Propylene ammoxidation catalyst taking modified silica sol as carrier and preparation method of propylene ammoxidation catalyst

Abstract

The invention discloses a propylene ammoxidation catalyst with modified silica sol as a carrier and a preparation method of the propylene ammoxidation catalyst, and belongs to the technical field of catalyst preparation, the preparation method comprises the following steps: step 1, diluting the modified silica sol in water to prepare a glue solution; 2, an active metal solution with the mass fraction of 50-65% and an auxiliary agent are added into the glue solution to be evenly stirred, and precursor slurry is obtained; 3, after the precursor slurry is fully homogenized, the precursor slurry is subjected to spray drying and roasting activation, the propylene ammoxidation catalyst is obtained, and the active metal solution contains molybdenum, bismuth, iron, manganese, cerium and praseodymium; the auxiliary agent comprises choline chloride and polyhydric alcohol in a mass volume ratio of 1g: (5-10) mL; and the weight of the auxiliary agent is 1-3% of the weight of the active metal solution. The propylene ammoxidation catalyst prepared by the invention has the advantages of good low-temperature activity, strong pressure resistance, good selectivity and high acrylonitrile monomer yield, and provides technical support for green production of acrylonitrile.

Description

Technical Field

[0001] The present invention relates to the technical field of catalyst preparation. Specifically, it relates to an acrylonitrile ammoxidation catalyst with modified silica sol as the carrier and a preparation method thereof. Background Art

[0002] Acrylonitrile (AN) is an important monomer for synthetic fibers, synthetic rubbers and synthetic resins. The products produced from acrylonitrile are constantly being developed and applied, and the demand for acrylonitrile is increasing continuously. The main methods for producing acrylonitrile are: acrylonitrile ammoxidation method, ethylene oxide method, and acetylene method. Among them, the acrylonitrile ammoxidation method is the main method for producing acrylonitrile, which uses propylene, ammonia and air as raw materials and reacts under the action of a catalyst to produce acrylonitrile.

[0003] Currently, the Mo-Bi series catalyst is the mainstream catalyst for acrylonitrile ammoxidation to acrylonitrile. It is mainly prepared by dissolving ammonium molybdate and nitrates of Bi and other additives, and then co-precipitating with silica sol. The obtained slurry is dried, granulated and calcined. The catalyst can improve the conversion efficiency, reduce the generation of by-products, and lower the energy consumption and cost. Therefore, the research and development of catalysts has always been a hot topic in the field of acrylonitrile synthesis.

[0004] Chinese Patent Publication No. CN116618060A discloses an acrylonitrile catalyst with silica sol as the carrier. By adding elements such as Ce, Pr, Nd, La and Sm, and adjusting the molar ratio between Mo, Bi and other elements, the catalytic performance and efficiency of the catalyst are improved through the mutual cooperation of various elements.

[0005] Chinese Patent Publication No. CN118681546A discloses an acrylonitrile ammoxidation catalyst with modified silica sol as the carrier. With modified silica sol as the carrier, through the mutual cooperation of Mo, Bi and elements such as Fe, Re, Be, Co, Al, Cr, etc., the selectivity of the catalyst for acrylonitrile and the conversion rate of propylene are improved.

[0006] To sum up, the reaction temperature of the existing Mo-Bi series acrylonitrile ammoxidation catalysts is mostly above 420°C, and the reaction pressure is 0.08 - 0.085 Mpa. There are generally problems of poor low-temperature activity and poor pressure resistance. Therefore, it is of great significance to find a highly efficient acrylonitrile ammoxidation catalyst with good low-temperature activity and strong pressure resistance. Summary of the Invention

[0007] In order to solve the above technical problems, the present invention provides an acrylonitrile ammoxidation catalyst with modified silica sol as the carrier and a preparation method thereof. This acrylonitrile catalyst has the advantages of good low-temperature activity, strong pressure resistance, good selectivity and high acrylonitrile monomer yield, providing technical support for the green production of acrylonitrile.

[0008] To achieve the above object, the present invention adopts the following technical solutions: The present invention provides a method for preparing an ammoxidation catalyst of propylene using modified silica sol as a carrier, comprising the following steps: Step 1: Dilute the modified silica sol in water to form a colloidal solution. Step 2: Add an active metal solution and an auxiliary agent to the colloidal solution obtained in Step 1 and stir evenly to obtain a precursor slurry. Step 3: After fully homogenizing the precursor slurry obtained in Step 2, perform spray drying and calcination activation to obtain the ammoxidation catalyst of propylene.

[0009] Preferably, the mass fraction of the active metal solution in Step 2 is 50-65%; preferably 55-60%.

[0010] Preferably, the molar ratio of molybdenum, bismuth, iron, manganese, cerium, and praseodymium in the active metal solution in Step 2 is 5-10:0.2-0.5:1-5:0.3-0.8:0.1-0.5:0.1-0.5; more preferably 7-8:0.3-0.4:2-3:0.5-0.6:0.3-0.4:0.2-0.3; even more preferably 8:0.3:2:0.5:0.3:0.2.

[0011] Preferably, the active metal in Step 2 is a water-soluble metal salt; more preferably, the metal salt is a sulfate or a nitrate.

[0012] Preferably, the auxiliary agent in Step 2 is choline chloride and a polyol, wherein the mass-volume ratio of choline chloride to glycerol is 1 g:5-10 mL; more preferably 1 g:7-9 mL; even more preferably 1 g:8 mL.

[0013] Preferably, the polyol is at least one of glycerol, ethylene glycol, butanediol, and xylitol.

[0014] Preferably, the auxiliary agent is 1-3% of the weight of the active metal solution; more preferably 1.8-2.2%, even more preferably 2%.

[0015] Preferably, the uniform stirring in Step 2 is: stirring at 400-500 rpm for 2-4 h.

[0016] Preferably, the modified silica sol in Step 1 is a molybdate-modified silica sol.

[0017] Preferably, the spray drying in Step 3 is at an inlet temperature of 340-360 °C and an outlet temperature of 120-140 °C; more preferably, the inlet temperature is 350 °C and the outlet temperature is 130 °C.

[0018] Preferably, the calcination in step 3 is: calcining in an air atmosphere for 1 - 3 h.

[0019] In some embodiments, the temperature of the calcination is 550 - 650 °C.

[0020] The present invention also provides an acrylonitrile ammoxidation catalyst using the modified silica sol as a carrier prepared by the above preparation method.

[0021] The present invention also provides a method for preparing acrylonitrile by ammoxidation of propylene, using propylene, ammonia and air as raw materials, and reacting with the above acrylonitrile ammoxidation catalyst as a catalyst. Among them, the molar ratio of propylene, ammonia and air is 1:1.2 - 1.3:9 - 11, the reaction temperature is 400 °C, the reaction pressure is 0.1 - 0.2 MPa; the propylene load of the catalyst is 0.1 - 0.15 h -1 .

[0022] The beneficial effects of the present invention are as follows: The acrylonitrile ammoxidation catalyst of the present invention uses a modified silica sol as a carrier, and loads 30 - 60% of metal active centers such as molybdenum, bismuth, iron, manganese, cerium and praseodymium. Among them, the multivalent elements such as iron, manganese, cerium and praseodymium are compounded with molybdenum and bismuth, which can promote the regeneration of the catalyst, improve the activity and selectivity of the catalyst. During the preparation process, additives are added to stabilize the active components, increase the active sites, and further improve the performance of the catalyst.

[0023] Compared with the prior art, the acrylonitrile ammoxidation catalyst prepared by the present invention has high selectivity and acrylonitrile monomer yield under the reaction conditions of low temperature and high pressure, and has a low abrasion rate, and has good low temperature activity and pressure resistance.

[0024] It is found through experiments that the present invention uses an additive composed of a specific ratio of choline chloride and polyol and a specific molar ratio of active metals in combination, which can significantly improve the selectivity, acrylonitrile monomer yield and abrasion rate of the acrylonitrile ammoxidation catalyst, and has achieved unexpected effects in improving the low temperature activity and pressure resistance of the acrylonitrile ammoxidation catalyst. Detailed embodiments

[0025] The following description of the embodiments is only used to help understand the method and its core idea of the present invention. It should be noted that for those of ordinary skill in the art of this technology, without departing from the principle of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention. The following description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but can be applied to a wider range consistent with the principles and novel features disclosed herein.

[0026] When the embodiments give a numerical range, it should be understood that unless otherwise specified in the present invention, both endpoints of each numerical range and any value between the two endpoints can be selected. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs. In the present invention, the molybdate-modified silica sol has an average particle size within 80 - 100 nm, a viscosity of 10 - 12 mPa·s at 25 °C, a SiO 2 mass fraction of 35 - 40%, and a pH of 9 - 10. The specific preparation method is the same as that in Example 2 of ZL202410726267.2. Unless otherwise specified, the solvents involved in the present invention are all water, and the temperatures involved are all room temperature (20 - 25 °C). Example 1 Preparation method of propylene ammoxidation catalyst using modified silica sol as carrier The steps are as follows: Step 1: Dilute the molybdate-modified silica sol in water to make 1000 g of ammonium molybdate-modified silica sol solution with a mass concentration of 40%. Step 2: According to the molar ratio of molybdenum, bismuth, iron, manganese, cerium, and praseodymium being 5:0.2:1:0.3:0.1:0.1, dissolve molybdenum nitrate, bismuth nitrate pentahydrate, iron sulfate, manganese sulfate, cerium sulfate, and praseodymium sulfate in water to make 1600 g of active metal salt solution with a mass concentration of 50%. Add the active metal solution and 8 g of auxiliary agent to the ammonium molybdate-modified silica sol solution obtained in Step 1, and stir evenly (stir at 500 rpm for 2 h) to obtain a precursor slurry. Among them, the auxiliary agent is choline chloride and glycerol with a mass-to-volume ratio of 1 g:5 mL. Step 3: After fully homogenizing the precursor slurry obtained in Step 2, spray dry it (the inlet temperature is 350 °C, the outlet temperature is 130 °C), and calcine and activate it in an air atmosphere (550 °C) for 3 h to obtain the propylene ammoxidation catalyst.

[0027] Example 2 Preparation method of propylene ammoxidation catalyst with modified silica sol as carrier The steps are as follows: Step 1: Dilute the molybdate-modified silica sol in water to prepare 1000 g of ammonium molybdate-modified silica sol solution with a mass concentration of 40%; Step 2: According to the molar ratio of molybdenum, bismuth, iron, manganese, cerium and praseodymium being 10:0.5:5:0.8:0.5:0.5, dissolve molybdenum nitrate, bismuth nitrate pentahydrate, iron sulfate, manganese sulfate, cerium sulfate and praseodymium sulfate in water to prepare 1620 g of active metal solution with a mass concentration of 65%; Add the active metal solution and 31.2 g of auxiliary agent to the ammonium molybdate-modified silica sol solution obtained in Step 1, and stir evenly (stir at 400 rpm for 4 h) to obtain a precursor slurry, wherein the auxiliary agent is choline chloride and glycerol with a mass-volume ratio of 1 g:10 mL; Step 3: After fully homogenizing the precursor slurry obtained in Step 2, perform spray drying (inlet temperature is 350 °C, outlet temperature is 130 °C), and calcine and activate (at 650 °C) for 1 h in an air atmosphere to obtain the propylene ammoxidation catalyst.

[0028] Example 3 Preparation method of propylene ammoxidation catalyst with modified silica sol as carrier The steps are as follows: Step 1: Dilute the molybdate-modified silica sol in water to prepare 1000 g of ammonium molybdate-modified silica sol solution with a mass concentration of 40%; Step 2: According to the molar ratio of molybdenum, bismuth, iron, manganese, cerium and praseodymium being 8:0.3:2:0.5:0.3:0.2, dissolve molybdenum nitrate, bismuth nitrate pentahydrate, iron sulfate, manganese sulfate, cerium sulfate and praseodymium sulfate in water to prepare 1600 g of active metal solution with a mass concentration of 60%; Add the active metal solution and 19.2 g of auxiliary agent to the ammonium molybdate-modified silica sol solution obtained in Step 1, and stir evenly (stir at 400 rpm for 3 h) to obtain a precursor slurry, wherein the auxiliary agent is choline chloride and glycerol with a mass-volume ratio of 1 g:8 mL; Step 3: After fully homogenizing the precursor slurry obtained in Step 2, perform spray drying (inlet temperature is 350 °C, outlet temperature is 130 °C), and calcine and activate (at 600 °C) for 2 h in an air atmosphere to obtain the propylene ammoxidation catalyst.

[0029] Comparative Example 1 The difference between this comparative example and Example 3 is that: the auxiliary agent is not added in Step 2.

[0030] The remaining steps are the same as those in Example 3.

[0031] Comparative Example 2 The difference between this comparative example and Example 3 lies in the different addition amounts of the auxiliary agent.

[0032] Specifically: Add the active metal solution and 48 g of the auxiliary agent to the ammonium molybdate-modified silica sol solution obtained in Step 1 and stir evenly (stir for 3 h at 400 rpm) to obtain a precursor slurry, where the auxiliary agent is choline chloride and glycerol with a mass-volume ratio of 1 g: 8 mL; The remaining steps are the same as those in Example 3.

[0033] Comparative Example 3 The difference between this comparative example and Example 3 lies in the different compositions of the auxiliary agent.

[0034] Specifically: The auxiliary agent is choline chloride and glycerol with a mass-volume ratio of 1 g: 2 mL; The remaining steps are the same as those in Example 3.

[0035] Comparative Example 4 The difference between this comparative example and Example 3 lies in the different compositions of the auxiliary agent.

[0036] Specifically: The auxiliary agent is choline chloride and glycerol with a mass-volume ratio of 1 g: 20 mL; The remaining steps are the same as those in Example 3.

[0037] Comparative Example 5 The difference between this comparative example and Example 3 lies in the different molar ratios of molybdenum, bismuth, iron, manganese, cerium, and praseodymium in the active metal solution.

[0038] Specifically: The molar ratio of molybdenum, bismuth, iron, manganese, cerium, and praseodymium in the active metal solution is 8:0.3:2:0.1:0.8:0.1.

[0039] The remaining steps are the same as those in Example 3.

[0040] Comparative Example 6 Catalyst 2 for the ammoxidation of propylene to acrylonitrile prepared by ZL202410726267.2. The specific method is as follows: 1) Preparation process of the acrylonitrile catalyst: S1: Dissolve 3.53 g of potassium nitrate, 7.81 g of cesium nitrate, 278.6 g of iron nitrate, 522.2 g of nickel nitrate, 123.5 g of magnesium nitrate, 156.4 g of barium nitrate, 5.97 g of praseodymium nitrate, and 109.7 g of bismuth nitrate in 60 ml of water, and then mix the obtained aqueous solution evenly to obtain Solution I; S2: Add 4000 g of the ammonium molybdate-modified silica sol prepared in Example 2 to Solution I and mix evenly at high speed to obtain Slurry 2; S3: Granulate and form the slurry obtained in step S2 by spray drying, and calcine at 620 °C for 3 hours to obtain Catalyst 2 for the ammoxidation of propylene to acrylonitrile.

[0041] Catalyst performance test Charge 400 g of the catalyst into a fluidized bed reactor with an inner diameter of 38 mm. Using propylene, ammonia, and air as raw materials (molar ratio 1:1.25:10), react under the conditions of a reaction temperature of 400 °C, a reaction pressure of 0.15 MPa, and a propylene load of 0.15 h -1 to evaluate the performance of the catalyst. The results are shown in Table 1.

[0042] Table 1

[0043] The results show that for the acrylonitrile ammoxidation catalysts prepared in Examples 1 - 3 of the present invention, under the reaction conditions of low temperature and high pressure (reaction temperature 400 °C, reaction pressure 0.15 MPa), the acrylonitrile selectivity is 94.2 - 95.5%, the acrylonitrile yield is 86.2 - 86.9%, and the hourly attrition rate is 0.08 - 0.12%; for the acrylonitrile ammoxidation catalyst provided in Comparative Example 6 (i.e., the prior art), the acrylonitrile selectivity is 90.2%, the acrylonitrile yield is 81.5%, and the hourly attrition rate is 0.34%; compared with the prior art, the acrylonitrile ammoxidation catalyst prepared by the present invention has good selectivity, a high acrylonitrile monomer yield, and better low-temperature activity; at the same time, it has a lower attrition rate, stronger pressure resistance, can maintain physical and chemical stability under high-pressure conditions, is not easily damaged, extends the service life, and reduces production costs.

[0044] Comparing Comparative Example 1 and Example 3, it can be seen that for the acrylonitrile ammoxidation catalyst prepared in Comparative Example 1 without adding additives, under the reaction conditions of low temperature and high pressure (reaction temperature 400 °C, reaction pressure 0.15 MPa), the acrylonitrile selectivity is 84.3%, the acrylonitrile yield is 42.6%, and the hourly attrition rate is 0.6%. This shows that in the preparation process of the acrylonitrile ammoxidation catalyst of the present invention, adding an additive composed of choline chloride and glycerol can effectively improve the selectivity, acrylonitrile monomer yield, and attrition rate of the acrylonitrile ammoxidation catalyst.

[0045] Comparing Comparative Examples 2 - 4 and Example 3, it can be seen that the addition amount of the additive and the composition ratio of choline chloride and glycerol in the additive have an important impact on the selectivity, acrylonitrile monomer yield, and attrition rate of the acrylonitrile ammoxidation catalyst. When the addition amount of the additive and the composition ratio of choline chloride and glycerol in the additive are not within the scope claimed in the present invention, the prepared acrylonitrile ammoxidation catalyst has poor low-temperature activity and pressure resistance and is not suitable for the reaction conditions of low temperature and high pressure.

[0046] Comparing Comparative Example 5 with Example 3, it can be seen that changing the molar ratios of molybdenum, bismuth, iron, manganese, cerium, and praseodymium in the active metal solution also has an important impact on the selectivity, acrylonitrile monomer yield, and abrasion rate of the propylene ammoxidation catalyst.

[0047] In summary, the propylene ammoxidation catalyst of the present invention uses modified silica sol as a carrier and loads 30-60% of metal active centers such as molybdenum, bismuth, iron, manganese, cerium, and praseodymium. Among them, the multi-valent elements such as iron, manganese, cerium, and praseodymium are compounded with molybdenum and bismuth, which can promote the regeneration of the catalyst, improve the activity and selectivity of the catalyst. Adding additives during the preparation process can stabilize the active components, increase the active sites, and further improve the performance of the catalyst.

[0048] Compared with the prior art, the propylene ammoxidation catalyst prepared by the present invention has high selectivity and acrylonitrile monomer yield and low abrasion rate under the reaction conditions of low temperature and high pressure, and has good low-temperature activity and pressure resistance.

[0049] Through experiments, it is found that the cooperation of additives and active metals with specific molar ratios in the present invention can significantly improve the selectivity, acrylonitrile monomer yield, and abrasion rate of the propylene ammoxidation catalyst, and achieve unexpected effects in improving the low-temperature activity and pressure resistance of the propylene ammoxidation catalyst.

[0050] The above is a further description of the present invention in combination with specific embodiments, but these embodiments are merely exemplary and do not constitute any limitation to the scope of the present invention. Those skilled in the art should understand that the details and forms of the technical solutions of the present invention can be modified or replaced without departing from the spirit and scope of the present invention, but these modifications and replacements all fall within the protection scope of the present invention.

Claims

1. A method for preparing a propylene ammoxidation catalyst using a modified silica sol as a carrier, characterized in that: The steps include: Step 1, diluting the modified silica sol in water to prepare a colloidal solution; Step 2, adding 50-65% by mass of active metal solution and additives to the glue obtained in step 1 and stirring evenly to obtain a precursor slurry; Step 3: After the precursor slurry obtained in step 2 is fully homogenized, spray-dried, calcined and activated to obtain the propylene ammoxidation catalyst. The molar ratio of molybdenum, bismuth, iron, manganese, cerium and praseodymium in the active metal solution is 5-10: 0.2-0.5: 1-5: 0.3-0.8: 0.1-0.5: 0.1-0.5; The auxiliary agent is choline chloride and polyol in a mass volume ratio of 1g:5-10mL; The additive is 1-3% by weight of the active metal solution.

2. The method for preparing a propylene ammoxidation catalyst using a modified silica sol as a carrier according to claim 1, characterized in that: The mass volume ratio of the choline chloride to the polyol is 1 g:7-9 mL.

3. The method for preparing a propylene ammoxidation catalyst using a modified silica sol as a carrier according to claim 1, characterized in that: The molar ratio of molybdenum, bismuth, iron, manganese, cerium and praseodymium in the active metal solution is 7-8: 0.3-0.4: 2-3: 0.5-0.6: 0.3-0.4: 0.2-0.3, the active metal is a water-soluble metal salt, and the metal salt is a sulfate or a nitrate.

4. The method for preparing a propylene ammoxidation catalyst using a modified silica sol as a carrier according to claim 1, characterized in that: The additive is 1.8-2.2% by weight of the active metal solution.

5. The method for preparing a propylene ammoxidation catalyst using a modified silica sol as a carrier according to claim 1, characterized in that: The polyol is at least one of glycerol, ethylene glycol, butylene glycol and xylitol.

6. The method for preparing a propylene ammoxidation catalyst using a modified silica sol as a carrier according to claim 1, characterized in that: The modified silica sol in step 1 is molybdate-modified silica sol.

7. The method for preparing a propylene ammoxidation catalyst using a modified silica sol as a carrier according to claim 1, characterized in that: The spray drying in step 3 has an inlet temperature of 340-360°C and an outlet temperature of 120-140°C. The calcination in step 3 is performed in an air atmosphere for 1-3 hours.

8. The method for preparing a propylene ammoxidation catalyst using a modified silica sol as a carrier according to claim 7, characterized in that: The calcination temperature is 550-650°C.

9. A propylene ammoxidation catalyst using a modified silica sol as a carrier, prepared by the method for preparing a propylene ammoxidation catalyst using a modified silica sol as a carrier according to any one of claims 1 to 8.

10. A method for preparing acrylonitrile by ammoxidation of propylene, characterized in that: The method is prepared by using propylene, ammonia and air as raw materials and the propylene ammoxidation catalyst with the modified silica sol as a carrier as claimed in claim 9 as a catalyst, wherein the molar ratio of propylene, ammonia and air is 1:1.2-1.3:9-11, the reaction temperature is 400°C, and the reaction pressure is 0.1-0.2MPa.

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