A catalyst for aldol condensation reaction, its preparation and application

Abstract

The present invention discloses a catalyst for aldol condensation reaction, its preparation and application, specifically relating to a method for preparing a catalyst for aldol condensation reaction using biomass-based SiO2 and using the catalyst to catalyze the preparation of methyl methacrylate from a mixed solution (or mixed aqueous solution) of formaldehyde and methyl propionate; the loading amount of the active metal on the catalyst is 1-10 wt%, and the total loading amount of the promoter is 0.5-5 wt%. The catalyst provided by the present invention has excellent water resistance and stability. The catalytic reaction is carried out in a fixed-bed reactor, and the carrier gas is an oxygen-containing inert atmosphere. The raw material formaldehyde in the reaction system can be obtained from methanol, and both methanol and the carrier SiO2 can be derived from biomass. Thus, under the background of aiming at "dual carbon" and popularizing green consumption, the high-value utilization of biomass resources is realized, and further the innovation of green and low-carbon technologies is achieved.

Description

Technical Field

[0001] The present invention relates to a catalyst for aldol condensation reaction, its preparation and application; specifically, it relates to a preparation method of an aldol condensation reaction catalyst using biomass-based SiO2 as a carrier and its application in catalyzing the preparation of methyl methacrylate from a mixed solution of formaldehyde and methyl propionate or its aqueous mixed solution. Background Art

[0002] Methyl methacrylate (MMA) is an important organic chemical raw material, mainly used for the production of polymethyl methacrylate (PMMA), and can also be used to manufacture lubricant additives, plastic PVC impact modifiers, surface coatings, adhesives and various industrial aids.

[0003] From the perspective of raw materials, the production methods of MMA can be divided into: acetone cyanohydrin method (ACH method), C2, C3 and C4 route methods. At present, the domestic MMA production process is mainly the ACH method, which has high production costs and serious pollution. The Alpha method is a new green production process route, which is mainly divided into two-step reactions. First, ethylene is carbonylated to synthesize methyl propionate, and then methyl propionate and formaldehyde are subjected to aldol condensation to synthesize MMA. It has the characteristics of easily available raw materials, safety, environmental friendliness and no pollution. There have been many literature reports on the catalysts for the synthesis of MMA by the aldol condensation of methyl propionate and formaldehyde (Appl. Catal. A, 2005, 288: 211-215; Ind. Eng. Chem. Res., 2014, 53: 1386-1394; Catal. Lett., 2013, 143: 829-838). In the aldol condensation of methyl propionate and formaldehyde to synthesize MMA, formaldehyde can be prepared from methanol, and both methanol and the carrier SiO2 can be derived from biomass. This is a MMA synthesis route based on C2 chemistry, thus realizing the high-value utilization of biomass and further realizing the innovation of green and low-carbon technologies. Summary of the Invention

[0004] The present invention provides a method for preparing a biomass-based SiO2 for use as a catalyst in aldol condensation reaction and its application in catalyzing the preparation of methyl methacrylate from a mixed solution of formaldehyde and methyl propionate (or mixed aqueous solution), explores a suitable catalytic system, and conducts aldol condensation reaction according to the C2 technical route to achieve the efficient conversion of formaldehyde and methyl propionate to synthesize methyl methacrylate.

[0005] A catalyst for aldol condensation reaction, its preparation and application are specifically as follows:

[0006] Preparation of biomass-based SiO2 carrier:

[0007] First, dry the biomass raw material rich in silicon at 80 - 150 °C for 1 - 12 h. After drying, calcine it once in an air atmosphere at 200 - 700 °C for 30 - 300 min, then mechanically pulverize it to 100 - 200 mesh, collect the product, and denote it as Z.

[0008] For the collected product Z, select a solvent rich in carboxyl functional groups to remove toxic metal impurities, then perform oxidation treatment with a strong oxidizing solution. Finally, calcine the treated biomass raw material rich in silicon in an air atmosphere at 500 - 700 °C for 30 - 500 min. The obtained product is biomass-based SiO₂. The biomass SiO₂ prepared by this method has a content > 99.50%, and has the characteristics of being amorphous, having a porous structure, controllable particle size, high purity, and large specific surface area. Its specific surface area is 100 - 350 m 2 / g, and the pore diameter is 5 - 100 nm, which can be used as a carrier completely.

[0009] Preparation of the aldol condensation reaction catalyst:

[0010] The aldol condensation reaction catalyst is prepared by the impregnation method. First, dissolve the active component S in deionized water to form an aqueous solution with a concentration of 1 - 10 wt%, denoted as solution A; add diammonium hydrogen phosphate (concentration 1 - 10 wt%) as a carrier stabilizer to solution A, denoted as solution B; weigh 5 - 50 g of biomass-based SiO₂ and disperse it in solution B, and continuously stir it for 6 - 24 h under the action of magnetic stirring; then perform suction filtration and dry it at 120 °C. The obtained sample is the precursor of the catalyst for producing methyl methacrylate, denoted as S-P / SiO₂; then use an auxiliary agent to adjust the acidity and alkalinity of the catalyst precursor. Dissolve a certain amount of auxiliary agent M in deionized water, denoted as solution C (concentration 0.05 - 0.5 wt%); disperse the catalyst precursor S-P / SiO₂ in solution C again, continuously stir it for 6 - 24 h under the action of magnetic stirring, perform suction filtration and drying again, and finally calcine it in a muffle furnace at 400 - 700 °C for 6 - 12 h; the obtained sample is the catalyst for the aldol condensation reaction using biomass-based SiO₂, tablet it to 40 - 60 mesh, and denote it as S-P-M / SiO₂.

[0011] The biomass raw material rich in silicon includes but is not limited to wheat husks, rice husks, wheat straw, rice straw, straw, corn cobs, peanut shells, bark, reed grass, and hemp stalks;

[0012] The solvent rich in carboxyl functional groups is one or more of citric acid solution, formic acid solution, acetic acid solution, oxalic acid solution, and lactic acid solution, and the concentration of the solution is 0.1 - 10 wt%;

[0013] The strong oxidizing substances are one or more of ozone, hydrogen peroxide, peracetic acid, potassium permanganate and other oxides, and the concentration of the strong oxidizing substance solution is 0.1-5 wt%.

[0014] Finally, the biomass raw material rich in silicon is calcined in an air atmosphere at 500-700 °C for 30-500 min, and the obtained product is biomass-based SiO2.

[0015] The active component S includes one or more of Li, Na, K, Cs, Sr, Ba;

[0016] The precursor reagents of the above active components are one or more of metal ion chlorides, nitrates, carbonates and ammonium salts;

[0017] The promoter M includes one or more of V, Nb, La, Fe, W, Zr, Sn;

[0018] The precursor reagents of the above promoters are one or more of metal ion nitrates, carbonates and ammonium salts;

[0019] The prepared catalyst is applied to the preparation of methyl methacrylate by aldol condensation reaction of a mixed solution of formaldehyde and methyl propionate or its aqueous mixed solution. The specific reaction process is as follows: Using a fixed-bed reactor, the middle section of the bed is filled with the aldol condensation reaction catalyst (catalyst size 40-60 mesh), and the upper and lower sections are filled with quartz sand; the raw materials are a mixed solution of formaldehyde and methyl propionate or its aqueous mixed solution; the reaction temperature is 200-450 °C, the pressure is 0.05-2 MPa, and the LHSV of the reaction process is 0.1-3 h -1 . The collected product is a mixed solution containing methyl methacrylate and methacrylic acid.

[0020] In the mixed solution of formaldehyde and methyl propionate or its aqueous mixed solution, the molar ratio of formaldehyde:methyl propionate:carrier gas is 1:(0.2-5):(0.02-0.5), the carrier gas is an oxygen-containing inert atmosphere (O2 content 1-5 vol%, the rest is N2), and the water content is 0-60 wt%.

[0021] The reaction involved in the present invention can be represented by the following reaction equation:

[0022]

[0023] The catalyst provided by the present invention has excellent water resistance and stability. This catalytic reaction is carried out in a fixed-bed reactor, and the carrier gas is an oxygen-containing inert atmosphere. The raw material formaldehyde in this reaction system can be prepared from methanol, and both methanol and the carrier SiO2 can be derived from biomass, realizing the high-value utilization of biomass resources and thus realizing the innovation of green and low-carbon technologies.

[0024] Beneficial technical effects of the present invention

[0025] 1. The prepared catalyst has cheap and easily available raw materials, and the preparation process is controllable and easy to operate. The aldol condensation reaction of a mixed solution of formaldehyde and methyl propionate or its aqueous mixed solution can be realized to prepare methyl methacrylate; both the catalyst support and the raw material formaldehyde can be derived from biomass, thus realizing the innovation of green and low-carbon technology.

[0026] 2. The catalyst has good stability and activity, and also has certain water resistance. The reaction process is simple, controllable and easy to operate, and the highest combined yield of methyl methacrylate and methacrylic acid can reach 39%. Specific embodiments

[0027] The following is a detailed description in combination with the preferred embodiments of the present invention, so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby making a clearer and more definite definition of the protection scope of the present invention.

[0028] Example 1

[0029] Weigh about 150 g of rice husks, dry them and then calcine them once in an air atmosphere at 300 °C for 90 min, and then mechanically pulverize them to about 150 meshes. Collect the product and put the collected product into a beaker containing no less than 1 L of 0.5 wt% citric acid solution. Stir continuously at 90 °C for 60 min. After filtration, put the solid into no less than 1 L of 1 wt% H2O2 solution and stir at 50 °C for 60 min. Wash twice with water, dry the solid in an oven at 120 °C for 2 h, and then calcine it twice in an air atmosphere at 500 °C for 100 min to obtain 17.9 g of biomass-based SiO2, with a SiO2 mass content of 99.56%, a specific surface area of about 320 m 2 / g or so, and a pore diameter of about 16 nm;

[0030] Weigh 0.809 g of cesium carbonate and dissolve it in deionized water to form a 1 wt% aqueous solution, denoted as solution A; add diammonium hydrogen phosphate (final concentration 2 wt%) as the carrier stabilizer to solution A, denoted as solution B; weigh 14 g of biomass-based SiO₂ and disperse it in solution B, and continuously stir for 6 h under magnetic stirring; then perform suction filtration and dry at 120 °C for 12 h. The obtained sample is the precursor of the catalyst for producing methyl methacrylate, denoted as Cs-P / SiO₂; then use an additive to adjust the acidity and alkalinity of the catalyst precursor. Weigh 0.071 g of ferric nitrate as the additive and dissolve it in deionized water, denoted as solution C (concentration 0.1 wt%); then disperse the catalyst precursor Cs-P / SiO₂ in solution C, continuously stir for 6 h under magnetic stirring, perform suction filtration again, dry at 120 °C for 12 h, and finally calcine in a muffle furnace at 500 °C for 6 h; the obtained sample is the catalyst Cs-P-Fe / SiO₂ for the aldol condensation reaction using biomass-based SiO₂, denoted as Cat-1.

[0031] Press the obtained Cat-1 into tablets with a mesh size of 40 - 60, and then load them into a stainless steel tube fixed-bed reactor (the inner diameter of the fixed bed is 8 mm). Fill the middle section of the bed with the aldol condensation reaction catalyst, and fill the upper and lower sections of the catalyst bed with quartz sand respectively; the raw material is a mixed solution of formaldehyde and methyl propionate, the reaction temperature is 340 °C, the pressure is 0.05 MPa, and LHSV = 3 h -1 , the molar ratio of formaldehyde: methyl propionate: carrier gas is 1:1:0.04, the carrier gas is an oxygen-containing inert atmosphere (O₂ content 1 vol%, the rest is N₂), and the water content of the raw material is 0 wt%. Online monitoring by gas chromatography; finally, after analysis, the conversion rate of methyl propionate is higher than 29%, and the selectivity of methyl methacrylate is higher than 90%.

[0032] Example 2

[0033] Weigh about 150 g of rice husks, dry them and then calcine them once in an air atmosphere at 300 °C for 60 min, then mechanically pulverize them to about 200 mesh, collect the product, put the collected product into a beaker containing no less than 1 L of 1 wt% citric acid solution, continuously stir at 90 °C for 60 min, after filtration, put the solid into no less than 1 L of 5 wt% H₂O₂ solution, stir at 50 °C for 90 min, wash twice with water, dry the solid in an oven at 120 °C for 2 h, and then calcine it twice in an air atmosphere at 500 °C for 60 min to obtain 17.0 g of biomass-based SiO₂, SiO₂ mass content = 99.60%, specific surface area is about 220 m 2 / g, and the pore diameter is about 13 nm;

[0034] Weigh 0.809 g of cesium carbonate and dissolve it in deionized water to form a 1 wt% aqueous solution, denoted as solution A; add diammonium hydrogen phosphate (final concentration 2 wt%) as a carrier stabilizer to solution A, denoted as solution B; weigh 14 g of biomass-based SiO₂ and disperse it in solution B, and continuously stir for 6 h under magnetic stirring; then perform suction filtration and dry at 120 °C for 12 h. The obtained sample is the precursor of the catalyst for producing methyl methacrylate, denoted as Cs-P / SiO₂; then use an auxiliary agent to adjust the acidity and alkalinity of the catalyst precursor. Weigh 0.035 g of cerium nitrate hexahydrate and dissolve it in deionized water, denoted as solution C (concentration 0.1 wt%); then disperse the catalyst precursor Cs-P / SiO₂ in solution C, continuously stir for 6 h under magnetic stirring, perform suction filtration again, dry at 120 °C for 12 h, and finally calcine in a muffle furnace at 500 °C for 6 h; the obtained sample is the catalyst Cs-P-Ce / SiO₂ for the aldol condensation reaction using biomass-based SiO₂, denoted as Cat-2.

[0035] Press the obtained Cat-2 into tablets of 40 - 60 mesh, and then load them into a stainless steel tube fixed-bed reactor (inner diameter of the fixed bed is 8 mm). Fill the middle section of the bed with the aldol condensation reaction catalyst, and fill the upper and lower sections of the catalyst bed with quartz sand respectively; the raw material is a mixed solution of formaldehyde and methyl propionate, the reaction temperature is 340 °C, the pressure is 0.05 MPa, and LHSV = 3 h -1 , the molar ratio of formaldehyde : methyl propionate : carrier gas is 1 : 2 : 0.04, the carrier gas is an oxygen-containing inert atmosphere (O₂ content 3 vol%, the rest is N₂), and the water content of the raw material is 10 wt%. Online monitoring by gas chromatography; finally, after analysis, the conversion rate of methyl propionate is higher than 27%, and the selectivity of methyl methacrylate is higher than 89%.

[0036] Example 3

[0037] Weigh about 150 g of wheat straw, dry it and calcine it once in an air atmosphere at 500 °C for 30 min, then mechanically pulverize it to about 150 mesh, collect the product, put the collected product into a beaker containing no less than 1 L of 1 wt% citric acid solution, continuously stir at 90 °C for 60 min, after filtration, put the solid into no less than 5 L of 1 wt% H₂O₂ solution, stir at 50 °C for 100 min, wash twice with water, dry the solid in an oven at 120 °C for 2 h, and then calcine it twice in an air atmosphere at 700 °C for 30 min to obtain 15.0 g of biomass-based SiO₂, SiO₂ mass content = 99.52%, specific surface area is about 220 m 2 / g, and the pore diameter is about 9 nm;

[0038] Weigh 0.834 g of potassium hydroxide and dissolve it in deionized water to form a 1 wt% aqueous solution, denoted as solution A; add diammonium hydrogen phosphate (final concentration 2 wt%) as a carrier stabilizer to solution A, denoted as solution B; weigh 14 g of biomass-based SiO₂ and disperse it in solution B, and continuously stir for 6 h under magnetic stirring; then perform suction filtration and dry at 120 °C for 12 h. The obtained sample is the precursor of the catalyst for producing methyl methacrylate, denoted as Cs-P / SiO₂; then use an auxiliary agent to adjust the acidity and alkalinity of the catalyst precursor. Weigh 0.071 g of iron nitrate and dissolve it in deionized water, denoted as solution C (concentration 0.1 wt%); then disperse the catalyst precursor K-P / SiO₂ in solution C, continuously stir for 6 h under magnetic stirring, perform suction filtration again, dry at 120 °C for 12 h, and finally calcine in a muffle furnace at 500 °C for 6 h; the obtained sample is the catalyst K-P-Fe / SiO₂ for the aldol condensation reaction using biomass-based SiO₂, denoted as Cat-3.

[0039] Press the obtained Cat-3 into tablets with a mesh size of 40 - 60, and then load them into a stainless steel tube fixed-bed reactor (inner diameter of the fixed bed is 8 mm). Fill the middle section of the bed with the aldol condensation reaction catalyst, and fill the upper and lower sections of the catalyst bed with quartz sand respectively; the raw material is a mixed solution of formaldehyde and methyl propionate, the reaction temperature is 340 °C, the pressure is 0.05 MPa, and LHSV = 3 h -1 , the molar ratio of formaldehyde:methyl propionate:carrier gas is 1:0.5:0.02, the carrier gas is an oxygen-containing inert atmosphere (O₂ content 5 vol%, the rest is N₂), and the water content of the raw material is 40 wt%. Online monitoring by gas chromatography; finally, after analysis, the conversion rate of methyl propionate is higher than 20%, and the selectivity of methyl methacrylate is higher than 76%.

[0040] Example 4

[0041] Weigh about 300 g of reed grass, dry it and calcine it once in an air atmosphere at 200 °C for 150 min, then mechanically pulverize it to about 100 mesh, collect the product, put the collected product into a beaker containing no less than 1 L of 1 wt% citric acid solution, continuously stir at 90 °C for 100 min, after filtration, put the solid into no less than 1 L of 5 wt% H₂O₂ solution, stir at 50 °C for 60 min, wash twice with water, dry the solid in an oven at 120 °C for 2 h, and then calcine it twice in an air atmosphere at 500 °C for 60 min to obtain 20.0 g of biomass-based SiO₂, SiO₂ mass content = 99.68%, specific surface area is 150 m 2 / g, pore diameter is 5 nm;

[0042] Weigh 0.809 g of cesium carbonate and dissolve it in deionized water to form a 1 wt% aqueous solution, denoted as solution A; add diammonium hydrogen phosphate (final concentration 2 wt%) as a carrier stabilizer to solution A, denoted as solution B; weigh 14 g of biomass-based SiO₂ and disperse it in solution B, and continuously stir for 6 h under magnetic stirring; then perform suction filtration and dry at 120 °C for 12 h. The obtained sample is the precursor of the catalyst for producing methyl methacrylate, denoted as Cs-P / SiO₂; then use an auxiliary agent to adjust the acidity and alkalinity of the catalyst precursor. Weigh 0.049 g of zirconium nitrate and dissolve it in deionized water, denoted as solution C (concentration 0.1 wt%); then disperse the catalyst precursor Cs-P / SiO₂ in solution C, continuously stir for 6 h under magnetic stirring, perform suction filtration again, dry at 120 °C for 12 h, and finally calcine in a muffle furnace at 500 °C for 6 h; the obtained sample is the catalyst Cs-P-Zr / SiO₂ for the aldol condensation reaction using biomass-based SiO₂, denoted as Cat-4.

[0043] Press the obtained Cat-4 into tablets of 40 - 60 mesh, and then load them into a stainless steel tube fixed-bed reactor (inner diameter of the fixed bed is 8 mm). Fill the middle section of the bed with the aldol condensation reaction catalyst, and fill the upper and lower sections of the catalyst bed with quartz sand respectively; the raw material is a mixed solution of formaldehyde and methyl propionate, the reaction temperature is 340 °C, the pressure is 0.05 MPa, and LHSV = 3 h -1 , the molar ratio of formaldehyde:methyl propionate:carrier gas is 1:1:0.04, the carrier gas is an oxygen-containing inert atmosphere (O₂ content 5 vol%, the rest is N₂), and the water content of the raw material is 60 wt%. Online monitoring by gas chromatography; finally, after analysis, the conversion rate of methyl propionate is higher than 18%, and the selectivity of methyl methacrylate is higher than 86%.

[0044] Example 5

[0045] Weigh about 200 g of rice straw, dry it and calcine it once in an air atmosphere at 500 °C for 30 min, then mechanically pulverize it to about 120 mesh, collect the product, put the collected product into a beaker containing no less than 1 L of 1 wt% citric acid solution, continuously stir at 50 °C for 120 min, after filtration, put the solid into no less than 5 L of 1 wt% H₂O₂ solution, stir at 30 °C for 200 min, wash twice with water, dry the solid in an oven at 120 °C for 2 h, and then calcine it twice in an air atmosphere at 600 °C for 90 min to obtain 14.0 g of biomass-based SiO₂, SiO₂ mass content = 99.51%, specific surface area is about 250 m 2 / g, and the pore diameter is about 10 nm;

[0046] Weigh 0.834 g of potassium hydroxide and dissolve it in deionized water to form a 1 wt% aqueous solution, denoted as solution A; add diammonium hydrogen phosphate (final concentration 2 wt%) as a carrier stabilizer to solution A, denoted as solution B; weigh 14.0 g of biomass-based SiO₂ and disperse it in solution B, and continuously stir for 6 h under magnetic stirring; then perform suction filtration and dry at 120 °C for 12 h. The obtained sample is the precursor of the catalyst for producing methyl methacrylate, denoted as K-P / SiO₂; then use an auxiliary agent to adjust the acidity and alkalinity of the catalyst precursor. Weigh 0.032 g of ammonium niobium oxalate and dissolve it in deionized water, denoted as solution C (concentration 0.1 wt%); then disperse the catalyst precursor K-P / SiO₂ in solution C and continuously stir for 6 h under magnetic stirring, perform suction filtration again, dry at 120 °C for 12 h, and finally calcine in a muffle furnace at 500 °C for 6 h; the obtained sample is the catalyst K-P-Nb / SiO₂ for the aldol condensation reaction using biomass-based SiO₂, denoted as Cat-5.

[0047] Press the obtained Cat-5 into tablets of 40 - 60 mesh, and then load them into a stainless steel tube fixed-bed reactor (inner diameter of the fixed bed is 8 mm). Fill the middle section of the bed with the aldol condensation reaction catalyst, and fill the upper and lower sections of the catalyst bed with quartz sand respectively; the raw material is a mixed solution of formaldehyde and methyl propionate, the reaction temperature is 340 °C, the pressure is 0.05 MPa, and LHSV = 3 h -1 , the molar ratio of formaldehyde:methyl propionate:carrier gas is 1:1:0.2, the carrier gas is an oxygen-containing inert atmosphere (O₂ content 4 vol%, the rest is N₂), and the water content of the raw material is 20 wt%. Online monitoring by gas chromatography; finally, after analysis, the conversion rate of methyl propionate is higher than 13%, and the selectivity of methyl methacrylate is higher than 74%.

[0048] Example 6

[0049] Weigh about 150 g of rice husks, dry them and then calcine them once in an air atmosphere at 300 °C for 60 min, then mechanically pulverize them to about 160 mesh, collect the product, put the collected product into a beaker containing no less than 1 L of 1 wt% citric acid solution, continuously stir at 60 °C for 120 min, after filtration, put the solid into no less than 1 L of 5 wt% H₂O₂ solution, stir at 70 °C for 30 min, wash twice with water, dry the solid in an oven at 120 °C for 2 h, and then calcine it twice in an air atmosphere at 550 °C for 90 min to obtain 17.8 g of biomass-based SiO₂, SiO₂ mass content = 99.69%, specific surface area is about 270 m 2 / g, and the pore diameter is about 12 nm;

[0050] Weigh 0.954 g of cesium acetate and dissolve it in deionized water to form a 1 wt% aqueous solution, denoted as solution A; add diammonium hydrogen phosphate as a carrier stabilizer (final concentration 2 wt%) to solution A, denoted as solution B; weigh 14 g of biomass-based SiO₂ and disperse it in solution B, and continuously stir for 6 h under magnetic stirring; then perform suction filtration and dry at 120 °C for 12 h. The obtained sample is the precursor of the catalyst for producing methyl methacrylate, denoted as Cs-P / SiO₂; then use an additive to adjust the acidity and alkalinity of the catalyst precursor. Weigh 0.037 g of lanthanum nitrate and dissolve it in deionized water, denoted as solution C (concentration 0.1 wt%); then disperse the catalyst precursor Cs-P / SiO₂ in solution C, continuously stir for 6 h under magnetic stirring, perform suction filtration again, dry at 120 °C for 12 h, and finally calcine in a muffle furnace at 500 °C for 6 h; the obtained sample is the catalyst Cs-P-La / SiO₂ for the aldol condensation reaction using biomass-based SiO₂, denoted as Cat-6.

[0051] Press the obtained Cat-6 into tablets with a mesh size of 40 - 60, and then load them into a stainless steel tube fixed-bed reactor (inner diameter of the fixed bed is 8 mm). The middle section of the bed is filled with the aldol condensation reaction catalyst, and the upper and lower sections of the catalyst bed are filled with quartz sand respectively; the raw material is a mixed solution of formaldehyde and methyl propionate, the reaction temperature is 340 °C, the pressure is 0.05 MPa, and LHSV = 3 h -1 , the molar ratio of formaldehyde:methyl propionate:carrier gas is 1:1:0.04, the carrier gas is an oxygen-containing inert atmosphere (O₂ content 1 vol%, the rest is N₂), and the water content of the raw material is 10 wt%. Online monitoring by gas chromatography; finally, after analysis, the conversion rate of methyl propionate is higher than 23%, and the selectivity of methyl methacrylate is higher than 87%.

[0052] Comparative Example 1

[0053] Weigh 0.809 g of cesium carbonate and dissolve it in deionized water to form a 1 wt% aqueous solution, denoted as solution A; add diammonium hydrogen phosphate (final concentration 2 wt%) as the carrier stabilizer to solution A, denoted as solution B; then disperse the commercially available SiO2 carrier (Macklin, with a content of 99.5 wt%) in solution B and continuously stir for 6 h under magnetic stirring; then perform suction filtration and dry at 120 °C for 12 h. The obtained sample is the precursor of the catalyst for producing methyl methacrylate, denoted as Cs-P / SiO2; then use an auxiliary agent to adjust the acidity and basicity of the catalyst precursor. Weigh 0.071 g of ferric nitrate as the auxiliary agent and dissolve it in deionized water, denoted as solution C (concentration 0.1 wt%); then disperse the catalyst precursor Cs-P / SiO2 in solution C and continuously stir for 6 h under magnetic stirring, perform suction filtration again and dry at 120 °C for 12 h, and finally calcine in a muffle furnace at 500 °C for 6 h; the obtained sample is the catalyst Cs-P-Fe / SiO2 for the aldol condensation reaction using the SiO2 carrier, denoted as Cat-7.

[0054] Press the obtained sample into tablets of 40 - 60 mesh, and then load it into a stainless steel fixed-bed reactor (inner diameter of the fixed bed is 8 mm). Fill the middle section of the bed with the aldol condensation reaction catalyst (the upper and lower sections of the catalyst bed after forming are filled with quartz sand respectively; the raw materials are a mixed solution of formaldehyde and methyl propionate, the reaction temperature is 340 °C, the pressure is 0.05 MPa, LHSV = 3 h -1 , the molar ratio of formaldehyde:methyl propionate:carrier gas is 1:1:0.04, the carrier gas is an oxygen-containing inert atmosphere (O2 content 1 vol%, the rest is N2), and the water content of the raw materials is 0 wt%. Online monitoring by gas chromatography; finally, after analysis, the conversion rate of methyl propionate is higher than 28%, and the selectivity of methyl methacrylate is higher than 86%.

[0055] Comparative Example 2

[0056] Weigh 0.809 g of cesium carbonate and dissolve it in deionized water to form a 1 wt% aqueous solution, denoted as solution A; add diammonium hydrogen phosphate (final concentration 2 wt%) as a carrier stabilizer to solution A, denoted as solution B; then disperse the commercially available SiO2 (Macklin, with a content of 99.5 wt%) carrier in solution B and continuously stir for 6 h under magnetic stirring; then perform suction filtration and dry at 120 °C for 12 h. The obtained sample is the precursor of the catalyst for producing methyl methacrylate, denoted as Cs-P / SiO2; then use an additive to adjust the acidity and basicity of the catalyst precursor. Weigh 0.035 g of cerium nitrate hexahydrate and dissolve it in deionized water, denoted as solution C (concentration 0.1 wt%); then disperse the catalyst precursor Cs-P / SiO2 in solution C and continuously stir for 6 h under magnetic stirring, perform suction filtration again and dry at 120 °C for 12 h, and finally calcine in a muffle furnace at 500 °C for 6 h; the obtained sample is the catalyst Cs-P-Ce / SiO2 for the aldol condensation reaction using the SiO2 carrier, denoted as Cat-8.

[0057] Press the obtained sample into tablets of 40 - 60 mesh, and then load them into a stainless steel fixed-bed reactor (inner diameter of the fixed bed is 8 mm). Fill the middle section of the bed with the above aldol condensation reaction catalyst (the upper and lower sections of the catalyst bed after forming are filled with quartz sand respectively; the raw materials are a mixed solution of formaldehyde and methyl propionate, the reaction temperature is 340 °C, the pressure is 0.05 MPa, LHSV = 3 h -1 , the molar ratio of formaldehyde:methyl propionate:carrier gas is 1:2:0.04, the carrier gas is an oxygen-containing inert atmosphere (O2 content 3 vol%, the rest is N2), and the water content of the raw materials is 10 wt%. Online monitoring by gas chromatography; finally, after analysis, the conversion rate of methyl propionate is higher than 24%, and the selectivity of methyl methacrylate is higher than 79%.

[0058] Comparative Example 3

[0059] Weigh 0.954 g of cesium acetate and dissolve it in deionized water to form a 1 wt% aqueous solution, denoted as solution A; add diammonium hydrogen phosphate (final concentration 2 wt%) as a carrier stabilizer to solution A, denoted as solution B; then disperse the commercially available SiO2 (Macklin, with a content of 99.5 wt%) carrier in solution B and continuously stir for 6 h under magnetic stirring; then perform suction filtration and dry at 120 °C for 12 h. The obtained sample is the precursor of the catalyst for producing methyl methacrylate, denoted as Cs-P / SiO2; then use an auxiliary agent to adjust the acidity and basicity of the catalyst precursor. Weigh 0.037 g of lanthanum nitrate and dissolve it in deionized water, denoted as solution C (concentration 0.1 wt%); then disperse the catalyst precursor Cs-P / SiO2 in solution C and continuously stir for 6 h under magnetic stirring, perform suction filtration again, dry at 120 °C for 12 h, and finally calcine in a muffle furnace at 500 °C for 6 h; the obtained sample is the catalyst Cs-P / SiO2 for the aldol condensation reaction using the SiO2 carrier, denoted as Cat-9.

[0060] Press the obtained sample into tablets with a mesh size of 40 - 60, and then load it into a stainless steel tube fixed-bed reactor (inner diameter of the fixed bed is 8 mm). Fill the middle section of the bed with the aldol condensation reaction catalyst (the upper and lower sections of the catalyst bed after forming are filled with quartz sand respectively; the raw material is a mixed solution of formaldehyde and methyl propionate, the reaction temperature is 340 °C, the pressure is 0.05 MPa, LHSV = 3 h -1 , the molar ratio of formaldehyde:methyl propionate:carrier gas is 1:1:0.04, the carrier gas is an oxygen-containing inert atmosphere (O2 content 1 vol%, the rest is N2), and the water content of the raw material is 10 wt%. Online monitoring by gas chromatography; finally, after analysis, the conversion rate of methyl propionate is higher than 20%, and the selectivity of methyl methacrylate is higher than 85%.

[0061] The above are only the embodiments of the present invention, and do not limit the patent scope of the present invention accordingly. Any equivalent structure or equivalent process transformation made using the content of the specification of the present invention, or directly or indirectly applied in other related technical fields, shall be equally included in the patent protection scope of the present invention.

[0062] Table 1 Conversion rate of MP and selectivity of MMA

[0063] Catalyst MP conversion rate / % MMA selectivity / % Cat-1 29.1 90.6 Cat-2 27.4 89.7 Cat-3 20.2 76.1 Cat-4 18.4 86.1 Cat-5 13.8 74.1 Cat-6 23.5 87.4 Cat-7 28.3 86.5 Cat-8 24.2 79.6 Cat-9 20.1 85.3

[0064] By comparing Comparative Example 1 with Example 1, Comparative Example 2 with Example 2, and Comparative Example 3 with Example 6, it was found that under the same catalyst preparation and evaluation conditions, the performance of the catalyst prepared using the commercially available SiO2 (Macklin, with a content of 99.5 wt%) support was slightly lower than that of the catalyst prepared using the biomass-based SiO2 support. The possible reason is that during the extraction of biomass-based SiO2, due to the action of acidic and oxidizing reagents, the biomass-based SiO2 support is more likely to combine with active metals and promoters, showing higher catalytic activity.

Claims

1. Application of a catalyst for aldol condensation reaction, characterized in that: The catalyst comprises an active component and a promoter. The active component is selected from one or more of Li, Na, K, Cs, Sr, and Ba; the promoter is selected from one or more of V, Nb, La, Fe, W, Zr, and Sn, and the active component and the promoter are supported on a biomass-based SiO2 carrier; The catalyst is applied to the preparation of methyl methacrylate by aldol condensation reaction of a mixed solution of formaldehyde and methyl propionate, or a mixed aqueous solution of formaldehyde and methyl propionate; The preparation process of the biomass-based SiO2 carrier is as follows: First, dry the biomass raw material rich in silicon at 80 - 150 °C for 1 - 12 h, and then calcine it once in an air atmosphere at 200 - 700 °C for 30 - 300 min, and then mechanically pulverize it to 100 - 200 mesh, collect the product, denoted as Z; The collected product Z is soaked in a solvent rich in carboxyl functional groups to remove toxic metal impurities, and then soaked in a strong oxidizing solution for oxidation treatment, and amorphous SiO2 with controllable particle size, high purity, and high specific surface area is prepared by low-temperature calcination method; The biomass raw material rich in silicon is selected from one or more of wheat husk, rice husk, wheat straw, rice straw, straw, corn cob, peanut shell, bark, reed grass, and hemp stalk; The solvent rich in carboxyl functional groups is one or more of citric acid solution, formic acid solution, acetic acid solution, oxalic acid solution, and lactic acid solution, and the concentration of the solution is 0.1 - 10 wt%; soak for more than 0.5 h at 25 - 100 °C; The strong oxidizing solution is one or more of hydrogen peroxide, peracetic acid, and potassium permanganate solution, and the concentration of the strong oxidizing substance solution is 0.1 - 5 wt%; soak for more than 0.5 h at 25 - 70 °C; Finally, the treated biomass raw material rich in silicon is calcined twice in an air atmosphere at 500 - 700 °C for 30 - 500 min, and the obtained product is the biomass-based SiO2.

2. The use of the catalyst according to claim 1, characterized in that: The loading amount of the active metal in the catalyst is 0.5 - 15 wt% calculated as metal oxide, and the total loading amount of the promoter is 0.5 - 10 wt% calculated as the oxide of the promoter.

3. The catalyst according to claim 1 or 2, characterized in that: The soaking time in the solvent rich in carboxyl functional groups is 1 - 10 h; The soaking time in the strong oxidizing solution is 0.5 - 5 h; The loading amount of the active metal in the catalyst is 1 - 10 wt% calculated as metal oxide, and the total loading amount of the promoter is 0.5 - 5 wt% calculated as the oxide of the promoter.

4. Use of the catalyst according to claim 1, characterized in that: The preparation process of the aldol condensation reaction catalyst is as follows: The catalyst is prepared by the impregnation method: First, dissolve the precursor reagent of the active component in deionized water, and mark the active component as S to form an aqueous solution of 1 - 10 wt%, denoted as solution A; Add ammonium dihydrogen phosphate with a final concentration of 1-10 wt% as a carrier stabilizer to solution A, denoted as solution B; weigh 5-50 g of biomass-based SiO2 and disperse it in solution B, and continuously stir for 6-24 h; then perform suction filtration and drying. The obtained sample is the precursor of the catalyst for producing methyl methacrylate, denoted as S-P / SiO2; Then, adjust the catalyst precursor with an auxiliary agent. Dissolve the precursor reagent of the auxiliary agent in deionized water, denoted as solution C. The concentration of solution C is 0.05-0.5 wt%, and the auxiliary agent is denoted as M; Disperse the catalyst precursor S-P / SiO2 in solution C, continuously stir for 6-24 h, then perform suction filtration and drying, and finally calcine in a muffle furnace at 400-700 °C for 6-12 h; the obtained sample is the catalyst for the aldol condensation reaction using biomass-based SiO2, tableted to 40-60 mesh, denoted as S-P-M / SiO2.

5. The application of the catalyst according to claim 4, wherein: The active component S is selected from one or more of the following alkali metals and alkaline earth metals: Alkali metals: Li, Na, K, Cs; Alkaline earth metals: Sr, Ba; The precursor reagent of the active component S is selected from one or more of metal ion chlorides, nitrates, and carbonates.

6. The application of the catalyst according to claim 4, wherein: The auxiliary agent M is selected from one or more of the following transition metals, rare earth metals, or other metals: Transition metals: V, Nb; Rare earth metals: La; Other metals: Fe, W, Zr, Sn; The precursor reagent of the above auxiliary agent M is one or two of metal ion nitrates and carbonates.

7. The application of the catalyst according to claim 1, wherein: Using a fixed-bed reactor, the middle section of the bed is filled with the aldol condensation reaction catalyst, the catalyst size is 40-60 mesh, and the upper and lower sections of the catalyst bed are filled with quartz sand respectively; the raw materials are a mixed solution of formaldehyde and methyl propionate, or a water-containing mixed solution of formaldehyde and methyl propionate, and an oxygen-containing inert atmosphere is used as the carrier gas; the reaction temperature is 200-450 °C, the pressure is 0.05-2 MPa, and the LHSV of the raw materials during the reaction process is 0.1-3 h -1 ; the product that can be collected is a mixed solution containing methyl methacrylate and methacrylic acid.

8. The application of the catalyst according to claim 1 or 7, wherein: In the mixed solution of formaldehyde and methyl propionate or its aqueous mixed solution, the molar ratio of formaldehyde: methyl propionate: carrier gas is 1:(0.2-5):(0.02-0.5). The carrier gas is an oxygen-containing inert atmosphere, wherein the O2 content is 1-5 vol%, and the rest is N2. The raw material water content is 0-60 wt%.

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