A process for the preparation of a catalyst for the synthesis of pyridine bases

Abstract

The application discloses a preparation method of a catalyst for synthesizing pyridine base, and comprises the following steps: mixing bismuth nitrate pentahydrate, cobalt nitrate hexahydrate and cadmium nitrate tetrahydrate to prepare a deionized aqueous solution, adjusting the pH to 5 by using nitric acid, immersing H-ZSM-5 type zeolite molecular sieve in the salt solution, continuously stirring and heat preservation, natural cooling, washing, drying, high-temperature calcination, uniformly mixing the modified molecular sieve and the binder of the remaining components, spray drying, continuing high-temperature calcination, loading the shaped catalyst into a fluidized bed reactor, and carrying out activity evaluation by using an aldehyde-ammonia condensation process. The application is used for improving the output of pyridine in pyridine base by loading bismuth, cobalt, cadmium or other metal oxides on ZSM-5 type zeolite molecular sieve to prepare a new catalyst and carrying out reaction under the aldehyde-ammonia synthesis process condition. The output ratio of pyridine / 3-methylpyridine can reach 20:1, and the total yield of pyridine base can be kept above 91.7%.

Description

Technical Field

[0001] This invention relates to the field of pyridine base synthesis technology, and in particular to a method for preparing a catalyst for synthesizing pyridine bases. Background Technology

[0002] Pyridine bases are a general term for pyridine and alkylpyridines. They are a widely used organic intermediate, especially in the fields of pesticides, pharmaceuticals and additives.

[0003] In the production of pyridine bases, the reaction generates pure pyridine as a byproduct of 3-methylpyridine and trace amounts of other alkylpyridines. In current known industrial production, the yield ratio of pyridine to 3-methylpyridine is relatively stable. These two raw materials have led to two completely different industrial chains. Pyridine consumption mainly relies on paraquat and diquat, while the downstream application of 3-methylpyridine is primarily nicotinamide. When the nicotinamide industry chain weakens, it leads to insufficient consumption of 3-methylpyridine, resulting in inventory accumulation, oversupply, and a drop in market prices. On the other hand, as the downstream industry chain of pyridine extends, the demand for pyridine continues to expand. Increasing the yield of pyridine in pyridine base production is highly beneficial for manufacturers to respond to market changes.

[0004] CN118598800A discloses a method for increasing the proportion of pyridine in a pyridine base reaction. Formaldehyde and crotonaldehyde are mixed, vaporized, and preheated before entering a reactor. Ammonia gas is introduced into the bottom of the reactor for reaction. Under the action of a catalyst, formaldehyde, crotonaldehyde, and ammonia react. The high-temperature gas after the reaction enters a quench tower from the top of the reactor, and then enters a subsequent distillation tower to obtain the pyridine base product. The mass ratio of pyridine to 3-methylpyridine in the pyridine base product is 5:1. Without changing the reaction equipment and catalyst, simply changing the feed materials and feed ratio, and adjusting the reaction temperature, reduces the proportion of 3-methylpyridine in the reaction product while ensuring the yield of the pyridine base reaction. However, the overall yield is only 45%, which is low.

[0005] The announcement number CN1263741C discloses a method for preparing pyridine and 3-methylpyridine. It mainly uses metal oxides of cobalt, lead or a mixture thereof supported on ZSM-5 zeolite as catalysts and adopts an aldehyde-ammonia condensation process in the gas phase to produce pyridine and 3-methylpyridine. The maximum pyridine / 3-methylpyridine yield ratio is 20:1, but the overall yield is only 78%, and the proportion of 2-methylpyridine and 4-methylpyridine is too high.

[0006] CN1172915C discloses a method for preparing pyridine bases, in which aliphatic aldehydes, aliphatic ketones, or mixtures thereof are reacted with ammonia in the gas phase in the presence of a zeolite catalyst, wherein the zeolite catalyst contains titanium and / or cobalt and silicon as zeolite constituent elements, wherein the atomic ratio of silicon to titanium and / or cobalt is about 5 to about 1000, and the total yield of pyridine bases is 72.8%, which is still not ideal.

[0007] US Patent 4861894 (1989) discloses a molecular sieve, made from high-silica ZSM-5 zeolite with a SiO2 / Al2O3 molar ratio of 225 as the raw material and SiO2 as the binder, as a catalyst for the synthesis of pyridine bases. Under reaction conditions of acetaldehyde / formaldehyde molar ratio of 1.4, ammonia / aldehyde molar ratio of 1.5, and atmospheric pressure, the catalyst achieved a pyridine yield of 47%, a methylpyridine yield (including 2-methylpyridine, 3-methylpyridine, and 4-methylpyridine) yield of 14%, and a total yield of pyridine and methylpyridine of 61%. However, the overall yield of pyridine bases from this catalyst is still not ideal.

[0008] In current industrial production, the yield ratio of pyridine to 3-methylpyridine is basically fixed. Therefore, there is an urgent need to find a method to increase the yield ratio of pyridine. Summary of the Invention

[0009] The purpose of this invention is to provide a method for preparing a catalyst for synthesizing pyridine bases, which can increase the yield ratio of pyridine / 3-methylpyridine to 20:1 and maintain the total yield of pyridine bases above 91.7%, thereby solving the problems mentioned in the background art.

[0010] To achieve the above objectives, the present invention provides the following technical solution:

[0011] A method for preparing a catalyst for synthesizing pyridine bases includes the following steps:

[0012] Step 1: Prepare a deionized aqueous solution by mixing bismuth nitrate pentahydrate, cobalt nitrate hexahydrate, and cadmium nitrate tetrahydrate;

[0013] Step 2: After adjusting the pH to 5 with nitric acid, H-ZSM-5 type zeolite molecular sieve is immersed in salt solution, continuously stirred and kept warm, then naturally cooled, washed, and dried in a drying oven at 70-95℃ for 6 hours. After drying, the modified molecular sieve is calcined in a muffle furnace at 400-600℃ for 4-10 hours.

[0014] Step 3: Mix 10% to 85% w / w of the modified molecular sieve with the remaining binder components, spray dry, and then calcine at high temperature. The resulting catalyst is then loaded into a fluidized bed reactor and its activity is evaluated using an aldehyde-ammonia condensation process.

[0015] Furthermore, the preparation of the H-ZSM-5 type zeolite molecular sieve includes the following steps:

[0016] ZSM-5 raw powder was prepared by hydrothermal synthesis using water glass and aluminum sulfate as silicon and aluminum sources, respectively, and hexamethylenediamine as a template agent. The raw powder was crystallized in a stainless steel reactor. After deamineting, the ZSM-5 raw powder was wet-mixed with a binder and extruded into strips. Ion exchange was performed using ammonium nitrate solution to obtain H-ZSM-5 molecular sieve.

[0017] Furthermore, the molar ratio of bismuth, cobalt, and cadmium atoms in the bismuth pentahydrate, cobalt hexahydrate, and cadmium tetrahydrate ranges from 1 to 4:1:0.3 to 1, and the mass ratio of the mixed metal elements to the modified molecular sieve is from 0.15% w / w to 1.1% w / w.

[0018] Furthermore, the process of evaluating activity using the aldehyde-amine condensation process is as follows:

[0019] The ratio of raw materials formaldehyde: acetaldehyde: liquid ammonia is 0.5~1.7:1:1.0~2.5, the reaction temperature is 300~550℃, and the reaction pressure is 0.02~0.15Mpa. After the shaped catalyst is collected by condensation, it is detected by gas chromatography, and the contents of pyridine and 3-methylpyridine are quantitatively analyzed by internal standard method.

[0020] Furthermore, the high-temperature calcination temperature in steps 2 and 3 is 400–600°C.

[0021] Furthermore, the ZSM-5 raw powder has a crystallization temperature of 115–195°C, a crystallization time of 0–25 h, and a crystallinity of 95.7%.

[0022] Furthermore, the fluidized bed reactor has an inner diameter of 80 mm and a length of 900 mm. It is equipped with a catalyst filter screen at the top and a distribution plate at the bottom to receive the catalyst. Below the distribution plate are the feed inlets for formaldehyde, acetaldehyde, and ammonia. A condenser is installed above the distribution plate. The fluidized bed reactor is placed in a three-stage heating furnace.

[0023] Furthermore, in step 2, the molecular sieve is immersed in a salt solution and kept at 45–85°C for 12 hours.

[0024] Furthermore, the binder in step 3 is at least one of silica sol and alumina sol, with SiO2 selected as the silica sol and alumina selected as the alumina sol, and the amount used is 0-25%.

[0025] Furthermore, the particle size of the modified molecular sieve after spray drying is 0.18–0.22 mm.

[0026] Compared with the prior art, the beneficial effects of the present invention are:

[0027] This invention modifies the molecular sieve and adds metal loading to change the acidic sites in the molecular sieve. By adjusting the Brønsted acid and Lewis acid centers, the yield ratio of pure pyridine / 3-methylpyridine in the product is increased to 20:1. Furthermore, without changing the raw materials and process conditions, the overall yield of pyridine base is maintained at over 91.7%. The overall preparation cost is low, making it very suitable for industrial production. Detailed Implementation

[0028] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0029] Example 1: Using water glass and aluminum sulfate as silicon and aluminum sources respectively, and hexamethylenediamine as a template agent, ZSM-5 raw powder was first synthesized by hydrothermal synthesis, and then crystallized at a crystallization temperature of 175℃ for 20h. The obtained ZSM-5 raw powder was deamined, wet-mixed with a binder, and extruded into strips. Then, it was ion-exchanged with ammonium nitrate solution to obtain H-ZSM-5 molecular sieve. This molecular sieve was used as catalyst A and evaluated according to the above-mentioned catalyst activity evaluation method.

[0030] Example 2: A certain amount of bismuth nitrate pentahydrate was dissolved in 500 ml of deionized water. A small amount of nitric acid was added to adjust the pH to 5. 20 g of molecular sieve A was weighed and immersed in a cobalt nitrate aqueous solution. The mixture was stirred thoroughly and kept at 85°C for 12 hours. After natural cooling, it was filtered, washed, and dried in a drying oven at 85°C for 4 hours. The dried modified molecular sieve was then calcined in a muffle furnace at 550°C for 6 hours. Finally, the modified molecular sieve and the remaining binder components were mixed evenly, dried to a suitable particle size using a spray dryer, and calcined at 550°C for 4 hours to obtain shaped catalyst B. The catalyst activity was evaluated according to the above-mentioned catalyst activity evaluation method. The bismuth loaded in B was 0.2% w / w.

[0031] Example 3: A certain amount of cobalt nitrate hexahydrate was dissolved in 500 ml of deionized water. The pH was adjusted to 5 using a small amount of nitric acid. 20 g of molecular sieve A was weighed and immersed in a zinc nitrate aqueous solution. The mixture was stirred thoroughly and kept at 85°C for 12 hours. After natural cooling, it was filtered, washed, and dried in a drying oven at 85°C for 4 hours. The dried modified molecular sieve was then calcined in a muffle furnace at 550°C for 6 hours. Finally, the modified molecular sieve and the remaining binder were mixed evenly, dried to a suitable particle size using a spray dryer, and calcined at 550°C for 4 hours to obtain the molded catalyst C. The catalyst activity was evaluated according to the above-mentioned catalyst activity evaluation method. The cobalt loaded in C was 0.2% w / w.

[0032] Example 4: A certain amount of cadmium nitrate tetrahydrate was dissolved in 500 ml of deionized water. The pH was adjusted to 5 using a small amount of nitric acid. 20 g of molecular sieve A was weighed and immersed in ferric nitrate aqueous solution. The mixture was stirred thoroughly and kept at 85°C for 12 hours. After natural cooling, it was filtered, washed, and dried in a drying oven at 85°C for 4 hours. The dried modified molecular sieve was then calcined in a muffle furnace at 550°C for 6 hours. Finally, the modified molecular sieve and the remaining binder were mixed evenly, dried to a suitable particle size using a spray dryer, and calcined at 550°C for 4 hours to obtain the molded catalyst D. The catalyst activity was evaluated according to the above-mentioned catalyst activity evaluation method. The cadmium loaded in D was 0.2% w / w.

[0033] Example 5: Bismuth nitrate pentahydrate and cobalt nitrate hexahydrate were mixed and dissolved in 500 mL of deionized water at an atomic molar ratio of 2:1. The pH was adjusted to 5 with a small amount of nitric acid. 20 g of molecular sieve A was weighed and impregnated in the mixed salt solution. The mixture was stirred thoroughly and kept at 85°C for 12 hours. After natural cooling, it was filtered, washed, and dried in a drying oven at 85°C for 4 hours. The dried modified molecular sieve was then calcined in a muffle furnace at 550°C for 6 hours. Finally, the modified molecular sieve and the remaining binder were mixed evenly, dried to a suitable particle size using a spray dryer, and calcined at 550°C for 4 hours to obtain the shaped catalyst E. The catalyst activity was evaluated according to the above-mentioned catalyst activity evaluation method.

[0034] Example 6: Bismuth nitrate pentahydrate and cadmium nitrate tetrahydrate were mixed and dissolved in 500 mL of deionized water at an atomic molar ratio of 2:1. The pH was adjusted to 5 with a small amount of nitric acid. 20 g of molecular sieve A was weighed and impregnated in the mixed salt solution. The mixture was stirred thoroughly and kept at 85°C for 12 hours. After natural cooling, it was filtered, washed, and dried in a drying oven at 85°C for 4 hours. The dried modified molecular sieve was then calcined in a muffle furnace at 550°C for 6 hours. Finally, the modified molecular sieve and the remaining binder were mixed evenly, dried to a suitable particle size using a spray dryer, and calcined at 550°C for 4 hours to obtain the shaped catalyst F. The catalyst activity was evaluated according to the above-mentioned catalyst activity evaluation method.

[0035] Example 7: Cobalt nitrate hexahydrate and cadmium nitrate tetrahydrate were mixed and dissolved in 500 mL of deionized water at an atomic molar ratio of 2:1. The pH was adjusted to 5 with a small amount of nitric acid. 20 g of molecular sieve A was weighed and impregnated in the mixed salt solution. The mixture was stirred thoroughly and kept at 85°C for 12 hours. After natural cooling, it was filtered, washed, and dried in a drying oven at 85°C for 4 hours. The dried modified molecular sieve was then calcined in a muffle furnace at 550°C for 6 hours. Finally, the modified molecular sieve and the remaining binder were mixed evenly, dried to a suitable particle size using a spray dryer, and calcined at 550°C for 4 hours to obtain the molded catalyst G. The catalyst activity was evaluated according to the above-mentioned catalyst activity evaluation method.

[0036] Example 8: Bismuth nitrate pentahydrate, cobalt nitrate hexahydrate, and cadmium nitrate tetrahydrate were mixed and dissolved in 500 mL of deionized water at an atomic molar ratio of 2:1:0.5. The pH was adjusted to 5 with a small amount of nitric acid. 20 g of molecular sieve A was weighed and immersed in the mixed salt solution. The mixture was stirred thoroughly and kept at 85°C for 12 hours. After natural cooling, it was filtered, washed, and dried in a drying oven at 85°C for 4 hours. The dried modified molecular sieve was then calcined in a muffle furnace at 550°C for 6 hours. Finally, the modified molecular sieve and the remaining binder were mixed evenly, dried to a suitable particle size using a spray dryer, and calcined at 550°C for 4 hours to obtain the molded catalyst H. The catalyst activity was evaluated according to the above-mentioned catalyst activity evaluation method.

[0037] Table 1: Catalyst Activity Test Results

[0038]

[0039] As shown in Table 1, bismuth, cobalt, and cadmium all have the effect of improving the yield of pure pyridine. In terms of the combined effect, the synergistic effect of the bimetallic combination of bismuth and cobalt is more obvious. After adding cadmium, the overall yield ratio decreased significantly. Therefore, it can be judged that the combination of metallic bismuth and cobalt has the best effect.

[0040] Comparative Example 1: Bismuth nitrate pentahydrate and cobalt nitrate hexahydrate were mixed and dissolved in 500 ml of water at an atomic molar ratio of 1:1. The pH was adjusted to 5 with a small amount of nitric acid. 20 g of molecular sieve A was weighed and impregnated in the mixed salt solution. The mixture was stirred thoroughly and kept at 85°C for 12 hours. After natural cooling, it was filtered, washed, and dried in a drying oven at 85°C for 4 hours. The dried modified molecular sieve was then calcined in a muffle furnace at 550°C for 6 hours. Finally, the modified molecular sieve and the remaining binder were mixed evenly, dried to a suitable particle size using a spray dryer, and calcined at 550°C for 4 hours to obtain the molded catalyst E1. The catalyst activity was evaluated according to the above-mentioned catalyst activity evaluation method.

[0041] Comparative Example 2: Bismuth nitrate pentahydrate and cobalt nitrate hexahydrate were mixed and dissolved in 500 ml of water at an atomic molar ratio of 3:1. The pH was adjusted to 5 with a small amount of nitric acid. 20 g of molecular sieve A was weighed and impregnated in the mixed salt solution. The mixture was stirred thoroughly and kept at 85°C for 12 hours. After natural cooling, it was filtered, washed, and dried in a drying oven at 85°C for 4 hours. The dried modified molecular sieve was then calcined in a muffle furnace at 550°C for 6 hours. Finally, the modified molecular sieve and the remaining binder were mixed evenly, dried to a suitable particle size using a spray dryer, and calcined at 550°C for 4 hours to obtain the shaped catalyst E2. The catalyst activity was evaluated according to the above-mentioned catalyst activity evaluation method.

[0042] Comparative Example 3: Bismuth nitrate pentahydrate and cobalt nitrate hexahydrate were mixed and dissolved in 500 ml of water at an atomic molar ratio of 1:2. The pH was adjusted to 5 with a small amount of nitric acid. 20 g of molecular sieve A was weighed and impregnated in the mixed salt solution. The mixture was stirred thoroughly and kept at 85°C for 12 hours. After natural cooling, it was filtered, washed, and dried in a drying oven at 85°C for 4 hours. The dried modified molecular sieve was then calcined in a muffle furnace at 550°C for 6 hours. Finally, the modified molecular sieve and the remaining binder were mixed evenly, dried to a suitable particle size using a spray dryer, and calcined at 550°C for 4 hours to obtain the molded catalyst E3. The catalyst activity was evaluated according to the above-mentioned catalyst activity evaluation method.

[0043] Comparative Example 4: Bismuth nitrate pentahydrate and cobalt nitrate hexahydrate were mixed and dissolved in 500 ml of water at an atomic molar ratio of 4:1. The pH was adjusted to 5 with a small amount of nitric acid. 20 g of molecular sieve A was weighed and impregnated in the mixed salt solution. The mixture was stirred thoroughly and kept at 85°C for 12 hours. After natural cooling, it was filtered, washed, and dried in a drying oven at 85°C for 4 hours. The dried modified molecular sieve was then calcined in a muffle furnace at 550°C for 6 hours. Finally, the modified molecular sieve and the remaining binder were mixed evenly, dried to a suitable particle size using a spray dryer, and calcined at 550°C for 4 hours to obtain the molded catalyst E4. The catalyst activity was evaluated according to the above-mentioned catalyst activity evaluation method.

[0044] Table 2: Comparative Activity Test Results

[0045]

[0046] As shown in Table 2, based on the activity test results of the modified molecular sieve catalysts with different molar ratios of bismuth and cobalt, the catalyst with a bismuth to cobalt atomic molar ratio of 3:1 exhibits stronger activity and better selectivity. This is because the ammonia-aldehyde condensation reaction is an acid-catalyzed reaction, which is completed synergistically by Brønsted acid (B acid) and Lewis acid (L acid). The number, proportion, and positional arrangement of acidic sites on the catalyst surface determine the selectivity of the reaction. By loading metal elements to adjust the ratio of Brønsted acid centers to Lewis acid centers, the activity and selectivity of the catalyst are directly affected. Therefore, we chose to load different metal elements onto the zeolite molecular sieve to improve the selectivity and activity of the catalyst.

[0047] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a catalyst for synthesizing pyridine bases, characterized in that, Includes the following steps: Step 1: Prepare a deionized aqueous solution by mixing bismuth nitrate pentahydrate, cobalt nitrate hexahydrate, and cadmium nitrate tetrahydrate, wherein the molar ratio of bismuth, cobalt, and cadmium atoms in the bismuth nitrate pentahydrate, cobalt nitrate hexahydrate, and cadmium nitrate tetrahydrate is in the range of 1~4:1:0.3~1; Step 2: Adjust the pH to 5 with nitric acid, immerse the H-ZSM-5 type zeolite molecular sieve in the salt solution, stir continuously and keep warm, then cool naturally, wash, dry, and calcine at high temperature; Step 3: Mix the modified molecular sieve with the binder of the remaining components, spray dry, and then continue to calcine at high temperature. The resulting catalyst is then loaded into a fluidized bed reactor and its activity is evaluated using an aldehyde-ammonia condensation process.

2. The method for preparing a catalyst for synthesizing pyridine bases as described in claim 1, characterized in that, The preparation of the H-ZSM-5 type zeolite molecular sieve includes the following steps: ZSM-5 raw powder was prepared by hydrothermal synthesis using water glass and aluminum sulfate as silicon and aluminum sources, respectively, and hexamethylenediamine as a template agent. The raw powder was crystallized in a stainless steel reactor. After deamineting, the ZSM-5 raw powder was wet-mixed with a binder and extruded into strips. Ion exchange was performed using ammonium nitrate solution to obtain H-ZSM-5 molecular sieve.

3. The method for preparing a catalyst for synthesizing pyridine bases as described in claim 1, characterized in that, The mass ratio of the mixed metal elements to the modified molecular sieve in step 1 is 0.15%w / w to 1.1%w / w.

4. The method for preparing a catalyst for synthesizing pyridine bases as described in claim 1, characterized in that, The high-temperature calcination temperature in steps 2 and 3 is 400~600℃.

5. The method for preparing a catalyst for synthesizing pyridine bases as described in claim 2, characterized in that, The crystallization temperature of the ZSM-5 raw powder is 115~195℃, and the crystallization time is 0~25h.

6. The method for preparing a catalyst for synthesizing pyridine bases as described in claim 1, characterized in that, In step 2, the molecular sieve is immersed in a salt solution and kept at 45~85℃ for 12 hours.

7. The method for preparing a catalyst for synthesizing pyridine bases as described in claim 1, characterized in that, The binder in step 3 is either silica sol or aluminum sol.

8. The method for preparing a catalyst for synthesizing pyridine bases as described in claim 1, characterized in that, The particle size of the modified molecular sieve after spray drying is 0.18~0.22mm.

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