Novel acrylonitrile catalyst and preparation method thereof

Abstract

The invention provides a novel acrylonitrile catalyst and a preparation method thereof. The novel acrylonitrile catalyst is prepared from the following raw materials: mixed salt, an active component, silica sol, a rare earth precursor, a carrier and a cosolvent, by introducing the cosolvent and optimizing the carrier structure, the dispersity of the rare earth precursor is improved, the production process is optimized, the doping efficiency of the rare earth precursor is remarkably improved, the activity, selectivity and stability of the novel acrylonitrile catalyst are improved, generation of by-products CO, CO2, acrolein and acrylic acid during acrylonitrile production can be reduced, and industrial efficient preparation is achieved.

Description

Technical Field

[0001] The present invention relates to the field of catalysts, and particularly to a novel acrylonitrile catalyst and a preparation method thereof. Background Art

[0002] Acrylonitrile, as a key intermediate in the petrochemical field, is an important raw material for synthetic fibers, engineering plastics, synthetic rubbers, and fine chemicals. The global annual production capacity of acrylonitrile exceeds 8 million tons, of which approximately 60% is used for the production of polyacrylonitrile fibers, 20% for ABS resins, and the rest for derivatives such as nitrile rubber, carbon fiber precursor, acrylamide, and pesticides. With the growth of new energy, automotive lightweighting, and high-end material demands, the downstream applications of acrylonitrile continue to expand, posing higher requirements for its production efficiency and environmental performance. Currently, the industrial production of acrylonitrile mainly adopts the propylene ammoxidation process, whose core reaction is the generation of acrylonitrile from propylene, ammonia, and oxygen under the action of a catalyst, with by-products including hydrogen cyanide, acetonitrile, acrolein, and carbon dioxide. Since the commercialization of this process in the 1960s, the optimization of catalyst performance has always been the core direction of technological upgrading.

[0003] The first-generation acrylonitrile catalyst is based on bismuth molybdate (Bi-Mo-O). To improve its catalytic performance, transition metal oxides such as iron, cobalt, and nickel are introduced as promoters. However, Bi-Mo-based catalysts are prone to deactivation due to sintering or volatilization of active components during long-term operation, with a service life usually less than 2 years, requiring frequent catalyst replacement and further driving up production costs. Researchers have attempted to introduce rare earth elements as electronic or structural promoters. Rare earth oxides have excellent oxygen storage capacity and redox characteristics, which can adjust the surface acidity and basicity of the catalyst and inhibit deep oxidation side reactions. For example, Patent CN102553546A reports a Ce-doped Mo-Bi-Fe-Co-Ni-O catalyst with acrylonitrile selectivity increased to 78%. However, the poor dispersion of cerium nitrate in the traditional impregnation method results in uneven distribution of active sites. Studies have shown that rare earth ions are prone to form strong interactions with the hydroxyl groups on the carrier surface, agglomerating during drying or calcination to form particles with a size exceeding 50 nm, reducing the effective specific surface area. In addition, when the rare earth doping amount exceeds 3 wt%, the mechanical strength of the catalyst significantly decreases, making it difficult to meet the anti-wear requirements of fluidized bed reactors. The propylene ammoxidation reaction is a highly exothermic process. High temperatures are likely to exacerbate the complete oxidation of propylene to produce COx and the decomposition of ammonia to produce HCN. Traditional catalysts enhance activity by increasing the molybdenum content, but excessive MoO3 will cover the surface acidic sites, leading to a decrease in selectivity. Although rare earth doping can partially alleviate this contradiction, its poor dispersion may introduce new inactive regions, instead increasing the formation of by-products. The preparation of existing catalysts mostly relies on multi-step impregnation, high-temperature calcination, and mechanical mixing, which not only consume high energy but also easily cause volatilization of active components.

[0004] In view of the problems existing in the prior art, the present application aims to invent a new acrylonitrile catalyst with high activity, selectivity and stability, which can reduce the generation of by-products during the production of acrylonitrile. Summary of the Invention

[0005] Object of the Invention: The object of the present invention is to provide a new acrylonitrile catalyst and its preparation method. By introducing a cosolvent and optimizing the carrier structure, the dispersion of the rare earth precursor is improved, and the production process is optimized, significantly enhancing the doping efficiency of the rare earth precursor, improving the activity, selectivity and stability of the new acrylonitrile catalyst, reducing the generation of by-products such as CO, CO2, acrolein and acrylic acid during the production of acrylonitrile, and realizing industrialized high-efficiency preparation.

[0006] Technical Solution of the Present Invention:

[0007] The present invention provides a new acrylonitrile catalyst. The raw materials for preparing the new acrylonitrile catalyst include: mixed salts, active components, silica sol, rare earth precursors, silica carriers, and cosolvents.

[0008] Further, the mixed salts include bismuth nitrate, iron nitrate, and nickel nitrate.

[0009] Further, the active components are Mo-Bi-Fe multi-metal oxides and transition metal oxides.

[0010] Further, the Mo-Bi-Fe multi-metal oxides are one or more mixtures of bismuth molybdate, bismuth molybdate ferrate, and bismuth ferrate.

[0011] Further, the transition metal oxides include one or more mixtures of cobalt oxide, nickel oxide, and manganese oxide.

[0012] Further, the mass ratio of the Mo-Bi-Fe multi-metal oxides to the transition metal oxides is 8-10:1.

[0013] Further, the mass concentration of the silica sol is 35-50%.

[0014] Further, the rare earth precursors are one or more mixtures of cerium nitrate, lanthanum nitrate, and praseodymium nitrate.

[0015] Further, the preparation of the silica carrier includes the following steps:

[0016] S1: Dissolve tetraethyl orthosilicate in ethanol, add an appropriate amount of water and ammonia water with a mass fraction of 25% to form a uniform silicon source solution, and adjust the pH value to 9-10;

[0017] S2: Add polyvinylpyrrolidone and sodium chloride to the silicon source solution in step S1, and then stir and react at a temperature of 40 - 60 °C for 12 - 48 hours.

[0018] S3: After the reaction, separate the product by methods such as centrifugation and filtration, wash it with deionized water and ethanol, and then dry it at a low temperature of 60 - 80 °C to obtain an orderly arranged silica support.

[0019] Further, the co - solvent is one or a mixture of ethylene glycol, glycerol, and polyethylene glycol.

[0020] Further, the mass ratio of the co - solvent to the rare - earth precursor is 1 - 3:1.

[0021] The present invention also provides a preparation method of a novel acrylonitrile catalyst, which is characterized by comprising the following steps:

[0022] Step (1): Weigh the mixed salt, active component, silica sol, rare - earth precursor, support, and co - solvent, and set aside.

[0023] Step (2): Then add the mixed salt to an appropriate amount of warm water according to a certain ratio, dissolve it at 50 - 100 °C, and then add silica sol, active component, rare - earth precursor, support, and co - solvent, and then stir evenly at high speed to obtain a slurry.

[0024] Step (3): Form the slurry prepared in step (2) by a spray dryer to obtain spherical particles with a particle size of 20 - 90 μm.

[0025] Step (4): Finally, put the particles prepared in step (3) into a roasting furnace and roast them at 200 - 300 °C for 2 - 4 h to obtain the novel acrylonitrile catalyst.

[0026] Further, the inlet temperature of the spray dryer in step (3) is 150 - 200 °C, the outlet temperature is 80 - 100 °C, the rotational speed of the atomizer is 18000 - 25000 rpm, and the tower pressure is - 500 - 500 Pa.

[0027] The present invention provides a novel acrylonitrile catalyst. A co - solvent is added in the pulping process, mixed with the rare - earth precursor, Mo - Bi - Fe active component, and silica support, and through high - speed stirring or ultrasonic dispersion, it ensures that the rare - earth elements are evenly dispersed in the slurry. During the sintering process, the co - solvent completely volatilizes at the low - temperature stage, avoiding residues; the sintering temperature and time are optimized according to the characteristics of the active component and support of the catalyst, ensuring that the rare - earth elements are fully combined with the support and active component. By introducing the co - solvent, the doping efficiency of the rare - earth elements is improved, and the active sites of the catalyst are increased. The uniform dispersion of the rare - earth elements helps to inhibit side reactions and improve the selectivity and yield of acrylonitrile.

[0028] Beneficial effects:

[0029] The present invention provides a novel acrylonitrile catalyst with the following beneficial effects:

[0030] 1. Improve the doping efficiency of rare earth elements: By introducing a co-solvent, the dispersion and doping efficiency of rare earth elements in the catalyst are significantly improved;

[0031] 2. Optimize the production process: The co-solvent completely volatilizes during the sintering process, avoiding residues and simplifying the subsequent treatment steps;

[0032] 3. Enhance the performance of the catalyst: The uniform dispersion of rare earth elements enhances the activity, selectivity and stability of the catalyst;

[0033] 4. Reduce the generation of by-products: By suppressing side reactions, the generation amount of by-products (such as CO, CO2, acrolein, acrylic acid) is significantly reduced. Specific embodiments

[0034] The present invention will be described below in conjunction with specific implementation embodiments. It should be noted that the following examples are examples of the present invention, only used to illustrate the present invention, and not used to limit the present invention. Other combinations and various improvements within the concept of the present invention can be made without departing from the main idea or scope of the present invention.

[0035] Unless otherwise specified, other chemical reagents used in the present invention are all ordinary commercially available analytical pure.

[0036] Preparation of silica support:

[0037] S1: Dissolve 15 ml of tetraethyl orthosilicate in 50 ml of ethanol, add 1.5 ml of water and 2 ml of 25% ammonia water by mass fraction to form a uniform silicon source solution, and adjust the pH value to 10;

[0038] S2: Add 1 g of polyvinylpyrrolidone and 0.2 g of sodium chloride to the silicon source solution in step S1, and then stir and react at 60 °C for 30 hours;

[0039] S3: After the reaction, separate the product by centrifugation, filtration and other methods, wash it with deionized water and ethanol, and then dry it at a low temperature of 60 °C to obtain an orderly arranged silica support.

[0040] Example 1:

[0041] Preparation of novel acrylonitrile catalyst:

[0042] Step (1): Weigh the mixed salts: 20 g of bismuth nitrate, 15 g of iron nitrate, 10 g of nickel nitrate, the active components: 16 g of bismuth molybdate, 2 g of cobalt oxide, 35 g of silica sol with a mass concentration of 40%, the rare earth precursor: 8 g of cerium nitrate, the carrier: 15 g of silica carrier, the cosolvent: 24 g of ethylene glycol (the mass ratio of the cosolvent to the rare earth precursor is 3:1), and set aside;

[0043] Step (2): Then add the mixed salts to 200 ml of warm water at 80°C and dissolve at 80°C. Then add the silica sol, active components, rare earth precursor, carrier, and cosolvent, and stir at a high speed of 1500 r / min for 1 hour to obtain a uniform slurry;

[0044] Step (3): Shape the slurry prepared in step (2) through a spray dryer, set the inlet temperature at 180°C, the outlet temperature at 90°C, the atomizer rotation speed at 20000 rpm, and the tower pressure at -200 Pa to obtain spherical particles with a particle size of 60 μm;

[0045] Step (4): Finally, put the particles prepared in step (3) into a roasting furnace and roast at 250°C for 3 h to obtain a novel acrylonitrile catalyst.

[0046] Example 2:

[0047] The difference between the preparation of this novel acrylonitrile catalyst and that of Example 1 lies in that the cosolvent is 8 g of ethylene glycol (the mass ratio of the cosolvent to the rare earth precursor is 1:1).

[0048] Example 3:

[0049] The difference between the preparation of this novel acrylonitrile catalyst and that of Example 1 lies in that the rare earth precursor is 4 g of cerium nitrate, 4 g of lanthanum nitrate, and 4 g of praseodymium nitrate, and the cosolvent is 12 g of glycerol (the mass ratio of the cosolvent to the rare earth precursor is 1:1).

[0050] Example 4:

[0051] The difference between the preparation of this novel acrylonitrile catalyst and that of Example 1 lies in that the cosolvent is 6.4 g of propylene glycol (the mass ratio of the cosolvent to the rare earth precursor is 1:0.8).

[0052] Comparative Example 1

[0053] The difference between the preparation of this novel acrylonitrile catalyst A and that of Example 1 lies in that no rare earth precursor is added.

[0054] Comparative Example 2:

[0055] The difference between the preparation of this novel acrylonitrile catalyst A and that of Example 1 lies in that no cosolvent is added.

[0056] Comparative Example 3

[0057] The difference between the preparation of this catalyst and the preparation of the novel acrylonitrile catalyst A in Example 1 lies in that no rare earth precursor and cosolvent are added.

[0058] The novel acrylonitrile catalysts prepared in Examples 1-4 and Comparative Examples 1-3 were subjected to the following experiments:

[0059] Production of acrylonitrile:

[0060] S1: Preheat propylene, ammonia, and air to 300 °C respectively. Control the volume ratio of air to propylene to be 9:1 and the volume ratio of ammonia to air to be 1:9. Precisely adjust the ratios of propylene, ammonia, and air through a flowmeter, and fully mix them through a static mixer;

[0061] S2: Add 50% of the novel acrylonitrile catalyst based on the volume of the fluidized bed reactor into the fluidized bed reactor. Raise the temperature to 450 °C and the reaction pressure to 0.09 MPa. Introduce the mixed gas from Step S1, and control the contact time between the gas and the catalyst to be 8 s;

[0062] S3: The reaction gas enters a quench tower, and the temperature drops rapidly to 100 °C. Spray dilute sulfuric acid with a mass concentration of 5% to neutralize the unreacted ammonia. Then absorb organic substances such as acrylonitrile, HCN, and ACN in the gas with warm water at 10 °C. The absorption liquid is sent to the rectification section, and through azeotropic rectification and vacuum distillation, products such as acrylonitrile, acrolein, and acrylic acid are obtained.

[0063] 1. Calculate the conversion rate of propylene, the yield of acrylonitrile, and the yields of by-products acrolein, acrylic acid, carbon monoxide, and carbon dioxide based on the above experimental tests. The results are shown in Table 1.

[0064] 2. Test the specific surface area, bulk density, tapped density, attrition rate, and particle size distribution of the prepared novel acrylonitrile catalyst. The results are shown in Table 2.

[0065] Table 1: Performance test results table

[0066]

[0067] Table 2: Catalyst data results table:

[0068]

[0069]

[0070] As can be seen from Table 1, the novel acrylonitrile catalyst prepared by the present invention has high activity, good selectivity, and stability, which can improve the yield of acrylonitrile and reduce the formation of by-products such as CO, CO2, acrolein, and acrylic acid during the production of acrylonitrile. Comparing Example 4 with Example 1, it can be seen that when the mass ratio of the cosolvent to the rare earth precursor is unreasonable, it will lead to a decrease in the activity of the novel acrylonitrile catalyst, resulting in a decrease in the conversion rate of acrylonitrile, poor selectivity, a decrease in the yield of acrylonitrile, and an increase in by-products, failing to achieve the expected effect; comparing Comparative Example 1 with Example 1, it can be seen that without adding the rare earth precursor, it will lead to a decrease in the activity of the novel acrylonitrile catalyst, resulting in a decrease in the conversion rate of acrylonitrile, poor selectivity, an increase in by-products, and failing to achieve the expected effect; comparing Comparative Example 2 with Example 1, it can be seen that without adding the cosolvent, it will lead to a decrease in the activity of the novel acrylonitrile catalyst, resulting in a decrease in the conversion rate of acrylonitrile, poor selectivity, an increase in by-products, and failing to achieve the expected effect; comparing Comparative Example 3 with Example 1, it can be seen that without adding the rare earth precursor and the cosolvent, it will lead to a decrease in the activity of the novel acrylonitrile catalyst, resulting in a decrease in the conversion rate of acrylonitrile, poor selectivity, an increase in by-products, a decrease in the yield of acrylonitrile, and failing to achieve the expected effect.

[0071] As can be seen from Table 2, the physical properties of the novel acrylonitrile catalysts prepared in Examples 1-3 are better than those in Examples 4 and Comparative Examples 1-3. Specifically, the physical properties of the novel acrylonitrile catalysts prepared in Examples 1-3 meet the catalyst indicators: specific surface area 36-48, bulk density 0.88-1.12, tap density 1.04-1.28, abrasion rate less than or equal to 4%, particle size distribution: less than 30% greater than 90 microns, 30-50% less than or equal to 45 microns, and less than or equal to 7% less than or equal to 20 microns, while the physical properties of the novel acrylonitrile catalysts prepared in Examples 4 and Comparative Examples 1-3 do not all meet the above indicators.

[0072] The present invention can also have various other embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and deformations according to the present invention, but these corresponding changes and deformations should all fall within the protection scope of the appended claims of the present invention.

Claims

1. A novel acrylonitrile catalyst, characterized in that, The raw materials for preparing the novel acrylonitrile catalyst include: mixed salts, active components, silica sol, rare earth precursors, silica carriers, and cosolvents.

2. The novel acrylonitrile catalyst according to claim 1, characterized in that, The mixed salts include bismuth nitrate, iron nitrate, and nickel nitrate.

3. The novel acrylonitrile catalyst according to claim 1, wherein The active components are Mo-Bi-Fe multi-metal oxides and transition metal oxides.

4. The novel acrylonitrile catalyst according to claim 3, wherein The Mo-Bi-Fe multi-metal oxides are one or more mixtures of bismuth molybdate, bismuth iron molybdate, and bismuth ferrate; The transition metal oxides include one or more mixtures of cobalt oxide, nickel oxide, and manganese oxide; The mass ratio of the Mo-Bi-Fe multi-metal oxides to the transition metal oxides is 8-10:

1.

5. The novel acrylonitrile catalyst according to claim 1, characterized in that, The mass concentration of the silica sol is 35-50%.

6. The novel acrylonitrile catalyst according to claim 1, wherein The rare earth precursors are one or more mixtures of cerium nitrate, lanthanum nitrate, and praseodymium nitrate.

7. The novel acrylonitrile catalyst according to claim 1, characterized in that, The preparation of the silica carrier includes the following steps: S1: Dissolve tetraethyl orthosilicate in ethanol, add appropriate amounts of water and 25% ammonia water to form a uniform silicon source solution, and adjust the pH value to 9-10; S2: Add polyvinylpyrrolidone and sodium chloride to the silicon source solution in step S1, and then stir and react at a temperature of 40-60°C for 12-48 hours, S3: After the reaction, separate the product by centrifugation, filtration and other methods, wash it with deionized water and ethanol, and then dry it at a low temperature of 60-80°C to obtain an orderly arranged silica carrier.

8. The novel acrylonitrile catalyst according to claim 1, wherein, The cosolvent is one or more mixtures of ethylene glycol, glycerol, and polyethylene glycol; the mass ratio of the cosolvent to the rare earth precursor is 1-3:

1.

9. The preparation method of the novel acrylonitrile catalyst according to any one of claims 1-8, characterized in that, It includes the following steps: Step (1): Weigh the mixed salts, active components, silica sol, rare earth precursors, carriers, and cosolvents for standby; Step (2): Then add the mixed salts to an appropriate amount of warm water in a certain proportion, dissolve them at 50-100°C, and then add silica sol, active components, rare earth precursors, carriers, and cosolvents, and then stir evenly at high speed to obtain a slurry; Step (3): Form the slurry prepared in step (2) through a spray dryer to obtain spherical particles with a particle size of 20-90 μm; Step (4): Finally, put the particles prepared in step (3) into a roasting furnace and roast them at 200-300°C for 2-4 h to obtain the novel acrylonitrile catalyst.

10. The preparation method of the novel acrylonitrile catalyst according to claim 9, characterized in that, The inlet temperature of the spray dryer in step (3) is 150-200°C, the outlet temperature is 80-100°C, the atomizer rotation speed is 18000-25000 rpm, and the tower pressure is -500-500 Pa.

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