A method for continuously dehydrating sorbitol to produce isosorbide

Abstract

The present application provides a kind of sorbitol continuous dehydration preparation isosorbide method, belong to the preparation field of bio-based chemicals. Using solvent containing dimethyl sulfoxide, sulfolane and other compounds to dissolve sorbitol, increase the mobility of sorbitol solution, and then realize the continuous dehydration of sorbitol to prepare isosorbide. The specific steps are as follows: the solid acid catalyst is loaded into the fixed bed reactor, the preheated sorbitol solution is continuously passed through the catalyst layer for dehydration reaction, and the mixture after reaction is separated to obtain isosorbide. The present application adds polar aprotic solvent to improve the flowability of the reaction solution during the dehydration reaction stage, realizes continuous reaction, and the dehydration reaction temperature is low, and the generated pyrolysis black substance is greatly reduced; aromatic hydrocarbon is used to extract high-boiling organic solvent in the product separation stage, and the separation effect is good and the energy consumption is low; the method has important application prospect.

Description

Technical Field

[0001] This invention belongs to the field of preparation of bio-based chemicals, and relates to a method for the continuous catalytic dehydration and separation of sorbitol to prepare isosorbide. Background Technology

[0002] Isosorbide, a dehydrated derivative of sorbitol, is an important bio-based diol with wide applications in pharmaceuticals, food, and polymers. In the pharmaceutical field, isosorbide is an oral osmotic diuretic used to treat cerebral edema and glaucoma. It can also be used as a raw material to produce isosorbide nitrate and isosorbide mononitrate for treating coronary heart disease and angina. In the polymer field, isosorbide can be used as a monomer to prepare biodegradable and environmentally friendly materials, showing promising development prospects. Therefore, the green and efficient preparation of isosorbide has significant application potential.

[0003] The selective dehydration reaction of sorbitol is the main route for preparing isosorbide. In traditional industrial processes, the dehydration of sorbitol to isosorbide is often carried out under batch conditions using liquid inorganic strong acids (such as sulfuric acid) as catalysts. These processes suffer from severe blackening of the product, difficulty in catalyst separation, and high levels of waste. Furthermore, numerous reports in the literature utilize solid acids as catalysts, but these systems mostly employ batch reaction methods. For example, Chinese patent CN 201710357390.1 reports a method for preparing isosorbide. This method uses a solid acidic molecular sieve as a catalyst, and the isosorbide reaction solution is prepared by a melt reaction at 180°C, followed by a series of separations to obtain isosorbide. This method uses a solvent-free reaction system, resulting in high viscosity of the molten sorbitol, severe blackening of the product under high temperature and strong acid conditions, and significant difficulties in product separation. In the process of dehydrating sorbitol to prepare isosorbide, changing the batch reaction to a continuous flow reaction has the following advantages: (1) The continuous flow reaction process can reduce backmixing of materials and reduce the black residues generated during the dehydration reaction; (2) It has more controllable reaction conditions, such as reaction temperature, reaction residence time, and pressure, which is conducive to simultaneously improving the conversion rate of sorbitol and the selectivity of isosorbide; (3) It improves production efficiency and realizes automated continuous production. The realization of continuous catalytic dehydration of sorbitol to prepare isosorbide is very attractive.

[0004] However, sorbitol is a polyhydroxy compound with a high melting point, is solid at room temperature, and is difficult to dissolve in most common organic solvents. Solvent-free molten sorbitol has high viscosity and poor flowability. If water is used as a solvent, the acidic catalyst is easily decomposed and deactivated under high-temperature reaction conditions. Using alcohol solvents in acidic environments easily produces a large amount of ether. There are few reports in the literature on the continuous dehydration reaction of sorbitol. Chinese invention patent CN 201910748764.1 discloses a method for the continuous reaction of sorbitol to prepare isosorbitol, using a packed confined acidic ionic liquid as a solid acid catalyst, and feeding sorbitol and solvent in a certain ratio. The reaction solvents used are benzene, toluene, xylene, ethylbenzene, p-xylene, m-xylene, etc. The reported sorbitol to solvent mass ratio is 1:20 to 100, that is, the sorbitol concentration is only 1-5%, which is related to the low solubility of sorbitol in aromatic solvents. Chinese patent CN101492457A discloses a method for preparing isosorbide in a fixed-bed reactor. This method uses an 8-15% sorbitol aqueous solution as the reaction liquid and a phosphoric acid-modified tetravalent metal oxide as a catalyst. The isosorbide is prepared by dehydration reaction in a fixed-bed reactor at 250-300℃. The reported isosorbide selectivity is 63% and the yield is 62%. However, the preparation method disclosed in this patent uses high-temperature water as a solvent, resulting in high reaction pressure, and the product selectivity and yield need further improvement. Developing a simple and efficient system for the continuous dehydration of sorbitol to prepare isosorbide remains both attractive and challenging. Summary of the Invention

[0005] The purpose of this invention is to provide a new process for the continuous dehydration of sorbitol to prepare isosorbitol, which aims to solve the problems of serious black residue formation and difficulty in continuous production in the current process of sorbitol dehydration to prepare isosorbitol.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A method for the continuous dehydration of sorbitol to prepare isosorbitol, the method comprising the following steps:

[0008] Step (1) involves dissolving solid sorbitol in a solvent to prepare a sorbitol solution, wherein the mass concentration of sorbitol in the sorbitol solution is 0.05-2 g / mL, preferably 0.1-1.0 g / mL.

[0009] Step (2) uses a solid acid as a catalyst and heats the catalyst bed in the fixed-bed reactor to 90-180℃. The preheated sorbitol solution is continuously flowed through the catalyst bed to carry out a dehydration reaction to obtain sorbitol reaction liquid. The liquid hourly space velocity (LISH) is 0.1-10 h⁻¹. -1 .

[0010] Step (3) purifies and separates the sorbitol reaction solution obtained in step (2) to obtain isosorbide.

[0011] Furthermore, the solvent in step (1) includes an organic solvent or a mixture of water and an organic solvent, wherein water accounts for 0-90% of the solvent by mass.

[0012] Furthermore, the organic solvent is a polar aprotic organic solvent, including one or a mixture of several of dimethyl sulfoxide, diethyl sulfoxide, tetramethylene sulfoxide, sulfolane, 3-methylsulfolane, 2,4-dimethylsulfolane, dimethyl sulfone, and diethyl sulfone. Preferably, the organic solvent is one or more of dimethyl sulfoxide, diethyl sulfoxide, sulfolane, 3-methylsulfolane, and 2,4-dimethylsulfolane.

[0013] Furthermore, the solid acid catalyst in step (2) is one or more of the following: supported heteropolyacid, acidic ion exchange resin, perfluorosulfonic acid resin, sulfated metal oxide, alumina, metal composite oxide, carbon-based solid acid, and molecular sieve.

[0014] Furthermore, step (3) specifically involves:

[0015] In step (3.1), the organic solvent is extracted: the sorbitol reaction solution obtained in step (2) is added to an aromatic solvent at 0-100℃ to extract the organic solvent from the sorbitol reaction solution. The volume ratio of the organic solvent to the aromatic hydrocarbon is 1:1-1:10, and the extraction is performed 2-6 times. After extraction, crude isosorbitol in a molten state is obtained. The aromatic hydrocarbon is one or more of toluene, xylene, p-xylene, m-xylene, o-xylene, 1,2,4-trimethylbenzene, and ethylbenzene.

[0016] Step (3.2), decolorization reaction: The crude isosorbide obtained in step (1) is dissolved in an alcohol solvent, wherein the volume ratio of the alcohol solvent to the crude isosorbide is 1:1-10:1. The solution obtained above is decolorized using activated carbon, with the amount of activated carbon used being 5-20 wt% of the crude product mass. The alcohol solvent is one or more of ethanol, methanol, and isopropanol, preferably ethanol or methanol.

[0017] In step (3.3), crystallization and purification: the activated carbon, alcohol solvent and water in step (2) are removed by filtration and rotary evaporation to obtain a viscous substance, which is then crystallized and separated using ethyl acetate to obtain isosorbide.

[0018] The beneficial effects of this invention are as follows:

[0019] (1) The present invention uses polar aprotic organic solvents such as dimethyl sulfoxide and sulfolane to dissolve sorbitol, which increases the fluidity of the sorbitol reaction solution and thus realizes the continuous dehydration of sorbitol to produce isosorbitol.

[0020] (2) The present invention uses a fixed-bed reactor and a solid acid catalyst. The high-boiling-point organic solvent used has high stability in the high-temperature acidic reaction environment, with few side reactions and good stability of the acid catalyst.

[0021] (3) The present invention has a low dehydration reaction temperature, a high sorbitol conversion rate, a significant reduction in the black residues produced during the reaction, and high selectivity for isosorbitol.

[0022] (4) This invention utilizes the differences in solubility of polyhydroxy compounds and dimethyl sulfoxide, sulfolane, etc. in aromatic hydrocarbons. In the separation of isosorbide, a high-boiling-point organic solvent added in the aromatic hydrocarbon extraction and dehydration reaction stage is used, which consumes less energy and has a good separation effect. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the continuous flow reactor used in the sorbitol dehydration reaction in Example 1.

[0024] Figure 2 The image shows the HPLC spectrum of isosorbide crystals isolated in Example 2. Detailed Implementation

[0025] The present invention is described in detail below with reference to the embodiments. The embodiments are implemented based on the technical solution of the present invention, and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0026] Example 1

[0027] Sorbitol was dissolved in 3-methylcyclobutane to prepare a 50 mL sorbitol solution with a concentration of 1.0 g / mL. A perfluorosulfonic acid resin catalyst was added to a fixed-bed reactor, and the catalyst bed was heated to 120 °C. The prepared sorbitol solution was continuously flowed through the catalyst bed of the fixed-bed reactor using a constant flow pump to carry out a dehydration reaction, yielding a sorbitol reaction solution. The liquid hourly space velocity (LISH) was 0.25 h⁻¹. -1 See attached process. Figure 1 The conversion rate of sorbitol was 71%, the selectivity of isosorbitol was 56%, and the main byproduct was 1,4-dehydrated sorbitol. The isosorbitol separation steps are as follows:

[0028] (1) The obtained reaction solution was extracted with toluene at 20°C. The volume ratio of toluene to 3-methylcyclobutane was 1:5. 150 mL of toluene was extracted in 4 portions. The lower layer was the crude isosorbide product in molten state.

[0029] (2) Dissolve the crude isosorbide obtained in step (1) in ethanol at a volume ratio of 1:1, with 25 mL of ethanol. Then add 5 wt% activated carbon for decolorization to obtain a nearly colorless reaction solution.

[0030] (3) Crystallization and purification: The activated carbon, ethanol and water in step (2) are removed by filtration and rotary evaporation to obtain a viscous substance, which is then crystallized and separated using ethyl acetate to obtain isosorbide.

[0031] Example 2

[0032] Sorbitol was dissolved in sulfolane to prepare a 50 mL solution with a concentration of 0.2 g / mL. An acidic ion exchange resin catalyst, specifically Amberlyst-36 acidic ion exchange resin, was added to a fixed-bed reactor. The catalyst bed was heated to 130 °C. The prepared sorbitol solution was continuously flowed through the catalyst bed of the fixed-bed reactor using a constant flow pump to carry out a dehydration reaction, yielding a sorbitol reaction solution. The liquid hourly space velocity (LISH) was 1.2 h⁻¹. -1 The conversion rate of sorbitol was greater than 99%, the selectivity of isosorbitol was 76%, and the main byproduct was 1,4-dehydrated sorbitol. The isosorbitol separation steps are as follows:

[0033] (1) The obtained reaction solution was extracted with 1,2,4-trimethylbenzene at 80℃ to remove sulfolane. The volume ratio of p-xylene to sulfolane was 1:10. 300 mL of 1,2,4-trimethylbenzene was used. The extraction was performed in two portions. The lower layer was the crude isosorbide product in molten state.

[0034] (2) The crude isosorbide obtained in step (1) was dissolved in methanol at a volume ratio of 5:1, with 70 mL of methanol. Then 20 wt% activated carbon was added for decolorization to obtain a nearly colorless reaction solution.

[0035] (3) Crystallization and purification: The activated carbon, methanol and water in step (2) were removed by filtration and rotary evaporation to obtain a viscous substance, which was then crystallized and separated using ethyl acetate to obtain isosorbide.

[0036] Example 3

[0037] Sorbitol was dissolved in diethyl sulfone (H₂O = 0.1 by mass) to prepare a 50 mL sorbitol solution with a concentration of 0.05 g / mL. A molecular sieve catalyst, specifically H-β molecular sieve, was added to a fixed-bed reactor. The catalyst bed was heated to 160 °C, and the prepared sorbitol solution was continuously flowed through the catalyst bed of the fixed-bed reactor using a constant flow pump to carry out a dehydration reaction, yielding a sorbitol reaction solution. The liquid hourly space velocity (LISH) was 10.0 h⁻¹. -1 The sorbitol conversion rate was greater than 99%, the isosorbitol selectivity was 86%, and the main byproduct was 1,4-dehydrated sorbitol. The isosorbitol separation steps are as follows:

[0038] (1) The obtained reaction solution was extracted with ethylbenzene at 40°C to remove diethyl sulfone. The volume ratio of ethylbenzene to diethyl sulfone was 1:5, with 150 mL of ethylbenzene added. The extraction was performed in 4 portions. The lower layer was the crude isosorbide product in molten state.

[0039] (2) Dissolve the crude isosorbide obtained in step (1) in methanol at a volume ratio of 2:1, with 5 mL of methanol. Then add 10 wt% activated carbon for decolorization to obtain a nearly colorless reaction solution.

[0040] (3) Crystallization and purification: The activated carbon, methanol and water in step (2) were removed by filtration and rotary evaporation to obtain a viscous substance, which was then crystallized and separated using ethyl acetate to obtain isosorbide.

[0041] Example 4

[0042] The reaction process and operation were the same as in Example 2, except that dimethyl sulfone was used instead of sulfolane as the organic solvent. The conversion rate of sorbitol was greater than 99%, the selectivity of isosorbitol was 72%, and the main byproduct was 1,4-dehydrated sorbitol.

[0043] Example 5

[0044] The reaction process and operation were the same as in Example 3, except that the solid acid catalyst was replaced with a supported heteropolyacid silver phosphotungstic acid instead of the H-β molecular sieve. The sorbitol conversion was greater than 99%, the isosorbitol selectivity was 87%, and the main byproduct was 1,4-dehydrated sorbitol.

[0045] Example 6

[0046] Sorbitol was dissolved in dimethyl sulfoxide to prepare a 50 mL sorbitol solution with a concentration of 1.5 g / mL. A carbon-based solid acid catalyst, specifically cellulose carbon-based solid acid (CCS), was added to a fixed-bed reactor. The catalyst bed was heated to 150 °C, and the prepared sorbitol solution was continuously flowed through the catalyst bed of the fixed-bed reactor using a constant flow pump to carry out a dehydration reaction to obtain a sorbitol reaction solution. The liquid hourly space velocity (LISH) was 3.0 h⁻¹. -1 The sorbitol conversion rate was greater than 99%, the isosorbitol selectivity was 81%, and the main byproduct was 1,4-dehydrated sorbitol. The isosorbitol separation steps are as follows:

[0047] (1) The obtained reaction solution was extracted with m-xylene at 100℃ to extract dimethyl sulfoxide. The volume ratio of m-xylene to dimethyl sulfoxide was 1:1. 30 mL of m-xylene was extracted in 6 times. The lower layer was the crude isosorbide product in molten state.

[0048] (2) Dissolve the crude isosorbide obtained in step (1) in isopropanol, with a volume ratio of isopropanol to crude product of 10:1, wherein 600 mL of isopropanol is added. Then, 6 wt% activated carbon is added for decolorization treatment to obtain a nearly colorless reaction solution.

[0049] (3) Crystallization and purification: The activated carbon, isopropanol and water in step (2) are removed by filtration and rotary evaporation to obtain a viscous substance. Isosorbide is obtained by crystallization using ethyl acetate.

[0050] Example 7

[0051] Sorbitol was dissolved in 2,4-dimethylcyclobutane sulfolane (H₂O 0.9% of solvent by mass) to prepare a 50 mL sorbitol solution with a concentration of 0.5 g / mL. A molecular sieve catalyst, specifically HZSM-5 molecular sieve, was added to a fixed-bed reactor. The catalyst bed was heated to 140 °C, and the prepared sorbitol solution was continuously flowed through the catalyst bed of the fixed-bed reactor using a constant flow pump to carry out a dehydration reaction, yielding a sorbitol reaction solution. The liquid hourly space velocity (LISH) was 6.0 h⁻¹. -1 The sorbitol conversion rate was 86%, the isosorbitol selectivity was 69%, and the main byproduct was 1,4-dehydrated sorbitol. The isosorbitol separation steps are as follows:

[0052] (1) The obtained reaction solution was extracted with o-xylene at 0℃ to extract 2,4-dimethylcyclobutane. The volume ratio of o-xylene to 2,4-dimethylcyclobutane was 1:1. 30 mL of o-xylene was extracted in 6 portions. The lower layer was the crude isosorbide product in molten state.

[0053] (2) The crude isosorbide obtained in step (1) was dissolved in methanol at a volume ratio of 8:1, with 150 mL of methanol. Then 15 wt% activated carbon was added for decolorization to obtain a nearly colorless reaction solution.

[0054] (3) Crystallization and purification: The activated carbon, methanol and water in step (2) were removed by filtration and rotary evaporation to obtain a viscous substance, which was then crystallized and separated using ethyl acetate to obtain isosorbide.

[0055] Example 8

[0056] Sorbitol was dissolved in tetramethylene sulfoxide (H₂O = 0.5 by mass) to prepare a 50 mL sorbitol solution with a concentration of 2.0 g / mL. A metal oxide catalyst, specifically phosphoric acid-modified Nb₂O₅, was added to a fixed-bed reactor. The catalyst bed was heated to 180 °C, and the prepared sorbitol solution was continuously flowed through the catalyst bed of the fixed-bed reactor using a constant flow pump to carry out a dehydration reaction, yielding a sorbitol reaction solution. The liquid hourly space velocity (LISH) was 0.1 h⁻¹. -1The sorbitol conversion rate was greater than 99%, the isosorbitol selectivity was 83%, and the main byproduct was 1,4-dehydrated sorbitol. The isosorbitol separation steps are as follows:

[0057] (1) Add o-xylene to the obtained reaction solution at 60°C to extract tetramethylene sulfoxide. The volume ratio of o-xylene to tetramethylene sulfoxide is 1:5. The o-xylene is 150 mL. The extraction is carried out in 3 times. The lower layer is the crude isosorbide product in molten state.

[0058] (2) Dissolve the crude isosorbide obtained in step (1) in ethanol, with a volume ratio of ethanol to crude product of 6:1, wherein 500 mL of ethanol is used. Then add 8 wt% activated carbon for decolorization treatment to obtain a nearly colorless reaction solution.

[0059] (3) Crystallization and purification: The activated carbon, ethanol and water in step (2) are removed by filtration and rotary evaporation to obtain a viscous substance, which is then crystallized and separated using ethyl acetate to obtain isosorbide.

[0060] Example 9

[0061] Sorbitol was dissolved in 2,4-dimethylcyclobutane sulfone to prepare a 250 mL sorbitol solution with a concentration of 0.5 g / mL. An acidic ion exchange resin catalyst, specifically Amberlyst-15 acidic ion exchange resin, was added to a fixed-bed reactor. The catalyst bed was heated to 140 °C. The prepared sorbitol solution was continuously flowed through the catalyst bed of the fixed-bed reactor using a constant flow pump to carry out a dehydration reaction, yielding a sorbitol reaction solution. The liquid hourly space velocity (LISH) was 0.5 h⁻¹. -1 It runs continuously for 24 hours, and samples are taken for analysis every 6 hours.

[0062] Sampling and analysis were performed at 6h, 12h, 18h, and 24h. HPLC analysis showed that the sorbitol conversion rate was greater than 99%, and the isosorbitol selectivity was 88%, 87%, 87%, and 86%, respectively, indicating that the catalyst has good stability.

[0063] The above embodiments are merely illustrative of the implementation methods of the present invention, but should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the protection scope of the present invention.

Claims

1. A method for the continuous dehydration of sorbitol to prepare isosorbide, characterized in that, The method includes the following steps: Step (1): Dissolve solid sorbitol in a solvent to prepare a sorbitol solution; Step (2) uses a solid acid as a catalyst and heats the catalyst bed in the fixed-bed reactor to 90-180°C. The preheated sorbitol solution is continuously flowed through the catalyst bed to carry out a dehydration reaction to obtain a sorbitol reaction solution. The liquid volume hourly space velocity is 0.1-10 h⁻¹. -1 ; Step (3) purifies and separates the sorbitol reaction solution obtained in step (2) to obtain isosorbide.

2. The method for the continuous dehydration of sorbitol to prepare isosorbide according to claim 1, characterized in that, In step (1), the mass concentration of sorbitol in the sorbitol solution is 0.05-2 g / mL.

3. The method for the continuous dehydration of sorbitol to prepare isosorbide according to claim 1, characterized in that, The preferred mass concentration of sorbitol in the sorbitol solution in step (1) is 0.1-1.0 g / mL.

4. The method for the continuous dehydration of sorbitol to prepare isosorbide according to claim 1, characterized in that, The solvent in step (1) includes an organic solvent or a mixture of water and an organic solvent. When it is a mixture of water and an organic solvent, the water accounts for 0-90% of the solvent by mass.

5. The method for the continuous dehydration of sorbitol to prepare isosorbide according to claim 4, characterized in that, The organic solvent is a polar aprotic organic solvent, including one or a mixture of several of dimethyl sulfoxide, diethyl sulfoxide, tetramethylene sulfoxide, sulfolane, 3-methylsulfolane, 2,4-dimethylsulfolane, dimethyl sulfone, and diethyl sulfone.

6. The method for continuous dehydration of sorbitol to prepare isosorbide according to claim 5, characterized in that, The organic solvent is preferably one or more of dimethyl sulfoxide, diethyl sulfoxide, sulfolane, 3-methylsulfolane, and 2,4-dimethylsulfolane.

7. The method for the continuous dehydration of sorbitol to prepare isosorbide according to claim 1, characterized in that, The solid acid catalyst in step (2) is one or more of the following: supported heteropolyacid, acidic ion exchange resin, perfluorosulfonic acid resin, sulfated metal oxide, alumina, metal composite oxide, carbon-based solid acid, and molecular sieve.

8. The method for the continuous dehydration of sorbitol to prepare isosorbide according to claim 1, characterized in that, Step (3) includes extraction of organic solvent, decolorization reaction, and crystallization purification, specifically as follows: In step (3.1), the organic solvent is extracted: the sorbitol reaction solution obtained in step (2) is added to the organic solvent in the sorbitol reaction solution at 0-100℃, the volume ratio of organic solvent to aromatic hydrocarbon is 1:1-1:10, and the extraction is performed multiple times. After extraction, the crude isosorbitol product in molten state is obtained. In step (3.2), the decolorization reaction is as follows: the crude isosorbide product obtained in step (1) is dissolved in an alcohol solvent, wherein the volume ratio of the alcohol solvent to the crude isosorbide product is 1:1-10:1; the solution obtained above is decolorized using activated carbon. In step (3.3), crystallization and purification: the activated carbon, alcohol solvent and water in step (2) are removed by filtration and rotary evaporation to obtain a viscous substance, which is then crystallized and separated using ethyl acetate to obtain isosorbide.

9. The method for the continuous dehydration of sorbitol to prepare isosorbide according to claim 8, characterized in that, In step (3.1), the aromatic hydrocarbon is one or more of toluene, xylene, p-xylene, m-xylene, o-xylene, 1,2,4-trimethylbenzene, and ethylbenzene; in step (3.2), the alcohol solvent is one or more of ethanol, methanol, and isopropanol, preferably ethanol or methanol.

10. The method for the continuous dehydration of sorbitol to prepare isosorbitol according to claim 8, characterized in that, The amount of activated carbon used is 5-20 wt% of the crude isosorbide product.

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