A multi-metal oxide doped calcium molybdate-based catalyst for methanol oxidation to formaldehyde and a preparation method and application thereof

Abstract

The application belongs to the field of preparation and application of catalysts, and particularly relates to a multi-metal oxide doped calcium molybdate-based catalyst for methanol oxidation to formaldehyde as well as a preparation method and application thereof. The calcium molybdate-based catalyst doped with multiple metal oxides for methanol oxidation to formaldehyde is prepared, CaMoO4 with a mass ratio of more than 95% is used as an active center to reduce the reaction temperature of methanol oxidation to formaldehyde; the doped metal oxides can improve the conversion rate of raw methanol and the selectivity of the target product formaldehyde, and can also improve the catalyst structure, increase the specific surface area of the catalyst, improve the stability of the catalyst and prolong the service life of the catalyst.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of catalyst preparation, and particularly relates to a multi-metal oxide doped calcium molybdate-based catalyst for methanol oxidation to formaldehyde as well as a preparation method and application thereof. BACKGROUND

[0002] Formaldehyde (HCHO) is the simplest aldehyde, and has a very active chemical property due to the existence of carbonyl O atom and alpha-H atom in its structure. As an important organic chemical raw material and chemical intermediate, formaldehyde is widely used in the production of synthetic resin industry, and the production of medicine, wood processing, textile, papermaking, pesticide and other industries.

[0003] Formaldehyde can be produced from raw materials such as methanol, dimethyl ether and natural gas, among which the methanol-to-formaldehyde process is most widely used. China is a large methanol producer, and the selection of methanol as the raw material for the preparation of formaldehyde conforms to the resource reserves and market needs of China. The widely used methanol-to-formaldehyde method in industry can be divided into methanol oxidation dehydrogenation method (silver method), methanol simple dehydrogenation method and methanol simple oxidation method (iron-molybdenum method) and the like. Under the condition of excess air, the iron-molybdenum catalyst can catalyze the oxidation of methanol to generate formaldehyde, and compared with the traditional silver method, it has the advantages of mild reaction conditions, high product formaldehyde concentration and the like, and has better economic benefits and market prospects. The "silver method" refers to the process of preparing formaldehyde from methanol and air under the action of electrolytic silver or pumice silver catalyst; the "iron method" is to use metal oxides such as iron oxide-molybdenum oxide as catalyst. The method for preparing formaldehyde from methanol and air in a proportion lower than the lower limit of explosion is also called excess air method. Compared with the "silver method", the "iron method" has low reaction temperature (543-623K), small methanol consumption (420-437kg / t based on 37% formaldehyde), long service life of catalyst (1-2 years) and high formaldehyde product concentration (more than 55%). This process is widely used in modern formaldehyde production. Since the 1980s, the world's new and expanded formaldehyde plants have basically adopted the "iron method".

[0004] However, the "iron method" is reduced in activity in the presence of excess methanol, and part of the methanol is converted into undesirable by-products. In addition, a major drawback of this catalyst is that under reaction conditions, part of the molybdenum reacts with methanol to form volatile substances, deactivating the catalyst and causing the Mo in the reaction zone to decrease from the catalyst. Therefore, there is a broad market prospect for the preparation of new catalysts, and some studies on vanadium-based catalysts have been published, including pure vanadium, mixed oxides and supports, especially vanadates of different transition metal oxides, which have high selectivity (> 90%) at high methanol conversion. However, some people have also proposed multi-component catalysts or catalysts containing copper, zinc, vanadium, etc. In addition, the low activity and stability of these catalysts make them less suitable for industrial applications. Therefore, non-oxidative dehydrogenation of methanol provides a strategy for the production of HCHO, thereby possibly reducing methanol waste. In this case, some studies have also extensively studied bulk and supported transition metal oxides, including CuO, Ag2O and ZnO, however these catalysts are deactivated due to loss of oxygen after a few hours of reaction. In order to improve the competitiveness of China's formaldehyde industry, new types of catalysts that are efficient and competitive for the selective conversion of methanol to formaldehyde need to be continuously researched, the production capacity of formaldehyde plants needs to be expanded, the concentration of formaldehyde products needs to be improved, downstream products of formaldehyde need to be developed, and new technologies need to be used to reduce energy consumption. SUMMARY

[0005] The purpose of the present application is to develop a preparation method and application of a multi-metal oxide doped calcium molybdate-based catalyst for the oxidation of methanol to formaldehyde.

[0006] To achieve the above-mentioned purpose, the technical solution of the present application is:

[0007] The present application provides a multi-metal oxide doped calcium molybdate-based catalyst for the oxidation of methanol to formaldehyde, wherein the mass percentage of calcium molybdate is 95-99%; the metal ions in the multi-metal oxide include Al ions and two or more other metal ions, wherein the two or more other metal ions are selected from Mg, Cu, Ba, K, Sr and Na ions.

[0008] Further, the metal ions in the multi-metal oxide include Al, Mg, Ba, Cu, Sr, Na, K ions, and the molar ratio is 0.75-0.80:1.20-1.25:0.35-0.40:0.60-0.65:1.90-2.0:0.40-0.45:0.25-0.30.

[0009] The present application also provides a preparation method of a multi-metal oxide doped CaMoO4-XO (X = Al, Mg, Cu, Ba, K, Sr, Na) catalyst for the oxidation of methanol to formaldehyde, the steps are as follows:

[0010] (1) A certain amount of ammonium molybdate is dissolved in deionized water, stirred uniformly, and adjusted to pH = 9-11 with an aqueous ammonium hydroxide solution to obtain solution A. A soluble metal salt and a certain amount of calcium nitrate are dissolved in deionized water, stirred uniformly, to obtain solution B. The aqueous ammonium hydroxide solution is prepared by mixing ammonium hydroxide and deionized water in a volume ratio of 1:1.

[0011] wherein the metal ions in the soluble metal salt are one or more of Al, Mg, Cu, Ba, K, Sr, and Na, n(Mo):n(Ca) = 1:1, and the mass ratio of the total mass of the metal in the metal salt to the mass of the theoretical yield of CaMoO4 is 0.03-0.50:9-9.5; preferably, the mass ratio is 0.3-0.4:9-9.5.

[0012] Further, the molar ratio of the metal ions Mg, Al, Ba, Cu, Sr, Na, and K is 1.20-1.25:0.75-0.80:0.35-0.40:0.60-0.65:1.90-2.0:0.40-0.45:0.25-0.30.

[0013] (2) Under constant temperature water bath conditions, solution B is added dropwise to solution A, stirring continues for 2-4 h, and 80-100℃ water bath evaporation is performed until the upper clear liquid disappears, and the precursor of the multiple metal-doped calcium molybdate-based catalyst is prepared by drying in an oven.

[0014] wherein the constant temperature water bath temperature is 50-60℃, the drying temperature is 30-120℃, and the drying time is 10-48 h.

[0015] (3) The catalyst precursor obtained in step (2) is calcined in a muffle furnace at a certain temperature to obtain a CaMoO4-XO catalyst.

[0016] wherein the calcination temperature is 400-800℃, and the calcination time is 3-6 h.

[0017] The application is: 0.2 g of the catalyst is loaded into a fixed bed reactor, anhydrous methanol solution is added, air is introduced for reaction, the gas flow rate is 50 mL / min, the reaction temperature is 260-360℃, the pressure is 0.1-2 MPa, and after the reaction, online chromatography is performed for analysis.

[0018] wherein the volume flow rate of the anhydrous methanol is 0.3 mL / min.

[0019] Compared with existing technologies, the beneficial effects of this invention are as follows: CaMoO4 is the reactive component, promoting the oxidative dehydrogenation of methanol to formaldehyde, improving the conversion rate of raw materials and the selectivity of products; the doped metals can increase the activity of the catalyst, reduce the reaction temperature, and save energy and protect the environment. The doped metals of this invention, such as Al and Mg, can improve the structure of the catalyst, provide more reactive sites, increase the thermal stability of the catalyst, and increase the specific surface area of ​​the catalyst, which is beneficial to improving the activity of the catalyst; the doped metals, such as Sr, can promote the dehydrogenation of methanol, improving the conversion rate of raw material methanol; the doped metals, such as Cu and Ba, can improve the selectivity of the catalyst for the target product formaldehyde, thereby resulting in a high formaldehyde concentration and a low methanol concentration in the produced product; the doped metals, such as K and Na, can prevent the catalyst from sintering during high-temperature dehydrogenation, while preventing excessive oxidation of methanol to CO2, improving the catalyst activity and extending the catalyst's service life. Attached Figure Description

[0020] Figure 1 This is the XRD characterization diagram of the catalyst prepared in Example 1.

[0021] Figure 2 These are SEM characterization images of the catalyst prepared in Example 1; (a)×30000, (b)×10000.

[0022] Figure 3 This is a comparison chart of the methanol conversion rates of Example 1 and the industrial catalyst under reaction conditions at various temperature points.

[0023] Figure 4 This is a comparison chart of the selectivity of formaldehyde between Example 1 and the industrial catalyst under reaction conditions at various temperature points. Detailed Implementation

[0024] The present invention will be further described below with reference to embodiments, but is not limited thereto.

[0025] Example 1

[0026] (1) 8.39g of (NH4)6Mo7O 24 Dissolve 4H₂O in 50 mL of deionized water, stir well, and adjust the pH to 10 with a 1:1 ammonium hydroxide aqueous solution to obtain solution A. Dissolve 0.32 g Mg(NO₃)₂·6H₂O, 0.29 g Al(NO₃)₃·9H₂O, 0.10 g Ba(NO₃)₂, 0.15 g Cu(NO₃)₂·3H₂O, 0.41 g Sr(NO₃)₂, 0.03 g NaNO₂, 0.03 g KNO₃, and 11.22 g Ca(NO₃)₂·4H₂O in 50 mL of deionized water, stir well, and obtain solution B.

[0027] (2) 60℃ constant temperature water bath conditions, the solution B is added to the solution A, continue to stir 2h, 90℃ water bath evaporation to the upper layer of clear liquid disappear, placed in the oven at 120℃ drying 12h, preparation of doped with multiple metal calcium molybdate catalyst precursor.

[0028] (3) CaMoO4-XO catalyst precursor is placed in the muffle furnace at 500℃ calcination 3h, CaMoO4-XO catalyst is obtained.

[0029] (4) 0.2g catalyst is loaded into the fixed bed reactor, and the volume flow rate of 0.3ml / min anhydrous methanol solution is added, and air is introduced for reaction, the gas flow rate is 50ml / min, the reaction temperature is 280℃, the pressure is 0.1MPa, and after reaction, online chromatography is used for analysis.

[0030] Example 2

[0031] (1) 8.39g (NH4) 6Mo7O 24 ·4H2O is dissolved in 50mL deionized water, and stirred uniformly to obtain solution A. 0.32g Mg(NO3)2·6H2O, 0.29g Al(NO3)3·9H2O, 0.10g Ba(NO3)2, 0.15g Cu(NO3)2·3H2O, 0.41g Sr(NO3)2, 0.03g NaNO2, 0.03g KNO3 and 11.22g Ca(NO3)2·4H2O are dissolved in 50mL deionized water, and stirred uniformly to obtain solution B.

[0032] (2) The above A, B solutions are transferred to a polytetrafluoroethylene lined high-pressure reactor, and reacted at 160℃ for 24h. After the reaction is completed, the product is collected by centrifugation, and washed with water for 5 times, and transferred to an oven for drying at 70℃ for 12h,

[0033] (3) CaMoO4-XO catalyst precursor is placed in the muffle furnace at 500℃ calcination 3h, CaMoO4-XO catalyst is obtained.

[0034] (4) 0.2g catalyst is loaded into the fixed bed reactor, and the volume flow rate of 0.3mL / min anhydrous methanol solution is added, and air is introduced for reaction, the gas flow rate is 50mL / min, the reaction temperature is 320℃, the pressure is 0.1MPa, and after reaction, online chromatography is used for analysis.

[0035] Example 3

[0036] Compared with example 1, the raw materials in step (1) are changed, and Mg, Ba and Sr metal salts are not used, and the remaining operations are the same as those in example 1.

[0037] Example 4

[0038] Compared with Example 1, the raw material in step (1) was changed, Cu, Sr, Na, K metal salt was not used, and the rest of the operation was the same as Example 1.

[0039] Example 5

[0040] Compared with Example 1, the calcination temperature in step (3) was changed to 900℃, and the calcination time was 10h, and the rest of the operation was the same as Example 1.

[0041] Comparative Example 1

[0042] Compared with Example 1, the difference is that in step (1), calcium nitrate is replaced by manganese nitrate of the same amount of substance, and the other steps are the same as Example 1.

[0043] Comparative Example 2

[0044] Compared with Example 1, the difference is that in step (1), calcium nitrate is replaced by bismuth subnitrate of the same amount of substance, and the other steps are the same as Example 1.

[0045] Comparative Example 3

[0046] Compared with Example 1, the difference is that in step (1), ammonium molybdate is replaced by ammonium metatungstate of the same amount of substance, and the other steps are the same as Example 1.

[0047] Comparative Example 4

[0048] Compared with Example 1, the difference is that in step (1), ammonium molybdate is replaced by ammonium chromate of the same amount of substance, and the other steps are the same as Example 1.

[0049] Comparative Example 5

[0050] Compared with Example 1, the difference is that in step (1), ammonium molybdate is not added, and the other steps are the same as Example 1.

[0051] The data after the reaction in the examples and comparative examples were analyzed, and the results are shown in Table 1:

[0052] Table 1. Comparison of methanol conversion and formaldehyde selectivity in examples and comparative examples

[0053] Methanol conversion, % Formaldehyde selectivity, % Example 1 98.2 99.7 Example 2 94.7 96.6 Example 3 88.9 82.1 Example 4 75.3 84.5 Example 5 68.3 74.6 Comparative Example 1 50.9 60.9 Comparative Example 2 45.0 48.3 Comparative Example 3 32.2 40.9 Comparative Example 4 33.8 36.4 Comparative Example 5 20.2 27.6

[0054] The CaMoO4-XO catalyst prepared in Example 1 was characterized by X-ray diffraction, transmission electron microscopy and X-ray fluorescence spectrometer. The results are shown in Figure 1 、 Figure 2 and Table 2.

[0055] Table 2. XRF characterization of CaMoO4-XO catalyst prepared in Example 1

[0056]

[0057] The application also compares the catalyst prepared in Example 1 with the industrial catalyst (iron molybdate) in the preparation of formaldehyde by oxidation of methanol at different temperatures. Figure 3 is a comparison chart of the conversion rate of methanol at each temperature point under the reaction conditions of Example 1 and the industrial catalyst. Figure 4 is a comparison chart of the selectivity of formaldehyde at each temperature point under the reaction conditions of Example 1 and the industrial catalyst.

[0058] The doped multi-metal calcium molybdate-based catalyst of the application has high conversion rate and selectivity for the preparation of formaldehyde by oxidation of methanol, simplifies the reaction steps of the preparation of formaldehyde by oxidation of methanol, requires simple equipment, and produces a product with high formaldehyde concentration and low methanol concentration, greatly saving the power consumption and equipment consumables in the concentration process of formaldehyde, also saving the cost of methanol treatment in wastewater, reducing the industrial production cost and being environmentally friendly, which has important significance for environmental improvement. The doped multi-metal calcium molybdate-based catalyst for the preparation of formaldehyde by oxidation of methanol prepared by the application can catalyze the oxidation dehydrogenation of methanol with CaMoO4 as the active center, reduce the reaction temperature of the preparation of formaldehyde by oxidation of methanol, prolong the service life of the catalyst, and is not sensitive to poisons; the doped metals improve the conversion rate of raw methanol and the selectivity of the target product formaldehyde, and can also improve the catalyst structure, increase the specific surface area of the catalyst, and thus improve the stability of the catalyst. The doped multi-metal calcium molybdate-based catalyst of the application will not sinter in the high-temperature dehydrogenation process, improves the catalyst activity, prolongs the service life of the catalyst, has high conversion rate and selectivity for the preparation of formaldehyde by oxidation of methanol, and produces a product with high formaldehyde concentration and low methanol concentration. The reaction process of the application simplifies the reaction steps, requires simple equipment, greatly saves the power consumption and equipment consumables in the concentration process of formaldehyde, also saves the cost of methanol treatment in wastewater, reduces the industrial production cost and is environmentally friendly, which has important significance for environmental improvement. The catalyst preparation method of the application is simple, the catalyst has low cost, high stability and long service life, and exhibits excellent catalytic activity and selectivity in the preparation of formaldehyde by oxidation of methanol, which has great competitive advantage.

[0059] The above embodiments are preferred embodiments of the application, but the application is not limited to the above embodiments, and any obvious improvements, replacements or modifications made by those skilled in the art without departing from the essential content of the application shall fall within the protection scope of the application.

Claims

1. Use of a multi-metal oxide doped calcium molybdate based catalyst for the oxidation of methanol to formaldehyde, characterized in that, The specific application method is: the multi-metal oxide doped calcium molybdate-based catalyst is loaded into a fixed bed reactor, anhydrous methanol is added, and air is introduced for reaction, the gas flow is 50 mL / min, the reaction temperature is 260-360 DEG C, and the pressure is 0.1-2 MPa; the mass percentage of calcium molybdate in the multi-metal oxide doped calcium molybdate-based catalyst is 95-99%; the metal ions in the multi-metal oxide include Al, Mg, Ba, Cu, Sr, Na, K ions, and the molar ratio is 0.75-0.80:1.20-1.25:0.35-0.40:0.60-0.65:1.90-2.0:0.40-0.45:0.25-0.

30.

2. Use according to claim 1, characterized in that, The preparation method of the multi-metal oxide doped calcium molybdate-based catalyst comprises the following steps: (1) the ammonium molybdate is dissolved in deionized water, stirred uniformly, and the pH is adjusted to 9-11 with an ammonium hydroxide solution to obtain solution A; the soluble metal salt and calcium nitrate are dissolved in deionized water and stirred uniformly to obtain solution B; wherein the molar ratio of molybdenum ions to calcium ions is 1:1; (2) under the condition of constant temperature water bath at 50-60 DEG C, solution B is added to solution A, and stirring is continued for 2-4 h, and the upper clear liquid disappears after water bath reaction at 80-100 DEG C, and the catalyst precursor of the multi-metal doped calcium molybdate is prepared by drying in an oven; (3) the catalyst precursor prepared in step (2) is calcined to obtain the multi-metal oxide doped calcium molybdate-based catalyst.

3. Use according to claim 2, characterized in that, The mass ratio of the total mass of metal ions in the metal salt to the mass of the theoretical yield of calcium molybdate is 0.03-0.5:9-9.

5.

4. Use according to claim 2, characterized in that, The drying temperature in step (2) is 30-120 DEG C, and the drying time is 10-48 h.

5. Use according to claim 2, characterized in that, The calcination temperature in step (3) is 400-800 DEG C, and the calcination time is 3-6 h.

6. Use according to claim 1, characterized in that, The amount of the multi-metal oxide doped calcium molybdate-based catalyst is 0.2 g, and the volume flow rate of anhydrous methanol is 0.3 mL / min.

Images