An ammoxidation catalyst of propylene with modified silica sol as a carrier and a preparation method thereof

Abstract

The present invention discloses an ammoxidation catalyst for propylene with modified silica sol as a carrier and a preparation method thereof, belonging to the technical field of catalyst preparation. The preparation method includes: Step 1, diluting the modified silica sol in water to form a colloidal solution; Step 2, adding an active metal solution with a mass fraction of 50-65% and an auxiliary agent to the colloidal solution and stirring evenly to obtain a precursor slurry; Step 3, fully homogenizing the precursor slurry, followed by spray drying and calcination activation to obtain the ammoxidation catalyst for propylene. The active metal solution contains molybdenum, bismuth, iron, manganese, cerium and praseodymium; the auxiliary agent is choline chloride and polyol with a mass-volume ratio of 1 g: 5-10 mL; the auxiliary agent is 1-3% of the weight of the active metal solution. The ammoxidation catalyst for propylene prepared by the present invention 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.

Description

Technical Field

[0001] The present invention relates to the technical field of catalyst preparation, and specifically, to an acrylonitrile ammoxidation catalyst using modified silica sol as a 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 have been continuously developed and applied, and the demand for acrylonitrile has been increasing. 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 produce acrylonitrile. It is mainly prepared by dissolving ammonium molybdate and nitrates of Bi and other additives, followed by coprecipitation with silica sol, and then 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 have always been a hot topic in the field of acrylonitrile synthesis.

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

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

[0006] In summary, 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 using modified silica sol as a 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:

[0009] The present invention provides a method for preparing an ammoxidation catalyst of propylene using modified silica sol as a carrier, comprising the following steps:

[0010] Step 1: Dilute the modified silica sol in water to form a colloidal solution;

[0011] 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;

[0012] 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.

[0013] Preferably, the mass fraction of the active metal solution in Step 2 is 50-65%; preferably 55-60%.

[0014] 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.

[0015] Preferably, the active metal in Step 2 is a water-soluble metal salt; more preferably, the metal salt is a sulfate or a nitrate.

[0016] 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.

[0017] Preferably, the polyol is at least one of glycerol, ethylene glycol, butanediol and xylitol.

[0018] 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%.

[0019] Preferably, the stirring evenly in Step 2 is: stirring at 400-500 rpm for 2-4 h.

[0020] Preferably, the modified silica sol in Step 1 is a molybdate-modified silica sol.

[0021] Preferably, the spray drying in step 3 is carried out 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.

[0022] Preferably, the calcination in step 3 is carried out in an air atmosphere for 1 - 3 h.

[0023] In some embodiments, the temperature of the calcination is 550 - 650°C.

[0024] The present invention also provides an acrylonitrile ammoxidation catalyst using the modified silica sol as a carrier prepared by the above preparation method.

[0025] The present invention also provides a method for preparing acrylonitrile by acrylonitrile ammoxidation, which uses propylene, ammonia and air as raw materials and carries out the reaction using the above acrylonitrile ammoxidation catalyst as a catalyst.

[0026] 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 .

[0027] The beneficial effects of the present invention are as follows:

[0028] 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.

[0029] 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 wear rate, and has good low temperature activity and pressure resistance.

[0030] It is found through experiments that the present invention combines the additive composed of a specific ratio of choline chloride and polyol with the active metals in a specific molar ratio, which can significantly improve the selectivity, acrylonitrile monomer yield and wear rate of the acrylonitrile ammoxidation catalyst, and achieves unexpected effects in improving the low temperature activity and pressure resistance of the acrylonitrile ammoxidation catalyst. Detailed embodiments

[0031] 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 that conforms to the principles and novel features disclosed herein.

[0032] 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 SiO₂ 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).

[0033] Example 1

[0034] Preparation method of propylene ammoxidation catalyst using modified silica sol as carrier

[0035] The steps are as follows:

[0036] Step 1: Dilute the molybdate-modified silica sol in water to make a 1000 g ammonium molybdate-modified silica sol solution with a mass concentration of 40%.

[0037] Step 2: According to the molar ratio of molybdenum, bismuth, iron, manganese, cerium, and praseodymium of 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 a 1600 g active metal salt solution with a mass concentration of 50%.

[0038] Add the active metal solution and 8 g of the additive 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, where the additive is choline chloride and glycerol with a mass-to-volume ratio of 1 g:5 mL.

[0039] Step 3: After fully homogenizing the precursor slurry obtained in Step 2, it is spray-dried (with an inlet temperature of 350 °C and an outlet temperature of 130 °C), and calcined and activated in an air atmosphere (at 550 °C) for 3 h to obtain the propylene ammoxidation catalyst.

[0040] Example 2

[0041] Preparation method of propylene ammoxidation catalyst using modified silica sol as carrier

[0042] The steps are as follows:

[0043] 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%.

[0044] 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 make 1620 g of active metal solution with a mass concentration of 65%.

[0045] Add the active metal solution and 31.2 g of an 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, where the auxiliary agent is choline chloride and glycerol with a mass-to-volume ratio of 1 g:10 mL.

[0046] Step 3: After fully homogenizing the precursor slurry obtained in Step 2, it is spray-dried (with an inlet temperature of 350 °C and an outlet temperature of 130 °C), and calcined and activated in an air atmosphere (at 650 °C) for 1 h to obtain the propylene ammoxidation catalyst.

[0047] Example 3

[0048] Preparation method of propylene ammoxidation catalyst using modified silica sol as carrier

[0049] The steps are as follows:

[0050] 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%.

[0051] 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 make 1600 g of active metal solution with a mass concentration of 60%.

[0052] Add the active metal solution and 19.2 g of the additive 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. Among them, the additive is choline chloride and glycerol with a mass-to-volume ratio of 1 g: 8 mL;

[0053] Step 3: After the precursor slurry obtained in Step 2 is fully homogenized, it is spray-dried (the inlet temperature is 350 °C and the outlet temperature is 130 °C), and calcined and activated (600 °C) for 2 h in an air atmosphere to obtain the propylene ammoxidation catalyst.

[0054] Comparative Example 1

[0055] The difference between this comparative example and Example 3 is that: the additive is not added in Step 2.

[0056] The remaining steps are the same as those in Example 3.

[0057] Comparative Example 2

[0058] The difference between this comparative example and Example 3 is that: the addition amount of the additive is different.

[0059] Specifically: Add the active metal solution and 48 g of the additive 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. Among them, the additive is choline chloride and glycerol with a mass-to-volume ratio of 1 g: 8 mL;

[0060] The remaining steps are the same as those in Example 3.

[0061] Comparative Example 3

[0062] The difference between this comparative example and Example 3 is that: the composition of the additive is different.

[0063] Specifically: The additive is choline chloride and glycerol with a mass-to-volume ratio of 1 g: 2 mL;

[0064] The remaining steps are the same as those in Example 3.

[0065] Comparative Example 4

[0066] The difference between this comparative example and Example 3 is that: the composition of the additive is different.

[0067] Specifically: The additive is choline chloride and glycerol with a mass-to-volume ratio of 1 g: 20 mL;

[0068] The remaining steps are the same as those in Example 3.

[0069] Comparative Example 5

[0070] The difference between this comparative example and Example 3 is that: the molar ratio of molybdenum, bismuth, iron, manganese, cerium and praseodymium in the active metal solution is different.

[0071] 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.

[0072] The remaining steps are the same as those in Example 3.

[0073] Comparative Example 6

[0074] The catalyst 2 for the ammoxidation of propylene to acrylonitrile prepared by ZL202410726267.2, the specific method is as follows:

[0075] 1) Preparation process of acrylonitrile catalyst:

[0076] 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;

[0077] S2: Add 4000 g of ammonium molybdate modified silica sol prepared in Example 2 to Solution I respectively, and mix evenly at high speed to obtain Slurry 2;

[0078] S3: After spray-drying the slurry obtained in step S2, granulate and form, and calcine at 620 °C for 3 hours to obtain the catalyst 2 for the ammoxidation of propylene to acrylonitrile.

[0079] Catalyst performance test

[0080] Charge 400 g of catalyst in a fluidized bed reactor with an inner diameter of 38 mm, use propylene, ammonia and air as raw materials (molar ratio 1:1.25:10), and react under the conditions of a reaction temperature of 400 °C, a reaction pressure of 0.15 MPa, and a catalyst propylene load of 0.15 h -1 to evaluate the performance of the catalyst, and the results are shown in Table 1.

[0081] Table 1

[0082]

[0083] Results show that for the propylene 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 propylene 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 propylene ammoxidation catalyst prepared by the present invention has good selectivity, 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, prolongs the service life, and reduces production costs.

[0084] Comparing Comparative Example 1 and Example 3, it can be seen that for the propylene ammoxidation catalyst prepared without adding additives in Comparative Example 1, 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%, indicating that in the preparation process of the propylene 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 propylene ammoxidation catalyst.

[0085] 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 important effects on the selectivity, acrylonitrile monomer yield, and attrition rate of the propylene 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 propylene ammoxidation catalyst has poor low temperature activity and pressure resistance and is not suitable for the reaction conditions of low temperature and high pressure.

[0086] Comparing Comparative Example 5 and Example 3, it can be seen that changing the molar ratio of molybdenum, bismuth, iron, manganese, cerium, and praseodymium in the active metal solution also has important effects on the selectivity, acrylonitrile monomer yield, and attrition rate of the propylene ammoxidation catalyst.

[0087] In summary, the propylene ammoxidation catalyst of the present invention uses modified silica sol as the 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 an additive during the preparation process can stabilize the active components, increase the active sites, and further improve the performance of the catalyst.

[0088] Compared with the prior art, the propylene 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.

[0089] It is found through experiments that by combining the promoter with the active metal in a specific molar ratio, the present invention can significantly improve the selectivity, acrylonitrile monomer yield and abrasion rate of the propylene ammoxidation catalyst, and achieves unexpected effects in improving the low-temperature activity and pressure resistance of the propylene ammoxidation catalyst.

[0090] 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 such modifications and replacements all fall within the protection scope of the present invention.

Claims

1. A preparation method of an ammoxidation catalyst of propylene with modified silica sol as a carrier, characterized in that, It includes the following steps: Step 1: Dilute the modified silica sol in water to make a colloidal solution; Step 2: Add an active metal solution with a mass fraction of 50 - 65% 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, carry out spray drying and calcination activation to obtain the propylene ammoxidation catalyst; In the active metal solution, the molar ratio of molybdenum, bismuth, iron, manganese, cerium and praseodymium 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 with a mass - volume ratio of 1 g:5 - 10 mL; The auxiliary agent is 1 - 3% of the weight of the active metal solution.

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

3. The preparation method of the propylene ammoxidation catalyst using modified silica sol as a carrier according to claim 1, characterized in that, In the active metal solution, the molar ratio of molybdenum, bismuth, iron, manganese, cerium and praseodymium 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 preparation method of the propylene ammoxidation catalyst using modified silica sol as a carrier according to claim 1, characterized in that, The auxiliary agent is 1.8 - 2.2% of the weight of the active metal solution.

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

6. The preparation method of the propylene ammoxidation catalyst using modified silica sol as a carrier according to claim 1, characterized in that, The modified silica sol in Step 1 is a molybdate - modified silica sol.

7. The preparation method of the propylene ammoxidation catalyst using modified silica sol as a carrier according to claim 1, characterized in that, In Step 3, the inlet temperature of the spray drying is 340 - 360 °C, and the outlet temperature is 120 - 140 °C. In Step 3, the calcination is carried out in an air atmosphere for 1 - 3 h.

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

9. The propylene ammoxidation catalyst supported on modified silica sol prepared by the preparation method of the propylene ammoxidation catalyst supported on modified silica sol according to any one of claims 1 - 8.

10. A method for preparing acrylonitrile by ammoxidation of propylene, characterized in that, Prepared by reacting with propylene, ammonia and air as raw materials and using the propylene ammoxidation catalyst supported on modified silica sol according to claim 9 as the 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 - 0.2 MPa.

Images