Supported iron-molybdenum catalyst for formaldehyde production as well as preparation method and application of supported iron-molybdenum catalyst

Abstract

The invention discloses a supported iron-molybdenum catalyst for formaldehyde production and a preparation method and application thereof, and belongs to the field of catalysts.The catalyst comprises a core-shell structure, the core of the catalyst is a carrier, molybdenum trioxide is supported on the carrier, and the shell of the catalyst is iron molybdate. The carrier is selected from at least one of silicon dioxide, aluminum oxide, titanium oxide, magnesium oxide, magnesium silicate, a molecular sieve, white carbon black and hydroxyapatite; the preparation method comprises the following steps: firstly, loading molybdenum trioxide on a carrier, then dispersing the carrier in deionized water, dropwise adding a molybdenum source solution and an iron source solution in a parallel flow manner under stirring to perform deposition loading of iron molybdate, and performing aging, drying, forming and calcining to obtain the catalyst. The catalyst is used for preparing formaldehyde by oxidizing methanol, dimethyl ether and methylal; according to the catalyst disclosed by the invention, the raw material cost and the pollutant treatment capacity are obviously reduced due to the reduction of the dosage of molybdenum and iron components, and the catalyst has relatively good activity and stability.

Description

[0001] The present invention relates to the technical field of catalysts, and in particular to a supported iron-molybdenum catalyst for formaldehyde production, a preparation method and application thereof. Background Art

[0002] As an important organic chemical raw material and chemical intermediate, formaldehyde is widely used in chemical production, pharmaceutical synthesis, material manufacturing and other fields. At present, my country has become the world's largest formaldehyde producer and consumer, and its formaldehyde production capacity accounts for 55% of the world's total production capacity. Formaldehyde is mainly produced by selective oxidation using methanol as raw material. According to the type of catalyst used, it is divided into "silver method" and "iron-molybdenum method". Among them, "iron-molybdenum method" has become the main production method used in new and renovated equipment in recent years due to its advantages such as low reaction temperature, low methanol consumption and high formaldehyde product concentration.

[0003] The above advantages of the iron-molybdenum method for producing formaldehyde are mainly due to the excellent performance of its catalyst. However, during the application of the iron-molybdenum catalyst, due to the high-temperature molybdenum sublimation and the formation of volatile gaseous compounds between molybdenum and methanol, molybdenum is lost, which in turn affects the stability and life of the catalyst. In order to alleviate the above problems caused by the loss of molybdenum, the industrial iron-molybdenum catalyst is composed of iron molybdate and excess molybdenum oxide. The excess molybdenum oxide can replenish the lost molybdenum to a certain extent. However, due to the rapid loss of molybdenum in the ordinary random blending structure of these two phases, the replenishment effect of excess molybdenum cannot be fully exerted. In order to extend the life, the amount of molybdenum in the catalyst must be increased, which in turn will lead to a significant increase in the cost of the catalyst.

[0004] Chinese patent application CN112916019A, A core-shell structured molybdenum-iron catalyst and its preparation and use, discloses a core-shell structured molybdenum-iron catalyst. Although this patent alleviates the loss of molybdenum trioxide to a certain extent, it still has the problems of rapid loss and high catalyst cost. Summary of the invention

[0005] One of the purposes of the present invention is to provide a supported iron-molybdenum catalyst for formaldehyde production to solve the above-mentioned problems.

[0006] In order to achieve the above-mentioned purpose, the technical solution adopted by the present invention is as follows: a supported iron-molybdenum catalyst for formaldehyde production, the catalyst contains a core-shell structure, the core of which is a carrier, the carrier is loaded with molybdenum trioxide, and the shell of which is iron molybdate.

[0007] As a preferred technical solution, the carrier is selected from at least one of silicon dioxide, aluminum oxide, titanium oxide, magnesium oxide, magnesium silicate, molecular sieve, white carbon black, and hydroxyapatite.

[0008] The second object of the present invention is to provide a method for preparing the above-mentioned supported iron-molybdenum catalyst for formaldehyde production, comprising the following steps: firstly, loading molybdenum trioxide on a carrier, then dispersing it in deionized water, dripping a molybdenum source and an iron source solution in parallel under stirring to deposit and load iron molybdate, and then aging, drying, molding, and calcining to form a supported iron-molybdenum catalyst with a coating structure.

[0009] As a preferred technical solution, the molybdenum source for loading molybdenum trioxide and iron molybdate is selected from at least one of sodium molybdate, potassium molybdate, ammonium molybdate and molybdenum trioxide.

[0010] As a preferred technical solution, the iron source for loading the iron molybdate is selected from at least one of ferric nitrate, ferrous nitrate, ferric chloride, ferrous chloride, ferrous sulfate and ferrous sulfate.

[0011] As a preferred technical solution, the loaded molybdenum trioxide accounts for 2% to 80% of the weight of the carrier, and the loaded outer layer of iron molybdate accounts for 2% to 70% of the weight of the carrier.

[0012] As a further preferred technical solution, the loaded molybdenum trioxide accounts for 30% to 80% of the weight of the carrier, and the loaded outer layer of iron molybdate accounts for 30% to 70% of the weight of the carrier.

[0013] As a preferred technical solution, the aging temperature is 10-90°C, the drying temperature is 90-150°C, and the calcination temperature is 300-600°C.

[0014] As a further preferred technical solution, the calcination temperature is 500°C.

[0015] The third object of the present invention is to provide an application of the above-mentioned catalyst, wherein the catalyst is used for oxidizing methanol, dimethyl ether and methylal to prepare formaldehyde.

[0016] (1) Compared with the prior art, the advantages of the present invention are as follows: the present application provides a coated structure supported iron-molybdenum catalyst for formaldehyde production, wherein molybdenum trioxide is supported on an inner core carrier, and has a certain interaction with the carrier, thereby "grasping" molybdenum oxide; the outer layer of iron molybdate coats the molybdenum trioxide inside, "wrapping" it, thereby inhibiting the loss of molybdenum oxide, and can give full play to the replenishment effect of molybdenum oxide, thereby bringing about better stability against molybdenum loss and longer catalyst life; (2) The coated structure supported iron-molybdenum catalyst provided in the present application for formaldehyde production has a significant reduction in raw material costs and pollutant treatment due to the reduction in the amount of molybdenum and iron components used; (3) The coated structure supported iron-molybdenum catalyst prepared by the method of the present application still has high activity and selectivity despite the addition of some carriers. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a transmission electron microscopy image of the catalyst prepared in Example 2; Figure 2 High resolution transmission electron microscopy Figure 1 The surface of the catalyst particles was further magnified for observation. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0019] It should be noted that the percentages “%” in the following embodiments and comparative examples refer to mass percentages unless otherwise specified. Example

[0020] 1.86g of ammonium heptamolybdate tetrahydrate was dissolved in 124ml of deionized water, 86g of alumina was added thereto and stirred evenly, and the mixture was dried at 120°C and then calcined at 500°C for 3 hours to obtain an alumina carrier loaded with 2% molybdenum oxide; based on the alumina carrier, 20.35g of ammonium heptamolybdate tetrahydrate and 30.05g of ferric nitrate nonahydrate were dissolved in 200ml of deionized water at a loading amount of 30% of iron molybdate; the carrier loaded with molybdenum oxide was dispersed in 800g of deionized water, and the prepared ammonium molybdate and ferric nitrate nonahydrate solutions were added dropwise in parallel under stirring conditions for 30 minutes, and the catalyst was aged at 80°C for 3 hours, filtered and washed, and dried at 120°C for 3 hours. After compression molding, the catalyst was calcined at 500°C for 4 hours to obtain a loaded iron-molybdenum catalyst with a coated structure. Example

[0021] 23.53g of molybdenum oxide was dispersed in 300g of 30% hydrogen peroxide, and then 58.82g of aluminum oxide was added thereto, stirred and reacted at 90°C for 10 hours, and dried at 120°C to obtain an aluminum oxide carrier loaded with 40% of molybdenum oxide; based on the aluminum oxide carrier, 15.8g of ammonium tetrahydrate heptamolybdate and 24.1g of ferric nitrate nonahydrate were dissolved in 200ml of deionized water according to a 30% loading of iron molybdate; the carrier loaded with molybdenum oxide was dispersed in 800g of deionized water, and the prepared ammonium molybdate and ferric nitrate nonahydrate solutions were added dropwise in parallel under stirring conditions for 30 minutes, and the catalyst was aged at 80°C for 3 hours, filtered and washed, and dried at 120°C for 3 hours. After compression molding, the catalyst was calcined at 500°C for 4 hours to obtain a supported iron-molybdenum catalyst with a coated structure.

[0022] The transmission electron microscopy image of the catalyst prepared in this example is as follows Figure 1 As shown, from Figure 1 It can be seen that a layer of black particles is deposited on the surface of the catalyst; Figure 2 When the high-resolution transmission electron microscope was used to further magnify the surface of the catalyst particles for observation, it can be clearly seen that the black particles and other parts of the catalyst surface are covered with a large number of lattice fringes with a crystal plane spacing of 0.3242 nanometers. This is the (-2,2,4) crystal plane of iron molybdate, indicating that iron molybdate is deposited on the carrier surface in the form of particles and layers.

[0023] Examples 3 to 10 have the same preparation methods and steps as Example 1, and the changed materials, addition amounts and process parameters are listed in Table 1.

[0024] Comparative Example 1: 99.46 g of ammonium heptamolybdate tetrahydrate and 95.62 g of ferric nitrate nonahydrate are dissolved in 400 ml of deionized water to obtain an ammonium heptamolybdate solution and a ferric nitrate solution respectively; then the rotation speed is controlled at 100 r / min and the reaction temperature is 50° C., the ferric nitrate solution is added to the ammonium molybdate solution within half an hour to react, the mixture is stirred for 30 minutes and then aged for 3 hours, the precipitate is filtered, dried at 120° C. for 3 hours, pressed into shape, and calcined at 500° C. for 4 hours to obtain a co-precipitation catalyst.

[0025] Comparative Example 2: Dissolve 95.62 g of ferric nitrate nonahydrate in 50 g of deionized water, weigh out 81 g of molybdenum trioxide that has been dried at 120°C for 2 hours, and immerse it in the above ferric nitrate solution. After ultrasonic treatment for half an hour, dry it at 120°C for 3 hours, and calcine it at 500°C for 4 hours to obtain a carrier-free coated iron-molybdenum catalyst.

[0026] The catalytic activity of the catalysts obtained in the above-mentioned embodiments and comparative examples was evaluated. The catalyst activity evaluation was carried out in a fixed bed reactor using methanol as a probe molecule. The raw material methanol vapor was mixed with air to form a reaction gas. The molar content of methanol in the reaction gas was 10%, and the reaction gas space velocity was 12000h -1 , the reaction temperature is 280℃, and the reaction pressure is normal pressure. The aging stability of the catalyst is evaluated by heating the catalyst to 500℃ for 10h in a nitrogen atmosphere, and then introducing the reaction gas again at 280℃ to evaluate the catalyst activity. See Table 1 below.

[0027] Table 1 Composition, cost and performance of catalysts in various embodiments and comparative examples

[0028] Table 1 lists the differences in the preparation process of each embodiment and comparative example and the performance comparison of the catalyst. It should be noted that the raw material cost calculation basis in Table 1 is the market price of the raw materials when this application was filed. In addition, conversion rate × selectivity = yield. Because the data before and after aging are relatively large and complicated, the above table only lists the "yield" for comparison, so as to reflect the comprehensive effect.

[0029] As can be seen from the table, compared with the random blended structure prepared by the co-precipitation method in Comparative Example 1, the cost of the coated structure-supported iron-molybdenum catalyst for formaldehyde production provided in the present application is significantly reduced, and after high-temperature aging treatment, the formaldehyde yield is generally reduced less and has better stability. In Examples 1 to 3, as the loading amount of the inner layer molybdenum oxide increases, the formaldehyde yield first increases and then tends to stabilize; Examples 2, 4, and 5 compare the effect of the loading amount of the outer layer iron molybdate, and the formaldehyde yield first increases and then tends to stabilize as the loading amount of iron molybdate increases; Examples 2, 6, and 7 exemplify the effect of the carrier, and it can be seen that different carriers have slight differences in formaldehyde yields, but are all beneficial to enhancing the stability of the catalyst; Examples 2, 8, and 9 further compare the effect of calcination temperature on catalytic performance, and it can be seen that 500°C is more conducive to improving the formaldehyde yield; Comparative Example 2 has the same raw material cost as Comparative Example 1, but the prepared coating structure exhibits better stability; It can be seen from Example 5 and Comparative Example 2 that although the total molybdenum content in the catalyst is reduced, the stability of the catalyst is improved, indicating that the carrier silicon oxide and molybdenum oxide have a synergistic effect on each other, which improves the stability of the catalyst.

[0030] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A supported iron-molybdenum catalyst for formaldehyde production, characterized in that: The catalyst has a core-shell structure, wherein the core is a carrier, molybdenum trioxide is loaded on the carrier, and the shell is iron molybdate.

2. The supported iron-molybdenum catalyst for formaldehyde production according to claim 1, characterized in that The carrier is selected from at least one of silicon dioxide, aluminum oxide, titanium oxide, magnesium oxide, magnesium silicate, molecular sieve, white carbon black and hydroxyapatite.

3. The method for preparing a supported iron-molybdenum catalyst for formaldehyde production according to claim 1 or 2, characterized in that: The method comprises the following steps: firstly, loading molybdenum trioxide on a carrier, then dispersing the carrier in deionized water, dripping a molybdenum source and an iron source solution in parallel under stirring to deposit and load iron molybdate, and then aging, drying, molding and calcining to form a loaded iron-molybdenum catalyst with a coating structure.

4. The method according to claim 3, characterized in that: The molybdenum source for loading molybdenum trioxide and iron molybdate is selected from at least one of sodium molybdate, potassium molybdate, ammonium molybdate and molybdenum trioxide.

5. The method according to claim 3, characterized in that: The iron source for loading the iron molybdate is selected from at least one of ferric nitrate, ferrous nitrate, ferric chloride, ferrous chloride, ferrous sulfate and ferrous sulfate.

6. The method according to claim 3, characterized in that: The loaded molybdenum trioxide accounts for 2% to 80% of the weight of the carrier, and the loaded outer layer of iron molybdate accounts for 2% to 70% of the weight of the carrier.

7. The method according to claim 6, characterized in that The loaded molybdenum trioxide accounts for 30% to 80% of the weight of the carrier, and the loaded outer layer of iron molybdate accounts for 30% to 70% of the weight of the carrier.

8. The method according to claim 3, characterized in that The aging temperature is 10-90°C, the drying temperature is 90-150°C, and the calcining temperature is 300-600°C.

9. The method according to claim 8, characterized in that The calcination temperature is 500°C.

10. Use of the catalyst according to claim 1 or 2, characterized in that: The catalyst is used for oxidizing methanol, dimethyl ether and methylal to prepare formaldehyde.

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