Preparation method and application of solid acid catalyst for synthesizing caprolactam

Abstract

The invention discloses a preparation method and application of a solid acid catalyst for synthesizing caprolactam, and belongs to the technical field of catalysts. The catalyst is an AHPW / UiO-67 solid acid catalyst, defect type UiO-67 serves as a carrier, quaternary ammonium salt type fixed positive potential sites are introduced to the surface of the carrier through amino organosilane grafting and quaternization treatment, and part of salinized phosphotungstic heteropoly acid is fixed to the surface of the carrier in an electrostatic bonding mode. The open metal site in the carrier provides a Lewis acid site, and the heteropoly acid provides a Bronsted acid site, so that a Lewis-Bronsted acid concerted catalysis system is formed. Effective distribution of acidic sites is realized by regulating and controlling the defect structure of the carrier and the salinization degree of heteropoly acid. The catalyst can be used for a liquid-phase Beckmann rearrangement reaction, caprolactam is prepared by taking cyclohexanone oxime as a raw material, and the catalyst has relatively high conversion rate and selectivity, is easy to separate and recover and can be recycled for multiple times.

Description

Technical Field

[0001] This invention belongs to the field of catalyst technology, specifically relating to a method for preparing a solid acid catalyst for the synthesis of caprolactam, using defective UiO-67 as a support, subjecting it to quaternization treatment by grafting amino-organosilanes, and confining and supporting phosphotungsten heteropolyacid. Background Technology

[0002] Caprolactam is an important bulk organic chemical raw material, mainly used in the production of polycaprolactam fiber (nylon 6) and engineering plastics. It is widely used in textiles, automobiles, electronics, machinery and other fields, and its market demand is huge. Catalyzing the Beckmann rearrangement reaction of cyclohexanone oxime is the core process for the industrial preparation of caprolactam.

[0003] Currently, the Beckmann rearrangement catalysts used in industry are mainly liquid strong acids (such as concentrated sulfuric acid and phosphoric acid). Although these catalysts have high catalytic activity, they are highly corrosive and will cause serious damage to production equipment. At the same time, they generate a large amount of waste acid after the reaction, which is difficult and costly to treat and easily causes environmental pollution. Moreover, the catalysts cannot be reused, which is contrary to the development trend of green chemical industry.

[0004] To overcome the inherent defects of liquid acid catalysts, researchers are dedicated to developing environmentally friendly solid acid catalysts. Among them, metal-organic frameworks (MOFs) have become a research hotspot due to their outstanding advantages such as large specific surface area, tunable pore structure, and abundant active sites. UiO-67, as a typical MOF material, contains a certain amount of open metal sites and can serve as a potential solid acid catalyst support. However, pure UiO-67 has weak acidity and limited catalytic activity, usually requiring the loading of acidic components such as heteropoly acids to enhance its catalytic performance. Phosphotungstic heteropoly acids are strong Brønsted acids with excellent catalytic activity, but their easy solubility in the reaction system leads to easy detachment during loading, poor dispersibility, and difficulty in recycling and reuse, greatly limiting their industrial applications. For example, Chinese patent CN201210151730.2 describes a supported solid acid catalyst prepared using heteropolyacid as the active component and mesoporous molecular sieve (HMS) as the support. The reaction conditions are mild and environmentally friendly, but the heteropolyacid loading is as high as 70 wt.%, which makes the catalyst easy to aggregate, resulting in a decrease in catalytic performance and reaction selectivity. Furthermore, it does not solve the problem that phosphotungsten heteropolyacid is easy to dissolve in the reaction system and easy to fall off.

[0005] Existing technologies lack sufficient structural control over the UiO-67 support, failing to fully utilize its defective structure to optimize the distribution of acidic sites. Furthermore, the loading methods for heteropolyacids lack specificity, making it impossible to achieve stable binding between acidic sites and the support surface. This results in the synergistic catalytic effect between the Lewis acid sites at the open metal sites of the support and the Brønsted acid sites of the heteropolyacids being difficult to fully realize, thereby affecting the conversion rate and selectivity of the cyclohexanone oxime Beckmann rearrangement reaction.

[0006] Furthermore, existing solid acid catalysts still cannot meet the requirements of industrial-scale production in terms of catalytic performance, stability, and reusability. Therefore, developing a solid acid catalyst that can achieve stable loading of heteropoly acids, efficient synergy of acidic sites, excellent catalytic performance, and reusability has important industrial application value and practical significance for the catalytic Beckmann rearrangement of cyclohexanone oxime to prepare caprolactam, and is also a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0007] The purpose of this invention is to prepare AHPW / UiO-67 solid acid catalyst by using defective UiO-67 as a support, subjecting it to quaternization treatment via grafting with amino organosilicon, and confining and loading phosphotungsten heteropolyacid and ion pairing. This aims to solve the technical problems in existing MOF solid acid catalyst technology, such as poor catalytic performance, insufficient synergistic catalytic effect, easy shedding and poor dispersibility of heteropolyacid during loading, and difficulty in catalyst recovery and reuse. At the same time, it achieves high reaction conversion, high caprolactam selectivity, and catalyst cycle stability.

[0008] Based on the above, the present invention relates to a method for preparing a solid acid catalyst for the synthesis of caprolactam and its application, characterized in that the preparation steps are as follows: (1) dissolving a zirconium source in N,N-dimethylformamide, adding 4,4′-biphenyl dicarboxylic acid and a modifier, performing a solvothermal reaction, and after washing and activation treatment, obtaining a defective UiO-67 support containing open metal sites; (2) dispersing the obtained support in an anhydrous organic solvent, adding an organosilane containing an amino group for a grafting reaction, and then performing a quaternization reaction to convert the amino group into a fixed positive potential point; (3) H3PW 12 O 40 A partial neutralization reaction is carried out with a cesium salt or an ammonium salt to produce a product with the general formula H. (3-X) A X PW 12 O 40 Partially salted phosphotungsten heteropolyacids, where A is Cs + or NH 4+X is 0.8-1.8; (4) The partially salted phosphotungsten heteropoly acid obtained in step (3) is reacted with the modified support obtained in step (2) so that the heteropoly acid is fixed on the surface of the support through ion pairing. After washing and drying activation, AHPW / UiO-67 solid acid catalyst is obtained.

[0009] In step (1) of the catalyst preparation method, the molar ratio of 4,4′-biphenyldicarboxylic acid to zirconium source is 1:1.0-1:1.6; the zirconium source is zirconium oxychloride, zirconium nitrate, or zirconium acetylacetonate. The solvothermal reaction temperature is 120-180℃, and the reaction time is 24-72h; the modulator is formic acid, acetic acid, or hydrochloric acid, and the amount used is 5%-20% of the mass of 4,4′-biphenyldicarboxylic acid; the activation conditions are vacuum activation at 80-120℃ for 6-12h.

[0010] In step (2) of the catalyst preparation method, the anhydrous organic solvent is anhydrous 1,4-dioxane, the amine-containing organosilane is 3-aminopropyltriethoxysilane or 3-aminopropyltrimethoxysilane, the mass ratio of organosilane to support is 1:3-1:7, the quaternizing agent is iodomethane, bromoethane or benzyl chloride, the quaternization reaction temperature is room temperature, and the reaction time is 12-24h.

[0011] In step (3) of the catalyst preparation method, H3PW 12 O 40 The neutralization reaction with cesium or ammonium salts is carried out in an aqueous solution at room temperature for 2-4 hours; the cesium salt is cesium nitrate or cesium chloride, and the ammonium salt is ammonium nitrate or ammonium chloride.

[0012] The AHPW / UiO-67 solid acid catalyst prepared by the method described above can be used to catalyze the liquid-phase Beckmann rearrangement reaction, converting cyclohexanone oxime into caprolactam.

[0013] The application of the AHPW / UiO-67 solid acid catalyst is characterized by the following reaction conditions for preparing caprolactam via the catalytic liquid-phase Beckmann rearrangement reaction: using cyclohexanone oxime as raw material, the catalyst dosage is 5%-15% of the cyclohexanone oxime mass, the reaction temperature is 60-100℃, the reaction pressure is atmospheric pressure, the reaction time is 4-12h, and the reaction atmosphere is air; after the reaction, the conversion rate of cyclohexanone oxime can reach over 95.1%, and the selectivity of caprolactam can reach over 98.3%. After centrifugation or filtration, the catalyst can be reused more than 5 times and still maintain high catalytic activity, with no significant decrease in caprolactam selectivity.

[0014] This invention solves this technical problem through the following technical solution: Zirconium oxychloride was dissolved in N,N-dimethylformamide at a molar ratio of 1.3:1. 4,4′-biphenyl dicarboxylic acid and 12.5% ​​formic acid (by mass) were added, and the mixture was thoroughly mixed and transferred to a sealed reactor. The reaction was carried out at 150°C for 48 h using a solvothermal method. After the reaction, the resulting solid product was washed sequentially with N,N-dimethylformamide and anhydrous ethanol, and then activated under vacuum at 100°C for 9 h to obtain a defective UiO-67 support. The UiO-67 support was dispersed in anhydrous 1,4-dioxane, and 3-aminopropyltriethoxysilane was added at a mass ratio of 1:5 to the support for grafting. After the grafting reaction, unreacted material was washed away, and iodomethane was added. The reaction was carried out at room temperature for 18 h to convert the amino groups on the support surface to fixed positive potential points, yielding a quaternized UiO-67 support. Simultaneously, phosphotungstic heteropolyacid H3PW... 12 O 40 Cesium nitrate was added to deionized water for partial neutralization, and the reaction was carried out at room temperature for 3 hours to obtain H. 1.7 CsP 1.3 W 12 O 40 Partially salted phosphotungsten heteropolyacid was then used. Finally, the partially salted phosphotungsten heteropolyacid solution was mixed with a quaternized UiO-67 support and subjected to a contact reaction under stirring. This allowed the phosphotungsten heteropolyacid to be immobilized on the support surface via ion-pair interactions. After the reaction, the resulting solid was washed and dried under mild conditions to obtain the AHPW / UiO-67 solid acid catalyst. Using cyclohexanone oxime as a raw material, 10% (by mass) of the obtained AHPW / UiO-67 solid acid catalyst was added to catalyze the liquid-phase Beckmann rearrangement reaction of cyclohexanone oxime to prepare caprolactam. The reaction conditions were: 80°C, atmospheric pressure, and air atmosphere for 8 hours. After the reaction, the conversion rate of cyclohexanone oxime was 96.2%, and the selectivity for caprolactam was 98.8%. The AHPW / UiO-67 catalyst, after centrifugation or filtration, could be reused more than 5 times while maintaining high catalytic activity, and the selectivity for caprolactam did not decrease significantly.

[0015] Compared with traditional methods, the present invention is characterized by: (1) This invention uses defective UiO-67 as a support, with open metal sites in its structure serving as Lewis acid sites. At the same time, partially salted phosphotungstic heteropolyacids are introduced to provide Brønsted acid sites. Through the synergistic regulation of the degree of defect in the support and the degree of salting of the heteropolyacids, the two types of acid sites coexist in the same catalytic system, satisfying the requirement of the liquid-phase Beckmann rearrangement reaction for the synergistic effect of the two acid sites, thus distinguishing it from single Lewis acid or single Brønsted acid catalytic systems.

[0016] (2) In this invention, an amino-based organosilane is used to modify the surface of the UiO-67 support, and the amino group is converted into a fixed positive potential point through a quaternization reaction, so that the partially salted phosphotungstic heteropoly acid is stably loaded on the support surface in the form of ion pairs, effectively suppressing the loss of heteropoly acid in the liquid phase reaction system, and overcoming the defects of traditional heteropoly acid catalysts that are easy to dissolve and difficult to recover.

[0017] (3) The AHPW / UiO-67 solid acid catalyst prepared by the present invention has both the structural stability of molecular sieve support and the acidic characteristics of heteropoly acid. It can achieve efficient conversion of cyclohexanone oxime to caprolactam in liquid phase Beckmann rearrangement reaction. At the same time, the catalyst can be separated into solid and liquid by centrifugation or filtration and reused. It can still maintain stable catalytic performance after multiple cycles, which solves the problem of difficult catalyst recovery in existing liquid phase Beckmann rearrangement catalytic systems.

[0018] Example 1: Zirconium oxychloride was dissolved in N,N-dimethylformamide at a molar ratio of 1.3:1. 4,4′-biphenyl dicarboxylic acid and 12.5% ​​formic acid (by mass) were added, and the mixture was thoroughly mixed and transferred to a sealed reactor. A solvothermal reaction was carried out at 150°C for 48 hours. After the reaction, the resulting solid product was washed sequentially with N,N-dimethylformamide and anhydrous ethanol, and then activated under vacuum at 100°C for 9 hours to obtain a defective UiO-67 support. The UiO-67 support was dispersed in anhydrous 1,4-dioxane, and 3-aminopropyltriethoxysilane was added at a mass ratio of 1:5 to the support for grafting. After the grafting reaction, unreacted material was washed away, and iodomethane was added. The reaction was carried out at room temperature for 18 hours to convert the amino groups on the support surface to fixed positive potential points, resulting in a quaternized modified UiO-67 support. Simultaneously, phosphotungstic heteropolyacid H3PW... 12 O 40 Cesium nitrate was added to deionized water for partial neutralization, and the reaction was carried out at room temperature for 3 hours to obtain H. 1.7 CsP 1.3 W 12 O 40Partially salted phosphotungsten heteropolyacid was then used. Finally, the partially salted phosphotungsten heteropolyacid solution was mixed with a quaternized UiO-67 support and subjected to a contact reaction under stirring. This allowed the phosphotungsten heteropolyacid to be immobilized on the support surface via ion-pair interactions. After the reaction, the resulting solid was washed and dried under mild conditions to obtain the AHPW / UiO-67 solid acid catalyst. Using cyclohexanone oxime as a raw material, 10% (by mass) of the obtained AHPW / UiO-67 solid acid catalyst was added to catalyze the liquid-phase Beckmann rearrangement reaction of cyclohexanone oxime to prepare caprolactam. The reaction conditions were: 80°C, atmospheric pressure, and air atmosphere for 8 hours. After the reaction, the conversion rate of cyclohexanone oxime was 96.2%, and the selectivity for caprolactam was 98.8%. The AHPW / UiO-67 catalyst, after centrifugation or filtration, could be reused more than 5 times while maintaining high catalytic activity, and the selectivity for caprolactam did not decrease significantly.

[0019] Comparative Example 1: In the catalyst preparation, formic acid was not added as a modifier, and all other preparation conditions were kept exactly the same as in Example 1, resulting in a defect-free UiO-67 support. The support was grafted and quaternized using the same method as in Example 1, and then reacted with H... 1.7 CsP 1.3 W 12 O 40 AHPW / UiO-67 solid acid catalyst was prepared by mixing partially salted phosphotungsten heteropoly acids. Under the same conditions as in Example 1, it catalyzed the liquid-phase Beckmann rearrangement reaction of cyclohexanone oxime to prepare caprolactam. After the reaction, the conversion rate of cyclohexanone oxime was 74.3%, the selectivity of caprolactam was 82.5%, the content of reaction byproducts increased significantly, and the active components of the catalyst were severely lost after one use, making it unusable.

[0020] Comparative Example 2: In catalyst preparation, the defective UiO-67 support prepared under the same conditions as in Example 1 was grafted with 3-aminopropyltriethoxysilane without quaternization treatment. The amine groups were not converted to positive potential sites and reacted directly with H. 1.7 CsP 1.3 W 12 O 40 AHPW / UiO-67 solid acid catalyst was prepared by mixing partially salted phosphotungsten heteropoly acids. Under the same conditions as in Example 1, it catalyzed the liquid-phase Beckmann rearrangement reaction of cyclohexanone oxime to prepare caprolactam. After the reaction, the conversion rate of cyclohexanone oxime was 65.1%, the selectivity of caprolactam was 80.2%, the product purity was low, and the catalyst could not be reused.

[0021] Comparative Example 3: In catalyst preparation, a quaternized UiO-67 support was prepared under the same conditions as in Example 1, while phosphotungstic heteropoly acid H3PW was added.12 O 40 Dissolving in deionized water without undergoing partial salting, and directly mixing with a quaternized UiO-67 support, an AHPW / UiO-67 solid acid catalyst was prepared. Under the same conditions as in Example 1, it catalyzed the liquid-phase Beckmann rearrangement of cyclohexanone oxime to prepare caprolactam. After the reaction, the conversion rate of cyclohexanone oxime was 85.7%, the selectivity of caprolactam was 81.2%, the content of reaction byproducts increased significantly, the catalyst could not be reused, and the lost pure heteropolyacid was highly acidic, which may corrode the reactor and increase the cost of wastewater treatment.

[0022] Example 2: Zirconium oxychloride was dissolved in N,N-dimethylformamide at a molar ratio of 1.0:1. 4,4′-biphenyl dicarboxylic acid and 5% (by mass) formic acid were added, and the mixture was thoroughly mixed and transferred to a sealed reactor. A solvothermal reaction was carried out at 120°C for 24 hours. After the reaction, the resulting solid product was washed sequentially with N,N-dimethylformamide and anhydrous ethanol, and then activated under vacuum at 80°C for 6 hours to obtain a defective UiO-67 support. The UiO-67 support was dispersed in anhydrous 1,4-dioxane, and 3-aminopropyltriethoxysilane was added at a mass ratio of 1:3 to the support for grafting. After the grafting reaction, unreacted material was washed away, and bromoethane was added. The reaction was carried out at room temperature for 12 hours to convert the amino groups on the support surface to a fixed positive potential, resulting in a quaternized modified UiO-67 support. Simultaneously, phosphotungstic heteropolyacid H3PW... 12 O 40 Dissolved in deionized water, cesium chloride was added to partially neutralize it, and the reaction was carried out at room temperature for 2 hours to obtain H. 2.2 CsP 0.8 W 12 O 40 Partially salted phosphotungsten heteropolyacid was then used. Finally, the partially salted phosphotungsten heteropolyacid solution was mixed with a quaternized UiO-67 support and subjected to a contact reaction under stirring. This allowed the phosphotungsten heteropolyacid to be immobilized on the support surface via ion-pair interactions. After the reaction, the resulting solid was washed and dried under mild conditions to obtain the AHPW / UiO-67 solid acid catalyst. Using cyclohexanone oxime as a raw material, 5% (by mass) of the obtained AHPW / UiO-67 solid acid catalyst was added to catalyze the liquid-phase Beckmann rearrangement reaction of cyclohexanone oxime to prepare caprolactam. The reaction conditions were: 60°C, atmospheric pressure, and air atmosphere for 4 hours. After the reaction, the conversion rate of cyclohexanone oxime was 95.1%, and the selectivity for caprolactam was 98.3%. After centrifugation or filtration, the AHPW / UiO-67 catalyst could be reused more than 5 times while maintaining high catalytic activity, and the selectivity for caprolactam did not decrease significantly.

[0023] Example 3: Zirconium nitrate was dissolved in N,N-dimethylformamide at a molar ratio of 1.6:1. 4,4′-biphenyl dicarboxylic acid and 20% (by mass) hydrochloric acid were added, and the mixture was thoroughly mixed and transferred to a sealed reactor. A solvothermal reaction was carried out at 180°C for 72 h. After the reaction, the resulting solid product was washed sequentially with N,N-dimethylformamide and anhydrous ethanol, and then vacuum activated at 120°C for 12 h to obtain a defective UiO-67 support. The UiO-67 support was dispersed in anhydrous 1,4-dioxane, and 3-aminopropyltrimethoxysilane was added at a mass ratio of 1:7 to the support for grafting. After the grafting reaction, unreacted material was washed away, and benzyl chloride was added. The reaction was carried out at room temperature for 24 h to convert the amine groups on the support surface to a fixed positive potential, resulting in a quaternized modified UiO-67 support. Simultaneously, phosphotungstic heteropoly acid H3PW... 12 O 40 Dissolved in deionized water, ammonium nitrate was added for partial neutralization, and the reaction was carried out at room temperature for 4 hours to obtain H. 2.2 NH4P 0.8 W 12 O 40 Partially salted phosphotungsten heteropolyacid was then used. Finally, the partially salted phosphotungsten heteropolyacid solution was mixed with a quaternized UiO-67 support and subjected to a contact reaction under stirring. This allowed the phosphotungsten heteropolyacid to be immobilized on the support surface via ion-pair interactions. After the reaction, the resulting solid was washed and dried under mild conditions to obtain the AHPW / UiO-67 solid acid catalyst. Using cyclohexanone oxime as a raw material, 15% (by mass) of the obtained AHPW / UiO-67 solid acid catalyst was added to catalyze the liquid-phase Beckmann rearrangement reaction of cyclohexanone oxime to prepare caprolactam. The reaction conditions were: 100°C, atmospheric pressure, and air atmosphere for 12 hours. After the reaction, the conversion rate of cyclohexanone oxime was 96.5%, and the selectivity for caprolactam was 98.7%. The AHPW / UiO-67 catalyst, after centrifugation or filtration, could be reused more than 5 times while maintaining high catalytic activity, and the selectivity for caprolactam did not decrease significantly.

[0024] Example 4: Zirconium acetylacetonate was dissolved in N,N-dimethylformamide at a molar ratio of 1.0:1. 4,4′-biphenyl dicarboxylic acid and 12.5% ​​(by mass) acetic acid were added, and the mixture was thoroughly mixed and transferred to a sealed reactor. A solvothermal reaction was carried out at 150°C for 48 h. After the reaction, the resulting solid product was washed sequentially with N,N-dimethylformamide and anhydrous ethanol, and then activated under vacuum at 100°C for 9 h to obtain a defective UiO-67 support. The UiO-67 support was dispersed in anhydrous 1,4-dioxane, and 3-aminopropyltrimethoxysilane was added at a mass ratio of 1:3 to the support for grafting. After the grafting reaction, unreacted material was washed away, and iodomethane was added. The reaction was carried out at room temperature for 18 h to convert the amino groups on the support surface to fixed positive potential points, resulting in a quaternized modified UiO-67 support. Simultaneously, phosphotungstic heteropoly acid H3PW... 12 O 40 Dissolved in deionized water, ammonium chloride was added to partially neutralize it, and the reaction was carried out at room temperature for 3 hours to obtain H. 1.2 NH4P 1.8 W 12 O 40 Partially salted phosphotungsten heteropolyacid was then used. Finally, the partially salted phosphotungsten heteropolyacid solution was mixed with a quaternized UiO-67 support and subjected to a contact reaction under stirring. This allowed the phosphotungsten heteropolyacid to be immobilized on the support surface via ion-pair interactions. After the reaction, the resulting solid was washed and dried under mild conditions to obtain the AHPW / UiO-67 solid acid catalyst. Using cyclohexanone oxime as a raw material, 5% (by mass) of the obtained AHPW / UiO-67 solid acid catalyst was added to catalyze the liquid-phase Beckmann rearrangement reaction of cyclohexanone oxime to prepare caprolactam. The reaction conditions were: 80°C, atmospheric pressure, and air atmosphere for 8 hours. After the reaction, the conversion rate of cyclohexanone oxime was 95.8%, and the selectivity for caprolactam was 98.5%. After centrifugation or filtration, the AHPW / UiO-67 catalyst could be reused more than 5 times while maintaining high catalytic activity, and the selectivity for caprolactam did not decrease significantly.

[0025] Example 5: Zirconium oxychloride was dissolved in N,N-dimethylformamide at a molar ratio of 1.6:1. 4,4′-biphenyl dicarboxylic acid and 20% formic acid (by mass) were added, and the mixture was thoroughly mixed and transferred to a sealed reactor. A solvothermal reaction was carried out at 180°C for 48 hours. After the reaction, the resulting solid product was washed sequentially with N,N-dimethylformamide and anhydrous ethanol, and then activated under vacuum at 100°C for 9 hours to obtain a defective UiO-67 support. The UiO-67 support was dispersed in anhydrous 1,4-dioxane, and 3-aminopropyltriethoxysilane was added at a mass ratio of 1:7 to the support for grafting. After the grafting reaction, unreacted material was washed away, and bromoethane was added. The reaction was carried out at room temperature for 18 hours to convert the amino groups on the support surface to a fixed positive potential, resulting in a quaternized modified UiO-67 support. Simultaneously, phosphotungstic heteropolyacid H3PW... 12 O 40 Cesium nitrate was added to deionized water for partial neutralization, and the reaction was carried out at room temperature for 4 hours to obtain H. 1.7 CsP 1.3 W 12 O 40 Partially salted phosphotungsten heteropolyacid was then used. Finally, the partially salted phosphotungsten heteropolyacid solution was mixed with a quaternized UiO-67 support and subjected to a contact reaction under stirring. This allowed the phosphotungsten heteropolyacid to be immobilized on the support surface through ion-pair interactions. After the reaction, the resulting solid was washed and dried under mild conditions to obtain the AHPW / UiO-67 solid acid catalyst. Using cyclohexanone oxime as a raw material, 15% (by mass) of the obtained AHPW / UiO-67 solid acid catalyst was added to catalyze the liquid-phase Beckmann rearrangement reaction of cyclohexanone oxime to prepare caprolactam. The reaction conditions were: 80°C, atmospheric pressure, and air atmosphere for 8 hours. After the reaction, the conversion rate of cyclohexanone oxime was 97.2%, and the selectivity of caprolactam was 98.9%. After centrifugation or filtration, the AHPW / UiO-67 catalyst could be reused more than 5 times while maintaining high catalytic activity, and the selectivity of caprolactam did not decrease significantly.

[0026] Example 6: Zirconium nitrate was dissolved in N,N-dimethylformamide at a molar ratio of 1.0:1. 4,4′-biphenyl dicarboxylic acid and 5% (by mass) hydrochloric acid were added, and the mixture was thoroughly mixed and transferred to a sealed reactor. A solvothermal reaction was carried out at 120°C for 48 hours. After the reaction, the resulting solid product was washed sequentially with N,N-dimethylformamide and anhydrous ethanol, and then activated under vacuum at 100°C for 9 hours to obtain a defective UiO-67 support. The UiO-67 support was dispersed in anhydrous 1,4-dioxane, and 3-aminopropyltrimethoxysilane was added at a mass ratio of 1:3 to the support for grafting. After the grafting reaction, unreacted material was washed away, and benzyl chloride was added. The reaction was carried out at room temperature for 18 hours to convert the amine groups on the support surface to a fixed positive potential, resulting in a quaternized modified UiO-67 support. Simultaneously, phosphotungstic heteropolyacid H3PW... 12 O 40 Dissolved in deionized water, ammonium nitrate was added for partial neutralization, and the reaction was carried out at room temperature for 2 hours to obtain H. 2.2 NH4P 0.8 W 12 O 40 Partially salted phosphotungsten heteropolyacid was then used. Finally, the partially salted phosphotungsten heteropolyacid solution was mixed with a quaternized UiO-67 support and subjected to a contact reaction under stirring. This allowed the phosphotungsten heteropolyacid to be immobilized on the support surface via ion-pair interactions. After the reaction, the resulting solid was washed and dried under mild conditions to obtain the AHPW / UiO-67 solid acid catalyst. Using cyclohexanone oxime as a raw material, 5% (by mass) of the obtained AHPW / UiO-67 solid acid catalyst was added to catalyze the liquid-phase Beckmann rearrangement reaction of cyclohexanone oxime to prepare caprolactam. The reaction conditions were: 80°C, atmospheric pressure, and air atmosphere for 8 hours. After the reaction, the conversion rate of cyclohexanone oxime was 95.3%, and the selectivity for caprolactam was 98.4%. The AHPW / UiO-67 catalyst, after centrifugation or filtration, could be reused more than 5 times while maintaining high catalytic activity, and the selectivity for caprolactam did not decrease significantly.

[0027] Example 7: Zirconium acetylacetonate was dissolved in N,N-dimethylformamide at a molar ratio of 1.6:1. 4,4′-biphenyl dicarboxylic acid and 12.5% ​​formic acid (by mass) were added, and the mixture was thoroughly mixed and transferred to a sealed reactor. A solvothermal reaction was carried out at 150°C for 24 hours. After the reaction, the resulting solid product was washed sequentially with N,N-dimethylformamide and anhydrous ethanol, and then activated under vacuum at 80°C for 6 hours to obtain a defective UiO-67 support. The UiO-67 support was dispersed in anhydrous 1,4-dioxane, and 3-aminopropyltriethoxysilane was added at a mass ratio of 1:5 to the support for grafting. After the grafting reaction, unreacted material was washed away, and iodomethane was added. The reaction was carried out at room temperature for 12 hours to convert the amino groups on the support surface to fixed positive potential points, resulting in a quaternized modified UiO-67 support. Simultaneously, phosphotungstic heteropoly acid H3PW... 12 O 40 Dissolved in deionized water, cesium chloride was added for partial neutralization, and the reaction was carried out at room temperature for 3 hours to obtain H. 1.7 CsP 1.3 W 12 O 40 Partially salted phosphotungsten heteropolyacid was then used. Finally, the partially salted phosphotungsten heteropolyacid solution was mixed with a quaternized UiO-67 support and subjected to a contact reaction under stirring. This allowed the phosphotungsten heteropolyacid to be immobilized on the support surface via ion-pair interactions. After the reaction, the resulting solid was washed and dried under mild conditions to obtain the AHPW / UiO-67 solid acid catalyst. Using cyclohexanone oxime as a raw material, 10% (by mass) of the obtained AHPW / UiO-67 solid acid catalyst was added to catalyze the liquid-phase Beckmann rearrangement reaction of cyclohexanone oxime to prepare caprolactam. The reaction conditions were: 60°C, atmospheric pressure, and air atmosphere for 4 hours. After the reaction, the conversion rate of cyclohexanone oxime was 96.0%, and the selectivity for caprolactam was 98.7%. After centrifugation or filtration, the AHPW / UiO-67 catalyst could be reused more than 5 times while maintaining high catalytic activity, and the selectivity for caprolactam did not decrease significantly.

[0028] Example 8: Zirconium oxychloride was dissolved in N,N-dimethylformamide at a molar ratio of 1.0:1. 4,4′-biphenyl dicarboxylic acid and 20% (by mass) acetic acid were added, and the mixture was thoroughly mixed and transferred to a sealed reactor. A solvothermal reaction was carried out at 180°C for 72 h. After the reaction, the resulting solid product was washed sequentially with N,N-dimethylformamide and anhydrous ethanol, and then vacuum activated at 120°C for 12 h to obtain a defective UiO-67 support. The UiO-67 support was dispersed in anhydrous 1,4-dioxane, and 3-aminopropyltrimethoxysilane was added at a mass ratio of 1:7 to the support for grafting. After the grafting reaction, unreacted material was washed away, and bromoethane was added. The reaction was carried out at room temperature for 24 h to convert the amino groups on the support surface to a fixed positive potential, resulting in a quaternized modified UiO-67 support. Simultaneously, phosphotungstic heteropolyacid H3PW... 12 O 40 Dissolved in deionized water, ammonium chloride was added to partially neutralize the solution, and the reaction was carried out at room temperature for 4 hours to obtain H. 1.2 NH4P 1.8 W 12 O 40 Partially salted phosphotungsten heteropolyacid was then used. Finally, the partially salted phosphotungsten heteropolyacid solution was mixed with a quaternized UiO-67 support and subjected to a contact reaction under stirring. This allowed the phosphotungsten heteropolyacid to be immobilized on the support surface through ion-pair interactions. After the reaction, the resulting solid was washed and dried under mild conditions to obtain the AHPW / UiO-67 solid acid catalyst. Using cyclohexanone oxime as a raw material, 15% (by mass) of the obtained AHPW / UiO-67 solid acid catalyst was added to catalyze the liquid-phase Beckmann rearrangement reaction of cyclohexanone oxime to prepare caprolactam. The reaction conditions were: 100°C, atmospheric pressure, and air atmosphere for 12 hours. After the reaction, the conversion rate of cyclohexanone oxime was 97.3%, and the selectivity of caprolactam was 99.0%. After centrifugation or filtration, the AHPW / UiO-67 catalyst could be reused more than 5 times while maintaining high catalytic activity, and the selectivity of caprolactam did not decrease significantly.

[0029] Example 9: Zirconium nitrate was dissolved in N,N-dimethylformamide at a molar ratio of 1.6:1. 4,4′-biphenyl dicarboxylic acid and 5% (by mass) formic acid were added, and the mixture was thoroughly mixed and transferred to a sealed reactor. A solvothermal reaction was carried out at 120°C for 24 hours. After the reaction, the resulting solid product was washed sequentially with N,N-dimethylformamide and anhydrous ethanol, and then activated under vacuum at 80°C for 6 hours to obtain a defective UiO-67 support. The UiO-67 support was dispersed in anhydrous 1,4-dioxane, and 3-aminopropyltriethoxysilane was added at a mass ratio of 1:3 to the support for grafting. After completion, unreacted material was washed away, and benzyl chloride was added. The reaction was carried out at room temperature for 12 hours to convert the amine groups on the support surface to a fixed positive potential, yielding a quaternized UiO-67 support. Simultaneously, phosphotungstic heteropolyacid H3PW... 12 O 40 Cesium nitrate was added to deionized water for partial neutralization, and the reaction was carried out at room temperature for 2 hours to obtain H. 2.2 CsP 0.8 W 12 O 40 Partially salted phosphotungsten heteropolyacid was then used. Finally, the partially salted phosphotungsten heteropolyacid solution was mixed with a quaternized UiO-67 support and subjected to a contact reaction under stirring. This allowed the phosphotungsten heteropolyacid to be immobilized on the support surface via ion-pair interactions. After the reaction, the resulting solid was washed and dried under mild conditions to obtain the AHPW / UiO-67 solid acid catalyst. Using cyclohexanone oxime as a raw material, 5% (by mass) of the obtained AHPW / UiO-67 solid acid catalyst was added to catalyze the liquid-phase Beckmann rearrangement reaction of cyclohexanone oxime to prepare caprolactam. The reaction conditions were: 60°C, atmospheric pressure, and air atmosphere for 4 hours. After the reaction, the conversion rate of cyclohexanone oxime was 95.5%, and the selectivity for caprolactam was 98.6%. The AHPW / UiO-67 catalyst, after centrifugation or filtration, could be reused more than 5 times while maintaining high catalytic activity, and the selectivity for caprolactam did not decrease significantly.

[0030] Product testing methods: The product was qualitatively and quantitatively analyzed using high-performance liquid chromatography (HPLC, UV detector), with C0 as the standard. 18 The chromatographic column was 4.6 × 250 mm, 5 μm; mobile phase: methanol-water = 50:50; flow rate: 1.0 mL / min; detection wavelength: 210 nm; column temperature: 30 °C. 1 mL of the reaction mixture was filtered through a 0.22 μm filter to remove the solid catalyst. The filtrate was then diluted with a methanol-water mixture before analysis. The external standard method (standard curve R) was used based on the peak area of ​​the sample. 2The caprolactam content was calculated using ≥0.999, and the cyclohexanone oxime conversion rate and caprolactam selectivity data were obtained. Three parallel tests were set up for each sample, and the relative standard deviation (RSD) was ≤2%.

[0031] Table 1. Comparison of the performance of different catalysts in the liquid-phase Beckmann rearrangement for the preparation of caprolactam.

[0032] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. However, these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions claimed by the present invention.

Claims

1. A method for preparing a solid acid catalyst for the synthesis of caprolactam, characterized in that, Includes the following steps: (1) The zirconium source was dissolved in N,N-dimethylformamide, 4,4′-biphenyldicarboxylic acid and modifier were added, and a solvothermal reaction was carried out. After washing and activation treatment, a defective UiO-67 support with an open metal site structure and lack of organic ligand was obtained by adding modifier to induce the formation of the structure. (2) The carrier obtained in step (1) is dispersed in an anhydrous organic solvent, and an organosilane containing an amino group is added to carry out a grafting reaction. Then, the amino group is converted into a fixed positive potential point through a quaternization reaction. (3) H3PW 12 O 40 A partial neutralization reaction is carried out with a cesium salt or an ammonium salt to produce a product with the general formula H. (3-X) A X PW 12 O 40 Partially salted phosphotungsten heteropolyacids, where A is Cs + or NH 4+ X is 0.8-1.8; (4) The partially salted phosphotungsten heteropoly acid obtained in step (3) is reacted with the modified support obtained in step (2) so that the partially salted phosphotungsten heteropoly acid is fixed on the support surface by forming electrostatic bonds with the quaternary ammonium groups on the support surface. After washing and drying activation, AHPW / UiO-67 solid acid catalyst is obtained.

2. The preparation method according to claim 1, characterized in that, In step (1), the molar ratio of 4,4′-biphenyldicarboxylic acid to zirconium source is 1:1.0-1:1.6; the zirconium source is zirconium oxychloride, zirconium nitrate or zirconium acetylacetonate.

3. The preparation method according to claim 1, characterized in that, In step (1), the temperature of the solvothermal reaction is 120-180℃, the reaction time is 24-72h, the modifier is formic acid, acetic acid or hydrochloric acid, and the amount is 5%-20% of the mass of 4,4′-biphenyldicarboxylic acid; the activation conditions are vacuum activation at 80-120℃ for 6-12h.

4. The preparation method according to claim 1, characterized in that, In step (2), the anhydrous organic solvent is anhydrous 1,4-dioxane, the amine-containing organosilane is 3-aminopropyltriethoxysilane or 3-aminopropyltrimethoxysilane, the mass ratio of organosilane to support is 1:3-1:7, the quaternizing agent is iodomethane, bromoethane or benzyl chloride, the quaternization reaction temperature is room temperature, and the reaction time is 12-24h.

5. The preparation method according to claim 1, characterized in that, In step (3), H3PW 12 O 40 The neutralization reaction with cesium or ammonium salts is carried out in an aqueous solution at room temperature for 2-4 hours; the cesium salt is cesium nitrate or cesium chloride, and the ammonium salt is ammonium nitrate or ammonium chloride.

6. The application of the AHPW / UiO-67 solid acid catalyst as described in claim 1 in the preparation of caprolactam via a catalytic liquid-phase Beckmann rearrangement reaction, characterized in that... The reaction conditions were as follows: cyclohexanone oxime was used as the raw material, the amount of catalyst was 5%-15% of the mass of cyclohexanone oxime, the reaction temperature was 60-100℃, the reaction pressure was atmospheric pressure, the reaction time was 4-12h, and the reaction atmosphere was air. After the reaction, the conversion rate of cyclohexanone oxime could reach more than 95.1%, the selectivity of caprolactam could reach more than 98.3%, and the catalyst could be reused more than 5 times after centrifugation or filtration and still maintain high catalytic activity, and the selectivity of caprolactam did not decrease significantly.

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