Method for preparing 5-hydroxymethylfurfural by using a temperature-sensitive heteropolyacid-based catalyst

Abstract

The present invention discloses a method for preparing 5-hydroxymethylfurfural, which includes: under the catalytic action of a temperature-sensitive heteropolyacid catalyst, subjecting a fructose-based carbohydrate to an intramolecular dehydration reaction at 80°C - 200°C in a biphasic reaction medium composed of a low-boiling organic solvent and a deep eutectic solvent to obtain the 5-hydroxymethylfurfural. The heteropolyacid catalyst used in the present invention has an increased solubility when the temperature is raised in the reaction medium and catalyzes the dehydration of fructose in the form of a liquid acid, greatly improving the fructose dehydration efficiency and the yield of the target product; after the reaction is completed and the temperature is lowered, the solubility decreases and it precipitates in the form of a solid, facilitating the separation and recycling of the catalyst from the product. The present invention meets the requirements of green chemistry and creates good conditions for the industrial production of the target product.

Description

Technical Field

[0001] The present invention relates to a method for producing biomass-based 5-hydroxymethylfurfural from saccharide carbohydrates, belonging to the field of fine chemicals. Background Art

[0002] Saccharide carbohydrates represented by fructose are an important part of biomass resources. Fructose can be dehydrated through an acid-catalyzed reaction to obtain an important high-value-added biomass-based platform compound: 5-hydroxymethylfurfural (HMF). HMF has active groups such as aldehyde groups and hydroxyl groups, and can undergo reactions such as hydrogenation, oxidative dehydrogenation, esterification, halogenation, polymerization, and hydrolysis, and is used to synthesize important materials such as polymers, drugs, resins, plastics, and fuel additives. Therefore, HMF is an important bridge connecting biomass resources and fuels and chemicals, and its use can effectively replace traditional fossil energy, thereby effectively alleviating the energy crisis and environmental pollution problems caused by the large-scale use of fossil resources at present. Therefore, developing a method for efficiently using saccharide compounds to prepare HMF is a key issue for the effective utilization of biomass resources.

[0003] The reaction media for the dehydration of fructose to HMF include aqueous solutions and supercritical aqueous solution systems (Motokucho S, Morikawa H, Nakatani H, et al. Tetrahedron Letters 2016, 57:4742-4745.), organic solvent systems (Gomes G R, Rampon D S, Ramos L P. Applied Catalysis A: General, 2017, 545:127-133.), biphasic reaction systems (James A. Dumesic, et al. Science, 2006, 312, 1933-1937) and ionic liquid systems (Bekbolat Kassanov J W, Yan F, Jie C. RSC Advances, 2017, 7:30755-30762.). The solvation effect of the reaction medium on fructose has an obvious influence on the subsequent reaction. Therefore, it is necessary to reasonably construct the reaction medium to improve the performance of the reaction system.

[0004] Catalysts for the dehydration of fructose to produce HMF include liquid acid catalysts and solid acid catalysts. Although traditional liquid acid catalysts (including sulfuric acid, hydrochloric acid, etc.) have strong acidity and high yields of target products, they cannot be separated and recovered from the target products after the reaction, are prone to corrode equipment, and cause serious acid pollution to the environment after being discharged. In contrast, solid acid catalysts have the advantages of easy product separation, recyclability, low pollution, and non-corrosion of equipment. For example, CN 110642812 A uses H-Beta zeolite, CN107001305 B uses titanium oxide TiO2 supported on silica, and CN 106622285 B uses sulfonic acid carbon-based solid acid to catalyze the dehydration of fructose to prepare HMF. However, solid acid catalysts generally have relatively large micro-sizes, and are affected by proton mass transfer efficiency and substrate adsorption and desorption in the above reaction media, resulting in a decrease in the fructose dehydration rate and a decrease in the yield of the target product. In addition, the preparation process of solid acid catalysts is complex, expensive, and easily deactivated, requiring a coupled complex catalyst regeneration process. Therefore, the production and use of solid acids also greatly limit the industrial production of HMF.

[0005] Therefore, in view of the above situation, it is urgent for us to overcome the disadvantages of liquid acid catalysts and solid acid catalysts, integrate the advantages of both, and couple with advanced reaction media to propose a method for continuously preparing HMF with high selectivity and high yield. Summary of the Invention

[0006] The object of the present invention is to overcome the above-mentioned disadvantages of the prior art and provide a method for preparing HMF using a temperature-sensitive heteropolyacid catalyst.

[0007] The catalyst used in the method of the present invention has typical temperature-sensitive properties, that is, the solubility of the catalyst in the reaction medium gradually increases with the increase of temperature, and it can be completely dissolved in the reaction medium at the reaction temperature to form a homogeneous acid catalytic system, greatly improving the fructose dehydration rate and the yield of the target product; after the reaction, the temperature gradually drops to room temperature, the solubility of the catalyst in the reaction medium gradually decreases and gradually precipitates, and returns to the solid state again, facilitating the separation and recovery of the catalyst from the reaction medium. In addition, the reaction medium used in the present invention has a good solvation effect on fructose, thereby further improving the reaction performance of fructose dehydration and increasing the yield of the target product.

[0008] A method for preparing HMF provided by the present invention includes: under the catalytic action of a temperature-sensitive heteropolyacid catalyst, subjecting a fructose-based carbohydrate to an intramolecular dehydration reaction in a biphasic reaction medium composed of a low-boiling organic solvent and a deep eutectic solvent at 80°C - 200°C to obtain the 5-hydroxymethylfurfural.

[0009] The temperature-sensitive heteropolyacid catalyst is selected from unmodified heteropolyacids, the heteroatom of which is selected from one or more of P or Si, and the metal atom of which is selected from one or more of W, Mo, Re, V, Nb and Ta, preferably one or more of tungsten-containing heteropolyacids, and more preferably one or more of phosphotungstic acid and silicotungstic acid.

[0010] The temperature-sensitive heteropolyacid catalyst may also be selected from temperature-sensitive heteropolyacid catalysts modified by quaternary ammonium bases and / or quaternary ammonium salts (hereinafter referred to as quaternary ammonium base / salts), preferably phosphotungstic acid or silicotungstic acid modified by quaternary ammonium base / salts.

[0011] The preparation method of the temperature-sensitive heteropolyacid catalyst modified by quaternary ammonium bases and / or quaternary ammonium salts includes: adding quaternary ammonium bases and / or quaternary ammonium salts to an aqueous solution of heteropolyacid, heating and reacting to produce a white precipitate, and after the reaction is completed, filtering, washing and drying the white precipitate.

[0012] The quaternary ammonium base and / or quaternary ammonium salt preferably contains a quaternary ammonium base and / or quaternary ammonium salt containing a carboxyl group, and more preferably one or several of betaine, betaine hydrochloride and C1-C 18 alkyl-substituted betaines.

[0013] The molar ratio of the sum of the quaternary ammonium base and quaternary ammonium / salt to the heteropolyacid is 0.1:1 - 10:1, preferably 0.2:1 - 5:1, and further preferably 0.5:1 - 3:1.

[0014] The heating temperature for the reaction of the quaternary ammonium base / salt with the heteropolyacid is 30°C - 100°C, preferably 50°C - 80°C; the reaction time is 0.5 - 10 hours, preferably 4 - 8 hours.

[0015] According to the method of the present invention, the amount of water used to dissolve the quaternary ammonium base / salt and the heteropolyacid is not particularly limited, and it is only appropriate that the concentrations of the quaternary ammonium base / salt and the heteropolyacid are moderate. Preferably, the concentration of the quaternary ammonium base / salt in water is 0.2 g / mL - 0.5 g / mL, and the concentration of the heteropolyacid in water is 0.1 g / mL - 0.3 g / mL.

[0016] In the fructose dehydration reaction, the fructose-based carbohydrate is selected from one or more of purified fructose, crude fructose, polyfructose, fructose syrup, and fructose-glucose syrup.

[0017] The low-boiling organic solvent is located in the upper layer of the two-phase reaction medium and is selected from one of acetone, butanone, methyl isobutyl ketone, 1,4-dioxane, tetrahydrofuran, and acetonitrile, preferably one or more of 1,4-dioxane, tetrahydrofuran, and acetonitrile.

[0018] The deep eutectic solvent is located in the lower layer of the two-phase reaction medium and is a homogeneous solvent formed by an organic quaternary ammonium salt as a hydrogen bond acceptor and a protonic solvent as a hydrogen bond donor through a hydrogen bond network.

[0019] The organic quaternary ammonium salt serving as a hydrogen bond acceptor is selected from organic quaternary halides (halides) with short carbon chains, preferably one of C1-C4 alkyl trimethyl quaternary ammonium chlorides, more preferably one or more of tetramethylammonium chloride, choline chloride, chlormequat chloride, allyltrimethylammonium chloride, and butyltrimethylammonium chloride.

[0020] The protonic solvent serving as a hydrogen bond donor is selected from one or more of water and polyols, preferably water and C1-C3 polyols, more preferably one or more of water, ethylene glycol, 1,2-propanediol, 1,3-propanediol, and glycerol.

[0021] The mass ratio of the hydrogen bond acceptor to the hydrogen bond donor of the deep eutectic solvent is 0.1:1 - 5:1, preferably 1.5:1 - 3:1.

[0022] The volume ratio of the deep eutectic solvent in the two-liquid-phase reaction medium is 5% - 50%, preferably 10% - 20%.

[0023] The mass ratio of the fructose-based carbohydrate to the two-liquid-phase reaction medium is 1:1 - 1:1000, preferably 1:2 - 1:100, more preferably 1:5 - 1:20.

[0024] The mass ratio of the thermosensitive heteropolyacid catalyst to the fructose-based carbohydrate is 1:1 - 1:100, preferably 1:2 - 1:20, more preferably 1:2 - 1:10.

[0025] The temperature of the dehydration reaction of the fructose-based carbohydrate is 80°C - 200°C, preferably 90°C - 160°C, more preferably 100°C - 130°C; the time of the fructose dehydration reaction is 0.1 - 12 hours, preferably 0.1 - 5 hours, more preferably 0.1 - 1 hour.

[0026] According to the method of the present invention, the fructose dehydration reaction process is stirred. The reaction does not require separate control of the reaction pressure and can be carried out under the self-generated pressure in a closed reactor at the above temperature.

[0027] The reactor required for the fructose dehydration reaction process can be a thick-walled pressure-resistant bottle, a stainless steel reaction kettle with a polytetrafluoroethylene lining, and reactors that can be easily conceived by those skilled in the art.

[0028] After the fructose dehydration reaction is completed, the conversion rate of the reaction substrate, the selectivity and yield of HMF during the reaction process can be analyzed and calculated by high performance liquid chromatography.

[0029] According to the common knowledge of those skilled in the art, ordinary commercially available heteropolyacids are highly soluble in water and thus also soluble in a mixed solution of water and an organic solvent, and do not have thermosensitive properties. However, the inventors of the present application unexpectedly found that in the presence of an organic quaternary ammonium salt, commercially available heteropolyacids have thermosensitive properties when water and the organic quaternary ammonium salt form a homogeneous solvent through hydrogen bonding. Specifically, in the present invention, after heating the two-liquid phase reaction system, ordinary commercially available heteropolyacid catalysts dissolve in the reaction system; after the reaction ends, the catalyst gradually re-precipitates as the temperature decreases and settles at the bottom of the reactor. This may be because after adding the organic quaternary ammonium salt to the aqueous phase, the newly formed eutectic solvent changes the polarity and the strength of the hydrogen bond network structure of the original aqueous solvent, affecting the solubility of conventional heteropolyacids in the aqueous phase and endowing them with a thermosensitive effect.

[0030] The inventors of the present application further found that the hydrophobic property of the heteropolyacid catalyst modified by a quaternary ammonium base and / or a quaternary ammonium salt is enhanced, resulting in a further enhancement of the thermosensitive property.

[0031] The present invention has the following advantages:

[0032] The heteropolyacid catalyst provided by the present invention has typical thermosensitive properties. At high temperatures, its solubility in the reaction medium increases, and it completely dissolves in the reaction system to catalyze the dehydration of fructose as a homogeneous acid catalyst, greatly improving the fructose dehydration rate and the HMF yield; after the reaction ends and the temperature decreases, the solubility of the catalyst in the reaction medium decreases and it precipitates in solid form, facilitating the separation and recovery of the catalyst from the reaction medium. The reaction medium provided by the present invention has good solubility for fructose and a high degree of fructose solvation, thereby further enhancing the reaction performance of the reaction medium and achieving the goal of optimizing the reaction performance from two factors, namely the catalyst and the reaction medium. Detailed implementation mode

[0033] In the examples, phosphotungstic acid and silicotungstic acid were both purchased from Innochem Co., Ltd.

[0034] Preparation Example 1

[0035] Add a certain amount of water to a 100 mL round-bottom flask, then add 5 g of betaine, and then place the round-bottom flask in an 80 °C oil bath and heat with stirring. When the betaine is completely dissolved in water, slowly add a certain amount of aqueous phosphotungstic acid solution, where the molar ratio of betaine to phosphotungstic acid is 0.5:1. Then continue to stir for 6 hours under oil bath heating, filter the white precipitate, and wash the precipitate thoroughly with deionized water until the filtrate is neutral. The catalyst prepared in this example is denoted as Catalyst I, and the molecular structure of the catalyst is as described in Preparation Formula 1.

[0036] Preparation Formula 1:

[0037]

[0038] Preparation Example 2

[0039] The catalyst was prepared according to the process of Preparation Example 1, except that the molar ratio of betaine to phosphotungstic acid was 1.5:1. The catalyst prepared in this example was denoted as Catalyst II, and the molecular structure of the catalyst was as described in Preparation Formula 2.

[0040] Preparation Formula 2:

[0041]

[0042] Preparation Example 3

[0043] The catalyst was prepared according to the process of Preparation Example 1, except that the molar ratio of betaine to phosphotungstic acid was 3:1. The catalyst prepared in this example was denoted as Catalyst III, and the molecular structure of the catalyst was as described in Preparation Formula 3.

[0044] Preparation Formula 3:

[0045]

[0046] Preparation Example 4

[0047] The catalyst was prepared according to the process of Preparation Example 1, except that betaine was replaced with dodecyl betaine. The catalyst prepared in this example was denoted as Catalyst IV, and the molecular structure of the catalyst was as described in Preparation Formula 4.

[0048] Preparation Formula 4:

[0049]

[0050] Preparation Example 5

[0051] The catalyst was prepared according to the process of Preparation Example 2, except that betaine was replaced with dodecyl betaine. The catalyst prepared in this example was denoted as Catalyst V, and the molecular structure of the catalyst was as described in Preparation Formula 5.

[0052] Preparation Formula 5:

[0053]

[0054] Preparation Example 6

[0055] The catalyst was prepared according to the process of Preparation Example 3, except that betaine was replaced with dodecyl betaine. The catalyst prepared in this example was denoted as Catalyst VI, and the molecular structure of the catalyst was as described in Preparation Formula 6.

[0056] Preparation Formula 6:

[0057]

[0058] Preparation Example 7

[0059] The catalyst was prepared according to the procedure of Preparation Example 1, except that phosphotungstic acid was replaced with silicotungstic acid. The catalyst prepared in this example was denoted as Catalyst VII, and the molecular structure of the catalyst was as described in Preparation Formula 7.

[0060] Preparation Formula 7:

[0061]

[0062] Comparative Preparation Example 1,

[0063] The catalyst was prepared according to the procedure of Preparation Example 1, except that betaine was replaced with cetylammonium chloride. The catalyst prepared in this example was denoted as Catalyst D I, and the molecular structure of the catalyst was as described in Comparative Preparation Formula 1.

[0064] Comparative Preparation Formula 1:

[0065]

[0066] Comparative Preparation Example 2,

[0067] The catalyst was prepared according to the procedure of Preparation Example 1, except that betaine was replaced with choline chloride. The catalyst prepared in this example was denoted as Catalyst D II, and the molecular structure of the catalyst was as described in Comparative Preparation Formula 2.

[0068]

[0069] Comparative Preparation Example 3,

[0070] CN102153527A discloses a method for preparing HMF by using a phosphotungstic acid supported on titanium dioxide. According to the catalyst preparation method provided therein, the phosphotungstic acid catalyst was supported on titanium dioxide, denoted as Catalyst D III.

[0071] Example 1,

[0072] In this example, the method for synthesizing HMF of the present invention was illustrated with phosphotungstic acid I.

[0073] 1.0 g of fructose, 0.2 g of phosphotungstic acid, 0.5 mL of water, 1.0 g of tetramethylammonium chloride, and 8.5 mL of 1,4-dioxane were added to a 15 mL pressure-resistant bottle. After the temperature of the multi-channel heater was heated to 110 °C, the pressure-resistant bottle was placed in the multi-channel heater and stirred at a speed of 600 r / min for 25 minutes. After the reaction was completed, the pressure-resistant bottle was taken out from the multi-channel heater and naturally cooled to room temperature. After the catalyst was filtered, the reaction solution was analyzed by high performance liquid chromatography. The conversion rate of fructose was measured to be 99.7%, and the yield of HMF was 85.2%. After the catalyst was separated, it was rinsed and dried, and then the recovery rate of phosphotungstic acid was calculated to be 90.7% according to the differential weight method.

[0074] Example 2

[0075] This example uses silicotungstic acid to illustrate the method for synthesizing HMF of the present invention.

[0076] The reaction was carried out according to Example 1, except that phosphotungstic acid was replaced with silicotungstic acid, the mass of the catalyst was increased to 0.25 g, and the reaction temperature was raised to 115 °C. The conversion rate of fructose was measured to be 99.2%, the yield of HMF was 84.9%, and the recovery rate of silicotungstic acid was 90.2%

[0077] Example 3

[0078] This example uses Catalyst I to illustrate the method for synthesizing HMF of the present invention.

[0079] The reaction was carried out according to Example 1, except that phosphotungstic acid was replaced with Catalyst I, the mass of the catalyst was increased to 0.25 g, the reaction temperature was raised to 115 °C, and the reaction time was extended to 35 minutes. The conversion rate of fructose was measured to be 99.5%, the yield of HMF was 85.1%, and the recovery rate of the catalyst was 95.6%.

[0080] Example 4

[0081] This example uses Catalyst II to illustrate the method for synthesizing HMF of the present invention.

[0082] The reaction was carried out according to Example 3, except that Catalyst I was replaced with Catalyst II, the mass of the catalyst was increased to 0.30 g, the reaction temperature was raised to 120 °C, and the reaction time was extended to 40 minutes. The conversion rate of fructose was measured to be 99.6%, the yield of HMF was 84.8%, and the recovery rate of the catalyst was 97.4%.

[0083] Example 5

[0084] This example uses Catalyst III to illustrate the method for synthesizing HMF of the present invention.

[0085] The reaction was carried out according to Example 3, except that Catalyst I was replaced with Catalyst III, the mass of the catalyst was increased to 0.35 g, the reaction temperature was raised to 125 °C, and the reaction time was extended to 45 minutes. The conversion rate of fructose was measured to be 99.8%, the yield of HMF was 84.6%, and the recovery rate of the catalyst was 98.9%.

[0086] Example 6

[0087] This example uses Catalyst IV to illustrate the method for synthesizing HMF of the present invention.

[0088] The reaction was carried out according to Example 3, except that Catalyst I was replaced with Catalyst IV, the mass of the catalyst was increased to 0.30 g, the reaction temperature was raised to 120 °C, and the reaction time was extended to 45 minutes. The conversion rate of fructose was determined to be 99.7%, the yield of HMF was 84.3%, and the recovery rate of the catalyst was 96.4%.

[0089] Example 7

[0090] In this example, the method for synthesizing HMF of the present invention is described using Catalyst V.

[0091] The reaction was carried out according to Example 3, except that Catalyst I was replaced with Catalyst V, the mass of the catalyst was increased to 0.35 g, the reaction temperature was raised to 125 °C, and the reaction time was extended to 45 minutes. The conversion rate of fructose was determined to be 99.8%, the yield of HMF was 84.2%, and the recovery rate of the catalyst was 98.3%.

[0092] Example 8

[0093] In this example, the method for synthesizing HMF of the present invention is described using Catalyst VI.

[0094] The reaction was carried out according to Example 3, except that Catalyst I was replaced with Catalyst VI, the mass of the catalyst was increased to 0.40 g, the reaction temperature was raised to 130 °C, and the reaction time was extended to 50 minutes. The conversion rate of fructose was determined to be 99.6%, the yield of HMF was 84.2%, and the recovery rate of the catalyst was 99.5%.

[0095] Example 9

[0096] In this example, the method for synthesizing HMF of the present invention is described using Catalyst I.

[0097] The reaction was carried out according to Example 3, except that tetramethylammonium chloride was replaced with choline chloride. The conversion rate of fructose was determined to be 99.3%, the yield of HMF was 84.7%, and the recovery rate of the catalyst was 95.7%.

[0098] Example 10

[0099] In this example, the method for synthesizing HMF of the present invention is described using Catalyst I.

[0100] The reaction was carried out according to Example 3, except that tetramethylammonium chloride was replaced with choline chloride (chlormequat chloride). The conversion rate of fructose was determined to be 99.4%, the yield of HMF was 84.6%, and the recovery rate of the catalyst was 95.7%

[0101] Example 11

[0102] In this example, the method for synthesizing HMF of the present invention is described using Catalyst I.

[0103] The reaction was carried out according to Example 3, except that tetramethylammonium chloride was replaced with allyltrimethylammonium chloride. The conversion rate of fructose was determined to be 99.3%, the yield of HMF was 84.1%, and the recovery rate of the catalyst was 95.7%

[0104] Example 12,

[0105] This example illustrates the method for synthesizing HMF of the present invention using Catalyst I.

[0106] The reaction was carried out according to Example 3, except that tetramethylammonium chloride was replaced with butyltrimethylammonium chloride. The conversion rate of fructose was determined to be 99.0%, the yield of HMF was 84.0%, and the recovery rate of the catalyst was 95.7%.

[0107] Example 13,

[0108] This example illustrates the method for synthesizing HMF of the present invention using Catalyst I.

[0109] The reaction was carried out according to Example 3, except that 1,4-dioxane was replaced with tetrahydrofuran. The conversion rate of fructose was determined to be 99.4%, the yield of HMF was 84.5%, and the recovery rate of the catalyst was 95.7%.

[0110] Example 14,

[0111] This example illustrates the method for synthesizing HMF of the present invention using Catalyst I.

[0112] The reaction was carried out according to Example 3, except that 1,4-dioxane was replaced with acetonitrile. The conversion rate of fructose was determined to be 99.6%, the yield of HMF was 84.9%, and the recovery rate of the catalyst was 95.7%.

[0113] Example 15,

[0114] This example illustrates the method for synthesizing HMF of the present invention using Catalyst I.

[0115] The reaction was carried out according to Example 3, except that water was replaced with ethylene glycol. The conversion rate of fructose was determined to be 99.7%, the yield of HMF was 85.0%, and the recovery rate of the catalyst was 95.7%.

[0116] Example 16,

[0117] This example illustrates the method for synthesizing HMF of the present invention using Catalyst I.

[0118] The reaction was carried out according to Example 3, except that water was replaced with 1,2-propanediol. The conversion rate of fructose was determined to be 99.4%, the yield of HMF was 84.5%, and the recovery rate of the catalyst was 95.7%.

[0119] Example 17,

[0120] This example uses Catalyst I to illustrate the method for synthesizing HMF according to the present invention.

[0121] The reaction was carried out according to Example 3, except that water was replaced with 1,3 - propanediol. The conversion rate of fructose was measured to be 99.5%, the yield of HMF was 84.7%, and the recovery rate of the catalyst was 95.7%.

[0122] Example 18

[0123] This example uses Catalyst I to illustrate the method for synthesizing HMF according to the present invention.

[0124] The reaction was carried out according to Example 3, except that water was replaced with glycerol. The conversion rate of fructose was measured to be 99.4%, the yield of HMF was 84.5%, and the recovery rate of the catalyst was 95.7%.

[0125] Example 19

[0126] This example uses Catalyst VII to illustrate the method for synthesizing HMF according to the present invention.

[0127] The reaction was carried out according to Example 3, except that Catalyst I was replaced with Catalyst VII, the reaction temperature was increased to 120 °C, and the reaction time was extended to 40 minutes. The conversion rate of fructose was measured to be 99.6%, the yield of HMF was 85.3%, and the recovery rate of the catalyst was 96.0%.

[0128] Example 20

[0129] This example uses Catalyst I to illustrate the method for synthesizing HMF according to the present invention.

[0130] The reaction was carried out according to Example 3, except that the mass of the catalyst was reduced to 0.10 g, the reaction temperature was increased to 120 °C, and the reaction time was extended to 50 minutes. The conversion rate of fructose was measured to be 99.7%, the yield of HMF was 85.0%, and the recovery rate of the catalyst was 95.5%.

[0131] Comparative Example 1

[0132] The reaction was carried out according to Example 3, except that Catalyst I was replaced with D I. The conversion rate of fructose was measured to be 72.4%, the yield of HMF was 40.6%, and the recovery rate of the catalyst was 99.8%.

[0133] Comparative Example 2

[0134] The reaction was carried out according to Example 3, except that Catalyst I was replaced with D II. The conversion rate of fructose was measured to be 75.3%, the yield of HMF was 42.0%, and the recovery rate of the catalyst was 99.8%.

[0135] Comparative Example 3

[0136] The reaction was carried out according to Example 3, except that Catalyst I was replaced with D III. The conversion rate of fructose was measured to be 65.7%, the yield of HMF was 38.4%, and the recovery rate of the catalyst was 99.8%.

[0137] Comparative Example 4

[0138] The reaction was carried out according to Example 3, except that tetramethylammonium chloride was replaced with octyltrimethylammonium chloride. The conversion rate of fructose was measured to be 95.4%, the yield of HMF was 70.1%, and the recovery rate of the catalyst was 95.7%.

[0139] Comparative Example 5

[0140] The reaction was carried out according to Example 3, except that water was replaced with 1,4-butanediol. The conversion rate of fructose was measured to be 97.2%, the selectivity of HMF was 80.1%, the yield of HMF was 75.9%, and the recovery rate of the catalyst was 95.7%.

[0141] Comparative Example 6

[0142] The reaction was carried out according to Example 3, except that tetramethylammonium chloride was replaced with an equimolar amount of NaCl (0.53 g), the water content was increased to 1.5 mL, and the reaction time was extended to 2.5 h. The conversion rate of fructose was measured to be 98.0%, the selectivity of HMF was 72.6%, the yield of HMF was 71.1%, and the recovery rate of the catalyst was 93.7%.

[0143] Comparing the results of Examples 1 and 2, it can be seen that phosphotungstic acid is slightly stronger in acidity than silicotungstic acid. Therefore, to achieve the same reaction results, the catalyst feeding amount and reaction temperature required for silicotungstic acid are slightly higher than those for phosphotungstic acid. However, regardless of the acidity of the two heteropolyacids, commercial heteropolyacids exhibit thermosensitive properties in the lower aqueous phase under the action of organic quaternary ammonium chlorides, demonstrating the universality of the thermosensitive properties of common commercially available heteropolyacids in this system.

[0144] Comparing the results of Example 1 and Examples 3-5, it can be seen that after the commercial phosphotungstic acid is modified with betaine, its hydrophobic property is enhanced, resulting in enhanced thermosensitive property, and the thermosensitive property gradually increases with the increase of the betaine addition amount. Therefore, the recovery rates of Catalysts I to III gradually increase after the temperature drops at the end of the reaction. According to the preparation formulas 1-3, the more betaine is added, the stronger acid protons on the phosphotungstic acid are replaced, resulting in the proton sites of the catalyst changing completely from the strong acid proton sites provided by the phosphotungstic acid to the weak acid proton sites provided by the carboxyl groups on the modifier, and the acidity of the catalyst weakens. Therefore, higher catalyst feeding amounts, reaction temperatures and longer reaction times are required to obtain the same reaction results. To ensure the recovery rate and acidity of the catalyst, the molar ratio of betaine to phosphotungstic acid is preferably not higher than 3:1, and is preferably 0.5:1-3:1.

[0145] Comparing the results of Examples 3-5 and Examples 6-8, it can be seen that dodecyl betaine has a similar effect to betaine, and the phosphotungstic acid modified with dodecyl betaine still has thermosensitive properties. When the molar ratio of the modifier to phosphotungstic acid is the same, the recovery rate of the catalyst modified with dodecyl betaine is higher after the reaction ends. This is because dodecyl betaine has a more hydrophobic alkyl side chain, and the catalyst obtained by modifying phosphotungstic acid has stronger hydrophobicity, so the recovery rate of the catalyst is higher. However, due to the larger molecular weight of dodecyl betaine, the amount of protons per unit mass of the catalyst obtained by modification at the same molar ratio decreases. Therefore, to obtain similar reaction results, it is necessary to increase the catalyst feeding amount and reaction temperature, and appropriately extend the reaction time.

[0146] Comparing the results of Example 3 and Comparative Example 1, it can be seen that when the modifier only contains a hydrophobic fatty side chain without a hydrophilic oxygen-containing side chain, the modified phosphotungstic acid catalyst does not have thermosensitive properties and always exists in a solid form during the reaction. The dissociation degree and acidity of protons are affected, and the adsorption effect of the solid acid catalyst on the product is strong, the desorption and diffusion of the product are affected, and the target product will be further decomposed to obtain by-products, resulting in a decrease in the selectivity and yield of HMF. Therefore, after the phosphotungstic acid loses its thermosensitive properties, both the selectivity and yield of HMF are lower than those of the thermosensitive solid acid catalyst in the present invention. Therefore, when using quaternary ammonium base / salt as the modifier, the modifier needs to contain a certain amount of hydrophilic oxygen-containing functional groups so that the prepared catalyst has thermosensitive properties.

[0147] Comparing the results of Example 3 and Comparative Example 2, it can be seen that when choline chloride is used as the modifier, although the modifier contains a hydrophilic oxygen-containing side chain - hydroxyl group, the modified phosphotungstic acid catalyst still does not have thermosensitive properties. The obtained catalyst is similar to the result of Comparative Example 1, and the catalyst always exists in a solid form during the reaction, resulting in a decrease in the selectivity and yield of HMF. Therefore, when using quaternary ammonium bases / salts as modifiers, the hydrophilic oxygen-containing functional groups on the modifiers need to have a certain degree of proton dissociation. Since the proton dissociation degree of the hydroxyl group in choline chloride is less than that of the carboxyl group in betaine, the prepared catalyst still does not have thermosensitive properties under the reaction conditions of the present invention. Therefore, quaternary ammonium bases / salts such as betaine, dodecyl betaine, and dodecyl betaine hydrochloride, which contain carboxyl hydrophilic functional groups, are preferred options for the modifiers in the present invention.

[0148] Comparing the results of Example 3 and Comparative Example 3, it can be seen that when the acidic sites are all phosphotungstic acid, the phosphotungstic acid does not have thermosensitive properties after being immobilized on titanium dioxide, which is similar to the results of Comparative Examples 1 and 2. The catalyst always exists in a solid form during the reaction, resulting in a decrease in the selectivity and yield of HMF. Therefore, after the supported phosphotungstic acid catalyst does not have thermosensitive properties, both the selectivity and yield of HMF are lower than those of the thermosensitive solid acid catalyst in the present invention. In addition, due to the low loading amount of phosphotungstic acid on titanium dioxide, when the mass of the solid acid catalyst is the same, the number of protons provided is less, so the fructose conversion rate and the HMF yield are much lower than those of the thermosensitive solid acid catalyst in the present invention.

[0149] Comparing the results of Example 3, Examples 9 - 12 and Comparative Example 4, it can be seen that when tetramethylammonium chloride is replaced by choline chloride, chlormequat chloride (CCC), allyltrimethylammonium chloride, and butyltrimethylammonium chloride, that is, when one methyl side chain (C1) of tetramethylammonium chloride is replaced by a long carbon chain side chain (C2 - C4), the fructose dehydration rate and the HMF yield decrease slowly, but the final HMF yield is still higher than 84%. When the substituent side chain continues to extend, the HMF yield further decreases, and due to the increase in the number of side chain carbons, the surface activity of the hydrogen bond acceptor of the deep eutectic solvent is enhanced, and at this time, a dual-liquid phase reaction system cannot be formed, but a single-liquid phase reaction system. Therefore, considering both the stability of the dual-liquid phase system and the HMF yield, the hydrogen bond acceptor of the deep eutectic solvent is preferably chloride of C1 - C4 alkyltrimethyl quaternary ammonium salt.

[0150] Comparing the results of Example 3 and Examples 13 - 14, it can be seen that when using different organic solvents such as 1,4-dioxane, tetrahydrofuran, and acetonitrile, the corresponding fructose conversion rate and HMF yield basically remain unchanged. If other low-boiling organic solvents are used, the fructose dehydration rate and the HMF yield will decrease significantly. Therefore, the organic solvents in the dual-liquid phase reaction medium are preferably 1,4-dioxane, tetrahydrofuran, and acetonitrile.

[0151] Comparing the results of Example 3, Examples 15 - 18 and Comparative Example 5, it can be seen that when water is replaced with ethylene glycol, 1,2 - propanediol, 1,3 - propanediol, and glycerol, the corresponding fructose conversion rate, HMF selectivity, and yield basically remain unchanged. When water is replaced with 1,4 - butanediol with a longer carbon chain length, the solvation effect of the eutectic solvent in the lower layer of the biphasic reaction medium on fructose weakens, and the fructose dehydration rate and the yield of the target product decrease. Therefore, the hydrogen bond donor of the eutectic solvent is preferably water and C1 - C3 polyols, including water, ethylene glycol, 1,2 - propanediol, 1,3 - propanediol, and glycerol.

[0152] Comparing the results of Example 3 and Example 19, it can be seen that when Catalyst I is replaced with Catalyst VII, both commercially available phosphotungstic acid and silicotungstic acid exhibit better thermosensitive properties under the modification of betaine with the same molar ratio, which further demonstrates the universality of the thermosensitive properties of the heteropolyacid catalyst modified by betaine in this system.

[0153] Comparing the results of Example 3 and Example 20, it can be seen that when the catalyst dosage is reduced to 1 / 10 of fructose, a higher reaction temperature and an extended reaction time are required to achieve similar reaction results.

[0154] Comparing the results of Example 3 and Comparative Example 6, it can be seen that when tetramethylammonium chloride is replaced with inorganic salt NaCl, NaCl simply dissolves in water and cannot act as a hydrogen bond acceptor to form a hydrogen bond structure with water to form a eutectic solvent. Therefore, to ensure that the volume of the lower reaction phase remains unchanged, the water content needs to be increased. In addition, since the eutectic solvent cannot be formed, the solvation effect of the reaction phase on fructose weakens, the conversion rate of fructose decreases, the time required to reach the optimal reaction result needs to be extended to 2.5 h, and the yield significantly decreases. In addition, due to the slowdown of the fructose dehydration rate and the increase in the reaction time, the exposure time of the catalyst under hydrothermal conditions is extended, the instability of the catalyst increases, resulting in a decrease in the catalyst recovery rate. Therefore, the present invention preferably uses organic chlorides rather than inorganic chlorides.

[0155] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0156] In addition, it should be noted that, in the case of no contradiction, the various specific technical features described in the above specific embodiments can be combined in any appropriate manner. To avoid unnecessary repetition, the present invention will not separately describe various possible combination methods.

[0157] In addition, any combination can be made among various different embodiments of the present invention, as long as it does not violate the idea of the present invention, and it should equally be regarded as the content disclosed by the present invention.

Claims

1. A method for preparing 5-hydroxymethylfurfural, comprising: Under the catalysis of the temperature-sensitive heteropolyacid catalyst, the fructose-based carbohydrate undergoes an intramolecular dehydration reaction at 80°C - 200°C in a biphasic reaction medium composed of a low-boiling organic solvent and a deep eutectic solvent to obtain the 5-hydroxymethylfurfural. The temperature-sensitive heteropolyacid catalyst is selected from phosphotungstic acid or silicotungstic acid modified by a quaternary ammonium base and / or quaternary ammonium salt containing a carboxyl group; the low-boiling organic solvent is selected from one or more of 1,4-dioxane, tetrahydrofuran, and acetonitrile; the deep eutectic solvent is a homogeneous solvent formed by an organic quaternary ammonium salt as a hydrogen bond acceptor and a protic solvent as a hydrogen bond donor through a hydrogen bond network. The organic quaternary ammonium salt is selected from C1-C4 alkyltrimethylammonium chloride, and the protic solvent is selected from one or more of water and C1-C3 polyols.

2. According to the method of claim 1, wherein, The quaternary ammonium base and / or quaternary ammonium salt containing carboxyl group is selected from one or more of betaine, betaine hydrochloride, and C1-C 18 alkyl-substituted betaines.

3. The method according to claim 1, wherein The preparation method of the temperature-sensitive heteropolyacid catalyst includes: adding a quaternary ammonium base and / or quaternary ammonium salt containing a carboxyl group to an aqueous solution of heteropolyacid selected from phosphotungstic acid or silicotungstic acid, heating and reacting to produce a white precipitate, and after the reaction is completed, filtering, washing, and drying the white precipitate.

4. The method according to claim 3, wherein The molar ratio of the sum of the quaternary ammonium base and quaternary ammonium salt containing a carboxyl group to the heteropolyacid is 0.1:1 - 10:

1.

5. The method according to claim 3, wherein, The molar ratio of the sum of the quaternary ammonium base and quaternary ammonium salt containing a carboxyl group to the heteropolyacid is 0.2:1 - 5:

1.

6. The method according to claim 3, wherein, The molar ratio of the sum of the quaternary ammonium base and quaternary ammonium salt containing a carboxyl group to the heteropolyacid is 0.5:1 - 3:

1.

7. The method according to claim 3, wherein, The heating temperature is 30°C - 100°C, and the reaction time is 0.5 - 10 hours.

8. The method according to claim 3, wherein The heating temperature is 50°C - 80°C, and the reaction time is 6 - 8 hours.

9. The method according to claim 1, wherein, The fructose-based carbohydrate is selected from one or more of purified fructose, crude fructose, polyfructose, fructose syrup, and fructose-glucose syrup.

10. The method according to claim 1, wherein, The organic quaternary ammonium salt is selected from one or more of tetramethylammonium chloride, choline chloride, chloroethylcholine chloride, allyltrimethylammonium chloride, and butyltrimethylammonium chloride.

11. The method according to claim 1, wherein, The mass ratio of the hydrogen bond acceptor to the hydrogen bond donor of the deep eutectic solvent is 0.1:1 - 5:

1.

12. According to the method of claim 1, wherein, The mass ratio of the hydrogen bond acceptor to the hydrogen bond donor of the deep eutectic solvent is 1.5:1 - 3:

1.

13. According to the method of claim 1, the volume percentage of the deep eutectic solvent in the biphasic reaction medium is 5% - 50%.

14. According to the method of claim 1, the volume percentage of the deep eutectic solvent in the biphasic reaction medium is 10% - 20%.

15. The method according to claim 1, wherein, The mass ratio of the fructose-based carbohydrate to the biphasic reaction medium is 1:1 - 1:1000.

16. The method according to claim 1, wherein The mass ratio of the fructose-based carbohydrate to the biphasic reaction medium is 1:2 - 1:

100.

17. The method according to claim 1, wherein, The mass ratio of the fructose-based carbohydrate to the biphasic reaction medium is 1:5 - 1:

20.

18. The method according to claim 1, wherein, The mass ratio of the temperature-sensitive heteropolyacid catalyst to the fructose-based carbohydrate is 1:1 - 1:

100.

19. The method according to claim 1, wherein, The mass ratio of the temperature-sensitive heteropolyacid catalyst to the fructose-based carbohydrate is 1:2 - 1:

20.

20. The method according to claim 1, wherein The mass ratio of the temperature-sensitive heteropolyacid catalyst to the fructose-based carbohydrate is 1:2 - 1:

10.

21. The method according to claim 1, wherein, The temperature of the dehydration reaction of the fructose-based carbohydrate is 90 - 160 °C, and the time of the fructose dehydration reaction is 0.1 - 12 hours.

22. The method according to claim 1, wherein, The temperature of the dehydration reaction of the fructose-based carbohydrate is 100 °C - 130 °C; the time of the fructose dehydration reaction is 0.1 - 1 hour.

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