Preparation method and application of a heteropoly acid catalyst

Abstract

The present application provides a preparation method of a heteropoly acid catalyst, comprising the following steps: mixing a compound containing active components of molybdenum, phosphorus, vanadium, copper, arsenic and the like with water, and heating to obtain a clear and transparent slurry; drying the slurry to obtain a catalyst powder, wherein the water content of the powder is 5-8%; molding the powder to obtain a catalyst molding; drying the molding at 25-70 DEG C to obtain a catalyst drying body, wherein the relative humidity change rate of the environment during the heating stage of the catalyst drying process is 0.1% / min-10% / min; and calcining the drying body to obtain the heteropoly acid catalyst, wherein the average heating rate from 70 DEG C to 250 DEG C during the calcination process is 0.1 DEG C / min-2 DEG C / min. The obtained catalyst exhibits excellent mechanical strength and catalytic activity when used in the production of unsaturated carboxylic acids.

Description

Technical Field

[0001] This invention relates to the field of catalysts, and more specifically to a method for preparing a heteropolyacid catalyst, which can be used for the preparation of unsaturated carboxylic acids, especially for the preparation of methacrylic acid from methacrolein. Background Technology

[0002] The gas-phase oxidation of methacrolein to methacrylic acid is a key step in the three-step process for producing methyl methacrylate (MMA) from tert-butanol / isobutene, and the catalyst is a heteropolyacid or heteropolyacid salt. Heteropolyacids (salts) have low specific surface areas and are sensitive to moisture, which results in poor batch stability of their strength and activity, making the industrial-scale production of the catalyst a major challenge.

[0003] CN 201080033562.6 mentions that when using water or an aqueous solution of alcohol as a binder and forming the catalyst by coating, the moisture content of the catalyst powder used for forming, the temperature and humidity of the forming process, and the humidity and temperature of the calcination process must be managed. Specifically, it requires that the moisture content of the catalyst powder be 8-10%, and that the formed catalyst be placed in a drying and calcination apparatus at a temperature of 15-90°C and an absolute humidity of 0.007-0.025 kg / kg DA, and that the temperature be raised to a level where the relative humidity reaches below 10% within 30 minutes of placement for calcination. However, this timeframe is relatively short and difficult to achieve in actual industrial production.

[0004] CN201080054242.9 mentions that the absolute humidity of the gas used to control the catalyst forming and calcination process is 0.007~0.025kg / kgDA, and believes that the absolute humidity value has a more significant impact on catalyst performance than the relative humidity value.

[0005] Although the literature has made many attempts to improve the stability of heteropolyacid catalyst preparation, it is clear that existing technologies still need to be improved due to their respective limitations. Summary of the Invention

[0006] To address the problems existing in the prior art, this invention provides a method for preparing a heteropolyacid catalyst, the resulting catalyst, and its applications. This preparation method is simple, reproducible, and the prepared catalyst exhibits excellent mechanical strength and catalytic activity when used in the production of unsaturated carboxylic acids. In particular, it demonstrates excellent conversion and selectivity when used for the oxidation of methacrolein to methacrylic acid.

[0007] To achieve its purpose, the present invention adopts the following technical solution:

[0008] In one aspect of the present invention, a method for preparing a heteropolyacid catalyst is provided, comprising the following steps:

[0009] (A) A compound containing active components such as molybdenum, phosphorus, vanadium, copper, and arsenic is mixed with water and heated to obtain a clear and transparent slurry;

[0010] (B) The above slurry is dried to obtain catalyst powder; the moisture content of the powder is 5-8%;

[0011] (C) The above powder is shaped to obtain a catalyst molded body;

[0012] (D) The above-mentioned molded body is dried at 25-70°C to obtain a dry catalyst body; the relative humidity change rate during the heating stage of the catalyst drying process is between 0.1% / min and 10% / min, preferably between 0.2% / min and 4% / min; and the time for the catalyst to be heated to less than 10% relative humidity is 30-120 min, preferably 40-100 min.

[0013] (E) The above-mentioned dry catalyst body is calcined to obtain the heteropolyacid catalyst; wherein the average heating rate of the catalyst calcination process from 70°C to 250°C is between 0.1°C / min and 2°C / min, preferably between 0.2°C / min and 1°C / min;

[0014] The moisture sources in the catalyst drying process include moisture from external gases and moisture volatilized during catalyst drying.

[0015] In a preferred embodiment of the present invention, the active component optionally further includes one or more of antimony (Sb), tellurium (Te), boron (B), germanium (Ge), tungsten (W), uranium (U), bismuth (Bi), iron (Fe), cobalt (Co), ruthenium (Ru), and nickel (Ni).

[0016] In a preferred embodiment of the present invention, the heating temperature in step (A) is 90-98°C (e.g., 92°C, 94°C, 96°C, etc.). Those skilled in the art will understand that, after determining the required active elements for the catalyst, they can prepare a suitable slurry by mixing these compounds containing the corresponding elements with water under conditions such as heating and dissolving. For example, adding molybdenum trioxide, vanadium pentoxide, phosphoric acid, arsenic acid, and copper oxide to water, followed by stirring and reflux under heating conditions, yields a clear and transparent slurry. The dosage of each compound depends on the proportion of each active element in the desired catalyst, which can be reasonably selected and adjusted by those skilled in the art.

[0017] In a preferred embodiment of the present invention, the drying method used in step (B) is not particularly limited. It can be a slow drying method similar to oven drying, or a fast drying method such as microwave drying, flash drying, or spray drying. Spray drying is preferred for drying the catalyst. The inlet temperature of the spray dryer can be 120-350°C, and the outlet temperature can be 80-130°C. The appropriate inlet and outlet temperatures can be selected according to the drying capacity of the equipment and the required drying effect.

[0018] In a preferred embodiment of the present invention, in step (C), an alcohol-water solution is used as a binder, for example, by centrifugal granulation in a centrifugal granulation and coating machine to coat the powder onto a carrier. In a preferred embodiment of the present invention, the concentration of the alcohol-water solution is 80-100%, preferably 85-95 wt%, such as 80 wt%, 90 wt%, 95 wt%, etc.; more preferably, the alcohol is one or more of methanol, ethanol, n-propanol, and isopropanol. The carrier of the present invention is an inert ceramic ball with a diameter of 3.0-4.5 mm. The ceramic ball mainly contains silicon oxide, alumina, aluminum silicate, etc. To facilitate the coating of the catalyst active component on the carrier, the surface and interior of the inert ceramic ball carrier are loose and porous, with a pore size of 10-1000 μm, a water absorption rate of 8%-15%, and a bulk density of 1-1.5 g / cm³. 3 The catalyst of this invention is formed at a temperature of 20–30°C, preferably 21–25°C. This forming temperature is ambient temperature; the actual internal temperature of the catalyst may vary slightly due to particle movement during the forming process. After forming, the catalyst of this invention has a final diameter of 3.5–5.5 mm, with the outer active component accounting for approximately 40–70 wt% of the total catalyst weight.

[0019] In a preferred embodiment of the present invention, in step (D), after the catalyst is formed, it is placed in a drying device for drying. Within the temperature range of 25–70°C, because water and alcohol evaporate simultaneously during the catalyst drying process, and the catalyst is subjected to physical or chemical forces from water and alcohol, the evaporation of water also affects the evaporation of alcohol. Therefore, it is necessary to control the rate of relative humidity change to a specific range to obtain a catalyst with high strength and high activity. The inventors have found that by controlling the rate of relative humidity change during the heating process to 0.1% / min–10% / min, preferably 0.2% / min–4% / min, the catalyst exhibits better overall performance. The drying process can be a “heating-constant temperature-heating-constant temperature” process, or a “heating-constant temperature” process, etc. For example, first, the temperature is raised to a certain temperature at a certain rate, then kept at a constant temperature for a period of time, and then the temperature is raised to 70°C and kept at a constant temperature for a period of time. Alternatively, the temperature can be raised to 70°C at a certain rate and kept at a constant temperature for a period of time. One, two, or more heating stages can be performed as needed. The relative humidity change rate needs to be controlled at 0.1% / min to 10% / min during each heating stage of the drying process. On an industrial scale, due to the large amount of moisture generated during the catalyst drying process, in addition to the moisture in the drying gas, the moisture discharged from the catalyst during drying will also affect the "perceived" humidity of the catalyst. Therefore, the relative humidity of the entire environment needs to be considered comprehensively.

[0020] In a preferred embodiment of the present invention, in step (E), the calcination endpoint temperature is 300-400°C, for example, 300°C, 310°C, 320°C…400°C; the calcination time is 1-10 hours, for example, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, etc. Before reaching the calcination temperature, a slow heating program can be set in a relatively low temperature range to completely remove organic matter such as ethanol and moisture. The inventors have found that during the process of gradually heating from 70°C to 250°C, controlling the average temperature rise rate to 0.1°C / min to 2°C / min, preferably 0.2°C / min to 1°C / min, results in better catalyst performance. Meanwhile, since the organic content of the catalyst varies at different stages and the reaction mechanism of organic transformation is different, different temperature rise rates can be considered for different stages. For example, a faster temperature rise rate can be used in the 70-90℃ range, while a slower temperature rise rate can be used in the 90-150℃ range, and a faster temperature rise rate can be used in the 150-250℃ range, which can be determined specifically according to the needs.

[0021] In another aspect of the invention, a catalyst is provided obtained by the preparation method described above, wherein the active element of the catalyst satisfies the following formula:

[0022] Mo 12 P a V b Cu c Asd X e O f

[0023] Where X is one or more of antimony, tellurium, boron, germanium, tungsten, uranium, bismuth, iron, cobalt, ruthenium, and nickel; a = 0.5-3 (e.g., 1, 1.5, 2, 2.5, etc.); b = 0.1-2 (e.g., 0.5, 1, 1.5, etc.); c = 0.01-1 (e.g., 0.05, 0.1, 0.5, etc.); d = 0.01-2 (e.g., 0.05, 0.1, 0.5, 1, 1.5, etc.); e = 0-0.5 (e.g., 0.1, 0.2, 0.3, 0.4, etc.); f is the atomic ratio of oxygen required to satisfy the valence of each element.

[0024] In a preferred embodiment of the present invention, the catalyst has a moisture content ≤1.0% and an attrition index <1%. At this moisture content, the catalyst can be stably stored for a long time, and even considering moisture absorption during the catalyst loading process, it does not affect its industrial use or catalytic performance.

[0025] In another aspect of the invention, the use of a catalyst obtained by the preparation method described above or a catalyst described above in the preparation of unsaturated carboxylic acids from unsaturated aldehydes is discussed.

[0026] In a particularly preferred embodiment of the present invention, the present invention relates to the use of a catalyst obtained by the preparation method described above or the catalyst described above in the preparation of methacrylic acid from methacrolein.

[0027] In a particularly preferred embodiment of the present invention, when the catalyst of the present invention is used to oxidize methacrolein to prepare methacrylic acid, the reaction conditions may be, for example, a reaction temperature of 280-360°C, a reaction pressure of 0.01-0.15 MPa, and a gas hourly space velocity (GHSV) of 800-2000 h⁻¹. -1 The molar concentration of methacrolein in the mixed gas is 3-8%, the molar ratio of oxygen to methacrolein is 1-4:1, the molar ratio of water vapor to methacrolein is 2-10:1, and the remaining gas in the mixed gas is mainly nitrogen.

[0028] In addition to the beneficial effects already mentioned above, compared with the prior art, the beneficial effects of the present invention are mainly reflected in the following: by controlling the spray drying process, coating post-treatment process and calcination process in the preparation of heteropoly acids, high-performance industrial catalysts can be stably manufactured. When applied to the production of unsaturated carboxylic acids (especially methacrylic acid), the catalyst exhibits excellent mechanical strength and catalytic activity. Detailed Implementation

[0029] The method provided by the present invention will be described in further detail below, but the present invention is not limited thereto.

[0030] Test methods

[0031] Testing and characterization of various parameters of the catalyst:

[0032] Catalyst powder moisture content: Weigh 10g of powder and place it in a crucible. Calcinate the powder in a muffle furnace at 400℃ for 2 hours. Record the weight loss m1 of the powder after calcination and calculate the moisture content of the powder.

[0033] The catalyst attrition rate (i.e., wear index) test reference standard: HG / T 2976-1999 (Determination of Attrition Rate of Fertilizer Catalyst), and the testing instrument is KM-5A particle attrition tester (produced by Dalian Penghui Technology Development Co., Ltd.);

[0034] Moisture content of catalyst product: Weigh 100g of catalyst product and place it in a 160℃ oven for constant temperature drying for 2 hours. Record the weight loss m2 of the catalyst after drying.

[0035] The conversion and selectivity of the oxidation of methacrolein to methacrylic acid are defined as follows:

[0036] Methacrolein conversion rate = (amount of methacrolein consumed / amount of methacrolein supplied from raw materials) × 100%;

[0037] Methacrylic acid selectivity = (amount of methacrylic acid produced / amount of methacrolein consumed) × 100%.

[0038] Catalyst activity evaluation:

[0039] Catalyst activity was evaluated using a Shimadzu GC-2010 gas chromatograph (30m length, 0.32m inner diameter, 0.5μm film thickness).

[0040] The chromatographic operating conditions are as follows:

[0041] Injector temperature: 260℃; Detector temperature: 250℃; Injection volume: 1μL; Column flow rate: 1ml / min; Split ratio: 50:1; Column oven temperature program: 50℃ for 13min, increase to 110℃ at a rate of 20℃ / min, hold for 3min, increase to 180℃ at a rate of 20℃ / min, hold for 10min.

[0042] Example

[0043] The porous inert ceramic balls used in this patent were purchased from Jiangxi Kepak Environmental Protection Chemical Co., Ltd. They have 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 / cm³. 3 .

[0044] All raw materials mentioned in this article, unless otherwise specified, are commercially available reagents.

[0045] Example 1

[0046] 1) Catalyst preparation

[0047] 500g of molybdenum trioxide, 25g of vanadium pentoxide, 44g of 85wt% phosphoric acid, 20g of 80wt% arsenic acid, and 3g of copper oxide were added to 4000g of deionized water. The mixture was stirred and refluxed at 95℃ for 10 hours to obtain a clear and transparent solution. This solution was then spray-dried in a spray dryer with an inlet temperature of 300℃ and an outlet temperature of 120℃ to obtain a spray-dried powder with a moisture content of 6.91%.

[0048] The composition of active elements in the powder is described as follows: Mo 12 P 1.32 V 0.95 Cu 0.13 As 0.39 O x (The oxygen ratio varies with the oxidation state of each element.)

[0049] At a temperature of 22℃, a centrifugal granulation and coating machine was used for molding. An 85% ethanol aqueous solution was introduced as a binder to coat 300g of powder onto a 190g ceramic ball carrier, resulting in a molded body.

[0050] The molded body was placed in a circulating blast furnace, where temperature and humidity changes were monitored using a thermometer and hygrometer. The catalyst was heated from 25°C to 45°C at a rate of 1°C / min and dried at this temperature for 0.5 hours. During this drying process, the relative humidity inside the furnace gradually decreased from 80% at 25°C to 30% at 45°C, and then gradually decreased to 26% during the temperature-controlled drying process. The temperature was then increased to 70°C at a rate of 2°C / min and dried at this temperature for 0.5 hours. During this drying process, the relative humidity inside the furnace gradually decreased from 26% at 45°C to 10% at 70°C, and then gradually decreased to 6% during the temperature-controlled drying process, resulting in a dried body. The relative humidity change rate during the heating phase of the entire drying process was 1.28–2.5% / min.

[0051] The dried material was gradually heated from 70℃ to 250℃ over 12 hours (average heating rate 0.25℃ / min), and then calcined at 320℃ for 3 hours at a rate of 3℃ / min to obtain the catalyst product.

[0052] Tests showed that the catalyst had a water content of 0.32% and an attrition index of 0.57%.

[0053] 2) Oxidation reaction of methacrolein

[0054] 280 ml of catalyst product was packed into a molten salt fixed-bed reactor with an inner diameter of 25 mm, and the reactor was subjected to a molar ratio of methacrolein / oxygen / water / nitrogen = 1 / 1.8 / 4 / 18.0 and a space velocity of 1000 h⁻¹. -1 The oxidation reaction of methacrolein was carried out at a pressure of 50 kPa and a molten salt temperature of 310 °C. After 24 hours of continuous reaction, samples were taken for analysis. The conversion rate of methacrolein was 85.2%, and the selectivity of methacrylic acid was 85.7%.

[0055] Comparative Example 1

[0056] 1) Catalyst preparation

[0057] The catalyst was prepared according to Example 1 of patent CN103861640. 500g of molybdenum trioxide, 25g of vanadium pentoxide, 44g of 85wt% phosphoric acid, 20g of 80wt% arsenic acid, and 3g of copper oxide were added to 4000g of deionized water. After stirring and refluxing at 98℃ for 10h, a clear and transparent solution was obtained. This solution was spray-dried in an air-jet spray dryer with an atomizing gas pressure (absolute pressure) of 0.35MPa, a compressed air velocity of 1500m / s from the nozzle, an inlet temperature of 140-150℃, and an outlet temperature of 70-80℃. The resulting powder had an average particle size of 2.5μm and a moisture content of 9.82%. The catalyst powder was then calcined in a flowing air atmosphere, specifically at 100℃ for 2h, 150℃ for 1h, 200℃ for 1h, and 320℃ for 5h.

[0058] The composition of the active element in the catalyst is described as follows: Mo 12 P 1.32 V 0.95 Cu 0.13 As 0.39 O x (The oxygen ratio varies with the oxidation state of each element.)

[0059] Tests showed that the catalyst had a water content of 0.37% and an attrition index of 3.39%.

[0060] 2) Oxidation reaction of methacrolein

[0061] 280 ml of catalyst product was packed into a molten salt fixed-bed reactor with an inner diameter of 25 mm, and the reactor was subjected to a molar ratio of methacrolein / oxygen / water / nitrogen = 1 / 1.8 / 4 / 18.0 and a space velocity of 1000 h⁻¹. -1The oxidation reaction of methacrolein was carried out at a pressure of 50 kPa and a molten salt temperature of 310 °C. After 24 hours of continuous reaction, samples were taken for analysis. The conversion rate of methacrolein was 71.6%, and the selectivity of methacrylic acid was 80.4%.

[0062] As can be seen from the comparison between Example 1 and Comparative Example 1, the catalyst prepared by the method of the present invention has higher strength, higher conversion rate and selectivity.

[0063] Example 2

[0064] 1) Catalyst preparation

[0065] 500g of molybdenum trioxide, 25g of vanadium pentoxide, 44g of 85wt% phosphoric acid, 20g of 80wt% arsenic acid, and 3g of copper oxide were added to 3000g of deionized water. The solution was stirred and refluxed at 95℃ for 10 hours to obtain a clear and transparent solution. This solution was then spray-dried in a spray dryer with an inlet temperature of 300℃ and an outlet temperature of 115℃ to obtain spray-dried powder with a moisture content of 7.87%.

[0066] The composition of active elements in the powder is described as follows: Mo 12 P 1.32 V 0.95 Cu 0.13 As 0.39 O x (The oxygen ratio varies with the oxidation state of each element.)

[0067] At a temperature of 25℃, a centrifugal granulation and coating machine was used for molding. A 90% ethanol aqueous solution was introduced as a binder to coat 300g of powder onto a 190g ceramic ball carrier, resulting in a molded body.

[0068] The molded body was placed in a circulating blast furnace, where temperature and humidity changes were monitored using a thermometer and hygrometer. The catalyst was heated from 25°C to 60°C at a rate of 2°C / min and dried at this temperature for 0.4 hours. During this process, the relative humidity inside the furnace gradually decreased from 75% at 25°C to 15% at 60°C, and then further decreased to 14% during the drying process. The temperature was then increased to 70°C at a rate of 2°C / min and dried at this temperature for 0.2 hours. During this process, the relative humidity inside the furnace gradually decreased from 14% at 60°C to 9% at 70°C, and then further decreased to 7% during the drying process, resulting in a dried body. The relative humidity change rate during the heating phase of the entire drying process was 1–3.4% / min.

[0069] The dried material was gradually heated from 70℃ to 250℃ over 4 hours (average heating rate 0.75℃ / min), and then calcined at 310℃ for 5 hours at a rate of 3℃ / min to obtain the catalyst product.

[0070] Tests showed that the catalyst had a water content of 0.57% and an attrition index of 0.39%.

[0071] 2) Oxidation reaction of methacrolein

[0072] 280 ml of catalyst product was packed into a molten salt fixed-bed reactor with an inner diameter of 25 mm, and the reactor was subjected to a molar ratio of methacrolein / oxygen / water / nitrogen = 1 / 1.8 / 4 / 18.0 and a space velocity of 1000 h⁻¹. -1 The oxidation reaction of methacrolein was carried out at a pressure of 50 kPa and a molten salt temperature of 310 °C. After 24 hours of continuous reaction, samples were taken for analysis. The conversion rate of methacrolein was 83.6%, and the selectivity of methacrylic acid was 86.2%.

[0073] Comparative Example 2

[0074] 1) Catalyst preparation

[0075] The catalyst was prepared according to Example 2, except that the drying process conditions were adjusted.

[0076] The procedures before drying the catalyst are the same as in Example 2.

[0077] The molded body was placed in a circulating blast furnace, where temperature and humidity changes were monitored using a thermometer and hygrometer. The catalyst was heated from 25°C to 60°C at a rate of 0.05°C / min and dried at this temperature for 0.4 hours. During this time, the relative humidity inside the furnace gradually decreased from 75% at 25°C to 14% at 60°C, and then further decreased to 13% during the isothermal process. The temperature was then increased to 70°C at a rate of 0.1°C / min and dried at this temperature for 0.2 hours. During this time, the relative humidity inside the furnace gradually decreased from 13% at 60°C to 9% at 70°C, with no significant change in relative humidity during the isothermal process, resulting in a dried body. The relative humidity change rate during the heating phase of the entire drying process was 0.04–0.09% / min.

[0078] The dried material was gradually heated from 70℃ to 250℃ over 4 hours (average heating rate 0.75℃ / min), and then calcined at 3℃ / min to 310℃ for 5 hours to obtain the catalyst product.

[0079] Tests showed that the catalyst had a water content of 0.57% and an attrition index of 4.17%.

[0080] 2) Oxidation reaction of methacrolein

[0081] 280 ml of catalyst product was packed into a molten salt fixed-bed reactor with an inner diameter of 25 mm, and the reactor was subjected to a molar ratio of methacrolein / oxygen / water / nitrogen = 1 / 1.8 / 4 / 18.0 and a space velocity of 1000 h⁻¹. -1The oxidation reaction of methacrolein was carried out at a pressure of 50 kPa and a molten salt temperature of 310 °C. After 24 hours of continuous reaction, samples were taken for analysis. The conversion rate of methacrolein was 74.5%, and the selectivity of methacrylic acid was 82.1%.

[0082] As can be seen from the comparison between Example 2 and Comparative Example 2, the catalyst prepared by the method of the present invention has higher strength, higher conversion rate and selectivity.

[0083] Comparative Example 3

[0084] 1) Catalyst preparation

[0085] The catalyst was prepared according to Example 2, except that the calcination process conditions were adjusted.

[0086] The procedures before catalyst calcination are the same as in Example 2.

[0087] The dried material was gradually heated from 70℃ to 250℃ over 1 hour (average heating rate 3℃ / min), and then calcined at 3℃ / min to 310℃ for 5 hours to obtain the catalyst product.

[0088] Tests showed that the catalyst had a water content of 0.46% and an attrition index of 2.35%.

[0089] 2) Oxidation reaction of methacrolein

[0090] 280 ml of catalyst product was packed into a molten salt fixed-bed reactor with an inner diameter of 25 mm, and the reactor was subjected to a molar ratio of methacrolein / oxygen / water / nitrogen = 1 / 1.8 / 4 / 18.0 and a space velocity of 1000 h⁻¹. -1 The oxidation reaction of methacrolein was carried out at a pressure of 50 kPa and a molten salt temperature of 310 °C. After 24 hours of continuous reaction, samples were taken for analysis. The conversion rate of methacrolein was 65.7%, and the selectivity of methacrylic acid was 76.1%.

[0091] As can be seen from the comparison between Example 2 and Comparative Example 3, the catalyst prepared by the method of the present invention has higher strength, higher conversion rate and selectivity.

[0092] Example 3

[0093] 1) Catalyst preparation

[0094] 500g of molybdenum trioxide, 22g of vanadium pentoxide, 44g of 85wt% phosphoric acid, 30g of 80wt% arsenic acid, and 4g of copper oxide were added to 6000g of deionized water. The solution was stirred and refluxed at 95℃ for 10 hours to obtain a clear and transparent solution. This solution was then spray-dried in a spray dryer with an inlet temperature of 300℃ and an outlet temperature of 125℃ to obtain spray-dried powder with a moisture content of 5.92%.

[0095] The composition of active elements in the powder is described as follows: Mo 12 P 1.32 V 0.84 Cu 0.17 As 0.59 O x (The oxygen ratio varies with the oxidation state of each element.)

[0096] At a temperature of 25℃, a centrifugal granulation and coating machine is used for molding. An 80% ethanol aqueous solution is introduced as a binder to coat 300g of powder onto a 190g ceramic ball carrier, thus obtaining the molded body.

[0097] The molded body was placed in a circulating blast furnace, where temperature and humidity changes were monitored using a thermometer and hygrometer. The catalyst was heated from 25°C to 50°C at a rate of 4°C / min and dried at this temperature for 0.5 hours. During this drying process, the relative humidity inside the furnace gradually decreased from 85% at 25°C to 24% at 50°C, and then gradually decreased to 22% during the temperature-controlled drying process. The temperature was then increased to 70°C at a rate of 4°C / min and dried at this temperature for 0.5 hours. During this drying process, the relative humidity inside the furnace gradually decreased from 22% at 50°C to 11% at 70°C, and then gradually decreased to 8% during the temperature-controlled drying process, resulting in a dried body. The relative humidity change rate during the heating phase of the entire drying process was 2.2–9.8% / min.

[0098] The dried material was gradually heated from 70℃ to 250℃ over 9 hours (average heating rate 0.33℃ / min), and then calcined at 310℃ for 5 hours at a rate of 3℃ / min to obtain the catalyst product.

[0099] Tests showed that the catalyst had a water content of 0.28% and an attrition index of 0.73%.

[0100] 2) Oxidation reaction of methacrolein

[0101] 280 ml of catalyst product was packed into a molten salt fixed-bed reactor with an inner diameter of 25 mm, and the reactor was subjected to a molar ratio of methacrolein / oxygen / water / nitrogen = 1 / 1.8 / 4 / 18.0 and a space velocity of 1000 h⁻¹. -1 The oxidation reaction of methacrolein was carried out at a pressure of 50 kPa and a molten salt temperature of 310 °C. After 24 hours of continuous reaction, samples were taken for analysis. The conversion rate of methacrolein was 84.7%, and the selectivity of methacrylic acid was 84.2%.

[0102] Comparative Example 4

[0103] 1) Catalyst preparation

[0104] The catalyst was prepared according to Example 3, the difference being the adjustment of the moisture content of the spray-dried powder and the drying process.

[0105] 500g of molybdenum trioxide, 22g of vanadium pentoxide, 44g of 85wt% phosphoric acid, 30g of 80wt% arsenic acid, and 4g of copper oxide were added to 6000g of deionized water. The solution was stirred and refluxed at 95℃ for 10 hours to obtain a clear and transparent solution. This solution was then spray-dried in a spray dryer with an inlet temperature of 300℃ and an outlet temperature of 105℃ to obtain spray-dried powder with a moisture content of 9.1%.

[0106] The composition of active elements in the powder is described as follows: Mo 12 P 1.32 V 0.84 Cu 0.17 As 0.59 O x (The oxygen ratio varies with the oxidation state of each element.)

[0107] At a temperature of 25℃, a centrifugal granulation and coating machine is used for molding. An 80% ethanol aqueous solution is introduced as a binder to coat 300g of powder onto a 190g ceramic ball carrier, thus obtaining the molded body.

[0108] The molded body was placed in a circulating blast furnace, where temperature and humidity changes were monitored using a thermometer and hygrometer. The catalyst was heated from 25°C to 50°C at a rate of 5°C / min and dried at this temperature for 0.2 hours. During this process, the relative humidity inside the furnace gradually decreased from 85% at 25°C to 26% at 50°C, and then gradually decreased to 24% during the constant temperature period. The temperature was then increased to 70°C at a rate of 5°C / min and dried at this temperature for 0.1 hours. During this process, the relative humidity inside the furnace gradually decreased from 24% at 50°C to 13% at 70°C, and then gradually decreased to 9% during the constant temperature period, resulting in a dried body. The relative humidity change rate during the heating phase of the entire drying process was 2.75–11.8% / min.

[0109] The dried material was gradually heated from 70℃ to 250℃ over 9 hours (average heating rate 0.33℃ / min), and then calcined at 310℃ for 5 hours at a rate of 3℃ / min to obtain the catalyst product.

[0110] Tests showed that the catalyst had a water content of 0.28% and an attrition index of 1.54%.

[0111] 2) Oxidation reaction of methacrolein

[0112] 280 ml of catalyst product was packed into a molten salt fixed-bed reactor with an inner diameter of 25 mm, and the reactor was subjected to a molar ratio of methacrolein / oxygen / water / nitrogen = 1 / 1.8 / 4 / 18.0 and a space velocity of 1000 h⁻¹. -1 The oxidation reaction of methacrolein was carried out at a pressure of 50 kPa and a molten salt temperature of 310 °C. After 24 hours of continuous reaction, samples were taken for analysis. The conversion rate of methacrolein was 76.9%, and the selectivity of methacrylic acid was 85.1%.

[0113] As can be seen from the comparison between Example 3 and Comparative Example 4, the catalyst prepared by the method of the present invention has higher strength and higher conversion rate.

[0114] Example 4

[0115] 1) Catalyst preparation

[0116] 500g of molybdenum trioxide, 25g of vanadium pentoxide, 44g of 85wt% phosphoric acid, 20g of 80wt% arsenic acid, and 3g of copper oxide were added to 4000g of deionized water. The mixture was stirred and refluxed at 95℃ for 10 hours to obtain a clear and transparent solution. This solution was then spray-dried in a spray dryer with an inlet temperature of 300℃ and an outlet temperature of 120℃ to obtain a spray-dried powder with a moisture content of 6.91%.

[0117] The composition of active elements in the powder is described as follows: Mo 12 P 1.32 V 0.95 Cu 0.13 As 0.39 O x (The oxygen ratio varies with the oxidation state of each element.)

[0118] At a temperature of 27°C, a centrifugal granulation and coating machine was used for molding. An 85% ethanol aqueous solution was introduced as a binder to coat 300g of powder onto a 190g ceramic ball carrier, resulting in a molded body.

[0119] The molded body was placed in a circulating blast furnace, where temperature and humidity changes were monitored using a thermometer and hygrometer. The catalyst was heated from 27°C to 70°C at a rate of 0.5°C / min and dried at this temperature for 0.2 hours. The relative humidity inside the furnace gradually decreased from 75% at 27°C to 11% at 70°C, and then gradually decreased to 9% during the constant temperature process, resulting in a dried body. The relative humidity change rate during the heating phase of the entire drying process was 0.74% / min.

[0120] The dried material was gradually heated from 70℃ to 250℃ over 3 hours (average heating rate 1℃ / min), and then calcined at 310℃ for 5 hours at a rate of 3℃ / min to obtain the catalyst product.

[0121] Tests showed that the catalyst had a water content of 0.57% and an attrition index of 0.98%.

[0122] 2) Oxidation reaction of methacrolein

[0123] 280 ml of catalyst product was packed into a molten salt fixed-bed reactor with an inner diameter of 25 mm, and the reactor was subjected to a molar ratio of methacrolein / oxygen / water / nitrogen = 1 / 1.8 / 4 / 18.0 and a space velocity of 1000 h⁻¹. -1 The oxidation reaction of methacrolein was carried out at a pressure of 50 kPa and a molten salt temperature of 310 °C. After 24 hours of continuous reaction, samples were taken for analysis. The conversion rate of methacrolein was 82.2%, and the selectivity of methacrylic acid was 85.9%.

[0124] Although the invention has been described in detail above for illustrative purposes, it should be understood that such detailed description is merely for illustration, and modifications can be made by those skilled in the art without departing from the spirit and scope of the invention, which is defined only by the claims.

Claims

1. A method for preparing a heteropolyacid catalyst, characterized in that, It includes the following steps: (A) A clear and transparent slurry is prepared by mixing a compound containing an active component with water and heating it; the active component includes molybdenum, phosphorus, vanadium, copper, and arsenic. (B) The above slurry is dried to obtain catalyst powder; the moisture content of the powder is 5-8%; (C) The above powder is shaped to obtain a catalyst shaped body; (D) The above-mentioned molded body is dried at 25~70℃ to obtain a dry catalyst body; the relative humidity change rate of the environment during the heating stage of the drying process is between 0.1% / min and 10% / min, and the time for the catalyst to be heated to less than 10% relative humidity is 30~120min. (E) The above-mentioned dried body is calcined to obtain the heteropolyacid catalyst; the average heating rate of the catalyst calcination process from 70°C to 250°C is between 0.1°C / min and 2°C / min.

2. The preparation method according to claim 1, wherein, The active component may optionally include one or more of antimony, tellurium, boron, germanium, tungsten, uranium, bismuth, iron, cobalt, ruthenium, and nickel.

3. The preparation method according to claim 1, wherein, The heating temperature in step (A) is 90-98℃.

4. The preparation method according to claim 1, wherein, In step (C), the catalyst forming temperature is 20~30℃.

5. The preparation method according to claim 1, wherein, In step (D), the relative humidity change rate during the heating phase of the drying process is between 0.2% / min and 4% / min.

6. The preparation method according to claim 1, wherein, The average heating rate of the catalyst calcination process from 70°C to 250°C is between 0.2°C / min and 1°C / min.

7. The preparation method according to claim 1, wherein, The final calcination temperature of the catalyst calcination process is 300~400℃.

8. The catalyst obtained by the preparation method according to any one of claims 1-7, wherein, The active element of the catalyst satisfies the following equation: Mo 12 P a V b With c Ace d X e A f Where X is one or more of antimony, tellurium, boron, germanium, tungsten, uranium, bismuth, iron, cobalt, ruthenium, and nickel; a = 0.5-3; b = 0.1-2; c = 0.01-1; d = 0.01-2; e = 0.0-0.5; f is the atomic ratio of oxygen required to satisfy the valence of each element.

9. Use of the catalyst obtained by the preparation method according to any one of claims 1-7 or the catalyst according to claim 8 in the preparation of unsaturated carboxylic acids from unsaturated aldehydes.

10. The use according to claim 9, wherein, Used to prepare methacrylic acid from methacrolein.

11. A method for preparing methacrylic acid by oxidizing methacrolein, using the catalyst of claim 8, wherein, The reaction temperature is 280-360℃, the reaction pressure is 0.01-0.15MPa, and the molar ratio of oxygen to methacrolein is 1-4:1.