A catalyst for efficiently preparing methyl methacrylate and application thereof

Abstract

The application discloses a catalyst for efficiently preparing methyl methacrylate and application thereof. The catalyst is prepared by impregnation of active components and high-temperature nitrogen-treated zeolite molecular sieves to obtain a modified nitrogen-doped molecular sieve composite catalyst. The catalyst provided by the application has high formaldehyde conversion rate and methyl propionate selectivity, and the catalyst has certain stability. The catalytic reaction is carried out in a high-pressure autoclave reactor, raw materials are cheap and easy to obtain, the preparation method is simple, the reaction operation process is short, no greenhouse gas carbon dioxide is generated in the preparation of methyl methacrylate, and the catalyst has good application prospect in the petrochemical industry.

Description

Technical Field

[0001] This invention relates to a catalyst for the preparation of methyl methacrylate by aldol condensation of formaldehyde and methyl propionate, its preparation method, and its application. It belongs to the field of methyl methacrylate synthesis technology. Specifically, it provides a method for the high-conversion and high-selectivity synthesis of methyl methacrylate by aldol condensation reaction of formaldehyde and methyl propionate using modified nitrogen-containing Beta molecular sieve as a catalyst. Background Technology

[0002] Methyl methacrylate (MMA) is an important organic chemical raw material and polymer monomer, mainly used to produce acrylic glass (PMMA), acrylic resin, molding compounds, lubricants, surface coatings, etc., and is widely used in aerospace, electronic information, medical, optical fiber and other fields.

[0003] Based on the different numbers of carbon atoms in the raw materials used in the MMA production process, the production methods are divided into:

[0004] Among the C2, C3, and C4 routes, the mainstream process for producing MMA in China is currently the acetone cyanohydrin method (C3). Although this process is technically mature, it has high production costs and causes significant pollution. The aldol condensation process (C2) is a relatively greener production route. This route has a shorter production flow, mainly consisting of two steps: First, methyl propionate is produced from ethylene, CO, and methanol through a carbonylation reaction; second, formaldehyde and methyl propionate are then condensed together via aldol condensation to produce MMA.

[0005] Currently, numerous studies on catalysts for the aldol condensation reaction of formaldehyde and methyl propionate to produce MMA have been reported both domestically and internationally (Appl. Catal. A-Gen, 2026,709: 120651; Chem. Eng. Sci., 2025, 317:122046; Mater. Today Chem, 2025,46: 102746; Catal. Lett., 2013,143(8): 829-838). Catalysts for the aldol condensation of formaldehyde and methyl propionate to produce methyl methacrylate are generally solid acids, solid bases, or bifunctional solid acid-base catalysts. Yue et al. (Mater. Today Chem, 2025, 46: 102746.) compared the reaction performance of molecular sieves of different types and mesh sizes (SiO2, γ-Al2O3, SBA-15, ZSM-5, HZSM-5, W-KIT-6, β-zeolite, TS-1 zeolite), and the results showed that the selectivity of solid acid catalyst MMA was generally low. Ai et al. (Appl. Catal. A-Gen, 2005, 288(1): 211-215.) loaded various alkali metal and alkaline earth metal hydroxides on silica and found that cesium hydroxide loaded on silica had the best performance. Li et al. (Catal. Lett., 2013, 143(8): 829-838.) prepared supported cesium catalysts using various supports. Through a series of characterizations, they found that the Zr–Mg–Cs / SiO2 catalyst exhibited moderate activity in the aldol condensation reaction of methyl propionate and formaldehyde to produce methyl methacrylate. However, the active components of alkali (earth) metal supported catalysts are easily lost, and deactivated catalysts are difficult to regenerate. The Cs-Nb / Al2O3 catalyst prepared by Liu et al. (Ind. Eng. Chem, 2023, 62: 21130.) showed excellent stability in the condensation reaction of methyl propionate and formaldehyde due to the Lewis acid-base pairs generated on its surface. The acid and base centers provided by bifunctional acid-base catalysts are relative, and there are two different reaction mechanisms in the forward process of the catalytic reaction. The synergistic effect of acid and base active sites can promote reactions such as hydrogenation, hydrogen transfer, and aldol condensation.

[0006] The different acidic and basic sites on the catalyst in the aldol condensation process for the preparation of methyl methacrylate (MMA) significantly affect the reaction performance. Using bifunctional catalysts can fully utilize the acid-base catalytic effect, resulting in a significant improvement in catalyst performance; however, this method has not yet been widely applied in industrial production. Therefore, this invention proposes to construct an acid-base bifunctional molecular sieve catalyst by introducing basic sites through ammonia nitridation on an acidic molecular sieve, and then using a one-step, highly efficient condensation of formaldehyde aqueous solution with methyl propionate to prepare MMA. Summary of the Invention

[0007] This invention provides a catalyst for the efficient aldol condensation of formaldehyde and methyl propionate to prepare methyl methacrylate, as well as its preparation and application, achieving high formaldehyde conversion and high selectivity for the target product MMA.

[0008] This invention provides a catalyst for the efficient aldol condensation of formaldehyde and methyl propionate to prepare methyl methacrylate. The catalyst is a modified nitrogen-doped molecular sieve catalyst. The catalyst comprises an active component and a support. The active component is selected from one or more elements selected from copper (Cu), zinc (Zn), aluminum (Al), vanadium (V), and phosphorus (P). The support is a nitrogen-doped molecular sieve, which is a molecular sieve subjected to high-temperature nitriding treatment. The catalyst exhibits high activity and good stability in the aldol condensation reaction.

[0009] The modified nitrogen-doped molecular sieve catalyst is an active component loaded on a nitrogen-doped molecular sieve. The catalyst catalyzes the aldol condensation reaction with high formaldehyde conversion (97%) and methyl propionate selectivity (87%), and low selectivity of byproducts methacrolein (5%) and methyl formate (0.6%). The catalyst also has good stability.

[0010] According to the above technical solution, as a preferred embodiment, the molecular sieve is a zeolite molecular sieve, specifically a Beta molecular sieve, with a Si / Al ratio of 6 to 40.

[0011] According to the above technical solution, as a preferred embodiment, the loading (mass fraction) of the active component in the modified nitrogen-doped molecular sieve catalyst is 0.1% to 10%, preferably 0.5% to 8%, for example 1%, 2%, 3%, or 4%.

[0012] According to the above technical solution, as a preferred method, the nitrogen-doped molecular sieve is prepared by placing the molecular sieve as a precursor in an ammonia atmosphere and treating it at a high temperature of 550~900 ℃ (preferably 800 ℃) for 8~16 h (preferably 12 h) to obtain the nitrogen-doped molecular sieve.

[0013] According to the above technical solution, as a preferred embodiment, the preparation method of the modified nitrogen-doped catalyst is as follows: After loading the active component onto the support, the catalyst is dried at room temperature for 0.5-2 hours, and then dried in an oven at 110-120°C for 1-4 hours to obtain a powdered catalyst. The powdered catalyst is then pressed into tablets, sieved, and calcined in a tube furnace under nitrogen at 200-600°C (430-450°C) for 0.5-6 hours (preferably 4-6 hours) to obtain a modified nitrogen-doped molecular sieve catalyst, which is the active component-supported molecular sieve catalyst. The catalyst particles are 40-60 mesh.

[0014] According to the above technical solution, as a preferred embodiment, the flow rate of nitrogen gas during the roasting is 30~60 mL / min.

[0015] According to the above technical solution, as a preferred embodiment, the carrier loaded with active components can be prepared by precipitation deposition, ion exchange or impregnation, with impregnation being the preferred method.

[0016] This invention also relates to the application of the methyl methacrylate catalyst described above in the aldol condensation reaction of formaldehyde and methyl propionate to produce methyl methacrylate.

[0017] According to the above technical solution, as a preferred embodiment, the application of the methyl methacrylate catalyst (modified nitrogen-doped molecular sieve catalyst) in the aldol condensation reaction is characterized by a reaction temperature of 300~500 ℃, preferably 340~380 ℃, and a reaction time of 2~8 h, preferably 3~5 h.

[0018] According to the above technical solution, as a preferred embodiment, in the application of the methyl methacrylate catalyst (modified nitrogen-doped molecular sieve catalyst) in the aldol condensation reaction, the molar ratio of formaldehyde to methyl propionate is 1:1 to 1:6, preferably 1:5.

[0019] According to the above technical solution, as a preferred embodiment, the application of the methyl methacrylate catalyst (modified nitrogen-doped molecular sieve catalyst) in the aldol condensation reaction involves mixing formaldehyde and methyl propionate solution and placing them into a high-pressure reactor. The amount of catalyst used is 0.05~2.0 g, preferably 0.1~0.3 g.

[0020] The application conditions of the catalyst of this invention are as follows: the reactor is filled with a modified nitrogen-doped molecular sieve catalyst, the amount of which is 0.05~2.0 g, preferably 0.1~0.3 g. The molar ratio of formaldehyde to methyl propionate is 1:4~1:6, preferably 1:5; the reaction temperature is 300~500 ℃, preferably 340~380 ℃; and the reaction time is 2~8 h, preferably 3~5 h.

[0021] This invention involves nitriding a molecular sieve with high-temperature ammonia gas to obtain a nitrogen-doped molecular sieve. The active component is then loaded onto the nitrogen-doped molecular sieve via an impregnation method to obtain a modified nitrogen-doped molecular sieve catalyst. This catalyst is then applied to the aldol condensation reaction of formaldehyde and methyl propionate to produce MMA. The highly active catalyst provided by this invention exhibits high formaldehyde conversion and methyl propionate selectivity, and also possesses a certain degree of stability. This catalytic reaction is carried out in a high-pressure autoclave reactor, and the reactants are inexpensive and readily available, the preparation method is simple, and the reaction operation is short.

[0022] The advantages of this invention are as follows: The catalyst raw materials, molecular sieves and metal salts, are inexpensive and readily available, and the preparation process is controllable and easy to operate.

[0023] The modified nitrogen-doped molecular sieve catalyst is an acid-base bifunctional catalyst that can realize the aldol condensation reaction of formaldehyde and methyl propionate in a mixed solution to prepare methyl methacrylate. The catalyst has high formaldehyde conversion (97%) and methyl propionate selectivity (87%), and very low selectivity for byproducts methacrolein (5%) and methyl formate (0.6%). In addition, the catalyst has good regeneration stability.

[0024] The preparation of methyl methacrylate does not involve direct oxygen participation, thus avoiding the generation of greenhouse gases (carbon dioxide), and has good application prospects in the petrochemical industry. Attached Figure Description

[0025] Figure 1 The graph shows the catalytic performance of HBeta molecular sieve and NBeta molecular sieve at different nitriding temperatures in the aldol condensation reaction of formaldehyde and methyl propionate.

[0026] Figure 2 This is a graph showing the catalytic performance of NBeta molecular sieves and NBeta molecular sieves supported with different active components in the aldol condensation reaction of formaldehyde and methyl propionate.

[0027] Figure 3 This is a graph showing the catalytic performance of NBeta molecular sieves with different Cu loadings in the aldol condensation reaction of formaldehyde and methyl propionate.

[0028] Figure 4 This is a graph showing the regeneration performance of the 2Cu / NB molecular sieve catalyst.

[0029] Figure 5 These are XRD patterns of HBeta, NBeta molecular sieves and NBeta molecular sieve catalysts with different Cu loadings. Detailed Implementation

[0030] The preferred embodiments of the present invention will be described in detail below so that the advantages and features of the present invention can be easily understood by those skilled in the art, thereby providing a clearer and more explicit definition of the scope of protection of the present invention.

[0031] Example The present invention will be specifically described below through embodiments, but the scope of the claims of the present invention is not limited to these embodiments. Furthermore, the embodiments only provide some conditions for achieving this objective, but do not imply that these conditions must be met to achieve this objective.

[0032] 1. Preparation of modified nitrogen-doped molecular sieves The preparation methods of the NBeta molecular sieve catalysts used in the following examples and comparative examples are as follows: Weigh 0.5g of HBeta (Zeolyst, Si / Al=19), place it in a tube furnace, introduce nitrogen gas, raise the temperature from room temperature to 400℃ at 2℃ / min, maintain the temperature at 400℃ for 400 min, then raise the temperature at 5℃ / min to the nitriding temperature, change the gas to NH3, maintain this temperature for a certain time, and then cool it to room temperature in a nitrogen atmosphere. This is denoted as NBeta (NB).

[0033] Example 1 Weigh 0.5 g of HBeta (Zeolyst, Si / Al=19), place it in a tube furnace, introduce nitrogen gas, raise the temperature from room temperature to 400 °C at 2 °C / min, maintain the temperature at 400 °C for 400 min, then raise the temperature to 600 °C at 5 °C / min, change the gas to NH3, maintain this temperature for 12 h, and then cool to room temperature in a nitrogen atmosphere. This is denoted as NB-600.

[0034] Example 2 Weigh 0.5 g of HBeta (Zeolyst, Si / Al=19), place it in a tube furnace, introduce nitrogen gas, raise the temperature from room temperature to 400 °C at 2 °C / min, maintain the temperature at 400 °C for 400 min, then raise the temperature to 700 °C at 5 °C / min, change the gas to NH3, maintain this temperature for 12 h, and then cool to room temperature in a nitrogen atmosphere. This is denoted as NB-700.

[0035] Example 3 Weigh 0.5 g of HBeta (Zeolyst, Si / Al=19), place it in a tube furnace, introduce nitrogen gas, raise the temperature from room temperature to 400 °C at 2 °C / min, maintain the temperature at 400 °C for 400 min, then raise the temperature to 800 °C at 5 °C / min, change the gas to NH3, maintain this temperature for 12 h, and then cool to room temperature in a nitrogen atmosphere. This is denoted as NB-800.

[0036] Example 4 Weigh 0.5 g of HBeta (Zeolyst, Si / Al=19), place it in a tube furnace, introduce nitrogen gas, raise the temperature from room temperature to 400 °C at 2 °C / min, maintain the temperature at 400 °C for 400 min, then raise the temperature to 850 °C at 5 °C / min, change the gas to NH3, maintain this temperature for 12 h, and then cool to room temperature in a nitrogen atmosphere. This is denoted as NB-850.

[0037] Example 5 Weigh 0.3 g of NB molecular sieve (NB-800) from Example 3, take 0.0231 g of copper nitrate, dissolve it in 1 ml of deionized water to obtain a copper nitrate solution, immerse the above NB molecular sieve in the above copper nitrate solution, stir for 30 min until uniformly mixed, place at room temperature for 1 h, dry at 120 ℃ for 2 h, the obtained powdered molecular sieve is pressed into tablets, sieved, and 40-60 mesh catalyst particles are taken, and then calcined in a tube furnace at 450 ℃ for 5 h in nitrogen (50 mL / min), denoted as 2Cu / NB-800, where 2Cu represents the Cu mass fraction determined by ICP is 2.0 wt%, the same below.

[0038] Example 6 Weigh 0.3 g of NB molecular sieve (NB-800) from Example 3, take 0.0280 g of zinc nitrate, dissolve it in 1 ml of deionized water to obtain a zinc nitrate solution, immerse the above NB molecular sieve in the above zinc nitrate solution, stir for 30 min until uniformly mixed, place at room temperature for 1 h, dry at 120 °C for 2 h, the obtained powdered molecular sieve is pressed into tablets, sieved, and 40-60 mesh catalyst particles are taken, and then calcined in a tube furnace at 450 °C for 5 h in nitrogen (50 mL / min), and recorded as 2Zn / NB-800.

[0039] Example 7 Weigh 0.3 g of NB molecular sieve (NB-800) from Example 3, take 0.0850 g of aluminum nitrate, dissolve it in 1 ml of deionized water to obtain an aluminum nitrate solution, immerse the above NB molecular sieve in the above aluminum nitrate solution, stir for 30 min until uniformly mixed, place at room temperature for 1 h, dry at 120℃ for 2 h, the obtained powdered molecular sieve is pressed into tablets, sieved, and 40-60 mesh catalyst particles are taken, and then calcined in a tube furnace at 450℃ for 5 h in nitrogen (50 mL / min), and recorded as 2Al / NB-800.

[0040] Example 8 Weigh 0.3 g of the NB molecular sieve (NB-800) from Example 3. Dissolve 0.0404 g of oxalic acid in 1 ml of deionized water to obtain an oxalic acid aqueous solution. Take 0.0187 g of ammonium metavanadate and add it to the oxalic acid aqueous solution until it is completely dissolved. Then, immerse the above NB molecular sieve in it and stir for 30 min until it is uniformly mixed. Let it stand at room temperature for 1 h and dry it at 120 °C for 2 h. The resulting powdered molecular sieve is pressed into tablets, sieved, and 40-60 mesh catalyst particles are taken. Then, it is calcined in a tube furnace at 450 °C for 5 h in nitrogen (50 mL / min) and recorded as 2V / NB-800.

[0041] Example 9 Weigh 0.3 g of NB molecular sieve (NB-800) from Example 3, take 0.0228 g of 85% phosphoric acid solution, dissolve it in 1 ml of deionized water to obtain a phosphoric acid solution, immerse the above NB molecular sieve in the above phosphoric acid solution, stir for 30 min until uniformly mixed, place at room temperature for 1 h, dry at 120 ℃ for 2 h, the obtained powdered molecular sieve is pressed into tablets, sieved, and 40-60 mesh catalyst particles are taken, and then calcined in a tube furnace at 450 ℃ for 5 h in nitrogen (50 mL / min), and recorded as 2P / NB-800.

[0042] Example 10 Weigh 0.3 g of NB molecular sieve (NB-800) from Example 3, take 0.0114 g of copper nitrate, dissolve it in 1 ml of deionized water to obtain a copper nitrate solution, immerse the above NB molecular sieve in the above copper nitrate solution, stir for 30 min until uniformly mixed, place at room temperature for 1 h, dry at 120 ℃ for 2 h, the obtained powdered molecular sieve is pressed into tablets, sieved, and 40-60 mesh catalyst particles are taken, and then calcined in a tube furnace at 450 ℃ for 5 h in nitrogen (50 mL / min), and recorded as 1Cu / NB-800.

[0043] Example 11 Weigh 0.3 g of NB molecular sieve (NB-800) from Example 3, take 0.035 g of copper nitrate, dissolve it in 1 ml of deionized water to obtain a copper nitrate solution, immerse the above NB molecular sieve in the above copper nitrate solution, stir for 30 min until uniformly mixed, place at room temperature for 1 h, dry at 120 ℃ for 2 h, the obtained powdered molecular sieve is pressed into tablets, sieved, and 40-60 mesh catalyst particles are taken, and then calcined in a tube furnace at 450 ℃ for 5 h in nitrogen (50 mL / min), and recorded as 3Cu / NB-800.

[0044] Example 12 Weigh 0.3 g of NB molecular sieve (NB-800) from Example 3, take 0.0472 g of copper nitrate, dissolve it in 1 ml of deionized water to obtain a copper nitrate solution, immerse the above NB molecular sieve in the above copper nitrate solution, stir for 30 min until uniformly mixed, place at room temperature for 1 h, dry at 120 ℃ for 2 h, the obtained powdered molecular sieve is pressed into tablets, sieved, and 40-60 mesh catalyst particles are taken, and then calcined in a tube furnace at 450 ℃ for 5 h in nitrogen (50 mL / min), and recorded as 4Cu / NB-800.

[0045] 2. Application of different catalysts in the aldol condensation reaction of methyl acetal acetate All reaction examples were conducted in a high-pressure autoclave reactor equipped with a stainless steel pressure gauge. Product analysis was performed using a Tianmei GC-7900 gas chromatograph with a dual FID / TCD detector. The catalytic performance of the catalyst was evaluated by detecting the trends in formaldehyde conversion, methyl propionate selectivity, and the selectivity of byproducts methacrolein and methyl formate.

[0046] Example 13 Examples 1, 2, 3, and 4 evaluate the aldol condensation reaction of formaldehyde and methyl propionate catalyzed by NB molecular sieves at different nitriding temperatures. The experiments were conducted in a high-pressure autoclave reactor under the following conditions: a mixed reaction solution of formaldehyde and methyl propionate (molar ratio of formaldehyde to methyl propionate 1:5) was placed in the autoclave; the catalyst dosage was 0.1 g; the rotation speed was 1200 rpm; after the rotation speed stabilized, heating was initiated, and the temperature was raised to 360 °C. This temperature was maintained for 4 hours, after which the rotation speed and heating were stopped. The reaction results are as follows: Figure 1 As shown.

[0047] Comparative Example 1 The aldol condensation reaction of formaldehyde and methyl propionate catalyzed by HB (HBeta) molecular sieve was evaluated. The experiment was carried out in a high-pressure autoclave reactor under the following conditions: a mixed reaction solution of formaldehyde and methyl propionate (molar ratio of formaldehyde to methyl propionate was 1:5) was placed in the autoclave, the catalyst dosage was 0.1 g, the rotation speed was 1200 rpm, and after the rotation speed stabilized, heating was started and the temperature was raised to 360 ℃. After maintaining this temperature for 4 h, the rotation speed and heating were stopped. The reaction results are as follows: Figure 1 As shown.

[0048] Example 14 Examples 5, 6, 7, 8, and 9 evaluated the aldol condensation reaction of formaldehyde and methyl propionate catalyzed by NB molecular sieves modified with different elements. The experiments were conducted in a high-pressure autoclave reactor under the following conditions: a mixed reaction solution of formaldehyde and methyl propionate (molar ratio of formaldehyde to methyl propionate was 1:5) was placed in the autoclave; the catalyst dosage was 0.1 g; the rotation speed was 1200 rpm; after the rotation speed stabilized, heating was initiated, and the temperature was raised to 360 °C. This temperature was maintained for 4 hours, after which the rotation speed and heating were stopped. The reaction results are as follows: Figure 2 As shown.

[0049] Example 15 Examples 5, 10, 11, and 12 evaluated the aldol condensation reaction of formaldehyde and methyl propionate catalyzed by Cu-modified NB molecular sieves with different mass fractions. The experiments were conducted in a high-pressure autoclave reactor under the following conditions: a mixed reaction solution of formaldehyde and methyl propionate (molar ratio of formaldehyde to methyl propionate was 1:5) was placed in the autoclave; the catalyst dosage was 0.1 g; the rotation speed was 1200 rpm; after the rotation speed stabilized, heating was initiated, and the temperature was raised to 360 °C. This temperature was maintained for 4 hours, after which the rotation speed and heating were stopped. The reaction results are as follows: Figure 3 As shown.

[0050] Figure 1 This study compares the catalytic performance of HBeta molecular sieves and NBeta molecular sieves at different nitriding temperatures in the aldol condensation reaction of formaldehyde and methyl propionate. HBeta molecular sieves achieved a formaldehyde conversion rate of approximately 92% and a methyl methacrylate selectivity of approximately 67%. As the nitriding temperature of HBeta molecular sieves gradually increased from 600℃ to 850℃, both the formaldehyde conversion rate and the methyl methacrylate selectivity showed a trend of first increasing and then decreasing. The molecular sieve nitrided at 800℃ exhibited the best performance; therefore, 800℃ is considered the optimal nitriding temperature.

[0051] Figure 2 This study compares the catalytic performance of NBeta molecular sieves with different supported active components in the aldol condensation reaction of formaldehyde and methyl propionate. Five different active components were supported on the NB molecular sieve catalysts. The methyl propionate selectivity was higher on both the 2Cu / NB800 and 2P / NB800 catalysts than on the unsupported NB catalysts. The 2Cu / NB800 catalyst exhibited the highest catalytic performance, making it a superior acid-base bifunctional catalyst, achieving a formaldehyde conversion rate of 97% and a methyl propionate selectivity of 87%.

[0052] Figure 3 This study compares the catalytic performance of NBeta molecular sieves with different mass fractions of Cu in the aldol condensation reaction of formaldehyde and methyl propionate. Four different mass fractions of NB molecular sieve catalysts were loaded. As the loading increased from 1 wt% to 4 wt%, the formaldehyde conversion remained almost constant, while the selectivity for methyl methacrylate initially increased and then decreased. The 2Cu / NB800 molecular sieve exhibited the best performance. Excessive addition of Cu led to a decrease in the selectivity of methyl methacrylate and an increase in byproducts; therefore, 2Cu / NB800 was selected as the catalyst for this reaction.

[0053] The above reaction evaluation results show that the 2Cu / NB800 modified nitrogen-containing molecular sieve catalyst proposed in this invention has the best reaction performance in the aldol condensation reaction of formaldehyde and methyl propionate to prepare methyl methacrylate.

[0054] 3. Catalyst regeneration cycle performance Example 16 Take 0.6 g of the catalyst after the reaction of 2Cu / NB-800 molecular sieve in Example 15, place it in a tube furnace, introduce nitrogen gas, and raise the temperature from room temperature to 120 °C at 2 °C / min. Maintain this temperature for 1 h, then change the gas to air, raise the temperature to 550 °C at 5 °C / min, and calcine at 550 °C for 4 h to obtain the catalyst, which is denoted as re-1.

[0055] Example 17 Take 0.6 g of the catalyst after the reaction of re-1 molecular sieve in Example 16, place it in a tube furnace, introduce nitrogen gas, and raise the temperature from room temperature to 120 °C at 2 °C / min. Maintain this temperature for 1 h, then change the gas to air, raise the temperature to 550 °C at 5 °C / min, and calcine at 550 °C for 4 h to obtain the catalyst, which is denoted as re-2.

[0056] Example 18 Take 0.6 g of the catalyst after the reaction of re-2 molecular sieve in Example 17, place it in a tube furnace, introduce nitrogen gas, and raise the temperature from room temperature to 120 °C at 2 °C / min. Maintain this temperature for 1 h, then change the gas to air, raise the temperature to 550 °C at 5 °C / min, and calcine at 550 °C for 4 h to obtain the catalyst, which is denoted as re-3.

[0057] Example 19 Take 0.6 g of the catalyst after the reaction of re-3 molecular sieve in Example 18, place it in a tube furnace, introduce nitrogen gas, and raise the temperature from room temperature to 120 °C at 2 °C / min. Maintain this temperature for 1 h, then change the gas to air, raise the temperature to 550 °C at 5 °C / min, and calcine at 550 °C for 4 h to obtain the catalyst, which is denoted as re-4.

[0058] Example 20 Take 0.6 g of the catalyst after the reaction of re-4 molecular sieve in Example 19, place it in a tube furnace, introduce nitrogen gas, and raise the temperature from room temperature to 120 °C at 2 °C / min. Maintain this temperature for 1 h, then change the gas to air, raise the temperature to 550 °C at 5 °C / min, and calcine at 550 °C for 4 h to obtain the catalyst, which is denoted as re-5.

[0059] Weigh 0.5 g of re-5 and place it in a tube furnace. Purge with nitrogen and raise the temperature from room temperature to 400 °C at a rate of 2 °C / min. Maintain the temperature at 400 °C for 400 min. Then raise the temperature to 850 °C at a rate of 5 °C / min. Change the gas to NH3 and maintain this temperature for 12 h. Then cool to room temperature under a nitrogen atmosphere to obtain the catalyst, denoted as re-5-n.

[0060] Example 21 Examples 16, 17, 18, 19, and 20 evaluate the catalytic performance of re-1, re-2, re-3, re-4, and re-5-n molecular sieves in the aldol condensation reaction of formaldehyde and methyl propionate. The experiments were conducted in a high-pressure autoclave reactor under the following conditions: a mixed reaction solution of formaldehyde and methyl propionate (molar ratio of formaldehyde to methyl propionate was 1:5) was placed in the high-pressure reactor; the catalyst dosage was 0.1 g; the rotation speed was 1200 rpm; after the rotation speed stabilized, heating was initiated, and the temperature was raised to 360 °C. This temperature was maintained for 4 hours, after which the rotation speed and heating were stopped. The reaction results are as follows: Figure 4 As shown, after four regenerations, the catalyst still maintains certain catalytic performance. The selectivity of the target product is reduced, but it is still above 75%. The catalyst after four regenerations is subjected to nitrogen supplementation in ammonia at 800 °C. The performance of the resulting re-5-n catalyst is further restored, with the selectivity of the target product increasing to 83% and the formaldehyde conversion rate increasing to 95%.

[0061] 4. XRD analysis of different catalysts Example 22 0.1 g of each of the HBeta molecular sieve and the molecular sieve catalysts from Examples 3, 5, 10, 11, and 12 were subjected to XRD analysis under the following conditions: tube voltage 40 kV, tube current 100 mA, CuKα X-ray source, scan rate 8 ° / min, and scan range 2θ = 5–50 °. The test results are as follows: Figure 5 As shown.

[0062] Figure 5 The images show the XRD patterns of HB and NB molecules loaded with different mass fractions of Cu. The Beta molecular sieve exhibits two main characteristic diffraction peaks at 2θ of 6.8° and 22.4°. Figure 4 As shown, characteristic diffraction peaks of Beta molecular sieves can be observed before and after high-temperature nitriding and before and after loading Cu elements. The positions of the main diffraction peaks did not change, indicating that the sample still maintains the BEA structure after nitriding and loading modification.

Claims

1. A catalyst for the aldol condensation of formaldehyde and methyl propionate to prepare methyl methacrylate, characterized in that: The catalyst is a modified nitrogen-doped molecular sieve catalyst; the catalyst includes an active component and a support, the active component is selected from one or more of Cu, Zn, Al, V and P elements, and the support is a nitrogen-doped molecular sieve, which is a molecular sieve that has undergone high-temperature nitriding treatment.

2. The catalyst according to claim 1, characterized in that: The molecular sieve is a zeolite molecular sieve, specifically a Beta molecular sieve, with a silica-to-alumina ratio of 6 to 40. The loading of the active component in the modified nitrogen-doped molecular sieve catalyst is 0.1 to 10%.

3. The catalyst according to claim 1, characterized in that: Nitrogen-doped molecular sieves were obtained by treating molecular sieves as precursors in an ammonia atmosphere at 550–900 °C for 8–16 h.

4. The catalyst according to claim 1, characterized in that: The active component was loaded onto a nitrogen-doped molecular sieve and dried at room temperature for 0.5–2 h. Then, it was dried in an oven at 110–120 °C for 1–4 h. The resulting powdered catalyst was pressed into tablets and sieved to obtain catalyst particles. The particles were then calcined in nitrogen at 200–600 °C for 0.5–6 h to obtain a modified nitrogen-doped molecular sieve catalyst. The catalyst particles were 40–60 mesh.

5. The method for preparing the catalyst according to claim 4, characterized in that: The carrier loaded with active components is prepared by precipitation deposition, ion exchange or impregnation.

6. The method for preparing the catalyst according to claim 4, characterized in that: The nitrogen flow rate during the roasting process is 30~60 mL / min.

7. The use of the methyl methacrylate catalyst according to any one of claims 1-6 in the reaction of formaldehyde and methyl propionate aldol condensation to produce methyl methacrylate.

8. The application according to claim 7, characterized in that: The reaction temperature is 300~500 ℃, and the reaction time is 2~8 h.

9. The application according to claim 7, characterized in that: The molar ratio of formaldehyde to methyl propionate is 1:1 to 1:

6.

10. The application according to claim 7, characterized in that: The amount of the catalyst used is 0.05~2.0 g.

Images