A method for pyridine alkylation

Abstract

The invention discloses a method for pyridine alkylation, comprising the following steps: using anhydrous titanium chloride and anhydrous ferric chloride solution as raw materials, adding a dispersant and then heating and stirring evenly, then adding ammonia to adjust the pH to a fixed value, grinding and sieving to obtain a catalyst support; immersing an equal volume of the catalyst support into a rare earth metal oxide solution dissolved in dilute sulfuric acid for aging, grinding and sieving to obtain a rare earth metal-modified solid superacid catalyst; after activation of the rare earth metal-modified solid superacid catalyst, the reaction temperature is lowered to be loaded into a fluidized bed reaction tube, pyridine and dimethyl carbonate are mixed and fed, and nitrogen is introduced into the air inlet valve at the same time. The raw material mixed nitrogen reacts in the catalyst layer to achieve high-selectivity pyridine alkylation. Using pyridine and green methylating agent dimethyl carbonate as raw materials, under the action of a rare earth metal-modified solid superacid catalyst, 2-methylpyridine can be synthesized with high selectivity.

Description

Technical Field

[0001] The present invention relates to the technical field of pyridine alkylation, in particular to a pyridine alkylation method. Background Art

[0002] Picoline compounds include 2-methylpyridine, 3-methylpyridine, 4-methylpyridine, 3,5-dimethylpyridine, and 2,4,6-trimethylpyridine. These are important chemical raw materials and organic intermediates used in the production of pesticides, pharmaceuticals, feed, and fertilizers. Currently, alkylpyridines are produced through direct synthesis using the aldehyde-ketone-ammonia method, direct alkylation of pyridine, and direct synthesis using unsaturated olefins and methyl nitrile. Direct alkylation of pyridine side chains offers the advantages of high selectivity and minimal byproducts, making them suitable for industrial production. However, there are drawbacks such as harsh reaction conditions and poor catalyst selectivity. To address this, several pyridine alkylation schemes have been developed. For example, Chinese Patent Publication No. CN109174168B discloses a method for preparing a catalyst for pyridine alkylation to produce 2-methylpyridine. The catalyst uses a sodium molecular sieve as a matrix, one or more of Ba, Mg, Ca, and Fe as a first additive, and one or more of Co, Bi, Cu, and Zn as a second additive. The catalyst is obtained by impregnation followed by calcination. The catalytic synthesis of 2-methylpyridine is simple, highly selective, and exhibits excellent catalyst regeneration. Using pyridine and methanol as raw materials, the pyridine conversion rate can reach 69.9%, and the maximum yield of 2-methylpyridine is 50.6%. Chinese Patent Publication No. CN110038630B discloses a method for synthesizing a molecular sieve catalyst for synthesizing 3-methylpyridine. This catalyst is prepared by mixing and calcining a HEU-1 molecular sieve with an aluminum source. When the catalyst is used in the reaction of synthesizing 3-methylpyridine from raw materials acrolein, propionaldehyde and ammonia, the selectivity for 3-methylpyridine is better, reaching a maximum of 63.80%.

[0003] When the above catalysts are used for pyridine alkylation, their conversion rates and yields are relatively low, resulting in high costs and failing to meet current industrial needs. Summary of the Invention

[0004] The present invention aims to provide a method for the alkylation of pyridine, which uses pyridine and a green methylating agent, dimethyl carbonate, as raw materials, and can achieve high-selectivity synthesis of 2-methylpyridine under the action of a rare earth metal modified solid superacid catalyst, thereby reducing costs and improving efficiency, thereby solving the problems raised in the above-mentioned background technology.

[0005] To achieve the above object, the present invention provides the following technical solution: a method for alkylation of pyridine, comprising the following steps:

[0006] Anhydrous titanium chloride and anhydrous ferric chloride solution are used as raw materials, a dispersant is added, and then heated and stirred evenly, and then ammonia water is added to adjust the pH to a constant value, and after precipitation and aging, the solution is filtered, washed, dried, and ground and sieved to obtain a catalyst carrier;

[0007] The catalyst support is immersed in an equal volume of rare earth metal oxide solution dissolved in dilute sulfuric acid for aging, filtered, washed, dried, calcined, ground and sieved to obtain a rare earth metal modified solid super acid catalyst;

[0008] After activation of the rare earth metal modified solid superacid catalyst is completed, the catalyst is cooled to the reaction temperature and loaded into the fluidized bed reaction tube. Pyridine and dimethyl carbonate are mixed and fed. At the same time, the air inlet valve is opened to introduce nitrogen. The raw materials and nitrogen react in the catalyst layer. The product is condensed and collected by a condensation device to achieve highly selective pyridine alkylation.

[0009] Furthermore, the anhydrous ferric chloride is dissolved in anhydrous ethanol, the concentration of which is controlled at 0.5 mol / L, the stoichiometric ratio of anhydrous titanium chloride to anhydrous ferric chloride solution is 1 / 6, and the anhydrous titanium chloride is added dropwise to the anhydrous ferric chloride solution.

[0010] Furthermore, the added dispersant was octadecanoic acid, and the mixture was heated and stirred at 40° C. for 2 h to be fully mixed.

[0011] Furthermore, the precipitation aging is carried out at room temperature, the solution pH is adjusted to 9.3, the aging time is 6 hours, and an equal volume of the catalyst support is immersed in a rare earth metal oxide solution dissolved in dilute sulfuric acid for 6 hours.

[0012] Furthermore, the washing conditions in the preparation step of the catalyst support are: washing with deionized water until there is no Cl - It was found that the drying conditions in the preparation step of the catalyst support were: the gel obtained after washing was dried at 180°C for 8 hours.

[0013] Furthermore, the rare earth metal oxide is Sc2O3, and the solution concentration is 0.3 mol / L.

[0014] Furthermore, the drying temperature of the calcination after the filtration, washing and drying is 120° C., the time is 14 hours, and the calcination process temperature is 400° C.-800° C., and the time is 1.5 hours.

[0015] Furthermore, the methylating agent is dimethyl carbonate, and the molar ratio of dimethyl carbonate to pyridine is 1.5-2.5.

[0016] Furthermore, in the rare earth metal-modified solid superacid catalyst, a composite metal oxide synthesized from TiO2 and Fe2O3 is used as the acid center, and the rare earth metal stabilizes the B acid center to produce an L acid center. During the reaction, the B acid center is activated, donating a proton to add to pyridine to form a positive carbon ion, which undergoes an alkylation reaction with dimethyl carbonate.

[0017] Furthermore, the feed flow rate in the fluidized bed reaction tube is 0.3 g / min, the reaction temperature is 300°C-700°C, the reaction pressure is 0.08 MPa-0.12 MPa, the reaction time is 4 h, and the rare earth metal modified solid super acid catalyst is activated at 500°C for two hours in an air atmosphere.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] The present invention uses a rare earth metal modified solid super acid catalyst to catalyze the alkylation of pyridine. Pyridine and dimethyl carbonate are used as raw materials to prepare a metal salt mixed solution in a certain molar ratio to obtain the desired rare earth metal modified solid super acid. The addition of rare earth metals makes the SO4 on the solid super acid 2- It is not easy to lose, thereby improving the stability of the catalyst, significantly improving the selectivity and yield of 2-methylpyridine, and has the advantages of high activity, high selectivity, low corrosiveness and long service life. At the same time, the use of green methylation reagent dimethyl carbonate has low toxicity and excellent environmental performance, reducing the pressure of hazardous waste treatment in the process. DETAILED DESCRIPTION

[0020] The following will describe the embodiments of the present invention in detail, however, the embodiments of the present invention are not limited thereto. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0021] Example 1: Anhydrous titanium chloride was added dropwise to anhydrous ferric chloride solution in a stoichiometric ratio of 1 / 6 and mixed, a dispersant was added, heated and stirred at 40°C for 2h, and then fully mixed, and ammonia was added to adjust the pH to 9.3. The gel was precipitated and aged at room temperature for 6h, filtered and washed, and then dried at 180°C for 8h, ground and sieved to obtain a catalyst support. An equal volume of the catalyst support was immersed in a 0.3 mol / L scandium oxide solution dissolved in dilute sulfuric acid and aged for 6h, filtered and washed, dried at 120°C for 14 hours, and then calcined at 400°C for 1.5h. The rare earth metal modified solid super acid catalyst 1 was ground and sieved.

[0022] Example 2: Anhydrous titanium chloride was added dropwise to anhydrous ferric chloride solution in a stoichiometric ratio of 1 / 6 and mixed, a dispersant was added, heated and stirred at 40°C for 2h, and then fully mixed, and ammonia was added to adjust the pH to 9.3. The gel was precipitated and aged at room temperature for 6h, filtered and washed, and then dried at 180°C for 8h, ground and sieved to obtain a catalyst support. An equal volume of the catalyst support was immersed in a 0.3 mol / L scandium oxide solution dissolved in dilute sulfuric acid and aged for 6h, filtered, washed, dried at 120°C for 14 hours, and then calcined at 500°C for 1.5h. The rare earth metal modified solid super acid catalyst 2 was ground and sieved.

[0023] Example 3: Anhydrous titanium chloride was added dropwise to anhydrous ferric chloride solution in a stoichiometric ratio of 1 / 6 and mixed, a dispersant was added, heated and stirred at 40°C for 2 hours, and then fully mixed, ammonia was added to adjust the pH to 9.3. The gel was precipitated and aged at room temperature for 6 hours, filtered and washed, and then dried at 180°C for 8 hours. The gel was ground and sieved to obtain a catalyst support. An equal volume of the catalyst support was immersed in a 0.3 mol / L scandium oxide solution dissolved in dilute sulfuric acid and aged for 6 hours. The solution was filtered, washed, dried at 120°C for 14 hours, and then calcined at 600°C for 1.5 hours. The rare earth metal modified solid super acid catalyst 3 was ground and sieved.

[0024] Example 4: Anhydrous titanium chloride was added dropwise to anhydrous ferric chloride solution in a stoichiometric ratio of 1 / 6 and mixed, a dispersant was added, heated and stirred at 40°C for 2 hours, and then fully mixed, and ammonia water was added to adjust the pH to 9.3. The gel was precipitated and aged at room temperature for 6 hours, filtered and washed, and then dried at 180°C for 8 hours. The gel was ground and sieved to obtain a catalyst support. An equal volume of the catalyst support was immersed in a 0.3 mol / L scandium oxide solution dissolved in dilute sulfuric acid and aged for 6 hours. The solution was filtered, washed, dried at 120°C for 14 hours, and then calcined at 700°C for 1.5 hours. The rare earth metal modified solid super acid catalyst 4 was ground and sieved.

[0025] Example 5: Anhydrous titanium chloride was added dropwise to anhydrous ferric chloride solution in a stoichiometric ratio of 1 / 6 and mixed, a dispersant was added, heated and stirred at 40°C for 2 hours, and then fully mixed, ammonia water was added to adjust the pH to 9.3. The gel was precipitated and aged at room temperature for 6 hours, filtered and washed, and then dried at 180°C for 8 hours. The gel was ground and sieved to obtain a catalyst support. An equal volume of the catalyst support was immersed in a 0.3 mol / L scandium oxide solution dissolved in dilute sulfuric acid and aged for 6 hours. The solution was filtered, washed, dried at 120°C for 14 hours, and then calcined at 800°C for 1.5 hours. The rare earth metal modified solid super acid catalyst 5 was ground and sieved.

[0026] 15g of each of the rare earth metal modified solid super acid catalysts 1-5 was loaded into a fluidized bed reaction tube. Before the reaction, the rare earth metal modified solid super acid catalysts 1-5 were activated at 500°C for 2 hours under an air atmosphere. Dimethyl carbonate was used as the methylating agent, with a molar ratio of dimethyl carbonate to pyridine of 1.5. After mixing, the reaction was carried out at a reaction temperature of 500°C, a reaction pressure of 0.12 MPa, a reaction time of 4 hours, and a feed flow rate of 0.3 g / min. The catalytic activity of the rare earth metal modified solid super acid catalyst for pyridine alkylation was tested by liquid chromatography, and the data shown in Table 1 were obtained.

[0027]

[0028] As can be seen from the results in Table 1, the conversion rate of pyridine alkylation can be improved by controlling the calcination temperature of the solid superacid, and the proportion of 2-methylpyridine in the product is relatively high. As for the yield of 2-methylpyridine, the calcination temperature of the solid superacid of Examples 1-3 gradually increases, so that the catalytic activity of the rare earth metal modified solid superacid catalysts 1-3 for pyridine alkylation also gradually increases. When the calcination temperature is 600°C, the yield of 2-methylpyridine reaches a maximum of 60.25%. As the calcination temperature of Examples 4-5 gradually increases, the yield of 2-methylpyridine shows a gradual downward trend. This is because the calcination temperature of Examples 4-5 is too high, which destroys the acid center and causes a significant decrease in catalytic efficiency.

[0029] The results of the investigation of the process conditions for pyridine alkylation using rare earth metal modified solid superacid catalysts are shown in Table 2:

[0030]

[0031] 15g of rare earth metal-modified solid superacid catalyst 3 was loaded into a fluidized bed reactor. Prior to the reaction, the catalyst was activated at 500°C for 2 hours under air. The raw materials were mixed using varying molar ratios of methylating agent to pyridine, and the reaction was conducted at various reaction temperatures and pressures for 4 hours. The results of pyridine alkylation using rare earth metal-modified solid superacid catalyst 3 using various process parameters are shown in Table 2. Using rare earth metal-modified solid superacid catalyst 3, the reaction temperature was 400°C, the molar ratio of methylating agent to pyridine was 1.75, and the reaction pressure was 0.12 MPa. The pyridine conversion reached 89.21%, the yield of 2-methylpyridine reached 78.52%, and the selectivity reached 88.02%. This demonstrates the catalyst's high recyclability and excellent catalytic activity and selectivity for 2-methylpyridine.

[0032] Comparative Example 1: Anhydrous titanium chloride was added dropwise to an anhydrous ferric chloride solution in a stoichiometric ratio of 1 / 6 and mixed, a dispersant was added, heated and stirred at 40°C for 2 hours, and then fully mixed, and ammonia water was added to adjust the pH to 9.3. The gel was precipitated and aged at room temperature for 6 hours, filtered and washed, and then dried at 180°C for 8 hours. The obtained gel was ground and sieved to obtain a catalyst support, and an equal volume of the catalyst support was immersed in a 0.3 mol / L dilute sulfuric acid solution and aged for 6 hours. After filtering and washing, it was dried at 120°C for 14 hours and calcined at 600°C for 1.5 hours. The rare earth metal unmodified solid super acid catalyst was ground and sieved.

[0033] Comparative Example 2: 21g SiO2 powder and 40g sesbania powder were added to 400g pseudo-boehmite powder, 300g water was added, the mixture was mechanically stirred and mixed, extruded into strips, dried at 120°C for 12h, and calcined at 600°C for 4h to obtain a carrier. 120g of the carrier was added to 100mL of an ethanol solution containing 175g nickel nitrate hexahydrate, 7.3g lanthanum nitrate hexahydrate, and ethylenediamine (ethylenediamine: metal ion = 2:1), stirred at room temperature for 3h, rotary evaporated at 60°C, dried at 120°C for 12h, and calcined at 450°C for 3h to obtain a catalyst precursor with a loading of 26.8% NiO-1.6% La2O3. The catalyst precursor was reduced with H2 (10%) at 450°C for 4h to obtain a SiO2-modified γ-Al2O3 catalyst.

[0034] Comparative Example 3: A commercially available metal-modified H-β zeolite catalyst was selected.

[0035] 15g of each catalyst from Comparative Examples 1-3 was loaded into a fluidized bed reactor. The catalysts were activated at 500°C for 2 hours under air before the reaction. Dimethyl carbonate was used as the methylating agent in a molar ratio of 1.75 to pyridine. After mixing, the reaction was carried out at 400°C, a pressure of 0.12 MPa, a reaction time of 4 hours, and a feed rate of 0.3 g / min. The catalytic activity of the catalysts from Example 3 and Comparative Examples 1-3 for the alkylation of pyridine was tested by liquid chromatography, yielding the data shown in Table 3.

[0036]

[0037] As can be seen from Table 3, compared with Comparative Example 1, the pyridine conversion rate, 2-methylpyridine yield and selectivity of the catalyst of Example 3 are significantly better than those of Comparative Example 1, indicating that the catalytic activity and stability of the solid superacid after rare earth metal modification are significantly enhanced. The reason is that the addition of rare earth metals makes the SO4 2-It is not easy to lose, thereby improving stability. Under the same reaction conditions, compared with Comparative Example 2 and Comparative Example 3, although Comparative Example 2 and Comparative Example 3 are also metal-modified catalysts, the pyridine conversion rate and 2-methylpyridine yield after catalysis by the solid superacid modified with rare earth metal are significantly higher than those in Comparative Example 2 and Comparative Example 3. This is because the average particle size of the catalyst matrix crystal is smaller when the rare earth metal is calcined, the specific surface area is larger, and the surface TiO2-Fe2O3 can be dispersed and stabilized, thereby reacting with more SO4 2- The combination forms acid sites, improving the reaction activity and stability of the catalyst. The rare earth metal-modified solid superacid catalyst proposed in the present invention can achieve a higher yield in the synthesis of 2-methylpyridine. At the same time, the use of a green methylation reagent reduces the generation of polluting by-products, which has obvious advantages.

[0038] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A method for pyridine alkylation, characterized in that: The steps include: Anhydrous titanium chloride and anhydrous ferric chloride solution are used as raw materials, anhydrous ferric chloride is dissolved in anhydrous ethanol, the concentration is controlled at 0.5 mol / L, the stoichiometric ratio of anhydrous titanium chloride and anhydrous ferric chloride solution is 1 / 6, the anhydrous titanium chloride is added dropwise to the anhydrous ferric chloride solution, a dispersant is added and heated and stirred evenly, the dispersant is octadecanoic acid, the mixture is heated and stirred at 40° C. for 2 hours and fully mixed, then ammonia water is added to adjust the pH to a constant value, the precipitation is aged, filtered, washed, dried, and ground and sieved to obtain a catalyst support; The catalyst support is immersed in an equal volume of a rare earth metal oxide solution dissolved in dilute sulfuric acid for aging, wherein the rare earth metal oxide is Sc2O3 and the solution concentration is 0.3 mol / L. The catalyst support is filtered, washed, dried, and then calcined. The drying temperature of the calcined catalyst support is 120°C for 14 hours, and the calcination process temperature is 400°C-800°C for 1.5 hours. The catalyst support is then ground and sieved to obtain a rare earth metal modified solid super acid catalyst. After activation of the rare earth metal modified solid superacid catalyst is completed, the catalyst is cooled to the reaction temperature and loaded into the fluidized bed reaction tube. Pyridine and dimethyl carbonate are mixed and fed. At the same time, the air inlet valve is opened to introduce nitrogen. The raw materials and nitrogen react in the catalyst layer. The product is condensed and collected by a condensation device to achieve highly selective pyridine alkylation.

2. The method for alkylation of pyridine according to claim 1, wherein The precipitation aging is carried out at room temperature, the solution pH is adjusted to 9.3, the aging time is 6 hours, and an equal volume of the catalyst support is immersed in a rare earth metal oxide solution dissolved in dilute sulfuric acid for 6 hours.

3. The method for alkylation of pyridine according to claim 1, wherein The washing conditions in the preparation step of the catalyst support are: rinse with deionized water until there is no Cl - It was found that the drying conditions in the preparation step of the catalyst support were: the gel obtained after washing was dried at 180°C for 8 hours.

4. The method for pyridine alkylation according to claim 1, wherein The methylating agent is dimethyl carbonate, and the molar ratio of dimethyl carbonate to pyridine is 1.5-2.

5.

5. The method for pyridine alkylation according to claim 1, wherein The feed flow rate in the fluidized bed reaction tube is 0.3 g / min, the reaction temperature is 300°C-700°C, the reaction pressure is 0.08 MPa-0.12 MPa, the reaction time is 4 hours, and the rare earth metal modified solid super acid catalyst is activated at 500°C for two hours in an air atmosphere.

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