A process for the oxidation of dimethyl ether to formaldehyde

Abstract

The present application relates to a kind of dimethyl ether oxidation method for preparing formaldehyde.The method uses dimethyl ether as reactant, under the catalysis of iron-vanadium-based composite element oxide catalyst, nitrogen-oxygen mixed gas as oxidant, and high-concentration formaldehyde is prepared by oxidation reaction.The reaction conditions are as follows:the reaction is carried out in a fixed bed reactor under normal pressure, the reaction temperature is 150 DEG C-430 DEG C, the volume space velocity is 2500-10000 h ‑1 The method is characterized as follows:the main active component of iron-vanadium-based composite element oxide catalyst is iron-vanadium metal oxide, doped with one or more element oxides, used for dimethyl ether oxidation to prepare formaldehyde, the dimethyl ether conversion rate can reach 92%, the formaldehyde selectivity is as high as 88%, the catalyst activity is better, and it has better stability, which has significant advantages in industrial production.

Description

Technical Field

[0001] This invention belongs to the field of ether oxidation to formaldehyde technology, specifically relating to a method for oxidizing dimethyl ether to formaldehyde. Background Technology

[0002] Formaldehyde is a colorless gas with a strong, pungent odor. It is readily soluble in water and alcohols; a 37% aqueous solution is known as formalin. Formaldehyde is an important organic chemical raw material, widely used in various fields such as resin synthesis, pharmaceutical synthesis, pesticide synthesis, textile industry, electronics industry, adhesives, and the synthesis of important organic intermediates. With the rapid development of the automotive and construction industries, formaldehyde has become a high-growth consumer product. In conclusion, due to its diverse uses and low price, formaldehyde occupies an important position in the chemical industry.

[0003] The main production routes for industrial formaldehyde include methanol oxidation, methane oxidation, methyl acetal oxidation, and dimethyl ether oxidation. Methanol oxidation is the mainstream process for formaldehyde production, accounting for over 90% of global formaldehyde production. Methanol oxidation mainly includes two methods: the iron-molybdenum method and the silver method. The silver method uses silver as a catalyst and has advantages such as high reaction temperature, high formaldehyde yield, and good product quality, but the catalyst cost is high. The iron-molybdenum method uses iron-molybdenum oxide as a catalyst and has advantages such as low reaction temperature and low catalyst cost, but the formaldehyde yield is relatively low. Dimethyl ether is a generally environmentally friendly molecule with physical properties similar to LPG (liquefied petroleum gas). It can be transported within existing LPG infrastructure and has the potential to be a new clean alternative fuel. The catalytic oxidation of dimethyl ether to synthesize the high-value-added chemical formaldehyde has the advantage of good atom economy, meaning high raw material utilization, fewer by-products, and lower carbon emissions, which is beneficial to environmental protection. Patent CN103896749A discloses a method for preparing formaldehyde and co-producing methyl acetal, characterized in that a feed gas containing dimethyl ether and oxygen is passed through a reactor carrying a biphasic catalyst, and the reaction is carried out at a reaction temperature of 250–400°C, a reaction pressure of 0.1–0.5 MPa, and a reaction volume hourly space velocity of 1000–10000 h⁻¹. -1 The process involves the production of formaldehyde and the co-production of methylal. Patent CN117772219A discloses a multi-metal oxide-doped calcium molybdate-based catalyst for the methanol oxidation to formaldehyde, its preparation method, and its application. Using CaMoO4 with a mass ratio of over 95% as the active center lowers the reaction temperature for methanol oxidation to formaldehyde. The doped metal oxides can improve the conversion rate of the raw material methanol and the selectivity of the target product formaldehyde. Simultaneously, they can improve the catalyst structure, increase the specific surface area of ​​the catalyst, enhance the stability of the catalyst, and extend the catalyst lifespan.

[0004] Although the mainstream method for formaldehyde preparation is currently methanol oxidation, research on dimethyl ether oxidation to formaldehyde is relatively limited. However, the theoretical maximum formaldehyde concentration obtained via the dimethyl ether route can be further increased from 62.5% to 76.9%, demonstrating high practical application value. Furthermore, it produces low byproducts and is environmentally friendly. Therefore, developing a solid catalyst system for the dimethyl ether oxidation to formaldehyde that is economical, stable, highly reactive, and exhibits good selectivity is of great significance. Summary of the Invention

[0005] The purpose of this invention is to provide a highly efficient and stable method for the oxidation of dimethyl ether to formaldehyde. This method involves a simple reaction process, uses a non-toxic catalyst with high selectivity for formaldehyde, exhibits good stability and a long lifespan, and is cost-effective.

[0006] The formaldehyde involved in this invention is prepared by the following method.

[0007] Using dimethyl ether as a raw material, the reaction is carried out in a fixed-bed reactor. A nitrogen-oxygen mixture (oxygen volume concentration of 3%-18%) is introduced as the oxidant under the action of an iron-vanadium-based composite element oxide catalyst. The dimethyl ether feed volume concentration is 0.5%-8%, the reaction temperature is 150℃-430℃, the catalyst packing height in the fixed bed is 7mm-27mm, the reaction is carried out at atmospheric pressure, and the dimethyl ether is fed into the system controlled by a flow meter to initiate the reaction. The reaction volume hourly space velocity is 2500-10000 h⁻¹. -1 The iron-vanadium-based composite element oxide catalyst is composed of active metallic iron, vanadium, and composite elements, wherein the composite elements are one or more of Cu, Co, Si, Sn, Bi, Mn, Al, Zr, Sm, and W. The catalyst is prepared and synthesized by one or more of the following methods: co-precipitation, solid-phase ball milling, impregnation, and sol-gel method. The precursor of the active component metallic iron is one or more of Fe(NO3)3, FeCl3, Fe2(SO4)3, FePO4, Fe2O3, and Fe(C2H3O2)2; the precursor of the active component metallic vanadium is one or more of VCl3, NH4VO3, V2O3, V2O5, F4V, VC, S3V2, VOSO4, VCl3, NV, and VOC2O4. The precursor of the composite element is one or more of the corresponding element's nitrate, chloride, sulfate, phosphate, oxide, citrate, stearate, and acetate. The catalyst contains 5 wt% to 60 wt% (by weight of oxide) of active metal iron, 10 wt% to 90 wt% (by weight of oxide) of active metal vanadium, and the remainder is oxide of composite elements.

[0008] The iron-vanadium-based composite element oxide catalyst for the oxidation of dimethyl ether to formaldehyde has the following characteristics: (1) The strong interaction between iron-vanadium and composite element oxide greatly enhances the redox properties of the catalyst, which helps to activate CH bonds, resulting in strong catalyst activity and further promoting the reaction. (2) The doping of composite elements enhances the interaction between the catalyst and the catalyst. DME is easily dissociated to form highly active species that can quickly react with the lattice oxygen on the catalyst surface, reducing the loss of active components and thus improving the lifetime stability of the catalyst.

[0009] The advantages of this method are: (1) The iron-vanadium based composite element oxide catalyst has a long service life and good stability, which reduces the frequency and cost of catalyst replacement. (2) Compared with some other precious metal catalysts, iron and vanadium have lower costs, which makes it more economically attractive.

[0010] Iron-vanadium-based composite element oxide catalysts are used in the oxidation of dimethyl ether to formaldehyde. The conversion rate of dimethyl ether can reach 92%, and the selectivity of formaldehyde is as high as 88%. The catalysts have good activity and good stability, which has significant advantages in industrial production. Detailed Implementation

[0011] To provide a more detailed description of the present invention, several specific implementation examples are given below, but the present invention is not limited to these embodiments.

[0012] After the iron-vanadium-based composite element oxide catalyst is prepared, it is directly extruded, granulated, sieved, and then packed into a fixed-bed reactor to carry out the dimethyl ether oxidation to formaldehyde reaction. The resulting reaction products are analyzed and calculated.

[0013] Example 1

[0014] The catalyst for the oxidation of dimethyl ether to formaldehyde was prepared by solid-phase ball milling. The specific operation process is as follows: 1.07 g of Fe2O3, 2.67 g of V2O5, and 1.60 g of Bi2O3 were weighed and added to a ball mill jar. Then, milling beads were added, and the mixture was placed in a planetary ball mill at 500 r / min in one direction for 2 hours. The sample was then removed and calcined in a muffle furnace at 400℃ for 4 hours to obtain a catalyst of 20 wt% Fe2O3-50 wt% V2O5-30 wt% Bi2O3. The catalyst was directly extruded and granulated, sieved to a 40-60 mesh, and 0.9 mL was loaded into a fixed-bed reactor to a height of 15 mm. The reaction temperature was 295℃. The reaction was initiated under atmospheric pressure by simultaneously introducing a DME / O2 / N2 mixed gas. The volume concentration of dimethyl ether was 3%, the volume concentration of oxygen was 10%, and the volume hourly space velocity (VHSV) was 4500 h⁻¹. -1 After 2 hours of reaction, gas and liquid samples were taken and analyzed separately. The conversion rate of dimethyl ether was 91%, and the selectivity of formaldehyde was 86%. After 3000 hours of stable operation, the conversion rate of dimethyl ether was 88%, and the selectivity of formaldehyde was 86%.

[0015] Example 2

[0016] The catalyst for the oxidation of dimethyl ether to formaldehyde was prepared by impregnation. The specific operation process is as follows: 5.39 g of Fe(NO3)3·9H2O and 3.33 g of Bi(NO3)3·5H2O were weighed and dissolved in 100 mL of water. Then, 2.67 g of vanadium oxide was weighed and added to the solution. The mixture was stirred and dried in an 80℃ water bath. The resulting solid was then calcined in a muffle furnace at 400℃ for 4 hours to obtain a catalyst of 20wt% Fe2O3-50wt% V2O5-30wt% Bi2O3. The catalyst was directly extruded and granulated, sieved to a 40-60 mesh, and 0.9 mL was packed into a fixed-bed reactor to a height of 15 mm. The reaction temperature was 295℃. The reaction was initiated under normal pressure by simultaneously introducing a DME / O2 / N2 mixed gas. The volume concentration of dimethyl ether was 3%, the volume concentration of oxygen was 10%, and the volume hourly space velocity was 4500 h⁻¹. -1 After 2 hours of reaction, gas and liquid samples were taken for analysis. The conversion rate of dimethyl ether was 83%, and the selectivity of formaldehyde was 82%.

[0017] Example 3

[0018] The catalyst for the oxidation of dimethyl ether to formaldehyde was prepared using the sol-gel method. The specific operation process is as follows: 5.39 g of Fe(NO3)3·9H2O, 3.43 g of NH4VO3, and 3.33 g of Bi(NO3)3·5H2O were weighed and dissolved in 100 mL of water. Citric acid solution (the concentration of citric acid and total metal ions was 0.25 mol / L) was added, and the mixture was stirred evenly. The solution was evaporated in a water bath at 70 °C to obtain a transparent sol. After drying at 100 °C for 12 h, a dry gel was obtained. The gel was then calcined in a muffle furnace at 400 °C for 10 h to obtain a catalyst of 20 wt% Fe2O3-50 wt% V2O5-30 wt% Bi2O3. The catalyst was directly extruded and granulated, sieved to a mesh size of 40-60, and 0.9 mL was packed into a fixed-bed reactor to a height of 15 mm. The reaction temperature was 295 °C. The reaction begins under normal pressure by simultaneously introducing a DME / O2 / N2 mixture, with a dimethyl ether volume concentration of 3%, an oxygen volume concentration of 10%, and a volume hourly space velocity (VHSV) of 4500 h⁻¹. -1 After 2 hours of reaction, gas and liquid samples were taken for analysis. The conversion rate of dimethyl ether was 84%, and the selectivity of formaldehyde was 78%.

[0019] Example 4

[0020] The catalyst for the oxidation of dimethyl ether to formaldehyde was prepared by a co-precipitation method. The specific operation process is as follows: 5.39 g of Fe(NO3)3·9H2O, 3.43 g of NH4VO3, and 3.33 g of Bi(NO3)3·5H2O were weighed and dissolved in 100 mL of water. The pH of the solution was adjusted to 10 with a 10% ammonia solution. The mixture was filtered to obtain a solid, dried, and then calcined in a muffle furnace at 400℃ for 10 h to obtain a catalyst of 20 wt% Fe2O3-50 wt% V2O5-30 wt% Bi2O3. The catalyst was directly extruded and granulated, sieved to 40-60 mesh, and 0.9 mL was packed into a fixed-bed reactor to a height of 15 mm. The reaction temperature was 295℃. The reaction was initiated under normal pressure by simultaneously introducing a DME / O2 / N2 mixed gas. The volume concentration of dimethyl ether was 3%, the volume concentration of oxygen was 10%, and the volume hourly space velocity was 4500 h⁻¹. -1 After 2 hours of reaction, gas and liquid samples were taken and analyzed separately. The conversion rate of dimethyl ether was 92%, and the selectivity of formaldehyde was 88%. After 3000 hours of stable operation, the conversion rate of dimethyl ether was 89%, and the selectivity of formaldehyde was 87%.

[0021] Example 5

[0022] The catalyst for the oxidation of dimethyl ether to formaldehyde was prepared by a co-precipitation method. The specific operation process is as follows: 5.39 g of Fe(NO3)3·9H2O, 3.43 g of NH4VO3, and 4.86 g of Cu(NO3)2·3H2O were weighed and dissolved in 100 mL of water. The pH of the solution was adjusted to 10 with a 10% ammonia solution. The mixture was filtered to obtain a solid, dried, and then calcined in a muffle furnace at 400℃ for 10 h to obtain a catalyst of 20 wt% Fe2O3-50 wt% V2O5-30 wt% CuO. The catalyst was directly extruded and granulated, sieved to 40-60 mesh, and 0.9 mL was packed into a fixed-bed reactor to a height of 15 mm. The reaction temperature was 295℃. The reaction was initiated under normal pressure by simultaneously introducing a DME / O2 / N2 mixed gas. The volume concentration of dimethyl ether was 3%, the volume concentration of oxygen was 10%, and the volume hourly space velocity was 4500 h⁻¹. -1 After 2 hours of reaction, gas and liquid samples were taken for analysis. The conversion rate of dimethyl ether was 81%, and the selectivity of formaldehyde was 83%.

[0023] Example 6

[0024] The catalyst for the oxidation of dimethyl ether to formaldehyde was prepared by a co-precipitation method. The specific operation process is as follows: 5.39 g of Fe(NO3)3·9H2O, 3.43 g of NH4VO3, and 6.23 g of Co(NO3)2·6H2O were weighed and dissolved in 100 mL of water. The pH of the solution was adjusted to 10 with a 10% ammonia solution. The mixture was filtered to obtain a solid, dried, and then calcined in a muffle furnace at 400℃ for 10 h to obtain a catalyst of 20 wt% Fe2O3-50 wt% V2O5-30 wt% CoO. The catalyst was directly extruded and granulated, sieved to 40-60 mesh, and 0.9 mL was packed into a fixed-bed reactor to a height of 15 mm. The reaction temperature was 295℃. The reaction was initiated under normal pressure by simultaneously introducing a DME / O2 / N2 mixed gas. The volume concentration of dimethyl ether was 3%, the volume concentration of oxygen was 10%, and the volume hourly space velocity was 4500 h⁻¹. -1 After 2 hours of reaction, gas and liquid samples were taken for analysis. The conversion rate of dimethyl ether was 83%, and the selectivity of formaldehyde was 80%.

[0025] Example 7

[0026] The catalyst for the oxidation of dimethyl ether to formaldehyde was prepared using the sol-gel method. The specific operation process is as follows: 5.39 g of Fe(NO3)3·9H2O, 3.43 g of NH4VO3, and 8.02 g of 20% silica sol were weighed and dissolved in 100 mL of water. Citric acid solution (the concentration of citric acid and total metal ions were both 0.25 mol / L) was added, and the mixture was stirred evenly. After evaporation in a water bath at 70℃, a transparent sol was obtained. After drying at 100℃ for 12 h, a dry gel was obtained. The gel was then calcined in a muffle furnace at 400℃ for 10 h to obtain a catalyst of 20 wt% Fe2O3-50 wt% V2O5-30 wt% SiO2. The catalyst was directly extruded and granulated, sieved to a mesh size of 40-60, and 0.9 mL was packed into a fixed-bed reactor to a height of 15 mm. The reaction temperature was 295℃. The reaction begins under normal pressure by simultaneously introducing a DME / O2 / N2 mixture, with a dimethyl ether volume concentration of 3%, an oxygen volume concentration of 10%, and a volume hourly space velocity (VHSV) of 4500 h⁻¹. -1 After 2 hours of reaction, gas and liquid samples were taken for analysis. The conversion rate of dimethyl ether was 88%, and the selectivity of formaldehyde was 86%.

[0027] Example 8

[0028] The catalyst for the oxidation of dimethyl ether to formaldehyde was prepared by a co-precipitation method. The specific operation process is as follows: 5.39 g of Fe(NO3)3·9H2O, 3.43 g of NH4VO3, and 2.52 g of Sn(CH3CO2)2 were weighed and dissolved in 100 mL of water. The pH of the solution was adjusted to 10 with a 10% ammonia solution. The mixture was filtered to obtain a solid, dried, and then calcined in a muffle furnace at 400℃ for 10 h to obtain a catalyst of 20 wt% Fe2O3-50 wt% V2O5-30 wt% SnO2. The catalyst was directly extruded and granulated, sieved to 40-60 mesh, and 0.9 mL was packed into a fixed-bed reactor to a height of 15 mm. The reaction temperature was 295℃. The reaction was initiated under normal pressure by simultaneously introducing a DME / O2 / N2 mixed gas. The volume concentration of dimethyl ether was 3%, the volume concentration of oxygen was 10%, and the volume hourly space velocity was 4500 h⁻¹. -1 After 2 hours of reaction, gas and liquid samples were taken for analysis. The conversion rate of dimethyl ether was 87%, and the selectivity of formaldehyde was 86%.

[0029] Example 9

[0030] The catalyst for the oxidation of dimethyl ether to formaldehyde was prepared by a co-precipitation method. The specific operation process is as follows: 5.39 g of Fe(NO3)3·9H2O, 3.43 g of NH4VO3, and 5.66 g of Mn(NO3)2·4H2O were weighed and dissolved in 100 mL of water. The pH of the solution was adjusted to 10 with a 10% ammonia solution. The mixture was filtered to obtain a solid, dried, and then calcined in a muffle furnace at 400℃ for 10 h to obtain a catalyst of 20 wt% Fe2O3-50 wt% V2O5-30 wt% MnO. The catalyst was directly extruded and granulated, sieved to 40-60 mesh, and 0.9 mL was packed into a fixed-bed reactor to a height of 15 mm. The reaction temperature was 295℃. The reaction was initiated under normal pressure by simultaneously introducing a DME / O2 / N2 mixed gas. The volume concentration of dimethyl ether was 3%, the volume concentration of oxygen was 10%, and the volume hourly space velocity was 4500 h⁻¹. -1 After 2 hours of reaction, gas and liquid samples were taken for analysis. The conversion rate of dimethyl ether was 81%, and the selectivity of formaldehyde was 84%.

[0031] Example 10

[0032] The catalyst for the oxidation of dimethyl ether to formaldehyde was prepared by a co-precipitation method. The specific operation process is as follows: 5.39 g of Fe(NO3)3·9H2O, 3.043 g of NH4VO3, and 11.81 g of Al(NO3)3·9H2O were weighed and dissolved in 100 mL of water. The pH of the solution was adjusted to 10 with a 10% ammonia solution. The mixture was filtered to obtain a solid, dried, and then calcined in a muffle furnace at 400℃ for 10 h to obtain a catalyst of 20 wt% Fe2O3-50 wt% V2O5-30 wt% AlO3. The catalyst was directly extruded and granulated, sieved to 40-60 mesh, and 0.9 mL was packed into a fixed-bed reactor to a height of 15 mm. The reaction temperature was 295℃. The reaction was initiated under normal pressure by simultaneously introducing a DME / O2 / N2 mixed gas. The volume concentration of dimethyl ether was 3%, the volume concentration of oxygen was 10%, and the volume hourly space velocity was 4500 h⁻¹. -1 After 2 hours of reaction, gas and liquid samples were taken for analysis. The conversion rate of dimethyl ether was 85%, and the selectivity of formaldehyde was 81%.

[0033] Example 11

[0034] The catalyst for the oxidation of dimethyl ether to formaldehyde was prepared by a co-precipitation method. The specific operation process is as follows: 5.39 g of Fe(NO3)3·9H2O, 3.43 g of NH4VO3, and 5.59 g of Zr(NO3)4·5H2O were weighed and dissolved in 100 mL of water. The pH of the solution was adjusted to 10 with a 10% ammonia solution. The mixture was filtered to obtain a solid, dried, and then calcined in a muffle furnace at 400℃ for 10 h to obtain a catalyst of 20 wt% Fe2O3-50 wt% V2O5-30 wt% ZrO2. The catalyst was directly extruded and granulated, sieved to 40-60 mesh, and 0.9 mL was packed into a fixed-bed reactor to a height of 15 mm. The reaction temperature was 295℃. The reaction was initiated under normal pressure by simultaneously introducing a DME / O2 / N2 mixed gas. The volume concentration of dimethyl ether was 3%, the volume concentration of oxygen was 10%, and the volume hourly space velocity was 4500 h⁻¹. -1 After 2 hours of reaction, gas and liquid samples were taken for analysis. The conversion rate of dimethyl ether was 81%, and the selectivity of formaldehyde was 79%.

[0035] Example 12

[0036] The catalyst for the oxidation of dimethyl ether to formaldehyde was prepared by a co-precipitation method. The specific operation process is as follows: 5.39 g of Fe(NO3)3·9H2O, 3.43 g of NH4VO3, and 4.08 g of Sm(NO3)3·6H2O were weighed and dissolved in 100 mL of water. The pH of the solution was adjusted to 10 with a 10% ammonia solution. The mixture was filtered to obtain a solid, which was then dried and calcined in a muffle furnace at 400℃ for 10 h to obtain a catalyst of 20 wt% Fe2O3-50 wt% V2O5-30 wt% Sm2O3. The catalyst was directly extruded and granulated, sieved to a 40-60 mesh, and 0.9 mL was filled into a fixed-bed reactor to a packing height of 15 mm. The reaction temperature was 295℃. The reaction was initiated under normal pressure by simultaneously introducing a DME / O2 / N2 mixed gas. The volume concentration of dimethyl ether was 3%, the volume concentration of oxygen was 10%, and the volume hourly space velocity was 4500 h⁻¹. -1 After 2 hours of reaction, gas and liquid samples were taken for analysis. The conversion rate of dimethyl ether was 89%, and the selectivity of formaldehyde was 86%.

[0037] Example 13

[0038] The catalyst for the oxidation of dimethyl ether to formaldehyde was prepared by a co-precipitation method. The specific operation process is as follows: 5.39 g of Fe(NO3)3·9H2O, 3.43 g of (NH4)2MoO4, and (NH4)6W7O were weighed. 24 1.86 g of ·6H₂O was dissolved in 100 mL of water, and the pH of the solution was adjusted to 10 with a 10% ammonia solution. The mixture was filtered to obtain a solid, which was then dried and calcined in a muffle furnace at 400 °C for 10 h to obtain a catalyst of 20 wt% Fe₂O₃-50 wt% V₂O₅-30 wt% WO₃. The catalyst was directly extruded and granulated, sieved through a 40-60 mesh sieve, and 0.9 mL was packed into a fixed-bed reactor to a height of 15 mm. The reaction temperature was 295 °C. The reaction was initiated under atmospheric pressure by simultaneously introducing a DME / O₂ / N₂ mixed gas, with a dimethyl ether volume concentration of 3%, an oxygen volume concentration of 10%, and a volume hourly space velocity (VHSV) of 4500 h⁻¹. -1 After 2 hours of reaction, gas and liquid samples were taken for analysis. The conversion rate of dimethyl ether was 86%, and the selectivity of formaldehyde was 84%.

[0039] Example 14

[0040] The catalyst for the oxidation of dimethyl ether to formaldehyde was prepared by a co-precipitation method. The specific operation process is as follows: 5.39 g of Fe(NO3)3·9H2O, 2.06 g of NH4VO3, and 5.55 g of Bi(NO3)3·5H2O were weighed and dissolved in 100 mL of water. The pH of the solution was adjusted to 10 with a 10% ammonia solution. The mixture was filtered to obtain a solid, dried, and then calcined in a muffle furnace at 400℃ for 10 h to obtain a catalyst of 20 wt% Fe2O3-30 wt% V2O5-50 wt% Bi2O3. The catalyst was directly extruded and granulated, sieved to 40-60 mesh, and 0.9 mL was filled into a fixed-bed reactor to a packing height of 15 mm. The reaction temperature was 295℃. The reaction was initiated under normal pressure by simultaneously introducing a DME / O2 / N2 mixed gas. The volume concentration of dimethyl ether was 3%, the volume concentration of oxygen was 10%, and the volume hourly space velocity was 4500 h⁻¹. -1 After 2 hours of reaction, gas and liquid samples were taken for analysis. The conversion rate of dimethyl ether was 77%, and the selectivity of formaldehyde was 82%.

[0041] Example 15

[0042] The catalyst for the oxidation of dimethyl ether to formaldehyde was prepared by a co-precipitation method. The specific operation process is as follows: 5.39 g of Fe(NO3)3·9H2O, 4.80 g of NH4VO3, and 1.11 g of Bi(NO3)3·5H2O were weighed and dissolved in 100 mL of water. The pH of the solution was adjusted to 10 with a 10% ammonia solution. The mixture was filtered to obtain a solid, dried, and then calcined in a muffle furnace at 400℃ for 10 h to obtain a catalyst of 20 wt% Fe2O3-70 wt% V2O5-10 wt% Bi2O3. The catalyst was directly extruded and granulated, sieved to 40-60 mesh, and 0.9 mL was filled into a fixed-bed reactor to a packing height of 15 mm. The reaction temperature was 295℃. The reaction was initiated under normal pressure by simultaneously introducing a DME / O2 / N2 mixed gas. The volume concentration of dimethyl ether was 3%, the volume concentration of oxygen was 10%, and the volume hourly space velocity was 4500 h⁻¹. -1 After 2 hours of reaction, gas and liquid samples were taken for analysis. The conversion rate of dimethyl ether was 85%, and the selectivity of formaldehyde was 86%.

[0043] Example 16

[0044] The catalyst for the oxidation of dimethyl ether to formaldehyde was prepared by a co-precipitation method. The specific operation process is as follows: 5.39 g of Fe(NO3)3·9H2O, 3.43 g of NH4VO3, and 3.33 g of Bi(NO3)3·5H2O were weighed and dissolved in 100 mL of water. The pH of the solution was adjusted to 10 with a 10% ammonia solution. The mixture was filtered to obtain a solid, which was then dried and calcined in a muffle furnace at 400℃ for 10 h to obtain a catalyst of 20 wt% Fe2O3-50 wt% V2O5-30 wt% Bi2O3. The catalyst was directly extruded and granulated, sieved to 40-60 mesh, and 0.9 mL was packed into a fixed-bed reactor to a height of 15 mm. The reaction temperature was 380℃. The reaction was initiated under normal pressure by simultaneously introducing a DME / O2 / N2 mixed gas. The volume concentration of dimethyl ether was 3%, the volume concentration of oxygen was 10%, and the volume hourly space velocity was 4500 h⁻¹. -1 After 2 hours of reaction, gas and liquid samples were taken for analysis. The conversion rate of dimethyl ether was 91%, and the selectivity of formaldehyde was 69%.

[0045] Example 17

[0046] 5.39 g of Fe(NO3)3·9H2O, 3.43 g of NH4VO3, and 3.33 g of Bi(NO3)3·5H2O were dissolved in 100 mL of water. The pH of the solution was adjusted to 10 with a 10% ammonia solution. The mixture was filtered to obtain a solid, which was then dried and calcined in a muffle furnace at 400 °C for 10 h to obtain a catalyst of 20 wt% Fe2O3-50 wt% V2O5-30 wt% Bi2O3. The catalyst was directly extruded and granulated, sieved to 40-60 mesh, and 0.9 mL was packed into a fixed-bed reactor to a height of 15 mm. The reaction temperature was 210 °C. The reaction was initiated under atmospheric pressure by simultaneously introducing a DME / O2 / N2 mixed gas, with a dimethyl ether volume concentration of 3%, an oxygen volume concentration of 10%, and a volume hourly space velocity of 4500 h⁻¹. -1 After 2 hours of reaction, gas and liquid samples were taken for analysis. The conversion rate of dimethyl ether was 76%, and the selectivity of formaldehyde was 88%.

[0047] Example 18

[0048] The catalyst for the oxidation of dimethyl ether to formaldehyde was prepared by a co-precipitation method. The specific operation process is as follows: 5.39 g of Fe(NO3)3·9H2O, 3.43 g of NH4VO3, and 3.33 g of Bi(NO3)3·5H2O were weighed and dissolved in 100 mL of water. The pH of the solution was adjusted to 10 with a 10% ammonia solution. The mixture was filtered to obtain a solid, dried, and then calcined in a muffle furnace at 400℃ for 10 h to obtain a catalyst of 20 wt% Fe2O3-50 wt% V2O5-30 wt% Bi2O3. The catalyst was directly extruded and granulated, sieved to 40-60 mesh, and 0.9 mL was packed into a fixed-bed reactor to a height of 15 mm. The reaction temperature was 295℃. The reaction was initiated under normal pressure by simultaneously introducing a DME / O2 / N2 mixed gas. The volume concentration of dimethyl ether was 3%, the volume concentration of oxygen was 10%, and the volume hourly space velocity was 3500 h⁻¹. -1 After 2 hours of reaction, gas and liquid samples were taken for analysis. The conversion rate of dimethyl ether was 92%, and the selectivity of formaldehyde was 81%.

[0049] Example 19

[0050] The catalyst for the oxidation of dimethyl ether to formaldehyde was prepared by a co-precipitation method. The specific operation process is as follows: 5.39 g of Fe(NO3)3·9H2O, 3.43 g of NH4VO3, and 3.33 g of Bi(NO3)3·5H2O were weighed and dissolved in 100 mL of water. The pH of the solution was adjusted to 10 with a 10% ammonia solution. The mixture was filtered to obtain a solid, dried, and then calcined in a muffle furnace at 400℃ for 10 h to obtain a catalyst of 20 wt% Fe2O3-50 wt% V2O5-30 wt% Bi2O3. The catalyst was directly extruded and granulated, sieved to 40-60 mesh, and 0.9 mL was packed into a fixed-bed reactor to a height of 15 mm. The reaction temperature was 295℃. The reaction was initiated under normal pressure by simultaneously introducing a DME / O2 / N2 mixed gas. The volume concentration of dimethyl ether was 3%, the volume concentration of oxygen was 10%, and the volume hourly space velocity was 8000 h⁻¹. -1 After 2 hours of reaction, gas and liquid samples were taken for analysis. The conversion rate of dimethyl ether was 78%, and the selectivity of formaldehyde was 86%.

[0051] Comparative Example 1

[0052] The catalyst for the oxidation of dimethyl ether to formaldehyde was prepared by a co-precipitation method. The specific operation process is as follows: 5.39 g of Fe(NO3)3·9H2O and 3.43 g of NH4VO3 were weighed and dissolved in 100 mL of water. The pH of the solution was adjusted to 10 with a 10% ammonia solution. The mixture was filtered to obtain a solid, which was then dried and calcined in a muffle furnace at 400℃ for 10 h to obtain a catalyst of 29 wt% Fe2O3-71 wt% V2O5. The catalyst was directly extruded and granulated, sieved to a 40-60 mesh, and 0.9 mL was packed into a fixed-bed reactor to a height of 15 mm. The reaction temperature was 295℃. The reaction was initiated under normal pressure by simultaneously introducing a DME / O2 / N2 mixed gas. The volume concentration of dimethyl ether was 3%, the volume concentration of oxygen was 10%, and the volume hourly space velocity was 4500 h⁻¹. -1 After 2 hours of reaction, gas and liquid samples were taken and analyzed separately. The conversion rate of dimethyl ether was 86%, and the selectivity of formaldehyde was 84%. After 3000 hours of stable operation, the conversion rate of dimethyl ether was 59%, and the selectivity of formaldehyde was 83%.

[0053] Comparative Example 2

[0054] The catalyst for the oxidation of dimethyl ether to formaldehyde was prepared by a co-precipitation method. The specific operation process is as follows: 5.3 g of Fe(NO3)3·9H2O and 3.33 g of Bi(NO3)3·5H2O were weighed and dissolved in 100 mL of water. The pH of the solution was adjusted to 10 with a 10% ammonia solution. The mixture was filtered to obtain a solid, which was then dried and calcined in a muffle furnace at 400℃ for 10 h to obtain a catalyst of 40 wt% Fe2O3-60 wt% Bi2O3. The catalyst was directly extruded and granulated, sieved to 40-60 mesh, and 0.9 mL was packed into a fixed-bed reactor to a height of 15 mm. The reaction temperature was 295℃. The reaction was initiated under normal pressure by simultaneously introducing a DME / O2 / N2 mixed gas. The volume concentration of dimethyl ether was 3%, the volume concentration of oxygen was 10%, and the volume hourly space velocity was 4500 h⁻¹. -1 After 2 hours of reaction, gas and liquid samples were taken for analysis. The conversion rate of dimethyl ether was 90%, and the selectivity of formaldehyde was 21%.

[0055] Comparative Example 3

[0056] The catalyst for the oxidation of dimethyl ether to formaldehyde was prepared by a co-precipitation method. The specific operation process is as follows: 3.43 g of NH4VO3 and 3.33 g of Bi(NO3)3·5H2O were weighed and dissolved in 100 mL of water. The pH of the solution was adjusted to 10 with a 10% ammonia solution. The mixture was filtered to obtain a solid, which was then dried and calcined in a muffle furnace at 400℃ for 10 h to obtain a catalyst of 63 wt% V2O5-37 wt% Bi2O3. The catalyst was directly extruded and granulated, sieved to 40-60 mesh, and 0.9 mL was packed into a fixed-bed reactor to a height of 15 mm. The reaction temperature was 295℃. The reaction was initiated under normal pressure by simultaneously introducing a DME / O2 / N2 mixed gas. The volume concentration of dimethyl ether was 3%, the volume concentration of oxygen was 10%, and the volume hourly space velocity was 4500 h⁻¹. -1 After 2 hours of reaction, gas and liquid samples were taken for analysis. The conversion rate of dimethyl ether was 39%, and the selectivity of formaldehyde was 51%.

[0057] The above descriptions are merely a few embodiments of this application and do not constitute any limitation on this application. Any changes or modifications made to the technical content disclosed above without departing from the scope of the technical solution of this application are equivalent to equivalent implementation cases and all fall within the scope of the technical solution.

Claims

1. A method for producing formaldehyde by oxidation of dimethyl ether, characterized in that: The process of oxidizing dimethyl ether to formaldehyde is as follows: using dimethyl ether as raw material and nitrogen-oxygen mixture as oxidant, formaldehyde is generated in a fixed-bed reactor under the action of iron-vanadium-based composite element oxide catalyst. The iron-vanadium-based composite element oxide catalyst is composed of active metal iron, vanadium and composite elements, wherein the composite elements are one or more of Cu, Co, Si, Sn, Bi, Mn, Al, Zr, Sm and W.

2. The method according to claim 1, characterized in that: The iron-vanadium-based composite element oxide catalyst is prepared and synthesized by using one or more of the following methods: co-precipitation, solid-phase ball milling, impregnation, or sol-gel method, with corresponding element precursor raw materials.

3. The method according to claim 1 or 2, characterized in that: The precursor of the active ingredient metallic iron is one or more of Fe(NO3)3, FeCl3, Fe2(SO4)3, FePO4, Fe2O3, and Fe(C2H3O2)2. The precursor of the active ingredient metallic vanadium is one or more of VCl3, NH4VO3, V2O3, V2O5, F4V, VC, S3V2, VOSO4, VCl3, NV, and VOC2O4. The precursor of the composite element is one or more of the following: nitrate, chloride, sulfate, phosphate, oxide, citrate, stearate, and acetate of the corresponding element.

4. The method according to claim 1 or 2, characterized in that: The iron-vanadium-based composite element oxide catalyst has an active metal iron content of 5wt% to 60wt% (based on oxide weight), an active metal vanadium content of 10wt% to 90wt% (based on oxide weight), and the remainder being a composite element oxide content of 1% to 70%.

5. The method according to claim 1 or 2, characterized in that: The iron-vanadium-based composite element oxide catalyst preferably has an active metal iron content of 10wt% to 50wt% (based on oxide weight), an active metal vanadium content of 15wt% to 85wt% (based on oxide weight), and the remainder being composite element oxides, preferably 1% to 50%.

6. The method according to any one of claims 1-5, characterized in that: The process of catalyzing the oxidation of dimethyl ether to formaldehyde using the iron-vanadium-based composite element oxide catalyst according to any one of claims 1-5 is as follows: Using dimethyl ether as raw material, a nitrogen-oxygen mixture is introduced as an oxidant (oxygen volume concentration of 3%-18%), and the dimethyl ether feed volume concentration is 0.5%-8%. The reaction is carried out in a fixed-bed reactor at a reaction temperature of 150℃-430℃.

7. The method according to claim 5, characterized in that: The catalyst is packed in a fixed bed at a height of 7 mm to 27 mm, the reaction is carried out at atmospheric pressure, and the volume hourly space velocity (VHSV) of the reactants (nitrogen-oxygen mixture and dimethyl ether) is 2500 to 10000 h⁻¹. -1 .

8. The method according to claim 5 or 6, characterized in that: The preferred reaction conditions are: a catalyst loading height of 12 mm to 22 mm in a fixed bed and a reaction volume hourly space velocity of 3000 to 9000 h⁻¹. -1 .