high boiling point (189 °C) and is miscible with common solvents and extractants. After the reaction is completed, it is difficult to separate and purify HMF, which greatly limits the application of DMSO in the industrial preparation of HMF.

[0006] Based on the above reasons, this application is hereby submitted. Summary of the Invention

[0007] Based on the above reasons, and in view of the problems or defects existing in the prior art, the purpose of this invention is to provide a method for preparing 5-hydroxymethylfurfural using sweet sorghum juice, thereby solving or at least partially solving the above-mentioned technical defects existing in the prior art. The main objective of this invention is to provide a method for preparing 5-hydroxymethylfurfural using inexpensive sweet sorghum juice instead of using sugars such as crystalline fructose, glucose, and sucrose in the prior art, so as to reduce the preparation cost of 5-hydroxymethylfurfural.

[0008] To achieve the first objective of this invention, the technical solution adopted by this invention is as follows:

[0009] A method for preparing 5-hydroxymethylfurfural using sweet sorghum juice involves using sweet sorghum juice as raw material, in a water and acetone solvent system, using Brønsted acid and / or Lewis acid as catalysts, heating the mixed reaction system, and then removing impurities, extracting, and distilling under reduced pressure to obtain the 5-hydroxymethylfurfural.

[0010] Furthermore, the method for preparing 5-hydroxymethylfurfural using sweet sorghum juice described above specifically includes the following steps:

[0011] (1) A certain amount of deionized water is added to the pretreated sweet sorghum juice for dilution to obtain a mixed sugar solution, and then a catalyst is added; the catalyst is Brønsted acid and / or Lewis acid;

[0012] (2) Add acetone to the mixed sugar solution described in step (1), mix well, and form a uniform mixed reaction solution;

[0013] (3) Place the mixed reaction solution described in step (2) in a reaction vessel, heat it to 90~180 ℃ and react at a constant temperature for 10~60 min; after the reaction is completed, cool it to room temperature; the obtained product is purified, extracted and distilled under reduced pressure to obtain the 5-hydroxymethylfurfural.

[0014] Furthermore, in the above technical solution, the concentration of the mixed sugar in the pretreated sweet sorghum juice in step (1) is controlled at 50-400 g / L. In a preferred embodiment of the present invention, the concentration of the mixed sugar in the pretreated sweet sorghum juice is 250-350 g / L.

[0015] Furthermore, in the above technical solution, the catalyst in step (1) is preferably Lewis acid.

[0016] Furthermore, in the above technical solution, the Brønsted acid mentioned in step (1) is at least one of hydrochloric acid (HCl), phosphoric acid (H3PO4), sulfuric acid (H2SO4), acidic resin, etc.

[0017] Preferably, in the above technical solution, when the catalyst is Brønsted acid, the Brønsted acid is added in the form of an aqueous solution. For example, when the Brønsted acid is an aqueous hydrochloric acid solution, the concentration of the aqueous hydrochloric acid solution is 0.05-0.40 mol / L.

[0018] Preferably, in the above technical solution, the concentration of the hydrochloric acid aqueous solution is 0.05 mol / L.

[0019] More preferably, in the above technical solution, the volume ratio of the pretreated sweet sorghum juice to the Brønsted acid solution in step (1) is 1:1.

[0020] Furthermore, in the above technical solution, the Lewis acid mentioned in step (1) is at least one of aluminum chloride (AlCl3), zinc chloride (ZnCl2), zinc bromide (ZnBr2), niobium chloride (NbCl5), etc.

[0021] Preferably, in the above technical solution, when the catalyst is a Lewis acid, the Lewis acid is added in the form of an aqueous solution. For example, when the Lewis acid is an aqueous solution of AlCl3, the concentration of the AlCl3 aqueous solution is 0.05-0.40 mol / L.

[0022] Preferably, in the above technical solution, the concentration of the AlCl3 aqueous solution is 0.20 mol / L.

[0023] Furthermore, in the above technical solution, the volume ratio of acetone to mixed sugar solution in step (2) is 1:1 to 4:1. In a preferred embodiment of the present invention, the volume ratio of acetone to mixed sugar solution is 4:1.

[0024] Furthermore, in the preferred embodiment of the present invention, when the catalyst is Brønsted acid, the reaction temperature in step (3) is 150 °C and the reaction time is 20-30 min.

[0025] Furthermore, in the preferred embodiment of the present invention, when the catalyst is Lewis acid, the reaction temperature in step (3) is 150 °C and the reaction time is 40-60 min.

[0026] Furthermore, in the above technical solution, the impurity removal process in step (3) includes: firstly, using activated carbon to adsorb and remove the humic substances generated after the reaction; and secondly, separating the acetone from the product after removing the humic substances by vacuum distillation.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] This invention utilizes raw biomass sweet sorghum juice as a raw material to replace fructose, thereby reducing the raw material cost of 5-hydroxymethylfurfural (5-HMF) production. Based on a green and inexpensive water (sweet sorghum juice is mainly water, and deionized water is also introduced for dilution) / acetone solvent system, and using Brønsted acids such as HCl as catalysts, it achieves 100% conversion of sucrose and fructose in sweet sorghum juice. The yield and selectivity of 5-HMF based on fructose conversion can reach over 90%, and 85% of the glucose in the sweet sorghum juice can be recovered after the reaction. Using Lewis acids such as AlCl3 as catalysts, the conversion rate of sucrose, glucose, and fructose in sweet sorghum juice can reach 100%, and the yield of 5-HMF can reach over 70%. The acetone used in the method of this invention can be extracted and reused by vacuum distillation; this invention uses green and inexpensive ethyl acetate as an extractant, which can completely extract 5-hydroxymethylfurfural and can be reused; this invention preferably uses HCl and / or AlCl3 as catalysts, which have the characteristics of being inexpensive and low-pollution. After the reaction is completed, a small amount of HCl is used for treatment, which can realize the reuse of AlCl3 and greatly reduce the production cost of 5-hydroxymethylfurfural. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 This invention relates to Example 1, which uses HCl as a catalyst to dehydrate a mixed syrup to produce 5-hydroxymethylfurfural (HMF) in acetone / water solvent systems with different volume ratios. (a) shows the concentrations of glucose, fructose, and HMF in acetone / water solvent systems with different volume ratios after the reaction. The black, blue, and yellow dashed lines represent the initial concentrations of sucrose, glucose, and fructose in the mixed syrup, respectively. (b) shows the HMF yield, HMF selectivity, and carbon balance in acetone / water solvent systems with different volume ratios after the reaction.

[0031] Figure 2 The HMF yields obtained by dehydration of simulated mixed syrup, hydrolyzed sweet sorghum juice, and clarified + hydrolyzed sweet sorghum juice in an 80 vol% acetone solvent system under the catalysis of HCl aqueous solutions of different concentrations in Example 2 of this invention are shown.

[0032] Figure 3The following are the changes in substrate and product concentrations over time (left) and HMF yield, HMF selectivity, and carbon balance over time (right) in HCl-catalyzed dehydration of mixed sugars in an 80 vol% acetone system according to Example 3 of this invention: (a) Dehydration of mixed syrup catalyzed by 5 mM HCl; (b) Dehydration of sweet sorghum juice catalyzed by 40 mM HCl; (c) Dehydration of clarified and hydrolyzed sweet sorghum juice catalyzed by 40 mM HCl. The black, green, and blue dashed lines represent the concentrations of sucrose, glucose, and fructose in the initial mixture, respectively.

[0033] Figure 4 In Example 5 of this invention, AlCl3 was used as a catalyst to dehydrate a mixed syrup to produce 5-hydroxymethylfurfural (HMF) in acetone / water solvent systems with different volume ratios. (a) shows the concentrations of glucose, fructose, and HMF in acetone / water solvent systems with different volume ratios after the reaction. The black, blue, and yellow dashed lines represent the initial concentrations of sucrose, glucose, and fructose in the mixed syrup, respectively. (b) shows the HMF yield, HMF selectivity, and carbon balance in acetone / water solvent systems with different volume ratios after the reaction.

[0034] Figure 5 The HMF yield obtained by dehydration of mixed syrup, hydrolyzed sweet sorghum juice and clarified + hydrolyzed sweet sorghum juice in an 80 vol% acetone solvent system under the catalysis of different concentrations of AlCl3 in Example 4 of this invention.

[0035] Figure 6 The following are the changes in substrate and product concentrations over time (left) and HMF yield, HMF selectivity, and carbon balance over time (right) in AlCl3-catalyzed dehydration of mixed sugars in an 80 vol% acetone system according to Example 6 of this invention: (a) Dehydration of mixed syrup catalyzed by 10 mM HCl; (b) Dehydration of sweet sorghum juice catalyzed by 20 mM HCl; (c) Dehydration of clarified and hydrolyzed sweet sorghum juice catalyzed by 20 mM HCl. The black, green, and blue dashed lines represent the concentrations of sucrose, glucose, and fructose in the initial mixture, respectively.

[0036] Figure 7 This is a flowchart of the overall process for producing 5-hydroxymethylfurfural using mixed sugars in this invention. Detailed Implementation

[0037] This invention discloses a method for preparing 5-hydroxymethylfurfural using inexpensive sweet sorghum juice. The method includes: preferably, in a water / acetone solvent system, using Brønsted HCl, H3PO4, H2SO4, or acidic resins as catalysts, the sucrose in the sweet sorghum juice is hydrolyzed to produce fructose and glucose. The fructose is converted to 5-hydroxymethylfurfural under Brønsted acid catalysis, while glucose does not participate in the reaction and is mostly retained for recovery. More preferably, in a water / acetone solvent system, using Lewis acids such as AlCl3, ZnCl2, ZnBr2, or NbCl5 as catalysts, the sucrose in the sweet sorghum juice is rapidly hydrolyzed to produce fructose and glucose. The glucose is isomerizes to fructose under the action of Lewis acids. The AlCl3 in the solution is then converted to 5-hydroxymethylfurfural. 3+ The isocation hydrolysis provides Brønsted acid, and fructose is dehydrated under the catalysis of Brønsted acid to generate 5-hydroxymethylfurfural, thus achieving the complete conversion of mixed sugars in sweet sorghum juice. The sweet sorghum juice used in this invention is rich in sucrose, glucose, and fructose, and is characterized by high yield, low cost, and ease of production. The preparation of 5-hydroxymethylfurfural using sweet sorghum juice in a green acetone / water solvent system is a preparation method with good potential for industrial application. Furthermore, in this invention, HCl is used as a catalyst, ensuring complete conversion of sucrose and fructose in the sweet sorghum juice, while retaining more than 85% of glucose. Based on the fructose conversion rate, the yield of 5-hydroxymethylfurfural can reach over 90%. Using AlCl3 as a catalyst, sucrose, glucose, and fructose in the sweet sorghum juice can be completely converted, and based on the total sugar conversion rate, the yield of 5-hydroxymethylfurfural can reach 70%.

[0038] The present invention will be further described below with reference to the accompanying drawings and specific embodiments to enable those skilled in the art to better understand the invention. However, the invention is not limited to the following embodiments. It should be noted that all other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0039] The equipment and raw materials used in this invention are all commercially available or commonly used in the field. Unless otherwise specified, the methods in the following embodiments are conventional methods in the field.

[0040] Example 1

[0041] (1) Raw material pretreatment. Since freshly squeezed sweet sorghum juice is extremely perishable and difficult to preserve, it needs to be pretreated in a timely manner to remove impurities, enzymes, microorganisms, etc. We prepared two types of sweet sorghum juice through two pretreatment methods: hydrolyzed sweet sorghum juice and clarified + hydrolyzed sweet sorghum juice. The pretreated sweet sorghum juice can be preserved for a longer period of time.

[0042] Preparation of hydrolyzed sweet sorghum juice: The pH of the crude sweet sorghum juice was adjusted to 2 at 80 °C using 50% (v / v) sulfuric acid, and stirred continuously for 1.5 hours. The supernatant was then centrifuged at 4000 rpm for 5 minutes. Finally, the pH of the supernatant was adjusted to 4 using 6 mol / L sodium hydroxide. After cooling, hydrolyzed sweet sorghum juice was obtained. The main components and contents of the hydrolyzed sweet sorghum juice are as follows: sucrose concentration of 38.39 g / L, glucose concentration of 135.27 g / L, and fructose concentration of 129.40 g / L.

[0043] Preparation of clarified and hydrolyzed sweet sorghum juice: First, the pH of the crude sweet sorghum juice was adjusted to 10 at 60 °C using calcium oxide, and stirred continuously for 1 hour. Then, it was centrifuged at 4000 rpm for 5 minutes to obtain the supernatant. Next, the pH of the supernatant was adjusted to 7 at 60 °C using phosphoric acid, and stirred continuously for 1 hour. It was then centrifuged again at 4000 rpm for 5 minutes to obtain a clarified supernatant. The pH of the clarified supernatant was adjusted to 2 at 80 °C using 50% (v / v) sulfuric acid, and stirred continuously for 1.5 hours. Finally, the pH of the supernatant was adjusted to 4 using 6 mol / L sodium hydroxide. After cooling, the clarified and hydrolyzed sweet sorghum juice was obtained. The main components and contents of the obtained clarified and hydrolyzed sweet sorghum juice are as follows: sucrose concentration of 51.79 g / L, glucose concentration of 130.23 g / L, and fructose concentration of 122.22 g / L.

[0044] Preparation of mixed syrup: Add 12.94g fructose, 13.52g glucose and 3.84g sucrose to a beaker, dissolve in a small amount of deionized water, and then make up to 100 mL in a volumetric flask to obtain mixed syrup.

[0045] (2) Add 1 mL of mixed syrup, 1 mL of HCl aqueous solution (0.05 mol / L), and 8 mL of deionized water; 1 mL of mixed syrup, 1 mL of HCl aqueous solution (0.05 mol / L), 3 mL of deionized water, and 5 mL of acetone; 1 mL of mixed syrup, 1 mL of HCl aqueous solution (0.05 mol / L), 2 mL of deionized water, and 6 mL of acetone; 1 mL of mixed syrup, 1 mL of HCl aqueous solution (0.05 mol / L), 1 mL of deionized water, and 7 mL of acetone; 1 mL of mixed syrup, 1 mL of HCl aqueous solution (0.05 mol / L), and 8 mL of acetone to thick-walled pressure-resistant glass tubes to form five different volume ratios of acetone / (mixed syrup + HCl aqueous solution + deionized water, referred to as water in this invention) (0 / 10, 5 / 5, 6 / 4, 7 / 3, and 8 / 2). After mixing evenly, immerse the mixture in an oil bath at 150°C and heat for 30 minutes. During the reaction, the mixture was stirred at 800 rpm using a magnetic stirrer. After the reaction was complete, the reaction tube was allowed to cool to room temperature, and the sample was removed and refrigerated at 4 °C until analysis. The conversion rate of the mixed syrup and the yield of 5-hydroxymethylfurfural were qualitatively and quantitatively analyzed by high-performance liquid chromatography (HPLC).

[0046] (3) Performance: Figure 1 a, Figure 1 b represents the concentration of each component, HMF yield, selectivity, and carbon balance during the dehydration of mixed syrup to prepare 5-hydroxymethylfurfural (HMF) at different acetone / water ratios in this embodiment; Figure 1 a, Figure 1 b shows that when the volume ratio of acetone to water is 8 / 2, all sucrose and fructose in the mixed sugar are converted, while most of the glucose is retained, resulting in the highest yield and selectivity of HMF.

[0047] Example 2: Effect of HCl concentration on the conversion of mixed sugars to 5-hydroxymethylfurfural

[0048] (1) Conduct 4 sets of experiments:

[0049] In the first experiment, 1 mL of mixed syrup, 1 mL of hydrolyzed sweet sorghum juice, and 1 mL of clarified + hydrolyzed sweet sorghum juice were added to 1 mL of 0.05 mol / L HCl aqueous solution in thick-walled pressure-resistant glass tubes, respectively. After stirring evenly, 8 mL of acetone was added. The glass tubes were placed in an oil bath at 150 ℃ and stirred with a magnetic stirrer at 800 rpm. The reaction was stopped after 30 min.

[0050] In the second experiment, 1 mL of mixed syrup, 1 mL of hydrolyzed sweet sorghum juice, and 1 mL of clarified + hydrolyzed sweet sorghum juice were added to 1 mL of 0.10 mol / L HCl aqueous solution in thick-walled pressure-resistant glass tubes, respectively. After stirring evenly, 8 mL of acetone was added. The glass tubes were placed in an oil bath at 150 ℃ and stirred with a magnetic stirrer at 800 rpm. The reaction was stopped after 30 min.

[0051] In the third experiment, 1 mL of mixed syrup, 1 mL of hydrolyzed sweet sorghum juice, and 1 mL of clarified + hydrolyzed sweet sorghum juice were added to 1 mL of 0.20 mol / L HCl aqueous solution in thick-walled pressure-resistant glass tubes, respectively. After stirring evenly, 8 mL of acetone was added. The glass tubes were placed in an oil bath at 150 ℃ and stirred with a magnetic stirrer at 800 rpm. The reaction was stopped after 30 min.

[0052] In the fourth experiment, 1 mL of mixed syrup, 1 mL of hydrolyzed sweet sorghum juice, and 1 mL of clarified + hydrolyzed sweet sorghum juice were added to 1 mL of 0.40 mol / L HCl aqueous solution in thick-walled, pressure-resistant glass tubes, respectively. After stirring thoroughly, 8 mL of acetone was added. The glass tubes were placed in an oil bath at 150 ℃ and stirred magnetically at 800 rpm for 30 min before the reaction was stopped. The conversion rate of the mixed sugar and the yield of 5-hydroxymethylfurfural were qualitatively and quantitatively analyzed by high-performance liquid chromatography (HPLC).

[0053] (2) Performance: From Figure 2 It can be seen that using simulated mixed syrup as raw material requires a smaller amount of catalyst, that is, 5 mM HCl solution can completely convert the sucrose and fructose in the mixed syrup; using hydrolyzed sweet sorghum juice and clarified + hydrolyzed sweet sorghum juice as raw material requires a larger amount of catalyst, and the concentration of HCl needs to reach 40 mM to complete the conversion.

[0054] Example 3: Effect of reaction time on the dehydration of mixed sugars to prepare 5-hydroxymethylfurfural

[0055] (1) Add 1 mL of mixed syrup and 1 mL of 0.05 mol / L HCl aqueous solution to a thick-walled pressure-resistant tube, mix well, add 8 mL of acetone and tighten the PTFE seal. Then place it in a preheated oil bath at 150 ℃, and take samples every 10 min. Stop the reaction after 1 h. Dilute the sample by a certain factor, filter it through a 0.22 μm filter membrane, and perform qualitative and quantitative analysis of the conversion rate of the simulated mixed syrup and the yield of 5-hydroxymethylfurfural by high performance liquid chromatography. Performance: Figure 3a) In this embodiment, 5-hydroxymethylfurfural is prepared by dehydration of a mixed syrup in an 80 vol% acetone solvent system under the catalysis of HCl aqueous solution. Figure 3 As can be seen, after 30 min of reaction, the sucrose and fructose in the mixed syrup were completely converted, and the HMF yield reached its maximum (>90%). With the increase of reaction time, the HMF yield did not decrease significantly, and after 60 min of reaction, more than 85% of the glucose could still be retained.

[0056] (2) Add 1 mL of hydrolyzed sweet sorghum juice and 1 mL of 0.4 mol / L HCl aqueous solution to a thick-walled pressure-resistant tube and mix thoroughly. Then add 8 mL of acetone and seal with a PTFE cap. Place the mixture in a preheated oil bath at 150 °C. Take samples every 10 min and continue the reaction for 1 h before stopping. The samples need to be appropriately diluted and filtered through a 0.22 μm filter membrane. The conversion rate of the mixed sugar and the yield of 5-hydroxymethylfurfural are qualitatively and quantitatively analyzed by high performance liquid chromatography. Figure 3 b demonstrates the process of preparing mixed sugars for dehydration to 5-hydroxymethylfurfural in 80 vol% acetone solvent catalyzed by an aqueous HCl solution. According to... Figure 3 According to result b, after 20 minutes of reaction, the sucrose and fructose in the hydrolyzed sweet sorghum juice were completely converted, reaching the highest HMF yield (>90%). With increasing reaction time, the HMF yield did not decrease significantly, and after 60 minutes of reaction, most of the glucose was also retained.

[0057] (3) Add 1 mL of clarified + hydrolyzed sweet sorghum juice and 1 mL of 0.4 mol / L HCl aqueous solution to a thick-walled pressure-resistant tube, mix well, then add 8 mL of acetone and tighten the PTFE seal. Then place the tube in an oil bath preheated to 150 ℃, take samples every 10 minutes, and continue the reaction for 1 hour. After sampling, dilute the samples by a certain factor, filter them through a 0.22 μm filter membrane, and use high performance liquid chromatography to qualitatively and quantitatively analyze the conversion rate of the mixed sugar and the yield of 5-hydroxymethylfurfural. Performance: Figure 3 c shows the results of the preparation of 5-hydroxymethylfurfural by dehydration of mixed sugars using 80 vol% acetone as a solvent system under HCl catalysis in this embodiment. From Figure 3 c shows that after 20 minutes of reaction, the sucrose and fructose in the hydrolyzed sweet sorghum juice were completely converted, and the HMF yield reached its maximum value (>90%). With the extension of reaction time, the HMF yield did not decrease significantly, and after 60 minutes of reaction, glucose was also basically retained.

[0058] Example 4

[0059] (1) Add the following components to a thick-walled, pressure-resistant glass tube respectively: 1 mL of simulated mixed syrup, 1 mL of 0.1 mol / L AlCl3 solution, and 8 mL of deionized water; 1 mL of simulated mixed syrup, 1 mL of 0.1 mol / L AlCl3 solution, 3 mL of deionized water, and 5 mL of acetone; 1 mL of simulated mixed syrup, 1 mL of 0.1 mol / L AlCl3 solution, 2 mL of deionized water, and 6 mL of acetone; 1 mL of simulated mixed syrup, 1 mL of 0.1 mol / L AlCl3 solution, 1 mL of deionized water, and 7 mL of acetone; 1 mL of mixed syrup, 1 mL of 0.1 mol / L AlCl3 solution, and 8 mL of acetone to form five different volume ratio acetone / water solvent systems (0 / 10, 5 / 5, 6 / 4, 7 / 3, and 8 / 2). After mixing evenly, immerse the glass tube in an oil bath at 150 ℃ and heat for 60 min. During the reaction, the mixture was stirred at 800 rpm using a magnetic stir bar. After the reaction was complete, the reaction tube was cooled to room temperature, the sample was removed and refrigerated at 4 °C until analysis. The conversion rate of the mixed syrup and the yield of 5-hydroxymethylfurfural were both qualitatively and quantitatively analyzed by high-performance liquid chromatography (HPLC).

[0060] (2) Figure 4 a, Figure 4 b represents the concentrations of each component, as well as the HMF yield, selectivity, and carbon balance, during the dehydration of mixed syrup to prepare 5-hydroxymethylfurfural (HMF) at different acetone / water ratios in this embodiment. Figure 4 a, Figure 4 b shows that when the volume ratio of acetone to water is 8 / 2, almost all sucrose, fructose, and glucose in the mixed sugar are converted, and the yield and selectivity of HMF are the highest.

[0061] Example 5: Effect of AlCl3 concentration on the conversion of mixed sugars to 5-hydroxymethylfurfural.

[0062] Three sets of experiments were conducted. 1 mL of mixed sugar (simulated mixed syrup, hydrolyzed sweet sorghum juice, and clarified + hydrolyzed sweet sorghum juice) and 1 mL of AlCl3 solution (0.05 mol / L, 0.10 mol / L, and 0.20 mol / L) were added to sealed, thick-walled, pressure-resistant glass tubes. After thorough stirring, 8 mL of acetone was added. The glass tubes were placed in an oil bath at 150 ℃ and stirred magnetically at 800 rpm for 30 min before the reaction was stopped. The conversion rate of the mixed sugar and the yield of 5-hydroxymethylfurfural were qualitatively and quantitatively analyzed by high-performance liquid chromatography (HPLC).

[0063] Performance: From Figure 5It can be seen that using simulated mixed syrup as raw material requires a smaller amount of catalyst, that is, 0.05 mol / L AlCl3 solution can completely convert sucrose, fructose and glucose in the mixed sugar; using hydrolyzed sweet sorghum juice and clarified + hydrolyzed sweet sorghum juice as raw material requires a larger amount of catalyst, and the concentration of AlCl3 needs to reach 0.2 mol / L to complete the conversion.

[0064] Example 6

[0065] (1) Add 1 mL of mixed syrup and 1 mL of 0.1 mol / L AlCl3 aqueous solution to a thick-walled pressure-resistant tube, mix well, add 8 mL of acetone and tighten the PTFE seal. Then place it in a preheated oil bath at 150 ℃, and take samples every 10 min. Stop the reaction after 1 h. Dilute the sample by a certain factor, filter it through a 0.22 μm filter membrane, and perform qualitative and quantitative analysis of the conversion rate of the simulated mixed syrup and the yield of 5-hydroxymethylfurfural by high performance liquid chromatography. Performance: Figure 6 a) In this embodiment, 5-hydroxymethylfurfural was prepared by dehydration of a mixed syrup in an 80 vol% acetone solvent system under the catalysis of AlCl3 aqueous solution. Figure 6 As can be seen, sucrose, glucose and fructose in the mixed syrup were completely converted after 60 min of reaction, and the HMF yield reached its maximum (69%) after 40 min of reaction; the HMF yield did not decrease significantly with increasing reaction time.

[0066] (2) Add 1 mL of hydrolyzed sweet sorghum juice and 1 mL of 0.2 mol / L AlCl3 aqueous solution to a thick-walled pressure-resistant tube and mix thoroughly. Then add 8 mL of acetone and seal with a PTFE cap. Place the mixture in a preheated oil bath at 150 ℃. Take samples every 10 min and continue the reaction for 1 h before stopping. The samples need to be appropriately diluted, filtered through a 0.22 μm filter membrane, and the conversion rate of the mixed sugars and the yield of 5-hydroxymethylfurfural are qualitatively and quantitatively analyzed by high performance liquid chromatography. Figure 6 The results showed that after 60 minutes of reaction, the sucrose, glucose and fructose in the hydrolyzed sweet sorghum juice were almost completely converted, reaching the highest HMF yield (>66%).

[0067] (3) Add 1 mL of clarified + hydrolyzed sweet sorghum juice and 1 mL of 0.2 mol / L AlCl3 aqueous solution to a thick-walled pressure-resistant tube, mix well, then add 8 mL of acetone and tighten the PTFE seal. Then place the tube in an oil bath preheated to 150 ℃, take samples every 10 minutes, and continue the reaction for 1 hour. After sampling, dilute the samples by a certain factor, filter them through a 0.22 μm filter membrane, and use high performance liquid chromatography to qualitatively and quantitatively analyze the conversion rate of the mixed sugar and the yield of 5-hydroxymethylfurfural. Performance: Figure 6 c shows the results of the preparation of 5-hydroxymethylfurfural by dehydration of mixed sugars using 80 vol% acetone as a solvent system under AlCl3 catalysis in this embodiment. From Figure 6 As can be seen from c, the clarified + hydrolyzed sweet sorghum juice achieved the highest HMF yield (70%) after 50 minutes of reaction, and was able to completely convert all sugars in the mixed sugar system. Compared with hydrolyzed sweet sorghum juice, clarified hydrolyzed sweet sorghum juice was more advantageous in obtaining a higher HMF yield, despite the change in the proportion of mixed sugars.

[0068] After the reaction was completed, the mixed solution was added to a beaker containing activated carbon, stirred thoroughly, and allowed to stand for 1 hour to allow the activated carbon to adsorb and remove the humic substances generated after the reaction. The mixed reaction system after the humic substances were removed was separated into acetone by vacuum distillation, and the acetone could be reused. An excess of ethyl acetate was added to the remaining system, and the mixture was heated and stirred to extract 5-hydroxymethylfurfural into ethyl acetate. Subsequently, ethyl acetate was removed by vacuum distillation to obtain 5-hydroxymethylfurfural. The remaining insoluble component in ethyl acetate was mainly unreacted glucose, which could be collected and reused.

[0069] All aspects, embodiments, features, and examples of this invention are to be regarded as illustrative in all respects and are not intended to limit the invention; the scope of the invention is defined only by the claims. Other embodiments, modifications, and uses will become apparent to those skilled in the art without departing from the spirit and scope of the invention as claimed.

[0070] The use of headings and sections in this invention is not intended to limit the invention; each section can be applied to any aspect, embodiment or feature of the invention.

[0071] Throughout this invention, wherever a composition is described as having, containing, or including specific components, or wherever a process is described as having, containing, or including specific process steps, it is contemplated that the compositions taught in this invention are also substantially composed of or comprised of the described components, and that the processes taught in this invention are also substantially composed of or comprised of the described process steps.

[0072] It should be understood that the order of the steps or the order in which specific actions are performed is not particularly important, as long as the teachings of this invention remain operable. Furthermore, two or more steps or actions can be performed simultaneously.

[0073] Although the invention has been described with reference to illustrative embodiments, those skilled in the art will understand that various other changes, omissions, and / or additions can be made without departing from the spirit and scope of the invention, and that elements of the embodiments can be substituted with substantially equivalents. Furthermore, many modifications can be made without departing from the scope of the invention to adapt particular situations or materials to the teachings of the invention. Therefore, the invention is not intended to be limited to the specific embodiments disclosed for carrying out the invention, but rather is intended to encompass all embodiments falling within the scope of the appended claims. Moreover, unless specifically stated otherwise, any use of the terms first, second, etc., does not indicate any order or importance, but is used to distinguish one element from another.

Claims

1. A method for preparing 5-hydroxymethylfurfural using sweet sorghum juice, characterized by, Specifically, the steps include the following: (1) Add calcium oxide to sweet sorghum juice, adjust the pH to 10 at 60 ℃, stir continuously for 1 hour, then centrifuge at 4000 rpm for 5 minutes to obtain supernatant, then add phosphoric acid to the supernatant, adjust the pH to 7 at 60 ℃, stir continuously for 1 hour, centrifuge again at 4000 rpm for 5 minutes to obtain clear supernatant, then add 50% sulfuric acid by volume to the clear supernatant, adjust the pH to 2 at 80 ℃, stir continuously for 1.5 hours to obtain sweet sorghum juice pretreatment solution, finally add 6 mol / L sodium hydroxide to the sweet sorghum juice pretreatment solution, adjust the pH to 4, and cool to obtain clear + hydrolyzed sweet sorghum juice. The concentration of mixed sugar in the clear + hydrolyzed sweet sorghum juice is controlled at 50~400 g / L. (2) A certain amount of deionized water was added to the clarified + hydrolyzed sweet sorghum juice for dilution to obtain a mixed sugar solution, and then a catalyst was added; the catalyst was a 0.40 mol / L hydrochloric acid aqueous solution; (3) Add acetone to the mixed sugar solution in step (2), mix well to form a uniform mixed reaction solution, wherein the volume ratio of acetone to mixed sugar solution is 4:1; (4) Place the mixed reaction solution described in step (3) in a reaction vessel, heat it to 150 °C and react at a constant temperature for 20 min; after the reaction is completed, cool it to room temperature; the obtained product is purified, extracted and distilled under reduced pressure to obtain the 5-hydroxymethylfurfural.

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