阅读说明：本技术 一种固体酸催化剂的制备方法及其应用 (Preparation method and application of solid acid catalyst ) 是由 景金磊 谢伦嘉 杜超 贺黎明 李伟 王瑞璞 曾佳 刘青 于 2019-08-30 设计创作，主要内容包括：本发明涉及一种固体酸催化剂的制备方法及山梨醇脱水制备异山梨醇的方法,所述固体酸催化剂的制备方法包括如下步骤：S1：将铌源和硫源混合得混合物A；S2：焙烧步骤S1所得的混合物A,得到所述固体酸催化剂。所述固体酸催化剂能够在无溶剂、减压和温和条件下较高效的催化山梨醇转化为异山梨醇。该催化剂具有制备工艺及再生程序简单、原料廉价易得和稳定性好等特点,且易于从反应产物中分离回收和重复使用,具有很强的可操作性和经济实用性。(The invention relates to a preparation method of a solid acid catalyst and a method for preparing isosorbide by dehydrating sorbitol, wherein the preparation method of the solid acid catalyst comprises the following steps: s1: mixing a niobium source and a sulfur source to obtain a mixture A; s2: and roasting the mixture A obtained in the step S1 to obtain the solid acid catalyst. The solid acid catalyst can efficiently catalyze the conversion of sorbitol into isosorbide under the conditions of no solvent, reduced pressure and mild conditions. The catalyst has the characteristics of simple preparation process and regeneration procedure, cheap and easily-obtained raw materials, good stability and the like, is easy to separate, recycle and reuse from reaction products, and has strong operability and economic practicability.)

1. A preparation method of a solid acid catalyst comprises the following steps:

s1: mixing a niobium source and a sulfur source to obtain a mixture A;

s2: and roasting the mixture A obtained in the step S1 to obtain the solid acid catalyst.

2. The method according to claim 1, wherein the niobium source is selected from one or more of niobium oxide, niobium chloride, niobium oxalate and sodium niobate, preferably from one or more of niobium oxide and niobium chloride.

3. A method according to claim 1 or 2, wherein the sulphur source is selected from one or more of sulphuric acid, ammonium sulphate, sodium sulphate and potassium sulphate, preferably from one or more of sulphuric acid and ammonium sulphate.

4. The method according to any one of claims 1 to 3, wherein the molar ratio of the sulfur element in the sulfur source to the niobium element in the niobium source is (0.05-4):1, preferably (0.2-3):1, more preferably (1.2-2): 1.

5. The method according to any one of claims 1 to 4, wherein the mixing in step S1 is at a temperature of 20 to 150 ℃ and for a time of 20 to 45 hours, preferably wherein the mixing is carried out in a plurality of stages, preferably two stages, more preferably wherein the first stage mixing is at a temperature of 20 to 40 ℃ and for a time of 15 to 30 hours and the second stage mixing is at a temperature of 60 to 150 ℃, preferably 80 to 100 ℃ and for a time of 5 to 15 hours.

6. The method according to any one of claims 1 to 5, wherein the temperature of the roasting in step S2 is 200-900 ℃, preferably 350-600 ℃, and more preferably 400-550 ℃; and/or the roasting time is 2-10h, preferably 3-6 h.

7. A process for preparing isosorbide by dehydration of sorbitol, comprising reacting sorbitol in the presence of a catalyst prepared by the process of any one of claims 1 to 6 to form isosorbide.

8. The process according to claim 7, characterized in that the mass of the catalyst is 5-20 wt.%, preferably 8-15 wt.%, more preferably 9-13 wt.% of the mass of sorbitol.

9. The process according to claim 7 or 8, characterized in that the reaction is carried out in two stages, preferably the reaction temperature in the first stage is 130-180 ℃, preferably 150-175 ℃, more preferably 155-170 ℃, the reaction time is 0.2-0.8h, and the reaction pressure is normal pressure; and/or the presence of a gas in the gas,

the reaction temperature of the second stage is 130-180 ℃, preferably 150-175 ℃, more preferably 155-170 ℃, the reaction time is 1-12h, preferably 2-6h, the reaction pressure is 30-300mbar, preferably 30-100mbar, more preferably, the reaction temperatures of the two stages are the same.

10. Use of a catalyst prepared according to the process of any one of claims 1 to 6 or the process of any one of claims 7 to 9 for the synthesis of isosorbide.

Technical Field

The invention relates to a preparation method of a solid acid catalyst and application thereof in synthesizing isosorbide by dehydrating sorbitol, belonging to the technical field of solid acid catalysis.

Background

Sorbitol is derivatized through dehydration and hydrogenolysis to obtain a series of high-added-value bio-based chemicals, and isosorbide is diol derivatized through secondary dehydration of sorbitol.

The compound is used as a bio-based platform compound, has application in many fields based on the special structural characteristics (rigid molecular structure and chiral center) of the compound, can be used as a substitute of a plurality of petroleum compounds, has wide sorbitol source, and has important significance in the context of green chemistry. Isosorbide has been used in many synthetic fields to date, for example isosorbide dinitrate has been used as a vasodilator for decades; dimethyl isosorbide is used as a solvent in cosmetics; isosorbide diesters are used as surfactants and PVC plasticizers; producing polycarbonates, epoxies, polyesters, polyamides, and the like. Particularly, in the polycarbonate synthesis, the method has important significance for opening the downstream market by replacing toxic isosorbide type polycarbonate with excellent bisphenol A synthesis performance on a large scale, and the production of isosorbide is greatly increased in the foreseeable future.

The dehydration of sorbitol to produce isosorbide is mainly acid catalyzed, and the traditional production of isosorbide uses liquid acids as catalysts, such as sulfuric acid, hydrochloric acid, phosphoric acid, p-toluenesulfonic acid, and the like. Although the catalytic activity of the liquid catalyst, particularly concentrated sulfuric acid, is very high, the separation of various byproducts and oligomers generated by the reaction is complex, the equipment corrosion is serious, the production cost is increased, the large-scale industrial application is not facilitated, and the green chemical requirement is not met.

Aiming at various defects of the liquid acid catalyst, numerous researchers report the research of the solid acid catalyst in the preparation of isosorbide through sorbitol dehydration, domestic patents on the production of isosorbide by using sorbitol are not numerous, and the research on the application of insoluble heteropoly acid, metal phosphate, mixed metal oxide, polymer type solid acid and the like in sorbitol dehydration is more.

Chinese patent CN107141301 discloses a method for preparing isosorbide by catalyzing sorbitol with insoluble heteropolyacid salt as a catalyst, wherein the reaction temperature is 170-230 ℃. The yield of the isosorbide obtained by the method can reach over 75 percent, but the stability is slightly poor, and the yield is obviously reduced after the regeneration and the repeated use.

Chinese patent CN108690039 discloses a WO₃/ZrO₂Or MoO₃/ZrO₂The method for preparing the isosorbide by catalyzing the dehydration of the sorbitol by the catalyst has the reaction temperature of 170-230 ℃. The yield of the isosorbide obtained by the method is over 72 percent, and after the isosorbide is repeatedly used for 3 times, the yield is obviously reduced.

In summary, the problems of poor catalytic activity, particularly poor selectivity, high reaction temperature, long reaction time, large proportion of by-products, high price, easy inactivation and the like of the existing solid acid catalyst also objectively exist, which directly causes the high price of the isosorbide in the market, thereby limiting the large-scale application of the isosorbide. Therefore, the development of efficient, green and economic catalysts and processes has been a difficult point in the research of preparing isosorbide by dehydrating sorbitol.

Disclosure of Invention

In order to solve the problems in the prior art, the invention provides a preparation method of a solid acid catalyst in a first aspect. The solid acid catalyst prepared by the method has the advantages of simple preparation process and regeneration procedure, cheap and easily obtained raw materials, easy separation and recovery from reaction products, good stability and the like.

In a second aspect of the invention, a method for preparing isosorbide by dehydration of sorbitol is provided.

According to a first aspect of the present invention, there is provided a process for the preparation of a solid acid catalyst, the process comprising the steps of:

s1: mixing a niobium source and a sulfur source to obtain a mixture A;

s2: and roasting the mixture A obtained in the step S1 to obtain the solid acid catalyst.

According to some preferred embodiments of the present invention, the preparation of the solid acid catalyst comprises the steps of:

1) preparing a sulfur source solution;

2) mixing a niobium source and a sulfur source solution in proportion, stirring for 15-30h at room temperature in a container, heating and stirring for 5-15h, transferring to a crucible, and roasting for 3-6h in a muffle furnace;

3) and after the muffle furnace is cooled to a certain temperature, taking out the crucible, grinding the cake-shaped material in the crucible into powder to obtain the catalyst, and putting the catalyst into a reagent bottle for later use.

According to some embodiments of the invention, the niobium source is selected from one or more of niobium oxide, niobium chloride, niobium oxalate and sodium niobate.

According to some embodiments of the invention, the niobium source is selected from one or more of niobium oxide and niobium chloride.

According to some embodiments of the invention, the source of sulfur is selected from one or more of sulfuric acid, ammonium sulfate, sodium sulfate and potassium sulfate.

According to some embodiments of the invention, the source of sulphur is selected from one or more of sulphuric acid and ammonium sulphate.

According to some embodiments of the present invention, the molar ratio of the sulfur element in the sulfur source to the niobium element in the niobium source is (0.05-4):1, preferably (0.2-2):1, and more preferably (1.2-2): 1.

According to some embodiments of the present invention, the mixing in step S1 is performed at a temperature of 20 to 150 ℃ for a time of 20 to 45 hours.

According to some embodiments of the invention, the mixing is performed in a plurality of stages, preferably two stages.

According to some embodiments of the invention, the first stage mixing is at a temperature of 20-40 ℃ for a period of 15-30 hours and the second stage mixing is at a temperature of 60-150 ℃, preferably 80-100 ℃ for a period of 5-15 hours, and the mixing is first carried out at a lower temperature so that the sulfur source and niobium source are thoroughly mixed under mild conditions, and then the temperature is raised to increase the evaporation rate of the water so that the water is removed as much as possible so that it does not splash during firing.

According to some embodiments of the present invention, the temperature of the calcination in step S2 is 200-900 deg.C, preferably 350-600 deg.C, and more preferably 400-550 deg.C.

According to some embodiments of the invention, the calcination time is 2 to 10 hours, preferably 3 to 6 hours.

According to a second aspect of the present invention, there is provided a process for the preparation of isosorbide by dehydration of sorbitol, said process comprising reacting sorbitol in the presence of a catalyst prepared by the above process to form isosorbide.

According to some embodiments of the invention, the method for preparing isosorbide by dehydration of sorbitol comprises: in the presence of a catalyst, sorbitol shown as a formula (I) is dehydrated twice to synthesize isosorbide shown as a formula (II), and the catalyst is a solid acid catalyst of sulfur element modified niobium oxide.

According to some embodiments of the invention, the mass of the catalyst is 5 to 20 wt%, preferably 8 to 15 wt%, more preferably 9 to 13 wt% of the mass of sorbitol.

According to some embodiments of the invention, the reaction is carried out in two stages.

According to some embodiments of the invention, the temperatures of the two reaction stages are the same.

According to some embodiments of the present invention, the reaction temperature in the first stage is 130-;

according to some embodiments of the present invention, the reaction temperature in the second stage is 130-.

In some preferred embodiments of the invention, the primary purpose of the first stage is to melt the solid sorbitol to avoid the loss of sorbitol by direct vacuum which would draw some of the sorbitol powder away.

According to some embodiments of the invention, the method for preparing isosorbide by dehydration of sorbitol comprises: adding sorbitol powder and catalyst into a reactor, heating, reacting under the conditions of no solvent and reduced pressure, wherein the vacuum pumping is carried out after heating for 0.5 h. The catalyst dosage is 5-20 wt%, the reaction temperature is 130-.

The method for preparing isosorbide by dehydrating sorbitol has good selectivity; can catalyze the dehydration of the sorbitol to prepare the isosorbide with high efficiency under relatively mild reaction conditions.

Compared with other used catalysts, the sulfur element modified niobium oxide solid acid catalyst provided by the invention has the advantages that the preparation process and the regeneration process are very simple, the catalyst can be regenerated only by simply heating and drying the catalyst, the used raw materials are low in price and easy to obtain, the catalyst is easy to separate, recover and reuse from reaction products, the stability is good, meanwhile, the catalyst can also be used for preparing isosorbide through reactive distillation, and the catalyst has important application value when being used for preparing isosorbide through sorbitol dehydration.

According to some embodiments of the present invention, the reaction conditions for the reactive distillation to produce isosorbide are preferably such that the reaction conditions include: the polymer solution is liquid polyalcohol, the catalyst consumption is 10 wt%, and the reaction temperature is 140 ℃ and 240 ℃.

In a third aspect, the invention provides a solid acid catalyst prepared by the above method or the use of the above method in the synthesis of isosorbide.

Detailed Description

The following describes in detail specific embodiments of the present invention. It should be understood that the detailed description and specific examples, while indicating the present invention, are given by way of illustration and explanation only, not limitation. It is also to be understood that the reference to method steps and data associated therewith in this embodiment does not exclude the interposition of other combinations of method steps and proportions of data, and the endpoints and any values of the ranges disclosed herein are not limited to the precise range or value, and such ranges or values are to be understood as encompassing values close to these ranges or values and are to be considered as the scope of the practice of the invention.

For the description of the examples, the chemicals involved, if not specified, are commercially available from chemical companies. The reaction product was detected by high performance liquid chromatography (LC1100) using Hi-Plex H as column, differential refractive index detector (1260RID) as detector, water as mobile phase, flow rate 0.60mL/min, column temperature 60 ℃.

Example 1

Drying the Nb₂O₅Mixing with diluted concentrated sulfuric acid (4mol/L) according to the molar ratio of sulfur to niobium atoms of 1.4:1, stirring at room temperature for 20 hours, heating and stirring for 12 hours, putting into a muffle furnace for roasting at the roasting temperature of 450 ℃, cooling, taking out, and grinding into powder for later use, wherein the catalyst is recorded as R1.

Example 2

Adding 6.00g of sorbitol and 0.30g of the catalyst R1 obtained in example 1 into a three-necked flask, heating and stirring at 150 ℃, reacting under the conditions of no solvent and reduced pressure, vacuumizing after 0.5h, reacting at the pressure of 60mbar for 3h, cooling to room temperature, and performing catalyst separation and product analysis to obtain the isosorbide yield of 5.10%.

Example 3

Adding 6.00g of sorbitol powder and 0.60g of the catalyst R1 obtained in example 1 into a three-necked flask, heating and stirring at 150 ℃, reacting under the conditions of no solvent and reduced pressure, vacuumizing after 0.5h, reacting at the pressure of 60mbar for 3h, cooling to room temperature, and performing catalyst separation and product analysis to obtain the isosorbide yield of 39.71%.

Example 4

Adding 6.00g of sorbitol and 0.60g of the catalyst R1 obtained in example 1 into a three-necked flask, heating and stirring at 160 ℃, reacting under the conditions of no solvent and reduced pressure, vacuumizing after 0.5h, reacting at 60mbar for 3h, cooling to room temperature, and performing catalyst separation and product analysis to obtain the isosorbide yield of 63.29%.

Example 5

Adding 6.00g of sorbitol and 0.60g of the catalyst R1 obtained in example 1 into a three-necked flask, heating and stirring at 160 ℃, reacting under the conditions of no solvent and reduced pressure, vacuumizing after 0.5h, reacting at 60mbar for 4h, cooling to room temperature, and performing catalyst separation and product analysis to obtain the isosorbide yield of 72.01%.

Example 6

The catalyst of example 5 was recovered and dried (temperature 120 ℃ C., time 2 hours), and the stability evaluation was performed according to the isosorbide preparation procedure of example 5, and the catalyst was recycled for 4 times, and the reaction results are shown in Table 1.

Table 1 stability evaluation results of catalysts

Example 7

Drying the Nb₂O₅Mixing with ammonium sulfate at a molar ratio of sulfur to niobium atoms of 1.4:1, stirring at room temperature for 20h, heating and stirring for 12h, placing into a muffle furnace for roasting at 450 deg.C for 4h, cooling, taking out, and grinding into powder.

Adding 6.00g of sorbitol powder and 0.60g of the obtained catalyst into a three-necked bottle, heating and stirring at 160 ℃, reacting under the conditions of no solvent and reduced pressure, vacuumizing after 0.5h, performing reaction at a reaction pressure of 60mbar for 4h, cooling to room temperature, performing catalyst separation and product analysis, and obtaining the yield of the isosorbide of 4.26%.

Example 8

NbCl₅Mixing with ammonium sulfate at a molar ratio of sulfur to niobium atoms of 1.4:1, adding an appropriate amount of deionized water, stirring at room temperature for 20h, heating and stirring for 12h, placing into a muffle furnace for roasting at 450 ℃ for 4h, cooling, taking out, and grinding into powder for later use.

Adding 6.00g of sorbitol powder and 0.60g of the obtained catalyst into a three-necked bottle, heating and stirring at 150 ℃, reacting under the conditions of no solvent and reduced pressure, vacuumizing after 0.5h, performing reaction at a reaction pressure of 60mbar for 4h, cooling to room temperature, performing catalyst separation and product analysis, and obtaining the yield of isosorbide of 6.35%.

Example 9

NbCl₅Mixing with sulfuric acid at a molar ratio of sulfur to niobium atoms of 1.4:1, adding a proper amount of deionized water, stirring at room temperature for 20h, heating and stirring for 12h, placing into a muffle furnace for roasting at 450 ℃ for 4h, cooling, taking out, and grinding into powder for later use.

Adding 6.00g of sorbitol powder and 0.60g of the obtained catalyst into a three-necked bottle, heating and stirring at 150 ℃, reacting under the conditions of no solvent and reduced pressure, vacuumizing after 0.5h, performing reaction at a reaction pressure of 60mbar for 4h, cooling to room temperature, performing catalyst separation and product analysis, and obtaining the isosorbide yield of 9.84%.

Example 10

Adding 6.00g of sorbitol and 0.48g of the catalyst R1 obtained in example 1 into a three-necked flask, heating and stirring at 150 ℃, reacting under the conditions of no solvent and reduced pressure, vacuumizing after 0.5h, reacting at the pressure of 60mbar for 3h, cooling to room temperature, and performing catalyst separation and product analysis to obtain the isosorbide yield of 21.31%.

Example 11

Adding 6.00g of sorbitol and 0.90g of the catalyst R1 obtained in example 1 into a three-necked flask, heating and stirring at 150 ℃, reacting under the conditions of no solvent and reduced pressure, vacuumizing after 0.5h, reacting at the pressure of 60mbar for 3h, cooling to room temperature, and performing catalyst separation and product analysis to obtain the isosorbide yield of 40.27%.

Example 12

Adding 6.00g of sorbitol and 0.60g of the catalyst R1 obtained in example 1 into a three-necked flask, heating and stirring at 160 ℃, reacting under the conditions of no solvent and reduced pressure, vacuumizing after 0.5h, reacting at 60mbar for 1h, cooling to room temperature, and performing catalyst separation and product analysis to obtain the isosorbide yield of 6.41%.

Example 13

Adding 6.00g of sorbitol and 0.60g of the catalyst R1 obtained in example 1 into a three-necked flask, heating and stirring at 160 ℃, reacting under the conditions of no solvent and reduced pressure, vacuumizing after 0.5h, reacting at 60mbar for 8h, cooling to room temperature, and performing catalyst separation and product analysis to obtain the isosorbide yield of 65.56%.

Example 14

Adding 6.00g of sorbitol and 0.60g of the catalyst R1 obtained in example 1 into a three-necked flask, heating and stirring at 120 ℃, reacting under the conditions of no solvent and reduced pressure, vacuumizing after 0.5h, cooling to room temperature under the reaction pressure of 60mbar for 3h, and carrying out catalyst separation and product analysis, wherein the reaction is basically absent at the temperature.

Example 15

Adding 6.00g of sorbitol and 0.60g of the catalyst R1 obtained in example 1 into a three-necked flask, heating and stirring at 180 ℃, reacting under the conditions of no solvent and reduced pressure, vacuumizing after 0.5h, reacting at the pressure of 60mbar for 3h, cooling to room temperature, and performing catalyst separation and product analysis to obtain the isosorbide yield of 54.61%.

Example 16

The procedure of example 1 was followed, wherein the calcination temperature was 350 ℃, 6.00g of sorbitol and 0.60g of the catalyst obtained in this example were added to a three-necked flask, the mixture was heated and stirred at 160 ℃, the reaction was carried out under solvent-free and reduced pressure conditions, after 0.5h, vacuum was applied at a reaction pressure of 60mbar and a reaction time of 3h, the mixture was cooled to room temperature, and the catalyst separation and product analysis were carried out, resulting in an isosorbide yield of 18.12%.

Example 17

The procedure of example 1 was followed, wherein the calcination temperature was 600 ℃, 6.00g of sorbitol and 0.60g of the catalyst obtained in this example were added to a three-necked flask, the mixture was heated and stirred at 160 ℃, the reaction was carried out under solvent-free and reduced pressure conditions, after 0.5h, vacuum was applied at a reaction pressure of 60mbar and a reaction time of 3h, the mixture was cooled to room temperature, and the catalyst separation and product analysis were carried out, resulting in an isosorbide yield of 6.70%.

Example 18

According to the preparation procedure of the catalyst in example 1, wherein the molar ratio of sulfur to niobium atoms is 0.5:1, 6.00g of sorbitol and 0.60g of the catalyst obtained in the example are added into a three-necked flask, heated and stirred, the temperature is 160 ℃, the reaction is carried out under the conditions of no solvent and reduced pressure, after 0.5h, vacuum pumping is carried out, the reaction pressure is 60mbar, the reaction time is 3h, the reaction is cooled to room temperature, and the catalyst separation and product analysis are carried out, so that the yield of the isosorbide is 11.47%.

Example 19

According to the preparation procedure of the catalyst in example 1, wherein the molar ratio of sulfur to niobium atoms is 2:1, 6.00g of sorbitol and 0.60g of the catalyst obtained in the example are added into a three-neck flask, heated and stirred, the temperature is 160 ℃, the reaction is carried out under the conditions of no solvent and reduced pressure, after 0.5h, the vacuum pumping is carried out, the reaction pressure is 60mbar, the reaction time is 3h, the reaction is cooled to room temperature, and the catalyst separation and the product analysis are carried out, so that the yield of the isosorbide is 64.52%.

Example 20

According to the preparation procedure of the catalyst in example 1, wherein the molar ratio of sulfur to niobium atoms is 1:1, 6.00g of sorbitol and 0.60g of the catalyst obtained in the example are added into a three-necked flask, heated and stirred, the temperature is 160 ℃, the reaction is carried out under the conditions of no solvent and reduced pressure, after 0.5h, vacuum pumping is carried out, the reaction pressure is 60mbar, the reaction time is 3h, the reaction is cooled to room temperature, and the catalyst separation and product analysis are carried out, so that the yield of the isosorbide is 51.83%.

Example 21

According to the preparation procedure of the catalyst in example 1, wherein the molar ratio of sulfur to niobium atoms is 3:1, 6.00g of sorbitol and 0.60g of the catalyst obtained in the example are added into a three-necked flask, heated and stirred, the temperature is 160 ℃, the reaction is carried out under the conditions of no solvent and reduced pressure, after 0.5h, vacuum pumping is carried out, the reaction pressure is 60mbar, the reaction time is 3h, the reaction is cooled to room temperature, and the catalyst separation and product analysis are carried out, so that the yield of the isosorbide is 65.18%.

Example 22

The catalysts of the above examples 4, 19 and 21 were recovered and dried (temperature 120 ℃ C., time 2 hours), and the stability evaluation was performed according to the procedure for the preparation of isosorbide of example 4, and the reaction results were shown in Table 2 after recycling 2 times.

TABLE 2

COMPARATIVE EXAMPLE 1 (Sulfur-free)

Drying the Nb₂O₅And putting the mixture into a muffle furnace for roasting for 4 hours at the roasting temperature of 450 ℃, and taking out the mixture for standby after cooling, wherein the mark is D1.

Adding 6.00g of sorbitol powder and 0.60g of the obtained catalyst into a three-mouth bottle, heating and stirring, reacting at 160 ℃, under the conditions of no solvent and reduced pressure, vacuumizing after 0.5h, with the reaction pressure of 60mbar and the reaction time of 3h, cooling to room temperature, and carrying out catalyst separation and product analysis, wherein almost no reaction is carried out under the conditions.

Comparative example 2

According to the procedure for the preparation of the catalyst in example 1, in which sulfuric acid was changed to phosphoric acid, and the molar ratio of phosphorus to niobium atoms was 1.4:1, 6.00g of sorbitol and 0.60g of the catalyst obtained in this example were charged in a three-necked flask, heated and stirred, the temperature was 160 ℃ and the reaction was carried out under solvent-free and reduced pressure, after 0.5h, vacuum was applied, the reaction pressure was 60mbar and the reaction time was 3h, the reaction was cooled to room temperature, and the catalyst separation and product analysis were carried out, under which conditions almost no reaction occurred.

In conclusion, the solid acid catalyst prepared from the sulfur element modified niobium oxide provided by the invention can be used for efficiently catalyzing sorbitol to dehydrate under relatively mild reaction conditions to prepare isosorbide. The catalyst of the present invention has simple preparation process, facile material, stable catalytic activity, capacity of maintaining excellent catalytic performance after repeated use, simple regeneration process and high isosorbide yield up to 72%.

It should be noted that the above-mentioned embodiments are only for explaining the present invention, and do not set any limit to the present invention. The present invention has been described with reference to exemplary embodiments, but the words which have been used herein are words of description and illustration, rather than words of limitation. The invention can be modified, as prescribed, within the scope of the claims and without departing from the scope and spirit of the invention. Although the invention has been described herein with reference to particular means, materials and embodiments, the invention is not intended to be limited to the particulars disclosed herein, but rather extends to all other methods and applications having the same functionality.