Method for preparing isosorbide by catalyzing dehydration of sorbitol through eutectic solvent

Abstract

The invention discloses a method for preparing isosorbide by catalyzing dehydration of sorbitol through a deep eutectic solvent, and belongs to the technical field of fine chemical engineering. A deep eutectic solvent (DES) prepared from choline chloride and p-toluenesulfonic acid is used as a catalyst, and sorbitol is catalyzed to be dehydrated to generate isosorbitol under solvent-free and vacuum conditions. The method comprises the following specific steps: preparation of a DES catalyst, a sorbitol melt dehydration reaction, reaction liquid extraction separation and catalyst recovery. The reaction efficiency is optimized by adjusting the molar ratio of choline chloride to p-toluenesulfonic acid in DES, the catalyst dosage, the reaction temperature and the reaction time. Extracting agents such as ethyl acetate are used for separating products, DES phase can be reused after reduced pressure distillation and recovery, and the activity of the catalyst is stable. According to the method, a homogeneous and separable catalytic system is adopted, the process is green and environment-friendly, corrosion to equipment is little, the separation process is simple, and the yield of isosorbide reaches 95%.

Description

Technical Field

[0001] The invention belongs to the technical field of fine chemicals, and in particular relates to a method for preparing isosorbide by dehydrating sorbitol catalyzed by a low eutectic solvent. Background Art

[0002] Sorbitol is one of the most promising biomass conversion platform chemicals. It is obtained by hydrolysis of natural product cellulose and is used to produce high value-added chemicals. It is a biomass conversion platform that complies with sustainable development. As one of the downstream products of sorbitol, isosorbide has a special rigid molecular structure and chiral center. It is widely used to form a variety of pharmaceutical compounds, cosmetics, food industry products, and polymers such as polyurethane, polycarbonate, polyester and polyamide. For example, isosorbide can be used as a more environmentally friendly monomer than bisphenol A to produce polycarbonate or epoxy resin; isosorbide monomers are incorporated into polyethylene terephthalate polymers, which may greatly improve their glass transition temperature and impact resistance.

[0003] The current isosorbide production processes mostly use concentrated sulfuric acid catalysis, vacuum distillation, recrystallization and other processes, which have high requirements for the corrosion resistance of the reaction equipment and cause great environmental pollution. In addition, strong acids lead to the generation of a large number of by-products, and the purity of the product isosorbide is not high. The catalyst cannot be reused, which limits the large-scale production of isosorbide.

[0004] In recent years, heterogeneous catalysts have been widely studied. These include niobium-based solid acids (CN114671883A, CN111253413A, CN112570011A), polymeric ionic liquids (CN115010718A), hydrophobic ionic liquids (CN109320522A), molecular sieves (CN112275315A, CN114437097A, CN112138708A), metal oxides (CN112619635A), etc. Heterogeneous catalysts achieve the reuse of catalysts, and the reduction of acidity avoids the generation of a large amount of colored polymers. In order to simplify the purification process of isosorbide, a higher reaction yield has always been a research hotspot, and the above-mentioned heterogeneous catalysts for sorbitol dehydration with high yields have a complex preparation process, limited reuse, and a large amount of catalyst.

[0005] A low eutectic solvent is a new type of ionic liquid. It has the high adjustability and stability of ionic liquids, as well as the characteristics of simple synthesis and green environmental protection. It can be used as a catalyst and is a highly designed type of liquid catalyst. The present invention aims at the problem of low yield of catalyst reuse and discloses a low eutectic solvent catalytic system. The catalyst is environmentally friendly, reusable and has a high catalytic efficiency. Summary of the invention

[0006] The invention provides a method for preparing isosorbide, which adopts a synthetic low eutectic solvent as a liquid catalyst and solid sorbitol as a raw material to prepare isosorbide.

[0007] In order to achieve the purpose of the invention, the technical solution adopted by the present invention is: A method for synthesizing isosorbide comprises the following steps: (1) According to a certain molar ratio, weigh appropriate amounts of choline chloride and p-toluenesulfonic acid, dry them in vacuum at 70°C for 1 hour, mix them in a wide-mouth bottle, heat to 80°C, and stir until a clear and transparent liquid is obtained. The obtained product is the low eutectic solvent catalyst ChCl- p- TSA; (2) Weighing appropriate amounts of substrate sorbitol and the catalyst prepared in step (1), respectively, adding them into a three-necked flask, stirring and heating at a certain temperature under vacuum conditions to react for a certain time; (3) After the reaction is completed, a certain amount of extractant is added to the reaction solution, and the mixture is heated and stirred at 60°C to obtain an extractant phase and a DES phase, wherein the DES phase is subjected to reduced pressure distillation at 160°C to remove impurities to recover the catalyst; the extractant phase is cooled and crystallized at a crystallization temperature of 5°C, and the crystals are filtered to obtain crystals; (4) Dissolve the crystals obtained in step (3) in ChCl- p- TSA, repeat the contents of step (3); (5) Drying the crystals obtained in step (4) to obtain isosorbide crystals.

[0008] According to the above method, optionally, in step (1), ChCl- p- The ratio of TSA is 0.5-2.

[0009] According to the above method, optionally, in step (1), ChCl- p- The added amount of TSA is 5wt%-10wt% of the mass of solid sorbitol.

[0010] According to the above method, the vacuum degree in step 2 is 0.09 MPa.

[0011] According to the above method, optionally, the reaction temperature in step (2) is 110°C-140°C.

[0012] According to the above method, optionally, the reaction time in step (2) is 3h-6h.

[0013] According to the above method, optionally, the extractant in step (3) is selected from any one of ethyl acetate, methyl acetate, propyl acetate, butyl acetate and acetone.

[0014] According to the above method, more preferably, the extractant in step (3) is ethyl acetate.

[0015] According to the above method, optionally, the amount of the extractant added in step (3) is 1-4 times the total mass of the reaction system.

[0016] Compared with the prior art, the present invention adopts an acidic deep eutectic solvent as a catalyst, takes molten sorbitol as a reaction substrate, and prepares isosorbide by vacuum direct dehydration reaction under solvent-free conditions, which has the advantages of high sorbitol conversion rate, high isosorbide yield, good selectivity, simple operation, and catalyst recycling. Wherein, the catalyst used is homogeneous in the reaction, can be more effectively contacted with the reactant, greatly improves the efficiency of the reaction, and improves the yield of isosorbide. The catalyst is insoluble in the extraction agent and is separated from the product. The addition amount of the catalyst is 5wt%-10wt% of the mass of solid sorbitol, which greatly reduces the amount of the catalyst. DETAILED DESCRIPTION

[0017] To further illustrate the technical solution of the present invention, the present invention is further described below in conjunction with specific embodiments, but the present application is not limited to these embodiments.

[0018] Using sorbitol as a raw material, a secondary dehydration reaction is carried out under the action of a low eutectic solvent catalyst to prepare isosorbide. The liquid collected after the reaction is sampled for analysis. The reactants are quantitatively analyzed by liquid chromatography, and an automatic sampler is used to improve reproducibility to determine the content of the product isosorbide and the by-products 2,5-anhydrosorbitol and 1,4-anhydrosorbitol.

[0019] Embodiment 1: (1) Take 6.98g of choline chloride and 4.75g of p-toluenesulfonic acid monohydrate in a sample bottle and stir at 80°C for 1h to obtain a clear and transparent liquid. After standing and cooling, the low eutectic solvent catalyst ChCl-0.5 is obtained. p- TSA; (2) Weigh 10 g of sorbitol into a three-necked flask, stir at 140° C. until all the solid melts, then add 1.86 g of the low eutectic solvent catalyst obtained in step (1) (where p-toluenesulfonic acid monohydrate is 7.5 wt % of the reactant), and stir the reaction at a pressure of 0.01 MPa for 3 h. The liquid after the reaction is detected by liquid chromatography, and the result shows that the yield of isosorbide is 12%.

[0020] Embodiment 2:

[0021] (1) Take 6.98g of choline chloride and 7.60g of p-toluenesulfonic acid monohydrate in a sample bottle and stir at 80°C for 1h to obtain a clear and transparent liquid. After standing and cooling, the low eutectic solvent catalyst ChCl-0.8 is obtained. p- TSA; (2) Weigh 10 g of sorbitol into a three-necked flask and place it at 140° C. until the solid is completely melted. Then add 1.44 g of the low eutectic solvent catalyst obtained in step (1) (where p-toluenesulfonic acid monohydrate is 7.5 wt % of the reactant), and stir the reaction at a pressure of 0.01 MPa for 3 h. The liquid after the reaction is detected by liquid chromatography, and the result shows that the yield of isosorbide is 15%.

[0022] Embodiment 3:

[0023] (1) Take 6.98g of choline chloride and 8.55g of p-toluenesulfonic acid monohydrate in a sample bottle and stir at 80°C for 1h to obtain a clear and transparent liquid. After standing and cooling, the low eutectic solvent catalyst ChCl-0.9 is obtained. p- TSA; (2) Weigh 10 g of sorbitol into a three-necked flask, place at 140° C. until all the solid melts, then add 1.36 g of the low eutectic solvent catalyst obtained in step (1) (where p-toluenesulfonic acid monohydrate is 7.5 wt % of the reactant), and stir the reaction at a pressure of 0.01 MPa for 3 h. The liquid after the reaction is detected by liquid chromatography, and the result shows that the yield of isosorbide is 24%.

[0024] Embodiment 4:

[0025] (1) Take 6.98g of choline chloride and 9.50g of p-toluenesulfonic acid monohydrate in a sample bottle and stir at 80°C for 1h to obtain a clear and transparent liquid. After standing and cooling, the low eutectic solvent catalyst ChCl-1.0 is obtained. p- TSA; (2) Weigh 10 g of sorbitol into a three-necked flask, place it at 140° C. until the solid is completely melted, then add 1.30 g of the low eutectic solvent catalyst obtained in step (1) (where p-toluenesulfonic acid monohydrate is 7.5 wt % of the reactant), and stir the reaction at a pressure of 0.01 MPa for 3 h. The liquid after the reaction is detected by liquid chromatography, and the result shows that the yield of isosorbide is 30%.

[0026] Embodiment 5:

[0027] (1) Take 6.98g of choline chloride and 10.45g of p-toluenesulfonic acid monohydrate in a sample bottle and stir at 80°C for 1h to obtain a clear and transparent liquid. After standing and cooling, the low eutectic solvent catalyst ChCl-1.1 is obtained. p- TSA; (2) Weigh 10 g of sorbitol into a three-necked flask, place it at 140° C. until the solid is completely melted, then add 1.25 g of the low eutectic solvent catalyst obtained in step (1) (where p-toluenesulfonic acid monohydrate is 7.5 wt % of the reactant), and stir the reaction at a pressure of 0.01 MPa for 3 h. The liquid after the reaction is detected by liquid chromatography, and the result shows that the yield of isosorbide is 74%.

[0028] Embodiment 6:

[0029] (1) Take 6.98g of choline chloride and 11.40g of p-toluenesulfonic acid monohydrate in a sample bottle and stir at 80°C for 1h to obtain a clear and transparent liquid. After standing and cooling, the low eutectic solvent catalyst ChCl-1.2 is obtained. p- TSA; (2) Weigh 10 g of sorbitol into a three-necked flask, place it at 140° C. until the solid is completely melted, then add 1.21 g of the low eutectic solvent catalyst obtained in step (1) (where p-toluenesulfonic acid monohydrate is 7.5 wt % of the reactant), and stir the reaction at a pressure of 0.01 MPa for 3 h. The liquid after the reaction is detected by liquid chromatography, and the result shows that the yield of isosorbide is 88%.

[0030] Embodiment 7:

[0031] (1) Take 6.98g of choline chloride and 19g of p-toluenesulfonic acid monohydrate in a sample bottle and stir at 80°C for 1h to obtain a clear and transparent liquid. After standing and cooling, the low eutectic solvent catalyst ChCl-2 is obtained. p- TSA; (2) Weigh 10 g of sorbitol into a three-necked flask, place it at 140° C. until the solid is completely melted, then add 1.03 g of the low eutectic solvent catalyst obtained in step (1) (where p-toluenesulfonic acid monohydrate is 7.5 wt % of the reactant), and stir the reaction at a pressure of 0.01 MPa for 3 h. The liquid after the reaction is detected by liquid chromatography, and the result shows that the yield of isosorbide is 87%.

[0032] Embodiment 8:

[0033] Weigh 10g of sorbitol into a three-necked flask, place it at 140°C until the solid is completely melted, then add 0.75g of p-toluenesulfonic acid monohydrate, and stir and react for 3h under a pressure of 0.01MPa. The liquid after the reaction is tested by liquid chromatography, and the result shows that the yield of isosorbide is 95%.

[0034] Embodiment 9:

[0035] (1) Take 6.98g of choline chloride and 11.40g of p-toluenesulfonic acid monohydrate in a sample bottle and stir at 80°C for 1h to obtain a clear and transparent liquid. After standing and cooling, the low eutectic solvent catalyst ChCl-1.2 is obtained. p- TSA; (2) Weigh 10 g of sorbitol into a three-necked flask, place it at 140° C. until the solid is completely melted, then add 0.81 g of the low eutectic solvent catalyst obtained in step (1) (where p-toluenesulfonic acid monohydrate is 5 wt% of the reactant), and stir the reaction at a pressure of 0.01 MPa for 3 h. The liquid after the reaction is detected by liquid chromatography, and the result shows that the yield of isosorbide is 81%.

[0036] Embodiment 10: (1) Take 6.98g of choline chloride and 11.40g of p-toluenesulfonic acid monohydrate in a sample bottle and stir at 80°C for 1h to obtain a clear and transparent liquid. After standing and cooling, the low eutectic solvent catalyst ChCl-1.2 is obtained. p- TSA; (2) Weigh 10 g of sorbitol into a three-necked flask, place it at 140° C. until the solid is completely melted, then add 1.61 g of the low eutectic solvent catalyst obtained in step (1) (where p-toluenesulfonic acid monohydrate is 10 wt % of the reactant), and stir the reaction at a pressure of 0.01 MPa for 3 h. The liquid after the reaction is detected by liquid chromatography, and the result shows that the yield of isosorbide is 83%.

[0037] Embodiment 11: (1) Take 6.98g of choline chloride and 11.40g of p-toluenesulfonic acid monohydrate in a sample bottle and stir at 80°C for 1h to obtain a clear and transparent liquid. After standing and cooling, the low eutectic solvent catalyst ChCl-1.2 is obtained. p- TSA; (2) Weigh 10 g of sorbitol into a three-necked flask, place it at 120° C. until the solid is completely melted, then add 1.21 g of the low eutectic solvent catalyst obtained in step (1) (where p-toluenesulfonic acid monohydrate is 7.5 wt % of the reactant), and stir the reaction at a pressure of 0.01 MPa for 6 h. During the reaction, the materials in the reaction system were continuously tested by liquid chromatography at regular intervals, and the results showed that the yield of isosorbide was 55%.

[0038] Embodiment 12: (1) Take 6.98g of choline chloride and 11.40g of p-toluenesulfonic acid monohydrate in a sample bottle and stir at 80°C for 1h to obtain a clear and transparent liquid. After standing and cooling, the low eutectic solvent catalyst ChCl-1.2 is obtained. p- TSA; (2) Weigh 10 g of sorbitol into a three-necked flask, place it at 130° C. until the solid is completely melted, then add 1.21 g of the low eutectic solvent catalyst obtained in step (1) (where p-toluenesulfonic acid monohydrate is 7.5 wt % of the reactant), and stir the reaction at a pressure of 0.01 MPa for 6 h. During the reaction, the materials in the reaction system were continuously tested by liquid chromatography at regular intervals, and the results showed that the yield of isosorbide was 87%.

[0039] Embodiment 13: (1) Take 6.98g of choline chloride and 11.40g of p-toluenesulfonic acid monohydrate in a sample bottle and stir at 80°C for 1h to obtain a clear and transparent liquid. After standing and cooling, the low eutectic solvent catalyst ChCl-1.2 is obtained. p- TSA; (2) Weigh 10 g of sorbitol into a three-necked flask, place it at 140° C. until the solid is completely melted, then add 1.21 g of the low eutectic solvent catalyst obtained in step (1) (where p-toluenesulfonic acid monohydrate is 7.5 wt % of the reactant), and stir the reaction at a pressure of 0.01 MPa for 6 h. During the reaction, the materials in the reaction system were continuously tested by liquid chromatography at regular intervals, and the results showed that the yield of isosorbide was 89%.

[0040] Embodiment 14: A method for separating isosorbide from a deep eutectic solvent using a solvent, the specific steps being as follows: (1) Take 6.98g of choline chloride and 11.40g of p-toluenesulfonic acid monohydrate in a sample bottle and stir at 80°C for 1h to obtain a clear and transparent liquid. After standing and cooling, the low eutectic solvent catalyst ChCl-1.2 is obtained. p- TSA; (2) Weigh 3 g of the catalyst obtained in step (1) into a sample bottle, add 20 g of isosorbide, stir at 60° C. to completely dissolve it, and let it stand; (3) Add 92 g of ethyl acetate (mass ratio of 4:1) to the solution obtained in step (2), stir and extract at 60° C. for 1 h, sample the upper liquid, and perform liquid chromatography detection. The results show that the mass fraction of isosorbide is 16%.

[0041] Embodiment 15: A method for separating isosorbide from a deep eutectic solvent using a solvent, the specific steps being as follows: (1) Take 6.98g of choline chloride and 11.40g of p-toluenesulfonic acid monohydrate in a sample bottle and stir at 80°C for 1h to obtain a clear and transparent liquid. After standing and cooling, the low eutectic solvent catalyst ChCl-1.2 is obtained. p- TSA; (2) Weigh 3 g of the catalyst obtained in step (1) into a sample bottle, add 20 g of isosorbide, stir at 60° C. to completely dissolve it, and let it stand; (3) Add 69 g of ethyl acetate (mass ratio of 3:1) to the solution obtained in step (2), stir and extract at 60°C for 1 hour, sample the upper liquid, and perform liquid chromatography detection. The results show that the mass fraction of isosorbide is 19%.

[0042] Embodiment 16: A method for separating isosorbide from a deep eutectic solvent using a solvent, the specific steps being as follows: (1) Take 6.98g of choline chloride and 11.40g of p-toluenesulfonic acid monohydrate in a sample bottle and stir at 80°C for 1h to obtain a clear and transparent liquid. After standing and cooling, the low eutectic solvent catalyst ChCl-1.2 is obtained. p- TSA; (2) Weigh 3 g of the catalyst obtained in step (1) into a sample bottle, add 20 g of isosorbide, stir at 60° C. to completely dissolve it, and let it stand; (3) To the solution obtained in step (2), 46 g of ethyl acetate (mass ratio of 2:1) was added, and the mixture was extracted with stirring at 60° C. for 1 h. The upper liquid was sampled and subjected to liquid chromatography detection. The results showed that the mass fraction of isosorbide was 25%.

[0043] Embodiment 17: A method for separating isosorbide from a deep eutectic solvent using a solvent, the specific steps being as follows: (1) Take 6.98g of choline chloride and 11.40g of p-toluenesulfonic acid monohydrate in a sample bottle and stir at 80°C for 1h to obtain a clear and transparent liquid. After standing and cooling, the low eutectic solvent catalyst ChCl-1.2 is obtained. p- TSA; (2) Weigh 3 g of the catalyst obtained in step (1) into a sample bottle, add 20 g of isosorbide, stir at 60° C. to completely dissolve it, and let it stand; (3) 23 g of ethyl acetate (mass ratio of 1:1) was added to the solution obtained in step (2), and the mixture was stirred and extracted at 60° C. for 1 h. The results showed that the mass fraction of isosorbide was 31%.

[0044] Embodiment 18: A method for separating isosorbide from a deep eutectic solvent using a solvent, the specific steps being as follows: (1) Take 6.98g of choline chloride and 11.40g of p-toluenesulfonic acid monohydrate in a sample bottle and stir at 80°C for 1h to obtain a clear and transparent liquid. After standing and cooling, the low eutectic solvent catalyst ChCl-1.2 is obtained. p- TSA; (2) Weigh 3 g of the catalyst obtained in step (1) into a sample bottle, add 15 g of isosorbide, stir at 60° C. to completely dissolve it, and let it stand; (3) Add 72 g of ethyl acetate (mass ratio of 4:1) to the solution obtained in step (2), stir and extract at 60° C. for 1 h, sample the upper liquid, and perform liquid chromatography detection. The results show that the mass fraction of isosorbide is 16%.

[0045] Embodiment 19: A method for separating isosorbide from a deep eutectic solvent using a solvent, the specific steps being as follows: (1) Take 6.98g of choline chloride and 11.40g of p-toluenesulfonic acid monohydrate in a sample bottle and stir at 80°C for 1h to obtain a clear and transparent liquid. After standing and cooling, the low eutectic solvent catalyst ChCl-1.2 is obtained. p- TSA; (2) Weigh 3 g of the catalyst obtained in step (1) into a sample bottle, add 15 g of isosorbide, stir at 60° C. to completely dissolve it, and let it stand; (3) To the solution obtained in step (2), 54 g of ethyl acetate (mass ratio of 3:1) was added, and the mixture was extracted with stirring at 60° C. for 1 h. The upper liquid was sampled and subjected to liquid chromatography detection. The results showed that the mass fraction of isosorbide was 19%.

[0046] Embodiment 20: A method for separating isosorbide from a deep eutectic solvent using a solvent, the specific steps being as follows: (1) Take 6.98g of choline chloride and 11.40g of p-toluenesulfonic acid monohydrate in a sample bottle and stir at 80°C for 1h to obtain a clear and transparent liquid. After standing and cooling, the low eutectic solvent catalyst ChCl-1.2 is obtained. p- TSA; (2) Weigh 3 g of the catalyst obtained in step (1) into a sample bottle, add 15 g of isosorbide, stir at 60° C. to completely dissolve it, and let it stand; (3) To the solution obtained in step (2), 36 g of ethyl acetate (mass ratio of 2:1) was added, and the mixture was extracted with stirring at 60° C. for 1 h. The upper liquid was sampled and subjected to liquid chromatography detection. The results showed that the mass fraction of isosorbide was 26%.

[0047] Embodiment 21: A method for separating isosorbide from a deep eutectic solvent using a solvent, the specific steps being as follows: (1) Take 6.98g of choline chloride and 11.40g of p-toluenesulfonic acid monohydrate in a sample bottle and stir at 80°C for 1h to obtain a clear and transparent liquid. After standing and cooling, the low eutectic solvent catalyst ChCl-1.2 is obtained. p- TSA; (2) Weigh 3 g of the catalyst obtained in step (1) into a sample bottle, add 15 g of isosorbide, stir at 60° C. to completely dissolve it, and let it stand; (3) 18 g of ethyl acetate (mass ratio of 1:1) was added to the solution obtained in step (2), and the mixture was extracted with stirring at 60° C. for 1 h. The upper liquid was sampled and subjected to liquid chromatography detection. The results showed that the mass fraction of isosorbide was 30%.

[0048] Embodiment 22: A method for separating isosorbide from a deep eutectic solvent using a solvent, the specific steps being as follows: (1) Take 6.98g of choline chloride and 11.40g of p-toluenesulfonic acid monohydrate in a sample bottle and stir at 80°C for 1h to obtain a clear and transparent liquid. After standing and cooling, the low eutectic solvent catalyst ChCl-1.2 is obtained. p- TSA; (2) Weigh 3 g of the catalyst obtained in step (1) into a sample bottle, add 30 g of isosorbide, stir at 60° C. to completely dissolve it, and let it stand; (3) 132 g of ethyl acetate (mass ratio of 4:1) was added to the solution obtained in step (2), and the mixture was extracted with stirring at 60° C. for 1 h. The upper liquid was sampled and subjected to liquid chromatography. The results showed that the concentration of isosorbide was 16%.

[0049] Embodiment 23: A method for separating isosorbide from a deep eutectic solvent using a solvent, the specific steps being as follows: (1) Take 6.98g of choline chloride and 11.40g of p-toluenesulfonic acid monohydrate in a sample bottle and stir at 80°C for 1h to obtain a clear and transparent liquid. After standing and cooling, the low eutectic solvent catalyst ChCl-1.2 is obtained. p- TSA; (2) Weigh 3 g of the catalyst obtained in step (1) into a sample bottle, add 30 g of isosorbide, stir at 60° C. to completely dissolve it, and let it stand; (3) Add 99 g of ethyl acetate (mass ratio of 3:1) to the solution obtained in step (2), stir and extract at 60° C. for 1 h, sample the upper liquid, and perform liquid chromatography detection. The results show that the concentration of isosorbide is 16%.

[0050] Embodiment 24: A method for separating isosorbide from a deep eutectic solvent using a solvent, the specific steps being as follows: (1) Take 6.98g of choline chloride and 11.40g of p-toluenesulfonic acid monohydrate in a sample bottle and stir at 80°C for 1h to obtain a clear and transparent liquid. After standing and cooling, the low eutectic solvent catalyst ChCl-1.2 is obtained. p- TSA; (2) Weigh 3 g of the catalyst obtained in step (1) into a sample bottle, add 30 g of isosorbide, stir at 60° C. to completely dissolve it, and let it stand; (3) To the solution obtained in step (2), 66 g of ethyl acetate (mass ratio of 2:1) was added, and the mixture was extracted with stirring at 60° C. for 1 h. The upper liquid was sampled and subjected to liquid chromatography detection. The results showed that the concentration of isosorbide was 26%.

[0051] Embodiment 25: A method for separating isosorbide from a deep eutectic solvent using a solvent, the specific steps being as follows: (1) Take 6.98g of choline chloride and 11.40g of p-toluenesulfonic acid monohydrate in a sample bottle and stir at 80°C for 1h to obtain a clear and transparent liquid. After standing and cooling, the low eutectic solvent catalyst ChCl-1.2 is obtained. p- TSA; (2) Weigh 3 g of the catalyst obtained in step (1) into a sample bottle, add 30 g of isosorbide, stir at 60° C. to completely dissolve it, and let it stand; (3) To the solution obtained in step (2), 33 g of ethyl acetate (mass ratio of 1:1) was added, and the mixture was extracted with stirring at 60° C. for 1 h. The upper liquid was sampled and subjected to liquid chromatography. The results showed that the concentration of isosorbide was 26%.

[0052] Embodiment 26: In this example, the reaction mixture is used as the extraction raw material.

[0053] (1) Take 5 g of the reaction mixture (84% isosorbide, 13% 1,4-anhydrosorbitol and 3% other substances), add 20 g of ethyl acetate, stir and extract at 60°C for 1 hour, and sample the upper liquid. Liquid chromatography detection shows that the extraction rate is 67.8%.

[0054] Embodiment 27: In this example, the reaction mixture is used as the extraction raw material.

[0055] (1) Take 5 g of the reaction mixture (84% isosorbide, 13% 1,4-anhydrosorbitol and 3% other substances), add 20 g of ethyl acetate and 5 g of acetone, stir and extract at 60°C for 1 hour, and sample the upper liquid. Liquid chromatography detection shows that the extraction rate is 81.6%.

[0056] Embodiment 28: In this example, the reaction mixture is used as the extraction raw material.

[0057] (1) Take 5 g of the reaction mixture (84% isosorbide, 13% 1,4-anhydrosorbitol and 3% other substances), add 20 g of ethyl acetate and 10 g of acetone, stir and extract at 60°C for 1 hour, and sample the upper liquid. Liquid chromatography detection shows that the extraction rate is 81.2%.

[0058] Embodiment 29: In this example, the reaction mixture is used as the extraction raw material.

[0059] (1) Take 5 g of the reaction mixture (84% isosorbide, 13% 1,4-anhydrosorbitol and 3% other substances), add 20 g of ethyl acetate and 15 g of acetone, stir and extract at 60°C for 1 hour, and sample the upper liquid. Liquid chromatography detection shows that the extraction rate is 83.2%.

Claims

1. A method for preparing isosorbide by dehydration of sorbitol catalyzed by a deep eutectic solvent, characterized in that: The following steps are involved: (1) Weigh appropriate amounts of choline chloride (ChCl) and p-toluenesulfonic acid ( p -TSA), and the two were vacuum dried at 70 ° C for 1 hour, and then the two were mixed in a wide-mouth bottle and heated to 80 ° C, and stirred until a clear and transparent liquid was obtained. The obtained product was a low eutectic solvent catalyst ChCl- p -TSA; (2) Weighing appropriate amounts of substrate sorbitol and the catalyst prepared in step (1), respectively, adding them into a three-necked flask, stirring and heating at a certain temperature under vacuum conditions to react for a certain time; (3) After the reaction is completed, a certain amount of extractant is added to the reaction solution, and the mixture is heated and stirred at 60°C to obtain an extractant phase and a low eutectic solvent phase, wherein the low eutectic solvent phase is subjected to reduced pressure distillation at 160°C to remove impurities to recover the catalyst; the extractant phase is cooled and crystallized at a crystallization temperature of 5°C, and the crystals are filtered to obtain crystals; (4) Dissolve the crystals obtained in step (3) in ChCl- p -TSA, repeat the steps in step (3); (5) Drying the crystals obtained in step (4) to obtain isosorbide crystals.

2. The method for preparing isosorbide according to claim 1, wherein In step (1), the molar ratio of choline chloride to p-toluenesulfonic acid is 0.5-2.

3. The method for preparing isosorbide according to claim 1, wherein In step (2), ChCl- p -The amount of TSA added is 5%-10% of the mass of solid sorbitol.

4. The method for preparing isosorbide according to claim 1, wherein The vacuum degree in step (2) is 0.09 MPa.

5. The method for preparing isosorbide according to claim 1, characterized in that The reaction temperature in step (2) is 110°C-140°C.

6. The method for preparing isosorbide according to claim 1, characterized in that The reaction time in step (2) is 3h-6h.

7. The method for preparing isosorbide according to claim 1, characterized in that The extractant in step (3) is selected from any one of ethyl acetate, methyl acetate, propyl acetate, butyl acetate and acetone.

8. The method according to claim 1, characterized in that The amount of the extractant added in step (3) is 1-4 times the total mass of the reaction system.