Catalyst for synthesizing methyl acrylate, its preparation method and application

Abstract

The present invention relates to a catalyst for synthesizing methyl acrylate, a preparation method thereof, and an application thereof. The catalyst comprises a carrier and an active component supported on the carrier. The preparation method of the catalyst for synthesizing methyl acrylate comprises the steps of: S1. contacting a solution containing an active component source with the carrier to obtain an intermediate-impregnated carrier; S2. mixing the intermediate-impregnated carrier with a liquid medium in a reactor and bringing the mixed solution under supercritical conditions of the liquid medium to obtain a catalyst precursor; S3. performing a calcination treatment on the catalyst precursor to obtain the catalyst. The present invention also includes the application of the catalyst in an aldol condensation reaction, particularly in the synthesis of methyl acrylate. The present invention uses a supercritical liquid to treat the intermediate-impregnated carrier obtained after impregnation, thereby being able to significantly improve the catalytic activity and selectivity of the obtained catalyst.

Description

Technical Field

[0001] The present invention relates to the field of catalysts. Specifically, it relates to a catalyst for synthesizing methyl acrylate, its preparation method and application. Background Art

[0002] The preparation methods of acrylic acid and its esters mainly include propylene oxidation method, acrylonitrile hydrolysis method, ketene method, propane oxidation method, methyl formate method, etc. However, these methods have disadvantages such as serious pollution, high energy consumption, and low product yield. Therefore, it is of great significance to develop a new green and efficient production process.

[0003] Lucite company has proposed a mature α-MMA process. The α-MMA process of Lucite company uses the preparation of methyl methacrylate from methyl propionate and formaldehyde. The process route of Lucite company starts from methyl propionate to synthesize the raw material of methyl methacrylate, and the consumed raw material is methyl propionate. Therefore, what is urgently needed in this field is to use industrial by-product methyl acetate as the raw material, adopt a safe, environmentally friendly and non-toxic solid base catalyst, and realize the green synthesis of methyl acrylate through a clean synthesis process.

[0004] In view of this, on the basis of the mature α-MMA process proposed by Lucite company, a method for synthesizing methyl acrylate with methyl acetate and formaldehyde as raw materials and using a new catalyst is proposed. A catalyst reaction-regeneration fluidized bed coupling system is adopted to solve the problems of short single-pass catalyst life, easy carbon deposition and frequent regeneration. At present, the single-pass conversion rate of methyl acetate is generally 15%, the selectivity of methyl acrylate can generally reach 85%, and the yield of methyl acrylate is generally 13.5%. However, industrialization still cannot be achieved at present. The main key is that the comprehensive improvement of yield, selectivity and catalyst stability cannot be achieved. Summary of the Invention

[0005] In order to overcome the problems existing in the prior art, the inventors of the present invention have conducted extensive and in-depth research and provided a catalyst for synthesizing methyl acrylate, its preparation method and application by improving the process. For example, one of the purposes of the present invention is to provide a catalyst for synthesizing methyl acrylate to solve the problems of low catalytic efficiency, low selectivity and poor catalyst stability of the catalyst in the industrial synthesis of methyl acrylate through aldol synthesis reaction. Another purpose of the present invention is to provide a preparation method of a catalyst for synthesizing methyl acrylate, which uses supercritical liquid to treat the impregnated catalyst to significantly improve the activity and selectivity of the catalyst.

[0006] To achieve the above object, a first aspect of the present invention provides a catalyst for synthesizing methyl acrylate, comprising a support and an active component supported on the support. Among them, the active component is selected from one or more of oxides, acetates, nitrates, and carbonates of alkali metals, and the alkali metal is preferably selected from one or more of K, Rb, and Cs. The active component is preferably selected from one or more of potassium oxide, rubidium oxide, cesium oxide, cesium carbonate, cesium acetate, and potassium carbonate; the average pore diameter of the support is 2 nm to 50 nm; the pore volume of the support is 0.2 ml / g to 2 ml / g. The active component includes alkali metal oxides, preferably one or more of K, Rb, and Cs oxides, and more preferably one or more of potassium oxide, rubidium oxide, and cesium oxide. The specific surface area, average pore diameter, pore volume, etc. of the support can be obtained by BET analysis.

[0007] In some embodiments of the present invention, the preparation method of the catalyst includes a step of treating a support impregnated with an active component source with a liquid medium in a supercritical state.

[0008] In some embodiments of the present invention, an equal-volume impregnation method or an excess impregnation method can be used to bring a solution containing an active component source into contact with the support, thereby obtaining a support impregnated with the active component source. The active component source is selected from alkali metal salts, preferably one or more of carbonates of alkali metals, nitrates of alkali metals, and acetates of alkali metals, and more preferably one or more of cesium carbonate, cesium acetate, and potassium carbonate.

[0009] According to the present invention, the alkali metal salt is formulated into a salt solution as the active component source.

[0010] According to the present invention, the concentration of the alkali metal salt in the salt solution is not particularly limited, and those skilled in the art can determine it according to the actual situation on site.

[0011] In some embodiments of the present invention, the liquid medium is a hydrophilic liquid, preferably one or more of methanol, ethanol, ethylene glycol, isopropanol, and propylene glycol.

[0012] In some embodiments of the present invention, the amount of the liquid medium added is 30% to 70% of the volume of the reactor used in the preparation.

[0013] In some embodiments of the present invention, the treatment time with the liquid medium in a supercritical state is 0.5 to 2 h.

[0014] According to the present invention, the supercritical conditions of the liquid medium refer to the conditions (including temperature and pressure) for bringing the liquid medium to the supercritical state. For example, when the liquid medium is methanol, the critical temperature of methanol is 240 °C and the critical pressure is 7.95 MPa. During treatment, the solution is in a state where the temperature is not less than 240 °C and the pressure is not less than 7.95 MPa.

[0015] In some embodiments of the present invention, the value of the temperature above the critical temperature in the supercritical state is 0 °C to 10 °C. For example, when the liquid medium is methanol, the critical temperature of methanol is 240 °C, and during treatment, the temperature of the solution is not less than 240 °C and not greater than 250 °C. For example, when the liquid medium is methanol, the critical pressure of methanol is 7.95 MPa, and the pressure of the mixed solution in step S2 is not less than 7.95 MPa and not greater than 8.50 MPa.

[0016] According to the present invention, the addition amount of the liquid medium will almost fill the reactor used in the preparation. When the liquid medium almost fills the reactor, as long as the temperature rises to not less than the critical temperature of the liquid medium (such as the critical temperature of methanol, 240 °C), the self-pressure generated by the system will exceed the critical pressure (such as the critical pressure of methanol, 7.95 MPa). Therefore, in the present invention, as long as it is ensured that the liquid medium fills the reactor and the temperature rises to not less than the critical temperature of the liquid medium, the liquid medium is in the supercritical state. If the pressure in the reactor does not exceed the critical pressure (such as when the addition amount of the liquid medium does not reach the amount that almost fills the reactor), it is only necessary to control the pressure in the reactor to be greater than the critical pressure of the liquid medium, and the present invention will not elaborate further.

[0017] In some embodiments of the present invention, after treating the carrier impregnated with the active component source with the liquid medium in the supercritical state, the catalyst preparation method may further include a step of performing a calcination treatment.

[0018] In some embodiments of the present invention, the conditions for calcination include: the temperature is 400 °C to 800 °C; the time is 4 to 15 hours.

[0019] In some embodiments of the present invention, by mass, the catalyst includes: 0 to 50 parts of the active component, preferably 1 to 20 parts; 50 to 80 parts of the carrier, preferably 60 to 75 parts.

[0020] In some embodiments of the present invention, the particle size of the carrier is 1 to 5 mm; and / or the specific surface area of the carrier is 100 to 500 m 2 / g; preferably, the carrier is selected from one or more of SiO2, Al2O3, and activated carbon.

[0021] According to the present invention, the measured particle size of the carrier is the average particle size.

[0022] The second aspect of the present invention provides a method for preparing a catalyst for synthesizing methyl acrylate, comprising the steps of:

[0023] S1. Contacting a solution containing an active component source with a support to obtain an intermediate-impregnated support;

[0024] S2. Mixing the intermediate-impregnated support with a liquid medium in a reactor and making the temperature of the mixed solution higher than the critical temperature of the liquid medium to obtain a catalyst precursor;

[0025] S3. Calcining the catalyst precursor to obtain the catalyst.

[0026] In some embodiments of the present invention, the active component source is selected from alkali metal salts, preferably one or more of carbonates of alkali metals, nitrates of alkali metals, and acetates of alkali metals, and more preferably one or more of cesium carbonate, cesium acetate, and potassium carbonate.

[0027] According to the present invention, in step S1, the equal-volume impregnation method or the excess impregnation method can be used to obtain the intermediate-impregnated support.

[0028] According to the present invention, the alkali metal salt is formulated into a salt solution as the active component source.

[0029] According to the present invention, the concentration of the alkali metal salt in the salt solution is not particularly limited, and those skilled in the art can determine it according to the on-site situation.

[0030] In some embodiments of the present invention, the average pore diameter of the support is 2 nm to 50 nm; and / or the pore volume of the support is 0.2 ml / g to 2 ml / g; and / or the particle size of the support is 1 to 5 mm; and / or the specific surface area of the support is 100 to 500 m 2 / g.

[0031] In some embodiments of the present invention, the support is selected from one or more of SiO2, Al2O3, and activated carbon.

[0032] In some embodiments of the present invention, in step S1, the conditions for the contact include: the temperature is 10 °C to 60 °C; the time is 5 to 20 h.

[0033] In some embodiments of the present invention, in step S2, the liquid medium is a hydrophilic liquid, preferably one or more of methanol, ethanol, ethylene glycol, isopropanol, and propylene glycol.

[0034] In some embodiments of the present invention, the amount of the liquid medium added is 30% to 70% of the volume of the reactor.

[0035] In some embodiments of the present invention, the mixing time is 0.5 to 2 h.

[0036] According to the present invention, in step S2, the supercritical conditions of the liquid medium refer to the conditions (including temperature and pressure) for bringing the liquid medium to the supercritical state. For example, when the liquid medium is methanol, the critical temperature of methanol is 240 °C and the critical pressure is 7.95 MPa. In step S2, the mixed solution is in a state where the temperature is not less than 240 °C and the pressure is not less than 7.95 MPa.

[0037] In some embodiments of the present invention, the value of the temperature above the critical temperature in the supercritical state is 0 °C to 10 °C; for example, when the liquid medium is methanol, the critical temperature of methanol is 240 °C, and the temperature of the mixed solution in step S2 is not less than 240 °C and not greater than 250 °C. For example, when the liquid medium is methanol, the critical pressure of methanol is 7.95 MPa, and the pressure of the mixed solution in step S2 is not less than 7.95 MPa and not greater than 8.50 MPa.

[0038] According to the present invention, the addition amount of the liquid medium will almost fill the reactor. When the liquid medium almost fills the reactor, as long as the temperature rises to not less than the critical temperature of the liquid medium (such as the critical temperature of methanol, 240 °C), the self-pressure generated by the system will exceed the critical pressure (such as the critical pressure of methanol, 7.95 MPa). Therefore, in the present invention, as long as it is ensured that the liquid medium fills the reactor and the temperature rises to not less than the critical temperature of the liquid medium, the liquid medium is in the supercritical state. If the pressure in the reactor does not exceed the critical pressure (such as when the addition amount of the liquid medium does not reach the amount to almost fill the reactor), it is only necessary to control the pressure in the reactor to be greater than the critical pressure of the liquid medium, and the present invention will not elaborate further.

[0039] In some embodiments of the present invention, in step S3, the calcination conditions include: the temperature is 400 °C to 800 °C; the time is 4 to 15 hours.

[0040] In some embodiments of the present invention, the preparation method of the catalyst for synthesizing methyl acrylate may include the steps:

[0041] (i) Mix a solution of a precursor salt containing an alkali metal element with a carrier to obtain an intermediate-impregnated carrier;

[0042] (ii) Load the intermediate-impregnated carrier into a fixed-bed reactor, and introduce a liquid medium into the fixed-bed reactor to fill it;

[0043] (iii) Close the inlet and outlet valves of the fixed-bed reactor, and heat the fixed-bed reactor to a temperature above the critical temperature of the liquid medium (for example, heat it to a temperature 0 °C to 10 °C higher than the critical temperature of the liquid medium);

[0044] (iv) Open the outlet valve of the fixed-bed reactor to discharge the supercritical liquid medium;

[0045] (v) Calcinate the solid matter in the reactor to obtain the catalyst.

[0046] According to the present invention, in step (i), an intermediate-impregnated carrier is obtained by an impregnation method. If the excess impregnation method is used, after the aging (impregnation) is completed, the excess impregnating solution can be filtered out by suction filtration to obtain the intermediate-impregnated carrier.

[0047] According to the present invention, in step (iii), the critical temperature of the liquid medium will change due to the pressure change in the fixed-bed reactor.

[0048] According to the present invention, the precursor salt containing an alkali metal element can form a catalytically active component by calcination.

[0049] The third aspect of the present invention provides an application of the catalyst according to the first aspect and / or the third aspect of the present invention in an aldol condensation reaction, particularly in the synthesis of methyl acrylate.

[0050] In some embodiments of the present invention, the raw materials for synthesizing methyl acrylate include methyl acetate and an aldehyde source, and the addition amount of the catalyst is 5% to 20% of the reactor volume.

[0051] In some embodiments of the present invention, the reaction temperature for synthesizing methyl acrylate is 200 °C to 450 °C. The aldehyde source is selected from one or more of formaldehyde or substances that can in-situ generate formaldehyde in the synthesis reaction system. That is to say, the aldehyde source is a substance that can provide formaldehyde without reacting with any substance in the synthesis reaction system; the aldehyde source is preferably one or more of trioxane, paraformaldehyde, methylal, or formaldehyde. The molar ratio of methyl acetate to formaldehyde is 3 to 100. The total mass space velocity of methyl acetate and the aldehyde source is 1 h -1 ~10 h -1 .

[0052] According to the present invention, in the reaction system for synthesizing methyl acrylate, methanol can be added to inhibit the hydrolysis side reaction. The amount of methanol added accounts for 5 to 50% of the total mass of methyl acetate, the aldehyde source, and methanol.

[0053] Compared with the prior art, the present invention includes at least one of the following beneficial effects:

[0054] 1) The present invention uses a supercritical liquid to treat the impregnated carrier of the intermediate obtained after impregnation. Due to the action of the hydrophilic supercritical liquid, the water on the catalyst surface is rapidly removed, and the active components have better dispersion on the carrier surface, thereby significantly improving the catalytic activity and selectivity of the catalyst.

[0055] 2) Since highly active catalysts are usually accompanied by an increase in side reactions, that is, a decrease in selectivity, it is difficult to obtain high activity while also having high selectivity. The catalyst of the present invention can be used in the catalytic aldol condensation reaction, especially in the condensation of methyl acetate and formaldehyde to prepare methyl acrylate. During the reaction process, the catalyst has the advantages of high activity and high selectivity, creatively solving the problem of the catalyst having both high activity and high selectivity, thereby enabling the industrialization of the preparation of methyl acrylate.

[0056] 3) The catalyst of the present invention is used in the condensation of methyl acetate and formaldehyde to prepare methyl acrylate, with high yields of methyl acrylate and high conversion rates of reactants. Moreover, the method for preparing methyl acrylate is simple and easy to carry out, suitable for large-scale production applications, and is expected to enable the industrialization of the synthesis of methyl acrylate from methyl acetate and aldehydes through the aldol synthesis reaction, obtaining good economic and social benefits. Detailed Embodiments

[0057] The present invention will be described in detail below through examples, but the protection scope of the present invention is not limited to the following description.

[0058] For those conditions not specified in the examples, they are carried out according to conventional conditions or the conditions recommended by the manufacturer. For raw materials, reagents or instruments whose manufacturers are not specified, they are all conventional products that can be obtained through commercial purchase or prepared according to the preparation methods disclosed in the prior art.

[0059] In the examples, the calculation formula for the conversion rate of formaldehyde is:

[0060]

[0061] In the examples, the selectivity of methyl acrylate is expressed as the percentage of the number of moles of methyl acrylate to the number of moles of aldehyde source converted. For example, when the aldehyde source is paraformaldehyde, the selectivity of methyl acrylate is defined as follows:

[0062]

[0063] Example 1

[0064] 1. Catalyst Preparation

[0065] Take 100 g of the solution obtained by mixing cesium carbonate with water (the cesium content is 12 g in terms of Cs2O); mix it with 60 g of silica microspheres (the microsphere diameter is 2.5 mm, the average pore diameter by the BET method is 22 nm, and the pore volume by the BET method is 1.1 ml / g), let it stand for 24 hours to obtain an intermediate-impregnated carrier; filter to remove the excess impregnating solution, put the obtained intermediate-impregnated carrier into a reactor, introduce methanol into the reactor to fill the reactor with methanol (the reactor capacity is about 300 ml, and about 150 ml of methanol is added), after closing the inlet and outlet valves of the reactor, heat the reactor to 240 °C (the pressure in the reactor is about 8 MPa), open the outlet valve to discharge the critical-state methanol, and then dry it under vacuum at 50 °C for 24 hours, and calcine it in an air atmosphere at 500 °C for 5 hours to obtain the finished catalyst A1.

[0066] In the finished catalyst A1, in terms of mass parts, the Cs2O content is 12 weight parts and the silica content is 60 weight parts.

[0067] 2. On-line reduction activation of the catalyst and synthesis of methyl acrylate

[0068] Take 15 g of the obtained finished catalyst A1 and put it into a fixed-bed reactor (inner diameter 16 mm, length 1500 mm). After replacing it with N2 three times, raise the reactor temperature to 300 °C and adjust the pressure to 0.5 MPa. With the total mass space velocity of methyl acetate and trioxane being 5 h -1 Introduce the reaction raw materials (the mass ratio of trioxane, methyl acetate and methanol is 5:40:4), take samples, add the internal standard toluene, and measure the content of each component in the reaction mixture by gas chromatography. Calculate that the formaldehyde conversion rate is 71.3% and the selectivity of methyl acrylate is 88.7%.

[0069] Example 2

[0070] 1. Catalyst preparation

[0071] Take 100 g of the solution obtained by mixing cesium carbonate with water (the cesium content is 2 g in terms of Cs2O); mix it with 75 g of silica microspheres (the microsphere diameter is 2.5 mm, the average pore diameter by the BET method is 22 nm, and the pore volume by the BET method is 1.1 ml / g), let it stand for 24 hours to obtain an intermediate-impregnated carrier; filter to remove the excess impregnating solution, put the obtained intermediate-impregnated carrier into a reactor, introduce methanol into the reactor to fill the reactor with methanol (the reactor capacity is about 300 ml, and about 150 ml of methanol is added), after closing the inlet and outlet valves of the reactor, heat the reactor to 240 °C (the pressure in the reactor is about 8 MPa), open the outlet valve to discharge the critical-state methanol, and then dry it under vacuum at 50 °C for 24 hours, and calcine it in an air atmosphere at 500 °C for 5 hours to obtain the finished catalyst A2.

[0072] In the finished catalyst A2, the content of Cs2O is 2 parts by weight and the content of silicon dioxide is 75 parts by weight, based on parts by mass.

[0073] 2. Online reduction activation of the catalyst and synthesis of methyl acrylate

[0074] Take 15 g of the prepared finished catalyst A2 and load it into a fixed-bed reactor (inner diameter 16 mm, length 1500 mm). After purging with N2 three times, the temperature of the reactor is raised to 300 °C and the pressure is adjusted to 0.5 MPa. With a total mass space velocity of acetic acid methyl ester and trioxane of 5 h -1 Feed the reaction raw materials (mass ratio of trioxane, acetic acid methyl ester and methanol is 5:40:4), take samples, add the internal standard toluene, measure the content of each component in the reaction mixture by gas chromatography, and calculate that the formaldehyde conversion rate is 62.4% and the selectivity of methyl acrylate is 91.0%.

[0075] Example 3

[0076] 1. Catalyst preparation

[0077] Take 100 g of a solution obtained by mixing cesium carbonate and water (cesium content is 20 g calculated as Cs2O); mix it with 20 g of silicon dioxide microspheres (microsphere diameter is 2.5 mm, average pore diameter by BET method is 22 nm, pore volume by BET method is 1.1 ml / g), let it stand for 24 hours to obtain an intermediate impregnated carrier; filter to remove the excess impregnating solution, load the obtained intermediate impregnated carrier into a reactor, feed methanol into the reactor to fill the reactor (reactor capacity is about 300 ml, about 150 ml of methanol is added), after closing the inlet and outlet valves of the reactor, heat the reactor to 240 °C (pressure in the reactor is about 8 MPa), open the outlet valve to discharge the critical state methanol, and then dry it under vacuum at 50 °C for 24 hours and calcine it in an air atmosphere at 500 °C for 5 hours to obtain the finished catalyst A3.

[0078] In the finished catalyst A3, the content of Cs2O is 20 parts by weight and the content of silicon dioxide is 20 parts by weight, based on parts by mass.

[0079] 2. Online reduction activation of the catalyst and synthesis of methyl acrylate

[0080] Take 15 g of the prepared finished catalyst A3 and load it into a fixed-bed reactor (inner diameter 16 mm, length 1500 mm). After purging with N2 three times, the temperature of the reactor is raised to 300 °C and the pressure is adjusted to 0.5 MPa. With a total mass space velocity of acetic acid methyl ester and trioxane of 5 h -1 Feed the reaction raw materials (mass ratio of trioxane, acetic acid methyl ester and methanol is 5:40:4), take samples, add the internal standard toluene, measure the content of each component in the reaction mixture by gas chromatography, and calculate that the formaldehyde conversion rate is 68.8% and the selectivity of methyl acrylate is 81.3%.

[0081] Example 4

[0082] 1. Catalyst preparation

[0083] Take 100 g of a solution obtained by mixing potassium carbonate and water (the potassium content is 12 g in terms of K2O); mix it with 60 g of silica microspheres (the microsphere diameter is 2.5 mm, the average pore diameter by the BET method is 22 nm, and the pore volume by the BET method is 1.1 ml / g), let it stand for 24 hours to obtain an intermediate impregnated carrier; filter to remove the excess impregnating solution, put the obtained intermediate impregnated carrier into a reactor, introduce methanol into the reactor to fill the reactor with methanol (the reactor capacity is about 300 ml, and the added methanol is about 150 ml), after closing the inlet and outlet valves of the reactor, heat the reactor to 240 °C (the pressure in the reactor is about 8 MPa), open the outlet valve to discharge the supercritical methanol, and then dry it under vacuum at 50 °C for 24 hours, and calcine it in an air atmosphere at 500 °C for 5 hours to obtain the finished catalyst A4.

[0084] In the finished catalyst A4, by mass fraction, the K2O content is 12 parts by weight and the silica content is 60 parts by weight.

[0085] 2. On-line reduction activation of the catalyst and synthesis of methyl acrylate

[0086] Take 15 g of the obtained finished catalyst A1 and put it into a fixed-bed reactor (inner diameter 16 mm, length 1500 mm). After purging with N2 three times, raise the reactor temperature to 300 °C and adjust the pressure to 0.5 MPa. With the total mass space velocity of methyl acetate and trioxane being 5 h -1 Introduce the reaction raw materials (the mass ratio of trioxane, methyl acetate and methanol is 5:40:4), take samples, add the internal standard toluene, and measure the content of each component in the reaction mixture by gas chromatography. The calculated formaldehyde conversion rate is 66.3% and the methyl acrylate selectivity is 90.2%.

[0087] Example 5

[0088] 1. Catalyst preparation

[0089] Take 100 g of the solution obtained by mixing cesium carbonate with water (the cesium content is 12 g in terms of Cs2O); mix it with 60 g of alumina microspheres (the microsphere diameter is 2.5 mm, the average pore diameter by the BET method is 17 nm, and the pore volume by the BET method is 1.2 ml / g), let it stand for 24 hours to obtain an intermediate-impregnated carrier; filter to remove the excess impregnating solution, put the obtained intermediate-impregnated carrier into a reactor, introduce methanol into the reactor to fill the reactor with methanol (the reactor capacity is about 300 ml, and about 150 ml of methanol is added), after closing the inlet and outlet valves of the reactor, heat the reactor to 240 °C (the pressure inside the reactor is about 8 MPa), open the outlet valve to export the supercritical methanol, and then dry it under vacuum at 50 °C for 24 hours, and calcine it in an air atmosphere at 500 °C for 5 hours to obtain the finished catalyst A5.

[0090] In the finished catalyst A5, in terms of mass fraction, the Cs2O content is 12 parts by weight, and the alumina content is 60 parts by weight.

[0091] 2. On-line reduction activation of the catalyst and synthesis of methyl acrylate

[0092] Take 15 g of the obtained finished catalyst A5 and put it into a fixed-bed reactor (inner diameter 16 mm, length 1500 mm). After replacing it with N2 three times, raise the reactor temperature to 300 °C and adjust the pressure to 0.5 MPa. With the total mass space velocity of methyl acetate and trioxane being 5 h -1 Introduce the reaction raw materials (the mass ratio of trioxane, methyl acetate and methanol is 5:40:4), take samples, add the internal standard toluene, measure the content of each component in the reaction mixture by gas chromatography, and calculate that the formaldehyde conversion rate is 73.9% and the selectivity of methyl acrylate is 84.6%.

[0093] Example 6

[0094] 1. Catalyst preparation

[0095] Take 100 g of the solution obtained by mixing cesium carbonate with water (the cesium content is 12 g in terms of Cs2O); mix it with 60 g of silica microspheres (the microsphere diameter is 2.5 mm, the average pore diameter by the BET method is 22 nm, and the pore volume by the BET method is 1.1 ml / g), let it stand for 24 hours to obtain an intermediate-impregnated carrier; filter to remove the excess impregnating solution, put the obtained intermediate-impregnated carrier into a reactor, introduce methanol into the reactor to fill the reactor with methanol (the reactor capacity is about 300 ml, and about 150 ml of methanol is added), after closing the inlet and outlet valves of the reactor, heat the reactor to 220 °C (the pressure inside the reactor is about 6 MPa), open the outlet valve to export the supercritical methanol, and then dry it under vacuum at 50 °C for 24 hours, and calcine it in an air atmosphere at 500 °C for 5 hours to obtain the finished catalyst A6.

[0096] In the finished catalyst A6, the content of Cs2O is 12 parts by mass, and the content of silicon dioxide is 60 parts by mass.

[0097] 2. On-line reduction activation of the catalyst and synthesis of methyl acrylate

[0098] Take 15 g of the prepared finished catalyst A6 and load it into a fixed-bed reactor (inner diameter 16 mm, length 1500 mm). After purging with N2 three times, the temperature of the reactor is raised to 300 °C, and the pressure is adjusted to 0.5 MPa. With a total mass space velocity of methyl acetate and trioxane of 5 h -1 Feed the reaction raw materials (mass ratio of trioxane, methyl acetate and methanol is 5:40:4), take samples, add the internal standard toluene, measure the content of each component in the reaction mixture by gas chromatography, and calculate the formaldehyde conversion rate to be 65.5% and the selectivity of methyl acrylate to be 89.4%.

[0099] Example 7

[0100] 1. Catalyst preparation

[0101] Take 100 g of a solution obtained by mixing cesium carbonate with water (cesium content is 12 g in terms of Cs2O); mix it with 60 g of silica microspheres (microsphere diameter is 2.5 mm, average pore diameter by BET method is 22 nm, and pore volume by BET method is 1.1 ml / g), let it stand for 24 hours to obtain an intermediate impregnated support; filter off the excess impregnating solution, load the obtained intermediate impregnated support into a reactor, feed methanol into the reactor to fill the reactor (reactor capacity is about 300 ml, and about 150 ml of methanol is added). After closing the inlet and outlet valves of the reactor, heat the reactor to 250 °C (the pressure inside the reactor is about 9.7 MPa), open the outlet valve to discharge the supercritical methanol, and then dry it under vacuum at 50 °C for 24 hours and calcine it in an air atmosphere at 500 °C for 5 hours to obtain the finished catalyst A7.

[0102] In the finished catalyst A7, the content of Cs2O is 12 parts by mass, and the content of silicon dioxide is 60 parts by mass.

[0103] 2. On-line reduction activation of the catalyst and synthesis of methyl acrylate

[0104] Take 15 g of the prepared finished catalyst A7 and load it into a fixed-bed reactor (inner diameter 16 mm, length 1500 mm). After purging with N2 three times, the temperature of the reactor is raised to 300 °C, and the pressure is adjusted to 0.5 MPa. With a total mass space velocity of methyl acetate and trioxane of 5 h -1 Feed the reaction raw materials (mass ratio of trioxane, methyl acetate and methanol is 5:40:4), take samples, add the internal standard toluene, measure the content of each component in the reaction mixture by gas chromatography, and calculate the formaldehyde conversion rate to be 72.8% and the selectivity of methyl acrylate to be 90.5%.

[0105] Example 8

[0106] 1. Catalyst preparation

[0107] Take 100 g of a solution obtained by mixing cesium carbonate with water (the cesium content is 12 g in terms of Cs2O); mix it with 60 g of silica microspheres (the microsphere diameter is 2.5 mm, the average pore diameter by the BET method is 22 nm, and the pore volume by the BET method is 1.1 ml / g), let it stand for 24 hours to obtain an intermediate-impregnated carrier; filter to remove the excess impregnating solution, load the obtained intermediate-impregnated carrier into a reactor, introduce methanol into the reactor to fill the reactor with methanol (the reactor capacity is about 300 ml, and the added methanol is about 150 ml). After closing the inlet and outlet valves of the reactor, heat the reactor to 260 °C (the pressure inside the reactor is about 11.3 MPa), open the outlet valve to export the supercritical methanol, and then dry it under vacuum at 50 °C for 24 hours, and calcine it in an air atmosphere at 500 °C for 5 hours to obtain the finished catalyst A8.

[0108] In the finished catalyst A8, in terms of mass parts, the Cs2O content is 12 weight parts, and the silica content is 60 weight parts.

[0109] 2. On-line reduction activation of the catalyst and synthesis of methyl acrylate

[0110] Take 15 g of the obtained finished catalyst A8 and load it into a fixed-bed reactor (inner diameter 16 mm, length 1500 mm). After purging with N2 three times, raise the reactor temperature to 300 °C and adjust the pressure to 0.5 MPa. With the total mass space velocity of methyl acetate and trioxane being 5 h -1 Introduce the reaction raw materials (the mass ratio of trioxane, methyl acetate and methanol is 5:40:4), take samples, add the internal standard toluene, and measure the content of each component in the reaction mixture by gas chromatography. The calculated formaldehyde conversion rate is 72.3%, and the methyl acrylate selectivity is 89.6%.

[0111] Example 9

[0112] 1. Catalyst preparation

[0113] Take 100 g of the solution obtained by mixing cesium carbonate with water (the cesium content is 12 g in terms of Cs2O); mix it with 60 g of silica microspheres (the microsphere diameter is 2.5 mm, the average pore diameter by the BET method is 22 nm, and the pore volume by the BET method is 1.1 ml / g), let it stand for 24 hours to obtain an intermediate-impregnated carrier; filter to remove the excess impregnating solution, put the obtained intermediate-impregnated carrier into a reactor, introduce ethylene glycol into the reactor to fill the reactor with ethylene glycol (the reactor capacity is about 300 ml, and about 150 ml of ethylene glycol is added), after closing the inlet and outlet valves of the reactor, heat the reactor to 370 °C (the pressure in the reactor is about 7.7 MPa), open the outlet valve to export the critical-state methanol, and then dry it under vacuum at 150 °C for 24 hours and calcine it in an air atmosphere at 500 °C for 5 hours to obtain the finished catalyst A9.

[0114] In the finished catalyst A9, in terms of mass parts, the Cs2O content is 12 parts by weight and the silica content is 60 parts by weight.

[0115] 2. On-line reduction activation of the catalyst and synthesis of methyl acrylate

[0116] Take 15 g of the obtained finished catalyst A9 and put it into a fixed-bed reactor (inner diameter 16 mm, length 1500 mm). After purging with N2 three times, raise the reactor temperature to 300 °C and adjust the pressure to 0.5 MPa. With the total mass space velocity of methyl acetate and trioxane being 5 h -1 Introduce the reaction raw materials (the mass ratio of trioxane, methyl acetate and methanol is 5:40:4), take samples, add the internal standard toluene, and measure the contents of each component in the reaction mixture by gas chromatography. The calculated formaldehyde conversion rate is 73.4% and the methyl acrylate selectivity is 87.8%.

[0117] Example 10

[0118] 1. Catalyst preparation

[0119] Take 100 g of the solution obtained by mixing cesium carbonate with water (the cesium content is 12 g in terms of Cs2O); mix it with 60 g of silica microspheres (the microsphere diameter is 2.5 mm, the average pore diameter by the BET method is 22 nm, and the pore volume by the BET method is 1.1 ml / g), let it stand for 24 hours to obtain an intermediate-impregnated carrier; filter to remove the excess impregnating solution, put the obtained intermediate-impregnated carrier into a reactor, introduce isopropanol into the reactor to fill the reactor with isopropanol (the reactor capacity is about 300 ml, and about 150 ml of isopropanol is added), after closing the inlet and outlet valves of the reactor, heat the reactor to 235 °C (the pressure in the reactor is about 4.8 MPa), open the outlet valve to export the critical-state methanol, and then dry it under vacuum at 60 °C for 24 hours and calcine it in an air atmosphere at 500 °C for 5 hours to obtain the finished catalyst A10.

[0120] In the finished catalyst A10, the content of Cs2O is 12 parts by mass, and the content of silicon dioxide is 60 parts by mass.

[0121] 2. On-line reduction activation of the catalyst and synthesis of methyl acrylate

[0122] Take 15 g of the prepared finished catalyst A10 and load it into a fixed-bed reactor (inner diameter 16 mm, length 1500 mm). After purging with N2 three times, the temperature of the reactor is raised to 300 °C, and the pressure is adjusted to 0.5 MPa. With the total mass space velocity of methyl acetate and trioxane being 5 h -1 Feed the reaction raw materials (mass ratio of trioxane, methyl acetate and methanol is 5:40:4), take samples, add the internal standard toluene, and measure the content of each component in the reaction mixture by gas chromatography. The calculated formaldehyde conversion rate is 70.8%, and the selectivity of methyl acrylate is 89.3%.

[0123] Comparative Example 1

[0124] 1. Catalyst preparation

[0125] Take 100 g of the solution obtained by mixing cesium carbonate and water (the cesium content is 12 g in terms of Cs2O); mix it with 60 g of silicon dioxide microspheres (microsphere diameter 2.5 mm, average pore diameter 22 nm by BET method, pore volume 1.1 ml / g by BET method, and the Na2O content is 2000 ppm), let it stand for 24 hours, then dry it in vacuum at 50 °C for 24 hours, and calcine it in an air atmosphere at 500 °C for 5 hours to obtain the finished catalyst B1.

[0126] 2. On-line reduction activation of the catalyst and synthesis of methyl acrylate

[0127] Take 15 g of the prepared finished catalyst B1 and load it into a fixed-bed reactor (inner diameter 16 mm, length 1500 mm). After purging with N2 three times, the temperature of the reactor is raised to 300 °C, and the pressure is adjusted to 0.5 MPa. With the total mass space velocity of methyl acetate and aldehyde being 5 h -1 Feed the reaction raw materials (mass ratio of trioxane, methyl acetate and methanol is 5:40:4), take samples, add the internal standard toluene, and measure the content of each component in the reaction mixture by gas chromatography. The calculated formaldehyde conversion rate is 57.4%, and the selectivity of methyl acrylate is 81.3%.

[0128] Comparative Example 2

[0129] 1. Catalyst preparation

[0130] Take 100 g of the solution obtained by mixing potassium carbonate with water (the potassium content is 12 g in terms of K2O); mix it with 60 g of silica microspheres (the microsphere diameter is 2.5 mm, the average pore diameter by the BET method is 22 nm, the pore volume by the BET method is 1.1 ml / g, and the Na2O content is 2000 ppm), let it stand for 24 hours, then vacuum dry it at 50 °C for 24 hours, and calcine it in an air atmosphere at 500 °C for 5 hours to obtain the catalyst product B2.

[0131] 2. Online reduction activation of the catalyst and synthesis of methyl acrylate

[0132] Take 15 g of the obtained catalyst product B2 and load it into a fixed-bed reactor (inner diameter 16 mm, length 1500 mm). After replacing it with N2 three times, raise the reactor temperature to 300 °C, adjust the pressure to 0.5 MPa, and use the total mass space velocity of methyl acetate and aldehyde of 5 h -1 Feed the reaction raw materials (the mass ratio of trioxane, methyl acetate and methanol is 5:40:4), take samples, add the internal standard toluene, and measure the contents of each component in the reaction mixture by gas chromatography. Calculate that the formaldehyde conversion rate is 51.3% and the selectivity of methyl acrylate is 84.2%.

[0133] Comparative Example 3

[0134] 1. Catalyst preparation

[0135] Take 100 g of the solution obtained by mixing rubidium carbonate with water (the rubidium content is 12 g in terms of Rb2O); mix it with 60 g of silica microspheres (the microsphere diameter is 2.5 mm, the average pore diameter by the BET method is 22 nm, the pore volume by the BET method is 1.1 ml / g, and the Na2O content is 2000 ppm), let it stand for 24 hours, then vacuum dry it at 50 °C for 24 hours, and calcine it in an air atmosphere at 500 °C for 5 hours to obtain the catalyst product B3.

[0136] 2. Online reduction activation of the catalyst and synthesis of methyl acrylate

[0137] Take 15 g of the obtained catalyst product B3 and load it into a fixed-bed reactor (inner diameter 16 mm, length 1500 mm). After replacing it with N2 three times, raise the reactor temperature to 300 °C, adjust the pressure to 0.5 MPa, and use the total mass space velocity of methyl acetate and aldehyde of 5 h -1 Feed the reaction raw materials (the mass ratio of trioxane, methyl acetate and methanol is 5:40:4), take samples, add the internal standard toluene, and measure the contents of each component in the reaction mixture by gas chromatography. Calculate that the formaldehyde conversion rate is 53.7% and the selectivity of methyl acrylate is 83.1%.

[0138] Comparing the formaldehyde conversion rates and methyl acrylate selectivities obtained in the above Examples 1-10 and Comparative Examples 1-3, the catalyst treated with supercritical fluid in the present invention has significantly improved both the formaldehyde conversion rate and the methyl acrylate selectivity, and the catalytic activity and selectivity of the catalyst have been significantly enhanced.

[0139] It should be noted that the above-described embodiments are only used to explain the present invention and do not constitute any limitation to the present invention. The present invention has been described by referring to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory words rather than limiting words. Modifications to the present invention can be made within the scope of the claims of the present invention as provided, and the present invention can be revised without departing from the scope and spirit of the present invention. Although the present invention described therein relates to specific methods, materials and embodiments, it does not mean that the present invention is limited to the specific examples disclosed therein. On the contrary, the present invention can be extended to all other methods and applications with the same function.

Claims

1. A catalyst for synthesizing methyl acrylate, comprising a carrier and an active component supported on the carrier, wherein, the average pore diameter of the carrier is 2 nm to 50 nm, and the pore volume of the carrier is 0.2 mL / g to 2 mL / g; the active component is selected from one or more of the oxides of alkali metals; the preparation method of the catalyst includes the step of mixing a carrier impregnated with an active component source with a liquid medium in a reactor and bringing the mixed solution into the supercritical state of the liquid medium, wherein the liquid medium is a hydrophilic liquid; the carrier is selected from one or more of SiO2, Al2O3 and activated carbon.

2. The catalyst according to claim 1, wherein The alkali metal is selected from one or more of K, Rb and Cs; and / or the active component is selected from one or more of potassium oxide, rubidium oxide, cesium oxide; and / or the liquid medium is selected from one or more of methanol, ethanol, ethylene glycol, isopropyl alcohol and propylene glycol.

3. The catalyst according to claim 1, wherein By mass, the catalyst comprises: 1 to 50 parts of active component; 50 to 80 parts of carrier.

4. The catalyst according to claim 3, characterized in that, By mass, the catalyst comprises: 2 to 20 parts of active component; 60 to 75 parts of carrier.

5. The catalyst according to any one of claims 1-4, characterized in that, The particle size of the carrier is 1 to 5 mm; and / or the specific surface area of the carrier is 100 to 500 m 2 / g.

6. A preparation method of the catalyst according to any one of claims 1-5, comprising the steps: S1. Contacting a solution containing an active component source with a carrier to obtain an intermediate impregnated carrier; S2. Mixing the intermediate impregnated carrier with a liquid medium in a reactor and bringing the mixed solution into the supercritical state of the liquid medium to obtain a catalyst precursor; S3. Calcining the catalyst precursor to obtain the catalyst.

7. The preparation method according to claim 6, characterized in that, The active component source is selected from alkali metal salts.

8. The preparation method according to claim 7, characterized in that, The active component source is selected from one or more of alkali metal carbonates, alkali metal nitrates and alkali metal acetates.

9. The preparation method according to claim 8, characterized in that, The active component source is selected from one or more of cesium carbonate, cesium acetate and potassium carbonate.

10. The preparation method according to any one of claims 6-9, characterized in that, In step S1, the conditions of the contact include: the temperature is 10°C to 60°C; the time is 5 to 20 h.

11. The preparation method according to any one of claims 6-9, characterized in that, In step S2, the amount of the liquid medium added is 30% to 70% of the volume of the reactor; and / or the mixing time is 0.5 to 2 h; the temperature above the critical temperature in the supercritical state is 0°C to 10°C.

12. The preparation method according to any one of claims 6-9, characterized in that, In step S3, the conditions of the calcination include: the temperature is 400°C to 800°C; the time is 4 to 15 hours.

13. An application of the catalyst according to any one of claims 1-5 or the catalyst prepared by the preparation method according to any one of claims 6-12 in an aldol condensation reaction.

14. The application according to claim 13, characterized in that, The application is in the synthesis of methyl acrylate.

15. The application according to claim 14, wherein The raw materials for synthesizing methyl acrylate include methyl acetate and an aldehyde source, and the addition amount of the catalyst is 1% to 10% of the total mass of methyl acetate and the aldehyde source.

16. The application according to claim 15, characterized in that, The reaction temperature for synthesizing methyl acrylate is 200°C to 450°C; and / or the aldehyde source is selected from one or more of formaldehyde or substances that can in-situ generate formaldehyde in the synthesis reaction system; and / or The total mass hourly space velocity of methyl acetate and aldehyde source is 1 h -1 ~10 h -1 .

17. The application according to claim 16, characterized in that, the aldehyde source is selected from one or more of trioxane, paraformaldehyde, methylal or formaldehyde; and / or the molar ratio of methyl acetate to formaldehyde is 3 to 100.

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