Method for preparing formaldehyde by dehydrogenation of methanol without oxygen

Abstract

The application discloses a method for preparing formaldehyde by dehydrogenation of methanol in the absence of oxygen. ‑1 Under the reaction conditions, methanol is contacted with a copper-based catalyst in a fixed bed reactor to generate formaldehyde and hydrogen through a dehydrogenation reaction; the copper-based catalyst comprises an active component Cu and an auxiliary element M, the molar ratio of Cu to M is (0.1-3):1, the M is selected from one or more than two combinations of Mg, Mn, Zn, La, Al, Ga, Zr, Cr and Ce, and the preparation process of the catalyst comprises four steps of coprecipitation, calcination, reduction and passivation. Through the regulation of the strong interaction between Cu and the multi-element auxiliary element, the sintering of Cu particles is effectively inhibited, the methanol conversion rate is as high as 90±5%, the formaldehyde selectivity is maintained at greater than or equal to 95%, the single-pass operation life is not less than 800 hours, the key technical problem of poor stability of the existing copper-based catalyst is effectively solved, and the method has important industrial application prospect.

Description

Technical Field

[0001] This invention belongs to the field of chemical catalysis technology, specifically relating to a method for the oxygen-free dehydrogenation of methanol to formaldehyde. Background Technology

[0002] Formaldehyde is an important basic chemical raw material, widely used in resins, plastics, pharmaceuticals, and other fields. Large-scale industrial production of formaldehyde is mainly achieved through the oxidative dehydrogenation of methanol (silver process or iron-molybdenum process). This process requires the introduction of air or oxygen, and the product is an aqueous formaldehyde solution. For fine chemical processes that require anhydrous formaldehyde as a raw material (such as polyoxymethylene production), the subsequent dehydration step is energy-intensive and complex.

[0003] The direct oxygen-free dehydrogenation of methanol to anhydrous formaldehyde (CH3OH → HCHO + H2) is an attractive atom-economical route that can co-produce high-value-added hydrogen. The core challenge of this route lies in developing highly active, highly selective catalysts with ultra-long operating life. Copper-based catalysts have been extensively studied due to their good dehydrogenation activity, but the oxygen-free dehydrogenation reaction of methanol to formaldehyde generally takes place at temperatures above 350°C, which leads to the easy sintering and rapid deactivation of copper species, resulting in a single-pass life of only tens of hours (Chemical Industry Progress, 2025, 44(3): 1347-1354), which seriously restricts its industrialization process. Therefore, developing catalysts with highly active sites, enhancing the interaction between metal and support, and extending the catalyst life are the core technical paths for preparing efficient and stable industrial-grade catalysts, and are also the key problems that urgently need to be solved in this field. Summary of the Invention

[0004] To overcome the technical drawbacks of harsh reaction conditions and easy catalyst deactivation in the anaerobic dehydrogenation of methanol to produce anhydrous formaldehyde, this invention aims to provide a highly efficient and stable method for the anaerobic dehydrogenation of methanol to produce formaldehyde. This method uses a copper-based catalyst, which features a simple preparation process, high selectivity for formaldehyde, and excellent catalyst stability, making it more suitable for industrial-scale applications. Compared to the oxidative dehydrogenation of methanol to produce formaldehyde, this method eliminates the need to introduce oxygen, directly dehydrogenating methanol to produce formaldehyde, thus eliminating the subsequent dehydration step, effectively reducing dehydration energy consumption, producing no wastewater, and efficiently co-producing high-value-added hydrogen.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] This invention provides a method for the anaerobic dehydrogenation of methanol to formaldehyde, wherein the process is carried out at 250-350°C, a pressure of 0.05-0.5 MPa, and a methanol mass hourly space velocity of 0.01-2 h⁻¹. -1 Under the reaction conditions, methanol is brought into contact with a copper-based catalyst to undergo a dehydrogenation reaction, producing formaldehyde and hydrogen gas; The copper-based catalyst comprises an active component Cu and an auxiliary element M, wherein the molar ratio of Cu to M is (0.1~3):1, and M is selected from one or more combinations of Mg, Mn, Zn, La, Al, Ga, Zr, Cr, and Ce. The preparation method of the catalyst includes the following steps: (1) Mix the aqueous solution of Cu-containing soluble salt and M-containing soluble salt with the precipitant solution to undergo a co-precipitation reaction and obtain a precipitate; (2) The precipitate obtained in step (1) is calcined in an oxygen-containing atmosphere to obtain the catalyst oxide precursor; (3) The catalyst oxide precursor obtained in step (2) is reduced in a hydrogen atmosphere to obtain the catalyst precursor; (4) The catalyst precursor obtained in step (3) is passivated in an oxygen-containing atmosphere to obtain a copper-based catalyst.

[0007] Based on the above technical solution, the molar ratio of Cu to M is further (0.3~3):1.

[0008] Based on the above technical solution, the average particle size of the copper-based catalyst is ≤25nm, and the average particle size of the Cu nanoparticles is ≤5nm.

[0009] Based on the above technical solution, further, M is selected from a combination of Mn and at least one of Zn, Al, La, Mg, Ga, Zr, Cr, and Ce.

[0010] Based on the above technical solution, further, the coprecipitation reaction in step (1) is carried out at 30~90℃ and pH value of 8~10, then aged for 4~12 h, and obtained after filtration and washing.

[0011] Based on the above technical solution, further, the soluble salt of Cu in step (1) is at least one of the nitrate, chloride, sulfate or acetate of Cu, preferably nitrate, and the soluble salt of M is at least one of the nitrate, chloride, sulfate or acetate of M, preferably nitrate.

[0012] Based on the above technical solution, further, the precipitant solution in step (1) is at least one of sodium hydroxide aqueous solution, potassium hydroxide aqueous solution, sodium carbonate aqueous solution, potassium carbonate aqueous solution, urea aqueous solution or ammonia solution.

[0013] Based on the above technical solution, further, the calcination in step (2) is to calcine the precipitate obtained in step (1) in a mixed atmosphere of oxygen and inert gas with an oxygen volume fraction of ≥10% at 300~700℃ for 2~10h.

[0014] Based on the above technical solution, further, the reduction in step (3) involves exposing the catalyst oxide precursor obtained in step (2) to a hydrogen atmosphere at a space velocity of 200-1000 h⁻¹. -1 Reduce at 200~500℃ for 2~10 hours.

[0015] Based on the above technical solution, further, the passivation in step (4) involves placing the catalyst precursor obtained in step (3) in a mixed atmosphere of oxygen and inert gas with an oxygen volume fraction of 0.2-2% at a space velocity of 20-500 h⁻¹. -1 Passivation treatment at 10~30℃ for 5~200 h.

[0016] Based on the above technical solution, furthermore, the reaction temperature is 250~320℃ and the pressure is 0.05~0.3 MPa.

[0017] Based on the above technical solution, furthermore, the mass hourly space velocity (MSV) of methanol is 0.1~1 h⁻¹. -1 Preferably, 0.2~0.8 h -1 .

[0018] Based on the above technical solution, the dehydrogenation reaction is further carried out in a fixed-bed reactor.

[0019] Based on the above technical solution, the methanol conversion rate of the dehydrogenation reaction is maintained at over 50%, the formaldehyde selectivity is maintained at over 90%, and the single-pass operating life is not less than 200 hours.

[0020] The preparation of the copper-based catalyst and the production of formaldehyde from methanol by oxygen-free dehydrogenation of methanol have the following core features: (1) The co-precipitation method can achieve uniform dispersion of multi-component auxiliary oxides and copper oxides. This dispersion state is conducive to the formation of strong oxide-oxide interactions during the calcination process, thereby effectively inhibiting the excessive growth of Cu species during the reduction process, laying a structural foundation for the high activity and stability of the subsequent catalyst; (2) The passivation process can effectively protect the metal Cu particles. If the metal Cu particles are directly exposed to the air, they are prone to deep oxidation and the formation of an oxide film on the surface, which eventually leads to a decrease in catalyst activity. Passivation treatment can avoid this problem and maintain the number of active sites of the catalyst; (3) The oxide-oxide interactions formed by the multi-component auxiliary can further disperse and stabilize Cu species, effectively inhibiting the sintering phenomenon of Cu particles during the reaction process. This is the key guarantee for the significant improvement of catalyst stability; (4) The highly dispersed state of Cu particles not only significantly improves the activity of methanol dehydrogenation reaction, but also reduces the selectivity of by-products such as methyl formate, thereby directionally improving the selectivity of formaldehyde. In summary, the copper-based catalyst of the present invention, which possesses strong oxide-oxide interaction, achieves a balance between high activity and good stability, ensuring a formaldehyde selectivity of over 90% and stability that meets the requirements for 800 hours of continuous operation without significant performance fluctuations, thus adapting to the requirements of industrial production.

[0021] Compared with the prior art, the present invention has the following beneficial effects: 1. Breakthrough improvement in lifespan: Compared with the single-pass lifespan of tens of hours of existing copper-based catalysts (Chemical Industry Progress, 2025, 44(3): 1347-1354), the catalyst of this invention has a single-pass lifespan of up to 800 hours, which is expected to realize the industrial application of methanol dehydrogenation to formaldehyde. 2. High-efficiency conversion under mild conditions: Existing technologies generally test at temperatures ≥350℃, while the temperature range used in this invention is set at 250~350℃. This reduces energy consumption and inhibits the sintering of Cu particles, ensuring that the formaldehyde selectivity is stable at ≥90% while the combined selectivity of byproducts such as CO and dimethyl ether is less than 10%. 3. Significant green economic advantages: Formaldehyde is produced directly without the need to introduce oxygen, eliminating the subsequent dehydration process (effectively reducing dehydration energy consumption), generating no wastewater, and co-producing high-value-added hydrogen. 4. Strong structural stability: Through oxide-oxide interactions formed by co-precipitation, the size of Cu nanoparticles is controlled at around 5 nm, avoiding particle growth during the reaction process. The catalytic activity shows no significant attenuation after long-term operation. The co-precipitation process parameters are controllable, the catalyst has good reproducibility, and after tableting, it is suitable for industrial fixed-bed reactors, facilitating large-scale production. Attached Figure Description

[0022] To more clearly illustrate the embodiments of the present invention, the accompanying drawings involved in the embodiments will be briefly described below.

[0023] Figure 1 The graph shows the changes in methanol conversion and formaldehyde selectivity of the catalyst Cu1Mn2Zn1 in Example 3 during the anaerobic dehydrogenation reaction of methanol over 800 hours. The horizontal axis represents the reaction time (hours), and the vertical axis represents the conversion and selectivity (%).

[0024] Figure 2 The images shown are transmission electron microscope (TEM) images of Cu1Mn2Zn1 from Example 3, where (a) is a TEM image of the catalyst; (b) is an HR-TEM image of the catalyst; (c) is statistical data on catalyst particle size; and (d) is statistical data on the size of Cu nanoparticles on the catalyst.

[0025] Figure 3 The graph shows the changes in methanol conversion and formaldehyde selectivity of the catalyst Cu1 / Mn2Zn1 in the oxygen-free dehydrogenation reaction of methanol in Comparative Example 1. The horizontal axis represents the reaction time (minutes), and the vertical axis represents the conversion and selectivity (%).

[0026] Figure 4 This is a comparison of XRD data before and after the reaction of the catalyst Cu1 / Mn2Zn1 in Comparative Example 1.

[0027] Figure 5 The graph shows the changes in methanol conversion and formaldehyde selectivity of catalyst Cu1Mn3 in the oxygen-free dehydrogenation reaction of methanol in Comparative Example 3 after 375 hours. The horizontal axis represents the reaction time (hours), and the vertical axis represents the conversion and selectivity (%).

[0028] Figure 6 This is a comparison of XRD data of the catalyst Cu1Mn3 before and after the reaction in Comparative Example 3. Detailed Implementation

[0029] The present invention will be described in detail below with reference to the embodiments. However, the implementation of the present invention is not limited thereto. Obviously, the embodiments described below are only some embodiments of the present invention. For those skilled in the art, other similar embodiments can be obtained without creative effort and all fall within the protection scope of the present invention.

[0030] Catalyst evaluation was performed using a fixed-bed reactor with an inner diameter of 10 mm and a length of 340 mm. The catalyst was tableted to 40-60 mesh, with a catalyst mass of 5 g. Both upstream and downstream of the catalyst were packed with 40-60 mesh quartz sand. Methanol was injected at the bottom of the reactor using a feed pump, reacting with the catalyst. The gaseous products generated at the top of the reactor were then heated to 150°C using a heating element and entered a gas chromatograph (Shimadzu). The chromatographic columns were GDX-401 and Molecular Sieve-5, with TCD detection. The column temperature program was 90°C for 4 min, then increased to 130°C at a rate of 10°C / min and held for 7 min. The detector temperature was 150°C. Carbon dioxide, water, dimethyl ether, methanol, and methyl formate (MF) eluted sequentially on the GDX-401 column, while hydrogen, carbon monoxide, and methane eluted sequentially on the Molecular Sieve-5 column.

[0031] Methanol conversion rate =

[0032] Methanol (in) is the peak area of ​​methanol obtained by passing methanol through the reactor and vaporizing it under conditions of fixed temperature and fixed methanol injection volume, without a catalyst, and then entering the chromatogram.

[0033] Methanol (out) is the methanol peak area obtained by chromatography of the mixed gas exiting the reactor after the catalyst is packed in the reactor under fixed temperature and fixed methanol injection conditions.

[0034] Selectivity of dimethyl ether (DME) =

[0035] Dimethyl ether (out) is 1.3. (Peak area of ​​dimethyl ether), 1.3 is the ratio of the corresponding factor of methanol to dimethyl ether; Formaldehyde selectivity =

[0036] Formaldehyde (out) =

[0037] H2(out) represents the amount of hydrogen gas produced after the reaction. Theoretically, it is basically the same as the amount of formaldehyde, or the same as the amount of methanol converted. This is based on the fact that 1 mol of methanol is converted into 1 mol of formaldehyde and 1 mol of hydrogen gas. CO(out) is the molar amount of carbon monoxide obtained after the reaction; CO2(out) is the molar amount of carbon dioxide obtained after the reaction; CH4 (out) represents the molar amount of methane obtained after the reaction; MF(out) is the molar amount of methyl formate obtained after the reaction; Carbon monoxide selectivity =

[0038] Carbon dioxide selectivity =

[0039] Methane selectivity =

[0040] methyl formate selectivity

[0041] Since the mechanism of by-product formation is relatively complex and its stoichiometric relationship is not easy to determine, in order to simplify the calculation and facilitate comparison, the formaldehyde selectivity in the embodiments of the present invention is estimated using a formula based on hydrogen balance, which has high accuracy under the condition of low by-product selectivity.

[0042] Example 1 Copper nitrate hexahydrate (0.05 mol) and manganese nitrate tetrahydrate (0.15 mol) were dissolved in 50 mL of water to obtain a solution. The solution was stirred and heated to 60 °C, and 0.1 mol / L NaOH solution was added dropwise until the pH ≈ 9. The solution was then stirred for 6 hours, followed by aging for 6 hours after stirring was stopped. The solution was filtered and washed to obtain a precipitate. The precipitate was calcined at 500 °C in air for 5 hours, and then subjected to hydrogen gas (purity >99.9%, space velocity 400 h⁻¹) at 300 °C. -1 Reduction was carried out for 2 hours in an atmosphere containing 1% oxygen (O2 / N2) and a space velocity of 200 h⁻¹. After cooling to room temperature, the mixture was then subjected to further reduction at an oxygen content of 1% (O2 / N2) and a space velocity of 200 h⁻¹. -1 The catalyst Cu1Mn3 was obtained by passivation in an atmosphere for 12 hours.

[0043] Catalyst evaluation was conducted using a fixed-bed reactor with an inner diameter of 10 mm and a length of 340 mm. The catalyst was flaked to a mesh size of 40-60 mesh, with a catalyst mass of 5 g. Both upstream and downstream of the catalyst were filled with 40-60 mesh quartz sand. Methanol was injected into the reactor via a feed pump at the bottom. The reaction conditions were 275 °C, 0.1 MPa, and a methanol mass hourly space velocity (MHSV) of 0.4 h⁻¹. -1 Under the given conditions, data were collected using gas chromatography over a reaction period of 24 hours.

[0044] The results showed that the methanol conversion rate was 81.9%, formaldehyde selectivity was 93.2%, CO selectivity was 4.4%, CO2 selectivity was 2.5%, CH4 selectivity was 1.6%, methyl formate selectivity was 0.2%, and dimethyl ether selectivity was 0.1%.

[0045] Example 2 Copper nitrate hexahydrate (0.05 mol) and zinc nitrate hexahydrate (0.15 mol) were dissolved in 50 mL of water to obtain a solution. The solution was stirred and heated to 60 °C, and 0.1 mol / L NaOH solution was added dropwise until the pH ≈ 9. The solution was then stirred for 6 hours, followed by aging for 6 hours after stirring was stopped. The precipitate was obtained by filtration and washing. The precipitate was calcined at 500 °C in air for 5 hours, and then subjected to hydrogen gas (purity >99.9%, space velocity 400 h⁻¹) at 300 °C. -1 Reduction was carried out for 2 hours in an atmosphere containing 1% oxygen (O2 / N2) and a space velocity of 200 h⁻¹. After cooling to room temperature, the mixture was then subjected to further reduction at an oxygen content of 1% (O2 / N2) and a space velocity of 200 h⁻¹. -1 The catalyst Cu1Zn3 was obtained by passivation in an atmosphere for 12 hours.

[0046] The catalyst evaluation method and process are the same as in Example 1.

[0047] Results: Methanol conversion rate: 62.8%, formaldehyde selectivity: 92.0%, CO selectivity: 4.5%, CO2 selectivity: 1.8%, CH4 selectivity: 1.3%, methyl formate selectivity: 0.3%, dimethyl ether selectivity: 0.1%.

[0048] Example 3 Copper nitrate hexahydrate (0.05 mol), manganese nitrate tetrahydrate (0.1 mol), and zinc nitrate hexahydrate (0.05 mol) were dissolved in 50 mL of water to obtain a solution. The solution was stirred and heated to 60 °C, and 0.1 mol / L NaOH solution was added dropwise until the pH ≈ 9. The solution was then stirred for 6 hours, followed by aging for 6 hours after stirring was stopped. The precipitate was obtained by filtration and washing. The precipitate was calcined at 500 °C in air for 5 hours, and then subjected to hydrogen gas (purity >99.9%, space velocity 400 h⁻¹) at 300 °C. -1 Reduction was carried out for 2 hours in an atmosphere containing 1% oxygen (O2 / N2) and a space velocity of 200 h⁻¹. After cooling to room temperature, the mixture was then subjected to further reduction at an oxygen content of 1% (O2 / N2) and a space velocity of 200 h⁻¹. -1 The catalyst Cu1Mn2Zn1 was obtained by passivation in an atmosphere for 12 hours.

[0049] The catalyst evaluation method and process are the same as in Example 1.

[0050] Results: Methanol conversion rate: 99.1%, formaldehyde selectivity: 96.3%, CO selectivity: 3.2%, CO2 selectivity: 0.2%, CH4 selectivity: 0.1%, methyl formate selectivity: 0.1%, dimethyl ether selectivity: 0.1%.

[0051] Based on the conversion rate of methanol and the selectivity of formaldehyde, it can be seen that the catalytic effect of the two-component catalyst in Example 3 is significantly better than that of the single-component catalysts in Examples 1 and 2, indicating that there is a synergistic effect within the two-component catalyst.

[0052] The catalyst Cu1Mn2Zn1 from Example 3 was used, and the catalyst evaluation method and procedure were the same as in Example 1, except that the evaluation time was extended to 800 hours. The results are as follows: Figure 1 As shown, based on Figure 1 The data shows that in the first 800 hours, the methanol conversion rate remained at 90±5% and the formaldehyde selectivity remained at around 96%, which indicates that the catalyst has very high stability.

[0053] Transmission electron microscopy (TEM) images of the catalyst Cu1Mn2Zn1 in Example 3 are shown below. Figure 2 As shown, Figure 2 (a) The morphology of the catalyst is mainly particulate; Figure 2 (b) is a high-resolution transmission electron microscope (HR-TEM) image of the catalyst. The particles are mainly classified as oxides and Cu nanoparticles, among which the main oxides are CuO, Cu2O, Mn2O3 and MnO. Figure 2 (c) shows the particle size statistics of the catalyst Cu1Mn2Zn1, with an average size of 17.0 nm; (d) shows the particle size statistics of Cu nanoparticles on the catalyst Cu1Mn2Zn1, with an average size of 4.2 nm.

[0054] The presence of multiple oxide species in the catalyst Cu1Mn2Zn1 enhances the interaction between oxides. The catalyst particle size is less than 20 nm, which limits the size of Cu nanoparticles in the catalyst. At the same time, the interaction between oxides can inhibit the sintering of Cu nanoparticles and ensure the stability of the catalyst.

[0055] Example 4 Copper nitrate hexahydrate (0.05 mol) and aluminum nitrate nonahydrate (0.15 mol) were dissolved in 50 mL of water to obtain a solution. The solution was stirred and heated to 90°C, and ammonia solution was added dropwise until the pH ≈ 9. The solution was then stirred for 6 hours, followed by aging for 6 hours. The precipitate was obtained by filtration and washing. The precipitate was calcined at 600°C in air for 5 hours, and then subjected to hydrogen gas (purity > 99.9%, space velocity 400 h⁻¹) at 250°C. -1 Reduction was carried out for 2 hours in an atmosphere containing 1% oxygen (O2 / N2) and a space velocity of 200 h⁻¹. After cooling to room temperature, the mixture was then subjected to further reduction at an oxygen content of 1% (O2 / N2) and a space velocity of 200 h⁻¹. -1 The catalyst Cu1Al3 was obtained by passivation in an atmosphere for 10 hours.

[0056] The catalyst evaluation method and process are the same as in Example 1.

[0057] Results: Methanol conversion rate: 75.7%, formaldehyde selectivity: 91.0%, CO selectivity: 4.8%, CO2 selectivity: 1.5%, CH4 selectivity: 0.9%, methyl formate selectivity: 0.5%, dimethyl ether selectivity: 1.3%.

[0058] Example 5 Copper nitrate hexahydrate (0.05 mol), manganese nitrate tetrahydrate (0.1 mol), and aluminum nitrate nonahydrate (0.05 mol) were dissolved in 50 mL of water to obtain a solution. The solution was stirred and heated to 90°C, and ammonia solution was added dropwise until the pH ≈ 9. The solution was then stirred for 6 hours, followed by aging for 6 hours after stirring was stopped. The precipitate was obtained by filtration and washing. The precipitate was calcined at 600°C in air for 5 hours, and then subjected to hydrogen gas (purity >99.9%, space velocity 400 h⁻¹) at 250°C. -1 Reduction was carried out for 2 hours in an atmosphere containing 1% oxygen (O2 / N2) and a space velocity of 200 h⁻¹. After cooling to room temperature, the mixture was then subjected to further reduction at an oxygen content of 1% (O2 / N2) and a space velocity of 200 h⁻¹. -1 The catalyst Cu1Mn2Al1 was obtained by passivation in an atmosphere for 10 hours.

[0059] The catalyst evaluation method and process are the same as in Example 1.

[0060] Results: Methanol conversion rate: 92.7%, formaldehyde selectivity: 94.6%, CO selectivity: 3.5%, CO2 selectivity: 0.8%, CH4 selectivity: 0.7%, methyl formate selectivity: 0.1%, dimethyl ether selectivity: 0.1%.

[0061] Based on the conversion rate of methanol and the selectivity of formaldehyde, it can be seen that the catalytic results of the two-component catalyst in Example 5 are significantly better than those of the single-component catalysts in Examples 1 and 4, indicating that there is a synergistic effect in the two-component catalyst.

[0062] Example 6 Copper nitrate hexahydrate (0.05 mol) and magnesium nitrate hexahydrate (0.15 mol) were dissolved in 50 mL of water to obtain a solution. The solution was stirred and heated to 80 °C, and 0.1 mol / L Na₂CO₃ solution was added dropwise until the pH ≈ 9. The solution was then stirred for 6 hours, followed by aging for 6 hours after stirring was stopped. The precipitate was obtained by filtration and washing. The precipitate was calcined at 500 °C in air for 5 hours, and then subjected to hydrogen gas (purity > 99.9%, space velocity 400 h⁻¹) at 300 °C. -1 Reduction was carried out for 2 hours in an atmosphere containing 1% oxygen (O2 / N2) and a space velocity of 200 h⁻¹. After cooling to room temperature, the mixture was then subjected to further reduction at an oxygen content of 1% (O2 / N2) and a space velocity of 200 h⁻¹. -1 The catalyst Cu1Mg3 was obtained by passivation in an atmosphere for 12 hours.

[0063] The catalyst evaluation method and process are the same as in Example 1.

[0064] Results: Methanol conversion rate: 39.5%, formaldehyde selectivity: 83.5%, CO selectivity: 6.9%, CO2 selectivity: 3.9%, CH4 selectivity: 4.1%, methyl formate selectivity: 1.5%, dimethyl ether selectivity: 0.1%.

[0065] Example 7 Copper nitrate hexahydrate (0.05 mol) and lanthanum nitrate hexahydrate (0.15 mol) were dissolved in 50 mL of water to obtain a solution. The solution was stirred and heated to 60 °C, and 0.1 mol / L urea solution was added dropwise until the pH ≈ 9. The solution was then stirred for 6 hours, followed by aging for 6 hours after stirring was stopped. The precipitate was obtained by filtration and washing. The precipitate was calcined at 550 °C in air for 5 hours, and then subjected to hydrogen (purity >99.9%, space velocity 400 h⁻¹) at 350 °C. -1 Reduction was carried out for 2 hours in an atmosphere containing 1% oxygen (O2 / N2) and a space velocity of 200 h⁻¹. After cooling to room temperature, the mixture was then subjected to further reduction at an oxygen content of 1% (O2 / N2) and a space velocity of 200 h⁻¹. -1 The catalyst Cu1La3 was obtained by passivation in an atmosphere for 4 hours.

[0066] The catalyst evaluation method and process are the same as in Example 1.

[0067] Results: Methanol conversion rate: 40.2%, formaldehyde selectivity: 86.1%, CO selectivity: 4.8%, CO2 selectivity: 4.1%, CH4 selectivity: 3.1%, methyl formate selectivity: 1.8%, dimethyl ether selectivity: 0.1%.

[0068] Example 8 Copper nitrate hexahydrate (0.05 mol), manganese nitrate tetrahydrate (0.1 mol), and lanthanum nitrate hexahydrate (0.05 mol) were dissolved in 50 mL of water to obtain a solution. The solution was stirred and heated to 60 °C, and 0.1 mol / L urea solution was added dropwise until the pH ≈ 9. The solution was then stirred for 6 hours, followed by aging for 6 hours after stirring was stopped. The precipitate was obtained by filtration and washing. The precipitate was calcined at 550 °C in air for 5 hours, and then subjected to hydrogen gas (purity >99.9%, space velocity 400 h⁻¹) at 350 °C. -1 Reduction was carried out for 2 hours in an atmosphere containing 1% oxygen (O2 / N2) and a space velocity of 200 h⁻¹. After cooling to room temperature, the mixture was then subjected to further reduction at an oxygen content of 1% (O2 / N2) and a space velocity of 200 h⁻¹. -1 The catalyst Cu1Mn2La1 was obtained by passivation in an atmosphere for 4 hours.

[0069] The catalyst evaluation method and process are the same as in Example 1.

[0070] Results: Methanol conversion rate: 88.2%, formaldehyde selectivity: 95.3%, CO selectivity: 3.8%, CO2 selectivity: 0.3%, CH4 selectivity: 0.1%, methyl formate selectivity: 0.3%, dimethyl ether selectivity: 0.1%.

[0071] Based on the conversion rate of methanol and the selectivity of formaldehyde, it can be seen that the catalytic results of the two-component catalyst in Example 8 are significantly better than those of the single-component catalysts in Examples 1 and 7, indicating that there is a synergistic effect in the two-component catalyst.

[0072] Example 9 Copper nitrate hexahydrate (0.05 mol) and gallium nitrate nonahydrate (0.15 mol) were dissolved in 50 mL of water to obtain a solution. The solution was stirred and heated to 60 °C, and 0.1 mol / L NaOH solution was added dropwise until the pH ≈ 9. The solution was then stirred for 6 hours, followed by aging for 6 hours after stirring was stopped. The precipitate was obtained by filtration and washing. The precipitate was calcined at 650 °C in air for 5 hours, and then subjected to hydrogen gas (purity > 99.9%, space velocity 400 h⁻¹) at 400 °C. -1 Reduction was carried out for 2 hours in an atmosphere containing 2% oxygen (O2 / N2) and a space velocity of 200 h⁻¹. -1 The catalyst Cu1Ga3 was obtained by passivation in an atmosphere for 3 hours.

[0073] The catalyst evaluation method and process are the same as in Example 1.

[0074] Results: Methanol conversion rate: 63.2%, formaldehyde selectivity: 92.8%, CO selectivity: 2.8%, CO2 selectivity: 0.7%, CH4 selectivity: 0.9%, methyl formate selectivity: 0.4%, dimethyl ether selectivity: 0.5%.

[0075] Example 10 Copper nitrate hexahydrate (0.05 mol) and zirconium nitrate pentahydrate (0.15 mol) were dissolved in 50 mL of water to obtain a solution. The solution was stirred and heated to 60 °C, and 0.1 mol / L NaOH solution was added dropwise until the pH ≈ 9. The solution was then stirred for 6 hours, followed by aging for 6 hours after stirring was stopped. The precipitate was obtained by filtration and washing. The precipitate was calcined at 650 °C in air for 5 hours, and then subjected to hydrogen gas (purity >99.9%, space velocity 400 h⁻¹) at 450 °C. -1 Reduction was carried out for 2 hours in an atmosphere containing 1% oxygen (O2 / N2) and a space velocity of 200 h⁻¹. After cooling to room temperature, the mixture was then subjected to further reduction at an oxygen content of 1% (O2 / N2) and a space velocity of 200 h⁻¹. -1 The catalyst Cu1Zr3 was obtained by passivation in an atmosphere for 12 hours.

[0076] The catalyst evaluation method and process are the same as in Example 1.

[0077] Results: Methanol conversion rate: 51.3%, formaldehyde selectivity: 93.8%, CO selectivity: 3.7%, CO2 selectivity: 0.7%, CH4 selectivity: 0.8%, methyl formate selectivity: 0.8%, dimethyl ether selectivity: 0.2%.

[0078] Example 11 Copper nitrate hexahydrate (0.05 mol) and chromium nitrate nonahydrate (0.15 mol) were dissolved in 50 mL of water to obtain a solution. The solution was stirred and heated to 60 °C, and 0.1 mol / L NaOH solution was added dropwise until the pH ≈ 9. The solution was then stirred for 6 hours, followed by aging for 6 hours after stirring was stopped. The precipitate was obtained by filtration and washing. The precipitate was calcined at 500 °C in air for 5 hours, and then subjected to hydrogen gas (purity >99.9%, space velocity 400 h⁻¹) at 300 °C. -1 Reduction was carried out for 2 hours in an atmosphere containing 1% oxygen (O2 / N2) and a space velocity of 200 h⁻¹. After cooling to room temperature, the mixture was then subjected to further reduction at an oxygen content of 1% (O2 / N2) and a space velocity of 200 h⁻¹. -1 The catalyst Cu1Cr3 was obtained by passivation in an atmosphere for 12 hours.

[0079] The catalyst evaluation method and process are the same as in Example 1.

[0080] Results: Methanol conversion rate: 13.2%, formaldehyde selectivity: 91.2%, CO selectivity: 4.1%, CO2 selectivity: 1.1%, CH4 selectivity: 0.9%, methyl formate selectivity: 2.5%, dimethyl ether selectivity: 0.2%.

[0081] Example 12 Copper nitrate hexahydrate (0.05 mol) and cerium nitrate nonahydrate (0.15 mol) were dissolved in 50 mL of water to obtain a solution. The solution was stirred and heated to 60 °C, and 0.1 mol / L NaOH solution was added dropwise until the pH ≈ 9. The solution was then stirred for 6 hours, followed by aging for 6 hours after stirring was stopped. The precipitate was obtained by filtration and washing. The precipitate was calcined at 500 °C in air for 5 hours, and then subjected to hydrogen gas (purity >99.9%, space velocity 400 h⁻¹) at 300 °C. -1 Reduction was carried out for 2 hours in an atmosphere containing 1% oxygen (O2 / N2) and a space velocity of 200 h⁻¹. After cooling to room temperature, the mixture was then subjected to further reduction at an oxygen content of 1% (O2 / N2) and a space velocity of 200 h⁻¹. -1 The catalyst Cu1Ce3 was obtained by passivation in an atmosphere for 12 hours.

[0082] The catalyst evaluation method and process are the same as in Example 1.

[0083] Results: Methanol conversion rate: 15.4%, formaldehyde selectivity: 90.8%, CO selectivity: 4.4%, CO2 selectivity: 1.3%, CH4 selectivity: 1.4%, methyl formate selectivity: 1.6%, dimethyl ether selectivity: 0.2%.

[0084] Example 13 The catalyst synthesis process was as described in Example 2, except that the amounts of copper and zinc salts were changed, with copper nitrate hexahydrate (0.15 mol) and zinc nitrate hexahydrate (0.05 mol) used to obtain the catalyst Cu3Zn1.

[0085] The catalyst evaluation method and process are the same as in Example 1.

[0086] Results: Methanol conversion rate: 22.4%, formaldehyde selectivity: 89.3%, CO selectivity: 5.0%, CO2 selectivity: 1.5%, CH4 selectivity: 0.6%, methyl formate selectivity: 2.0%, dimethyl ether selectivity: 0.2%.

[0087] Example 14 The catalyst synthesis process was as described in Example 2, except that the amounts of copper and zinc salts were changed, namely copper nitrate hexahydrate (0.1 mol) and zinc nitrate hexahydrate (0.1 mol), to obtain the catalyst Cu1Zn1.

[0088] The catalyst evaluation method and process are the same as in Example 1.

[0089] Results: Methanol conversion rate: 50.2%, formaldehyde selectivity: 90.7%, CO selectivity: 4.5%, CO2 selectivity: 2.0%, CH4 selectivity: 1.0%, methyl formate selectivity: 1.6%, dimethyl ether selectivity: 0.2%.

[0090] Example 15 The catalyst synthesis process is as described in Example 2, except that the calcination temperature of the precipitate is changed to 700°C to obtain the catalyst Cu1Zn3-O700.

[0091] The catalyst evaluation method and process are the same as in Example 1.

[0092] Results: Methanol conversion rate: 51.3%, formaldehyde selectivity: 90.2%, CO selectivity: 4.9%, CO2 selectivity: 2.4%, CH4 selectivity: 1.8%, methyl formate selectivity: 0.6%, dimethyl ether selectivity: 0.1%.

[0093] Example 16 The catalyst synthesis process is as described in Example 2, except that the reduction temperature is changed to 500℃ to obtain the catalyst Cu1Zn3-H500.

[0094] The catalyst evaluation method and process are the same as in Example 1.

[0095] Results: Methanol conversion rate: 23.6%, formaldehyde selectivity: 88.6%, CO selectivity: 5.6%, CO2 selectivity: 2.7%, CH4 selectivity: 2.1%, methyl formate selectivity: 0.7%, dimethyl ether selectivity: 0.3%.

[0096] Example 17 The catalyst synthesis process is as described in Example 2, except that the passivation time was changed to 1 hour to obtain the catalyst Cu1Zn3-P.

[0097] The catalyst evaluation method and process are the same as in Example 1.

[0098] Results: Methanol conversion rate: 31.5%, formaldehyde selectivity: 90.5%, CO selectivity: 4.7%, CO2 selectivity: 2.2%, CH4 selectivity: 1.7%, methyl formate selectivity: 0.5%, dimethyl ether selectivity: 0.2%.

[0099] Example 18 The catalyst of Example 2 was used, and the catalyst evaluation method and process were the same as in Example 2, except that the reaction temperature was changed to 320°C.

[0100] Results: Methanol conversion rate: 81.4%, formaldehyde selectivity: 81.1%, CO selectivity: 9.7%, CO2 selectivity: 4.8%, CH4 selectivity: 3.8%, methyl formate selectivity: 0.3%, dimethyl ether selectivity: 0.1%.

[0101] Example 19 The catalyst of Example 2 was used, and the catalyst evaluation method and process were the same as in Example 2, except that the reaction pressure was changed to 0.4 MPa.

[0102] Results: Methanol conversion rate: 21.5%, formaldehyde selectivity: 88.1%, CO selectivity: 3.5%, CO2 selectivity: 1.4%, CH4 selectivity: 1.2%, methyl formate selectivity: 5.3%, dimethyl ether selectivity: 0.5%.

[0103] Example 20 The catalyst used in Example 2 was evaluated using the same method and procedure as in Example 2, except that the methanol mass hourly space velocity (MHSV) was changed to 0.8 h⁻¹. -1 .

[0104] Results: Methanol conversion rate: 39.6%, formaldehyde selectivity: 90.8%, CO selectivity: 4.6%, CO2 selectivity: 1.8%, CH4 selectivity: 1.5%, methyl formate selectivity: 1.3%, dimethyl ether selectivity: 0.2%.

[0105] Example 21 The catalyst of Example 2 was used, and the catalyst evaluation method and process were the same as in Example 2. The methanol mass hourly space velocity was changed to 0.2 h⁻¹. -1 .

[0106] Results: Methanol conversion rate: 99.1%, formaldehyde selectivity: 96.0%, CO selectivity: 3.2%, CO2 selectivity: 0.4%, CH4 selectivity: 0.2%, methyl formate selectivity: 0.1%, dimethyl ether selectivity: 0.1%.

[0107] Comparative Example 1 Manganese nitrate tetrahydrate (0.1 mol) and zinc nitrate hexahydrate (0.05 mol) were dissolved in 50 mL of water to obtain a solution. The solution was stirred and heated at 60°C, and 0.1 mol / L NaOH solution was added dropwise until the pH ≈ 9. The solution was then stirred for 6 hours, and then aged for 6 hours without stirring. After filtration and washing, precipitate 1 was obtained. Copper nitrate hexahydrate (0.05 mol) was dissolved in 50 mL of water to obtain a solution. The solution was stirred and heated at 60°C, and 0.1 mol / L NaOH solution was added dropwise until the pH ≈ 9. The solution was then stirred for 6 hours, and then aged for 6 hours without stirring. After filtration and washing, precipitate 2 was obtained. Precipitates 1 and 2 were mixed and ground, and then calcined at 500°C in air for 5 hours. The calcination was then carried out under hydrogen gas (purity > 99.9%, space velocity 400 h⁻¹) at 300°C. -1 Reduction was carried out for 2 hours in an atmosphere containing 1% oxygen (O2 / N2) and a space velocity of 200 h⁻¹. After cooling to room temperature, the mixture was then subjected to further reduction at an oxygen content of 1% (O2 / N2) and a space velocity of 200 h⁻¹. -1 Passivation at a certain atmosphere for 12 hours yielded the catalyst Cu1 / Mn2Zn1.

[0108] The catalyst evaluation method and process are as described in Example 1.

[0109] Results: Methanol conversion rate: 26.3%, formaldehyde selectivity: 93.0%, CO selectivity: 4.3%, CO2 selectivity: 1.2%, CH4 selectivity: 1.0%, methyl formate selectivity: 0.4%, dimethyl ether selectivity: 0.1%.

[0110] Catalytic data were collected over 24 hours (1440 minutes) using chromatography, and the results are shown below. Figure 3 ,Depend on Figure 3 It can be seen that the methanol conversion rate decreased rapidly from 90% to 26%, indicating that the catalyst Cu1 / Mn2Zn1 in Comparative Example 1 was deactivated more quickly. XRD data of Cu1 / Mn2Zn1 before and after the reaction are shown below. Figure 4 As shown in the figure, the catalyst's crystalline phase is mainly composed of MnO and metallic Cu particles, with no characteristic peaks of Zn species, indicating a high degree of Zn dispersion. After the reaction, the peaks attributed to Cu particles and MnO became significantly sharper, indicating that both particles increased in size. This resulted in weaker interactions between Cu particles and the promoter, as well as weaker interactions between Mn oxides and Zn oxides on the promoter, leading to MnO particle growth. Therefore, the increase in copper particle size led to rapid catalyst deactivation.

[0111] Comparative Example 2 Copper nitrate hexahydrate (0.05 mol) was dissolved in 50 mL of water to obtain a solution. The solution was stirred and heated to 60°C, and 0.1 mol / L NaOH solution was added dropwise until the pH ≈ 9. The solution was then stirred for 6 hours, followed by aging for 6 hours after stirring was stopped. The precipitate was obtained by filtration and washing. The precipitate was calcined at 500°C in air for 5 hours, and then subjected to hydrogen gas (purity >99.9%, space velocity 400 h⁻¹) at 300°C. -1 Reduction was carried out for 2 hours in an atmosphere containing 1% oxygen (O2 / N2) and a space velocity of 200 h⁻¹. After cooling to room temperature, the mixture was then subjected to further reduction at an oxygen content of 1% (O2 / N2) and a space velocity of 200 h⁻¹. -1 Passivation at a certain atmosphere for 12 hours yielded the catalyst CuOx.

[0112] The catalyst evaluation method and process are as described in Example 1.

[0113] Results: Methanol conversion rate: 81.9%, formaldehyde selectivity: 93.2%, CO selectivity: 4.4%, CO2 selectivity: 2.5%, CH4 selectivity: 1.6%, methyl formate selectivity: 0.2%, dimethyl ether selectivity: 0.1%.

[0114] Comparative Example 3 The catalyst Cu1Mn3 from Example 1 was used.

[0115] The catalyst evaluation process is the same as in Example 1, except that the evaluation time is extended to 375 hours.

[0116] The results are as follows Figure 5 As shown, by Figure 5 It can be seen that in the first 200 hours, without catalyst regeneration, the methanol conversion rate remained at 80-82%, and the decline was very slow; however, after 200 hours, the rate of decline in conversion rate accelerated, and after 375 hours of online operation, the conversion rate was 63%; the formaldehyde selectivity remained at approximately 93%. This further demonstrates that the synergistic effect of the two-component additive is beneficial to the stability of the copper catalyst.

[0117] XRD patterns of Cu1Mn3 before and after the reaction are shown below. Figure 6 The significant enhancement of Cu particles in the catalyst after the reaction indicates Cu species sintering, which leads to a decrease in reaction activity. This reflects the limitations of single-component additives and suggests that oxide-oxide interactions in multi-component additives can effectively disperse and stabilize Cu species, greatly improving the stability of the catalyst.

[0118] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for producing formaldehyde from methanol via oxygen-free dehydrogenation, characterized in that, At 250~350℃, pressure 0.05~0.5 MPa, and methanol mass hourly space velocity 0.01~2h⁻¹, the methanol was subjected to the following conditions: -1 Under the reaction conditions, methanol is brought into contact with a copper-based catalyst to undergo a dehydrogenation reaction, producing formaldehyde and hydrogen gas; The copper-based catalyst comprises an active component Cu and an auxiliary element M, wherein the molar ratio of Cu to M is (0.1~3):1, and M is selected from one or more combinations of Mg, Mn, Zn, La, Al, Ga, Zr, Cr, and Ce. The preparation method of the catalyst includes the following steps: (1) Mix the aqueous solution of Cu-containing soluble salt and M-containing soluble salt with the precipitant solution to undergo a co-precipitation reaction and obtain a precipitate; (2) The precipitate obtained in step (1) is calcined in an oxygen-containing atmosphere to obtain the catalyst oxide precursor; (3) The catalyst oxide precursor obtained in step (2) is reduced in a hydrogen atmosphere to obtain the catalyst precursor; (4) The catalyst precursor obtained in step (3) is passivated in an oxygen-containing atmosphere to obtain a copper-based catalyst.

2. The method for producing formaldehyde from methanol by anaerobic dehydrogenation according to claim 1, characterized in that, The molar ratio of Cu to M is (0.3~3):1; the average particle size of the copper-based catalyst is ≤25nm, and the average particle size of Cu nanoparticles is ≤5nm.

3. The method for producing formaldehyde from methanol by anaerobic dehydrogenation according to claim 1, characterized in that, The coprecipitation reaction described in step (1) is carried out at 30~90℃ and pH 8~10, then aged for 4~12 h, and the precipitate is obtained after filtration and washing.

4. The method for producing formaldehyde from methanol by anaerobic dehydrogenation according to claim 1, characterized in that, The soluble salt of Cu in step (1) is at least one of the nitrate, chloride, sulfate or acetate of Cu, preferably nitrate; the soluble salt of M is at least one of the nitrate, chloride, sulfate or acetate of M, preferably nitrate; the precipitant solution is at least one of the following: sodium hydroxide aqueous solution, potassium hydroxide aqueous solution, sodium carbonate aqueous solution, potassium carbonate aqueous solution, urea aqueous solution or ammonia solution.

5. The method for producing formaldehyde from methanol by anaerobic dehydrogenation according to claim 1, characterized in that, The calcination in step (2) involves calcining the precipitate obtained in step (1) in a mixed atmosphere of oxygen and inert gas with an oxygen volume fraction of ≥10% at 300~700℃ for 2~10h.

6. The method for producing formaldehyde from methanol by anaerobic dehydrogenation according to claim 1, characterized in that, The reduction described in step (3) involves exposing the catalyst oxide precursor obtained in step (2) to a hydrogen atmosphere at a space velocity of 200-1000 h⁻¹. -1 Reduce at 200~500℃ for 2~10 hours.

7. The method for producing formaldehyde from methanol by anaerobic dehydrogenation according to claim 1, characterized in that, The passivation in step (4) involves placing the catalyst precursor obtained in step (3) in a mixed atmosphere of oxygen and inert gas with an oxygen volume fraction of 0.2-2% at a space velocity of 20-500 h⁻¹. -1 Passivation treatment at 10~30℃ for 5~200 h.

8. The method for producing formaldehyde from methanol by anaerobic dehydrogenation according to claim 1, characterized in that, The dehydrogenation reaction occurs at a temperature of 250–320 °C and a pressure of 0.05–0.3 MPa; the mass hourly space velocity (WHSV) of methanol is 0.1–1 h⁻¹. -1 Preferably, 0.2~0.8 h -1 .

9. The method for producing formaldehyde from methanol by anaerobic dehydrogenation according to claim 1, characterized in that, The dehydrogenation reaction is carried out in a fixed-bed reactor.

10. The method for producing formaldehyde from methanol by anaerobic dehydrogenation according to claim 1, characterized in that, The methanol conversion rate of the dehydrogenation reaction is maintained above 50%, the formaldehyde selectivity is maintained above 90%, and the single-pass operating life is not less than 200 hours.

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