A supported acrylonitrile catalyst and its preparation method

Abstract

This invention belongs to the field of catalyst technology, specifically providing a supported acrylonitrile catalyst and its preparation method. By weight, the acrylonitrile catalyst comprises the following raw materials: 50-60 parts of active component, 6-10 parts of rare earth precursor, 50-65 parts of MnO2 / SiO2 composite support, 18-28 parts of co-solvent, and 160-200 parts of deionized water. The acrylonitrile catalyst of this invention can be used in the propylene ammoxidation process, exhibiting a high acrylonitrile yield, a low acrolein yield, and good mechanical strength.

Description

Technical Field

[0001] This invention belongs to the field of catalyst technology, specifically relating to a supported acrylonitrile catalyst and its preparation method. Background Technology

[0002] Acrylonitrile is an irreplaceable intermediate in the production of bulk chemicals such as acrylic fibers, ABS resin, nitrile rubber, acrylamide, and adiponitrile. With the development of the global economy and the continuous expansion of industrial production, the demand for acrylonitrile continues to grow, prompting the industry to seek more efficient acrylonitrile production methods.

[0003] Acrylonitrile production processes mainly include propylene ammoxidation, acetylene oxidation, and propane ammoxidation. Propylene ammoxidation is currently the most mainstream industrial process. This method uses propylene, ammonia, and oxygen as raw materials, reacting them in the presence of a catalyst to produce acrylonitrile. The core of this process lies in the high-performance catalyst. The catalyst not only determines the propylene conversion rate, acrylonitrile single-pass yield, and selectivity, but also directly affects the reaction temperature, ammonia ratio, oxygen ratio, reactor coking rate, and the level of "three wastes" emissions, thus influencing the energy consumption, material consumption, and environmental indicators of the entire plant. However, traditional catalysts may have characteristics such as low selectivity, easy generation of various byproducts, poor stability, and easy deactivation after long-term use.

[0004] Chinese patent CN 119215917 A discloses a supported catalyst and its preparation method, as well as a method for synthesizing nitrile compounds from low-carbon olefins. The catalyst prepared by this invention uses Mo-Bi-La-Ce-Mg-Ni as the main active element and can be used in the industrial production of nitrile compounds by ammoxidation of low-carbon olefins. However, using only silica as a support still needs to be improved in terms of mechanical strength and active phase anchoring.

[0005] Therefore, there is an urgent need for a supported acrylonitrile catalyst, which introduces a reinforced composite support to improve the activity and mechanical strength of the acrylonitrile catalyst. Summary of the Invention

[0006] To address the existing technical problems, the present invention aims to provide a supported acrylonitrile catalyst and its preparation method. The acrylonitrile catalyst of the present invention can be used in the propylene ammoxidation process, exhibiting a high acrylonitrile yield, while having a low acrolein yield and good mechanical strength.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] This invention provides a supported acrylonitrile catalyst and its preparation method. By weight, the acrylonitrile catalyst comprises the following raw materials: 50-60 parts of active component, 6-10 parts of rare earth precursor, 50-65 parts of MnO2 / SiO2 composite support, 18-28 parts of co-solvent, and 160-200 parts of deionized water; wherein the active component is a composition of multi-metal compound, transition metal oxide and mixed salt.

[0009] The reaction mechanism and function of this invention are as follows:

[0010] Currently, SiO2 is commonly used as the single support for acrylonitrile ammoxidation catalysts. However, while a single SiO2 support can provide high specific surface area and chemical inertness, it is difficult to meet the requirements of long-term, high-load industrial operation. This invention prepares a MnO2 / SiO2 composite support to improve the overall performance of the catalyst.

[0011] On the one hand, the surface of SiO2 is weakly acidic, making it difficult to efficiently activate NH3, resulting in low utilization of active centers and insufficient adsorption of acrolein intermediates, which in turn reduces the selectivity of acrylonitrile; on the other hand, the surface of MnO2 has Lewis acid sites of moderate strength, which can adsorb and activate NH3 to generate active -NH2 or -NH species, thereby improving the selectivity of acrylonitrile.

[0012] On the other hand, the carbon layer with high thermal conductivity in the MnO2 / SiO2 composite support of the present invention can rapidly conduct heat inside the catalyst, while MnO2 can also play a certain role in heat insulation, thereby significantly inhibiting the sintering of the active phase and improving the active reaction. Furthermore, the mechanical strength of SiO2 needs improvement; it is prone to breakage after long-term operation, producing fine powder, leading to high catalyst wear rate and increased replenishment costs. Polyaspartic acid, after in-situ carbonization, forms a glassy carbon-like network, which can significantly improve the mechanical strength of the MnO2 / SiO2 composite support and further inhibit the breakage and pulverization of MnO2. More importantly, the composite framework formed by the carbon layer and MnO2 / SiO2 can effectively anchor the active phase, preventing its migration and aggregation at high temperatures, thereby improving the selectivity of acrylonitrile.

[0013] In some embodiments, the multimetallic compound is bismuth molybdate and / or bismuth ferrite.

[0014] In some embodiments, the transition metal oxide is any one or more of cobalt oxide, nickel oxide, and manganese oxide.

[0015] In some embodiments, the mixed salt is a composition of ferric nitrate, nickel nitrate, and ammonium molybdate.

[0016] In some embodiments, the mass ratio of the multi-metal compound, the transition metal oxide, and the mixed salt is 1:(7-9):(20-25).

[0017] In some embodiments, the rare earth precursor is any one or more of cerium nitrate, lanthanum nitrate, and praseodymium nitrate.

[0018] In some embodiments, the co-solvent is any one or more of ethylene glycol, glycerol, and polyethylene glycol.

[0019] In some embodiments, the preparation method of the MnO2 / SiO2 composite support includes the following steps:

[0020] S1. Mix manganese source, polyaspartic acid, and deionized water, stir, and obtain a solution;

[0021] S2. Add ammonia to the solution obtained in step S1, sonicate for 4-8 minutes, continue stirring, first add anhydrous ethanol, then add hydrogen peroxide aqueous solution, stir the reaction at room temperature for 10-15 minutes, then add KMnO4 aqueous solution, stir the reaction at room temperature for 20-30 minutes to obtain the pre-oxidized product;

[0022] S3. Add tetraethyl orthosilicate to the pre-oxidized product obtained in step S2, stir, centrifuge, wash, dry, and carbonize at 450-600℃ under a protective atmosphere, then cool to obtain the MnO2 / SiO2 composite support.

[0023] In some embodiments, the mass ratio of manganese source to polyaspartic acid in step S1 is 1:(1.5-2.5).

[0024] Preferably, the manganese source is manganese acetate tetrahydrate.

[0025] In some embodiments, the mass ratio of hydrogen peroxide to KMnO4 in step S2 is (6-8):1.

[0026] Another aspect of the present invention provides a method for preparing a supported acrylonitrile catalyst, comprising the following steps:

[0027] (1) Add the mixed salt to deionized water, heat to 50-90℃, then add multi-metal compound, transition metal oxide, rare earth precursor, MnO2 / SiO2 composite support and co-solvent, stir to obtain slurry;

[0028] (2) The slurry obtained in step (1) is shaped by spray drying and then placed in a calcining furnace and calcined at 200-300℃ for 2-4 hours to obtain acrylonitrile catalyst.

[0029] Preferably, the inlet temperature of the spray dryer in step (2) is 150-200℃, the outlet temperature is 80-100℃, and the atomizer speed is 18000-25000rpm.

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0031] 1. The acrylonitrile catalyst of the present invention can be used in the production process of propylene ammoxidation, with a high acrylonitrile yield, and a low acrolein yield and good mechanical strength.

[0032] 2. This invention prepares a MnO2 / SiO2 composite supported catalyst, whose main advantages include: enhanced NH3 activation ability, improved thermal stability, increased mechanical strength, and stable active phase, thereby improving acrylonitrile selectivity and catalyst lifetime, and meeting the requirements of long-cycle, high-load industrial operation. Detailed Implementation

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

[0034] Acrylonitrile catalysts were prepared according to the proportions and preparation methods of the raw materials specified in the following examples and comparative examples.

[0035] To facilitate implementation of this invention by those skilled in the art, the sources of some raw materials in the embodiments and comparative examples are described below:

[0036] Polyaspartic acid: purchased from Chiping Jinshun Chemical Co., Ltd.;

[0037] Nano-silica: Purchased from Shanghai Zhenlishi Network Technology Co., Ltd.

[0038] Unless otherwise specified, all other raw materials can be purchased from the market.

[0039] Preparation Example 1

[0040] The preparation method of MnO2 / SiO2 composite support A includes the following steps:

[0041] S1. Mix 75 mg manganese acetate tetrahydrate, 150 mg polyaspartic acid, and 15 mL deionized water, and stir until homogeneous to obtain a solution;

[0042] S2. Add 2 mL of 25 wt% ammonia water to the solution obtained in step S1, sonicate at 200 W for 5 min, continue stirring, add 15 mL of anhydrous ethanol dropwise over 5 min, then add 0.2 mL of 30 wt% hydrogen peroxide aqueous solution dropwise (completed in 30 s), stir the reaction at room temperature for 10 min, then add 0.6 mL of 0.1 M KMnO4 aqueous solution dropwise (completed in 1 min), stir the reaction at room temperature for 30 min, and obtain the pre-oxidized product;

[0043] S3. Add 0.3 mL of tetraethyl orthosilicate to the pre-oxidized product obtained in step S2, stir at 30 °C for 6 h, centrifuge, wash twice with anhydrous ethanol, dry in an oven at 80 °C for 8 h, carbonize at 500 °C for 2 h under a nitrogen atmosphere with a heating rate of 5 °C / min, and cool naturally to room temperature to obtain MnO2 / SiO2 composite support A.

[0044] Preparation Example 2

[0045] The preparation method of MnO2 / SiO2 composite carrier B is the same as that of preparation example 1, except that the amount of polyaspartic acid added is 98 mg.

[0046] Preparation Example 3

[0047] The preparation method of MnO2 / SiO2 composite support C includes the following steps:

[0048] S1. Mix 75 mg manganese acetate tetrahydrate, 150 mg polyaspartic acid, and 15 mL deionized water, and stir until homogeneous to obtain a solution;

[0049] S2. Add 2 mL of 25 wt% ammonia water to the solution obtained in step S1, sonicate at 200 W for 5 min, continue stirring, add 15 mL of anhydrous ethanol dropwise within 5 min, and then add 0.8 mL of 30 wt% hydrogen peroxide aqueous solution dropwise (completed in 90 s), stir the reaction at room temperature for 30 min to obtain the pre-oxidized product;

[0050] S3. Add 0.3 mL of tetraethyl orthosilicate to the pre-oxidized product obtained in step S2, stir at 30 °C for 6 h, centrifuge, wash twice with anhydrous ethanol, dry in an oven at 80 °C for 8 h, carbonize at 500 °C for 2 h under a nitrogen atmosphere with a heating rate of 5 °C / min, and cool naturally to room temperature to obtain MnO2 / SiO2 composite support C.

[0051] Example 1

[0052] A supported acrylonitrile catalyst, by weight, comprises the following raw materials: 55 parts of active component, 8 parts of cerium nitrate, 57.5 parts of MnO2 / SiO2 composite support A, 23 parts of ethylene glycol, and 180 parts of deionized water; wherein the active component is composed of bismuth molybdate, cobalt oxide, and a mixed salt in a mass ratio of 1:8:22, and the mixed salt is a composition of ferric nitrate, nickel nitrate, and ammonium molybdate in a mass ratio of 1:1:1.5.

[0053] The preparation method of the acrylonitrile catalyst in this embodiment includes the following steps:

[0054] (1) Add the mixed salt to deionized water, heat to 75°C, then add bismuth molybdate, cobalt oxide, cerium nitrate, MnO2 / SiO2 composite carrier A, and ethylene glycol, stir evenly to obtain a slurry;

[0055] (2) The slurry obtained in step (1) is formed by spray drying and then placed in a calcining furnace and calcined at 250°C for 3 hours to obtain acrylonitrile catalyst; the inlet temperature of the spray dryer is 175°C, the outlet temperature is 90°C, and the atomizer speed is 22000 rpm.

[0056] Example 2

[0057] A supported acrylonitrile catalyst, by weight, comprises the following raw materials: 50 parts of active component, 6 parts of praseodymium nitrate, 50 parts of MnO2 / SiO2 composite support A, 18 parts of glycerol, and 160 parts of deionized water; wherein the active component is composed of bismuth molybdate, nickel oxide, and a mixed salt in a mass ratio of 1:7:20, and the mixed salt is a composition of ferric nitrate, nickel nitrate, and ammonium molybdate in a mass ratio of 1:1:1.5.

[0058] The preparation method of the acrylonitrile catalyst in this embodiment includes the following steps:

[0059] (1) Add the mixed salt to deionized water, heat to 50°C, then add bismuth molybdate, nickel oxide, praseodymium nitrate, MnO2 / SiO2 composite carrier A, and glycerol, stir evenly to obtain a slurry;

[0060] (2) The slurry obtained in step (1) is formed by spray drying and then placed in a calcining furnace and calcined at 300°C for 2 hours to obtain acrylonitrile catalyst; the inlet temperature of the spray dryer is 200°C, the outlet temperature is 100°C, and the atomizer speed is 25000 rpm.

[0061] Example 3

[0062] A supported acrylonitrile catalyst, by weight, comprises the following raw materials: 60 parts of active component, 10 parts of lanthanum nitrate, 65 parts of MnO2 / SiO2 composite support A, 28 parts of ethylene glycol, and 200 parts of deionized water; wherein the active component is composed of bismuth molybdate, cobalt oxide, and a mixed salt in a mass ratio of 1:9:25, and the mixed salt is a composition of ferric nitrate, nickel nitrate, and ammonium molybdate in a mass ratio of 1:1:1.5.

[0063] The preparation method of the acrylonitrile catalyst in this embodiment includes the following steps:

[0064] (1) Add the mixed salt to deionized water, heat to 90°C, then add bismuth molybdate, cobalt oxide, lanthanum nitrate, MnO2 / SiO2 composite carrier A, and ethylene glycol, stir evenly to obtain a slurry;

[0065] (2) The slurry obtained in step (1) is formed by spray drying and then placed in a calcining furnace and calcined at 200°C for 4 hours to obtain acrylonitrile catalyst; the inlet temperature of the spray dryer is 150°C, the outlet temperature is 80°C, and the atomizer speed is 18000 rpm.

[0066] Example 4

[0067] A supported acrylonitrile catalyst and its preparation method are disclosed. The specific implementation method is the same as that in Example 1, except that an equal amount of MnO2 / SiO2 composite support B is used to replace MnO2 / SiO2 composite support A.

[0068] Example 5

[0069] A supported acrylonitrile catalyst and its preparation method are described. The specific implementation method is the same as in Example 1, except that an equal amount of MnO2 / SiO2 composite support C is used to replace MnO2 / SiO2 composite support A.

[0070] Example 6

[0071] A supported acrylonitrile catalyst and its preparation method are described. The specific implementation method is the same as that in Example 1, except that the active component is composed of bismuth molybdate, cobalt oxide and mixed salt in a mass ratio of 1:8:18.

[0072] Example 7

[0073] A supported acrylonitrile catalyst and its preparation method are described. The specific implementation method is the same as that in Example 1, except that the active component is composed of bismuth molybdate, cobalt oxide and mixed salt in a mass ratio of 1:6:22.

[0074] Comparative Example 1

[0075] A supported acrylonitrile catalyst and its preparation method are described. The specific implementation method is the same as in Example 1, except that commercially available nano-silica is used as the support instead of MnO2 / SiO2 composite support A.

[0076] Effect evaluation:

[0077] The acrylonitrile catalysts prepared in Examples 1-7 and Comparative Example 1 were tested after production applications. The specific results are shown in Table 1.

[0078] The production process of acrylonitrile is as follows:

[0079] Q1. Preheat propylene and air to 300℃ respectively. Precisely adjust the ratio of propylene, ammonia and air using a flow meter to control the volume ratio of ammonia, air and propylene to be 1:9:1. Mix thoroughly using a static mixer to obtain a mixed gas.

[0080] Q2. Add 50% of the volume of acrylonitrile catalyst to the fluidized bed reactor, raise the temperature to 450℃ and the reaction pressure to 0.09MPa, introduce the mixed gas obtained in step Q1, and control the contact time between the mixed gas and the acrylonitrile catalyst to 8s to obtain the reaction gas.

[0081] Q3. The reaction gas obtained in step Q2 is fed into a quench tower, where the temperature drops rapidly to 100°C. Unreacted ammonia is neutralized by spraying with 5% dilute sulfuric acid. Then, acrylonitrile, HCN, ACN and other organic compounds in the gas are absorbed by water at 10°C. The absorbent is sent to the distillation section, where acrylonitrile, acrolein, acrylic acid and other products are obtained through azeotropic distillation and vacuum distillation.

[0082] Performance testing:

[0083] (1) Yields of acrylonitrile and acrolein: determined by gas chromatography;

[0084] (2) Catalyst attrition rate: tested according to standard ASTM D5757;

[0085] Table 1

[0086]

[0087] As shown in Table 1, the acrylonitrile catalysts prepared in Examples 1-3 have a high acrylonitrile yield, and a low acrolein yield with good mechanical strength, meeting the requirements of long-cycle, high-load industrial operation.

[0088] Compared to Example 1, Example 4 changed the mass ratio of manganese acetate tetrahydrate and polyaspartic acid during the preparation of the MnO2 / SiO2 composite support, resulting in poor mechanical stability of the catalyst and increased wear.

[0089] Compared to Example 1, in the preparation of the MnO2 / SiO2 composite support, potassium permanganate was not added, which prevented manganese acetate tetrahydrate from being completely converted into divalent manganese dioxide. In Comparative Example 1, the commercially available nano-silica sol support replaced MnO2 / SiO2 composite support A, resulting in poor catalyst stability. Both of these factors affected the yield of acrylonitrile and acrolein, and also reduced mechanical strength.

[0090] Compared to Example 1, Examples 6-7 changed the mass ratio of the multi-metal compound, transition metal oxide, and mixed salt. The changes in the proportions of the active ingredients significantly affected the yields of acrylonitrile and acrolein.

[0091] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present application in any way. Although the present application discloses the preferred embodiment as described above, it is not intended to limit the present application. Any changes or modifications made by those skilled in the art without departing from the scope of the technical solution of the present application using the disclosed technical content are equivalent to equivalent implementation cases. Any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention shall still fall within the scope of the technical solution.

Claims

1. A supported acrylonitrile catalyst characterized in that, The acrylonitrile catalyst comprises, by weight, the following raw materials: 50-60 parts of active component, 6-10 parts of rare earth precursor, 50-65 parts of MnO2 / SiO2 composite support, 18-28 parts of co-solvent, and 160-200 parts of deionized water; wherein the active component is a composition of multi-metal compounds, transition metal oxides, and mixed salts. The multi-metal compound is bismuth molybdate and / or bismuth ferrite; The transition metal oxide is any one or more of cobalt oxide, nickel oxide, and manganese oxide; The mixed salt is a composition of ferric nitrate, nickel nitrate, and ammonium molybdate; The rare earth precursor is any one or more of cerium nitrate, lanthanum nitrate, and praseodymium nitrate; The preparation method of the supported acrylonitrile catalyst includes the following steps: (1) adding mixed salt to deionized water, heating to 50-90℃, then adding multi-metal compound, transition metal oxide, rare earth precursor, MnO2 / SiO2 composite support, and co-solvent, stirring to obtain a slurry; (2) shaping the slurry obtained in step (1) by spray drying, then placing it in a calcining furnace, and calcining at 200-300℃ for 2-4 hours to obtain the acrylonitrile catalyst; The preparation method of the MnO2 / SiO2 composite support includes the following steps: S1. Mix manganese source, polyaspartic acid, and deionized water, stir, and obtain a solution; S2. Add ammonia to the solution obtained in step S1, sonicate for 4-8 minutes, continue stirring, first add anhydrous ethanol, then add hydrogen peroxide aqueous solution, stir the reaction at room temperature for 10-15 minutes, then add KMnO4 aqueous solution, stir the reaction at room temperature for 20-30 minutes to obtain the pre-oxidized product; S3. Add tetraethyl orthosilicate to the pre-oxidized product obtained in step S2, stir, centrifuge, wash, dry, and carbonize at 450-600℃ under a protective atmosphere, then cool to obtain the MnO2 / SiO2 composite support.

2. The supported acrylonitrile catalyst according to claim 1, characterized in that, The mass ratio of the multi-metal compound, transition metal oxide and mixed salt is 1:(7-9):(20-25).

3. The supported acrylonitrile catalyst according to claim 1, wherein The co-solvent is any one or more of ethylene glycol, glycerol, and polyethylene glycol.

4. The supported acrylonitrile catalyst according to claim 1, characterized in that, The mass ratio of manganese source to polyaspartic acid in step S1 is 1:(1.5-2.5).

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