Modified composite catalyst, preparation method thereof and application of modified composite catalyst in methyl methacrylate synthesis reaction

Abstract

The application relates to the fine chemical industry, and discloses a modified composite catalyst, a preparation method thereof and application of the modified composite catalyst in a methyl methacrylate synthesis reaction. The modified composite catalyst has a bimodal pore size distribution, a first pore size is 0.4-0.6 nm, and a second pore size is 9-15 nm; the modified composite catalyst is obtained by acidizing treatment of a micropore-mesopore composite material, the micropore-mesopore composite material comprises hydrogen type ZSM-35 molecular sieve and aluminum oxide, and the content of the hydrogen type ZSM-35 molecular sieve is 30-90% by weight and the content of the aluminum oxide is 10-70% by weight based on the total weight of the micropore-mesopore composite material. The modified composite catalyst is used in a methacrylate esterification reaction, and higher methacrylic acid conversion rate and methyl methacrylate selectivity can be obtained.

Description

Technical Field

[0001] This invention relates to the field of fine chemicals, specifically to a modified composite catalyst, its preparation method, and its application in the synthesis reaction of methyl methacrylate. Background Technology

[0002] As an important organic chemical product and raw material, the industrial production level and capacity of methyl methacrylate (MMA) have a significant impact on the development of my country's chemical industry. MMA is mainly used in industries such as PMMA (polymethyl methacrylate), coatings, textiles, adhesives, leather, papermaking, floor polishing, unsaturated resin modification, higher methacrylates, wood impregnating agents, printing and dyeing auxiliaries, and plasticizers. In recent years, the demand for MMA polymers, profiles, sheets, coatings, and emulsions has increased both domestically and internationally, and its application areas are constantly expanding, driving the rapid development of the MMA industry.

[0003] Esterification catalysts are a core technology in MMA production. For the esterification reaction of methacrylic acid and methanol, traditional production processes using inorganic acids such as sulfuric acid, phosphoric acid, and boric acid as catalysts are gradually being phased out. Using organic acids such as p-benzenesulfonic acid as catalysts also suffers from severe environmental pollution, low selectivity, and difficulty in product separation. In comparison, esterification catalysts for heterogeneous reactions are currently a more active research area. Recent reports indicate that researchers are continuously exploring the use of acidic resins, organotin compounds, rare-earth solid superacids, and Lewis acids as catalysts in the synthesis of carboxylic acid esters, achieving meaningful experimental results.

[0004] Currently, acidic cation exchange resins are widely used in the industrial production of methyl methacrylate (MMA). Cation exchange resins exhibit advantages such as good stability, high selectivity, low cost, and easy separation in esterification reactions. However, cation exchange resins themselves have poor heat resistance (generally decomposing at temperatures below 250℃), small specific surface area and pore volume, and are prone to swelling, resulting in poor reactivity and low ester yield as esterification catalysts. With the increasing demand for MMA, the synthesis of MMA using green and environmentally friendly processes holds great promise. Currently, supported esterification catalysts are receiving increasing attention in the synthesis of MMA. For researchers, developing high-performance esterification catalysts to improve reaction efficiency and suppress byproduct formation is an important future research direction. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems of low methacrylic acid conversion and low methacrylic acid yield in the current methacrylic acid production process, and to provide a modified composite catalyst, its preparation method, and its application in the synthesis reaction of methacrylic acid. This modified composite catalyst, when used in the methacrylic acid esterification reaction, can achieve higher methacrylic acid conversion and methacrylic acid selectivity.

[0006] To achieve the above objectives, the first aspect of the present invention provides a modified composite catalyst, wherein the pore size of the modified composite catalyst exhibits a bimodal distribution, with a first pore size of 0.4-0.6 nm and a second pore size of 9-15 nm; the modified composite catalyst is obtained by acidification treatment of a microporous-mesoporous composite material, wherein the microporous-mesoporous composite material comprises hydrogen-form ZSM-35 molecular sieve and alumina, and based on the total weight of the microporous-mesoporous composite material, the content of hydrogen-form ZSM-35 molecular sieve is 30-90% by weight, and the content of alumina is 10-70% by weight.

[0007] A second aspect of the present invention provides a method for preparing the aforementioned modified composite catalyst, wherein the preparation method includes:

[0008] (1) The microporous-mesoporous composite material was mixed with an aqueous solution of acid to carry out a contact reaction, and a mixture was obtained;

[0009] (2) The mixture is filtered to obtain a solid product, and the solid product is washed, dried and calcined to obtain a modified composite catalyst.

[0010] A third aspect of the present invention provides the application of the aforementioned modified composite catalyst in the synthesis reaction of methyl methacrylate.

[0011] Compared with the prior art, the technical solution of the present invention has the following advantages through the above technical solution:

[0012] (1) The modified composite catalyst provided by the present invention has a stable structure, does not deform or swell during the reaction, and has a high conversion rate of methacrylic acid and high selectivity of methacrylic acid when used to synthesize methyl methacrylate.

[0013] (2) The modified composite catalyst provided by the present invention has readily available raw materials, a simple preparation method, easy-to-control conditions, and good product repeatability.

[0014] (3) The modified composite catalyst provided by the present invention has mild process conditions and low requirements for reaction equipment when used to synthesize methyl methacrylate.

[0015] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0016] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the following detailed description to explain the invention, but do not constitute a limitation thereof. In the drawings:

[0017] Figure 1 This is the XRD pattern of the modified composite catalyst A prepared in Example 1 of this invention;

[0018] Figure 2 This is a pore size distribution diagram of the modified composite catalyst A prepared in Example 1 of this invention. Detailed Implementation

[0019] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0020] As previously stated, the first aspect of this invention provides a modified composite catalyst, characterized in that the pore size of the modified composite catalyst exhibits a bimodal distribution, with a first pore size of 0.4-0.6 nm and a second pore size of 9-15 nm; the modified composite catalyst is obtained by acidification treatment of a microporous-mesoporous composite material, wherein the microporous-mesoporous composite material comprises hydrogen-form ZSM-35 molecular sieve and alumina, and based on the total weight of the microporous-mesoporous composite material, the content of hydrogen-form ZSM-35 molecular sieve is 30-90% by weight, and the content of alumina is 10-70% by weight.

[0021] According to the present invention, in a preferred embodiment, the modified composite catalyst has a bimodal pore size distribution, with the first pore size being 0.5-0.6 nm and the second pore size being 9.8-14.8 nm.

[0022] The inventors of this invention have discovered that, in the prior art, esterification catalysts used to produce methyl methacrylate are divided into two categories: homogeneous and heterogeneous. Homogeneous catalysts mainly include inorganic acid solutions and organic acids, while heterogeneous catalysts mainly include solid acids and cation exchange resins. Homogeneous catalysts are advantageous due to their low cost and good catalytic activity; however, they are gradually being phased out due to drawbacks such as difficulty in separating the product from the catalyst, numerous side reactions, and easy corrosion of equipment. Solid esterification catalysts, while solving the problems of difficult product separation and severe equipment corrosion, are rarely used in industrial production due to their poor catalytic activity, high reaction temperature, and low product selectivity. Compared to the above catalysts, using acidic cation exchange resins as esterification catalysts to produce methyl methacrylate is currently the main process used in industry. Resin catalysts have advantages such as high selectivity, low cost, and easy separation; however, the yield of methyl methacrylate is relatively low during the esterification reaction of methyl methacrylate, and their high-temperature resistance is also poor. Resins are organic polymer materials that easily swell in organic solvents and are easily deformed or even decomposed in high-temperature environments, which is the main reason for the poor temperature resistance of resin catalysts. Developing novel solid catalyst systems to compensate for the performance defects of resin catalysts is a good approach to solving this problem. To address the structural defects of resin catalysts and improve the catalytic performance of esterification catalysts, the first step is to select novel materials with excellent structural characteristics. Compared to resin catalysts, hydrogen-form ZSM-35 molecular sieves possess a certain pore structure and surface acidity, making them suitable for catalyzing the esterification of small molecules. However, the pore size of ZSM-35 molecular sieves is relatively small (average pore size 0.4-0.6 nm), which may inhibit the diffusion of large molecular products during the reaction; moreover, the number of acidic sites on the surface of ZSM-35 molecular sieves is relatively small, resulting in lower efficiency in catalyzing esterification reactions. Therefore, ZSM-35 molecular sieve materials are not suitable for direct use as catalysts in the synthesis of methyl methacrylate. Combining ZSM-35 molecular sieves with materials possessing mesoporous structures can improve the pore distribution and facilitate the diffusion of large molecular reactants and products. Alumina materials themselves have mesoporous pores, and alumina precursors exhibit good adhesion. If alumina is used as a mesoporous material and combined with ZSM-35 molecular sieve, not only can the problem of pore distribution be solved, but also the problem of ZSM-35 molecular sieve forming can be solved at the same time.

[0023] The inventors of this invention also discovered that the surface acidity of the microporous-mesoporous composite material obtained by combining alumina with ZSM-35 molecular sieve is still relatively weak, resulting in poor efficiency in catalyzing esterification reactions. However, by appropriately modifying the surface of the microporous-mesoporous composite material with sulfuric acid to increase acid density and strength, an esterification catalyst with excellent catalytic performance can be obtained. This catalyst exhibits excellent catalytic activity and methyl methacrylate selectivity in the esterification reaction of methacrylic acid and methanol.

[0024] According to the present invention, the specific surface area of ​​the modified composite catalyst is 220-380 m². 2 / g, pore volume 0.2-0.8cm³ 3 / g; preferably, the specific surface area of ​​the modified composite catalyst is 250-350m². 2 / g, pore volume 0.3-0.7cm³ 3 / g; more preferably, the specific surface area of ​​the modified composite catalyst is 287-331m². 2 / g, pore volume 0.4-0.6cm³ 3 / g. In this invention, a modified composite catalyst with the aforementioned specific parameters is used, which enables the catalyst to exhibit better catalytic activity and ester selectivity when used in the methacrylic acid esterification reaction.

[0025] According to the present invention, the specific surface area of ​​the microporous-mesoporous composite material is 250-400 m². 2 / g, pore volume 0.3-0.9cm³ 3 / g; preferably, the specific surface area of ​​the microporous-mesoporous composite material is 280-370m². 2 / g, pore volume is 0.4-0.8cm³ 3 / g; more preferably, the specific surface area of ​​the microporous-mesoporous composite material is 304-344m². 2 / g, pore volume 0.5-0.7cm³ 3 / g. In this invention, the use of a microporous-mesoporous composite material with the aforementioned specific parameters enables the further prepared modified composite catalyst to exhibit better catalytic activity and ester selectivity when used in the methacrylic acid esterification reaction.

[0026] According to the present invention, based on the total weight of the microporous-mesoporous composite material, the content of the hydrogen-form ZSM-35 molecular sieve is 40-80% by weight, and the content of alumina is 20-60% by weight; more preferably, based on the total weight of the microporous-mesoporous composite material, the content of the hydrogen-form ZSM-35 molecular sieve is 50-70% by weight, and the content of alumina is 30-50% by weight. In the present invention, by using the aforementioned specific content of hydrogen-form ZSM-35 molecular sieve and alumina, the prepared microporous-mesoporous composite material can exhibit better catalytic activity and ester selectivity when used in the methacrylate esterification reaction.

[0027] According to the present invention, the preparation method of the microporous-mesoporous composite material includes: uniformly mixing hydrogen-form ZSM-35 molecular sieve, aluminum-containing precursor and extrusion aid, adding dilute nitric acid, stirring evenly and then extruding and molding, and obtaining microporous-mesoporous composite material after drying and calcination.

[0028] According to the present invention, the SiO2 / Al2O3 molar ratio of the hydrogen-form ZSM-35 molecular sieve is 10-200; preferably, the SiO2 / Al2O3 molar ratio of the ZSM-35 zeolite molecular sieve is 20-90. In this invention, the ZSM-35 molecular sieve can be obtained commercially. Specifically, the ZSM-35 molecular sieve is more preferably: a ZSM-35 molecular sieve with a SiO2 / Al2O3 molar ratio of 20 purchased from Nanjing Xianfeng Nanomaterials Technology Co., Ltd.; a ZSM-35 molecular sieve with a SiO2 / Al2O3 molar ratio of 30 purchased from Tianjin Nanhua Catalyst Co., Ltd.; and a ZSM-35 molecular sieve with a SiO2 / Al2O3 molar ratio of 90 purchased from Nanjing Jicang Nanotechnology Co., Ltd.

[0029] According to the present invention, the aluminum-containing precursor is selected from one or more of boehmite, aluminum sol, boehmite monohydrate, and aluminum hydroxide gel, preferably boehmite. The oxide remaining after calcination of the aluminum-containing precursor is aluminum oxide. In this invention, the boehmite can be obtained commercially or prepared. Specifically, the boehmite includes: SB type German-imported boehmite powder (purchased from Beijing Asia-Pacific Aohua Chemical Additives Co., Ltd., with a specific surface area of ​​241 m²). 2 / g, pore volume is 0.53cm³ 3 / g), pseudoboehmite powder of type P-DF-09-LSi (purchased from Shandong Aluminum Co., Ltd., with a specific surface area of ​​286m²). 2 / g, pore volume is 1.08cm³ 3 / g) and macroporous pseudoboehmite powder of model PB-0101 (purchased from Zibo Hengqi Powder New Material Co., Ltd., with a specific surface area of ​​327m²). 2 / g, pore volume is 1.02cm³ 3 One or more of the following: / g).

[0030] According to the present invention, the extrusion aid is one or more of guar gum powder, cellulose, polyethylene glycol, polyvinyl alcohol or starch, preferably guar gum powder and polyethylene glycol.

[0031] According to the present invention, the mass percentage concentration of the dilute nitric acid is 0.5-15%, preferably 1-10%.

[0032] According to the present invention, the weight ratio of the hydrogen-form ZSM-35 molecular sieve, the aluminum-containing precursor and the extrusion aid is 1:(0.1-3.5):(0.03-0.40), preferably 1:(0.3-2.5):(0.05-0.30).

[0033] According to the present invention, the preferred drying conditions are: drying temperature 70-160℃ and drying time 4-10 hours.

[0034] According to the present invention, the preferred calcination conditions are: calcination temperature of 450-650℃, preferably 500-600℃; and calcination time of 3-20 hours, preferably 5-16 hours.

[0035] According to the present invention, the microporous-mesoporous composite material can be spherical, granular, strip-shaped, cylindrical, toothed, or clover-shaped.

[0036] A second aspect of the present invention provides a method for preparing the aforementioned modified composite catalyst, wherein the preparation method includes:

[0037] (1) The microporous-mesoporous composite material was reacted with an aqueous solution of acid to obtain a mixture;

[0038] (2) The mixture is filtered, washed, dried and calcined to obtain a modified composite catalyst.

[0039] According to the present invention, the acid is sulfuric acid.

[0040] According to the present invention, the molar concentration of the aqueous solution of the acid is 0.05-0.3 mol / L, preferably 0.1-0.2 mol / L.

[0041] According to the present invention, the weight ratio of the microporous-mesoporous composite material to the aqueous solution of the acid is 1:(3-50), preferably 1:(5-30).

[0042] According to the present invention, the conditions for reacting the microporous-mesoporous composite material with an aqueous acid solution include: a temperature of 40-90°C, preferably 50-80°C; and a time of 0.2-8 h, preferably 0.5-5 h. Preferably, to achieve better mixing, rapid stirring or ultrasonic means can be used to improve reaction efficiency during the reaction of the microporous-mesoporous composite material with the aqueous acid solution.

[0043] According to the present invention, the mixture is filtered to obtain a solid product. The filtration process has no special requirements and can be any filtration method known in the art, including gravity filtration, pressure filtration, vacuum filtration, or centrifugal filtration. Preferably, the filtration process specifically includes: using a vacuum flask to create a vacuum at the bottom of a funnel or using a centrifugal filter.

[0044] According to the present invention, the solid product is subjected to washing, drying and calcination treatment. The method of washing the solid product is not particularly required. For example, deionized water can be used to wash the solid product, the volume ratio of deionized water to solid product can be 5-20, and the number of washing times can be 2-8.

[0045] According to the present invention, the drying conditions include: a temperature of 70-130°C, preferably 90-120°C; and a time of 1-30 hours, preferably 3-20 hours.

[0046] According to the present invention, the calcination conditions include: a temperature of 300-500℃, preferably 350-450℃; and a time of 3-15h, preferably 5-10h.

[0047] A third aspect of the present invention provides the application of the aforementioned modified composite catalyst in the synthesis reaction of methyl methacrylate.

[0048] According to the present invention, the application includes simultaneously contacting methacrylic acid and methanol with a modified composite catalyst.

[0049] According to the present invention, the contact conditions between the methacrylic acid and methanol and the catalyst include: a contact temperature of 40-150°C, preferably 60-120°C; a contact pressure of 0.01-5.0 MPa, preferably 0.1-3.0 MPa; and a mass hourly space velocity (HHSV) of methacrylic acid of 0.01-30 h⁻¹. -1 Preferably 0.1-10h -1 The mass hourly space velocity (MSV) of methanol can range from 0.01 to 50 h⁻¹. -1 Preferably 0.1-30h -1 .

[0050] The present invention will be described in detail below through embodiments.

[0051] In the following examples and comparative examples:

[0052] XRD tests on the samples were performed on a Philips X'Pert MPD X-ray powder diffractometer with a Cu Kα target and a scanning range of 2θ = 5-90°.

[0053] The pore structure parameters of the samples were analyzed using an ASAP2020-M+C adsorption analyzer manufactured by Micromeritics, USA. Before measurement, the samples were degassed under vacuum at 40°C for 4 hours. The specific surface area of ​​the samples was calculated using the BET method, and the pore volume was calculated using the BJH model.

[0054] Elemental analysis of the samples was performed on an Eagle III energy-dispersive X-ray fluorescence spectrometer manufactured by EDAX Corporation in the United States.

[0055] The drying oven was manufactured by Shanghai Yiheng Scientific Instruments Co., Ltd., model DHG-9030A.

[0056] The muffle furnace is manufactured by CARBOLITE, model CWF1100.

[0057] All other reagents used in the examples and comparative examples were purchased from Sinopharm Chemical Reagent Co., Ltd., and the reagent purity was analytical grade.

[0058] Example 1

[0059] This embodiment is intended to illustrate the modified composite catalyst prepared according to the present invention.

[0060] (1) Preparation of microporous-mesoporous composite materials

[0061] 60g of ZSM-35 molecular sieve (SiO2 / Al2O3=30) was mixed evenly with 57g of pseudoboehmite powder of type P-DF-09-LSi and 6g of guar gum powder. Then, 90g of 3% nitric acid was added, and the mixture was stirred evenly. The mixture was then extruded and cut into cylindrical shapes with a diameter of 2mm and a length of 2mm. The mixture was dried at 110℃ for 6 hours and finally calcined at 580℃ for 8 hours to obtain microporous-mesoporous composite material A.

[0062] Based on the total weight of the microporous-mesoporous composite material A, the content of ZSM-35 molecular sieve is 60% by weight, and the content of alumina is 40% by weight. The specific surface area of ​​the microporous-mesoporous composite material A is 344 m². 2 / g, pore volume is 0.7ml / g.

[0063] (2) Preparation of modified composite catalysts

[0064] In a round-bottom flask, 10 g of microporous-mesoporous composite material A was mixed with 100 g of 0.15 mol / L sulfuric acid solution, heated to 70 °C, and stirred under reflux for 2 hours. The reaction system was cooled to room temperature and filtered to obtain a solid product. The solid product was washed 6 times with 100 ml of deionized water, dried in air at 110 °C for 8 hours, and then calcined at 400 °C for 7 hours to obtain modified composite catalyst A.

[0065] Figure 1This is the XRD pattern of modified composite catalyst A. It can be seen that the wide-angle X-ray diffraction angles of this sample are mainly: 2θ = 9.4°, 22.4°, 22.7°, 23.3°, 23.7°, 24.5°, 25.3°, 36.8°, 42.8°, and 66.9°. Among these, the diffraction signals at 2θ = 9.4°, 22.4°, 22.7°, 23.3°, 23.7°, 24.5°, and 25.3° are consistent with the diffraction pattern of ZSM-35 molecular sieve, indicating that the crystal phase of ZSM-35 molecular sieve did not undergo significant changes during catalyst preparation and still maintains a good FER-type topological framework structure. The diffraction signals at 2θ = 36.8°, 42.8° and 66.9° are consistent with the diffraction pattern of γ-Al2O3, indicating that after calcination at 580℃, the modified composite catalyst A mainly exists in the γ-Al2O3 crystalline phase after dehydration of boehmite.

[0066] Figure 2 This is the pore size distribution diagram of modified composite catalyst A. As can be seen from the diagram, the sample exhibits a distinct dual-channel structure with pore sizes of 0.5 nm and 12.3 nm, respectively. The 0.5 nm channel is provided by hydrogen-form ZSM-35 molecular sieve, while the most probable mesoporous channel with a 12.3 nm diameter is provided by alumina.

[0067] The specific surface area of ​​the modified composite catalyst A is 331 m². 2 / g, pore volume is 0.6ml / g.

[0068] (3) Evaluation of catalyst reaction performance

[0069] The esterification performance of the catalyst was evaluated in a fixed-bed reactor. 5.0 g of modified composite catalyst A was loaded into a stainless steel fixed-bed reactor with an inner diameter of 8 mm. The reaction temperature was 95 °C, the reaction pressure was 0.5 MPa, and the weight hourly space velocity (WHSV) of methacrylic acid was 1.0 h⁻¹. -1 The weight hourly space velocity (WHSV) of methanol is 2.7 h⁻¹. -1 The reaction time was 20 hours. After cooling, the product was analyzed using an Agilent 7890A gas chromatograph equipped with an FFAP capillary column and a flame ionization detector (FID). Quantitative analysis was performed using a programmed temperature rise and correction factors. The conversion rate of methacrylic acid was 97.0%, and the selectivity for methyl methacrylate was 99.7%.

[0070] Example 2

[0071] This embodiment is intended to illustrate the modified composite catalyst prepared according to the present invention.

[0072] (1) Preparation of microporous-mesoporous composite materials

[0073] 70g of ZSM-35 molecular sieve (SiO2 / Al2O3=90) was mixed with 41g of pseudoboehmite powder of type SB and 4g of polyethylene glycol. Then, 75g of 5% nitric acid was added, stirred evenly, extruded and cut into toothed spheres with a diameter of 3mm. The mixture was dried at 130℃ for 4 hours and finally calcined at 550℃ for 12 hours to obtain microporous-mesoporous composite material B.

[0074] Based on the total weight of the microporous-mesoporous composite material B, the content of ZSM-35 molecular sieve is 70% by weight, and the content of alumina is 30% by weight. The specific surface area of ​​the microporous-mesoporous composite material B is 335 m². 2 / g, pore volume is 0.5ml / g.

[0075] (2) Preparation of modified composite catalysts

[0076] In a round-bottom flask, 10 g of the microporous-mesoporous composite material B was mixed with 300 g of a 0.1 mol / L sulfuric acid solution, heated to 80 °C, and stirred under reflux for 0.5 hours. The reaction system was cooled to room temperature and filtered to obtain a solid product. The solid product was washed four times with 200 ml of deionized water, dried in air at 120 °C for 3 hours, and then calcined at 350 °C for 10 hours to obtain the modified composite catalyst B.

[0077] The modified composite catalyst B has a distinct dual-channel structure with pore sizes of 0.6 nm and 11.7 nm, respectively.

[0078] The specific surface area of ​​the modified composite catalyst B is 302 m². 2 / g, pore volume is 0.4ml / g.

[0079] (3) Evaluation of catalyst reaction performance

[0080] The esterification performance of catalyst B was tested according to step (3) in Example 1. The conversion rate of methacrylic acid was 96.8%, and the selectivity of methyl methacrylate was 99.5%.

[0081] Example 3

[0082] This embodiment is intended to illustrate the modified composite catalyst prepared according to the present invention.

[0083] (1) Preparation of microporous-mesoporous composite materials

[0084] 50g of ZSM-35 molecular sieve (SiO2 / Al2O3=20) was mixed evenly with 71g of pseudoboehmite powder (model PB-0101) and 12g of guar gum powder. Then, 85g of 8% nitric acid was added, and the mixture was stirred evenly. The mixture was then extruded and cut into spheres with a diameter of 2mm. The spheres were dried at 90℃ for 10 hours and then calcined at 600℃ for 5 hours to obtain microporous-mesoporous composite material C.

[0085] Based on the total weight of the microporous-mesoporous composite material C, the content of ZSM-35 molecular sieve is 50% by weight, and the content of alumina is 50% by weight. The specific surface area of ​​the microporous-mesoporous composite material C is 304 m² / g, and the pore volume is 0.6 ml / g.

[0086] (2) Preparation of modified composite catalysts

[0087] In a round-bottom flask, 10 g of the microporous-mesoporous composite material C was mixed with 50 g of a 0.2 mol / L sulfuric acid solution, heated to 50 °C, and stirred under reflux for 5 hours. The reaction system was cooled to room temperature and filtered to obtain a solid product. The solid product was washed 8 times with 100 ml of deionized water, dried in air at 90 °C for 20 hours, and then calcined at 450 °C for 5 hours to obtain the modified composite catalyst C.

[0088] The modified composite catalyst C has a distinct dual-channel structure with pore sizes of 0.5 nm and 13.9 nm, respectively.

[0089] The specific surface area of ​​the modified composite catalyst C is 287 m². 2 / g, pore volume is 0.5ml / g.

[0090] (3) Evaluation of catalyst reaction performance

[0091] The esterification performance of catalyst C was tested according to step (3) in Example 1. The conversion rate of methacrylic acid was 96.5%, and the selectivity of methyl methacrylate was 99.4%.

[0092] Example 4

[0093] This embodiment is intended to illustrate the modified composite catalyst prepared according to the present invention.

[0094] (1) Preparation of microporous-mesoporous composite materials

[0095] 80g of ZSM-35 molecular sieve (SiO2 / Al2O3=90) was mixed evenly with 27g of pseudoboehmite powder of type SB and 8g of guar gum powder. Then, 80g of 2% nitric acid was added, stirred evenly, extruded and cut into toothed spheres with a diameter of 3mm. The mixture was dried at 130℃ for 4 hours and finally calcined at 550℃ for 12 hours to obtain microporous-mesoporous composite material D.

[0096] Based on the total weight of the microporous-mesoporous composite material D, the content of ZSM-35 molecular sieve is 80% by weight, and the content of alumina is 20% by weight. The specific surface area of ​​the microporous-mesoporous composite material D is 370 m². 2 / g, pore volume is 0.4ml / g.

[0097] (2) Preparation of modified composite catalysts

[0098] In a round-bottom flask, 10 g of the microporous-mesoporous composite material D was mixed with 300 g of a 0.08 mol / L sulfuric acid solution, heated to 80 °C, and stirred under reflux for 0.5 hours. The reaction system was cooled to room temperature and filtered to obtain a solid product. The solid product was washed four times with 200 mL of deionized water, dried in air at 120 °C for 3 hours, and then calcined at 350 °C for 10 hours to obtain the modified composite catalyst D.

[0099] The modified composite catalyst D has a distinct dual-channel structure with pore sizes of 0.6 nm and 10.9 nm, respectively.

[0100] The specific surface area of ​​the modified composite catalyst D is 350 m². 2 / g, pore volume is 0.3ml / g.

[0101] (3) Evaluation of catalyst reaction performance

[0102] The esterification performance of catalyst D was tested according to step (3) in Example 1. The conversion rate of methacrylic acid was 95.8%, and the selectivity of methyl methacrylate was 99.0%.

[0103] Example 5

[0104] This embodiment is intended to illustrate the modified composite catalyst prepared according to the present invention.

[0105] (1) Preparation of microporous-mesoporous composite materials

[0106] 40g of ZSM-35 molecular sieve (SiO2 / Al2O3=20) was mixed evenly with 86g of pseudoboehmite powder of type P-DF-09-LSi and 10g of guar gum powder. Then, 95g of 10% nitric acid was added, stirred evenly, and extruded and cut into spheres with a diameter of 2mm. The mixture was dried at 90℃ for 10 hours and finally calcined at 600℃ for 5 hours to obtain microporous-mesoporous composite material E.

[0107] Based on the total weight of the microporous-mesoporous composite material E, the content of ZSM-35 molecular sieve is 40% by weight, and the content of alumina is 60% by weight. The specific surface area of ​​the microporous-mesoporous composite material E is 280 m². 2 / g, pore volume is 0.8ml / g.

[0108] (2) Preparation of modified composite catalysts

[0109] In a round-bottom flask, 10 g of the microporous-mesoporous composite material E was mixed with 50 g of a 0.25 mol / L sulfuric acid solution, heated to 50 °C, and stirred under reflux for 5 hours. The reaction system was cooled to room temperature and filtered to obtain a solid product. The solid product was washed eight times with 100 mL of deionized water, dried in air at 90 °C for 20 hours, and then calcined at 450 °C for 5 hours to obtain the modified composite catalyst E.

[0110] The modified composite catalyst E has a distinct dual-channel structure with pore sizes of 0.5 nm and 14.2 nm, respectively.

[0111] The specific surface area of ​​the modified composite catalyst E is 250 m². 2 / g, pore volume is 0.7ml / g.

[0112] (3) Evaluation of catalyst reaction performance

[0113] The esterification performance of catalyst E was tested according to step (3) in Example 1. The conversion rate of methacrylic acid was 95.5%, and the selectivity of methyl methacrylate was 98.7%.

[0114] Example 6

[0115] This embodiment is intended to illustrate the modified composite catalyst prepared according to the present invention.

[0116] (1) Preparation of microporous-mesoporous composite materials

[0117] 90g of ZSM-35 molecular sieve (SiO2 / Al2O3=90) was mixed evenly with 14g of pseudoboehmite powder of type SB and 8g of guar gum powder. Then, 70g of 15% nitric acid was added, stirred evenly, extruded and cut into toothed spheres with a diameter of 3mm. The mixture was dried at 160℃ for 4 hours and finally calcined at 480℃ for 20 hours to obtain microporous-mesoporous composite material F.

[0118] Based on the total weight of the microporous-mesoporous composite material F, the content of ZSM-35 molecular sieve is 90% by weight, and the content of alumina is 10% by weight. The specific surface area of ​​the microporous-mesoporous composite material F is 400 m². 2 / g, pore volume is 0.3ml / g.

[0119] (2) Preparation of modified composite catalysts

[0120] In a round-bottom flask, 10 g of the microporous-mesoporous composite material F was mixed with 300 g of a 0.05 mol / L sulfuric acid solution, heated to 90 °C, and stirred under reflux for 0.2 h. The reaction system was cooled to room temperature and filtered to obtain a solid product. The solid product was washed twice with 150 ml of deionized water, dried in air at 130 °C for 1 h, and then calcined at 300 °C for 15 h to obtain the modified composite catalyst F.

[0121] The modified composite catalyst F has a distinct dual-channel structure with pore sizes of 0.6 nm and 9.8 nm, respectively.

[0122] The specific surface area of ​​the modified composite catalyst F is 380 m². 2 / g, pore volume is 0.2ml / g.

[0123] (3) Evaluation of catalyst reaction performance

[0124] The esterification performance of catalyst F was tested according to step (3) in Example 1. The conversion rate of methacrylic acid was 95.0%, and the selectivity of methyl methacrylate was 98.3%.

[0125] Example 7

[0126] This embodiment is intended to illustrate the modified composite catalyst prepared according to the present invention.

[0127] (1) Preparation of microporous-mesoporous composite materials

[0128] 30g of ZSM-35 molecular sieve (SiO2 / Al2O3=20) was mixed evenly with 100g of pseudoboehmite powder of type P-DF-09-LSi and 12g of guar gum powder. Then, 105g of 0.5% nitric acid was added, and the mixture was stirred evenly. The mixture was then extruded and cut into spheres with a diameter of 2mm. The spheres were dried at 70℃ for 10 hours and then calcined at 650℃ for 3 hours to obtain microporous-mesoporous composite material G.

[0129] Based on the total weight of the microporous-mesoporous composite material G, the content of ZSM-35 molecular sieve is 30% by weight, and the content of alumina is 70% by weight. The specific surface area of ​​the microporous-mesoporous composite material G is 250 m². 2 / g, pore volume is 0.9ml / g.

[0130] (2) Preparation of modified composite catalysts

[0131] In a round-bottom flask, 10 g of the microporous-mesoporous composite material G was mixed with 50 g of a 0.3 mol / L sulfuric acid solution, heated to 40 °C, and stirred under reflux for 8 hours. The reaction system was cooled to room temperature and filtered to obtain a solid product. The solid product was washed six times with 100 mL of deionized water, dried in air at 70 °C for 30 hours, and then calcined at 500 °C for 3 hours to obtain the modified composite catalyst G.

[0132] The modified composite catalyst G has a distinct dual-channel structure with pore sizes of 0.5 nm and 14.8 nm, respectively.

[0133] The specific surface area of ​​the modified composite catalyst G is 220 m². 2 / g, pore volume is 0.8ml / g.

[0134] (3) Evaluation of catalyst reaction performance

[0135] The esterification performance of catalyst G was tested according to step (3) in Example 1. The conversion rate of methacrylic acid was 94.7%, and the selectivity of methyl methacrylate was 98.0%.

[0136] Comparative Example 1

[0137] (1) Preparation of microporous-mesoporous composite materials

[0138] 95g of ZSM-35 molecular sieve (SiO2 / Al2O3=90) was mixed evenly with 7g of pseudoboehmite powder of type SB and 3g of guar gum powder. Then, 55g of 20% nitric acid was added, and the mixture was stirred evenly. The mixture was then extruded and cut into cylindrical particles with a diameter of 2mm and a height of 2mm. The particles were dried at 160℃ for 4 hours and then calcined at 430℃ for 20 hours to obtain microporous-mesoporous composite material D1.

[0139] Based on the total weight of the microporous-mesoporous composite material D1, the content of ZSM-35 molecular sieve is 95% by weight, and the content of alumina is 5% by weight. The specific surface area of ​​the microporous-mesoporous composite material D1 is 427 m². 2 / g, pore volume is 0.26ml / g.

[0140] (2) Preparation of modified composite catalysts

[0141] In a round-bottom flask, 10 g of the microporous-mesoporous composite material D1 was mixed with 200 g of a 0.02 mol / L sulfuric acid solution, heated to 90 °C, and stirred under reflux for 0.2 h. The reaction system was cooled to room temperature and filtered to obtain a solid product. The solid product was washed twice with 150 ml of deionized water, dried in air at 130 °C for 1 h, and then calcined at 280 °C for 15 h to obtain the modified composite catalyst D1.

[0142] The specific surface area of ​​the modified composite catalyst D1 is 394 m². 2 / g, pore volume is 0.18ml / g, and the pore diameters of the two pores are 0.6nm and 12.1nm, respectively.

[0143] (3) Evaluation of catalyst reaction performance

[0144] The esterification performance of catalyst D1 was tested according to step (3) in Example 1. The conversion rate of methacrylic acid was 85.5%, and the selectivity of methyl methacrylate was 95.2%.

[0145] Comparative Example 2

[0146] (1) Preparation of microporous-mesoporous composite materials

[0147] 12g of ZSM-35 molecular sieve (SiO2 / Al2O3=20) was mixed with 125g of pseudoboehmite powder (model P-DF-09-LSi) and 15g of polyethylene glycol. Then, 110g of 2% nitric acid was added, and the mixture was stirred evenly. The mixture was then extruded and cut into spheres with a diameter of 2mm. The spheres were dried at 70℃ for 10 hours and then calcined at 700℃ for 3 hours to obtain the microporous-mesoporous composite material D2.

[0148] Based on the total weight of the microporous-mesoporous composite material D2, the content of ZSM-35 molecular sieve is 12% by weight, and the content of alumina is 88% by weight. The specific surface area of ​​the microporous-mesoporous composite material D2 is 234 m². 2 / g, pore volume is 0.94ml / g.

[0149] (2) Preparation of modified composite catalysts

[0150] In a round-bottom flask, 10 g of the microporous-mesoporous composite material D2 was mixed with 40 g of a 0.5 mol / L sulfuric acid solution, heated to 30 °C, and stirred under reflux for 4 hours. The reaction system was cooled to room temperature and filtered to obtain a solid product. The solid product was washed six times with 100 mL of deionized water, dried in air at 70 °C for 30 hours, and then calcined at 550 °C for 6 hours to obtain the modified composite catalyst D2.

[0151] The specific surface area of ​​the modified composite catalyst D2 is 203 m². 2 / g, pore volume is 0.85ml / g, and the pore diameters of the two pores are 0.5nm and 13.5nm, respectively.

[0152] (3) Evaluation of catalyst reaction performance

[0153] The esterification performance of catalyst D2 was tested according to step (3) in Example 1. The conversion rate of methacrylic acid was 83.4%, and the selectivity of methyl methacrylate was 94.8%.

[0154] Comparative Example 3

[0155] (1) Preparation of shaped zeolite molecular sieve materials

[0156] 100g of ZSM-35 molecular sieve (SiO2 / Al2O3=30) and 6g of guar gum powder were mixed evenly, and then 85g of 3% nitric acid was added. After stirring evenly, the mixture was extruded and cut into cylindrical shapes with a diameter of 2mm and a length of 2mm. The mixture was dried at 110℃ for 6 hours and then calcined at 580℃ for 8 hours to obtain the shaped zeolite molecular sieve material.

[0157] (2) Preparation of modified catalysts

[0158] In a round-bottom flask, 10 g of shaped zeolite molecular sieve material was mixed with 100 g of 0.15 mol / L sulfuric acid solution, heated to 70 °C, and stirred under reflux for 2 hours. The reaction system was cooled to room temperature and filtered to obtain a solid product. The solid product was washed 6 times with 100 mL of deionized water, dried in air at 110 °C for 8 hours, and then calcined at 400 °C for 7 hours to obtain modified catalyst D3.

[0159] The specific surface area of ​​the modified catalyst D3 is 418 m². 2 / g, pore volume is 0.15ml / g.

[0160] (3) Evaluation of catalyst reaction performance

[0161] The esterification performance of catalyst D3 was tested according to step (3) in Example 1. The conversion rate of methacrylic acid was 81.4%, and the selectivity of methyl methacrylate was 94.1%.

[0162] Comparative Example 4

[0163] (1) Preparation of shaped alumina

[0164] 143g of pseudoboehmite powder (model P-DF-09-LSi) and 8g of guar gum powder were mixed evenly, and then 100g of 3% dilute nitric acid was added. After stirring evenly, the mixture was extruded and cut into cylindrical shapes with a diameter of 2mm and a length of 2mm. The mixture was dried at 110℃ for 6 hours and then calcined at 580℃ for 8 hours to obtain shaped alumina.

[0165] The specific surface area of ​​the shaped alumina is 201 m². 2 / g, pore volume is 0.98ml / g.

[0166] (2) Preparation of modified catalysts

[0167] In a round-bottom flask, 10 g of shaped alumina was mixed with 100 g of a 0.15 mol / L sulfuric acid solution, heated to 70 °C, and stirred under reflux for 2 hours. The reaction system was cooled to room temperature and filtered to obtain a solid product. The solid product was washed six times with 100 mL of deionized water, dried in air at 110 °C for 8 hours, and then calcined at 400 °C for 7 hours to obtain modified catalyst D4.

[0168] The specific surface area of ​​the modified catalyst D4 is 182 m². 2 / g, pore volume is 0.89ml / g.

[0169] (3) Evaluation of catalyst reaction performance

[0170] The esterification performance of catalyst D4 was tested according to step (3) in Example 1. The conversion rate of methacrylic acid was 82.9%, and the selectivity of methyl methacrylate was 94.3%.

[0171] Comparative Example 5

[0172] The composite catalyst was prepared using the same method as in Example 1, except that:

[0173] Cancel step (1) in Example 1;

[0174] Replace “microporous-mesoporous composite material A” in step (2) of Example 1 with “commercially available silica (purchased from Qingdao Hailang Silica Gel Desiccant Factory, specific surface area 329 m²)”. 2 / g, pore volume 0.6cm³ 3 / g)”.

[0175] Catalyst D5 was obtained, with a specific surface area of ​​382 m². 2 / g, pore volume is 0.4ml / g.

[0176] The catalytic performance of catalyst D5 was tested using the same esterification reaction performance evaluation method as in step (3) of Example 1; the results showed that the conversion rate of methacrylic acid was 79.8% and the selectivity of methyl methacrylate was 93.7%.

[0177] Comparative Example 6

[0178] Microporous-mesoporous composite material A was prepared using the same method as step (1) of Example 1.

[0179] Cancel step (2).

[0180] Using microporous-mesoporous composite material A as catalyst D6, the catalytic performance of catalyst D6 was tested according to the same esterification reaction performance evaluation method as in step (3) of Example 1. The results showed that the conversion rate of methacrylic acid was 32.7%, and the selectivity for methyl methacrylate was 90.8%.

[0181] The results above show that the modified composite catalyst provided by the present invention can directly convert methacrylic acid and methanol into methyl methacrylate, resulting in a high conversion rate of methacrylic acid and a high selectivity for methyl methacrylate.

[0182] In Comparative Example 1, the ZSM-35 molecular sieve content in the microporous-mesoporous composite material was too high, while the alumina content was too low. Because the distribution of micropores and mesopores in the microporous-mesoporous composite material is not within the range defined in this invention, it affects molecular diffusion during the reaction. Furthermore, the conditions and parameters in the preparation process of the modified composite catalyst are not within the range defined in this invention, resulting in poor modification effects. These two reasons ultimately lead to a low conversion rate of methacrylic acid and a low selectivity for methyl methacrylate.

[0183] In Comparative Example 2, the microporous-mesoporous composite material had a low content of ZSM-35 molecular sieve and a high content of alumina. The low content of ZSM-35 molecular sieve, which has a certain degree of acidity, resulted in insufficient active sites in the reaction. Furthermore, the conditions and parameters used in the preparation of the modified composite catalyst were not within the limits specified in this invention, leading to poor modification effects. These two reasons ultimately resulted in a low conversion rate of methacrylic acid and low selectivity for methyl methacrylate.

[0184] In Comparative Example 3, the molded zeolite molecular sieve material contained only ZSM-35 molecular sieve and no alumina. Because the material only contains microporous channels and no mesoporous channels, molecular diffusion is affected during the reaction. This results in low conversion of methacrylic acid and low selectivity for methyl methacrylate.

[0185] In Comparative Example 4, the molded alumina material contained only alumina and no ZSM-35 molecular sieve with certain acidity, resulting in insufficient active sites in the reaction, leading to low conversion rate of methacrylic acid and low selectivity of methyl methacrylate.

[0186] In Comparative Example 5, the modified composite catalyst did not contain microporous-mesoporous composite material and used silica gel instead. Since silica gel does not have the pore characteristics of microporous-mesoporous composite material, the conversion rate of methacrylic acid was low and the selectivity of methyl methacrylate was low.

[0187] In Comparative Example 6, since the alumina was not acidified with sulfuric acid and was simply combined with ZSM-35 molecular sieve, the surface acidity of the resulting microporous-mesoporous composite material was still relatively weak, resulting in low conversion rate of methacrylic acid and low selectivity of methyl methacrylate.

[0188] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. Use of a modified composite catalyst in a methyl methacrylate synthesis reaction, said use comprising: Methacrylic acid and methanol are simultaneously contacted with a modified composite catalyst, characterized in that the modified composite catalyst has a bimodal pore size distribution, a first pore size of 0.4-0.6 nm, and a second pore size of 9-15 nm; the modified composite catalyst is obtained by acid treatment of a microporous-mesoporous composite material, wherein the microporous-mesoporous composite material comprises hydrogen type ZSM-35 molecular sieve and alumina, and the content of the hydrogen type ZSM-35 molecular sieve is 30-90 wt% and the content of the alumina is 10-70 wt% based on the total weight of the microporous-mesoporous composite material; The preparation method of the modified composite catalyst comprises: (1) contacting the microporous-mesoporous composite material with an aqueous acid solution to react, wherein the acid is sulfuric acid; to obtain a mixture; (2) filtering, washing, drying and calcining the mixture to obtain the modified composite catalyst.

2. The use according to claim 1, wherein, The modified composite catalyst has a bimodal pore size distribution, a first pore size of 0.5-0.6 nm, and a second pore size of 9.8-14.8 nm.

3. The use according to claim 2, wherein, The specific surface area of the modified composite catalyst is 220-380 m 2 / g, and the pore volume is 0.2-0.8 cm 3 / g.

4. Use according to claim 3, wherein, The specific surface area of the modified composite catalyst is 250-350 m 2 The pore volume is 0.3-0.7 cm 3 / g.

5. Use according to claim 4, wherein, The specific surface area of the modified composite catalyst is 287-331 m 2 / g, and the pore volume is 0.4-0.6 cm 3 / g.

6. The use according to any one of claims 1 to 5, wherein The content of the hydrogen type ZSM-35 molecular sieve is 40-80 wt% and the content of the alumina is 20-60 wt% based on the total weight of the microporous-mesoporous composite material.

7. Use according to claim 6, wherein, The content of the hydrogen type ZSM-35 molecular sieve is 50-70 wt% and the content of the alumina is 30-50 wt% based on the total weight of the microporous-mesoporous composite material.

8. The use according to any one of claims 1 to 5, wherein The specific surface area of the micro-mesoporous composite is 250-400 m 2 / g, and the pore volume is 0.3-0.9 cm 3 / g.

9. Use according to claim 8, wherein, The specific surface area of the micro-mesoporous composite is 280-370 m 2 / g, and the pore volume is 0.4-0.8 cm 3 / g.

10. Use according to claim 9, wherein, The specific surface area of the micro-mesoporous composite is 304-344 m 2 / g, and the pore volume is 0.5-0.7 cm 3 / g.

11. The use according to any one of claims 1 to 5, wherein, The preparation method of the microporous-mesoporous composite material comprises: The hydrogen type ZSM-35 molecular sieve, the aluminum-containing precursor and the extrusion aid are mixed and then contacted with dilute nitric acid, and then subjected to stirring, extrusion molding, drying and calcination to obtain the microporous-mesoporous composite material.

12. Use according to claim 11, wherein, The aluminum-containing precursor is selected from one or more of pseudoboehmite, aluminum sol, monohydrate gibbsite and aluminum hydroxide gel.

13. Use according to claim 12, wherein, The aluminum-containing precursor is pseudoboehmite.

14. The use according to claim 11, wherein, The concentration of the dilute nitric acid is 0.5-15%; And / or, the weight ratio of the use amount of the hydrogen type ZSM-35 molecular sieve, the aluminum-containing precursor and the extrusion aid is 1:(0.1-3.5):(0.03-0.40); And / or, the calcination conditions include a temperature of 450-650°C and a time of 3-20 hours.

15. Use according to claim 14, wherein, The concentration of the dilute nitric acid is 1-10%; And / or, the weight ratio of the use amount of the hydrogen type ZSM-35 molecular sieve, the aluminum-containing precursor and the extrusion aid is 1:(0.3-2.5):(0.05-0.30).

16. The use according to claim 1, wherein, The molar concentration of the aqueous acid solution is 0.05-0.3 mol / L; And / or, the weight ratio of the use amount of the microporous-mesoporous composite material and the aqueous acid solution is 1:(3-50); And / or, the calcination conditions include a temperature of 300-500°C and a time of 3-15h.

17. Use according to claim 16, wherein, The acid is sulfuric acid; And / or, the molar concentration of the aqueous acid solution is 0.1-0.2 mol / L; And / or, the weight ratio of the use amount of the microporous-mesoporous composite material and the aqueous acid solution is 1:(5-30).

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