Formaldehyde catalyst and preparation method thereof

Abstract

The invention provides a formaldehyde catalyst and a preparation method thereof, and belongs to the technical field of formaldehyde catalyst preparation methods. According to the method, spraying is matched with uniform doping of silicon dioxide into the catalyst, so that the specific surface area of the iron-molybdenum catalyst is reduced, the loss speed of molybdenum in catalytic reaction is effectively reduced, the influence on the service life of the catalyst due to excessive carbon deposition is prevented, the heat dissipation performance of the catalyst is improved, paraformaldehyde generated due to accumulation of reaction heat is reduced, and the service life of the catalyst is prolonged. Therefore, the yield of formaldehyde is improved.

Description

Technical Field

[0001] The invention relates to the technical field of molecular sieve catalyst preparation methods, and in particular to a formaldehyde catalyst and a preparation method thereof. Background Art

[0002] Formaldehyde, also known as formic aldehyde, is an important chemical raw material, mainly used in the production of trialdehyde resin, pentaerythritol, hexamethylenetetramine, polyoxymethylene and other bulk chemical products. In addition, formaldehyde is also widely used in disinfectants, water treatment, pesticides, textiles and medicine. At present, the main methods for preparing formaldehyde are methanol oxidation, dimethyl ether oxidation and methanol dehydrogenation. Among them, methanol oxidation accounts for more than 90% of the global formaldehyde products and is the mainstream process for preparing formaldehyde. In industry, silver-based catalysts and FeMo catalysts are the two main catalysts for catalyzing methanol to formaldehyde. Silver-based catalysts have high requirements for the purity of raw methanol and catalytic reaction conditions, and the catalyst has problems such as easy poisoning and low methanol conversion rate. FeMo catalysts are composed of a mixed phase of Fe2(MoO4)3 and MoO3, which can overcome the above shortcomings of silver-based catalysts. Since it was applied to the formaldehyde production industry in 1950, it has been used ever since.

[0003] Industrially, FeMo catalysts are prepared by co-precipitation of iron salt solution and ammonium molybdate solution. When FeMo catalysts are prepared by co-precipitation, it is generally recognized in the industry that increasing the specific surface area of ​​the catalyst can improve its catalytic performance. However, as the specific surface area increases, the loss of Mo during the catalytic process will be accelerated. After the loss of Mo, the carbide of formaldehyde will enter the interior of the catalyst, resulting in more and more carbon deposits inside the catalyst, which in turn affects the life of the catalyst. In addition, the oxidation of methanol to prepare aldehydes is an exothermic reaction, and heat causes formaldehyde polymerization. Industrial loading adopts the method of mixing ceramic rings and catalysts in sections to ensure heat transfer. The present invention adds a small amount of silicon dioxide in the catalyst synthesis stage to ensure uniformity and extract heat faster. Summary of the invention

[0004] In order to improve the problem that excessive carbon deposition inside the catalyst affects the life of the catalyst due to the loss of Mo during the reaction of the formaldehyde catalyst, the present invention provides a formaldehyde catalyst and a preparation method thereof.

[0005] The technical solution of the present invention is a method for preparing a formaldehyde catalyst, which comprises the following steps: A molybdate solution with a pH value of 5 to 7, an iron salt solution with a pH value of 1 to 2, and silica sol are mixed at 50 to 80° C. for 20 to 50 minutes to obtain a catalyst solution, and the catalyst solution is sprayed to obtain the formaldehyde catalyst.

[0006] Wherein, the spray temperature is 50-150°C; In the formaldehyde catalyst, the atomic ratio of molybdenum to iron is 2-3:1, and the mass content of silicon dioxide is 3-10%; The molybdate is ammonium heptamolybdate.

[0007] Some specific preparation methods of formaldehyde catalysts, the pH value of the molybdate solution is 6~7, and the pH value of the iron salt solution is 1~1.5.

[0008] In some specific preparation methods of formaldehyde catalysts, the temperature of the spray mixing reaction is 90-150°C; The atomic ratio of molybdenum to iron in the formaldehyde catalyst is 2-2.5:1, and the mass content of silicon dioxide is 5-10%.

[0009] In some specific preparation methods of formaldehyde catalysts, the iron salt is selected from ferric nitrate, ferric chloride, and ferric sulfate.

[0010] In some specific preparation methods of formaldehyde catalysts, the molybdate is ammonium heptamolybdate, the iron salt is ferric nitrate, and ammonia water is used to adjust the pH values ​​of the molybdate solution and the iron salt solution.

[0011] In some specific preparation methods of formaldehyde catalysts, the substances obtained after the spray mixing reaction are sequentially washed, dried and calcined.

[0012] Some specific preparation methods of formaldehyde catalysts have a drying temperature of 80~100°C and a drying time of 10~40h.

[0013] Some specific preparation methods of formaldehyde catalysts have a calcination temperature of 200~450°C and a drying time of 8~15h.

[0014] The catalyst prepared by the preparation method.

[0015] The catalyst is used in catalyzing the reaction of preparing formaldehyde from methanol.

[0016] Beneficial effects of the present invention: The present invention provides a formaldehyde catalyst and a preparation method. The method reduces the specific surface area of ​​the iron-molybdenum catalyst by spraying and uniformly incorporating silicon dioxide into the catalyst, effectively reduces the loss rate of molybdenum during the catalytic reaction, prevents the catalyst life from being affected by excessive carbon deposition, and improves the heat dissipation performance of the catalyst, reduces the generation of polyformaldehyde due to the accumulation of reaction heat, and thus increases the yield of formaldehyde. DETAILED DESCRIPTION

[0017] Example 1: Preparation of Catalyst A1 50 g of ammonium heptamolybdate was dissolved in 250 ml of water, and the pH value was adjusted to 6.5 by 8% ammonia water. 50.22 g of ferric nitrate nonahydrate was dissolved in 200 ml of water, and the pH value was adjusted to 1.05 by 8% ammonia water. The obtained ammonium heptamolybdate solution, ferric nitrate solution and 33.62 g of 15% silica sol were mixed at 65 °C for 30 min, and then pumped into a sprayer and sprayed at 110 °C. The obtained material was washed with water, dried at 80 °C for 20 h, and calcined at 300 °C for 10 h to obtain the target catalyst A1.

[0018] Example 2: Preparation of Catalyst A2 Dissolve 50 g of ammonium heptamolybdate in 250 ml of water, adjust the pH value to 6.0 with 8% ammonia water, dissolve 50.22 g of ferric nitrate nonahydrate in 200 ml of water, adjust the pH value to 1.5 with 8% ammonia water, mix the obtained ammonium heptamolybdate solution, ferric nitrate solution and 33.62 g of 15% silica sol at 55 °C for 40 min, pump into a sprayer and spray at 125 °C, wash the obtained material with water, dry it at 80 °C for 20 h, and calcine it at 300 °C for 10 h to obtain the target catalyst A2.

[0019] Example 3: Preparation of Catalyst A3 Dissolve 50 g of ammonium heptamolybdate in 250 ml of water, adjust the pH value to 6.8 with 8% ammonia water, dissolve 50.22 g of ferric nitrate nonahydrate in 200 ml of water, adjust the pH value to 1.2 with 8% ammonia water, mix the obtained ammonium heptamolybdate solution, ferric nitrate solution and 21.01 g of 15% silica sol at 75 °C for 25 min, pump into a sprayer and spray at 135 °C, wash the obtained material with water, dry it at 100 °C for 12 h, and calcine it at 400 °C for 9 h to obtain the target catalyst A3.

[0020] Example 4: Preparation of Catalyst A4 50 g of ammonium heptamolybdate was dissolved in 250 ml of water, and the pH value was adjusted to 5.5 by 8% ammonia water. 55.22 g of ferric nitrate nonahydrate was dissolved in 200 ml of water, and the pH value was adjusted to 1.8 by 8% ammonia water. The obtained ammonium heptamolybdate solution, ferric nitrate solution and 33.62 g of 15% silica sol were mixed at 65 ° C for 30 min, and then pumped into a sprayer and sprayed at 110 ° C. The obtained material was washed with water, dried at 80 ° C for 20 h, and calcined at 300 ° C for 10 h to obtain the target catalyst A4.

[0021] Example 5: Preparation of Catalyst A5 50 g of ammonium heptamolybdate was dissolved in 250 ml of water, and the pH value was adjusted to 6.5 by 8% ammonia water. 60.59 g of ferric nitrate nonahydrate was dissolved in 200 ml of water, and the pH value was adjusted to 1.05 by 8% ammonia water. The obtained ammonium heptamolybdate solution, ferric nitrate solution and 35.81 g of 15% silica sol were mixed at 65°C for 30 min, and then pumped into a sprayer and sprayed at 110°C. The obtained material was washed with water, dried at 80°C for 20 h, and calcined at 300°C for 10 h to obtain the target catalyst A5.

[0022] Example 6: Preparation of Catalyst A6 Dissolve 50 g of ammonium heptamolybdate in 250 ml of water, adjust the pH value to 6.4 with 8% ammonia water, dissolve 40.40 g of ferric nitrate nonahydrate in 200 ml of water, adjust the pH value to 1.05 with 8% ammonia water, mix the obtained ammonium heptamolybdate solution, ferric nitrate solution and 31.55 g of 15% silica sol at 65 °C for 30 min, pump into a sprayer and spray at 110 °C, wash the obtained material with water, dry it at 80 °C for 20 h, and calcine it at 300 °C for 10 h to obtain the target catalyst A6.

[0023] Example 7: Preparation of Catalyst A7 Dissolve 50 g of ammonium heptamolybdate in 250 ml of water, adjust the pH value to 6.4 with 8% ammonia water, dissolve 50.22 g of ferric nitrate nonahydrate in 200 ml of water, adjust the pH value to 1.05 with 8% ammonia water, mix the obtained ammonium heptamolybdate solution, ferric nitrate solution and 63.0 g of 10% silica sol at 65 °C for 30 min, pump into a sprayer and spray at 110 °C, wash the obtained material with water, dry it at 80 °C for 20 h, and calcine it at 300 °C for 10 h to obtain the target catalyst A7.

[0024] Comparative Example 1: Preparation of Catalyst V1 50 g of ammonium heptamolybdate was dissolved in 250 ml of water, and the pH value was adjusted to 6.5 by 8% ammonia water. 50.22 g of ferric nitrate nonahydrate was dissolved in 200 ml of water, and the pH value was adjusted to 1.05 by 8% ammonia water. The obtained ammonium heptamolybdate solution and ferric nitrate solution were added into the reaction bottle by pump, reacted at 65°C for 1 hour, aged at 70°C for 20 hours, and then 33.62 g of 15% silica sol was added and mixed at 65°C for 1 hour. The obtained material was filtered, washed with water, dried at 80°C for 20 hours, and calcined at 300°C for 10 hours to obtain the target catalyst V1.

[0025] Comparative Example 2: Preparation of Catalyst V2 Dissolve 50 g of ammonium heptamolybdate in 250 ml of water, adjust the pH value to 6.5 with 8% ammonia water, dissolve 50.22 g of ferric nitrate nonahydrate in 200 ml of water, adjust the pH value to 1.05 with 8% ammonia water, add the obtained ammonium heptamolybdate solution and ferric nitrate solution into the reaction bottle through a pump, react at 65 ° C for 1 h, age at 70 ° C for 20 h, filter the obtained material, wash with water, dry at 80 ° C for 20 h, and calcine at 300 ° C for 10 h to obtain the target catalyst V2.

[0026] Test Example: The catalysts prepared in Examples 1-7 and Comparative Examples 1-2 were added with 0.5% graphite and formed into catalyst particles with an outer diameter of 5±0.1 mm, an inner diameter of 2.4±0.02 mm, a height of 2.6±0.1 mm, a bulk density of 0.87±0.02 g / ml, and an average mass of 0.0718 g of a single catalyst particle by Raschig ring forming method. The formed catalyst was then calcined at 400°C for 6 h, and the calcined catalyst was loaded into a fixed bed for catalyzing the methanol oxidation to formaldehyde reaction to evaluate the catalytic performance of the catalyst. The air flow rate was 2 L / min, the methanol flow rate was 30.5 ml / min, and the specific data were shown in Table 1 after online gas chromatography analysis.

[0027] Table 1 Catalyst performance data of examples and comparative examples catalyst Methanol conversion rate / % Formaldehyde selectivity / % Catalyst life / h Catalyst A1 94.0 95.7 8990 Catalyst A2 93.5 94.8 9200 Catalyst A3 93.0 94.3 9070 Catalyst A4 92.1 93.9 9300 Catalyst A5 90.1 91.5 8994 Catalyst A6 88.5 90.3 9120 Catalyst A7 93.9 95.5 9150 Catalyst V1 84.6 88.7 8640 Catalyst V2 84.3 87.9 8160 It can be seen from the data in the table that the catalyst prepared in the present application has a better methanol conversion rate and selectivity, and the service life of the catalyst is longer.

Claims

1. A method for preparing a formaldehyde catalyst, characterized in that: Use the following steps: A molybdate solution with a pH value of 5 to 7, an iron salt solution with a pH value of 1 to 2, and silica sol are mixed at 50 to 80° C. for 20 to 50 minutes to obtain a catalyst solution, and the catalyst solution is sprayed to obtain the formaldehyde catalyst; Wherein, the spray temperature is 50-150°C; In the formaldehyde catalyst, the atomic ratio of molybdenum to iron is 2-3:1, and the mass content of silicon dioxide is 3-10%; The molybdate is ammonium heptamolybdate.

2. The method for preparing the formaldehyde catalyst according to claim 1, characterized in that: The pH value of molybdate solution is 6~7, and the pH value of iron salt solution is 1~1.

5.

3. The method for preparing the formaldehyde catalyst according to claim 1, characterized in that: The spray temperature is 90~150℃; In the formaldehyde catalyst, the atomic ratio of molybdenum to iron is 2-2.5:1, and the mass content of silicon dioxide is 5-10%.

4. The method for preparing the formaldehyde catalyst according to any one of claims 1 to 3, characterized in that: The iron salt is selected from ferric nitrate, ferric chloride and ferric sulfate.

5. The method for preparing the formaldehyde catalyst according to claim 4, characterized in that: The iron salt is ferric nitrate, and ammonia water is used to adjust the pH values ​​of the molybdate solution and the iron salt solution.

6. The method for preparing the formaldehyde catalyst according to any one of claims 1 to 3, characterized in that: The material obtained after spraying is washed with water, dried and calcined in sequence to obtain the catalyst.

7. The method for preparing the formaldehyde catalyst according to claim 6, characterized in that: The drying temperature is 80~100, the drying time is 10~40h, the roasting temperature is 200~450, and the drying time is 8~15h.

8. A catalyst prepared according to the preparation method according to any one of claims 1 to 3.

9. Use of the catalyst prepared by the preparation method according to claim 8 in catalyzing the reaction of methanol to formaldehyde.