A core-shell composite catalyst for aldol condensation reaction and its preparation method and application

Abstract

The application discloses a core-shell type composite catalyst for aldol condensation reaction, which is characterized in that ZSM-35 molecular sieve modified by Silicalite-1 full-silicon molecular sieve is used as a shell, cesium-cerium composite metal oxide is used as a core, and a binder is further included; the catalyst is composed of the following components in parts by weight based on 100% of the total weight of the catalyst: the core is 50-70%, the shell is 20-35%, and the binder is 8-15%. Meanwhile, the application further discloses a preparation method and application of the catalyst. The catalyst is a core-shell type acid-base bifunctional catalyst, ZSM-35 molecular sieve is subjected to surface modification, and then the modified molecular sieve is used to wrap metal active components, so that the loss is inhibited, the catalytic service life is greatly improved, and the catalytic activity does not obviously decrease within the service life experimental range of 2000h.

Description

Technical Field

[0001] The invention belongs to the technical field of aldol condensation, and particularly relates to a core-shell composite catalyst for aldol condensation reaction, a preparation method and application thereof. Background Art

[0002] Methyl methacrylate (MMA) is an important polymer monomer and chemical raw material, commonly used in the production of polymethyl methacrylate (PMMA) and acrylic resins. It is also widely used in the production of plastics, coatings, adhesives, and various industrial additives. In recent years, my country's MMA industry and demand have generally shown rapid growth.

[0003] The traditional methyl methacrylate production process, the acetone cyanohydrin process, requires the highly toxic raw material hydrocyanic acid, which severely pollutes the environment, poses significant safety risks, and is outdated. Subsequently, isobutylene oxidation (also known as C4 oxidation) and ethylene routes were developed. While cleaner than the acetone cyanohydrin route, the raw materials are heavily dependent on petroleum refining products. Therefore, the development of a clean and efficient coal-based synthesis route would not only help alleviate the imbalance between supply and demand of my country's petroleum resources, but also effectively utilize coal chemical products and address overcapacity.

[0004] In recent years, the process of directly or indirectly preparing methyl methacrylate by aldol condensation reaction with formaldehyde and methyl acetate (methyl propionate or acetaldehyde, propionaldehyde, acetic acid, propionic acid, etc.) as raw materials has attracted widespread attention. This route has the advantages of cheap raw materials and wide sources, short process flow and simple operation. CN101829558A discloses a Cs-Zr-Ce / SiO2 catalyst, and adds a water-soluble nonionic surfactant as a dispersion promoter of the active component on the carrier surface during the impregnation preparation process. By changing the concentration or type of the dispersion promoter, the dispersion degree of the active component Cs on the carrier surface is increased, thereby improving the catalytic performance of the catalyst. CN103551148A discloses a water-resistant catalyst for aldol condensation, wherein the main active ingredient includes one or more of the oxide or salt of Cs, the active auxiliary agent is one or more of the oxide or salt of Sb, Nb, Ag, Al, and Zr, and the carrier includes SiO2 and a carrier auxiliary agent. CN112844356 A discloses a catalyst for the production of methyl methacrylate from methyl propionate and formaldehyde, and its preparation method. The catalyst comprises Cs and Al as the main active components, one or more of Zr, La, Ce, and Zn as the auxiliary agent, and a porous SiO2 carrier. In Chinese patent CN103551148A, the Southwest Chemical Research and Design Institute discloses a water-resistant catalyst for aldol condensation, comprising one or more oxides or salts of Cs as the main active component, one or more oxides or salts of Sb, Nb, Ag, Al, and Zr as the auxiliary agent, and a SiO2 carrier and a support auxiliary agent. CN110694608 A discloses a catalyst for aldol condensation, its preparation method, and application. The catalyst comprises Cs as the active component, an auxiliary agent, and a support, wherein the active component is an acid-treated modified SiO2 support, and the auxiliary agent is one or more of P, V, W, Sn, B, Bi, Nb, Ba, La, Ti, Al, Sb, Ce, Zr, and Fe.

[0005] Aldol condensation is a typical carbon chain growth reaction that can occur in the presence of acidic catalysts, basic catalysts, and acid-base bifunctional catalysts. Bifunctional acid-base catalysts, based on acidic molecular sieves and alkaline metals as active components, offer superior performance compared to single acidic and single alkaline catalysts due to their high selectivity and high activity. However, conventional supported catalysts suffer from the tendency to lose their active components, resulting in rapid catalyst deactivation and poor stability, which has limited their further development and application. Summary of the Invention

[0006] In view of the defects of the prior art, the present invention provides a core-shell composite catalyst for aldol condensation reaction and a preparation method thereof, and also provides the use of the catalyst in preparing methyl methacrylate through aldol condensation reaction. The catalyst has good stability and long service life.

[0007] A core-shell composite catalyst for aldol condensation reaction, comprising a ZSM-35 molecular sieve modified with Silicalite-1 all-silicon molecular sieve as a shell, a cesium-cerium composite metal oxide as a core, and a binder. Based on 100% of the total weight of the catalyst, the catalyst comprises the following components in parts by weight: 50-70% core, 20-35% shell, and 8-15% binder.

[0008] Preferably, the molar ratio of cesium to cerium in the cesium-cerium composite metal oxide is (1-5):1.

[0009] Preferably, in the ZSM-35 molecular sieve modified with the Silicalite-1 all-silicon molecular sieve, the mass ratio of the ZSM-35 molecular sieve to the Silicalite-1 all-silicon molecular sieve is (3-20):1.

[0010] More preferably, the silicon to aluminum ratio of the ZSM-35 molecular sieve is 20-90.

[0011] Preferably, the binder is silica sol, γ-aminopropyltriethoxysilane (APTES), γ-aminopropyltrimethoxysilane (APTMS) or glycidyloxypropyltrimethoxysilane.

[0012] The method for preparing the core-shell composite catalyst for aldol condensation reaction comprises the following steps:

[0013] (1) Preparation of cesium-cerium composite metal oxide by co-current coprecipitation;

[0014] (2) Preparation of ZSM-35 molecular sieve modified with Silicalite-1 all-silicon molecular sieve:

[0015] (21) The hydrothermal synthesis method was used to mix the silicon source, organic template, ethanol, and deionized water and stir at room temperature for 3-10 h to obtain the Silicalite-1 molecular sieve precursor;

[0016] (22) The Silicalite-1 molecular sieve precursor and the ZSM-35 molecular sieve were transferred to a hydrothermal reactor, sealed, and crystallized at 100-200°C at a speed of 3-10 rpm for 18-56 hours. The mixture was cooled to room temperature, and the product was washed with deionized water until the pH of the filtrate was 7-8. The product was dried at room temperature overnight and then calcined in a muffle furnace to obtain a Silicalite-1 all-silicon molecular sieve modified ZSM-35 molecular sieve, which was recorded as ZSM-35@Silicalite-1.

[0017] (3) Preparation of catalyst:

[0018] The surface of the cesium-cerium composite metal oxide is impregnated with a binder to wet the surface, the cesium-cerium composite metal oxide with the wetted surface is added to a container containing ZSM-35@Silicalite-1, and the container is rotated at a constant speed to coat the surface of the cesium-cerium composite metal oxide with ZSM-35@Silicalite-1. The impregnation and coating process is repeated until the ZSM-35@Silicalite-1 is completely coated on the surface of the cesium-cerium composite metal oxide, and then the container is dried overnight at room temperature and calcined to obtain a core-shell composite catalyst having a ZSM-35 molecular sieve modified with Silicalite-1 all-silicon molecular sieve as a shell and a cesium-cerium composite metal oxide as a core.

[0019] Preferably, the silicon source is TEOS, and the organic template is TPAOH; the molar ratio of the silicon source, the organic template, ethanol, and deionized water is (1.0-10): (0.01-0.1): (10-50): (200-400).

[0020] Preferably, the preparation of the cesium-cerium composite metal oxide by co-current co-precipitation in step (1) is specifically as follows: water-soluble metal salts of cesium and cerium are dissolved in water to prepare an active component solution, and the active component solution and the precipitant are respectively and simultaneously added dropwise into deionized water under stirring at 60-90° C., and the pH of the system is controlled to be 8.0-9.5 during the addition process. After the addition is completed, the temperature is maintained and the aging is continued for 4-10 hours, and the solid obtained by centrifugation is washed to neutrality, dried, roasted, and ground to obtain the cesium-cerium composite metal oxide.

[0021] Preferably, the precipitant is a 20-30 wt% ammonia solution, and the total molar concentration of cesium and cerium in the active component solution is 0.1-3.0 mol / L.

[0022] Preferably, the calcination is carried out by heating the temperature to 450-750° C. at a heating rate of 1-5° C. / min and calcining for 3-10 hours.

[0023] A method for preparing methyl methacrylate by aldol condensation reaction is as follows: a catalyst is loaded into a fixed-bed reactor, a raw material mixture is introduced into a preheating furnace for vaporization at a flow rate of 0.1-1.0 mL / min through a horizontal flow pump under nitrogen entrainment, and after vaporization, the mixture is introduced into the fixed-bed reactor for reaction at 220-350° C. and 0 MPa, and the reaction product is condensed and collected; wherein the raw material mixture is a mixture of at least one of methyl acetate, methyl propionate, acetaldehyde, propionaldehyde, acetic acid, and propionic acid and formaldehyde in a molar ratio of 1:(1-5); the liquid space velocity of the raw material mixture is 6, and the temperature of the preheating furnace is 20-30° C. lower than the reaction temperature; and the catalyst is the catalyst described in the present invention.

[0024] Advantages of the present invention:

[0025] (1) The catalyst provided by the present invention is a core-shell acid-base bifunctional catalyst. The surface of the ZSM-35 molecular sieve is modified, and then the modified molecular sieve is used to wrap the metal active component, thereby inhibiting the loss and greatly improving the catalytic life. The catalytic activity does not decrease significantly within the 2000h life test range;

[0026] (2) Surface modification of molecular sieves eliminates strong acid sites on the surface of molecular sieves, which is beneficial to further improve the selectivity of products, while inhibiting the coking reaction and enhancing the catalyst's ability to resist carbon deposition;

[0027] (3) The catalyst preparation method is simple, with short steps, a wide source of raw materials, low cost, and suitable for mass production. At the same time, the reaction conditions are mild, and it has good industrial application prospects. Implementation Method

[0028] The ZSM-35 molecular sieve used in the embodiment of the present invention is a commercially available ZSM-35 molecular sieve with a silicon-aluminum ratio of 28.

[0029] Example 1

[0030] 1. A core-shell composite catalyst for aldol condensation reaction, comprising a ZSM-35 molecular sieve modified with Silicalite-1 all-silicon molecular sieve as a shell, a cesium-cerium composite metal oxide as a core, and a binder, silica sol. The catalyst is composed of the following components in parts by weight, based on 100% by weight of the total catalyst: 50% core, 35% shell, and 15% binder.

[0031] The molar ratio of cesium to cerium in the cesium-cerium composite metal oxide is 1:1; and the mass ratio of ZSM-35 molecular sieve to Silicalite-1 all-silicon molecular sieve in the ZSM-35 molecular sieve modified by Silicalite-1 all-silicon molecular sieve is 3:1.

[0032] 2. The method for preparing the core-shell composite catalyst for aldol condensation reaction comprises the following steps:

[0033] (1) Preparation of cesium-cerium composite metal oxide by co-precipitation:

[0034] Cesium nitrate and cerium nitrate are dissolved in water to prepare an active component solution with a total metal molar concentration of 0.1 mol / L, and a 20 wt% ammonia aqueous solution is used as a precipitant. The active component solution and the precipitant are respectively and simultaneously added dropwise to deionized water under stirring at 60° C., and the pH of the system is controlled to be 8.0-9.5 during the addition process. After the addition is completed, the temperature is maintained and the mixture is aged for 10 hours, centrifuged, and the solid obtained by centrifugation is washed to neutrality, dried at 100° C. for 6 hours, heated to 450° C. at a heating rate of 1° C. / min, calcined for 10 hours, and ground to obtain a cesium-cerium composite metal oxide;

[0035] (2) Preparation of ZSM-35 molecular sieve modified with Silicalite-1 all-silicon molecular sieve:

[0036] (21) The Silicalite-1 molecular sieve precursor was obtained by hydrothermal synthesis by mixing silicon source TEOS, organic template TPAOH, ethanol, and deionized water in a molar ratio of 1:0.01:10:200 and stirring at room temperature for 3 h.

[0037] (22) ZSM-35 molecular sieve and Silicalite-1 molecular sieve precursor were mixed in a mass ratio of 3:1 and transferred to a hydrothermal autoclave, sealed, and crystallized at 100 °C at a speed of 10 rpm for 56 h. The mixture was cooled to room temperature, washed with deionized water until the pH of the filtrate was 7, dried at room temperature overnight, and then placed in a muffle furnace and heated to 750 °C at a heating rate of 5 °C / min for 3 h to obtain ZSM-35 molecular sieve modified with Silicalite-1 all-silicon molecular sieve, which was recorded as ZSM-35@Silicalite-1.

[0038] (3) Preparation of catalyst:

[0039] The surface of the cesium-cerium composite metal oxide is impregnated with a binder to wet the surface, and the cesium-cerium composite metal oxide with the wetted surface is added to a container containing ZSM-35@Silicalite-1. The container is rotated at a constant speed so that the surface of the cesium-cerium composite metal oxide is coated with ZSM-35@Silicalite-1. The impregnation and coating process is repeated until ZSM-35@Silicalite-1 is completely coated on the surface of the cesium-cerium composite metal oxide. The catalyst is then dried at room temperature overnight and calcined at 750°C in a muffle furnace at a heating rate of 5°C / min for 3 hours to obtain a core-shell composite catalyst with ZSM-35 molecular sieve modified with Silicalite-1 all-silicon molecular sieve as a shell and a cesium-cerium composite metal oxide as a core.

[0040] 3. A method for preparing methyl methacrylate by aldol condensation reaction using the catalyst, comprising: loading the catalyst into a fixed-bed reactor, passing a raw material mixture through a horizontal flow pump at a flow rate of 0.1 mL / min into a preheating furnace under nitrogen entrainment, the preheating temperature being 200°C, vaporizing the mixture, and then passing the mixture into the fixed-bed reactor for reaction at 220°C and 0 MPa. The reaction product is condensed and collected, and quantitatively analyzed by gas chromatography; wherein the raw material mixture is a mixture of methyl acetate and formaldehyde in a molar ratio of 1:1, and the liquid space velocity of the raw material mixture is 6.

[0041] Example 2

[0042] 1. A core-shell composite catalyst for an aldol condensation reaction, comprising a ZSM-35 molecular sieve modified with Silicalite-1 as a shell, a cesium-cerium composite metal oxide as a core, and a binder, silica sol. The catalyst comprises the following components in parts by weight, based on 100% of the total catalyst weight: 56% core, 34% shell, and 10% binder. The molar ratio of cesium to cerium in the cesium-cerium composite metal oxide is 5:1. The mass ratio of ZSM-35 molecular sieve to Silicalite-1 in the ZSM-35 molecular sieve modified with Silicalite-1 is 20:1.

[0043] 2. The method for preparing the core-shell composite catalyst for aldol condensation reaction comprises the following steps:

[0044] (1) Preparation of cesium-cerium composite metal oxide by co-precipitation:

[0045] Cesium nitrate and cerium nitrate are dissolved in water to prepare an active component solution with a total metal molar concentration of 1.0 mol / L, and a 20 wt% ammonia aqueous solution is used as a precipitant. The active component solution and the precipitant are respectively and simultaneously added dropwise to deionized water under stirring at 90° C., and the pH of the system is controlled to be 8.0-9.5 during the addition. After the addition is completed, the temperature is maintained and the solution is further aged for 4 hours, centrifuged, and the solid obtained by centrifugation is washed until neutral, dried at 100° C. for 6 hours, calcined at 750° C. for 3 hours at a heating rate of 5° C. / min, and ground to obtain a cesium-cerium composite metal oxide;

[0046] (2) Preparation of ZSM-35 molecular sieve modified with Silicalite-1 all-silicon molecular sieve:

[0047] (21) The Silicalite-1 molecular sieve precursor was obtained by hydrothermal synthesis by mixing silicon source TEOS, organic template agent TPAOH, ethanol, and deionized water in a molar ratio of 10:0.1:50:400 and stirring at room temperature for 10 h.

[0048] (22) ZSM-35 molecular sieve and Silicalite-1 molecular sieve precursor were mixed in a mass ratio of 20:1 and transferred to a hydrothermal autoclave, sealed, and crystallized at 200 °C at a speed of 3 rpm for 18 h. The mixture was cooled to room temperature, washed with deionized water until the pH of the filtrate was 7, dried at room temperature overnight, and then placed in a muffle furnace and heated to 450 °C at a heating rate of 1 °C / min for 10 h to obtain ZSM-35 molecular sieve modified with Silicalite-1 all-silicon molecular sieve, which was recorded as ZSM-35@Silicalite-1.

[0049] (3) Preparation of catalyst:

[0050] The surface of the cesium-cerium composite metal oxide is impregnated with a binder to wet the surface, and the cesium-cerium composite metal oxide with the wetted surface is added to a container containing ZSM-35@Silicalite-1. The container is rotated at a constant speed to coat the surface of the cesium-cerium composite metal oxide with ZSM-35@Silicalite-1. The impregnation and coating process is repeated until the ZSM-35@Silicalite-1 is completely coated on the surface of the cesium-cerium composite metal oxide. The catalyst is then dried at room temperature overnight and calcined at 450°C in a muffle furnace at a heating rate of 1°C / min for 10 hours to obtain a core-shell composite catalyst having a ZSM-35 molecular sieve modified with Silicalite-1 all-silicon molecular sieve as a shell and a cesium-cerium composite metal oxide as a core.

[0051] 3. A method for preparing methyl methacrylate by aldol condensation reaction using the catalyst, comprising: loading the catalyst into a fixed-bed reactor, passing a raw material mixture through a horizontal flow pump at a flow rate of 1.0 mL / min into a preheating furnace under nitrogen entrainment, and vaporizing the mixture at a preheating temperature of 320°C. After vaporization, the mixture is passed into the fixed-bed reactor for reaction at 350°C and 0 MPa. The reaction product is condensed and collected, and quantitatively analyzed by gas chromatography. The raw material mixture is a mixture of methyl acetate and formaldehyde in a molar ratio of 1:5, and the liquid space velocity of the raw material mixture is 6.

[0052] Example 3

[0053] 1.A core-shell composite catalyst for aldol condensation reaction, the catalyst has a ZSM-35 molecular sieve modified by Silicalite-1 full-silica molecular sieve as a shell, a cesium-cerium composite metal oxide as a core, and further comprises a binder silica sol; the catalyst is composed of the following components in parts by weight based on 100% of the total weight of the catalyst: 60% of the core, 28% of the shell, and 12% of the binder; the molar ratio of cesium to cerium in the cesium-cerium composite metal oxide is 4:1; and the mass ratio of the ZSM-35 molecular sieve to the Silicalite-1 full-silica molecular sieve in the ZSM-35 molecular sieve modified by Silicalite-1 full-silica molecular sieve is 10:1.

[0054] 2.A preparation method of the core-shell composite catalyst for aldol condensation reaction, comprising the following steps:

[0055] (1) preparing a cesium-cerium composite metal oxide by using parallel flow co-precipitation:

[0056] Cesium nitrate and cerium nitrate are dissolved in water to prepare an active component solution with a total metal molar concentration of 0.5 mol / L, 30 wt% ammonia solution is used as a precipitator, the active component solution and the precipitator are simultaneously added dropwise into deionized water under stirring at 75 ℃, the pH of the system is controlled to be 8.0-9.5 during the dropwise adding process, the temperature is maintained to continue aging for 8 h after the dropwise adding process is completed, the obtained solid is centrifuged and washed to neutral, dried at 100 ℃ for 6 h, calcined at 550 ℃ with a temperature rising rate of 2 ℃ / min for 6 h, and ground to obtain the cesium-cerium composite metal oxide;

[0057] (2) preparing a ZSM-35 molecular sieve modified by Silicalite-1 full-silica molecular sieve:

[0058] (21) using a hydrothermal synthesis method, a Silicalite-1 molecular sieve precursor is obtained by mixing a silicon source TEOS, an organic template TPAOH, ethanol, and deionized water in a molar ratio of 3.5:0.06:24:260 and stirring at room temperature for 7 h;

[0059] (22) the ZSM-35 molecular sieve and the Silicalite-1 molecular sieve precursor are mixed in a mass ratio of 10:1 and transferred to a hydrothermal kettle, sealed, crystallized at 150 ℃ with stirring at a speed of 4 rpm for 48 h, cooled to room temperature, washed with deionized water until the pH of the filtrate is 8, dried at room temperature overnight, and then placed in a muffle furnace to be calcined at 550 ℃ with a temperature rising rate of 2 ℃ / min for 6 h to obtain the ZSM-35 molecular sieve modified by Silicalite-1 full-silica molecular sieve, denoted as ZSM-35@Silicalite-1;

[0060] (3) preparing the catalyst:

[0061] The surface of the cesium-cerium composite metal oxide is impregnated with a binder to wet the surface, the surface-wetted cesium-cerium composite metal oxide is added to a container containing ZSM-35@Silicalite-1, and is uniformly rotated so that the surface of the cesium-cerium composite metal oxide is coated with ZSM-35@Silicalite-1, and the impregnation and coating process is repeated until the ZSM-35@Silicalite-1 is completely coated on the surface of the cesium-cerium composite metal oxide, then dried overnight at room temperature, and calcined at 580℃ for 5h in a muffle furnace at a temperature rising rate of 2℃ / min, to obtain a core-shell type composite catalyst with Silicalite-1 all-silica molecular sieve modified ZSM-35 molecular sieve as the shell and cesium-cerium composite metal oxide as the core.

[0062] 3. A method for preparing methyl methacrylate by using the catalyst through aldol condensation reaction, specifically as follows: the catalyst is loaded into a fixed bed reactor, a raw material mixture is fed into a preheating furnace for vaporization at a flow rate of 0.5mL / min under the entrainment of nitrogen, the preheating temperature is 230℃, after vaporization, the raw material mixture is introduced into the fixed bed reactor for reaction at 250℃ and 0MPa, the reaction product is condensed and collected, and is quantitatively analyzed by gas chromatography; wherein the raw material mixture is a mixture of methyl propionate and formaldehyde with a molar ratio of 1:3, and the liquid hourly space velocity of the raw material mixture is 6.

[0063] Example 4

[0064] 1. A core-shell type composite catalyst for aldol condensation reaction, the catalyst has Silicalite-1 all-silica molecular sieve modified ZSM-35 molecular sieve as the shell and cesium-cerium composite metal oxide as the core, and further comprises a binder of silica sol; the catalyst is composed of the following components in parts by weight based on 100% of the total weight of the catalyst: core 65%, shell 27%, and binder 8%; wherein the molar ratio of cesium to cerium in the cesium-cerium composite metal oxide is 2:1; and the mass ratio of ZSM-35 molecular sieve to Silicalite-1 all-silica molecular sieve in the Silicalite-1 all-silica molecular sieve modified ZSM-35 molecular sieve is 15:1.

[0065] 2. A preparation method of the core-shell type composite catalyst for aldol condensation reaction, comprising the following steps:

[0066] (1) preparing cesium-cerium composite metal oxide by using parallel flow co-precipitation:

[0067] Cesium nitrate and cerium nitrate are dissolved in water to prepare an active component solution with a total metal molar concentration of 0.8 mol / L, and a 30 wt% ammonia aqueous solution is used as a precipitant. The active component solution and the precipitant are respectively and simultaneously added dropwise to deionized water under stirring at 75° C., and the pH of the system is controlled to be 8.0-9.5 during the addition process. After the addition is completed, the temperature is maintained and the solution is further aged for 8 hours, centrifuged, and the solid obtained by centrifugation is washed until neutral, dried at 100° C. for 6 hours, calcined at 550° C. at a heating rate of 2° C. / min for 6 hours, and ground to obtain a cesium-cerium composite metal oxide;

[0068] (2) Preparation of ZSM-35 molecular sieve modified with Silicalite-1 all-silicon molecular sieve:

[0069] (21) The Silicalite-1 molecular sieve precursor was obtained by hydrothermal synthesis by mixing silicon source TEOS, organic template agent TPAOH, ethanol, and deionized water in a molar ratio of 5.0:0.04:16:300 and stirring at room temperature for 7 h.

[0070] (22) ZSM-35 molecular sieve and Silicalite-1 molecular sieve precursor were mixed in a mass ratio of 15:1 and transferred to a hydrothermal autoclave, sealed, and crystallized at 150 °C at a speed of 4 rpm for 48 h. The mixture was cooled to room temperature, washed with deionized water until the pH of the filtrate was 7, dried at room temperature overnight, and then placed in a muffle furnace and heated to 550 °C at a heating rate of 2 °C / min for 6 h to obtain ZSM-35 molecular sieve modified with Silicalite-1 all-silicon molecular sieve, which was recorded as ZSM-35@Silicalite-1.

[0071] (3) Preparation of catalyst:

[0072] The surface of the cesium-cerium composite metal oxide is impregnated with a binder to wet the surface, and the cesium-cerium composite metal oxide with the wetted surface is added to a container containing ZSM-35@Silicalite-1. The container is rotated at a constant speed to coat the surface of the cesium-cerium composite metal oxide with ZSM-35@Silicalite-1. The impregnation and coating process is repeated until the ZSM-35@Silicalite-1 is completely coated on the surface of the cesium-cerium composite metal oxide. The catalyst is then dried at room temperature overnight and calcined at 580°C in a muffle furnace at a heating rate of 2°C / min for 5 hours to obtain a core-shell composite catalyst having a ZSM-35 molecular sieve modified with Silicalite-1 all-silicon molecular sieve as a shell and a cesium-cerium composite metal oxide as a core.

[0073] 3. A method for preparing methyl methacrylate by aldol condensation reaction using the catalyst, comprising: loading the catalyst into a fixed-bed reactor, passing a raw material mixture through a horizontal flow pump at a flow rate of 0.3 mL / min into a preheating furnace under nitrogen entrainment, the preheating temperature being 250°C, and then passing the mixture into the fixed-bed reactor for reaction at 270°C and 0 MPa. The reaction product is condensed and collected, and quantitatively analyzed by gas chromatography; wherein the raw material mixture is a mixture of acetaldehyde and formaldehyde in a molar ratio of 1:3, and the liquid space velocity of the raw material mixture is 6.

[0074] Example 5

[0075] 1. A core-shell composite catalyst for an aldol condensation reaction, comprising a ZSM-35 molecular sieve modified with Silicalite-1 as a shell, a cesium-cerium composite metal oxide as a core, and a binder, silica sol. The catalyst comprises the following components in parts by weight, based on 100% of the total catalyst weight: 70% core, 20% shell, and 10% binder. The molar ratio of cesium to cerium in the cesium-cerium composite metal oxide is 3:1. The mass ratio of the ZSM-35 molecular sieve to the Silicalite-1 molecular sieve is 15:1.

[0076] 2. The method for preparing the core-shell composite catalyst for aldol condensation reaction comprises the following steps:

[0077] (1) Preparation of cesium-cerium composite metal oxide by co-precipitation:

[0078] Cesium nitrate and cerium nitrate are dissolved in water to prepare an active component solution with a total metal molar concentration of 0.3 mol / L, and a 30 wt% ammonia aqueous solution is used as a precipitant. The active component solution and the precipitant are respectively and simultaneously added dropwise to deionized water under stirring at 75° C., and the pH of the system is controlled to be 8.0-9.5 during the addition process. After the addition is completed, the temperature is maintained and the solution is further aged for 8 hours, centrifuged, and the solid obtained by centrifugation is washed until neutral, dried at 100° C. for 6 hours, calcined at 550° C. for 6 hours at a heating rate of 2° C. / min, and ground to obtain a cesium-cerium composite metal oxide;

[0079] (2) Preparation of ZSM-35 molecular sieve modified with Silicalite-1 all-silicon molecular sieve:

[0080] (21) The Silicalite-1 molecular sieve precursor was obtained by hydrothermal synthesis by mixing silicon source TEOS, organic template agent TPAOH, ethanol, and deionized water in a molar ratio of 7.0:0.08:42:360 and stirring at room temperature for 7 h.

[0081] (22) ZSM-35 molecular sieve and Silicalite-1 molecular sieve precursor were mixed in a mass ratio of 15:1 and transferred to a hydrothermal autoclave, sealed, and crystallized at 150 °C at a speed of 4 rpm for 48 h. The mixture was cooled to room temperature, washed with deionized water until the pH of the filtrate was 7, dried at room temperature overnight, and then placed in a muffle furnace and heated to 550 °C at a heating rate of 2 °C / min for 6 h to obtain ZSM-35 molecular sieve modified with Silicalite-1 all-silicon molecular sieve, which was recorded as ZSM-35@Silicalite-1.

[0082] (3) Preparation of catalyst:

[0083] The surface of the cesium-cerium composite metal oxide is impregnated with a binder to wet the surface, and the cesium-cerium composite metal oxide with the wetted surface is added to a container containing ZSM-35@Silicalite-1. The container is rotated at a constant speed to coat the surface of the cesium-cerium composite metal oxide with ZSM-35@Silicalite-1. The impregnation and coating process is repeated until the ZSM-35@Silicalite-1 is completely coated on the surface of the cesium-cerium composite metal oxide. The catalyst is then dried at room temperature overnight and calcined at 580°C in a muffle furnace at a heating rate of 2°C / min for 5 hours to obtain a core-shell composite catalyst having a ZSM-35 molecular sieve modified with Silicalite-1 all-silicon molecular sieve as a shell and a cesium-cerium composite metal oxide as a core.

[0084] 3. A method for preparing methyl methacrylate by aldol condensation reaction using the catalyst, comprising: loading the catalyst into a fixed-bed reactor, passing a raw material mixture through a horizontal flow pump at a flow rate of 0.6 mL / min into a preheating furnace under nitrogen entrainment, the preheating temperature being 280°C, and then passing the mixture into the fixed-bed reactor for reaction at 300°C and 0 MPa. The reaction product is condensed and collected, and quantitatively analyzed by gas chromatography; wherein the raw material mixture is a mixture of propionaldehyde and formaldehyde in a molar ratio of 1:3, and the liquid space velocity of the raw material mixture is 6.

[0085] Example 6

[0086] A method for preparing methyl methacrylate by aldol condensation reaction using the catalyst of Example 5 is as follows: the catalyst is loaded into a fixed-bed reactor, and the raw material mixture is passed through a horizontal flow pump at a flow rate of 0.6 mL / min into a preheating furnace under nitrogen entrainment for vaporization, the preheating temperature being 300° C. After vaporization, the mixture is passed into the fixed-bed reactor and reacted at 320° C. and 0 MPa. The reaction product is condensed and collected, and quantitatively analyzed by gas chromatography; wherein the raw material mixture is a mixture of acetic acid and formaldehyde in a molar ratio of 1:3, and the liquid space velocity of the raw material mixture is 6.

[0087] Example 7

[0088] A method for preparing methyl methacrylate by aldol condensation reaction using the catalyst of Example 5 is as follows: the catalyst is loaded into a fixed-bed reactor, and the raw material mixture is passed through a horizontal flow pump at a flow rate of 0.6 mL / min into a preheating furnace under nitrogen entrainment for vaporization, the preheating temperature being 300° C. After vaporization, the mixture is passed into the fixed-bed reactor and reacted at 320° C. and 0 MPa. The reaction product is condensed and collected, and quantitatively analyzed by gas chromatography; wherein the raw material mixture is a mixture of propionic acid and formaldehyde in a molar ratio of 1:3, and the liquid space velocity of the raw material mixture is 6.

[0089] Comparative Example 1

[0090] The supported catalyst includes a support and an active component supported on the support, wherein the support is a ZSM-35 molecular sieve and the active component is a cesium-cerium composite metal oxide. The active component accounts for 70% by weight of the catalyst. The specific preparation method is as follows:

[0091] (1) Carrier treatment: The ZSM-35 molecular sieve carrier was treated with alkali in a 75°C water bath for 4 h. The alkali solution was a 0.1% NaOH aqueous solution. The carrier was filtered and washed until neutral. The carrier was dried at 110°C for 8 h. Finally, the alkali-treated molecular sieve was subjected to ammonium exchange treatment in an 80°C water bath for 5 h. The ammonium source was a 1.0 mol / L ammonium nitrate solution. The carrier was filtered and washed until neutral. The carrier was dried at 105°C for 7 h. The carrier was heated to 600°C at a rate of 3°C / min and maintained for 8 h in a muffle furnace to obtain a catalyst carrier.

[0092] (2) Preparation of aqueous solution of active component and auxiliary agent: Weigh cesium nitrate and 9.78 cerium nitrate and add them into water to prepare active component solution with a total molar concentration of 0.3 mol / L and a molar ratio of Cs to Ce of 3;

[0093] (3) Loading active components: The carrier obtained in step (1) is added to the aqueous solution of the active components by ion exchange method, ion exchange is carried out in a 75°C water bath for 5 hours, and the mixture is dried in an oven at 105°C for 8 hours. The temperature is increased to 550°C at a rate of 2°C / min and maintained for 7 hours to obtain a catalyst with ZSM-35 molecular sieve as the carrier and cesium-cerium composite metal oxide as the active component loaded on the carrier.

[0094] Comparative Example 2

[0095] The core-shell composite catalyst uses ZSM-35 molecular sieve with a silicon-aluminum ratio of 28 as the shell, and the rest is the same as Example 5.

[0096] Comparative Example 3

[0097] A supported catalyst comprises a support and an active component supported on the support, wherein the support is a ZSM-35 molecular sieve modified with Silicalite-1 all-silicon molecular sieve, and the active component is a cesium-cerium composite metal oxide, and the active component accounts for 70% by weight of the catalyst. The specific preparation method is as follows:

[0098] (1) Preparation of ZSM-35 molecular sieve modified with Silicalite-1 all-silicon molecular sieve, as in Example 5;

[0099] (2) Preparation of catalyst: Weigh cesium nitrate and 9.78 cerium nitrate and dissolve them in water to prepare an active component solution with a total metal concentration of 0.3 mol / L, wherein the molar ratio of Cs to Ce is 3; use the ion exchange method to add the ZSM-35 molecular sieve modified with Silicalite-1 all-silicon molecular sieve to the active component solution, perform ion exchange in a 75°C water bath for 5 hours, dry in a 105°C oven for 8 hours, and heat to 550°C at a rate of 2°C / min and maintain for 7 hours to obtain a catalyst with the ZSM-35 molecular sieve modified with Silicalite-1 all-silicon molecular sieve as a carrier and the cesium-cerium composite metal oxide loaded on the carrier as the active component.

[0100] 1. Catalyst Evaluation

[0101] The reaction results of Examples 1-7 are shown in Table 1.

[0102] Table 1 Reaction results

[0103]

[0104] In order to further study the life of the catalyst, a method for preparing methyl methacrylate by aldol condensation reaction using the catalysts of Example 5 and Comparative Examples 1-3 was as follows: the catalyst was loaded into a fixed-bed reactor, and the raw material mixture was passed into a preheating furnace for vaporization at a flow rate of 0.1 mL / min through a horizontal flow pump under nitrogen entrainment. The preheating temperature was 240°C. After vaporization, the mixture was passed into the fixed-bed reactor and reacted at 260°C and 0 MPa. The reaction observation period was 2000 h. The reaction product was condensed and collected, and quantitatively analyzed by gas chromatography. The raw material mixture was a mixture of methyl acetate and formaldehyde in a molar ratio of 1:3, and the liquid space velocity of the reaction liquid was 1.2. The reaction results are shown in Table 2.

[0105] Table 2 Reaction results at different times

[0106] .

Claims

1. A core-shell composite catalyst for aldol condensation reaction, characterized in that: The catalyst uses a ZSM-35 molecular sieve modified with Silicalite-1 all-silicon molecular sieve as a shell, a cesium-cerium composite metal oxide as a core, and also includes a binder. Based on the total weight ratio of the catalyst as 100%, the catalyst is composed of the following components in parts by weight: 50-70% core, 20-35% shell, and 8-15% binder.

2. The core-shell composite catalyst for aldol condensation reaction according to claim 1, wherein: The molar ratio of cesium to cerium in the cesium-cerium composite metal oxide is (1-5):

1.

3. The core-shell composite catalyst for aldol condensation reaction according to claim 2, characterized in that: In the ZSM-35 molecular sieve modified with the Silicalite-1 all-silicon molecular sieve, the mass ratio of the ZSM-35 molecular sieve to the Silicalite-1 all-silicon molecular sieve is (3-20):

1.

4. The core-shell composite catalyst for aldol condensation reaction according to claim 3, characterized in that: The binder is silica sol, γ-aminopropoxytriethoxysilane, γ-aminopropoxytrimethoxysilane or glycidyloxypropyltrimethoxysilane.

5. The method for preparing the core-shell composite catalyst for aldol condensation reaction according to claim 3, characterized in that: The following steps are involved: (1) Preparation of cesium-cerium composite metal oxide by co-current coprecipitation; (2) Preparation of ZSM-35 molecular sieve modified with Silicalite-1 all-silicon molecular sieve: (21) The hydrothermal synthesis method was used to mix the silicon source, organic template, ethanol, and deionized water and stir at room temperature for 3-10 h to obtain the Silicalite-1 molecular sieve precursor; (22) The Silicalite-1 molecular sieve precursor and the ZSM-35 molecular sieve were transferred to a hydrothermal reactor, sealed, and crystallized at 100-200°C at a speed of 3-10 rpm for 18-56 hours. The mixture was cooled to room temperature, and the product was washed with deionized water until the pH of the filtrate was 7-8. The product was dried at room temperature overnight and then calcined in a muffle furnace to obtain a Silicalite-1 all-silicon molecular sieve modified ZSM-35 molecular sieve, which was recorded as ZSM-35@Silicalite-1. (3) Preparation of catalyst: The surface of the cesium-cerium composite metal oxide is impregnated with a binder to wet the surface, the cesium-cerium composite metal oxide with the wetted surface is added to a container containing ZSM-35@Silicalite-1, and the container is rotated at a constant speed to coat the surface of the cesium-cerium composite metal oxide with ZSM-35@Silicalite-1. The impregnation and coating process is repeated until the ZSM-35@Silicalite-1 is completely coated on the surface of the cesium-cerium composite metal oxide, and then the container is dried overnight at room temperature and calcined to obtain a core-shell composite catalyst having a ZSM-35 molecular sieve modified with Silicalite-1 all-silicon molecular sieve as a shell and a cesium-cerium composite metal oxide as a core.

6. The method for preparing a core-shell composite catalyst for aldol condensation reaction according to claim 5, wherein: The silicon source is TEOS, and the organic template is TPAOH; the molar ratio of the silicon source, the organic template, ethanol, and deionized water is (1.0-10): (0.01-0.1): (10-50): (200-400).

7. The method for preparing a core-shell composite catalyst for aldol condensation reaction according to claim 6, wherein: The method of preparing the cesium-cerium composite metal oxide by co-precipitation in step (1) is as follows: dissolving water-soluble metal salts of cesium and cerium in water to prepare an active component solution; adding the active component solution and the precipitant dropwise into deionized water at 60-90° C. while stirring; controlling the pH of the system to be 8.0-9.5 during the addition process; maintaining the temperature for 4-10 hours after the addition is completed; centrifuging; washing the solid obtained by centrifugation to neutrality; drying, roasting, and grinding to obtain the cesium-cerium composite metal oxide.

8. The method for preparing a core-shell composite catalyst for aldol condensation reaction according to claim 7, wherein: The precipitant is a 20-30 wt% ammonia solution, and the total molar concentration of cesium and cerium in the active component solution is 0.1-3.0 mol / L.

9. The method for preparing a core-shell composite catalyst for aldol condensation reaction according to claim 8, wherein: The calcination is carried out by heating the temperature to 450-750° C. at a heating rate of 1-5° C. / min and calcining for 3-10 hours.

10. A method for preparing methyl methacrylate by aldol condensation reaction, characterized in that: The catalyst is loaded into a fixed-bed reactor, and the raw material mixture is passed through a horizontal flow pump at a flow rate of 0.1-1.0 mL / min into a preheating furnace under nitrogen entrainment for vaporization. After vaporization, the mixture is passed into the fixed-bed reactor, and reacted at a reaction temperature of 220-350° C. and a reaction pressure of 0 MPa, and the reaction product is condensed and collected; The raw material mixture is a mixture of at least one of methyl acetate, methyl propionate, acetaldehyde, propionaldehyde, acetic acid, and propionic acid and formaldehyde in a molar ratio of 1:(1-5); the liquid space velocity of the raw material mixture is 6, and the temperature of the preheating furnace is 20-30°C lower than the reaction temperature; and the catalyst is the catalyst according to any one of claims 1 to 4.

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