A catalyst for acrylonitrile and a method for preparing the same

Abstract

The application provides an acrylonitrile catalyst and a preparation method thereof. Raw materials for preparing the acrylonitrile catalyst include mixed salt, active component, silica sol, rare earth precursor, carrier and cosolvent. The dispersion of the rare earth precursor is improved by introducing the cosolvent and optimizing the structure of the carrier, the production process is optimized, the doping efficiency of the rare earth precursor is significantly improved, the activity, selectivity and stability of the acrylonitrile catalyst are improved, the generation of by-products CO, CO2, acrolein and acrylic acid during the production of acrylonitrile is reduced, and industrialized efficient preparation is realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of catalysts, in particular to a catalyst for acrylonitrile and a preparation method thereof. BACKGROUND

[0002] As a key intermediate in the field of petrochemical industry, acrylonitrile is an important raw material for the synthesis of fibers, engineering plastics, synthetic rubber and fine chemicals. The global acrylonitrile production capacity exceeds 8 million tons, of which about 60% is used for the production of polyacrylonitrile fibers, 20% for ABS resins, and the rest for nitrile rubber, carbon fiber precursor, acrylamide and pesticide derivatives. With the growth of new energy, automobile lightweight and high-end material demand, the downstream applications of acrylonitrile continue to expand, and higher requirements are put forward for its production efficiency and environmental performance. Currently, the industrial production of acrylonitrile mainly adopts the propylene ammoxidation method, the core reaction of which is the generation of acrylonitrile from propylene, ammonia and oxygen under the action of a catalyst, and the by-products include hydrogen cyanide, acetonitrile, propylene aldehyde 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 of acrylonitrile catalysts is based on bismuth molybdate (Bi-Mo-O). To improve the catalytic performance, transition metal oxides such as iron, cobalt and nickel are introduced as cocatalysts. However, Bi-Mo-based catalysts are prone to deactivation due to sintering or volatilization of active components during long-term operation, and the service life is usually less than 2 years, requiring frequent replacement of catalysts, further increasing production costs. Researchers have attempted to introduce rare earth elements as electronic or structural additives. Rare earth oxides have excellent oxygen storage capacity and redox properties, which can adjust the surface acidity and alkalinity 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 dispersibility of cerium nitrate in the traditional impregnation method is insufficient, leading to uneven distribution of active sites. Studies have shown that rare earth ions easily form strong interactions with the surface hydroxyl groups of the carrier, and during drying or calcination, they agglomerate 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 decreases significantly, making it difficult to meet the anti-wear requirements of the fluidized bed reactor. The propylene ammoxidation reaction is a strong exothermic process, and high temperatures can easily accelerate the complete oxidation of propylene to COx and the decomposition of ammonia to HCN. Traditional catalysts enhance activity by increasing molybdenum content, but excessive MoO3 will cover the surface acid sites, leading to a decrease in selectivity. Although rare earth doping can partially alleviate this contradiction, its poor dispersibility may introduce new non-active areas, thereby increasing the generation of by-products. Existing catalyst preparation relies on multi-step impregnation, high-temperature calcination and mechanical mixing, which not only consumes a lot of energy, but also easily causes volatilization of active components.

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

[0005] The present application aims to provide an acrylonitrile catalyst and a preparation method thereof, which improves the dispersibility of rare earth precursors by introducing a cosolvent and optimizing the structure of the carrier, optimizes the production process, significantly improves the doping efficiency of the rare earth precursors, improves the activity, selectivity and stability of the acrylonitrile catalyst, reduces the generation of by-products CO, CO2, acrolein and acrylic acid during the production of acrylonitrile, and realizes industrialized and efficient preparation.

[0006] The present application provides an acrylonitrile catalyst, and the raw materials for preparing the acrylonitrile catalyst include mixed salt, active component, silica sol, rare earth precursor, silica carrier and cosolvent.

[0007] Further, the mixed salt includes bismuth nitrate, iron nitrate and nickel nitrate.

[0008] Further, the active component is Mo-Bi-Fe multi-metal oxide or transition metal oxide.

[0009] Further, the Mo-Bi-Fe multi-metal oxide is one or a mixture of bismuth molybdate, bismuth molybdate and bismuth ferrite.

[0010] Further, the transition metal oxide includes one or a mixture of cobalt oxide, nickel oxide and manganese oxide.

[0011] Further, the mass ratio of the Mo-Bi-Fe multi-metal oxide to the transition metal oxide is 8-10:1.

[0012] Further, the mass concentration of the silica sol is 35-50%.

[0013] Further, the rare earth precursor is one or a mixture of cerium nitrate, lanthanum nitrate and praseodymium nitrate.

[0014] Further, the preparation of the silica carrier includes the following steps:

[0015] S1: Dissolve tetraethyl orthosilicate in ethanol, add an appropriate amount of water and 25% ammonia water, form a uniform silica source solution, and adjust the pH value to 9-10;

[0016] S2: Add polyvinylpyrrolidone and sodium chloride to the silica source solution of step S1, and then stir and react at a temperature of 40-60℃ for 12-48 hours,

[0017] S3: After the reaction, the product is separated by centrifugation, filtration and the like, and then washed with deionized water and ethanol, and then dried at a low temperature of 60-80℃ to obtain a silica carrier with ordered arrangement.

[0018] Further, the cosolvent is one or more of ethylene glycol, glycerol, and polyethylene glycol.

[0019] Further, the mass ratio of the cosolvent to the rare earth precursor is 1-3:1.

[0020] The application also provides a preparation method of the propylene cyanide catalyst, characterized by comprising the following steps:

[0021] Step (1): weigh the mixed salt, active component, silica sol, rare earth precursor, carrier, and cosolvent, and prepare them for use;

[0022] Step (2): then add the mixed salt into a proper amount of warm water in a certain proportion, dissolve at 50-100℃, and then add the silica sol, active component, rare earth precursor, carrier, and cosolvent, and then uniformly stir at high speed to prepare a slurry;

[0023] Step (3): form the slurry prepared in step (2) through a spray dryer to prepare spherical particles with a particle size of 20-90μm;

[0024] Step (4): finally, put the particles prepared in step (3) into a calcination furnace, calcine at 200-300℃ for 2-4h to prepare the propylene cyanide catalyst.

[0025] Further, the inlet temperature of the spray dryer in step (3) is 150-200℃, the outlet temperature is 80-100℃, the speed of the atomizer is 18000-25000rpm, and the tower pressure is -500-500Pa.

[0026] The application provides a propylene cyanide catalyst, which adds a cosolvent in the slurry preparation process, mixes the cosolvent with a rare earth precursor, Mo-Bi-Fe active component, and a silica carrier, and uniformly disperses the rare earth elements in the slurry through high-speed stirring or ultrasonic dispersion, so that the cosolvent is completely volatilized at a low temperature stage in the sintering process and avoids residue; the sintering temperature and time are optimized according to the characteristics of the active component and carrier of the catalyst, so that the rare earth elements are fully combined with the carrier and active component; the doping efficiency of the rare earth elements is improved through the introduction of the cosolvent, the active sites of the catalyst are increased, the uniform dispersion of the rare earth elements helps to inhibit the side reaction, and the selectivity and yield of propylene cyanide are improved.

[0027] Advantages:

[0028] The application provides a propylene cyanide catalyst with the following advantages:

[0029] 1. Improved rare earth doping efficiency: The dispersion of rare earth elements in the catalyst and the doping efficiency are significantly improved by the introduction of a cosolvent;

[0030] 2. Optimized production process: The cosolvent completely volatilizes during the sintering process, avoiding residues and simplifying subsequent processing steps;

[0031] 3. Enhanced catalyst performance: The uniform dispersion of rare earth elements enhances the activity, selectivity, and stability of the catalyst;

[0032] 4. Reduced byproduct formation: By suppressing side reactions, the formation of byproducts such as CO, CO2, acrolein, and acrylic acid is significantly reduced. DETAILED DESCRIPTION

[0033] The following will illustrate the present application with specific embodiments. It should be noted that the following examples are examples of the present application and are only used to illustrate the present application, but not to limit the present application. Other combinations and various modifications within the concept of the present application can be made without departing from the spirit or scope of the present application.

[0034] Other chemical reagents used in the present application are commercially available unless otherwise specified.

[0035] Preparation of silica carrier:

[0036] 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, form a uniform silica source solution, and adjust the pH value to 10;

[0037] S2: Add 1 g of polyvinylpyrrolidone and 0.2 g of sodium chloride to the silica source solution of step S1, then stir and react at 60°C for 30 hours;

[0038] S3: After the reaction is complete, separate the product by centrifugation, filtration, etc., and wash with deionized water and ethanol, then dry at 60°C to obtain an ordered arrangement of silica carrier.

[0039] Example 1

[0040] Preparation of acrylonitrile catalyst:

[0041] Step (1): Weigh the mixed salt: bismuth nitrate 20 g, iron nitrate 15 g, nickel nitrate 10 g, active component: bismuth molybdate 16 g, cobalt oxide 2 g, silica sol with a mass concentration of 40% 35 g, rare earth precursor: cerium nitrate 8 g, carrier: silica carrier 15 g, cosolvent: ethylene glycol 24 g (mass ratio of cosolvent to rare earth precursor is 3:1), ready for use;

[0042] Step (2): Then the mixed salt was added into 200 ml of 80℃ warm water, dissolved at 80℃, and then silica sol, active component, rare earth precursor, carrier, and cosolvent were added, and stirred at a speed of 1500 r / min for 1 hour to prepare a uniform slurry;

[0043] Step (3): The slurry prepared in step (2) was shaped by a spray dryer, with an inlet temperature of 180℃, an outlet temperature of 90℃, an atomizer speed of 20000 rpm, and a tower pressure of -200 Pa, to prepare spherical particles with a particle size of 60 μm;

[0044] Step (4): Finally, the particles prepared in step (3) were placed in a calcination furnace and calcined at 250℃ for 3 hours to prepare an acrylonitrile catalyst.

[0045] Example 2

[0046] The preparation was different from the preparation of the acrylonitrile catalyst of Example 1 in that the cosolvent was ethylene glycol 8 g (mass ratio of cosolvent to rare earth precursor was 1:1).

[0047] Example 3

[0048] The preparation was different from the preparation of the acrylonitrile catalyst of Example 1 in that the rare earth precursor was cerium nitrate 4 g, lanthanum nitrate 4 g, and praseodymium nitrate 4 g, and the cosolvent was glycerol 12 g (mass ratio of cosolvent to rare earth precursor was 1:1).

[0049] Example 4

[0050] The preparation was different from the preparation of the acrylonitrile catalyst of Example 1 in that the cosolvent was propylene glycol 6.4 g (mass ratio of cosolvent to rare earth precursor was 1:0.8).

[0051] Comparative Example 1

[0052] The preparation was different from the preparation of the acrylonitrile catalyst A of Example 1 in that no rare earth precursor was added.

[0053] Comparative Example 2

[0054] The preparation was different from the preparation of the acrylonitrile catalyst A of Example 1 in that no cosolvent was added.

[0055] Comparative Example 3

[0056] The preparation was different from the preparation of the acrylonitrile catalyst A of Example 1 in that no rare earth precursor and no cosolvent were added.

[0057] The acrylonitrile catalysts prepared in the above Examples 1-4 and Comparative Examples 1-3 were subjected to the following experiments:

[0058] Production of acrylonitrile:

[0059] S1: preheat propylene, ammonia gas, air to 300℃ respectively, control the volume ratio of air to propylene to be 9:1, the volume ratio of ammonia gas to air to be 1:9, accurately adjust the proportion of propylene, ammonia gas, air through a flow meter, and mix them thoroughly through a static mixer;

[0060] S2: add 50% of the volume of the fluidized bed reactor with acrylonitrile catalyst, raise the temperature to 450℃, and the reaction pressure to 0.09MPa, then pass the mixed gas in step S1, and control the contact time of the gas and the catalyst to be 8s;

[0061] S3: the reaction gas enters a quenching tower, the temperature is suddenly reduced to 100℃, the unreacted ammonia gas is neutralized by spraying 5% dilute sulfuric acid, then 10℃ warm water is used to absorb acrylonitrile, HCN, ACN and other organic matters in the gas, and the absorption liquid is sent to a rectification section to obtain acrylonitrile, propylene aldehyde, propylene acid and other products through azeotropic rectification and vacuum distillation.

[0062] 1. Calculate the conversion rate of propylene, the yield of acrylonitrile, the yield of by-products propylene aldehyde, propylene acid, carbon monoxide and carbon dioxide according to the above experimental test, see Table 1.

[0063] 2. Test the specific surface area, loose density, tight density, abrasion rate and particle size distribution of the prepared acrylonitrile catalyst, see Table 2.

[0064] Table 1: performance test result table

[0065]

[0066] Table 2: catalyst data result table

[0067]

[0068] From Table 1, it can be seen that the acrylonitrile catalyst prepared by the application has high activity, good selectivity and stability, which can improve the yield of acrylonitrile and reduce the generation of by-products CO, CO2, propylene aldehyde and propylene acid in the production of acrylonitrile. From the comparison between Example 4 and Example 1, it can be seen that when the mass ratio of the cosolvent and the rare earth precursor is unreasonable, the activity of the acrylonitrile catalyst will be reduced, the conversion rate of acrylonitrile will be reduced, the selectivity will be poor, the yield of acrylonitrile will be reduced, and the by-products will be more, which cannot achieve the expected effect. From the comparison between Comparative Example 1 and Example 1, it can be seen that without adding the rare earth precursor, the activity of the acrylonitrile catalyst will be reduced, the conversion rate of acrylonitrile will be reduced, the selectivity will be poor, the by-products will be more, which cannot achieve the expected effect. From the comparison between Comparative Example 2 and Example 1, it can be seen that without adding the cosolvent, the activity of the acrylonitrile catalyst will be reduced, the conversion rate of acrylonitrile will be reduced, the selectivity will be poor, the by-products will be more, which cannot achieve the expected effect.

[0069] From the comparison of the comparative example 3 and the example 1, it can be seen that without adding the rare earth precursor and the dissolving agent, the activity of the acrylonitrile catalyst is reduced, the conversion rate of the acrylonitrile is reduced, the selectivity is poor, the by-products are more, the yield of the acrylonitrile is reduced, and the expected effect cannot be achieved.

[0070] From the table 2, it can be seen that the physical properties of the acrylonitrile catalyst prepared in the examples 1-3 are better than those prepared in the example 4 and the comparative examples 1-3, which is embodied in that the physical properties of the acrylonitrile catalyst prepared in the examples 1-3 meet the catalyst indexes: the specific surface area is 36-48, the loose density is 0.88-1.12, the tight density is 1.04-1.28, the abrasion rate is less than or equal to 4%, the particle size distribution is: less than 30% of greater than 90 microns, 30-50% of less than or equal to 45 microns, and less than or equal to 7% of less than or equal to 20 microns, while the physical properties of the acrylonitrile catalyst prepared in the example 4 and the comparative examples 1-3 do not all meet the above indexes.

[0071] The present application can also be embodied in other various embodiments, and those skilled in the art can make various corresponding changes and modifications according to the present application without departing from the spirit and essence of the present application, but these corresponding changes and modifications should all belong to the protection scope of the claims attached to the present application.

Claims

1. An acrylonitrile catalyst, characterized in that, The raw materials for preparing the acrylonitrile catalyst include: mixed salt, active component, silica sol, rare earth precursor, silica support, and co-solvent; The preparation of the silica carrier includes the following steps: S1: Dissolve tetraethyl orthosilicate in ethanol, add appropriate amount of water and 25% ammonia water to form a homogeneous 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 the reaction at 40-60℃ for 12-48 hours. S3: After the reaction is complete, the product is separated by centrifugation and filtration, washed with deionized water and ethanol, and then dried at a low temperature of 60-80℃ to obtain an ordered silica support.

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

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

4. The acrylonitrile catalyst according to claim 3, characterized in that, The Mo-Bi-Fe multi-metal oxide is one or more of bismuth molybdate, bismuth molybdate ferroate, and bismuth ferrite. The transition metal oxide includes one or more of cobalt oxide, nickel oxide, and manganese oxide; The mass ratio of the Mo-Bi-Fe multi-metal oxide to the transition metal oxide is 8-10:

1.

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

6. The acrylonitrile catalyst according to claim 1, characterized in that, The rare earth precursor is one or a mixture of cerium nitrate, lanthanum nitrate, and praseodymium nitrate.

7. The acrylonitrile catalyst according to claim 1, characterized in that, The co-solvent is one or more of ethylene glycol, glycerol, and polyethylene glycol; the mass ratio of the co-solvent to the rare earth precursor is 1-3:

1.

8. The method for preparing the acrylonitrile catalyst according to any one of claims 1-7, characterized in that, Includes the following steps: Step (1): Weigh the mixed salt, active component, silica sol, rare earth precursor, carrier, and co-solvent for later use; Step (2): Then add the mixed salt to an appropriate amount of warm water in a certain proportion and dissolve it at 50-100℃. Then add silica sol, active components, rare earth precursors, carriers and co-solvents, and stir at high speed until uniform to obtain a slurry. Step (3): The slurry obtained in step (2) is shaped by spray drying to obtain spherical particles with a particle size of 20-90μm; Step (4): Finally, the particles obtained in step (3) are placed in a calcining furnace and calcined at 200-300℃ for 2-4 hours to obtain an acrylonitrile catalyst.

9. The method for preparing the acrylonitrile catalyst according to claim 8, characterized in that, In step (3), the inlet temperature of the spray dryer is 150-200℃, the outlet temperature is 80-100℃, the atomizer speed is 18000-25000rpm, and the tower pressure is -500 to 500Pa.

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