A coated heteropolyacid catalyst and its preparation method and application

Abstract

The present invention provides a coated and molded heteropolyacid catalyst, its preparation method, and application. After calcination, the fiber additive in the heteropolyacid catalyst has two cylindrical rod-like forms: a short, thin S-type and a long, thick L-type. The quantitative ratio of the two forms of fiber additives satisfies the following relationship: N(s):N(l)=0.7-1.3:1. The active component of the heteropolyacid catalyst has the following general formula: Mo 12 P a V b Cu c As d X e O f The present invention also provides a catalyst preparation method, use, and a method for preparing methacrylic acid. After the final calcination and forming, the heteropolyacid catalyst contains two different forms of fiber additives, which makes the catalyst have a large specific surface area and excellent structural strength and catalytic activity.

Description

Technical Field

[0001] The present invention relates to the field of catalysts, and in particular to a coated and formed heteropolyacid catalyst, a preparation method thereof, and an application thereof. Background Art

[0002] Methyl methacrylate is mainly used to produce polymethyl methacrylate (PMMA) and acrylic resin materials. It can also be used to manufacture resins, plastics, coatings, adhesives, lubricants, wetting agents, glazing agents, insulating potting materials and pharmaceutical functional polymer materials. It is an important organic chemical raw material.

[0003] The production of methacrylic acid using tert-butyl alcohol / isobutylene as raw materials requires a two-step reaction. First, a Mo-Bi-based multi-metal oxide catalyst converts tert-butyl alcohol / isobutylene into methacrolein, which is then catalytically oxidized to produce methacrylic acid via gas-phase oxidation. Currently, known catalysts for the second step include heteropolyacids or heteropolyacid salts, represented by phosphomolybdic acid. Methacrylic acid is prone to over-oxidation to form carbon oxides on heteropolyacid catalysts, so maintaining a high methacrolein conversion rate and methacrylic acid selectivity at the same time is a research challenge. Furthermore, heteropolyacids (salts) have a low specific surface area and are sensitive to moisture, which results in poor activity, strength, and batch stability, making industrial scale-up of catalysts a major challenge.

[0004] In summary, the current heteropolyacid catalysts used in the industrialization of MMA production using the isobutylene process have problems such as low specific surface area, low catalyst activity, poor strength, and poor batch quality in industrial catalyst production. Summary of the Invention

[0005] In response to the problems existing in the above-mentioned prior art, one of the objects of the present invention is to provide a heteropolyacid catalyst prepared by coating molding, wherein the heteropolyacid catalyst contains two different forms of fiber additives inside after the final calcination molding, so that the catalyst has a large specific surface area while having excellent structural strength and catalytic activity.

[0006] In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical solutions:

[0007] A coated and formed heteropolyacid catalyst, wherein the fiber additive in the calcined and formed heteropolyacid catalyst has two cylindrical rod-like forms: a short and thin S-type and a long and thick L-type. The quantity ratio of the two forms of fiber additives satisfies the following relationship:

[0008] N(s):N(l)=0.7~1.3:1

[0009] Where N(s) is the number of s-types, and N(l) is the number of l-types;

[0010] Wherein, the size of the S-type fiber additive satisfies the following conditions: diameter D≤15μm, length L≤30μm, and D:L=1:1~20;

[0011] Among them, the size of the type I fiber additive meets the following requirements: diameter D>15μm, length L>30μm, and D:L=1:1~100.

[0012] The present invention proposes a heteropolyacid catalyst prepared by coating and molding, wherein a fiber additive is added to the catalyst during the coating and molding preparation process, and by controlling the ratio of powder to additive and the rotation speed of the coating turntable, the catalyst after final calcination and molding has a fiber additive of a specific form and a specific ratio. Different fiber additives can improve the catalyst strength while optimizing the pore structure of the catalyst, effectively increasing the specific surface area of ​​the catalyst. The increase in specific surface area can effectively improve the reaction activity of the catalyst, increase the conversion rate of methacrolein and the selectivity of methacrylic acid; the increase in mechanical strength can reduce the breakage of the catalyst due to wear and tear, further increasing the life of the catalyst. At the same time, the preparation process of the heteropolyacid catalyst is simple, the process requirements are not very complicated, the industrial production batch stability is good, and the application prospects are broad.

[0013] In one embodiment of the present invention, the BET specific surface area of ​​the catalyst particles after calcination is 3 to 10 m 2 / g.

[0014] In one embodiment of the present invention, the catalyst after calcination and grinding into a 200 mesh powder has a BET specific surface area of ​​1.5 to 6 m 2 / g.

[0015] In one embodiment of the present invention, the fiber additive is an inorganic ceramic fiber, preferably one or more of silicon carbide fiber, alumina fiber, mullite fiber, aluminum silicate fiber, and silicon nitride fiber.

[0016] In one embodiment of the present invention, the active component of the heteropolyacid catalyst has the following general formula:

[0017] Mo 12 P a V b Cu c As d X e O f

[0018] Among them, Mo is molybdenum, P is phosphorus, V is vanadium, Cu is copper, As is arsenic, and O is oxygen;

[0019] Wherein, X is an active agent selected from one or more of boron, antimony, tungsten, germanium, bismuth, iron, cobalt, magnesium, ruthenium, nickel, zinc, and lead;

[0020] The atomic molar ratios of the various elements in the above general formula are: a=1-3, b=0.1-1, c=0.1-1, d=0.1-1, e=0.01-1, and f is the number of oxygen atoms required to satisfy the valence of each element.

[0021] Another object of the present invention is to provide a method for preparing a heteropolyacid catalyst.

[0022] A method for preparing the above-mentioned heteropolyacid catalyst comprises the following steps:

[0023] S1: placing a compound of Mo, P, V, Cu, As and X additive element in water to obtain a solution, and drying the solution to obtain a powder;

[0024] S2: Coating the powder with a fiber additive to obtain a catalyst precursor;

[0025] S3: calcining the precursor to obtain the target heteropolyacid catalyst.

[0026] In one embodiment of the present invention, the moisture content of the powder in S1 is 2%-20%.

[0027] In S1 of the present invention, various drying methods in the art can be adopted, such as airflow spray drying, and there is no significant difference in the drying effects obtained by different drying modes.

[0028] In one embodiment of the present invention, the coating molding in S2 includes a slow stage, a fast stage and a polishing stage; preferably, the mass ratio of powder to fiber additive in the slow stage is 100:1-15, and the coating machine turntable speed is 50-150 rpm; preferably, the mass ratio of powder to fiber additive in the fast stage is 100:2-10, and the coating machine turntable speed is 200-400 rpm; preferably, only fiber additive is added in the polishing stage, and the coating machine turntable speed is 150-250 rpm.

[0029] In one embodiment of the present invention, the fiber additive in S2 is one or more of silicon carbide fiber, alumina fiber, mullite fiber, aluminum silicate fiber, and silicon nitride fiber; preferably, the fiber additive accounts for 0.1% to 10% of the total mass of the catalyst particles.

[0030] In one embodiment of the present invention, the total mass of the powder added in the above three stages is 5 to 80 wt % based on the total mass of the catalyst particles.

[0031] In one embodiment of the present invention, the coating molding method described in S2 can be achieved using a common coating pill making machine on the market. During the coating process, some organic matter needs to be added as a binder, including but not limited to ethanol, glycerol, gum arabic, etc. The above coating process is a conventional method.

[0032] In one embodiment of the present invention, the calcination method described in S3 is a staged calcination method; preferably, the catalyst precursor is first kept at 80-240°C for 0.5-5 hours, and then kept at 250-400°C for 1-5 hours.

[0033] Another object of the present invention is to provide a use of a heteropolyacid catalyst.

[0034] A use of a heteropolyacid catalyst, wherein the heteropolyacid catalyst is the above catalyst or a catalyst prepared by the above method, and the catalyst is used for catalyzing the gasification and oxidation of methacrolein to prepare methacrylic acid.

[0035] Another object of the present invention is to provide a method for preparing methacrylic acid by catalyzing the gasification and oxidation of methacrolein.

[0036] A method for preparing methacrylic acid by catalytic gasification and oxidation of methacrolein, the method using the above-mentioned catalyst or the catalyst prepared by the above-mentioned method, wherein the reaction temperature is 260-380° C., the reaction pressure is 0.01-0.20 MPaG, and the molar ratio of oxygen to methacrolein is 1-6:1.

[0037] Unless otherwise specified, % in the present invention refers to wt%.

[0038] Compared with the prior art, the positive effects of this application are:

[0039] (1) Improving the catalyst strength while optimizing the catalyst pore structure, effectively increasing the specific surface area of ​​the catalyst. The increase in specific surface area can effectively improve the reaction activity of the catalyst, increase the conversion rate of methacrolein and the selectivity of methacrylic acid;

[0040] (2) Increased mechanical strength can reduce the breakage of the catalyst due to wear and tear, further increasing the life of the catalyst.

[0041] (3) The preparation process is simple, the process requirements are not very complicated, the industrial production batches have good stability, and the application prospects are broad. DETAILED DESCRIPTION

[0042] The method provided by the present invention is described in further detail below, but the present invention is not limited thereto.

[0043] Test Method

[0044] Testing and characterization of various parameters of catalysts:

[0045] The statistical method for the number and length of internal fiber additives after the final calcination of the heteropolyacid catalyst is as follows:

[0046] (1) Weigh 20 g of the calcined heteropolyacid catalyst and place it in a beaker. Add 200 g of deionized water to the beaker and place the beaker in an ultrasonic device for 10 minutes.

[0047] (2) Pour the deionized water and catalyst from the beaker into a filtration funnel using a 5 μm filter membrane. Filter and wash five times.

[0048] (3) The white solid collected by the filter membrane is dried at 200° C. overnight to obtain a white powder, which is the fiber additive.

[0049] (4) The length of the white powder was measured and counted using a scanning electron microscope (SEM). The scanning electron microscope used was a JEOL JSM-IT800 with a magnification of 500 times.

[0050] The catalyst attrition rate (i.e., catalyst strength) test reference standard: HG / T 2976-1999 (Determination of attrition rate of fertilizer catalysts), the testing instrument is KM-5A particle attrition tester (produced by Dalian Penghui Technology Development Co., Ltd.).

[0051] The conversion and selectivity of methacrolein oxidation to methacrylic acid are defined as follows:

[0052] Methacrolein conversion rate = (amount of methacrolein consumed / amount of methacrolein supplied as raw material) × 100%;

[0053] Methacrylic acid selectivity=(the amount of substance of methacrylic acid produced / the amount of substance of methacrolein consumed)×100%.

[0054] Catalyst activity evaluation:

[0055] The catalyst activity was evaluated by using a Shimadzu GC-2010 gas chromatograph from Japan, with a chromatographic column model of DB-FFAP (length 30 m, inner diameter 0.32 m, film thickness 0.5 μm).

[0056] The chromatographic operating conditions were as follows: injection port temperature: 260°C; detector temperature: 250°C; injection volume: 1 μL; column flow rate: 1 ml / min; split ratio 50:1; column oven heating program: 50°C for 13 min, then increase to 110°C at a heating rate of 20°C / min, then increase to 180°C at a heating rate of 20°C / min, then increase to 10 min.

[0057] The porous inert porcelain balls in the present invention were purchased from Jiangxi Kepak Environmental Protection Chemical Co., Ltd., with a diameter of 3.4 mm, an internal pore size of 50-500 μm, a water absorption rate of 8-12%, and a bulk density of 1.2-1.4 g / cm 3 .

[0058] Different types of ceramic fibers were purchased from the following companies:

[0059] Alumina ceramic fiber and mullite ceramic fiber were purchased from Zhejiang Desheng New Materials Co., Ltd., with models DS-1260, DS-1400, DS-1430, and DS-1600.

[0060] Aluminum silicate ceramic fiber was purchased from Shijiazhuang Baijiang Mineral Products Co., Ltd. (Al2O3 content 31%, SiO2 content 62%, purity 99%, compressive strength 2100 MPa, hardness 8HB).

[0061] Silicon carbide ceramic fiber and silicon nitride ceramic fiber were purchased from Sinoma High-Tech Nitride Ceramics Co., Ltd. (silicon nitride was SM-SGO1 and silicon carbide was SM-SGH1).

[0062] Other raw materials not specifically mentioned herein are conventional commercially available reagents.

[0063] Example 1

[0064] 1) Preparation of catalyst

[0065] To 5000g of deionized water, 500g of molybdenum trioxide, 70g of vanadium pentoxide, 36g of cobalt nitrate, 50g of 85wt% phosphoric acid, 18g of 80wt% arsenic acid, and 6g of copper oxide were added. The mixture was stirred and refluxed overnight at 90°C to obtain a clear and transparent solution. The solution was spray-dried in a spray dryer with an inlet temperature of 237°C and an outlet temperature of 133°C to obtain a spray-dried powder with a moisture content of 6.8%. The non-oxygen elements in the active components of the powder can be described as: Mo 12 P 1.5 V 0.67 Cu 0.26 As 0.43 Co 0.32 .

[0066] Molding was performed using a centrifugal granulation coating machine at a temperature of 22°C and a relative humidity of 45%. 200g of catalyst powder was uniformly mixed with 6g of alumina fiber powder (Zhejiang Desheng New Materials Co., Ltd., DS-1400) and designated as mixed powder 1. 200g of catalyst powder was uniformly mixed with 8g of alumina fiber powder (Zhejiang Desheng New Materials Co., Ltd., DS-1400) and designated as mixed powder 2. 580g of porcelain ball carrier was placed in the coating machine and introduced with an 85% ethanol aqueous solution as a binder. Molding was first performed at a speed of 150 rpm for 10 minutes, during which time mixed powder 1 was uniformly added. Molding was then performed at a speed of 300 rpm for 12 minutes, during which time mixed powder 2 was uniformly added. Molding was then performed at 250 rpm for 4 minutes, during which time 6g of alumina fiber powder (Zhejiang Desheng New Materials Co., Ltd., DS-1400) was uniformly added. Finally, polishing was performed for 2 minutes to obtain Molded Body 1. The molded body 1 was gradually heated from 30°C to 210°C over 12 hours (average heating rate 0.25°C / min), and after staying for 1 hour, the temperature was further increased to 300°C at a rate of 1°C / min and calcined for 3 hours to obtain catalyst product 1.

[0067] Catalyst Product 1 was washed and filtered using the method described in the aforementioned "Statistical Method for Quantifying the Quantity and Length of Internal Fiber Additives after Final Calcination of Heteropolyacid Catalysts." SEM observation revealed cylindrical fiber additives. A certain number of cylindrical fiber additives were randomly selected for diameter and length measurement. Fiber additives with a diameter ≤ 15 μm, a length ≤ 30 μm, and a D:L ratio of 1:1 to 20 were classified as short and fine fibers; and those with a diameter > 15 μm, a length > 30 μm, and a D:L ratio of 1:1 to 100 were classified as long and coarse fibers. Quantitative statistics revealed that N(s):N(l) = 0.94:1, where N(s) represents the number of short and fine fibers and N(l) represents the number of long and coarse fibers.

[0068] The BET test of catalyst product 1 showed a final result of 8.75m 2 / g, crushed to 200 mesh and then subjected to BET test, the final result was 5.8m 2 / g.

[0069] Catalyst product 1 was subjected to a strength test, and the final result was 0.45%.

[0070] 2) Oxidation reaction of methacrolein

[0071] 280 ml of catalyst product 1 was loaded into a molten salt fixed bed reactor with an inner diameter of 25 mm, and the mixture was heated at a molar ratio of methacrolein / oxygen / water / nitrogen = 1 / 1.8 / 4 / 18.0 and a space velocity of 1100 h -1The oxidation reaction of methacrolein was carried out at a pressure of 0.06 MPaG and a molten salt temperature of 305°C. After continuous reaction for 24 hours, sampling and analysis showed that the methacrolein conversion rate was 87.5% and the methacrylic acid selectivity was 84.9%.

[0072] Example 2

[0073] 1) Preparation of catalyst

[0074] To 3000g of deionized water, 300g of molybdenum trioxide, 42g of vanadium pentoxide, 21.6g of cobalt nitrate, 30g of 85wt% phosphoric acid, 10.8g of 80wt% arsenic acid, and 3.6g of copper oxide were added. The mixture was stirred and refluxed overnight at 100°C to obtain a clear and transparent solution. The solution was spray-dried in a spray dryer with an inlet temperature of 237°C and an outlet temperature of 133°C to obtain a spray-dried powder with a moisture content of 7.50%. The non-oxygen elements in the active components of the powder can be described as: Mo 12 P 1.5 V 0.67 Cu 0.26 As 0.43 Co 0.32 .

[0075] Molding was performed using a centrifugal granulation coating machine at a temperature of 22°C and a relative humidity of 45%. 400g of catalyst powder was uniformly mixed with 40g of silicon carbide fiber (Sinoma High-Tech Nitride Ceramics Co., Ltd.) powder, referred to as mixed powder 1. 200g of catalyst powder was uniformly mixed with 20g of silicon carbide fiber powder (Sinoma High-Tech Nitride Ceramics Co., Ltd.), referred to as mixed powder 2. 320g of porcelain ball carriers were placed in the coating machine and introduced with an 85% ethanol aqueous solution as a binder. Molding was first performed at a speed of 120 rpm for 10 minutes, during which time mixed powder 1 was uniformly added. Molding was then performed at a speed of 400 rpm for 10 minutes, during which time mixed powder 2 was uniformly added. Finally, molding was performed at 250 rpm for 4 minutes, during which time 20g of silicon carbide fiber powder (Sinoma High-Tech Nitride Ceramics Co., Ltd.) was uniformly added. Finally, polishing was performed for 3 minutes to obtain molded body 1. The molded body 1 was gradually heated from 30°C to 220°C over 12 hours, and after being kept for 2 hours, the temperature was further raised to 310°C at a rate of 1°C / min and calcined for 3.5 hours to obtain catalyst product 2.

[0076] Catalyst Product 2 was washed and filtered using the method described in the aforementioned "Statistical Method for Quantifying the Quantity and Length of Internal Fiber Additives after Final Calcination of Heteropolyacid Catalysts." After SEM observation, cylindrical fiber additives were observed. A certain number of cylindrical fiber additives were randomly selected for diameter and length measurement. Fiber additives with a diameter ≤ 15 μm, a length ≤ 30 μm, and a D:L ratio of 1:1 to 20 were classified as short and fine fiber additives; fiber additives with a diameter > 15 μm, a length > 30 μm, and a D:L ratio of 1:1 to 100 were classified as long and coarse fiber additives. After quantitative statistics, N(s):N(l) = 0.86:1, where N(s) is the number of short and fine fiber additives and N(l) is the number of long and coarse fiber additives.

[0077] The BET test of catalyst product 2 showed a final result of 8.67m 2 / g, crushed to 200 mesh and then subjected to BET test, the final result was 5.21m 2 / g.

[0078] Catalyst product 2 was subjected to a strength test, and the final result was 0.14%.

[0079] 2) Oxidation reaction of methacrolein

[0080] 280 ml of catalyst product 2 was loaded into a molten salt fixed bed reactor with an inner diameter of 25 mm, and the mixture was heated in a mixture of methacrolein / oxygen / water / nitrogen at a molar ratio of 1 / 2 / 4 / 20 and a space velocity of 1000 h -1 The oxidation reaction of methacrolein was carried out at a pressure of 0.02 MPaG and a molten salt temperature of 310°C. After continuous reaction for 24 hours, sampling and analysis showed that the methacrolein conversion rate was 88.2% and the methacrylic acid selectivity was 83.8%.

[0081] Example 3

[0082] 1) Preparation of catalyst

[0083] The process of preparing the catalyst powder is the same as that in Example 1.

[0084] Molding was performed using a centrifugal granulation coating machine at a temperature of 22°C and a relative humidity of 45%. 300g of the catalyst powder was uniformly mixed with 24g of a mixture of 50wt% alumina (Zhejiang Desheng New Materials Co., Ltd., DS-1260) and 50wt% mullite fiber (Zhejiang Desheng New Materials Co., Ltd., DS-1430), referred to as mixed powder 1. 500g of the catalyst powder was uniformly mixed with 40g of a mixture of 50wt% alumina (Zhejiang Desheng New Materials Co., Ltd., DS-1260) and 50wt% mullite fiber (Zhejiang Desheng New Materials Co., Ltd., DS-1430), referred to as mixed powder 2. 610g of porcelain ball carriers were placed in a coating machine and introduced with an 85% ethanol aqueous solution as a binder. Molding was first performed at a speed of 100 rpm for 12 minutes, during which time mixed powder 1 was evenly added. Molding was then performed at a speed of 250 rpm for 12 minutes, during which time mixed powder 2 was evenly added. Finally, molding was performed at 200 rpm for 5 minutes, during which time 26g of a mixture of 50wt% alumina (Zhejiang Desheng New Materials Co., Ltd., DS-1260) and 50wt% mullite fiber (Zhejiang Desheng New Materials Co., Ltd., DS-1430) was evenly added. Finally, polishing was performed for 3 minutes to obtain Molded Body 1. Molded Body 1 was gradually heated from 30°C to 240°C over 12 hours, held for 3 hours, and then heated at a rate of 1°C / min to 400°C and calcined for 3 hours to obtain Catalyst Product 2.

[0085] Catalyst product 3 was washed and filtered using the method described in the aforementioned "Statistical Method for Quantifying the Quantity and Length of Internal Fiber Additives after Final Calcination of Heteropolyacid Catalysts." After SEM observation, cylindrical fiber additives were observed. A certain number of cylindrical fiber additives were randomly selected for diameter and length measurement. Fiber additives with a diameter ≤ 15 μm, a length ≤ 30 μm, and a D:L ratio of 1:1 to 20 were considered short and fine fibers; and those with a diameter > 15 μm, a length > 30 μm, and a D:L ratio of 1:1 to 100 were considered long and coarse fibers. Quantitative statistics revealed that N(s):N(l) = 1.13:1, where N(s) represents the number of short and fine fibers and N(l) represents the number of long and coarse fibers.

[0086] The BET test of catalyst product 3 showed a final result of 9.06m 2 / g, crushed to 200 mesh and then subjected to BET test, the final result was 5.63m 2 / g.

[0087] Catalyst product 3 was subjected to a strength test, and the final result was 0.19%.

[0088] 2) Oxidation reaction of methacrolein

[0089] 300 ml of the catalyst product 3 was loaded into a molten salt fixed bed reactor with an inner diameter of 25 mm, and the mixture was heated at a molar ratio of methacrolein / oxygen / water / nitrogen = 1 / 1.8 / 4 / 18 and a space velocity of 1200 h -1 The oxidation reaction of methacrolein was carried out at a pressure of 0.01 MPaG and a molten salt temperature of 300°C. After continuous reaction for 20 hours, sampling and analysis showed that the methacrolein conversion rate was 91.56% and the methacrylic acid selectivity was 80.87%.

[0090] Example 4

[0091] 1) Preparation of catalyst

[0092] To 10,000 g of deionized water, 1,000 g of molybdenum trioxide, 180 g of vanadium pentoxide, 124 g of bismuth nitrate, 100 g of 85 wt% phosphoric acid, 24 g of 80 wt% arsenic acid, and 14 g of copper oxide were added. The mixture was stirred and refluxed overnight at 100°C to obtain a clear, transparent solution. The solution was spray-dried in a spray dryer at an inlet temperature of 237°C and an outlet temperature of 130°C to obtain a spray-dried powder with a moisture content of 9.56%. The non-oxygen elements in the active components of the powder can be described as: Mo 12 P 1.5 V 0.86 Cu 0.3 As 0.50 Bi 0.47 .

[0093] Molding was performed using a centrifugal granulation coating machine at a temperature of 25°C and a relative humidity of 55%. 200g of catalyst powder was uniformly mixed with 10g of alumina fiber powder (Zhejiang Desheng New Materials Co., Ltd., DS-1600) and designated as mixed powder 1. 250g of catalyst powder was uniformly mixed with 20g of alumina fiber powder (Zhejiang Desheng New Materials Co., Ltd., DS-1600) and designated as mixed powder 2. 500g of porcelain ball carrier was placed in the coating machine and introduced with an 85% ethanol aqueous solution as a binder. Molding was performed at 80 rpm for 12 minutes, during which time mixed powder 1 was uniformly added. Molding was then performed at 250 rpm for 20 minutes, during which time mixed powder 2 was uniformly added. Finally, molding was performed at 200 rpm for 6 minutes, during which time 20g of alumina fiber powder (Zhejiang Desheng New Materials Co., Ltd., DS-1600) was uniformly added. Finally, polishing was performed for 2 minutes to obtain Molded Body 1. The molded body 1 was gradually heated from 30°C to 220°C over 12 hours, and after being kept for 2 hours, the temperature was further raised to 330°C at a rate of 1°C / min and calcined for 3 hours to obtain catalyst product 4.

[0094] Catalyst product 4 was washed and filtered using the method described in the aforementioned "Statistical Method for Quantifying the Quantity and Length of Internal Fiber Additives after Final Calcination of Heteropolyacid Catalysts." SEM observation revealed cylindrical fiber additives. A certain number of cylindrical fiber additives were randomly selected for diameter and length measurement. Fiber additives with a diameter ≤ 15 μm, a length ≤ 30 μm, and a D:L ratio of 1:1 to 20 were classified as short and fine fibers; and those with a diameter > 15 μm, a length > 30 μm, and a D:L ratio of 1:1 to 100 were classified as long and coarse fibers. Quantitative statistics revealed that N(s):N(l) = 0.98:1, where N(s) represents the number of short and fine fibers and N(l) represents the number of long and coarse fibers.

[0095] The BET test of catalyst product 4 showed a final result of 8.65m 2 / g, crushed to 200 mesh and then subjected to BET test, the final result was 4.62m 2 / g.

[0096] Catalyst product 4 was subjected to a strength test, and the final result was 0.29%.

[0097] 2) Oxidation reaction of methacrolein

[0098] 280 ml of catalyst product 4 was loaded into a molten salt fixed bed reactor with an inner diameter of 25 mm, and the mixture was heated at a molar ratio of methacrolein / oxygen / water / nitrogen = 1 / 3 / 4 / 20 and a space velocity of 1200 h -1 The oxidation reaction of methacrolein was carried out at a pressure of 0.02 MPaG and a molten salt temperature of 320°C. After continuous reaction for 20 hours, sampling and analysis showed that the methacrolein conversion rate was 85.6% and the methacrylic acid selectivity was 79.4%.

[0099] Example 5

[0100] 1) Preparation of catalyst

[0101] To 8000g of deionized water, 800g of molybdenum trioxide, 41.8g of vanadium pentoxide, 22.6g of bismuth nitrate, 60g of 85wt% phosphoric acid, 57.6g of 80wt% arsenic acid, and 18.1g of copper oxide were added. The mixture was stirred and refluxed overnight at 100°C to obtain a clear and transparent solution. The solution was spray-dried in a spray dryer with an inlet temperature of 240°C and an outlet temperature of 130°C to obtain a spray-dried powder with a moisture content of 8.78%. The non-oxygen elements in the active components of the powder can be described as: Mo 12 P 1.1 V 0.25 Cu 0.49 As 0.86 Fe 0.16 .

[0102] Molding was performed using a centrifugal granulation coating machine at a temperature of 25°C and a relative humidity of 50%. 450g of catalyst powder was uniformly mixed with 50g of aluminum silicate fiber powder (Shijiazhuang Baijiang Mineral Products Co., Ltd.), and this was recorded as mixed powder 1. 550g of catalyst powder was uniformly mixed with 50g of aluminum silicate fiber powder (Shijiazhuang Baijiang Mineral Products Co., Ltd.), and this was recorded as mixed powder 2. 800g of porcelain ball carrier was placed in a coating machine, and an 85% ethanol aqueous solution was introduced as a binder. Molding was first performed at a speed of 100rpm for 15 minutes, during which time mixed powder 1 was evenly added. Molding was then performed at a speed of 200rpm for 15 minutes, during which time mixed powder 2 was evenly added. Molding was finally performed at 150rpm for 6 minutes, during which time 100g of aluminum silicate fiber powder (Shijiazhuang Baijiang Mineral Products Co., Ltd.) was evenly added. Finally, polishing was performed for 2 minutes to obtain molded body 1. The molded body 1 was gradually heated from 30°C to 160°C over 12 hours, kept for 2.5 hours, and then continued to be heated to 300°C at a rate of 1°C / min for 4 hours to obtain catalyst product 5.

[0103] Catalyst product 5 was washed and filtered using the method described in the aforementioned "Statistical Method for Quantifying the Quantity and Length of Internal Fiber Additives after Final Calcination of Heteropolyacid Catalysts." SEM observation revealed cylindrical fiber additives. A certain number of cylindrical fiber additives were randomly selected for diameter and length measurement. Fiber additives with a diameter ≤ 15 μm, a length ≤ 30 μm, and a D:L ratio of 1:1 to 20 were classified as short and fine fibers; and those with a diameter > 15 μm, a length > 30 μm, and a D:L ratio of 1:1 to 100 were classified as long and coarse fibers. Quantitative statistics revealed that N(s):N(l) = 0.79:1, where N(s) represents the number of short and fine fibers and N(l) represents the number of long and coarse fibers.

[0104] The BET test of catalyst product 5 showed a final result of 4.59m 2 / g, crushed to 200 mesh and then tested by BET, the final result was 1.51m 2 / g.

[0105] Catalyst product 5 was subjected to a strength test, and the final result was 0.44%.

[0106] 2) Oxidation reaction of methacrolein

[0107] 300 ml of the catalyst product 5 was loaded into a molten salt fixed bed reactor with an inner diameter of 25 mm, and the mixture was heated at a molar ratio of methacrolein / oxygen / water / nitrogen = 1 / 6 / 4 / 20 and a space velocity of 1000 h -1The oxidation reaction of methacrolein was carried out at a pressure of 0.05 MPaG and a molten salt temperature of 330°C. After 48 hours of continuous reaction, sampling and analysis showed that the methacrolein conversion rate was 79.6% and the methacrylic acid selectivity was 77.6%.

[0108] Comparative Example 1

[0109] Compared with Example 1, the difference is that the coating molding process does not go through the slow and fast stages, and the coating is directly performed using a conventional coating method.

[0110] 1) Preparation of catalyst

[0111] The process of preparing the catalyst powder is the same as that in Example 1.

[0112] Molding was performed using a centrifugal granulation coating machine at a temperature of 22°C and a relative humidity of 45%. 400g of catalyst powder was mixed evenly with 20g of alumina fiber powder (Zhejiang Desheng New Materials Co., Ltd., DS-1400). 580g of porcelain ball carrier was placed in the coating machine, and an 85% ethanol aqueous solution was introduced as a binder. Molding was carried out at a speed of 200rpm for 26 minutes; finally, polishing was performed for 2 minutes to obtain Molded Body 1. Molded Body 1 was gradually heated from 40°C to 220°C over 12 hours (average heating rate of 0.25°C / min), then held for 1 hour and then heated to 290°C at a rate of 1°C / min and calcined for 2.5 hours to obtain Catalyst Comparative Product 1.

[0113] Catalyst comparison product 1 was washed and filtered using the method described in the aforementioned "Statistical method for the number and length of internal fiber additives after the final calcination of heteropolyacid catalysts." SEM observation revealed cylindrical fiber additives. A certain number of cylindrical fiber additives were randomly selected for diameter and length measurement. Fiber additives with a diameter ≤ 15 μm, a length ≤ 30 μm, and a D:L ratio of 1:1 to 20 were classified as short and fine fiber additives; fiber additives with a diameter > 15 μm, a length > 30 μm, and a D:L ratio of 1:1 to 100 were classified as long and coarse fiber additives. After quantitative statistics, N(s):N(l)=0.25:1, where N(s) is the number of short and fine fiber additives; N(l) is the number of long and coarse fiber additives.

[0114] The BET test of catalyst comparison product 1 showed a final result of 6.49m 2 / g, crushed to 200 mesh and then subjected to BET test, the final result was 4.56m 2 / g.

[0115] The catalyst comparative product 1 was subjected to a strength test, and the final result was 0.95%.

[0116] 2) Oxidation reaction of methacrolein

[0117] 250 ml of catalyst comparative product 1 was loaded into a molten salt fixed-bed reactor with an inner diameter of 25 mm. Methacrolein oxidation was carried out at a molar ratio of methacrolein / oxygen / water / nitrogen of 1 / 1.8 / 4 / 18.0, a space velocity of 900 h⁻¹, a pressure of 0.05 MPaG, and a molten salt temperature of 300°C. After 24 hours of continuous reaction, samples were collected and analyzed, revealing a methacrolein conversion of 82.1% and a methacrylic acid selectivity of 80.2%.

[0118] Comparative Example 2

[0119] Compared with Example 1, the difference is that no fiber auxiliary agent is added during the coating process.

[0120] 1) Preparation of catalyst

[0121] The process of preparing the catalyst powder is the same as that in Example 1.

[0122] Molding was performed using a centrifugal granulation coating machine at a temperature of 22°C and a relative humidity of 45%. 580g of porcelain ball carriers were placed in the coating machine, and an 85% ethanol aqueous solution was introduced as a binder. 420g of catalyst powder was added at a rotation speed of 200rpm. Molding was completed for 26 minutes. Finally, the molding process lasted for 2 minutes, resulting in Molded Body 1. Molded Body 1 was gradually heated from 35°C to 215°C over 12 hours (average heating rate of 0.25°C / min), held for 1.5 hours, and then heated to 300°C at a rate of 1°C / min and calcined for 2.5 hours to obtain Catalyst Comparison Product 2.

[0123] Catalyst comparison product 2 was washed and filtered using the method described in the aforementioned "Statistical method for the number and length of internal fiber additives after the final calcination of heteropolyacid catalysts" and observed through SEM. No cylindrical fiber additives were found.

[0124] The BET test of catalyst comparison product 2 showed a final result of 2.85m 2 / g, crushed to 200 mesh and then subjected to BET test, the final result was 1.02m 2 / g.

[0125] The catalyst comparative product 2 was subjected to a strength test, and the final result was 2.49%.

[0126] 2) Oxidation reaction of methacrolein

[0127] 250 ml of catalyst comparative product 2 was loaded into a molten salt fixed-bed reactor with an inner diameter of 25 mm. Methacrolein oxidation was carried out at a molar ratio of methacrolein / oxygen / water / nitrogen = 1 / 1.8 / 4 / 18.0, a space velocity of 1100 h⁻¹, a pressure of 0.05 MPaG, and a molten salt temperature of 300°C. After 24 hours of continuous reaction, samples were collected and analyzed, revealing a methacrolein conversion of 76.3% and a methacrylic acid selectivity of 77.4%.

[0128] Comparative Example 3

[0129] Compared with Example 2, the difference is that the coating process is divided into two stages, slow and fast, but no fiber additive is added.

[0130] 1) Preparation of catalyst

[0131] The process of preparing the catalyst powder is the same as that in Example 2.

[0132] Molding was performed using a centrifugal granulation coating machine at a temperature of 22°C and a relative humidity of 45%. 320g of porcelain ball carriers were placed in the coating machine and fed with an 85% ethanol aqueous solution as a binder. Molding was first performed at a rotational speed of 120 rpm for 10 minutes, during which time 400g of catalyst powder was evenly added. Molding was then continued at a rotational speed of 400 rpm for another 10 minutes, during which time 200g of catalyst powder was evenly added. Finally, the product was polished for 3 minutes to obtain Molded Body 1. Molded Body 1 was gradually heated from 30°C to 80°C over 12 hours, held for 2 hours, and then heated again at a rate of 1°C / min to 310°C and calcined for 3.5 hours to obtain Catalyst Comparative Product 3.

[0133] Catalyst comparison product 3 was washed and filtered using the method described in the aforementioned "Statistical method for the number and length of internal fiber additives after the final calcination of the heteropolyacid catalyst" and then observed through SEM. No cylindrical fiber additives were visible.

[0134] The BET test of catalyst comparison product 3 showed a final result of 3.58m 2 / g, crushed to 200 mesh and then tested by BET, the final result was 5.85m 2 / g.

[0135] Catalyst product 2 was subjected to a strength test, and the final result was 7.52%.

[0136] 2) Oxidation reaction of methacrolein

[0137] 280 ml of comparative catalyst product 3 was loaded into a molten salt fixed-bed reactor with an inner diameter of 25 mm. Methacrolein oxidation was carried out at a molar ratio of methacrolein / oxygen / water / nitrogen = 1 / 2 / 4 / 20, a space velocity of 1100 h⁻¹, a pressure of 0.02 MPaG, and a molten salt temperature of 300°C. After 24 hours of continuous reaction, samples were collected and analyzed, revealing a methacrolein conversion of 74.58% and a methacrylic acid selectivity of 80.15%.

[0138] Comparative Example 4

[0139] Compared with Example 4, the difference is that fiber additives are added during the coating process and the process is divided into two stages, slow and fast, but there is no polishing stage.

[0140] 1) Preparation of catalyst

[0141] The process of preparing the catalyst powder is the same as that in Example 4.

[0142] Molding was performed using a centrifugal granulation coating machine at a temperature of 25°C and a relative humidity of 55%. 200g of catalyst powder was uniformly mixed with 25g of alumina fiber powder (Zhejiang Desheng New Materials Co., Ltd., DS-1600), designated as mixed powder 1. Another 200g of catalyst powder was uniformly mixed with 25g of alumina fiber powder (Zhejiang Desheng New Materials Co., Ltd., DS-1600), designated as mixed powder 2. 400g of porcelain ball carriers were placed in the coating machine and an 85% ethanol aqueous solution was introduced as a binder. Molding was first performed at a speed of 100 rpm for 12 minutes, during which time mixed powder 1 was evenly added. Molding was then performed at a speed of 250 rpm for 20 minutes, during which time mixed powder 2 was evenly added. Finally, molding was performed at 200 rpm for 6 minutes, during which time 100g of catalyst powder was evenly added. Finally, polishing was performed for 2 minutes to obtain Molded Body 1. The molded body 1 was gradually heated from 30°C to 120°C over 12 hours, and after staying for 2 hours, the temperature was further raised to 305°C at a rate of 1°C / min and calcined for 3 hours to obtain catalyst comparison product 4.

[0143] Catalyst comparison product 4 was washed and filtered using the method described in the aforementioned "Statistical method for the number and length of internal fiber additives after the final calcination of heteropolyacid catalysts." SEM observation revealed cylindrical fiber additives. A certain number of cylindrical fiber additives were randomly selected for diameter and length measurement. Fiber additives with a diameter ≤ 15 μm, a length ≤ 30 μm, and a D:L ratio of 1:1 to 20 were classified as short and fine fiber additives; fiber additives with a diameter > 15 μm, a length > 30 μm, and a D:L ratio of 1:1 to 100 were classified as long and coarse fiber additives. Quantitative statistics revealed that N(s):N(l) = 2.4:1, where N(s) represents the number of short and fine fiber additives and N(l) represents the number of long and coarse fiber additives.

[0144] The BET test of catalyst comparison product 4 was conducted, and the final result was 6.59m 2 / g, crushed to 200 mesh and then subjected to BET test, the final result was 1.48m 2 / g.

[0145] The catalyst comparative product 4 was subjected to a strength test, and the final result was 3.58%.

[0146] 2) Oxidation reaction of methacrolein

[0147] 250 ml of the catalyst comparative product 4 was loaded into a molten salt fixed bed reactor with an inner diameter of 25 mm, and the mixture was heated to 1 % by mass under a molar ratio of methacrolein / oxygen / water / nitrogen of 1 / 4 / 4 / 20 and a space velocity of 1000 h -1 The oxidation reaction of methacrolein was carried out at a pressure of 0.02 MPaG and a molten salt temperature of 310°C. After 20 hours of continuous reaction, sampling and analysis showed that the methacrolein conversion rate was 73.59% and the methacrylic acid selectivity was 74.98%.

[0148] It will be readily understood that the above embodiments are merely examples for clarity of description and are not intended to limit the present invention to these embodiments. Persons skilled in the art will readily appreciate that other variations or modifications based on the above descriptions are possible. It is not necessary and impossible to provide an exhaustive list of all possible implementations. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A coated heteropolyacid catalyst, characterized in that: The fiber additives in the calcined and formed heteropolyacid catalyst have two cylindrical rod-like forms: a short and thin S-type and a long and thick L-type. The quantity ratio of the two forms of fiber additives satisfies the following relationship: N(s):N(l)=0.7~1.3:1 Where N(s) is the number of s-types, and N(l) is the number of l-types; Wherein, the size of the S-type fiber additive satisfies the following conditions: diameter D≤15μm, length L≤30μm, and D:L=1:1~20; Among them, the size of the l-type fiber additive meets the following requirements: diameter D>15μm, length L>30μm, and D:L=1:1~100; Wherein, the fiber additive is inorganic ceramic fiber.

2. The catalyst according to claim 1, characterized in that The BET specific surface area of ​​the catalyst particles after calcination is 3 to 10 m 2 / g; And / or, the catalyst after calcination and molding is ground into a 200 mesh powder with a BET specific surface area of ​​1.5 to 6 m 2 / g.

3. The catalyst according to claim 1 or 2, characterized in that The fiber additive is one or more of silicon carbide fiber, alumina fiber, mullite fiber, aluminum silicate fiber, and silicon nitride fiber.

4. The catalyst according to claim 1, characterized in that The active component of the heteropolyacid catalyst has the following general formula: Mo 12 P a V b With c Ace d X e A f Among them, Mo is molybdenum, P is phosphorus, V is vanadium, Cu is copper, As is arsenic, and O is oxygen; Wherein, X is an active agent selected from one or more of boron, antimony, tungsten, germanium, bismuth, iron, cobalt, magnesium, ruthenium, nickel, zinc, and lead; The atomic molar ratios of the various elements in the above general formula are: a=1-3, b=0.1-1, c=0.1-1, d=0.1-1, e=0.01-1, and f is the number of oxygen atoms required to satisfy the valence of each element.

5. A method for preparing the heteropolyacid catalyst according to any one of claims 1 to 4, characterized in that: The method comprises the following steps: S1: placing a compound of Mo, P, V, Cu, As and X additive element in water to obtain a solution, and drying the solution to obtain a powder; S2: Coating the powder with a fiber additive to obtain a catalyst precursor; S3: calcining the precursor to obtain the target heteropolyacid catalyst; Among them, the coating molding in S2 includes a slow stage, a fast stage and a polishing stage; In the slow stage, the mass ratio of powder to fiber additive is 100:1-15, and the rotating disk speed of the coating machine is 50-150 rpm; In the rapid stage, the mass ratio of powder to fiber additive is 100:2-10, and the rotating speed of the coating machine is 200-400 rpm; Only fiber additives are added during the polishing stage, and the coating machine turntable speed is 150-250 rpm.

6. The method according to claim 5, characterized in that The moisture content of the powder in S1 is 2%-20%.

7. The method according to claim 5, characterized in that The fiber additive in S2 is one or more of silicon carbide fiber, alumina fiber, mullite fiber, aluminum silicate fiber, and silicon nitride fiber.

8. The method according to claim 7, characterized in that The fiber additive in S2 accounts for 0.1% to 10% of the total mass of the formed catalyst particles.

9. The method according to claim 5, characterized in that The roasting method described in S3 is a staged roasting method.

10. The method according to claim 9, characterized in that In S3, the catalyst precursor is first kept at 80-240° C. for 0.5-5 h, and then kept at 250-400° C. for 1-5 h.

11. Use of a heteropolyacid catalyst, wherein the heteropolyacid catalyst is the catalyst according to any one of claims 1 to 4, or the catalyst prepared by the method according to any one of claims 5 to 10, and the catalyst is used for catalyzing the gasification and oxidation of methacrolein to produce methacrylic acid.

12. A method for preparing methacrylic acid by catalytic gasification and oxidation of methacrolein, the method using the catalyst according to any one of claims 1 to 4, or the catalyst prepared by the method according to any one of claims 5 to 10, wherein the reaction temperature is 260 to 380° C., the reaction pressure is 0.01 to 0.20 MPaG, and the molar ratio of oxygen to methacrolein is 1 to 6:1.