Mesoporous solid acid composite catalyst as well as preparation method and application thereof

Abstract

The invention discloses a mesoporous solid acid composite catalyst as well as preparation and application thereof, and particularly relates to a preparation method and application of an acid-functionalized COF polymer and Beta molecular sieve composite catalyst. The solid acid composite catalyst is prepared from an acid functionalized COF polymer and a molecular sieve material through mechanical grinding, and the preparation method is simple and convenient. The solid acid composite catalyst has the advantages of high crystallinity, large specific surface area, rich pore structure, good chemical stability and the like. The prepared composite catalyst is stable in performance and high in activity at low temperature, polyoxymethylene dialkyl ether can be selectively synthesized, and the effect that reaction products do not conform to Schulz-Flory distribution is achieved by adjusting the composition of the composite catalyst.

Description

Technical Field

[0001] The invention belongs to the technical field of heterogeneous catalysis, and relates to a mesoporous solid acid composite catalyst, in particular to a preparation method of the mesoporous solid acid composite catalyst, and application of the catalyst in synthesizing polymethoxydialkyl ether. Background Art

[0002] Polymethoxydialkyl ether (RO(CH 2 O)nR) is a class of polyether oxygenated compounds with high oxygen content. It has many advantages such as high cetane number, good diesel miscibility, and excellent low-temperature fluidity. It is a recognized green diesel additive. Adding an appropriate proportion of polyether oxygenated compounds to diesel can significantly improve the combustion efficiency of diesel engines, reduce the soot particles and organic pollutants generated during diesel combustion, and improve the anti-knock performance of diesel engines, which is of great significance to sustainable development and environmental protection. Compared with polymethoxy dimethyl ether, polymethoxy diethyl ether with a long-chain -R group has higher cetane number, boiling point, viscosity and flash point, and lower density and freezing point. In addition, polymethoxy diethyl ether has good solubility and volatility, and can be miscible with a variety of organic reagents.

[0003] The synthesis of polyoxymethylene dialkyl ether is an acid-catalyzed reaction, and the preparation of catalysts has always been a hot topic and difficulty in research. Traditional liquid acid catalysts have certain reactivity, but they have disadvantages such as corrosiveness, difficulty in separation and harm to the environment. Compared with liquid acid catalysts, solid acid catalysts have many advantages such as easy separation and reusability. According to literature reports, homogeneous acids and solid acids are used as catalysts to synthesize polyoxymethylene dimethyl ether CH 3 O(CH 2 O) n CH 3 (DMMn, 2≤n≤8) has been studied in some depth, but the polyoxyethylene diethyl ether CH 3 CH 2 O(CH 2 O) n CH 2 CH 3 The research on (DEMn, 2≤n≤8) is very limited. Therefore, it is urgent to develop new solid acid catalysts to achieve the effective synthesis of polyoxyethylene diethyl ether under mild conditions. Summary of the invention

[0004] The invention aims to disclose a mesoporous solid acid composite catalyst and a preparation method thereof, so as to realize the synthesis of polymethoxy diethyl ether under consistent conditions.

[0005] The mesoporous solid acid composite catalyst of the present invention is prepared by preparing the composite catalyst by simple mechanical grinding, vacuum drying and other steps of preparing the acid functionalized COF polymer material and the activated molecular sieve material. The solid acid composite catalyst developed by the present invention can make the catalyst have a special structure (pore structure, specific surface area, etc.) by adjusting different mixed components, so that the catalyst exhibits special performance in the synthesis reaction of polymethoxydiethyl ether, so that the reaction product does not conform to the Schulz-Flory distribution.

[0006] The method for preparing the mesoporous solid acid composite catalyst of the present invention comprises the following steps: 1) Preparation of acid-functionalized COF polymer materials Dissolve trialdehyde phloroglucinol and 2,5-diaminobenzenesulfonic acid in tetrahydrofuran, then add 1~5 mol∙L -1 The acetic acid solution or p-toluenesulfonic acid solution is used as a catalyst, mixed evenly, and ultrasonicated for 30-45 minutes to form a uniform mixed solution. The mixed solution after ultrasonication is poured into a reactor, and the temperature is raised to 100-120°C in a drying oven to react for 60-80 hours. After the reaction, a red solid powder is obtained, which is centrifugally washed multiple times with anhydrous N,N-dimethylformamide, anhydrous tetrahydrofuran, and anhydrous ethanol, and vacuum dried to obtain an acid-functionalized COF polymer material. The molar ratio of the trialdehyde phloroglucinol to 2,5-diaminobenzenesulfonic acid is 2:(3-4).

[0007] (2) Preparation of activated molecular sieve materials Beta molecular sieves with different silicon-aluminum ratios are heated to 500-550° C. in an air atmosphere of a muffle furnace, calcined for 2-4 hours, and adsorbed moisture and impurities are removed to obtain activated molecular sieve materials; the silicon-aluminum ratio of the Beta molecular sieve is 25-60.

[0008] (3) Preparation of solid acid composite catalyst The molecular sieve material activated in step (2) and the acid-functionalized COF polymer material prepared in step (1) are weighed in a mass ratio of 10:1 to 10:2 and added to a mortar, and ground and mixed evenly. The ground material is vacuum dried to obtain the target solid acid composite catalyst.

[0009] Another object of the present invention is to provide an application of the above mesoporous solid acid composite catalyst in the preparation of polymethoxy dialkyl ether. Specifically, diethoxymethane, trioxymethylene and the mesoporous solid acid composite catalyst are uniformly mixed, reacted at 40-70° C. for 60-120 minutes under normal pressure to synthesize polymethoxy diethyl ether. The amount of the mesoporous solid acid composite catalyst is 5%-10% of the total mass of the reactants.

[0010] Compared with the prior art, the present invention has the following beneficial effects: The solid acid composite catalyst provided by the present invention is prepared by mechanical grinding of an acid-functionalized COF polymer and a molecular sieve material, and the preparation method is simple and convenient. The solid acid composite catalyst prepared by the present invention is used for acetalization reaction, especially polymethoxy diethyl ether synthesis reaction, and the reaction conditions are mild, the catalyst is active at low temperatures, and the target product can be selectively obtained. At the same time, the composite catalyst prepared by the present invention has stable performance, and the composite catalyst has a special structure (pore structure, specific surface area, etc.) by adjusting the composition of the composite catalyst, so that the distribution of the polymethoxy dialkyl ether product does not conform to the Schulz-Flory distribution, and a specific target product is obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 This is a scanning electron microscope (SEM) image of catalyst C3 prepared in Example 2 of the present invention.

[0012] Figure 2 This is the XRD spectrum of catalyst C3 prepared in Example 2 of the present invention.

[0013] Figure 3 This is the nitrogen physical adsorption-desorption isotherm curve of the catalyst C3 prepared in Example 2 of the present invention.

[0014] Figure 4 This is the thermogravimetric spectrum of catalyst C3 prepared in Example 2 of the present invention.

[0015] Figure 5 This is a distribution diagram of the synthetic products of Example 4 of the present invention.

[0016] Figure 6 This is the infrared spectrum of the acid-functionalized COF polymer material prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0017] The present invention is further explained below with reference to specific embodiments.

[0018] Example 1 (1) Preparation of acid-functionalized COF polymer materials 0.3216 g of trialdehyde phloroglucinol (Tp) and 0.4322 g of 2,5-diaminobenzenesulfonic acid (DABA) were dissolved in 15 mL of tetrahydrofuran, and then 3 mol∙L -11.5 mL of acetic acid solution was used as a catalyst, mixed evenly, and ultrasonicated for 30 min to form a uniform mixed solution. The mixed solution after ultrasonication was poured into a reactor and heated in a drying oven at 120°C for 3 days. After the reaction, a red solid powder was obtained, which was centrifuged and washed three times with anhydrous N,N-dimethylformamide, anhydrous tetrahydrofuran, and anhydrous ethanol. The obtained material after centrifugation was dried in a vacuum drying oven at 100°C for 12 hours to obtain an acid-functionalized COF polymer material. Physical adsorption and desorption analysis found that the specific surface area of ​​the prepared COF polymer material was 65 and the pore size was about 6.5-8.2nm. The infrared spectrum is shown in Figure 6 As shown, the prepared COF polymer material has a wavelength of 1180 cm -1 , 1076 cm -1 and 1018 cm -1 The strong peak at is believed to be related to -SO 3 The S=O stretching vibration of the H group indicates that the prepared material contains -SO 3 H group.

[0019] (2) Activated molecular sieve materials Beta molecular sieve with a silicon-aluminum ratio of 60 was calcined at 550°C for 3 hours in an air atmosphere of a muffle furnace to remove adsorbed moisture and impurities to obtain an activated molecular sieve material.

[0020] (3) Preparation of solid acid composite catalyst In order to compare the difference between COF polymer material and molecular sieve at different mass ratios, two composite catalysts with different mass ratios were prepared. Weigh 0.1002g of the acid-functionalized COF polymer material prepared in the above step and 1.003g of the activated molecular sieve material, add them to a mortar at a mass ratio of 1:10, and add 4-5 drops of tetrahydrofuran at the same time. After simple mechanical grinding for 60 min, mix evenly, and dry the ground material in a vacuum drying oven at 120°C for 12h to obtain the target solid acid composite catalyst, recorded as C1. Scanning electron microscopy shows that the catalyst has a coral ball-like morphology. At the same time, the mapping diagram shows that the catalyst contains C, N, O, and S elements, and the sulfur content in catalyst C1 is 2.42%. After physical adsorption and desorption analysis, it was found that the prepared catalyst C1 has a specific surface area of ​​459 and a pore size of about 2.5-12.0nm.

[0021] Continue to weigh 0.2005g of the acid-functionalized COF polymer material prepared in the above method and 1.004g of the activated molecular sieve material, add the two to the mortar in a mass ratio of 2:10, and add 4-5 drops of tetrahydrofuran at the same time. After simple mechanical grinding for 60 min, mix evenly, and dry the ground material in a vacuum drying oven at 120°C for 12h to obtain the target solid acid composite catalyst, recorded as C2. It can be seen from the scanning electron microscope that the catalyst has a spherical morphology. At the same time, the mapping diagram shows that the catalyst contains C, N, O, and S elements, and the sulfur content in the catalyst C2 is 2.15%. After physical adsorption and desorption analysis, it was found that the specific surface area of ​​the prepared catalyst C2 was 395 and the pore size was about 2.5-11.0nm. By comparison, it was found that after increasing the mass ratio of COF polymer material to molecular sieve, the specific surface area of ​​the composite catalyst was significantly reduced.

[0022] Example 2 (1) Preparation of acid-functionalized COF polymer materials Acid-functionalized COF polymer materials were prepared by a solvothermal method through a simple Schiff base reaction. 0.5362 g of trialdehyde phloroglucinol (Tp) and 0.7203 g of 2,5-diaminobenzenesulfonic acid (DABA) were weighed and dissolved in 25 mL of tetrahydrofuran, where the molar ratio of the reactants Tp and DABA was 2:3, and then 3 mol∙L -1 2.5 mL of p-toluenesulfonic acid aqueous solution was used as a catalyst, mixed evenly, and ultrasonicated for 40 min to form a uniform mixed solution. The mixed solution after ultrasonication was poured into a reactor and heated in a drying oven at 120°C for 3 days. After the reaction, a red solid powder was obtained, which was washed three times by centrifugation with anhydrous N,N-dimethylformamide, anhydrous tetrahydrofuran, and anhydrous ethanol. The obtained material after centrifugation was dried in a vacuum drying oven at 100°C for 12h to obtain an acid-functionalized COF polymer material.

[0023] The catalyst was replaced with an aqueous solution of p-toluenesulfonic acid, and physical adsorption and desorption analysis revealed that the specific surface area of ​​the prepared COF polymer material was 112, and the pore size was about 10.6-15.2 nm. Compared with Example 1, its specific surface area was larger and the pore size range was wider.

[0024] (2) Activated molecular sieve materials Beta molecular sieve with a silicon-aluminum ratio of 60 was calcined at 550°C for 3 hours in an air atmosphere of a muffle furnace to remove adsorbed moisture and impurities to obtain an activated molecular sieve material.

[0025] (3) Preparation of solid acid composite catalyst In order to compare the difference between different mass ratios of COF polymer material and molecular sieve, two composite catalysts with different mass ratios were prepared. 0.5002g of the acid-functionalized COF polymer material prepared above and 5.0020g of the molecular sieve material activated in the step were weighed, and the two were added to a mortar at a mass ratio of 1:10, and 8-9 drops of tetrahydrofuran were added at the same time. After simple mechanical grinding for 60 min, the material was mixed evenly, and the ground material was dried in a vacuum drying oven at 120°C for 12h to obtain the target solid acid composite catalyst, which was recorded as C3.

[0026] The scanning electron microscope image of catalyst C3 is as follows Figure 1 As shown, it can be seen that the catalyst has a coral ball-like morphology. At the same time, the mapping diagram shows that the catalyst contains C, N, O, and S elements, which are distributed relatively evenly.

[0027] XRD spectrum Figure 2 As shown, catalyst C3 has a very strong diffraction peak at 23°, and relatively weak diffraction peaks at 8°, 25°, 26°, 28°, 30°, 32°, and 34°, indicating that the catalyst has a certain crystal structure.

[0028] Physical adsorption-desorption curves are shown in Figure 3 As shown, catalyst C3 presents a typical type IV isotherm, has a mesoporous structure, a specific surface area of ​​459, and a pore size range of about 2-12 nm.

[0029] Thermogravimetric images Figure 4 As shown in FIG. 1 , the mass of catalyst C3 changes with temperature. At about 400°C, 86% of the mass can be maintained, and at 700°C, the mass of the catalyst is about 80%, indicating that the catalyst has good thermal stability.

[0030] Continue to weigh 1.0020g of the acid-functionalized COF polymer material prepared above and 5.0005g of the activated molecular sieve material, add the two to the mortar in a mass ratio of 2:10, and add 8-9 drops of tetrahydrofuran at the same time. After simple mechanical grinding for 60 min, mix evenly, and dry the ground material in a vacuum drying oven at 120°C for 12h to obtain the target solid acid composite catalyst, recorded as C4. It can be seen from the scanning electron microscope that the catalyst has a coral ball-like morphology. At the same time, the mapping diagram shows that the catalyst contains C, N, O, and S elements, and the sulfur content in the catalyst C4 is 1.6%. After physical adsorption and desorption analysis, it was found that the specific surface area of ​​the prepared catalyst C4 was 396 and the pore size was about 2.9-13.3nm. By comparison, it was found that after increasing the mass ratio of COF polymer material to molecular sieve, the specific surface area of ​​the composite catalyst was significantly reduced.

[0031] Example 3 The solid acid composite catalyst C1 prepared in Example 1 of the present invention was used in the reaction of trioxymethane and diethoxymethane to synthesize polyoxymethylene diethyl ether. 1g diethoxymethane and 0.5g trioxymethane were added to the reactor, and 0.075g of C1 catalyst was added. The reaction was carried out at 40°C and normal pressure for 1h. After the reaction was completed, the reaction was cooled and the product was subjected to chromatographic analysis. The analysis found that the conversion rate of the reactant trioxymethylene was 20%, and the product polyoxymethylene diethyl ether DEM was 1.34%. 2-8 The selectivity is 95%, and the product is polymethoxy diethyl ether DEM 3-8 The selectivity is 28%, and the product distribution does not conform to the Schulz-Flory distribution.

[0032] Example 4 The solid acid composite catalyst C3 prepared in Example 2 of the present invention was used in the reaction of trioxymethane and diethoxymethane to synthesize polyoxyethylene diethyl ether. 1g diethoxymethane and 0.5g trioxymethane were added to the reactor, and 0.075g of C3 catalyst was added. The reaction was carried out at 40°C and normal pressure for 1h. After the reaction was completed, the reaction was cooled and the product was subjected to chromatographic analysis. The analysis found that the conversion rate of the reactant trioxymethane was 8%, and the product DEM was 1.3447 W / m. 2-8 The selectivity is 89%, and the product DEM 3-8 The selectivity is 20%. Figure 5 As shown, the amount of DEM4 of the synthesized product polymethoxy diethyl ether is higher than that of DEM3, and the amount of DEM7 of polymethoxy diethyl ether is higher than that of DEM6, and the product distribution does not conform to the Schulz-Flory distribution. The reaction results show that the composite catalyst C3 exhibits specific catalytic performance at low temperature.

[0033] Example 5 The solid acid composite catalyst C1 prepared in Example 1 of the present invention was used in the reaction of trioxymethane and diethoxymethane to synthesize polyoxymethylene diethyl ether. 1.2g diethoxymethane and 0.6g trioxymethane were added to the reactor, and 0.0900g of C1 catalyst was added. The reaction was carried out at 40°C and normal pressure for 2h. After the reaction was completed, the reaction was cooled and the product was subjected to chromatographic analysis. The analysis found that the conversion rate of the reactant trioxymethylene was 59%, and the product polyoxymethylene diethyl ether DEM was 1.34%. 2-8 The selectivity is 98%, and the product is polymethoxy diethyl ether DEM 3-8 The selectivity is 55%, and the product distribution does not conform to the Schulz-Flory distribution. The reaction results show that the conversion rate of the reactants increases with the extension of the reaction time.

[0034] Example 6 The solid acid composite catalyst C2 prepared in Example 1 of the present invention was used in the reaction of trioxymethane and diethoxymethane to synthesize polyoxymethylene diethyl ether. 1g diethoxymethane and 0.5g trioxymethane were added to the reactor, and 0.075g of C2 catalyst was added. The reaction was carried out at 60°C and normal pressure for 2h. After the reaction was completed, the reaction was cooled and the product was subjected to chromatographic analysis. The analysis found that the conversion rate of the reactant trioxymethylene was 4.9%, and the product polyoxymethylene diethyl ether DEM was 1.3%. 2-8 The selectivity is 60.88%, and the product DEM 3-8 The selectivity is 11.14%, the product distribution does not conform to the Schulz-Flory distribution, and the product DEM 4 Higher than DEM 3 Through physical adsorption and desorption tests, it was found that when the mass ratio of COF to molecular sieve was 2:10, its specific surface area was significantly reduced after mechanical grinding. At the same time, elemental analysis tests found that the amount of exposed sulfur element was reduced. The reduction in specific surface area and the amount of accessible acidic group sulfonic acid group decreased, resulting in a decrease in the conversion rate of the reactant trioxymethylene in low-temperature reactions, and the product distribution did not conform to the Schulz-Flory distribution.

[0035] Comparative Example 1 According to the method in Example 6, the catalyst was replaced with a pure acid-functionalized COF polymer material, the catalyst amount was 5% by mass, and the other conditions remained the same. Analysis showed that the conversion rate of the reactant trioxymethylene was only about 1%, and only the product polyoxyethylene diethyl ether DEM was generated. 2 The experimental results show that the catalytic activity of the simple acid-functionalized COF polymer is poor when reacting at low temperature.

Claims

1. A method for preparing a mesoporous solid acid composite catalyst, characterized in that: The following steps are involved: 1) Preparation of acid-functionalized COF polymer materials The trialdehyde phloroglucinol and 2,5-diaminobenzenesulfonic acid are dissolved in tetrahydrofuran, and then the corresponding acid solution is added as a catalyst, mixed evenly, and ultrasonicated for 30-45 minutes to form a uniform mixed solution. The mixed solution after ultrasonication is poured into a reactor, and the temperature is raised to 100-120°C in a drying oven to react for 60-80 hours. After the reaction is completed, a red solid powder is obtained, which is centrifugally washed with anhydrous N,N-dimethylformamide, anhydrous tetrahydrofuran and anhydrous ethanol for multiple times, and vacuum dried to obtain an acid-functionalized COF polymer material. (2) Preparation of activated molecular sieve materials Beta molecular sieves with different silicon-aluminum ratios are heated to 500-550°C in an air atmosphere of a muffle furnace and calcined for 2-4 hours to remove adsorbed moisture and impurities to obtain activated molecular sieve materials; (3) Preparation of solid acid composite catalyst The molecular sieve material activated in step (2) and the acid-functionalized COF polymer material prepared in step (1) are weighed in a mass ratio of 10:1 to 10:2 and added to a mortar, and ground and mixed evenly. The ground material is vacuum dried to obtain the target solid acid composite catalyst.

2. The method for preparing a mesoporous solid acid composite catalyst according to claim 1, characterized in that: In step 1), the molar ratio of trialdehyde pyrogallol to 2,5-diaminobenzenesulfonic acid is 2:(3~4).

3. The method for preparing a mesoporous solid acid composite catalyst according to claim 1, characterized in that: In step 1), the corresponding acid solution is 1~5 mol∙L -1 acetic acid solution or p-toluenesulfonic acid solution.

4. The method for preparing a mesoporous solid acid composite catalyst according to claim 1, characterized in that: In step 2), the silicon-aluminum ratio of the Beta molecular sieve is 25-60.

5. A mesoporous solid acid composite catalyst prepared by the method as claimed in claim 1.

6. Use of the mesoporous solid acid composite catalyst prepared by the method of claim 1 in the preparation of polymethoxy dialkyl ether, characterized in that: Diethoxymethane, trioxymethylene and a mesoporous solid acid composite catalyst are uniformly mixed and reacted at 40-70°C for 60-120min under normal pressure to obtain polymethoxy dialkyl ether.

7. Use of the mesoporous solid acid composite catalyst in the preparation of polymethoxy dialkyl ethers as claimed in claim 6, characterized in that: The amount of the mesoporous solid acid composite catalyst used is 5%-10% of the total mass of the reactants.

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