Process for the isolation of isosorbide

Abstract

The present application relates to the chemical industry field, disclose a kind of method for separating isosorbide, the method comprises the following steps: (1) the reaction liquid to be handled is mixed with adjuvant, then the mixture is distilled, and distillation fraction is obtained, wherein the adjuvant is selected from water-soluble carbonate;(2) the distillation fraction is dissolved with solvent, and the dissolved material is sequentially subjected to adsorption impurity removal and first solid-liquid separation;(3) the liquid phase obtained by the first solid-liquid separation is sequentially subjected to crystallization and second solid-liquid separation.The isosorbide obtained by the method has high yield and purity, and the produced humic substance is a solid material at room temperature, which can be further crushed and granulated for use as organic fertilizer, turning waste into treasure, reducing the production cost of the product, solving the environmental pollution problem, and further reducing the production amount of humic substance at the bottom of the distillation kettle.

Description

Technical Field

[0001] This invention relates to the field of chemical engineering, and specifically to a method for separating isosorbide. Background Technology

[0002] Isosorbide, as an important biomass platform compound, possesses a unique chiral molecular structure and is a safe, non-toxic, and green diol. It is widely used not only in pharmaceuticals, solvents, and plastic additives, but also plays a crucial role in the field of novel polymer materials. For example, isosorbide itself can serve as an excellent antihypertensive drug and diuretic; it can also be used to synthesize isosorbide dimethyl ether as a green solvent; it can be used to synthesize novel green plasticizers to replace phthalate plasticizers; furthermore, isosorbide can be used to modify PET, significantly improving its high-temperature properties and impact resistance; in polycarbonate new material technology, it serves as an important raw material to replace bisphenol A, which poses health risks, thereby improving the environmentally friendly performance of polycarbonate. Therefore, in recent years, the synthesis technology of isosorbide and its related applications have received considerable attention.

[0003] The domestic technology for preparing polymer-grade isosorbide from sorbitol through dehydration faces numerous challenges. For instance, the isosorbide product exhibits low purity, with a pH generally below 6.5, and tends to yellow after standing, making it unsuitable as a monomer for polymerization. Furthermore, the dehydration of polyols in this process inevitably generates significant amounts of humic substances. These humic substances occur during both the reaction and purification stages, resulting in low product yields. Moreover, as a viscous, flowing substance at room temperature, humic substances hinder further processing and currently have no known applications, only being treated as chemical waste, thus increasing production costs. The primary cause of these problems is the numerous products generated during the dehydration of the sorbitol raw material. These include intermediates from primary dehydration such as 1,5-monohydrated sorbitol, 2,5-monohydrated sorbitol, and 2,6-monohydrated sorbitol; and compounds from secondary dehydration such as isosorbide, isomannitol, and isoadurel. During the distillation process, these polyols undergo further high-temperature oxidation, dehydration, and polymerization, generating various impurities, such as formic acid and oligomers, which ultimately form a large amount of dark brown viscous substance, known as piracetam. This leads to complex and time-consuming subsequent separation processes, reduced isosorbide yield, and environmental pollution, directly increasing the production cost of isosorbide and failing to meet the requirements of green chemistry, further limiting industrial-scale production.

[0004] In response to the shortcomings of existing isosorbide processes, numerous researchers have conducted studies on catalysts and the separation and purification of isosorbide in the dehydration of sorbitol. However, there are few patents in China on the separation and purification of isosorbide, and the processes are cumbersome and have poor operability. Furthermore, there are few reports on further research on the humic substances.

[0005] CN102757445A discloses a preparation process for isosorbide, the separation process of which includes: dehydration reaction, neutralization and decolorization, electrodialysis desalination, concentration and dehydration, extraction and crystallization, freeze drying, quality inspection and packaging. Although this method avoids high-temperature distillation, its separation process is very complex and not very feasible for large-scale production.

[0006] CN112574228A discloses a method for separating isosorbide. This method mainly involves adding a high-boiling-point substance, such as polypropylene glycol, to the isosorbide reaction solution to be separated during the distillation process to dilute the viscosity of the reaction solution and reduce the carbonization of the substrate during the high-temperature distillation process. However, it does not block the generation of viscous, flowing black matter and still has problems such as complex subsequent separation processes, long time consumption, and environmental pollution. Summary of the Invention

[0007] The purpose of this invention is to overcome the problems existing in the prior art where, during the distillation and purification of isosorbide reaction stock solution, the substrate further reacts to generate various impurities. These impurities carbonize severely at high temperatures, resulting in a large amount of viscous black matter at the bottom of the distillation vessel. This leads to low isosorbide yield, low purity, and low pH, long processing time, and environmental pollution. The invention provides a method for separating isosorbide. The isosorbide separated using this method has a high yield and purity. The generated black matter is a solid substance at room temperature, which can be further pulverized and granulated for use as organic fertilizer, turning waste into treasure, reducing production costs, solving environmental pollution problems, and further reducing the amount of black matter generated at the bottom of the distillation vessel.

[0008] To achieve the above objective, a first aspect of the present invention provides a method for separating isosorbide, the method comprising the following steps:

[0009] (1) The reaction stock solution to be treated is mixed with the auxiliary agent, and then the mixture is distilled to obtain the distillate fraction, wherein the auxiliary agent is selected from water-soluble carbonates;

[0010] (2) Dissolve the above distilled fraction in a solvent, and then subject the dissolved product to adsorption purification and first solid-liquid separation in sequence;

[0011] (3) The liquid phase obtained from the first solid-liquid separation is subjected to crystallization and the second solid-liquid separation in sequence.

[0012] A second aspect of the present invention provides a method for separating isosorbide, the method comprising the following steps: mixing the reaction stock solution to be treated with an auxiliary agent, and then distilling the mixture to obtain a distillate containing isosorbide, wherein the auxiliary agent is selected from water-soluble carbonates.

[0013] The above technical solution achieves at least the following beneficial technical effects:

[0014] (1) The isosorbide obtained by the method of the present invention has high purity. In the preferred embodiment, the purity of isosorbide in the distillate obtained after distillation is more than 98.5%; the purity of isosorbide in the product obtained after recrystallization is more than 99.8%.

[0015] (2) The method of the present invention can further reduce the carbonization degree of the substrate and reduce the amount of humic substances produced; at the same time, it changes the physical state of humic substances at room temperature. The humic substances produced are solid substances at room temperature, which can be further crushed and granulated for use as organic fertilizer, turning waste into treasure, reducing the production cost of the product, and solving the environmental pollution problem.

[0016] (3) The isosorbide product obtained by the method of the present invention has a high pH value. In the preferred embodiment, the pH value of the distillate obtained after distillation is above 6.5, and the pH value of the product obtained after recrystallization can be stable above 7. The product quality is good (it is not easy to turn yellow after being stored, and the polymerization effect as a polymer monomer is good).

[0017] (4) The isosorbide obtained by the method of the present invention has a high yield. In the preferred embodiment, the yield of isosorbide in the distillate obtained after distillation is more than 75%; the yield of isosorbide in the product obtained after recrystallization is more than 69%. Detailed Implementation

[0018] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0019] The first aspect of this invention provides a method for separating isosorbide, the method comprising the following steps:

[0020] (1) The reaction stock solution to be treated is mixed with the auxiliary agent, and then the mixture is distilled to obtain a distillate (light fraction / light component), wherein the auxiliary agent is selected from water-soluble carbonates;

[0021] (2) Dissolve the above distilled fraction in a solvent, and then subject the dissolved product to adsorption purification and first solid-liquid separation in sequence;

[0022] (3) The liquid phase obtained from the first solid-liquid separation is subjected to crystallization and the second solid-liquid separation in sequence.

[0023] In this invention, the additive can be a water-soluble carbonate commonly found in the art. Preferably, the additive is selected from potassium carbonate and / or sodium carbonate.

[0024] In this invention, preferably, the molar amount of the auxiliary agent is 15-50 mmol, more preferably 20-40 mmol, based on the mass of 100g of the reaction stock solution to be treated.

[0025] According to some embodiments of the present invention, in step (1), the reaction stock solution to be treated is a reaction solution for the preparation of isosorbide from sorbitol by dehydration after the recovery of the solid acid catalyst. The reaction stock solution to be treated mainly contains isosorbide and other polyols, and the content of isosorbide in the reaction stock solution to be treated is usually 80-90 wt%; the other polyols generally include at least one of 1,5-monohydrated sorbitol, 2,5-monohydrated sorbitol, 2,6-monohydrated sorbitol, isomannitol, and isoadenomyol, and the content of each is usually in the range of 0.1-15 wt%.

[0026] In one embodiment of the present invention, the preparation method of the reaction stock solution to be treated includes: in the presence of a catalyst (preferably a solid acid catalyst, such as sulfonic acid resin), sorbitol undergoes a dehydration reaction; after the dehydration reaction is completed, the catalyst is separated while hot to obtain the reaction stock solution to be treated.

[0027] Preferably, the mass ratio of the catalyst to sorbitol is 1:(15-200).

[0028] Preferably, the conditions for the dehydration reaction include: temperature 110-145℃, pressure 20-200mbar, and time 2-12h.

[0029] According to some embodiments of the present invention, in step (1), the distillation method is vacuum distillation;

[0030] Preferably, the distillation conditions include: a pressure of 40-1000 Pa, more preferably 80-1000 Pa; and a temperature of 120-260 °C, more preferably 120-250 °C.

[0031] Preferably, the distillation time is such that the weight of the distillate is 40-95 wt% of the weight of the original reaction solution to be treated, more preferably 65 wt%-85 wt%.

[0032] In this invention, isosorbide separation is carried out in a reaction vessel. As the distillation temperature rises, the temperature of the mixture of the reaction stock solution and the auxiliary agent reaches above 140°C. Substances with lower boiling points are stably distilled out to obtain distilled fractions. Distillation ends when the temperature of the distilled fractions drops below 100°C.

[0033] In this invention, the distillation fraction is a crude product containing isosorbide obtained by distillation, which is in a solid state after cooling.

[0034] According to some embodiments of the present invention, in step (2), the amount of solvent used is 5-80g relative to 20g of the distillate fraction.

[0035] According to some embodiments of the present invention, in step (2), the solvent is preferably at least one of ethyl acetate, isopropanol and ethanol.

[0036] In this invention, in order to fully dissolve and mix the distillate and the solvent, preferably, in step (2), the dissolution method includes stirring the distillate and the solvent at 40℃-70℃ for 30-120 minutes.

[0037] According to some embodiments of the present invention, in step (2), the adsorption and impurity removal method includes mixing the dissolved substance with the adsorbent. To improve the efficiency of adsorption and impurity removal, preferably, the mixing method includes stirring the dissolved substance and the adsorbent at 50°C-65°C for 0.5-1.5 hours.

[0038] Preferably, the adsorbent is selected from at least one of activated carbon, alumina, and silica gel.

[0039] Preferably, the amount of adsorbent used is 0.1-4g relative to 20g of the distillate fraction.

[0040] According to some embodiments of the present invention, in step (3), the crystallization method is cooling crystallization.

[0041] Preferably, the crystallization method includes allowing the liquid phase obtained from the first solid-liquid separation to stand at 30-40℃ for 10-30 min, and then standing at -10℃-20℃ for 0.5-10 h.

[0042] According to some embodiments of the present invention, in step (2), the first solid-liquid separation is carried out by filtration.

[0043] In this invention, preferably, the pore size of the filter screen is 15-25 μm.

[0044] According to some embodiments of the present invention, in step (3), the second solid-liquid separation method is vacuum filtration.

[0045] Preferably, the filter screen of the reduced pressure filtration has a particle size of 15-25 μm and a pressure of 0.1-95 kPa.

[0046] According to some embodiments of the present invention, the method further includes drying the solid phase obtained from the second solid-liquid separation in step (3).

[0047] Preferably, the drying conditions include a temperature of 45-60°C and a time of 1-24 hours.

[0048] A second aspect of the present invention provides a method for separating isosorbide, the method comprising the following steps: mixing a reaction stock solution to be treated with an auxiliary agent, and then distilling the mixture to obtain a distillate containing isosorbide, wherein the auxiliary agent is selected from water-soluble carbonates. In this embodiment, the type, amount, and operating conditions of the auxiliary agent are preferably as described above, and will not be repeated here.

[0049] According to a particularly preferred embodiment of the present invention, a method for separating isosorbide is provided, the method comprising the following steps:

[0050] (1) Add the reaction stock solution and auxiliary agent to the reaction vessel, and perform vacuum distillation on the mixture. After the vacuum distillation is completed, the distilled fraction (crude product containing isosorbide) is obtained; the residue at the bottom of the vessel (black matter) becomes a hard solid after cooling to room temperature.

[0051] The auxiliary agent is potassium carbonate, and the molar amount of the auxiliary agent is 20-40 mmol relative to 100g of the reaction stock solution to be treated.

[0052] The conditions for vacuum distillation include: a pressure of 80-100 Pa and a temperature of 160-180 °C.

[0053] (2) Add the crude product containing isosorbide obtained by vacuum distillation and ethanol to a three-necked flask. Stir at 60-70℃ for 30-45 min until the solution is homogeneous. Then add activated carbon and stir for 1-1.5 h. Filter while hot (the pore size of the filter screen is 20-25 μm) to obtain the filtrate.

[0054] The amount of solvent used is 5-20g relative to 20g of the distillate fraction;

[0055] The amount of activated carbon used is 0.6-3g relative to 20g of the distillate fraction;

[0056] (3) Cool the above filtrate at 30-40℃ and let it stand for 10-30 min, then let it stand at -10 to 20℃ for 0.5-4 h, and then perform vacuum filtration at a pressure of 100-2000 Pa (the pore size of the filter screen is 20-25 μm) to obtain a filter cake. Place the filter cake in a vacuum drying oven at 45-60℃ and dry it for 6-20 h to obtain isosorbide product.

[0057] The present invention will be described in detail below through embodiments.

[0058] In the comparative example, polyethylene glycol 2000 was purchased from Beijing Innocare Technology Co., Ltd.

[0059] In the following examples and comparative examples, the purity of isosorbide was determined by high performance liquid chromatography (HPLC). The HPLC instrument was LC1100, the column was Hi-Plex H, the detector was a differential refractive index detector (1260RID), water was used as the mobile phase, the flow rate was 0.60 mL / min, and the column temperature was 60 °C.

[0060] In the following examples and comparative examples, the ethanol used is anhydrous ethanol with a volume concentration of 99.9%.

[0061] Unless otherwise specified, all chemical reagents used in the following examples and comparative examples are commercially available.

[0062] Preparation Example

[0063] 90g of solid acid catalyst sulfonic acid resin and 3000g of sorbitol were added to a three-necked flask. The reaction was carried out at a temperature of 135±5℃ and a pressure of 100mbar for 7h. Isosorbitol was prepared by dehydration. After the reaction was completed, the catalyst was separated by hot filtration to obtain 2260.5g of the original reaction solution to be treated. The content of isosorbitol in the reaction solution to be separated was 86.84wt%.

[0064] Example 1

[0065] (1) Add 200g of the reaction stock solution to be treated (preparation example) and 5.53g of potassium carbonate (the molar amount of potassium carbonate is 20mmol relative to 100g of the reaction stock solution to be treated) to the reaction vessel. Gradually heat the mixture to 120℃ and maintain the temperature for 10min. After the material flow in the vessel is good, slowly raise the temperature to 160℃ and evacuate the vacuum. Control the system pressure to 80Pa. After the distillation temperature reaches 140℃, the product is stably distilled out. After the distillation temperature drops to 95℃, the vacuum distillation ends and the distillation fraction (crude product containing isosorbide) is obtained. Weigh the crude product and obtain 150.13g of crude product. The purity of isosorbide in the crude product is 98.53% and the pH value is 6.63. Release the residue at the bottom of the vessel while it is hot. The residue at the bottom of the vessel (black matter) becomes a hard solid after cooling to room temperature (the weight of the black matter is 52.61g).

[0066] (2) Add 20g of the crude isosorbide-containing product obtained by vacuum distillation and 11g of ethanol to a three-necked flask, heat to 60℃, and after the solution is homogenized, add 0.6g of activated carbon, stir for 1h, and filter while hot (the pore size of the filter screen is 20μm) to obtain the filtrate; cool the filtrate to 30℃ and let it stand for 30min, then let it stand at 20℃ for 4h, and then filter under vacuum at a pressure of 2000Pa (the pore size of the filter screen is 20μm) to obtain the filter cake. Place the filter cake in a vacuum drying oven at 45℃ and dry for 6h. Weigh 13.83g of product. The pH value of the product is 7.17. The purity of isosorbide in the product was 99.87% as determined by liquid chromatography.

[0067] Example 2

[0068] (1) Add 200g of the original reaction solution to be treated (preparation example) and 11.06g of potassium carbonate (the molar amount of potassium carbonate is 40mmol relative to 100g of the original reaction solution to be treated) to the reaction vessel. Gradually heat the mixture to 120℃ and maintain the temperature for 10min. After the material flow in the vessel is good, slowly raise the temperature to 160℃ and evacuate the vacuum. Control the system pressure to 80Pa. After the distillation temperature reaches 140℃, the product is stably distilled out. After the distillation temperature drops to 80℃, the vacuum distillation ends and the distillation fraction (crude product containing isosorbide) is obtained. Weigh the crude product and obtain 147.69g of crude product. The purity of isosorbide in the crude product is 98.51% and the pH value is 6.79. Release the residue at the bottom of the vessel while it is hot. The residue at the bottom of the vessel (black matter) becomes a hard solid after cooling to room temperature (the weight of the black matter is 57.56g).

[0069] (2) Add 20g of the crude isosorbide-containing product obtained by vacuum distillation and 11g of ethanol to a three-necked flask, heat to 60℃, and after the solution is homogenized, add 0.6g of activated carbon, stir for 1h, and filter while hot (the pore size of the filter screen is 20μm) to obtain the filtrate; cool the filtrate to 30℃ and let it stand for 30min, then stand at 20℃ for 4h, and then filter under vacuum at a pressure of 2000Pa (the pore size of the filter screen is 20μm) to obtain the filter cake. Place the filter cake in a vacuum drying oven at 45℃ and dry for 6h. Weigh 13.74g of product. The pH value of the product is 7.36. The purity of isosorbide in the product was 99.81% as determined by liquid chromatography.

[0070] Example 3

[0071] (1) Add 200g of the original reaction solution to be treated (preparation example) and 6.72g of sodium bicarbonate (the molar amount of sodium bicarbonate is 40mmol relative to 100g of the original reaction solution to be treated) to the reaction vessel. Gradually heat the mixture to 120℃ and maintain the temperature for 10min. After the material flow in the vessel is good, slowly raise the temperature to 160℃ and evacuate the vacuum. Control the system pressure to 80Pa. After the distillation temperature reaches 140℃, the product is stably distilled out. After the distillation temperature drops to 80℃, the vacuum distillation ends and the distillation fraction (crude product containing isosorbide) is obtained. Weigh the crude product and obtain 138.4g of crude product. The purity of isosorbide in the crude product is 98.59% and the pH value is 6.61. While hot, release the residue at the bottom of the vessel. The residue at the bottom of the vessel (black matter) becomes a hard solid after cooling to room temperature (the weight of the black matter is 63.94g).

[0072] (2) Add 20g of the crude isosorbide-containing product obtained by vacuum distillation and 11g of ethanol to a three-necked flask, heat to 60℃, and after the solution is homogenized, add 0.6g of activated carbon, stir for 1h, and filter while hot (the pore size of the filter screen is 20μm) to obtain the filtrate; cool the filtrate to 30℃ and let it stand for 30min, then stand at 20℃ for 4h, and then filter under vacuum at a pressure of 2000Pa (the pore size of the filter screen is 20μm) to obtain the filter cake. Place the filter cake in a vacuum drying oven at 45℃ and dry for 6h. Weigh 12.79g of product. The pH value of the product is 7.12. The purity of isosorbide in the product was 99.61% as determined by liquid chromatography.

[0073] Example 4

[0074] The method of Example 1 is followed, except that in step (1), 2.77g of potassium carbonate (10 mmol molar amount of potassium carbonate relative to 100g of the reaction stock solution to be treated) is added, and the vacuum distillation is completed to obtain the distillate (crude product containing isosorbide). The crude product is weighed to obtain 137.32g of crude product. The purity of isosorbide in the crude product is 98.45%, and the pH value is 5.31. The residue at the bottom of the vessel is released while hot. The residue at the bottom of the vessel (black matter) is cooled to room temperature and becomes a free-flowing viscous liquid (the weight of the black matter is 62.18g).

[0075] The crude product containing isosorbide obtained by vacuum distillation was subjected to adsorption, filtration, recrystallization and vacuum filtration according to the method of Example 1 to obtain a filter cake. The filter cake was dried in a vacuum drying oven at 45°C for 6 hours and weighed to obtain 12.32g of product. The pH of the product was 6.37. The purity of isosorbide in the product was 99.55% as determined by liquid chromatography.

[0076] Comparative Example 1

[0077] The method of Example 1 is different in that no additives are added in step (1). After the vacuum distillation is completed, the distillate (crude product containing isosorbide) is obtained. The crude product is weighed and 106.6g of crude product is obtained. The purity of isosorbide in the crude product is 95.6% and the pH value is 4.13. The residue at the bottom of the vessel is released while it is hot. After the residue at the bottom of the vessel (black matter) is cooled to room temperature, it becomes a free-flowing viscous liquid (the weight of black matter is 88.73g).

[0078] The crude product containing isosorbide obtained by vacuum distillation was subjected to adsorption, filtration, recrystallization and vacuum filtration according to the method of Example 1 to obtain a filter cake. The filter cake was dried in a vacuum drying oven at 45°C for 6 hours and weighed to obtain 11.85g of product. The pH of the product was 5.49. The purity of isosorbide in the product was 98.86% as determined by liquid chromatography.

[0079] Comparative Example 2

[0080] The method of Example 1 is followed, except that the auxiliary agent added in step (1) is 5.68g of disodium hydrogen phosphate (the molar amount of disodium hydrogen phosphate is 20mmol relative to 100g of the reaction stock solution to be treated). After the vacuum distillation is completed, the distillate fraction (crude product containing isosorbide) is obtained. The crude product is weighed to obtain 134.5g of crude product. The purity of isosorbide in the crude product is 98.18%, and the pH value is 4.57. The residue at the bottom of the vessel is released while hot. After the residue at the bottom of the vessel (black matter) is cooled to room temperature, it becomes a free-flowing viscous liquid (the weight of black matter is 67.62g).

[0081] The crude product containing isosorbide obtained by vacuum distillation was subjected to adsorption, filtration, recrystallization, and vacuum filtration according to the method in Example 1 to obtain a filter cake. The filter cake was dried in a vacuum drying oven at 45°C for 6 hours and weighed to obtain 12.06 g of product. The pH of the product was 5.57, and the purity of isosorbide in the product was 99.39% as determined by liquid chromatography.

[0082] Comparative Example 3

[0083] The method of Example 1 is followed, except that the auxiliary agent added in step (1) is 1.6g of sodium hydroxide (the molar amount of sodium hydroxide is 20mmol relative to 100g of the reaction stock solution to be treated). After the vacuum distillation is completed, the distillate fraction (crude product containing isosorbide) is obtained. The crude product is weighed to obtain 136.6g of crude product. The purity of isosorbide in the crude product is 98.14%, and the pH value is 4.5. The residue at the bottom of the vessel is released while hot. After the residue at the bottom of the vessel (black matter) is cooled to room temperature, it becomes a free-flowing viscous liquid (the weight of black matter is 61.1g).

[0084] The crude product containing isosorbide obtained by vacuum distillation was subjected to adsorption, filtration, recrystallization and vacuum filtration according to the method of Example 1 to obtain a filter cake. The filter cake was dried in a vacuum drying oven at 45°C for 6 hours and weighed to obtain 12.13g of product. The pH of the product was 5.75. The purity of isosorbide in the product was 99.47% as determined by liquid chromatography.

[0085] Comparative Example 4

[0086] The method of Example 1 is followed, except that the auxiliary agent added in step (1) is 9.3g of tetrabutylphosphine hydroxide (the molar amount of tetrabutylphosphine hydroxide is 20 mmol relative to 100g of the reaction stock solution to be treated). After the vacuum distillation is completed, the distillation fraction (crude product containing isosorbide) is obtained. The crude product is weighed to obtain 129.9g of crude product. The purity of isosorbide in the crude product is 98.39%, and the pH value is 4.34. The residue at the bottom of the vessel is released while hot. After the residue at the bottom of the vessel (black matter) is cooled to room temperature, it becomes a free-flowing viscous liquid (the weight of black matter is 75.43g).

[0087] The crude product containing isosorbide obtained by vacuum distillation was subjected to adsorption, filtration, recrystallization and vacuum filtration according to the method of Example 1 to obtain a filter cake. The filter cake was dried in a vacuum drying oven at 45°C for 6 hours and weighed to obtain 12.24 g of product. The pH of the product was 5.53. The purity of isosorbide in the product was 99.52% as determined by liquid chromatography.

[0088] Comparative Example 5

[0089] The method of Example 1 is followed, except that the auxiliary agent added in step (1) is 40g of polyethylene glycol 2000 (the molar amount of polyethylene glycol 2000 is 20mmol relative to 100g of the reaction stock solution to be treated). After the vacuum distillation is completed, the distillate (crude product containing isosorbide) is obtained. The crude product is weighed and 123.4g of crude product is obtained. The purity of isosorbide in the crude product is 95.9% and the pH value is 4.21. The residue at the bottom of the vessel is released while hot. After the residue at the bottom of the vessel (black matter) is cooled to room temperature, it becomes a free-flowing viscous liquid (the weight of black matter is 110.77g).

[0090] The crude product containing isosorbide obtained by vacuum distillation was subjected to adsorption, filtration, recrystallization, and vacuum filtration according to the method in Example 1 to obtain a filter cake. The filter cake was dried in a vacuum drying oven at 45°C for 6 hours and weighed to obtain 12.14 g of product. The product pH was 5.34, and the purity of isosorbide in the product was 99.12% as determined by liquid chromatography.

[0091] A comparison of Examples 1-3 with Example 4 shows that the preferred embodiment of the present invention can change the physical form of the generated toxic substances at room temperature, making the generated toxic substances solid at room temperature, and can also reduce the amount of toxic substances generated at the bottom of the distillation vessel, thus solving the environmental pollution problem; at the same time, it can further improve the yield, purity and pH of isosorbide products, and improve product quality.

[0092] Compared with the examples, Comparative Example 1 did not add any auxiliary agent during vacuum distillation, and Comparative Examples 2-5 replaced the water-soluble carbonate with different auxiliary agents. In all cases, the residue (black matter) generated at the bottom of the reactor became a free-flowing viscous liquid after cooling to room temperature (which could not be further processed into granulation, causing environmental pollution). The weight of the black matter increased significantly, the yield and purity of isosorbide decreased, and the pH was lower than 6.5 (the product was prone to yellowing after standing, resulting in poor polymerization effect as a monomer).

[0093] In summary, the isosorbide obtained by the method of this invention has high yield and purity. The resulting humic substance is a solid at room temperature, which can be further crushed and granulated for use as organic fertilizer, turning waste into treasure, reducing production costs, solving environmental pollution problems, and further reducing the amount of humic substance generated at the bottom of the distillation vessel. In addition, the pH value of the crude isosorbide obtained after distillation is above 6.5, and the pH value of the product obtained after recrystallization can be stabilized above 7, indicating good product quality (it does not easily turn yellow after standing and has good polymerization effect as a monomer).

[0094] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for separating isosorbide, characterized in that, The method includes the following steps: (1) The reaction stock solution to be treated is mixed with the auxiliary agent, and then the mixture is distilled to obtain the distillate fraction, wherein the auxiliary agent is selected from water-soluble carbonates; (2) Dissolve the above distilled fraction in a solvent, and then subject the dissolved product to adsorption purification and first solid-liquid separation in sequence; (3) The liquid phase obtained from the first solid-liquid separation is subjected to crystallization and the second solid-liquid separation in sequence.

2. The method according to claim 1, wherein, The additive is selected from potassium carbonate and / or sodium carbonate; And / or, in step (1), the reaction stock solution to be treated is the reaction solution for preparing isosorbide by dehydration of sorbitol after the recovery of solid acid catalyst.

3. The method according to claim 1 or 2, wherein, In step (1), the molar amount of the auxiliary agent is 15-50 mmol, preferably 20-40 mmol, based on the mass of 100g of the reaction stock solution to be treated.

4. The method according to any one of claims 1-3, wherein, In step (1), the distillation method is vacuum distillation; Preferably, the distillation conditions include: a pressure of 40-1000 Pa and a temperature of 120-260 °C; Preferably, the distillation time is such that the weight of the distillate is 40wt%-95wt% of the weight of the original reaction solution to be treated.

5. The method according to any one of claims 1-4, wherein, In step (2), the amount of solvent used is 5-80g relative to 20g of the distillate; And / or, in step (2), the solvent is selected from at least one of ethyl acetate, isopropanol and ethanol.

6. The method according to any one of claims 1-5, wherein, In step (2), the dissolution method includes stirring the distillate and solvent at 40℃-70℃ for 30-120 min; And / or, in step (2), the adsorption and impurity removal method includes mixing the dissolved substance with the adsorbent; Preferably, the adsorbent is selected from at least one of activated carbon, alumina, and silica gel; Preferably, the amount of adsorbent used is 0.1-4g relative to 20g of the distillate fraction.

7. The method according to any one of claims 1-6, wherein, In step (3), the crystallization method is cooling crystallization; Preferably, the crystallization method includes allowing the liquid phase obtained from the first solid-liquid separation to stand at 30-40°C for 10-30 min, and then standing at -10°C to 20°C for 0.5-10 h.

8. The method according to any one of claims 1-7, wherein, In step (2), the first solid-liquid separation method is filtration; And / or, wherein, in step (3), the second solid-liquid separation method is vacuum filtration; Preferably, the filter screen of the reduced pressure filtration has a particle size of 15-25 μm and a pressure of 0.1-95 kPa.

9. The method according to any one of claims 1-8, wherein, The method further includes drying the solid phase obtained from the second solid-liquid separation in step (3); Preferably, the drying conditions include a temperature of 45-60°C and a time of 1-24 hours.

10. A method for separating isosorbide, characterized in that, The method includes the following steps: mixing the reaction stock solution to be treated with an auxiliary agent, and then distilling the mixture to obtain a distillate containing isosorbide, wherein the auxiliary agent is selected from water-soluble carbonates; Preferably, the additive is selected from potassium carbonate and / or sodium carbonate.