High-selectivity pyridine alkylation method

Abstract

The invention discloses a high-selectivity pyridine alkylation method which comprises the following steps: taking anhydrous titanium chloride and an anhydrous ferric chloride solution as raw materials, adding a dispersing agent, heating and uniformly stirring, adding ammonia water to adjust the pH value to a fixed value, grinding and sieving to obtain a catalyst carrier; dipping the catalyst carrier into a rare earth metal oxide solution dissolved by dilute sulphuric acid in an equivalent volume manner, aging, grinding and sieving to obtain a rare earth metal modified solid superacid catalyst; the method comprises the following steps: activating a rare earth metal modified solid superacid catalyst, cooling to a reaction temperature, filling a fluidized bed reaction tube with the catalyst, mixing pyridine and dimethyl carbonate, starting feeding, opening an air inlet valve, introducing nitrogen, and carrying out a reaction on the raw material mixed nitrogen in a catalyst layer to realize high-selectivity pyridine alkylation. Pyridine and a green methylation reagent dimethyl carbonate are used as raw materials, and high-selectivity synthesis of 2-methylpyridine can be realized under the action of a rare earth metal modified solid superacid catalyst.

Description

Technical Field

[0001] The present invention relates to the technical field of pyridine alkylation, and specifically provides a method for highly selective pyridine alkylation. Background Art

[0002] Methylpyridines include 2-methylpyridine, 3-methylpyridine, 4-methylpyridine, 3,5-dimethylpyridine, 2,4,6-trimethylpyridine, etc. These are all important chemical raw materials and organic intermediates, and can be used in the production of pesticides, pharmaceuticals, feeds, fertilizers, etc. Currently, the production methods of alkylpyridines include direct synthesis by the aldehyde-ketone-ammonia method, direct synthesis by pyridine alkylation, and direct synthesis by unsaturated olefins and methyl cyanide. Among them, direct modification of the pyridine side chain by alkylation has the advantages of high corresponding selectivity and low by-product content, which is beneficial to industrial production. However, it has the disadvantages of harsh reaction conditions and poor catalyst selectivity. Based on this, there are currently some pyridine alkylation schemes. For example, Chinese Patent No. CN109174168B discloses a preparation method of a catalyst for pyridine alkylation to prepare 2-methylpyridine. Using sodium-type molecular sieve as the matrix, one or more elements of Ba, Mg, Ca, Fe as the first auxiliary agent, and one or more elements of Co, Bi, Cu, Zn as the second auxiliary agent, the catalyst is obtained by impregnation and then calcination. The catalytic synthesis of 2-methylpyridine is simple in operation, high in selectivity, and good in catalyst regeneration performance. Using pyridine and methanol as raw materials for the reaction, the pyridine conversion rate can reach 69.9%, and the highest yield of 2-methylpyridine is 50.6%; Chinese Patent No. CN110038630B discloses a synthesis method of a molecular sieve catalyst for synthesizing 3-methylpyridine. It is prepared by mixing HEU-1 molecular sieve and an aluminum source and calcining. When the catalyst is used in the reaction of raw materials acrolein, propionaldehyde and ammonia to synthesize 3-methylpyridine, the selectivity for 3-methylpyridine is better, and the highest can reach 63.80%.

[0003] When the above catalysts are used for pyridine alkylation, their conversion rates and yields are both relatively low, resulting in high costs and not meeting the current industrial requirements. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for highly selective pyridine alkylation. Using pyridine and the green methylation reagent dimethyl carbonate as raw materials, under the action of a rare earth metal modified solid superacid catalyst, highly selective synthesis of 2-methylpyridine can be achieved, reducing costs and increasing benefits, so as to solve the problems raised in the above background art.

[0005] To achieve the above purpose, the present invention provides the following technical solution: A method for highly selective pyridine alkylation, characterized in that it includes the following steps: Using anhydrous titanium chloride and anhydrous ferric chloride solution as raw materials, after adding a dispersant, heat and stir evenly, then add ammonia water to adjust the pH to a fixed value. After precipitation aging, filter by suction, wash and then dry, grind and sieve to obtain a catalyst support; Impregnate the catalyst support with the same volume into the rare earth metal oxide solution dissolved in dilute sulfuric acid for aging, filter by suction, wash, dry and then calcine, grind and sieve to obtain a rare earth metal modified solid superacid catalyst; After the activation of the rare earth metal modified solid superacid catalyst is completed, it is cooled to the reaction temperature and loaded into the fluidized bed reaction tube. Mix pyridine and dimethyl carbonate and start feeding, and at the same time open the intake valve to introduce nitrogen. The raw material mixed with nitrogen reacts in the catalyst layer, and the product is condensed and collected through a condensing device to achieve highly selective pyridine alkylation.

[0006] Further, the anhydrous ferric chloride is dissolved in anhydrous ethanol, and the concentration 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.

[0007] Further, the added dispersant is stearic acid, and heat and stir at 40 °C for 2 h for sufficient mixing.

[0008] Further, the precipitation aging is carried out at room temperature, the pH of the solution is adjusted to 9.3, and the aging time is 6 h. The time for impregnating the catalyst support with the same volume into the rare earth metal oxide solution dissolved in dilute sulfuric acid for aging is 6 h.

[0009] Further, the washing condition in the preparation step of the catalyst support is: rinse with deionized water until no Cl - is detected. The drying condition in the preparation step of the catalyst support is: the gel obtained after washing is dried at 180 °C for 8 h.

[0010] Further, the rare earth metal oxide is Sc2O3, and the solution concentration is 0.3 mol / L.

[0011] Further, the drying temperature after filtration, washing and drying and then calcining is 120 °C, the time is 14 hours, the temperature during the calcination process is 400 °C - 800 °C, and the time is 1.5 h.

[0012] Further, the methylation reagent is dimethyl carbonate, and the molar ratio of dimethyl carbonate to pyridine is 1.5 - 2.5.

[0013] Further, in the rare earth metal modified solid superacid catalyst, the 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 generate the L acid center. During the reaction, the B acid center is activated, gives protons to add to pyridine to form a carbocation and undergoes an alkylation reaction with dimethyl carbonate.

[0014] 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 superacid catalyst is activated at 500°C for two hours in an air atmosphere.

[0015] Compared with the prior art, the present invention has the following beneficial effects: The present invention uses a rare earth metal modified solid superacid 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 superacid. The addition of the rare earth metal makes the SO4 on the solid superacid 2- It is not easy to lose, thus 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 corrosion and long service life. At the same time, the green methylation reagent dimethyl carbonate is used, which has low toxicity and excellent environmental protection performance, reducing the pressure of hazardous waste treatment in the process. DETAILED DESCRIPTION

[0016] The embodiments of the present invention will be described in detail below, 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 creative work are within the scope of protection of the present invention.

[0017] Example 1: Anhydrous titanium chloride is added dropwise into anhydrous ferric chloride solution in a stoichiometric ratio of 1 / 6 for mixing, a dispersant is added, heated and stirred at 40°C for 2h, and ammonia water is added to adjust the pH to 9.3 after thorough mixing. The gel is 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 carrier, an equal volume of the catalyst carrier is 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 calcined at 400°C for 1.5h, and ground and sieved to obtain a rare earth metal modified solid superacid catalyst 1.

[0018] Example 2: Anhydrous titanium chloride is added dropwise into anhydrous ferric chloride solution in a stoichiometric ratio of 1 / 6 for mixing, a dispersant is added, heated and stirred at 40°C for 2 hours, and ammonia water is added to adjust the pH to 9.3. The gel is precipitated and aged at room temperature for 6 hours, filtered and washed, and then dried at 180°C for 8 hours. The catalyst carrier is obtained by grinding and sieving. An equal volume of the catalyst carrier is immersed in a 0.3 mol / L scandium oxide solution dissolved in dilute sulfuric acid and aged for 6 hours. The catalyst carrier is filtered, washed, dried at 120°C for 14 hours, and then calcined at 500°C for 1.5 hours. The rare earth metal modified solid super acid catalyst 2 is obtained by grinding and sieving.

[0019] Example 3: Titanium tetrachloride anhydrous was added dropwise to the ferric chloride anhydrous solution according to the stoichiometric ratio of 1 / 6 for mixing. A dispersant was added, and the mixture was heated and stirred at 40 °C for 2 h. After sufficient mixing, ammonia water was added to adjust the pH to 9.3. The precipitate was aged at room temperature for 6 h, then filtered and washed. The obtained gel was dried at 180 °C for 8 h, ground and sieved to obtain a catalyst support. The catalyst support was impregnated with a 0.3 mol / L scandium oxide solution dissolved in dilute sulfuric acid in an equal volume and aged for 6 h. After filtration, washing, and drying at 120 °C for 14 h, it was calcined at 600 °C for 1.5 h, ground and sieved to obtain a rare earth metal-modified solid superacid catalyst 3.

[0020] Example 4: Titanium tetrachloride anhydrous was added dropwise to the ferric chloride anhydrous solution according to the stoichiometric ratio of 1 / 6 for mixing. A dispersant was added, and the mixture was heated and stirred at 40 °C for 2 h. After sufficient mixing, ammonia water was added to adjust the pH to 9.3. The precipitate was aged at room temperature for 6 h, then filtered and washed. The obtained gel was dried at 180 °C for 8 h, ground and sieved to obtain a catalyst support. The catalyst support was impregnated with a 0.3 mol / L scandium oxide solution dissolved in dilute sulfuric acid in an equal volume and aged for 6 h. After filtration, washing, and drying at 120 °C for 14 h, it was calcined at 700 °C for 1.5 h, ground and sieved to obtain a rare earth metal-modified solid superacid catalyst 4.

[0021] Example 5: Titanium tetrachloride anhydrous was added dropwise to the ferric chloride anhydrous solution according to the stoichiometric ratio of 1 / 6 for mixing. A dispersant was added, and the mixture was heated and stirred at 40 °C for 2 h. After sufficient mixing, ammonia water was added to adjust the pH to 9.3. The precipitate was aged at room temperature for 6 h, then filtered and washed. The obtained gel was dried at 180 °C for 8 h, ground and sieved to obtain a catalyst support. The catalyst support was impregnated with a 0.3 mol / L scandium oxide solution dissolved in dilute sulfuric acid in an equal volume and aged for 6 h. After filtration, washing, and drying at 120 °C for 14 h, it was calcined at 800 °C for 1.5 h, ground and sieved to obtain a rare earth metal-modified solid superacid catalyst 5.

[0022] 15 g of each of the above rare earth metal-modified solid superacid catalysts 1-5 were respectively loaded into a fluidized bed reaction tube. Before the reaction, the rare earth metal-modified solid superacid catalysts 1-5 were activated at 500 °C for 2 h in an air atmosphere. The raw material used dimethyl carbonate as the methylation reagent, and the molar ratio of dimethyl carbonate to pyridine was 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 h, and a feed flow rate of 0.3 g / min. The catalytic activity of the rare earth metal-modified solid superacid catalysts for the alkylation of pyridine was tested by a liquid chromatograph, and the data in Table 1 below were obtained.

[0023]

[0024] As can be seen from the results in Table 1, by controlling the calcination temperature of the solid superacid, the conversion rate of pyridine alkylation can be increased, and the proportion of 2-methylpyridine in the product is relatively high. For the yield of 2-methylpyridine, the calcination temperatures of the solid superacids in Examples 1-3 increased gradually, so that the catalytic activities of the rare-earth metal-modified solid superacid catalysts 1-3 for pyridine alkylation also increased gradually. When the calcination temperature was 600 °C, the yield of 2-methylpyridine reached the highest of 60.25%. As the calcination temperatures of Examples 4-5 increased gradually, the yield of 2-methylpyridine showed a gradually decreasing trend. This was because the calcination temperatures of Examples 4-5 were too high, which destroyed the acid centers and led to a significant decrease in the catalytic efficiency.

[0025] The investigation results of the process conditions of the rare-earth metal-modified solid superacid catalyst for pyridine alkylation are shown in Table 2 below:

[0026] Take 15 g of the rare-earth metal-modified solid superacid catalyst 3 and load it into the fluidized bed reaction tube. Before the reaction, the rare-earth metal-modified solid superacid catalyst was activated at 500 °C for 2 h in an air atmosphere. The raw materials used different molar ratios of different methylation reagents to pyridine. After mixing, the reaction was carried out at different reaction temperatures and pressures for 4 h. The results of the rare-earth metal-modified solid superacid catalyst 3 for pyridine alkylation after using different process parameters are shown in Table 2. When using the rare-earth metal-modified solid superacid catalyst 3, the reaction temperature was 400 °C, the molar ratio of the methylation reagent to pyridine was 1.75, the reaction pressure was 0.12 MPa, the conversion rate of pyridine reached 89.21%, the yield of 2-methylpyridine reached 78.52%, and the selectivity could reach 88.02%. It shows that the catalyst has strong renewable recycling ability and excellent catalytic activity and selectivity for 2-methylpyridine.

[0027] Comparative Example 1: Titanium tetrachloride anhydrous was added dropwise to the ferric chloride anhydrous solution according to the stoichiometric ratio of 1 / 6 for mixing. After adding a dispersant and heating and stirring at 40 °C for 2 h for full mixing, ammonia water was added to adjust the pH to 9.3. After precipitation and aging at room temperature for 6 h, the gel obtained after suction filtration and washing was dried at 180 °C for 8 h, ground and sieved to obtain a catalyst support. The catalyst support was impregnated with an equal volume of 0.3 mol / L dilute sulfuric acid solution for aging for 6 h, suction filtered and washed, dried at 120 °C for 14 h, and then calcined at 600 °C for 1.5 h, ground and sieved to obtain a rare-earth metal-unmodified solid superacid catalyst.

[0028] Comparative Example 2: 21 g of SiO2 powder and 40 g of sesbania powder were added to 400 g of pseudo-boehmite powder. 300 g of water was added, and the mixture was mechanically stirred and mixed, extruded into strips, dried at 120 °C for 12 h, and calcined at 600 °C for 4 h to obtain a support. 120 g of the support was added to 100 mL of an ethanol solution containing 175 g of nickel nitrate hexahydrate, 7.3 g of lanthanum nitrate hexahydrate, and ethylenediamine (ethylenediamine: metal ion = 2:1). The mixture was stirred at room temperature for 3 h, rotary evaporated at 60 °C, dried at 120 °C for 12 h, and calcined at 450 °C for 3 h 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 4 h to obtain a SiO2-modified γ-Al2O3 catalyst.

[0029] Comparative Example 3: A commercially available metal-modified H-β zeolite catalyst was selected.

[0030] 15 g of the catalysts of Comparative Examples 1 - 3 were respectively loaded into a fluidized bed reaction tube. Before the reaction, the catalysts were activated at 500 °C in an air atmosphere for 2 h. The raw material used dimethyl carbonate as the methylation reagent, and the molar ratio of dimethyl carbonate to pyridine was 1.75. After mixing, the reaction was carried out at a reaction temperature of 400 °C, a pressure of 0.12 MPa, a reaction time of 4 h, and a feed flow rate of 0.3 g / min. The catalytic activities of the catalysts of Example 3 and Comparative Examples 1 - 3 for the alkylation of pyridine were tested by a liquid chromatograph, and the data in Table 3 below were obtained.

[0031]

[0032] As can be seen from Table 3, compared with Comparative Example 1, when using the catalyst of Example 3, the pyridine conversion rate, the yield and selectivity of 2-methylpyridine are significantly better than those of Comparative Example 1, indicating that the catalytic activity and stability of the solid superacid catalyst modified by rare earth metals are significantly enhanced. The reason is that the addition of rare earth metals makes the SO4 on the solid superacid 2- not easily lost, thereby improving the stability. Under the same reaction conditions, compared with Comparative Examples 2 and 3, although Comparative Examples 2 and 3 are also metal-modified catalysts, the pyridine conversion rate and the yield of 2-methylpyridine after catalysis with the solid superacid modified by rare earth metals are significantly higher than those of Comparative Examples 2 and 3. This is because when the rare earth metals are calcined, the average crystal particle size of the catalyst matrix is smaller, the specific surface area is larger, and it can better disperse and stabilize the surface TiO2-Fe2O3, so as to combine with more SO4 2- to form acid sites, improving the reaction activity and stability of the catalyst. The rare earth metal-modified solid superacid catalyst proposed by the present invention has a higher yield of synthesizing 2-methylpyridine. At the same time, a green methylation reagent is used to reduce the generation of polluting by-products, which has obvious advantages.

[0033] Although embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for highly selective pyridine alkylation, characterized in that: It includes the following steps: Using anhydrous titanium chloride and anhydrous ferric chloride solution as raw materials, adding a dispersant and then heating and stirring evenly, adding ammonia water to adjust the pH to a fixed value, aging the precipitate, filtering, washing and drying, and grinding and sieving to obtain a catalyst support; Impregnating the catalyst support with an equal volume into a rare earth metal oxide solution dissolved in dilute sulfuric acid for aging, filtering, washing, drying and then calcining, grinding and sieving to obtain a rare earth metal-modified solid superacid catalyst; After the activation of the rare earth metal-modified solid superacid catalyst is completed, it is cooled to the reaction temperature and loaded into a fluidized bed reaction tube. Pyridine and dimethyl carbonate are mixed and fed, and at the same time, the inlet valve is opened to introduce nitrogen. The raw material mixture and nitrogen react in the catalyst layer, and the product is condensed and collected through a condensation device to achieve highly selective pyridine alkylation.

2. The method for highly selective pyridine alkylation according to claim 1, characterized in that, The anhydrous ferric chloride is dissolved in absolute ethanol, and the concentration is controlled at 0.5 mol / L. The stoichiometric ratio of anhydrous titanium chloride to anhydrous ferric chloride solution is 1 / 6. The anhydrous titanium chloride is added dropwise to the anhydrous ferric chloride solution.

3. The method for highly selective pyridine alkylation according to claim 1, characterized in that, The dispersant added is stearic acid, and it is heated and stirred at 40 °C for 2 h for full mixing.

4. The method for highly selective pyridine alkylation according to claim 1, characterized in that, The precipitation aging is carried out at room temperature, the pH of the solution is adjusted to 9.3, and the aging time is 6 h. The aging time for impregnating the catalyst support with an equal volume into a rare earth metal oxide solution dissolved in dilute sulfuric acid is 6 h.

5. The method for highly selective pyridine alkylation according to claim 1, characterized in that, The washing condition in the preparation step of the catalyst support is: rinsing with deionized water until no Cl is detected. - The drying condition in the preparation step of the catalyst support is: drying the gel obtained after washing at 180 °C for 8 h.

6. The method for highly selective pyridine alkylation according to claim 1, characterized in that, The rare earth metal oxide is Sc2O3, and the solution concentration is 0.3 mol / L.

7. The method for highly selective pyridine alkylation according to claim 1, characterized in that, The drying temperature for drying after filtering, washing and calcining is 120 °C, and the time is 14 hours. The temperature during the calcination process is 400 °C - 800 °C, and the time is 1.5 h.

8. The method for highly selective pyridine alkylation according to claim 1, characterized in that, The methylation reagent is dimethyl carbonate, and the molar ratio of dimethyl carbonate to pyridine is 1.5 - 2.

5.

9. The method for highly selective pyridine alkylation according to claim 8, characterized in that, 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 generate an L acid center. During the reaction, the B acid center is activated, giving protons to add to pyridine to form a carbocation and undergo an alkylation reaction with dimethyl carbonate.

10. The method for highly selective pyridine alkylation according to claim 1, characterized in that, 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, and the reaction time is 4 h. The rare earth metal-modified solid superacid catalyst is activated at 500 °C in an air atmosphere for two hours.

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