Supported phosphotungstic acid catalyst as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of catalysts, and particularly relates to a supported phosphotungstic acid catalyst as well as a preparation method and application thereof. The preparation method of the supported phosphotungstic acid catalyst comprises the following steps: adding activated carbon with neutral pH into a mixed solution of a silanization reagent and phosphotungstic acid for dipping, maintaining for 2-3 hours at 150-200 DEG C under an anaerobic condition for curing, and cleaning the cured material to obtain the supported phosphotungstic acid catalyst, wherein the mass ratio of the silanization reagent to the phosphotungstic acid in the mixed solution is (1-4): (2-15), and the mass ratio of the activated carbon to the phosphotungstic acid is 20: (2-15). The supported phosphotungstic acid catalyst is applied to catalysis of sorbitol for synthesis of isosorbitol, silanization modification is beneficial to rapid discharge of water out of a reaction system, the final conversion rate of sorbitol is greater than 95%, the selectivity of isosorbitol is 75-90%, and the catalytic performance is not attenuated after 5 times of cycle use.

Description

Technical Field

[0001] This invention belongs to the field of catalyst technology, specifically relating to a supported phosphotungstic acid catalyst, its preparation method, and its application. Background Technology

[0002] Isosorbide is a chiral diol derived from sorbitol through bimolecular dehydration. As an important bio-based platform compound, it possesses a stable molecular structure, combining a rigid furan ring and an active hydroxyl group, exhibiting excellent biocompatibility, low toxicity, and good thermal stability. It is widely used in key application areas such as high-performance polymers, pharmaceuticals, cosmetics, and functional materials.

[0003] The most common industrial method for preparing isosorbide is through the catalytic dehydration of sorbitol using acidic catalysts, including solid acids and liquid inorganic acids. While liquid inorganic acid catalysts exhibit high catalytic activity, they also suffer from drawbacks such as environmental pollution, equipment corrosion, difficulty in separation from the homogeneous mixture of the catalyst and reaction products, and challenges in catalyst recycling. Common solid acid catalysts, such as molecular sieves, acidic oxides, and acidic resins, are also used in the dehydration reaction of sorbitol, but they all suffer from harsh reaction conditions, weak acidity, and low catalytic activity. Developing strongly acidic heterogeneous catalysts is currently a hot topic and a challenge in isosorbide research.

[0004] From an acidity perspective, heteropoly acids are stronger than acidic oxides, molecular sieves, and acidic resins. Among a range of heteropoly acids, phosphotungstic acid is a relatively strong acid and is widely used in acid-catalyzed reactions. However, phosphotungstic acid suffers from problems such as easy solubility in polar reaction media and difficulty in fully exposing its acidic sites. Chinese patent CN 107573358 A discloses a method for preparing a series of heteropoly acid salt catalysts with different metal ions via ion exchange for catalyzing the dehydration of sorbitol to isosorbide. The exchange of metal ions alters the acidity and solubility of the heteropoly acids, thus enabling their use in catalyzing the dehydration of sorbitol to isosorbide. Chinese patent CN 110295068 A discloses a method for synthesizing biodiesel using activated carbon-supported heteropoly acid catalysts. The use of activated carbon loading addresses the separation and recovery issues of heteropoly acids. Phosphotungstic acid, as a promising solid acid catalyst for the dehydration of sorbitol to isosorbide, faces challenges in its application. These challenges include its high solubility in the reaction system, difficulty in separating it from the reaction products, and limited reusability. Furthermore, the water generated during the sorbitol dehydration reaction accelerates the dissolution of phosphotungstic acid. Therefore, loading and solidifying phosphotungstic acid to reduce ineffective dissolution and increase the number of reusable reactions are key to its successful application in the sorbitol catalysis. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a supported phosphotungstic acid catalyst, its preparation method, and its application.

[0006] A method for preparing a supported phosphotungstic acid catalyst includes the following steps: Neutral activated carbon was impregnated in a mixed solution of silanizing agent and phosphotungstic acid. After impregnation, the activated carbon was removed and dried. It was then cured at 150°C to 200°C for 2 to 3 hours under anaerobic conditions. The cured material was then cleaned to obtain the supported phosphotungstic acid catalyst. In the mixed solution, the mass ratio of silanizing agent to phosphotungstic acid is 1~4:2~15, and the mass ratio of activated carbon to phosphotungstic acid is 20:2~15.

[0007] This invention simultaneously modifies activated carbon with silanization and loads phosphotungstic acid. By adjusting the concentrations of the organosilicon reagent and phosphotungstic acid, the concentration of catalytic sites and the number of hydrophobic groups in the activated carbon structure are precisely controlled. This creates a local microenvironment on and within the activated carbon that is conducive to isosorbide formation and unfavorable to water retention, thereby synergistically promoting the efficient and highly selective formation of isosorbide both thermodynamically and kinetically. When the supported phosphotungstic acid catalyst is applied to catalyze the synthesis of isosorbide from sorbitol, the silanization modification facilitates the rapid removal of water from the reaction system, resulting in a final sorbitol conversion greater than 95% and an isosorbide selectivity of 75%-90%. The catalytic performance shows no decline after five cycles.

[0008] Preferably, the activated carbon is a neutral activated carbon obtained by acid washing with hydrochloric acid solution, then alkaline washing with sodium hydroxide solution, and finally washing with distilled water.

[0009] Preferably, the concentrations of both the hydrochloric acid solution and the sodium hydroxide solution are 1 mol / L to 3 mol / L.

[0010] Preferably, the activated carbon has a mesh size of 20-200 mesh and a specific surface area ≥1000 m². 2 / g, iodine adsorption value ≥1000mg / g.

[0011] Preferably, the silanizing agent is selected from one or more of n-octyltriethoxysilane, n-decyltriethoxysilane, dodecyltriethoxysilane, and hexadecyltriethoxysilane.

[0012] Preferably, the solvent used in the mixed solution is selected from one or more of methanol, ethanol, and isopropyl ether.

[0013] A supported phosphotungstic acid catalyst prepared by the method described above.

[0014] The application of the supported phosphotungstic acid catalyst in the catalytic synthesis of isosorbide from sorbitol.

[0015] Preferably, the steps for synthesizing isosorbide are as follows: sorbitol and the supported phosphotungstic acid catalyst are added to a reaction vessel to carry out a dehydration catalytic reaction to prepare isosorbide; The supported phosphotungstic acid catalyst has a mass of 1% to 5% of the mass of sorbitol.

[0016] Preferably, the conditions for the dehydration catalytic reaction are a temperature of 140℃~180℃, a pressure of 10mmHg~50mmHg, and stirring for 1-3 hours.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: Simultaneous silanization modification of activated carbon and phosphotungstic acid loading shorten the catalyst preparation process. By adjusting the amounts of silanizing reagent and phosphotungstic acid, the concentration of catalytic sites and the number of hydrophobic groups are controlled, promoting the dehydration reaction towards the product. Activated carbon loading facilitates catalyst recovery and reuse, while reducing the ineffective dissolution of phosphotungstic acid during the reaction, thus lowering catalyst usage costs. It exhibits high catalytic activity, with a sorbitol conversion rate greater than 95% within 1-3 hours of feeding. It also demonstrates high selectivity, with few byproducts; the selectivity for isosorbide is 75%-90%, and the catalytic performance shows no decline after 5 cycles. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of the supported phosphotungstic acid catalyst prepared in this invention. Detailed Implementation

[0019] The specific embodiments of the present invention are described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention. Unless otherwise specified, the experimental methods described in the embodiments of the present invention are conventional methods.

[0020] Activated carbon's large specific surface area and abundant porous structure make it a natural support material for phosphotungstic acid (PPA). The loading of PPA onto the activated carbon structure provides highly dispersed acidic sites for the catalytic reaction, preventing ineffective aggregation and dissolution of PPA, thus enhancing its stability as a catalyst. However, when using activated carbon-supported PPA to catalyze the dehydration of sorbitol to isosorbide, activated carbon is easily saturated with water, and the competitive adsorption of water molecules occupies the active sites of the catalyst, reducing the efficiency of the catalytic reaction and hindering further dehydration of sorbitol. By modifying activated carbon with silanization, its affinity for water can be significantly reduced. The establishment of a moisture-proof, hydrophobic barrier promotes the rapid expulsion of water molecules from the catalyst surface and the pores of the activated carbon, shifting the reaction equilibrium towards the formation of isosorbide.

[0021] In the catalyst preparation stage, this invention completes the loading of phosphotungstic acid while silanizing and modifying activated carbon. By adjusting the concentration of organosilicon reagent and phosphotungstic acid, the concentration of catalytic sites and the number of hydrophobic groups in the activated carbon structure are precisely controlled. A local microenvironment that is conducive to the formation of isosorbide and unfavorable to the retention of product water is jointly created on the surface and inside of the activated carbon. Thus, the efficient and highly selective formation of isosorbide is promoted in a thermodynamic and kinetic way.

[0022] Example 1 A method for preparing a supported phosphotungstic acid catalyst includes the following steps: Weigh out 20g of 20-mesh activated carbon. The specific surface area of ​​the activated carbon is 1000m². 2 / g, iodine adsorption value is 1000 mg / g. Activated carbon was acid-washed with 1 mol / L hydrochloric acid, then alkaline-washed with 1 mol / L sodium hydroxide, and finally washed with distilled water. After adjusting the pH of the activated carbon filtrate to neutral, it was dried at 105℃ for 6 hours until constant weight was achieved.

[0023] Weigh 1 g of n-octyltriethoxysilane and 2.3 g of phosphotungstic acid, dissolve them in 20 mL of methanol solvent, and stir thoroughly to obtain a mixture. Completely impregnate 20 g of pretreated activated carbon in the mixture for 2 hours to ensure thorough impregnation. Remove the impregnated sample and dry it in a forced-air environment for 4 hours to evaporate the methanol solvent. Then place the dried sample in a tube furnace, purge with nitrogen, raise the temperature to 150 °C, and hold at that temperature for 2 hours to solidify. Wash the solidified activated carbon sample repeatedly with anhydrous acetone until transparent to obtain the supported phosphotungstic acid catalyst. The phosphotungstic acid loading in the prepared supported phosphotungstic acid catalyst is 10%.

[0024] Example 2 A method for preparing a supported phosphotungstic acid catalyst includes the following steps: Weigh out 20g of 50-mesh activated carbon. The specific surface area of ​​the activated carbon is 1200m². 2 / g, with an iodine adsorption value of 1200mg / g. The activated carbon was acid-washed with 1mol / L hydrochloric acid, followed by alkaline washing with 1mol / L sodium hydroxide, and finally washed with distilled water. After adjusting the pH of the activated carbon filtrate to neutral, it was dried at 110℃ for 8 hours until constant weight was achieved.

[0025] Weigh 1g of n-decyltriethoxysilane and 3g of phosphotungstic acid, dissolve them in 20mL of methanol solvent, and stir thoroughly to obtain a mixture. Completely impregnate 20g of pretreated activated carbon in the mixture for 2 hours to ensure thorough impregnation. Remove the impregnated sample and dry it in a forced-air environment for 5 hours to evaporate the methanol solvent. Then place the dried sample in a tube furnace, purge with nitrogen, raise the temperature to 160℃, and hold at that temperature for 2 hours to solidify. Wash the solidified activated carbon sample repeatedly with anhydrous acetone until transparent to obtain the supported phosphotungstic acid catalyst. The phosphotungstic acid loading in the prepared supported phosphotungstic acid catalyst is 12.5%.

[0026] Example 3 A method for preparing a supported phosphotungstic acid catalyst includes the following steps: Weigh out 20g of 100-mesh activated carbon. The specific surface area of ​​the activated carbon is 1500m². 2 / g, iodine adsorption value is 1500mg / g. Activated carbon was acid-washed with 2mol / L hydrochloric acid, then alkaline-washed with 2mol / L sodium hydroxide, and finally washed with distilled water. After adjusting the pH of the activated carbon filtrate to neutral, it was dried at 120℃ for 10 hours until constant weight was achieved.

[0027] Weigh 1g of n-octyltriethoxysilane, 1g of n-decyltriethoxysilane, and 5g of phosphotungstic acid, dissolve them in 30mL of ethanol solvent, and stir thoroughly to obtain a mixture. Completely impregnate 20g of pretreated activated carbon into the mixture for 2 hours to ensure thorough impregnation. Remove the impregnated sample and dry it in a forced-air oven for 8 hours to evaporate the ethanol solvent. Then place the dried sample in a tube furnace, purge with nitrogen, raise the temperature to 200℃, and hold at that temperature for 3 hours to solidify. Wash the solidified activated carbon sample repeatedly with anhydrous acetone until transparent to obtain the supported phosphotungstic acid catalyst. The phosphotungstic acid loading in the prepared supported phosphotungstic acid catalyst is 18.5%.

[0028] Example 4 A method for preparing a supported phosphotungstic acid catalyst includes the following steps: Weigh out 20g of 150-mesh activated carbon. The specific surface area of ​​the activated carbon is 2500m². 2 / g, iodine adsorption value is 1800mg / g. Activated carbon was acid-washed with 2mol / L hydrochloric acid, then alkaline-washed with 2mol / L sodium hydroxide, and finally washed with distilled water. After adjusting the pH of the activated carbon filtrate to neutral, it was dried at 120℃ for 12 hours until constant weight was achieved.

[0029] Weigh 1g of n-decyltriethoxysilane and 8g of phosphotungstic acid, dissolve them in 30mL of ethanol solvent, and stir thoroughly. Completely impregnate 20g of pretreated activated carbon in the mixture of ethanol, phosphotungstic acid, and n-decyltriethoxysilane for 2 hours to ensure thorough impregnation. Remove the impregnated sample and dry it in a forced-air environment for 8 hours to evaporate the ethanol solvent. Then place the dried sample in a tube furnace, purge with nitrogen, raise the temperature to 200℃, and hold at that temperature for 3 hours to solidify. Wash the solidified activated carbon sample repeatedly with anhydrous acetone until transparent to obtain the supported phosphotungstic acid catalyst. The phosphotungstic acid loading in the prepared supported phosphotungstic acid catalyst is 27.6%.

[0030] Example 5 A method for preparing a supported phosphotungstic acid catalyst includes the following steps: Weigh out 20g of 200-mesh activated carbon. The specific surface area of ​​the activated carbon is 3500m². 2 / g, iodine adsorption value is 2800mg / g. Activated carbon was acid-washed with 3mol / L hydrochloric acid, then alkaline-washed with 3mol / L sodium hydroxide, and finally washed with distilled water. After adjusting the pH of the activated carbon filtrate to neutral, it was dried at 120℃ for 12 hours until constant weight was achieved.

[0031] Weigh 1g of n-decyltriethoxysilane, 1g of dodecyltriethoxysilane, and 10g of phosphotungstic acid, and dissolve them in 30mL of a mixed solvent of methanol and ethanol, stirring thoroughly. Completely impregnate 20g of pretreated activated carbon in the mixture of methanol, ethanol, phosphotungstic acid, n-decyltriethoxysilane, and dodecyltriethoxysilane for 2 hours to ensure thorough impregnation. Remove the impregnated sample and dry it in a forced-air environment for 8 hours to evaporate the methanol and ethanol solvents. Then place the dried sample in a tube furnace, purge with nitrogen, raise the temperature to 200℃, and hold at that temperature for 2.5 hours to solidify. Wash the solidified activated carbon sample repeatedly with anhydrous acetone until transparent to obtain the supported phosphotungstic acid catalyst. The phosphotungstic acid loading in the prepared supported phosphotungstic acid catalyst is 31.2%.

[0032] Example 6 A method for preparing a supported phosphotungstic acid catalyst includes the following steps: Weigh out 20g of 200-mesh activated carbon. The specific surface area of ​​the activated carbon is 3500m². 2 / g, iodine adsorption value is 2800mg / g. Activated carbon was acid-washed with 3mol / L hydrochloric acid, then alkaline-washed with 3mol / L sodium hydroxide, and finally washed with distilled water. After adjusting the pH of the activated carbon filtrate to neutral, it was dried at 120℃ for 12 hours until constant weight was achieved.

[0033] Weigh 1g of n-decyltriethoxysilane and 14g of phosphotungstic acid, dissolve them in 50mL of isopropyl ether solvent, and stir thoroughly. Completely impregnate 20g of pretreated activated carbon in the mixture of isopropyl ether, phosphotungstic acid, and n-decyltriethoxysilane for 2 hours to ensure thorough impregnation. Remove the impregnated sample and dry it in a forced-air environment for 8 hours to evaporate the isopropyl ether solvent. Then place the dried sample in a tube furnace, purge with nitrogen, raise the temperature to 200℃, and maintain the temperature for 3 hours to solidify. Wash the solidified activated carbon sample repeatedly with anhydrous acetone until transparent to obtain the supported phosphotungstic acid catalyst. The phosphotungstic acid loading in the prepared supported phosphotungstic acid catalyst is 40%.

[0034] Comparative Example 1 The main difference between Comparative Example 1 and Example 1 is that it does not contain phosphotungstic acid, as detailed below: Weigh out 20g of 200-mesh activated carbon. The specific surface area of ​​the activated carbon is 3500m². 2 / g, iodine adsorption value 2800mg / g. The activated carbon was acid-washed with 3mol / L hydrochloric acid, then alkaline-washed with 3mol / L sodium hydroxide, and finally washed with distilled water. After adjusting the pH of the activated carbon filtrate to neutral, it was dried at 120℃ for 12 hours until constant weight was achieved.

[0035] Weigh 1g of n-decyltriethoxysilane and dissolve it in 50mL of methanol solvent. Stir thoroughly, add 20g of pretreated activated carbon, and impregnate for 2 hours to ensure thorough impregnation. Remove the impregnated sample and dry it in a forced-air oven for 8 hours to evaporate the methanol solvent. Then place the dried sample in a tube furnace, purge with nitrogen, raise the temperature to 200℃, and maintain the temperature for 3 hours to solidify. Wash the solidified activated carbon sample repeatedly with anhydrous acetone until it becomes transparent to obtain the catalyst.

[0036] Comparative Example 2 The main difference between Comparative Example 2 and Example 1 is that alkylation is not performed, as detailed below: Weigh out 20g of 200-mesh activated carbon. The specific surface area of ​​the activated carbon is 3500m². 2 / g, iodine adsorption value 2800mg / g. The activated carbon was acid-washed with 3mol / L hydrochloric acid, then alkaline-washed with 3mol / L sodium hydroxide, and finally washed with distilled water. After adjusting the pH of the activated carbon filtrate to neutral, it was dried at 120℃ for 12 hours until constant weight was achieved.

[0037] Weigh 1g of n-decyltriethoxysilane and 14g of phosphotungstic acid and dissolve them in 50mL of methanol. Stir thoroughly, then add 20g of pretreated activated carbon and impregnate for 2 hours to ensure complete impregnation. Remove the impregnated sample and dry it in a forced-air oven for 8 hours to evaporate the methanol solvent. Place the dried sample in a tube furnace, purge with nitrogen, heat to 200℃, and maintain the temperature for 3 hours to cure. Wash the cured activated carbon sample repeatedly with anhydrous acetone until it becomes transparent to obtain the catalyst.

[0038] Example 7 A method for synthesizing isosorbide from sorbitol via the dehydration reaction catalyzed by a supported phosphotungstic acid catalyst includes: Weigh 10g of sorbitol and 0.1g of the supported phosphotungstic acid catalyst prepared in Example 1, mix them thoroughly, place them in a reaction flask, set the reaction temperature to 140℃, and stir continuously for 1 hour under reduced pressure (10mmHg). After the reaction is complete, cool to room temperature, centrifuge to separate the catalyst, take the supernatant, and analyze the sample using liquid chromatography.

[0039] Example 8 A method for synthesizing isosorbide from sorbitol via the dehydration reaction catalyzed by a supported phosphotungstic acid catalyst includes: Weigh 10g of sorbitol and 0.2g of the supported phosphotungstic acid catalyst prepared in Example 2. Mix them thoroughly and place them in a reaction flask. Set the reaction temperature to 150℃ and stir continuously for 1.5 hours under reduced pressure (15mmHg). After the reaction is complete, cool to room temperature, centrifuge to separate the catalyst, collect the supernatant, and analyze the sample using liquid chromatography.

[0040] Example 9 A method for synthesizing isosorbide from sorbitol via the dehydration reaction catalyzed by a supported phosphotungstic acid catalyst includes: Weigh 10g of sorbitol and 0.3g of the supported phosphotungstic acid catalyst prepared in Example 3, mix them thoroughly, place them in a reaction flask, set the reaction temperature to 150℃, and stir continuously for 2 hours under reduced pressure (30mmHg). After the reaction is complete, cool to room temperature, centrifuge to separate the catalyst, take the supernatant, and analyze the sample using liquid chromatography.

[0041] Example 10 A method for synthesizing isosorbide from sorbitol via the dehydration reaction catalyzed by a supported phosphotungstic acid catalyst includes: Weigh 10g of sorbitol and 0.3g of the supported phosphotungstic acid catalyst prepared in Example 4. Mix them thoroughly and place them in a reaction flask. Set the reaction temperature to 160℃ and stir continuously for 3 hours under reduced pressure (50mmHg). After the reaction is complete, cool to room temperature, centrifuge to separate the catalyst, collect the supernatant, and analyze the sample using liquid chromatography.

[0042] Example 11 A method for synthesizing isosorbide from sorbitol via the dehydration reaction catalyzed by a supported phosphotungstic acid catalyst includes: Weigh 10g of sorbitol and 0.4g of the supported phosphotungstic acid catalyst prepared in Example 5. Mix them thoroughly and place them in a reaction flask. Set the reaction temperature to 180℃ and stir continuously for 2.5 hours under reduced pressure (40mmHg). After the reaction is complete, cool to room temperature, centrifuge to separate the catalyst, collect the supernatant, and analyze the sample using liquid chromatography.

[0043] Example 12 A method for synthesizing isosorbide from sorbitol via the dehydration reaction catalyzed by a supported phosphotungstic acid catalyst includes: Weigh 10g of sorbitol and 0.5g of the supported phosphotungstic acid catalyst prepared in Example 6, mix them thoroughly, place them in a reaction flask, set the reaction temperature to 180℃, and stir continuously for 3 hours under reduced pressure (50mmHg). After the reaction is complete, cool to room temperature, centrifuge to separate the catalyst, take the supernatant, and analyze the sample using liquid chromatography.

[0044] The conversion rates of sorbitol and the selectivity of isosorbitol in Examples 7 to 12 are shown in Table 1.

[0045] The formulas for calculating the conversion rate of sorbitol and the selectivity of isosorbitol in this invention are as follows: Table 1: Results of sorbitol conversion and isosorbide selectivity Effect verification: 1. The supported phosphotungstic acid catalyst prepared in Example 6 was dried, quantitatively added at 5% of the weight of sorbitol, and used in a cycle of 4 times. The activity of the catalyst was compared with that of 5 consecutive uses. The results are shown in Table 2.

[0046] Table 2: Effect of catalyst recycling on sorbitol dehydration performance Table 2 shows the catalytic performance changes of the prepared catalyst after five consecutive uses. As can be seen from the table, the conversion rate of sorbitol and the selectivity of isosorbide remained almost unchanged in the first four uses. After the fifth cycle, the catalytic performance decreased slightly, but the conversion rate of sorbitol still remained at 95%. This is mainly because repeated cycles may cause carbon buildup on the catalyst surface, reducing the exposure of acidic catalytic sites and leading to a decrease in product selectivity. However, the catalyst prepared in this invention can still maintain high catalytic performance after multiple cycles.

[0047] 2. To verify the difference in catalytic performance of the present invention in the sorbitol dehydration reaction, comparative experiments were conducted under the same conditions. Catalysts from Comparative Example 1 and Comparative Example 2 were used for the catalytic reaction, and the verification results are as follows.

[0048] Weigh out two 10g portions of sorbitol, and separately take 0.5g of the catalyst from Comparative Example 1 and Comparative Example 2, respectively. Mix them thoroughly and place them in a reaction flask. Set the reaction temperature to 180℃ and the pressure to 50mmHg under reduced pressure, and stir continuously for 3 hours. After the reaction is complete, cool to room temperature, centrifuge to separate the catalyst, collect the supernatant, and analyze the sample using liquid chromatography.

[0049] Catalyst samples from Comparative Examples 1 and 2 were centrifuged, dried, and quantitatively added at 5% of the weight of sorbitol. The samples were cycled 4 times, and the catalyst activity was compared with that under 5 consecutive cycles. The results are shown in Table 3.

[0050] Table 3: Catalytic performance of sorbitol dehydration by catalysts in Comparative Example 1 and Comparative Example 2 Note: " / " indicates no data.

[0051] The data in Table 3 show that in Comparative Example 1, the silanization modification of activated carbon catalyzed the dehydration reaction of sorbitol, but the reaction did not occur. This directly proves that phosphotungstic acid is the catalyst responsible for the reaction. When phosphotungstic acid is not loaded, activated carbon and n-decyltriethoxysilane alone cannot play a catalytic role. In Comparative Example 2, phosphotungstic acid was directly loaded onto activated carbon. The conversion rate and selectivity of the catalyst during the first use were not significantly different from the results in Table 2. However, the catalytic performance deteriorated significantly after filtration, drying, and recycling. This is mainly because the water generated during the dehydration reaction dissolved the phosphotungstic acid loaded on the activated carbon, allowing it to enter the reaction product and be lost with the filtrate after filtration. This further confirms that the silanization modification of activated carbon creates a local microenvironment on the surface and inside the activated carbon that is conducive to the formation of isosorbitol and unfavorable to the retention of product water. This allows for the rapid removal of water and reduces the dissolution of phosphotungstic acid, making it possible to reuse phosphotungstic acid multiple times in the sorbitol dehydration reaction, thereby promoting the efficient and highly selective formation of isosorbitol.

[0052] It should be noted that when numerical ranges are mentioned in the claims of this invention, it should be understood that the two endpoints of each numerical range and any value between the two endpoints can be selected. To avoid redundancy, the present invention describes preferred embodiments.

[0053] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0054] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for preparing a supported phosphotungstic acid catalyst, characterized by, The method comprises the following steps: The activated carbon with neutral pH is dipped in a mixed solution of silanization reagent and phosphotungstic acid, dried after dipping, solidified at 150-200 DEG C for 2-3 hours under anaerobic condition, and cleaned to obtain the supported phosphotungstic acid catalyst. The mass ratio of silanization reagent to phosphotungstic acid in the mixed solution is 1-4:2-15, and the mass ratio of activated carbon to phosphotungstic acid is 20:2-15.

2. The production method according to claim 1, characterized by, The activated carbon is obtained by acid washing with hydrochloric acid solution, alkali washing with sodium hydroxide solution, and finally washing with distilled water to obtain activated carbon with neutral pH.

3. The production method according to claim 2, characterized by, The concentration of hydrochloric acid solution and sodium hydroxide solution is 1-3 mol / L.

4. The method of claim 1, wherein, The mesh number of the activated carbon is 20-200 mesh, the specific surface area is ≥1000 m 2 / g, and the iodine adsorption value is ≥1000 mg / g.

5. The preparation method according to claim 1, characterized in that, The silanization reagent is selected from one or more of n-octyltriethoxysilane, n-decyltriethoxysilane, dodecyltriethoxysilane and hexadecyltriethoxysilane.

6. The method of claim 1, wherein, The solvent used in the mixed solution is selected from one or more of methanol, ethanol and isopropyl ether.

7. The supported phosphotungstic acid catalyst prepared by the preparation method of any one of claims 1-6.

8. The application of the supported phosphotungstic acid catalyst of claim 7 in catalyzing synthesis of isosorbide from sorbitol.

9. Use according to claim 8, characterized in that, The steps of synthesizing isosorbide are as follows: sorbitol and the supported phosphotungstic acid catalyst are added into a reaction container to prepare isosorbide through dehydration catalytic reaction. The mass of the supported phosphotungstic acid catalyst is 1-5% of the mass of sorbitol.

10. Use according to claim 9, characterized in that, The dehydration catalytic reaction is carried out at a temperature of 140-180 DEG C, a pressure of 10-50 mmHg, and stirring for 1-3 hours.

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