CN111185239B - A kind of preparation method and application of CO2 epoxidation immobilized catalyst - Google Patents

Abstract

The invention discloses a preparation method and application of a fixed catalyst for CO ₂ epoxidation. First, a template agent is introduced in the preparation process by a hydrothermal method, and then the template agent is removed by calcination to obtain ZnWO ₄ solid powder with a larger specific surface area. The prepared ZnWO ₄ was then dissolved in an organic solvent, and 2-methylimidazole was grafted onto the surface of ZnWO ₄ by in situ growth under solvothermal conditions. After centrifugation and washing, the ZnWO ₄ powder grafted with 2-methylimidazole was dissolved in an organic solvent, and zinc salt was added at the same time, and then through a solvothermal reaction, the zinc ions were anchored on the surface of the material through coordination bonds. The sequence of adding 2-methylimidazole and zinc salts in turn was repeated to synthesize a layered structure material with ZnWO ₄ as the core and alternating 2-methylimidazole and zinc ions. The catalytic material prepared by this method not only has a good microstructure, but also has Lewis acid-base active sites, and the number and distribution of the active sites can be precisely regulated by the amount of 2-methylimidazole and zinc ions introduced. .

Description

A kind of preparation method and application of CO2 epoxidation immobilized catalyst

technical field

The invention discloses a preparation method of a fixed catalyst for CO ₂ epoxidation. More specifically, the present invention relates to the introduction of basic groups on the modified support by in-situ growth technology, wherein the basic groups are uniformly distributed on the catalyst surface, and the catalyst prepared by this method not only has relatively high performance on the CO ₂ epoxidation process. High activity and stability, and high selectivity to the target product.

Background technique

With the rapid advancement of the industry, the combustion and utilization of various energy sources has led to an increasing trend of carbon dioxide in the air year by year, which has brought serious harm to the climate and environment. Carbon dioxide has the characteristics of non-toxicity, easy access and cheapness, and is a natural C ₁ resource with abundant reserves. In recent years, the synthesis of other fine chemicals using carbon dioxide as a starting material has attracted worldwide attention, and a large number of reaction routes have been reported.

Researchers from all over the world have tried to convert carbon dioxide into chemicals such as dimethyl carbonate, diphenyl carbonate, cyclic carbamate, formic acid and cyclic carbonate through chemical methods. Among these chemicals, cyclic carbonates have excellent physical and chemical properties and can be used as ideal polar solvents, intermediates and compounds for the synthesis of drugs, dielectrics for lithium-ion batteries, and precursors for the synthesis of polycarbonates and polyurethanes. body and other industries. Therefore, the chemical conversion of carbon dioxide into cyclic carbonate has broad application prospects and is of great significance.

So far, domestic and foreign researchers have done a lot of research on carbon dioxide epoxidation fixation. The developed catalysts are mainly divided into homogeneous ionic liquids, functional polyesters, quaternary ammonium salts, quaternary phosphorus salts, heterogeneous metal oxides, Schiff alkali metal complexes, metal organic framework materials and other catalytic materials. For example, the team of Professor Qinghai Cai of Harbin Normal University modified the surface of benzyl bromide polymer with nitrogen-methylimidazole as active group, synthesized functionalized polymer, and applied the polymer to the coupling process of carbon dioxide and propylene oxide , 71.4% propylene oxide conversion and 96.8% propylene carbonate selectivity were obtained. In order to study the difference in catalytic carbon dioxide epoxidation of imidazolium ionic liquids with oxygen-containing groups, the team of Professor Jianmin Sun of Harbin Institute of Technology used two imidazolium-based ionic liquids containing hydroxyl and carboxyl groups to catalyze the carbon dioxide epoxidation process. It is found that ionic liquids containing hydroxyl groups can better promote the reaction between carbon dioxide and propylene oxide. The team of Professor Zhenshan Hou from East China University of Science and Technology loaded the imidazolyl ionic liquid on carboxymethyl cellulose by chemical method, and loaded NbCl ₅ together with the supported catalyst into the catalytic system of CO ₂ and propylene oxide. The test showed that: At a system pressure of 1.5 MPa, a reaction temperature of 130 °C, and a reaction of 3 h, 98.1% conversion rate and 98.3% cyclic carbonate selectivity were obtained. The Dae-Won Park team of Pusan National University in South Korea used silicon-supported ionic liquids containing different metal ions (Zn, Ni, Mn, Cu, Co) to catalyze the reaction of carbon dioxide with allyl glycidyl ether. The results showed that: under the same reaction conditions (0.86 MPa, 110 °C, 6 h), the supported catalyst containing Zn had the highest catalytic activity, and the yield corresponding to cyclic carbonic acid was up to 71.7%. UIO-66, MIL-101, and MIL-125 were functionalized and modified with amino groups, respectively, and styrene oxide and epichlorohydrin were used as probes to react with carbon dioxide. After comparative research: functionalized modified metallo-organic The catalytic activity of the framework material for _CO epoxidation is significantly improved. When ZIF-8 and MOF-5 were added to the mixed system of carbon dioxide and epichlorohydrin at the same time, the catalytic effect showed higher catalytic activity than single materials. When using these catalysts to catalyze the epoxidation process, most systems require the addition of co-catalysts, organic solvents and the reaction is carried out at high temperature and high pressure. For a homogeneous system, catalyst separation is more difficult, and the subsequent product purification process is also more complicated. Mechanism studies show that the reaction of carbon dioxide and epoxy compounds to form cyclic carbonates is mainly divided into the processes of epoxide ring opening, CO ₂ insertion into ring-opened intermediates, and intermediate ring closure to form cyclic carbonates. It is jointly determined by the Lewis acid-base active site. Therefore, it is of great significance to develop a structurally stable catalyst with Lewis acid-base active sites for catalyzing _CO synthesis of cyclic carbonates.

SUMMARY OF THE INVENTION

Technical problem: In order to solve the problems existing in the activity and stability of the catalyst for catalyzing the epoxy addition of carbon dioxide in the prior art, a new preparation method and application of a fixed catalyst with CO ₂ cyclization are provided. The catalyst prepared by the method is used in the CO ₂ epoxy addition reaction and has high catalytic activity and stability.

Technical scheme: the preparation method of a CO ₂ epoxidation immobilized catalyst of the present invention comprises the following steps:

Step 1: Synthesis of Zinc Tungstate ZnWO ₄

Add sodium tungstate NaWO ₄ into the deionized aqueous solution with surfactant dissolved in 0.01～10g/L according to the solid-liquid ratio of 0.01～10mmol/L, stir at 20～70℃ for 1～12 hours, then add and NaWO ₄ equimolar amounts of zinc salt, continue to stir at 20～70℃ for 1～12 hours, then transfer to the hydrothermal reaction kettle, statically react at 120～180℃ for 12～48h, then cool to room temperature, put the obtained precipitate Filtration and washing 3 times, drying at 80°C for 24h, and calcination at 500～900°C for 3～10h to obtain ZnWO ₄ ;

Step 2: In situ growth method to introduce layered metal-organic structures

The ZnWO ₄ prepared in step 1 is put into the hydrothermal reactor, and then the organic solvent with a solid-to-liquid ratio of 0.01 to 10 mmol/L is added to the hydrothermal reactor, and stirred for 0.1 to 2 hours at a temperature of 20 to 60 °C;

a) Add ₂ methylimidazole with equimolar amount of ZnWO to the hydrothermal reaction kettle, stir at 20～60 ℃ for 1～6 hours, after sealing, statically react at 120～180 ℃ for 12～48h, Cool to room temperature, filter and wash the sediment in the hydrothermal kettle for 3 times, and then dissolve it in an organic solvent;

b) Add equimolar zinc salt with 2 methylimidazole to the hydrothermal reaction kettle, stir at 20～60℃ for 0.1～2 hours, after sealing, statically react at 120～180℃ for 12～48h, Cool to room temperature, filter and wash the sediment in the hydrothermal kettle for 3 times;

By adjusting the repetition times of steps a) and b) and controlling the number of layers, a layered CO ₂ epoxidation immobilization catalyst with ZnWO ₄ as the inner core and alternating 2-methylimidazole and zinc ions was synthesized.

in,

The surfactant described in step 1 is dodecyl trimethyl ammonium bromide, hexadecyl trimethyl ammonium bromide, hexamethylene tetramine, tetraethyl ammonium bromide, tetrapropyl bromide One or more of ammonium or tetrabutylammonium bromide.

The zinc salt described in step 1 is one or more of zinc nitrate, zinc chloride, zinc acetate, zinc perchlorate, zinc bromide or zinc sulfate.

The solvent for washing described in step 1 is one or more of deionized water, methanol, ethanol or nitrosodimethylformamide.

The calcination process described in step 1 is to use a programmed heating rate of 5°C/min to reach the target temperature in an air atmosphere.

The organic solvent described in step 2 is one or more of methanol, ethanol, nitrosodimethylformamide, azodiethylformamide or tetrahydrofuran.

The washing solution of washing 2-methylimidazole described in the step 2 is methanol, ethanol, nitrogen nitrogen dimethyl formamide, nitrogen nitrogen diethyl formamide, dichloromethane, chloroform, tetrachloromethane or tetrahydrofuran. One or more; the washing solution for washing the zinc salt is one or more of deionized water, methanol, ethanol, and nitrosodimethylformamide.

The zinc salt described in step 2 is one or more of zinc nitrate, zinc chloride, zinc acetate, zinc perchlorate, zinc bromide or zinc sulfate.

After one cycle of a) and b) described in step 2, a layer of metal-organic structure is formed on the surface of ZnWO ₄ , and the layer thickness is equal to the distance between two zinc ions and different nitrogen atoms in 2-methylimidazole to form a stable structure.

The CO ₂ epoxidation fixed catalyst prepared by the method of the invention can promote the reaction of CO ₂ with epoxy compounds, and the epoxy compounds are propylene oxide, epichlorohydrin, butylene oxide, styrene oxide, One or more of epoxy cyclohexane and allyl glycidyl ether.

Beneficial effect: The fixed catalyst for CO ₂ epoxidation prepared by this method has a layered structure with ZnWO ₄ as the core, and organic ligands and metal ions alternately appear outside the core, which promotes the reaction of reactants and products during the reaction process. diffusion. As the inner core structure, ZnWO ₄ can provide Lewis acid active sites required for the epoxidation process, and the organic ligands in the outer layer have the function of Lewis basic sites, which promotes the activation of CO ₂ during the epoxidation process. By controlling the number of layered structures introduced outside _ZnWO4 , and regulating the number and ratio of Lewis acid and base of the synthesized catalyst, an ideal catalyst for _CO2 epoxidation with high catalytic activity and stable reaction was synthesized. Using a catalyst with 0.75% weight of epoxide at 100 °C for 7 hours to catalyze the reaction of _CO2 with epichlorohydrin, the conversion of epichlorohydrin was as high as 97.84%, and the corresponding cyclic carbonate yield was 95.58%.

Detailed ways

The present invention will be further elaborated below through examples, it should be noted that: the following examples are only used to illustrate the present invention and not to limit the scope of the present invention.

Example 1: Preparation of a catalyst with ZnWO ₄ as the core and a layered structure introduced on the surface

1) Dissolve 10 mmol NaWO ₄ in 100 mL of deionized aqueous solution containing 2 g/L dodecyl trimethyl ammonium bromide, stir at 50 ° C for 1 hour, then add an equimolar amount of zinc nitrate, continue to Stir at 50°C for 1 hour, then transfer to a hydrothermal reactor, statically react at 120°C for 12h, then cool to room temperature, filter, and wash with deionized water 3 times; dry at 80°C for 24h, and calcinate at 600°C for 3h to obtain pores ZnWO ₄ with rich structure and large specific surface area;

2) Dissolve 5 mmol of ZnWO ₄ prepared in step (1) in 100 mL methanol solution, stir at 20°C for 0.1 hour, then add equimolar amount of 2methylimidazole, continue stirring at 20°C for 1 hour, Then it was transferred into a hydrothermal reactor, statically reacted at 120 °C for 12 h, then cooled to room temperature, filtered and washed with methanol 3 times; dissolved in methanol solution containing equimolar zinc nitrate again, stirred at 20 °C for 0.1 hour, and transferred to Hydrothermal reaction kettle, static reaction at 120℃ for 12h, cooled to room temperature, filtered and washed with deionized water 3 times to obtain a composite catalyst with ZnWO4 as the core and organic ligands and metal ions as the layered structure.

The CO ₂ epoxidation fixed catalyst prepared by the method of the invention can promote the reaction of CO ₂ with epoxy compounds, and the epoxy compounds are propylene oxide, epichlorohydrin, butylene oxide, styrene oxide, One or more of epoxy cyclohexane and allyl glycidyl ether.

Example 2:

The preparation steps and methods are the same as in Example 1, except that 10 mmol of zinc nitrate in step 1) of Example 1 is changed to 10 mmol of zinc chloride.

Example 3:

The preparation steps and methods are the same as in Example 1, except that the 2g/L dodecyltrimethylammonium bromide solution in step 1) of Example 1 is changed to 2g/L hexamethylenetetramine solution.

Example 4: Preparation of a catalyst with ZnWO ₄ as the core and two layered structures introduced on the surface The preparation steps and methods are the same as those in Example 1, except that the layered structure introduced in step 2) of Example 1 is increased to two layers.

Example 5: Preparation of the catalyst with ZnWO ₄ as the core and the surface of the catalyst introduced with 3-layer structure The preparation steps and methods are the same as those in Example 1, except that the layered structure introduced in step 2) of Example 1 is increased to 3 layers.

Example 6: Preparation of a catalyst with ZnWO ₄ as the core and a layered structure introduced on the surface

1) The preparation steps and methods are the same as in Example 1, except that the 2g/L dodecyltrimethylammonium bromide solution in step 1) of Example 1 is changed to 2g/L hexamethylenetetramine solution.

2) Dissolve 5 mmol of ZnWO ₄ prepared in step (1) in 100 mL methanol solution, stir at 20°C for 0.1 hour, then add equimolar amount of 2methylimidazole, continue stirring at 20°C for 1 hour, Then it was transferred to a hydrothermal reactor, statically reacted at 120°C for 24h, then cooled to room temperature, filtered and washed with methanol for 3 times; dissolved in methanol solution containing equimolar amount of zinc bromide again, stirred at 20°C for 1 hour, turned Into a hydrothermal reactor, statically reacted at 120°C for 24h, cooled to room temperature, filtered and washed with deionized water for 3 times to obtain a composite catalyst with ZnWO4 as the core and organic ligands and metal ions as the layered structure.

Catalytic performance evaluation

The catalyst activities in Examples 1-6 were compared with epichlorohydrin as the reaction substrate. The reaction conditions were as follows: 20g epichlorohydrin and 0.15g catalyst were added to a 100mL stainless steel reaction kettle, and after sealing, the internal gas was washed with CO ₂ for 3 times, and then filled with CO ₂ again to make the initial gas pressure reach 3.0 MPa, and then the temperature was raised to 100 °C After 7 hours of reaction, it was rapidly cooled to room temperature with ice water, the reaction mixture was taken out, and the organic liquid without catalyst was obtained by centrifugation. The catalysts in Examples 1-6 were respectively tested for catalytic CO ₂ and epichlorohydrin, and the test results are shown in Table 1.

Table 1 Example _1-6CO2 and epichlorohydrin are converted into cyclic carbonate catalytic performance comparison

From the data in Table 1, in the catalysts prepared in Examples 1-6, the introduction of ZnWO ₄ into the metal-organic layered structure significantly enhanced the catalytic activity of the coupling process of CO ₂ and epichlorohydrin, and with the introduction of the layered structure With the increase of layered structure, the catalytic activity showed a downward trend, which may be due to the decrease of the proportion of ZnWO ₄ in the structure with the increase of layered structure, that is, the proportion of active sites with Lewis acid function decreased, which is not conducive to epoxide ring opening. process, resulting in a decrease in catalytic activity. In conclusion, the introduction of an appropriate amount of metal-organic layered structure on the outer surface of ZnWO ₄ can significantly improve the catalytic activity.

Claims (10)

1. CO (carbon monoxide)₂A process for preparing an epoxidation fixed catalyst, which process comprises the steps of:

step 1: synthesis of zinc tungstate ZnWO₄

Sodium tungstate NaWO₄Adding the mixture into deionized water solution with 0.01-10 g/L dissolved with surfactant according to the solid-to-liquid ratio of 0.01-10 mmol/L, stirring for 1-12 hours at the temperature of 20-70 ℃, and then adding the mixture and NaWO₄Continuously stirring zinc salt with equal molar weight at the temperature of 20-70 ℃ for 1-12 hours, then transferring the zinc salt into a hydrothermal reaction kettle, statically reacting at the temperature of 120-180 ℃ for 12-48 hours, then cooling to room temperature, filtering and washing the obtained precipitate for 3 times, drying at the temperature of 80 ℃ for 24 hours, and calcining at the temperature of 500-900 ℃ for 3-10 hours to obtain ZnWO₄；

Step 2: in-situ growth method for introducing layered metal organic structure

ZnWO prepared in the step 1₄Putting the mixture into a hydrothermal reaction kettle, adding an organic solvent with a solid-to-liquid ratio of 0.01-10 mmol/L into the hydrothermal reaction kettle, and stirring the mixture for 0.1-2 hours at the temperature of 20-60 ℃;

a) adding ZnWO into the hydrothermal reaction kettle₄Stirring 2-methylimidazole with an equal molar amount at the temperature of 20-60 ℃ for 1-6 hours, sealing, carrying out static reaction at the temperature of 120-180 ℃ for 12-48 hours, cooling to room temperature, filtering and washing precipitates in a hydrothermal kettle for 3 times, and dissolving in an organic solvent;

b) adding zinc salt with the same molar weight as 2-methylimidazole into the hydrothermal reaction kettle, stirring for 0.1-2 hours at the temperature of 20-60 ℃, sealing, carrying out static reaction for 12-48 hours at the temperature of 120-180 ℃, cooling to room temperature, filtering and washing precipitates in the hydrothermal reaction kettle for 3 times;

synthesizing ZnWO by regulating and controlling the repeated times of the procedures a) and b) and controlling the quantity of the layers₄2-methylimidazole and zinc ion alternately appearing layered structure CO as core₂The catalyst is fixed by epoxidation.

2. CO according to claim 1₂The preparation method of the epoxidation fixed catalyst is characterized in that the surfactant in the step 1 is dodecyl trimethyl bromideOne or more of ammonium bromide, hexadecyl trimethyl ammonium bromide, hexamethylene tetramine, tetraethyl ammonium bromide, tetrapropyl ammonium bromide or tetrabutyl ammonium bromide.

3. CO according to claim 1₂The preparation method of the epoxidation fixed catalyst is characterized in that the zinc salt in the step 1 is one or more of zinc nitrate, zinc chloride, zinc acetate, zinc perchlorate, zinc bromide or zinc sulfate.

4. CO according to claim 1₂The preparation method of the epoxidation fixed catalyst is characterized in that the solvent for washing in the step 1 is one or more of deionized water, methanol, ethanol or nitrogen-nitrogen dimethyl formamide.

5. CO according to claim 1₂The preparation method of the epoxidation fixed catalyst is characterized in that the calcination process in the step 1 is to adopt a temperature programming rate of 5 ℃/min to reach a target temperature in an air atmosphere.

6. CO according to claim 1₂The preparation method of the epoxidation fixed catalyst is characterized in that the organic solvent in the step 2 is one or more of methanol, ethanol, nitrogen-nitrogen dimethyl formamide, nitrogen-nitrogen diethyl formamide or tetrahydrofuran.

7. CO according to claim 1₂The preparation method of the epoxidation fixed catalyst is characterized in that the washing solution in the step 2 a) is one or more of methanol, ethanol, nitrogen-nitrogen dimethylformamide, nitrogen-nitrogen diethylformamide, dichloromethane, trichloromethane, tetrachloromethane or tetrahydrofuran; b) the washing solution adopted in the washing is one or more of deionized water, methanol, ethanol and nitrogen-nitrogen dimethyl formamide.

8. CO according to claim 1₂Preparation of epoxidation fixed catalystThe method is characterized in that the zinc salt in the step 2 is one or more of zinc nitrate, zinc chloride, zinc acetate, zinc perchlorate, zinc bromide or zinc sulfate.

9. CO according to claim 1₂The preparation method of the epoxidation fixed catalyst is characterized in that after a) and b) are circulated in the step 2, the epoxidation fixed catalyst is subjected to ZnWO reaction₄The surface of the metal organic structure is provided with a layer of metal organic structure, and the thickness of the layer of metal organic structure is equal to the distance between two zinc ions and different nitrogen atoms in 2 methylimidazole to form a stable structure.

10. CO produced by the process of claim 1₂Use of an epoxidation fixed catalyst, characterized in that the catalyst is capable of promoting CO₂And reacting with epoxy compound, wherein the epoxy compound is one or more of propylene oxide, epichlorohydrin, butylene oxide, styrene oxide, cyclohexene oxide and allyl glycidyl ether.