Highly selective catalyst for alkylpyridines and method for its preparation

Abstract

The application discloses a high-selectivity catalyst for alkyl pyridine and a preparation method thereof, raw material components include heteropoly acid and ionic liquid, after dissolving ammonium heptamolybdate, dilute sulfuric acid is added to adjust pH, and MnSO4 aqueous solution is slowly and uniformly added to the (NH4)6Mo7O 24 solution after acidification, ZnSO4 aqueous solution is added dropwise for reaction after reaction, cooling crystallization is carried out, and filtration, washing and drying are carried out, so that the heteropoly acid is obtained, the prepared heteropoly acid is dissolved, the ionic liquid is added, reaction is placed and precipitated, and through filtration, deionized water washing and drying, the heteropoly acid ionic liquid catalyst is obtained. The heteropoly acid ionic liquid catalyst has increased catalytic activity, and acid active sites are dispersed; through adjustment of transition metal content and proportion, selective catalysis is realized, and the yield of 3-methyl pyridine, dimethyl pyridine and trimethyl pyridine can be greatly improved.

Description

Technical Field

[0001] This invention relates to the field of catalyst synthesis and preparation technology, specifically to an alkylpyridine highly selective catalyst and its preparation method. Background Technology

[0002] Alkylpyridines, including monomethylpyridine and polymethylpyridines, are important chemical intermediates, used in pharmaceuticals, pesticides, fine chemical auxiliaries, and daily chemicals. Among them, 3-methylpyridine, 2,3-dimethylpyridine, 3,5-dimethylpyridine, and 2,3,5-trimethylpyridine are key intermediates for common drugs such as piroxicam, nicotinamide, pranoprofen, and omeprazole. Alkylpyridines are produced via aldehyde-ammonia condensation, side-chain alkylation synthesis, and alkyne and cyanocycloaddition. However, current industrial processes typically involve the simultaneous synthesis of pyridine and multiple alkylpyridines, with alkylpyridine bases being a low-proportion byproduct and the yield ratios of each pyridine base being fixed. This makes it difficult to flexibly adjust the pyridine base ratios to meet market demands. Therefore, achieving controllable alkylpyridine yield ratios and improving the overall yield of alkylpyridines are key areas for future research.

[0003] Patent application CN119215933A discloses a catalyst for the efficient synthesis of 3-methylpyridine and its preparation method. The catalyst is a S-doped Ni-Al composite layered metal oxide / SiO2 complex supported on W / Cu oxide, prepared by a co-precipitation method, possessing a large specific surface area and total pore volume. 3-methylpyridine is synthesized by hydrogenation and dehydrogenation of 2-methylpentanilonitrile under the catalytic action, achieving a yield of up to 97%. However, the raw material is not readily available, resulting in low feasibility for practical industrial production. Patent application CN121178207A discloses a supported catalyst for the synthesis of 3,5-dimethylpyridine and its preparation method. The catalyst was prepared by equal volume impregnation and calcination to produce modified HY molecular sieves supported on Fe, Mo and La oxides. It catalyzes the synthesis of 3,5-dimethylpyridine from methanol, propionaldehyde and ammonia, with a maximum yield of 70.5%. There is still room for improvement in the reaction conversion rate, and the by-product separation process is cumbersome.

[0004] Therefore, the industry focuses on improving production efficiency and adapting to market demands and process complexity by changing the catalyst composition to achieve controllability of the alkylpyridine production ratio during pyridine synthesis. Summary of the Invention

[0005] The purpose of this invention is to provide a highly selective alkylpyridine catalyst and its preparation method, which enables the controllability of the alkylpyridine production ratio during pyridine synthesis, thereby solving the problems of low alkylpyridine yield and fixed yield ratio of each pyridine base in existing pyridine synthesis processes.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A highly selective alkylpyridine catalyst, comprising a heteropolyacid and an ionic liquid as feedstock, wherein the molar ratio of the ionic liquid to the heteropolyacid is 3.5-1.5, wherein the heteropolyacid feedstock comprises (NH4)6Mo7O 24 The raw materials are MnSO4 and ZnSO4, wherein the molar mass ratio of the raw materials is Mo:(Mn+Zn)=6:1.

[0007] Further, the ionic liquid includes [MeO(CH2)2MIM]Tf2N (1-methoxyethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide), [OMIM]BF4 (1-octyl-3-methylimidazolium tetrafluoroborate), [BMIM]PF6 (1-butyl-3-methylimidazolium hexafluorophosphate), and [BMIM]N(CN)2 (1-butyl-3-methylimidazolium dicyanamide).

[0008] This invention provides a preparation method for preparing a highly selective alkylpyridine catalyst, comprising the following steps: Step 1: Add (NH4)6Mo7O 24 After complete dissolution, dilute sulfuric acid is added to adjust the pH. The MnSO4 aqueous solution is then slowly and evenly added dropwise to the acidified (NH4)6Mo7O. 24 After adding the solution dropwise and reacting for a period of time, ZnSO4 aqueous solution is slowly and evenly added dropwise to continue the reaction. After the reaction is complete, the solution is cooled to crystallize, filtered, washed, and dried to obtain heteropolyacids. Step 2: Dissolve the prepared heteropolyacid, slowly add the ionic liquid, allow the reaction to stand and precipitate, filter, wash with deionized water, and dry at 60°C for 8 hours to obtain the heteropolyacid ionic liquid catalyst.

[0009] Furthermore, the heteropolyacid obtained in step 1 is an Anderson-type heteropolyacid.

[0010] Furthermore, in step 1, dilute sulfuric acid is added to adjust the pH to 3.1~3.4.

[0011] Furthermore, in the reaction of step 1, the stoichiometric ratio of Mn:Zn is 0~1.

[0012] Furthermore, in step 1, after adding the MnSO4 aqueous solution, the reaction is carried out at a temperature of 25-30℃ for 0.5-1.0 h, and after adding the ZnSO4 aqueous solution, the reaction is carried out at a temperature of 60-65℃ for 2-3 h. When adding the MnSO4 aqueous solution and the ZnSO4 aqueous solution, the pH is maintained at 3.1-3.4.

[0013] Furthermore, the cooling crystallization conditions are as follows: rotary evaporation under reduced pressure at 60°C until the solution volume is 30-35%, followed by cooling and crystallization in an ice bath.

[0014] Furthermore, during the filtration in step 1, the sample is first washed with ice water and then with ethanol, and then vacuum dried at 50°C for 2 hours.

[0015] Furthermore, the solutions in both steps 1 and 2 are prepared with deionized water, and the reaction in step 2 is allowed to stand in an ice bath for 18 hours to allow precipitation.

[0016] Compared with the prior art, the beneficial effects of the present invention are: This invention employs an aqueous phase method to condense molybdate and heteroatom salt under acidic conditions to form heteropolyacids. These heteropolyacid ionic liquid catalysts are then synthesized through ion exchange with ionic liquids. The chemical bonds are weakened and the reaction difficulty is reduced through a dual-acidic-center catalytic mechanism and hydrogen bond activation. Compared to single heteropolyacids and single ionic liquids, the heteropolyacid ionic liquid catalysts of this invention exhibit increased catalytic activity and dispersed acidic active sites. Selective catalysis is achieved by adjusting the content and ratio of transition metals, resulting in significantly improved yields of 3-methylpyridine, dimethylpyridine, and trimethylpyridine, meeting the demands of industrial production. Detailed Implementation

[0017] The embodiments of the present invention will be described in detail below; however, the embodiments of the present invention are not limited thereto. 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. Example 1

[0018] Heteropolyacid ionic liquid catalysts with different ionic liquids.

[0019] (NH4)6Mo7O 24 After the ammonium heptamolybdate was completely dissolved, dilute sulfuric acid was added to adjust the pH to 3.2. The manganese sulfate aqueous solution was slowly added dropwise to the acidified ammonium heptamolybdate solution, and the reaction was carried out at 30°C for 1.0 h. Then, zinc sulfate aqueous solution was slowly added dropwise, and the reaction was carried out at 62°C for 3 h. The stoichiometric ratio of manganese sulfate to zinc sulfate solution was Mn:Zn=1:1. After the reaction was completed, the solution was rotary evaporated under reduced pressure at 60°C to 30% of its volume. The solution was cooled and crystallized in an ice bath. The solution was then filtered, washed, and dried (washed with ice water and then ethanol during filtration, and dried under vacuum at 50°C for 2 h) to obtain heteropoly acid.

[0020] The prepared heteropolyacid was dissolved, and the ionic liquid [MeO(CH2)2MIM]Tf2N was slowly added. The reaction was allowed to stand and precipitate (standing in an ice bath for 18 h). After filtration, washing with deionized water, and drying at 60 °C for 8 h, the heteropolyacid ionic liquid catalyst 1 was obtained.

[0021] The prepared heteropolyacid was dissolved, and the ionic liquid [OMIM]BF4 was slowly added. The reaction was allowed to stand and precipitate (standing in an ice bath for 18 hours). After filtration, washing with deionized water, and drying at 60°C for 8 hours, the heteropolyacid ionic liquid catalyst 2 was obtained.

[0022] The prepared heteropolyacid was dissolved, and the ionic liquid [BMIM]PF6 was slowly added. The reaction was allowed to stand and precipitate (standing in an ice bath for 18 hours). After filtration, washing with deionized water, and drying at 60°C for 8 hours, the heteropolyacid ionic liquid catalyst 3 was obtained.

[0023] The prepared heteropolyacid was dissolved, and the ionic liquid [BMIM]N(CN)2 was slowly added. The reaction was allowed to stand and precipitate (standing in an ice bath for 18 hours). After filtration, washing with deionized water, and drying at 60°C for 8 hours, the heteropolyacid ionic liquid catalyst 4 was obtained.

[0024] Heteropolyacid ionic liquid catalysts 1-4 were loaded into a fixed-bed reactor. Before reaction, they were activated and calcined in air at 300℃ for 1 hour. The raw materials were formaldehyde, acetaldehyde, and ammonia, with 1% catalyst. The mixture was then reacted at a temperature of 260℃, a pressure of 0.20 MPa, a reaction time of 3 hours, and a feed flow rate of 0.6 g / min. The catalytic activity of the heteropolyacid ionic liquid catalysts with different ionic liquids was evaluated, and the data are shown in Table 1 below.

[0025]

[0026] As shown in Table 1, the yield ratio of pyridine base can be altered by changing the type of ionic liquid. When using heteropolyacid ionic liquid catalyst 1, the pyridine yield reaches 63%. When using heteropolyacid ionic liquid catalyst 2, the pyridine proportion decreases, while the 3-methylpyridine proportion increases to 35%. Of the four selected ionic liquids, those with imidazole as the parent structure exhibit the best catalytic activity and selectivity. Specifically, heteropolyacid ionic liquid catalyst 2 has a long alkyl side chain with increased steric hindrance, leading to enhanced selectivity. The anion BF4... - It is a weakly coordinating anion with weak interactions, and its reaction selectivity is relatively good based on hydrogen bonding. Example 2

[0027] Heteropolyacid ionic liquid catalysts with different stoichiometric ratios of manganese sulfate and zinc sulfate solutions.

[0028] After completely dissolving ammonium heptamolybdate, dilute sulfuric acid was added to adjust the pH to 3.2. A manganese sulfate aqueous solution was slowly added dropwise to the acidified ammonium heptamolybdate solution, and the reaction was carried out at 30°C for 1.0 h. Then, a zinc sulfate aqueous solution was slowly added dropwise, and the reaction was carried out at 62°C for 3 h. The stoichiometric ratio of manganese sulfate to zinc sulfate was 3:1. After the reaction was complete, the solution was rotary evaporated under reduced pressure at 60°C until it reached 30% of its original volume. The solution was then cooled and crystallized in an ice bath. The crystals were then filtered, washed, and dried to obtain a heteropoly acid (during filtration, the solution was first washed with ice water and then with ethanol, and then dried under vacuum at 50°C for 2 h).

[0029] The prepared heteropolyacid was dissolved, and the ionic liquid [OMIM]BF4 was slowly added. The reaction was allowed to stand and precipitate (standing in an ice bath for 18 hours). After filtration, washing with deionized water, and drying at 60°C for 8 hours, the heteropolyacid ionic liquid catalyst 5 was obtained.

[0030] After completely dissolving ammonium heptamolybdate, dilute sulfuric acid was added to adjust the pH to 3.2. A manganese sulfate aqueous solution was slowly added dropwise to the acidified ammonium heptamolybdate solution, and the reaction was carried out at 30°C for 1.0 h. Then, a zinc sulfate aqueous solution was slowly added dropwise, and the reaction was carried out at 62°C for 3 h. The stoichiometric ratio of manganese sulfate to zinc sulfate was 2:1 (Mn:Zn). After the reaction was complete, the solution was rotary evaporated under reduced pressure at 60°C until 30% of its volume was reached. The solution was then cooled and crystallized in an ice bath. The crystals were then filtered, washed, and dried (during filtration, the solution was first washed with ice water and then with ethanol, and then dried under vacuum at 50°C for 2 h) to obtain a heteropoly acid.

[0031] The prepared heteropolyacid was dissolved, and the ionic liquid [OMIM]BF4 was slowly added. The reaction was allowed to stand and precipitate (standing in an ice bath for 18 hours). After filtration, washing with deionized water, and drying at 60°C for 8 hours, the heteropolyacid ionic liquid catalyst 6 was obtained.

[0032] After completely dissolving ammonium heptamolybdate, dilute sulfuric acid was added to adjust the pH to 3.2. A manganese sulfate aqueous solution was slowly added dropwise to the acidified ammonium heptamolybdate solution, and the reaction was carried out at 30°C for 1.0 h. Then, a zinc sulfate aqueous solution was slowly added dropwise, and the reaction was carried out at 62°C for 3 h. The stoichiometric ratio of manganese sulfate to zinc sulfate was Mn:Zn = 1:2. After the reaction was complete, the solution was rotary evaporated under reduced pressure at 60°C until 30% of its volume was reached. The solution was then cooled and crystallized in an ice bath. The crystals were then filtered, washed, and dried (during filtration, the solution was first washed with ice water and then with ethanol, and then dried under vacuum at 50°C for 2 h) to obtain a heteropoly acid.

[0033] The prepared heteropolyacid was dissolved, and the ionic liquid [OMIM]BF4 was slowly added. The reaction was allowed to stand and precipitate (standing in an ice bath for 18 hours). After filtration, washing with deionized water, and drying at 60°C for 8 hours, the heteropolyacid ionic liquid catalyst 7 was obtained.

[0034] After completely dissolving ammonium heptamolybdate, dilute sulfuric acid was added to adjust the pH to 3.2. A manganese sulfate aqueous solution was slowly added dropwise to the acidified ammonium heptamolybdate solution, and the reaction was carried out at 30°C for 1.0 h. Then, a zinc sulfate aqueous solution was slowly added dropwise, and the reaction was carried out at 62°C for 3 h. The stoichiometric ratio of manganese sulfate aqueous solution to zinc sulfate solution was 1:3 (Mn:Zn). After the reaction was complete, the solution was rotary evaporated under reduced pressure at 60°C until 30% of its volume was reached. The solution was then cooled and crystallized in an ice bath. The crystals were then filtered, washed, and dried (during filtration, the solution was first washed with ice water and then with ethanol, and then dried under vacuum at 50°C for 2 h) to obtain a heteropoly acid.

[0035] The prepared heteropolyacid was dissolved, and the ionic liquid [OMIM]BF4 was slowly added. The reaction was allowed to stand and precipitate (standing in an ice bath for 18 hours). After filtration, washing with deionized water, and drying at 60°C for 8 hours, the heteropolyacid ionic liquid catalyst 8 was obtained.

[0036] Comparative Example 1 After completely dissolving ammonium heptamolybdate, dilute sulfuric acid was added to adjust the pH to 3.2. A manganese sulfate aqueous solution was slowly added dropwise to the acidified ammonium heptamolybdate solution, and the reaction was carried out at 30°C for 1.0 h. Then, a zinc sulfate aqueous solution was slowly added dropwise, and the reaction was carried out at 62°C for 3 h. The stoichiometric ratio of manganese sulfate to zinc sulfate was 1:1 (Mn:Zn). After the reaction was complete, the solution was rotary evaporated under reduced pressure at 60°C until 30% of its volume was reached. The solution was then cooled and crystallized in an ice bath. The crystals were then filtered, washed, and dried (during filtration, the solution was first washed with ice water and then with ethanol, and then dried under vacuum at 50°C for 2 h) to obtain the heteropolyacid catalyst.

[0037] Comparative Example 2 The ionic liquid [OMIM]BF4 catalyst was purchased from the market.

[0038] Heteropolyacid ionic liquid catalyst 2, heteropolyacid ionic liquid catalysts 5-8, and catalysts from comparative examples 1-2 were loaded into a fixed-bed reactor and activated and calcined in air at 300℃ for 1 hour before reaction. The raw materials were formaldehyde, acetaldehyde, ammonia, and 1% catalyst. The mixture was reacted at a temperature of 260℃, a pressure of 0.20 MPa, a reaction time of 3 hours, and a feed flow rate of 0.6 g / min. The catalytic activity of the heteropolyacid ionic liquid catalysts with different ionic liquids was evaluated, and the data are shown in Table 2 below.

[0039]

[0040] As shown in Table 2, the yield ratio of pyridine bases can be controlled by adjusting the manganese and zinc transition metal content. With increasing manganese content, the yields of 2,3-methylpyridine and 3,5-methylpyridine increase, with the total yield reaching 45%. With increasing zinc content, the yield of 3-methylpyridine increases significantly. When the stoichiometric ratio of manganese to zinc is 1:3, the yield of 3-methylpyridine is 53%, while the yields of 2,3-dimethylpyridine, 3,5-dimethylpyridine, and 2,3,5-trimethylpyridine all reach over 10%. This is because zinc, after modification, strongly coordinates with pyridine, promoting electrophilic attack on pyridine alkylation. The controllability of alkylpyridine synthesis can be achieved by adjusting the proportion of each metal in the catalyst.

[0041] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A highly selective alkylpyridine catalyst, characterized in that, The raw material components include heteropolyacids and ionic liquids, with the ratio of the amount of ionic liquid to the molar amount of heteropolyacid being 3.5-1.

5. The raw material components of the heteropolyacid include (NH₄)₆Mo₇O₇. 24 The raw materials are MnSO4 and ZnSO4, wherein the molar mass ratio of the raw materials is Mo:(Mn+Zn)=6:

1.

2. The alkylpyridine highly selective catalyst according to claim 1, characterized in that, The ionic liquid includes 1-methoxyethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt, 1-octyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium hexafluorophosphate, and 1-butyl-3-methylimidazolium dicyanamide salt.

3. A preparation method for preparing the alkylpyridine highly selective catalyst of claim 1, characterized in that, Includes the following steps: Step 1: Add (NH4)6Mo7O 24 After complete dissolution, dilute sulfuric acid is added to adjust the pH. The MnSO4 aqueous solution is then slowly and evenly added dropwise to the acidified (NH4)6Mo7O. 24 After adding the solution dropwise and reacting for a period of time, ZnSO4 aqueous solution is slowly and evenly added dropwise to continue the reaction. After the reaction is complete, the solution is cooled to crystallize, filtered, washed, and dried to obtain heteropolyacids. Step 2: Dissolve the prepared heteropolyacid, slowly add the ionic liquid, allow the reaction to stand and precipitate, filter, wash with deionized water, and dry at 60°C for 8 hours to obtain the heteropolyacid ionic liquid catalyst.

4. The method for preparing an alkylpyridine highly selective catalyst according to claim 3, characterized in that, The heteropolyacid obtained in step 1 is an Anderson-type heteropolyacid.

5. The method for preparing an alkylpyridine highly selective catalyst according to claim 3, characterized in that, When adding MnSO4 aqueous solution and ZnSO4 aqueous solution dropwise, the pH is adjusted to be maintained at 3.1~3.4 using dilute sulfuric acid.

6. The method for preparing an alkylpyridine highly selective catalyst according to claim 3, characterized in that, In the reaction of step 1, the stoichiometric ratio of Mn:Zn is 0~1.

7. A method for preparing an alkylpyridine highly selective catalyst according to claim 3, characterized in that, In step 1, after adding the MnSO4 aqueous solution, the reaction is carried out at a temperature of 25-30℃ for 0.5-1.0 h, and after adding the ZnSO4 aqueous solution, the reaction is carried out at a temperature of 60-65℃ for 2-3 h.

8. The method for preparing an alkylpyridine highly selective catalyst according to claim 3, characterized in that, The cooling crystallization conditions are as follows: rotary evaporation under reduced pressure at 60°C until the solution volume is 30-35%, followed by cooling and crystallization in an ice bath.

9. The method for preparing an alkylpyridine highly selective catalyst according to claim 3, characterized in that, In step 1, the filter is first washed with ice water and then with ethanol, and then dried under vacuum at 50°C for 2 hours.

10. The method for preparing an alkylpyridine highly selective catalyst according to claim 3, characterized in that, The solutions in both steps 1 and 2 are prepared with deionized water, and the reaction in step 2 is allowed to stand in an ice bath for 18 hours to allow the precipitation to occur.

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