Preparation method and application of a shaped aldol condensation catalyst

Abstract

This invention discloses a method for preparing and applying a molded aldol condensation catalyst. The preparation method includes: based on a sol-gel synthesis process, preparing a hydrosol solution by promoting the hydrolysis of a silicon source with an acidic active component; adding the hydrosol dropwise to an alkaline molding agent composed of an organic solvent and ammonia; and forming a spherical support precursor containing acidic active centers under surface tension and rapid local condensation of the sol. After drying and calcination, alkaline active centers are introduced into the molded support using an impregnation method to obtain the corresponding molded catalyst system. This preparation process has the advantages of short flow, easy operation, and repeatability, enabling large-scale preparation. The catalyst, when applied to the synthesis of methyl acrylate, exhibits high catalytic performance and stability, demonstrating promising industrial application prospects.

Description

Technical Field

[0001] This invention relates to a method for preparing a molded aldol condensation catalyst and its application. Specifically, a molded catalyst is used in the synthesis process of methyl acetate-formaldehyde to methyl acrylate. This invention belongs to the field of molded catalytic material preparation technology. Background Technology

[0002] In the field of aldol condensation to methyl acrylate (MA) technology, commercially available alumina, silica, and molecular sieves are typically used as supports to load active components for the synthesis of various catalyst systems, and molded catalysts are used in industrial plants. Among these, catalyst systems prepared using silica as a support have the advantages of low cost and high activity. Currently, spherical water-resistant silica gel produced by domestic manufacturers is mostly synthesized using a precipitation method and then molded using a spherical rolling method. However, this molding technology leads to problems such as low support strength, surface cracks, and dust shedding during use, posing potential risks to the industrial application of the catalyst. Furthermore, using commercial silica gel as a support and synthesizing catalysts via impregnation methods results in uneven distribution of active components, affecting catalyst performance and stability. Therefore, developing a molded catalyst preparation technology with a uniform distribution of active components is one effective way to solve these problems.

[0003] Patents related to catalyst preparation technology have been published. Chinese patent CN1204964C discloses a method for preparing spherical alumina, which involves dripping alumina sol into an oil-ammonia column to form spherical gel particles, followed by aging, drying, and calcination to obtain the spherical alumina product. Chinese patent CN115608405A discloses a method for preparing millimeter-scale spherical composite supports and catalysts, which utilizes alumina precursor mixed with MFI structured molecular sieves, then mixed with an acidic aqueous solution to form a sol, and finally dripping the sol into an oil-ammonia column forming device, followed by spherical formation, aging, drying, and calcination to obtain the spherical composite support. Similarly, Chinese patent CN103962056B and US patent USP4542113, among others, modify the oil-ammonia column method to obtain spherical alumina. Furthermore, US patent US2620314 and Chinese patent CN105502447, among others, obtain alumina microspheres by dripping the prepared alumina sol or alumina slurry into a hot oil column. Chinese patent CN113289595A describes a method for preparing spherical alumina based on the sol-gel properties of polymer materials. The process uses an upper oil phase and a lower curing agent solution to shape the precursor solution. Additionally, Chinese patent CN114950425A discloses a method for preparing a millimeter-scale dimethyl oxalate hydrogenation catalyst. This method uses sodium alginate as a thickener to convert a silica precursor into a viscous liquid, which is then dropped into a hot oil column to obtain a spherical silica support, followed by catalyst preparation.

[0004] In the field of catalyst forming technology, the oil-ammonia column method or hot oil column method is the main method for forming supports / catalysts, often used to synthesize spherical alumina supports or catalysts. During the synthesis process of the oil-ammonia column or hot oil column method, some additives (urea, hexamethylenetetramine, etc.) or curing agents need to be added to the precursor solution; the oil-ammonia column or oil column consists of an oil phase and an aqueous phase, and electrolytes, surfactants, and other substances are added to it. Furthermore, the oil-ammonia column or hot oil column needs to be heated during the forming process, all of which lead to a more complex preparation process and increased costs. In view of the current state of the technology, this invention develops a novel, simple, and feasible catalyst forming technology for synthesizing a catalyst system suitable for the aldol condensation reaction to methyl acrylate. Summary of the Invention

[0005] This invention provides a method for preparing a molded aldol condensation catalyst and applies the catalyst to the one-step aldol condensation reaction of acetic acid (methyl ester) and formaldehyde to produce acrylic acid (methyl ester). The preparation method includes the synthesis of a molded support and the catalyst. A hydrosol is prepared by promoting the hydrolysis of a silicon source with an acidic component. The molded support is obtained using a local rapid sol-gel polymerization method, and then an alkaline component is introduced by impregnation to obtain the corresponding catalyst system. This novel molded catalyst preparation technology offers advantages such as a short process, ease of operation, and reproducibility, enabling large-scale production and possessing broad industrial application prospects.

[0006] The present invention can achieve the above objectives through the following technical solutions:

[0007] A method for preparing a shaped aldol condensation catalyst, characterized in that the preparation method includes a method for synthesizing a shaped support and a catalyst, wherein the shaped support is prepared by a sol-gel local rapid condensation method, wherein a precursor aqueous sol solution containing acidic components is dropped into a shaped agent, and the surface tension and local alkaline environment of the mixture system are used to cause the droplets to rapidly condense into spheres. On this basis, the alkaline active components are loaded onto the spherical support to obtain the corresponding shaped catalyst system.

[0008] The method for preparing the shaped catalyst support is characterized in that, when preparing the shaped support precursor hydrosol, the molar ratio of water to silicon is in the range of 10-30.

[0009] The method for preparing the shaped catalyst support is characterized in that the forming agent is composed of a water-soluble organic solvent and ammonia, wherein the water-soluble organic solvent is preferably selected from one or more of methanol, ethanol, DMF, and DMSO, and the mass ratio of the organic solvent to ammonia is in the range of 0.5-50.

[0010] During the formation of the carrier precursor, the drop rate of the hydrosol solution should be controlled at 1-10 drops / second, and the carrier should be allowed to stand and age at room temperature for 6-12 hours after formation.

[0011] The shaped aldol condensation catalyst prepared by the above method is characterized in that the catalyst is composed of acidic centers and basic centers, wherein the basic component is selected from one or more of Na, K, and Cs; and the acidic component is selected from one or more of Zn, Ce, Al, Ti, Zr, Fe, and Cu.

[0012] The loading of the active components of the above catalysts is calculated in terms of oxides, with the loading of basic components between 10-15% and the loading of acidic components between 3-6%.

[0013] Based on the above requirements for the molding support and catalyst synthesis technology, the specific preparation steps are as follows:

[0014] (1) Prepare an aqueous solution of a certain concentration containing acidic components and mix it with tetraethyl silicate (TEOS) until it is uniformly stirred to form a clear and transparent molding precursor hydrosol.

[0015] (2) Weigh a certain mass of organic solvent and ammonia water in proportion to form a mixed system, which is used as the forming agent of the precursor hydrosol in (1);

[0016] (3) The precursor hydrosol in (1) is added dropwise to the molding agent in (2) at a certain dropping rate. After molding and aging, a spherical carrier precursor containing acidic centers is obtained.

[0017] (4) After the precursor in (3) is completely dried in a forced-air drying oven at 50-80 ℃, it is transferred to a muffle furnace and calcined at 500-550 ℃ for 4-6 h to obtain a spherical carrier containing acidic centers.

[0018] (5) Take a certain mass of spherical support and add it to the impregnation solution containing the alkaline active component. Stir evenly and let it stand at room temperature for 6-10 h for impregnation. After impregnation, a spherical catalyst precursor is obtained.

[0019] (6) After the catalyst precursor in (5) is completely dried in an oven at 80-120 ℃, it is transferred to a muffle furnace and calcined at 450-500 ℃ for 6-8 h to obtain the corresponding spherical catalyst.

[0020] A molded aldol condensation catalyst was applied to the aldol condensation reaction of methyl acetate and formaldehyde to produce methyl acrylate. The application conditions were as follows: catalytic evaluation was conducted in a fixed-bed reactor, with a methyl acetate / formaldehyde ratio of 2:1 to 1:2, a methanol / formaldehyde ratio of 1:1 to 3:1, and a feed space velocity of 0.3 to 1.8 h⁻¹. -1 The reaction temperature is 330 ℃~390 ℃.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] (1) A new method for preparing a shaped aldol condensation catalyst is proposed. A spherical support is prepared by local rapid sol-gel polycondensation, and then a spherical catalyst is synthesized by impregnation. The synthesis process is simple, has high raw material utilization, low cost, and strong repeatability. The obtained product has good sphericity, smooth surface, high strength, and high yield.

[0023] (2) When synthesizing spherical supports, the added acidic components promote the hydrolysis of TEOS and are in situ incorporated into the hydrosol framework network, achieving uniform dispersion of the components. The catalyst synthesized from it has uniformly distributed acid-base active components and exhibits superior catalytic performance.

[0024] (3) The catalyst preparation technology is highly efficient and stable, and can be mass-produced, with broad prospects for industrial application. Attached Figure Description

[0025] Figure 1 Images of the spherical catalysts prepared in the embodiments of the present invention. Detailed Implementation

[0026] The present invention will be further described in detail through specific embodiments, but should not be limited to the following embodiments. Various substitutions and modifications made based on ordinary technical knowledge and common practice in the art without departing from the above-described technical concept of the present invention should be included within the scope of the present invention.

[0027] Example 1:

[0028] (1) Weigh 2.79 g Zr(NO3)4·5H2O, dissolve it in 60 mL of deionized water, and sonicate for 10 min. Then mix 70.86 g TEOS and zirconium aqueous solution evenly to form a clear and transparent molding precursor hydrosol solution.

[0029] (2) Mix 100 g of methanol and 5 g of ammonia water evenly to prepare a molding agent for later use;

[0030] (3) The solution in step (1) is added dropwise to the molding agent in (2) at a rate of 6 drops / second to form a spherical carrier precursor containing Zr acid centers, and aged at room temperature for 8 h.

[0031] (4) After drying the carrier precursor in (3) in a forced-air drying oven at 75 °C for 6 h, it was transferred to a muffle furnace and calcined at 520 °C for 4-6 h to obtain a spherical carrier containing Zr acidic centers.

[0032] (5) Weigh 5.0 g of the spherical carrier in (4), pour it into the impregnation solution containing 0.69 g of cesium nitrate, stir evenly, and let it stand at room temperature for 8 h for impregnation;

[0033] (6) After the catalyst precursor in (5) is completely dried in an oven at 110 °C, it is transferred to a muffle furnace and calcined at 500 °C for 7 h to obtain the corresponding spherical catalyst, which is denoted as Cat-1.

[0034] Example 2:

[0035] (1) Weigh 2.79 g Zr(NO3)4·5H2O, dissolve it in 60 mL of deionized water, and sonicate for 10 min. Then mix 70.86 g TEOS and zirconium aqueous solution evenly to form a clear and transparent molding precursor hydrosol solution.

[0036] (2) Mix 100 g of ethanol and 5 g of ammonia water evenly to prepare a molding agent for later use;

[0037] (3) The solution in step (1) is added dropwise to the molding agent in (2) at a rate of 6 drops / second to form a spherical carrier precursor containing Zr acid active centers, and aged at room temperature for 8 h.

[0038] (4) After drying the carrier precursor in (3) in a forced-air drying oven at 75 °C for 6 h, it was transferred to a muffle furnace and calcined at 520 °C for 4-6 h to obtain a spherical carrier containing Zr acidic centers.

[0039] (5) Weigh 5.0 g of the spherical carrier in (4), pour it into the impregnation solution containing 0.69 g of cesium nitrate, stir evenly, and let it stand at room temperature for 8 h for impregnation;

[0040] (6) After the catalyst precursor in (5) is completely dried in an oven at 110 °C, it is transferred to a muffle furnace and calcined at 500 °C for 7 h to obtain the corresponding spherical catalyst, which is denoted as Cat-2.

[0041] Example 3:

[0042] (1) Weigh 2.79 g Zr(NO3)4·5H2O, dissolve it in 60 mL of deionized water, and sonicate for 10 min. Then mix 70.86 g TEOS and zirconium aqueous solution evenly to form a clear and transparent molding precursor hydrosol solution.

[0043] (2) Mix 100 g DMF and 5 g ammonia water evenly to prepare a molding agent for later use;

[0044] (3) The solution in step (1) is added dropwise to the molding agent in (2) at a rate of 6 drops / second to form a spherical carrier precursor containing Zr acid centers, and aged at room temperature for 8 h.

[0045] (4) After drying the carrier precursor in (3) in a forced-air drying oven at 75 °C for 12 h, it is transferred to a muffle furnace and calcined at 520 °C for 4-6 h to obtain a spherical carrier containing Zr acidic centers.

[0046] (5) Measure 5.0 g of the spherical carrier in (4), pour it into the impregnation solution containing 0.69 g of cesium nitrate, stir evenly, and let it stand at room temperature for 8 h for impregnation;

[0047] (6) After the catalyst precursor in (5) is completely dried in an oven at 110 °C, it is transferred to a muffle furnace and calcined at 500 °C for 7 h to obtain the corresponding spherical catalyst, which is denoted as Cat-3.

[0048] Example 4:

[0049] (1) Weigh 2.79 g Zr(NO3)4·5H2O, dissolve it in 60 mL of deionized water, and sonicate for 10 min. Then mix 70.86 g TEOS and zirconium aqueous solution evenly to form a clear and transparent molding precursor hydrosol solution.

[0050] (2) Mix 100 g DMSO and 5 g ammonia water evenly to prepare a molding agent for later use;

[0051] (3) The solution in step (1) is added dropwise to the molding agent in (2) at a rate of 6 drops / second to form a spherical carrier precursor containing Zr acid centers, and aged at room temperature for 8 h.

[0052] (4) After drying the carrier precursor in (3) in a forced-air drying oven at 75 °C for 8 h, it was transferred to a muffle furnace and calcined at 520 °C for 4-6 h to obtain a spherical carrier containing Zr acidic centers.

[0053] (5) Weigh 5.0 g of the spherical carrier in (4), pour it into the impregnation solution containing 0.69 g of cesium nitrate, stir evenly, and let it stand at room temperature for 8 h for impregnation;

[0054] (6) After the catalyst precursor in (5) is completely dried in an oven at 110 °C, it is transferred to a muffle furnace and calcined at 500 °C for 7 h to obtain the corresponding spherical catalyst, which is denoted as Cat-4.

[0055] Example 5:

[0056] (1) Weigh 5.89 g Al(NO3)3·9H2O, dissolve it in 60 mL of deionized water, and sonicate for 10 min. Then mix 70.86 g TEOS and aluminum aqueous solution evenly to form a clear and transparent molding precursor hydrosol solution.

[0057] (2) Mix 90 g of methanol and 5 g of ammonia water evenly to prepare a molding agent for later use;

[0058] (3) The solution in step (1) is added dropwise to the molding agent in (2) at a rate of 4 drops / second to form a spherical carrier precursor containing Al acidic centers, and aged at room temperature for 8 h.

[0059] (4) After drying the carrier precursor in (3) in a forced-air drying oven at 75 °C for 6 h, it was transferred to a muffle furnace and calcined at 520 °C for 4-6 h to obtain a spherical carrier containing Al acidic centers.

[0060] (5) Weigh 5.0 g of the spherical carrier in (4), pour it into the impregnation solution containing 0.69 g of cesium nitrate, stir evenly, and let it stand at room temperature for 8 h for impregnation;

[0061] (6) After the catalyst precursor in (5) is completely dried in an oven at 110 °C, it is transferred to a muffle furnace and calcined at 500 °C for 7 h to obtain the corresponding spherical catalyst, which is denoted as Cat-5;

[0062] Comparative Example 1:

[0063] (1) Weigh 0.52 g Zr(NO3)4·5H2O, dissolve it in 4.5 mL of deionized water, and sonicate for 10 min to prepare a clear and transparent solution A;

[0064] (2) Take 5 g of 20-40 mesh a-SiO2 support (domestic), quickly add it to solution A prepared in step (1), stir evenly, and let it stand at room temperature for 8 h for soaking;

[0065] (3) The Zr / a-SiO2 precursor obtained in (2) was dried in a forced-air drying oven at 75 °C for 10 h, and then calcined in a muffle furnace at 520 °C for 4-6 h to obtain the Zr / a-SiO2 support.

[0066] (4) Weigh 5 g of the support in (4), pour it into the impregnation solution containing 0.69 g of cesium nitrate, stir evenly, and let it stand at room temperature for 8 h to obtain the Cs / Zr / a-SiO2 catalyst, which is denoted as Cat-6;

[0067] Comparative Example 2:

[0068] (1) Weigh 0.52 g Zr(NO3)4·5H2O, dissolve it in 4.5 mL of deionized water, and sonicate for 10 min to prepare a clear and transparent solution A;

[0069] (2) Take 5 g of 20-40 mesh b-SiO2 support (imported) and quickly add it to solution A prepared in step (1), stir evenly, and let it stand at room temperature for 8 h for soaking;

[0070] (3) The Zr / b-SiO2 precursor obtained in (2) was dried in a forced-air drying oven at 75 °C for 10 h, and then calcined in a muffle furnace at 520 °C for 4-6 h to obtain the Zr / b-SiO2 support.

[0071] (4) Weigh 5 g of the support in (4) and pour it into an impregnation solution containing 0.69 g of cesium nitrate. Stir evenly and let it stand at room temperature for 8 h to obtain the Cs / Zr / b-SiO2 catalyst, which is denoted as Cat-7.

[0072] Application Example: Catalyst activity testing was conducted in a fixed-bed reactor with a catalyst loading of 6 mL, a methyl acetate / formaldehyde molar ratio of 2:1, a methanol / formaldehyde molar ratio of 2:1, and a space velocity of 0.8 h⁻¹. -1 The reaction temperature was 370 ℃, and the results are shown in Tables 1 and 2:

[0073] Table 1

[0074] Example Catalyst number Methyl acetate conversion rate / % methyl acrylate selectivity / % 1 Cat-1 26.0 73.7 2 Cat-2 26.0 72.6 3 Cat-3 26.4 72.2 4 Cat-4 4.3 54.5 5 Cat-5 25.3 78.0

[0075] Table 2

[0076] Comparative Examples Catalyst number Methyl acetate conversion rate / % methyl acrylate selectivity / % 1 Cat-6 21.1 66.7 2 Cat-7 21.5 65.2

[0077] As can be seen from the evaluation results of the examples in Table 1, the shaped catalysts obtained using different shaping agents exhibited better catalytic activity in the reaction. Compared with the evaluation results of the comparative examples in Table 2, the catalyst synthesized in this invention has higher performance than the catalyst synthesized by the traditional impregnation method. This is because during the formation of the hydrosol, the acidic component promotes the hydrolysis of TEOS and is simultaneously incorporated in situ into the sol framework network, achieving uniform dispersion of the components. Using this support to prepare the catalyst further promotes the dispersion of the alkaline component, thereby resulting in higher conversion and selectivity.

Claims

1. A method for preparing a shaped aldol condensation catalyst, characterized in that, The preparation method includes the synthesis of a molded support and a catalyst. The molded catalyst is in the shape of millimeter-sized spheres, and the active component consists of basic and acidic centers. The support component is SiO2. The preparation method involves preparing a molded support containing acidic centers using a sol-gel local rapid polycondensation method, and then preparing the molded catalyst using an impregnation method. The specific steps are as follows: (1) Prepare an aqueous solution of a certain concentration containing acid-active components and mix it with tetraethyl orthosilicate (TEOS) until homogeneous to form a clear and transparent hydrosol of the molding carrier precursor; wherein the acid-active components are selected from one or more of Zn, Ce, Al, Ti, Zr, Fe, and Cu. (2) Weigh a certain amount of organic solvent and ammonia water in proportion to form a uniform mixture system, which is used as the forming agent of the precursor hydrosol in (1); the organic solvent is selected from one or more of methanol, ethanol, DMF, and DMSO, and the mass ratio of organic solvent to ammonia water is 0.5-50. (3) The precursor solution in (1) is added dropwise to the molding agent in (2) at a certain dropping rate. After molding and aging, a spherical carrier precursor containing acid active centers is obtained. (4) After the precursor in (3) is completely dried in a forced-air drying oven at 50-80 ℃, it is transferred to a muffle furnace and calcined at 500-550 ℃ for 4-6 h to obtain a spherical carrier containing acidic centers. (5) Take a certain mass of spherical support and add it to the impregnation solution containing the alkaline active component. Stir evenly and let it stand at room temperature for 6-10 h for impregnation. After impregnation, a spherical catalyst precursor is obtained. The alkaline active component is selected from one or more of Na, K, and Cs. (6) After the catalyst precursor in (5) is completely dried in an oven at 80-120 ℃, it is transferred to a muffle furnace and calcined at 450-500 ℃ for 6-8 h to obtain the corresponding spherical catalyst.

2. The method for preparing the catalyst according to claim 1, characterized in that, When preparing the hydrosol precursor for the molding carrier, the molar ratio of water to silicon ranges from 10 to 30.

3. The method for preparing the catalyst according to any one of claims 1-2, characterized in that, The dropping rate of the precursor solution is controlled at 1-10 drops / second.

4. The method for preparing the catalyst according to any one of claims 1-2, characterized in that, After the spherical carrier is formed, it is left to age at room temperature for 6-12 hours.

5. The application of a shaped aldol condensation catalyst synthesized by the preparation method according to any one of claims 1-4, characterized in that, The application is to catalyze the direct synthesis of methyl acrylate from methyl acetate and formaldehyde.

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