A Cr(III)-Salen-MOF heterogeneous catalyst and its application

Abstract

The present invention discloses a preparation method of a Cr(III)-Salen-MOF heterogeneous catalyst. This method uses 1,2-cyclohexanediamine and 5-carboxyl salicylaldehyde as raw materials, and reacts them at 70-80 °C in the presence of a solvent to synthesize a Salen complex; the Salen complex and anhydrous chromium dichloride are first reacted at room temperature in an N2 atmosphere in the presence of a solvent, and then reacted again in an air atmosphere to obtain a Cr(III)-Salen ligand. In the presence of a solvent, the Cr(III)-Salen ligand reacts with cadmium dichloride to obtain a Cr(III)-Salen-MOF catalyst; the catalyst is applied to catalyze the copolymerization reaction of SO2 and epoxides, and the yield of the product polysulfite reaches 97.8%, and the selectivity reaches 98.7%; the method of the present invention is simple, easy to operate, has mild reaction conditions and low energy consumption, and provides a new method and idea for developing environmentally friendly and highly efficient catalysts.

Description

Technical Field

[0001] The present invention belongs to the technical field of SO2 fixation, and specifically relates to the preparation of a Cr(III)-Salen-MOF heterogeneous catalyst and its application in the adsorption and catalysis of the copolymerization reaction of SO2 and epoxides. Background Art

[0002] With the rapid development of industry and the large consumption of fossil fuels, the concentration of SO2 in the atmosphere has been continuously increasing, leading to frequent human respiratory problems and the increasingly prominent emergence of a series of environmental problems such as acid rain. At present, there are mainly three ways to control SO2: controlling emissions at the source, capturing and storing, and absorption and conversion. Compared with the high-energy-consuming gas capture and storage technology, the resource utilization of SO2 can not only control the SO2 emission amount and effectively reduce its concentration, but also fix SO2 into value-added products and improve the SO2 utilization rate. At present, the reaction of SO2 and epoxides to convert into poly(sulfite) (PCS) with high industrial value is a green, economic and effective strategy. This measure will effectively relieve the pressure of the current serious pollution caused by SO2 to the environment and solve the problem of imperfect utilization of SO2 resources, so it is of great significance to obtain high-value-added materials.

[0003] In recent years, with the continuous in-depth research in the field of SO2 fixation technology by researchers, homogeneous metal-based catalysts such as alkali metal salt systems and transition metal complexes have now become the mainstream catalysts in the catalytic field. Although they show good catalytic performance in SO2 fixation, most of them have disadvantages such as difficult separation and recovery and easy resource waste. Therefore, the heterogeneousization of homogeneous metal-based catalyst reactions has been a direction that people have been exploring, and a series of heterogeneous catalysts have been developed for the fixation and catalysis of SO2, such as polymer polymers, mesoporous silica, magnetic particles, etc. However, most of these catalysts used have a cumbersome preparation process, harsh preparation conditions, are easy to decompose or denature, and cannot achieve green and sustainable development. Therefore, there is an urgent need for a catalyst that not only ensures high selectivity of the catalyst but also is environmentally friendly, which has become the research key.

[0004] Metal-organic frameworks (MOFs) have received extensive attention from researchers due to their adjustable porosity, diverse topological structures, and easy separation from reaction systems. Since metal ligands can incorporate different metal species into frameworks for specific purposes, when metal ions coordinate with carboxyl groups, the carbonyl and hydroxyl groups in the carboxyl groups react, and through the assistance of metal ions, the hydroxyl groups undergo a condensation reaction with the carbonyl groups to form coordination bonds of metal carboxylates, which can effectively prevent ligands from forming complexes with metals too quickly. In addition, by combining the rigidity of metal ligands, a stable network with permanent porosity can be constructed. Therefore, metal ligands are usually directly introduced as organic linkers to combine with inorganic metal nodes to realize the construction of crystalline porous materials MOFs with periodic network structures. The metal ligands selected are usually mixed ligands of nitrogen-containing heterocycles and carboxylic acids, which not only overcome the instability of neutral nitrogen-containing heterocyclic skeletons but also prevent the slow crystal growth caused by MOF crystals formed by strong acid dissolution. Under the synergistic effect of metal ligands and MOF frameworks, the catalytic performance is effectively improved, and there is great application potential in the field of catalysis. Summary of the Invention

[0005] The present invention provides a preparation method of a Cr(III)-Salen-MOF heterogeneous catalyst, which is specifically as follows:

[0006] 1. Using 1,2-cyclohexanediamine and 5-carboxylsalicylaldehyde as raw materials, reacting at 70 - 80 °C in the presence of a solvent for 1 - 5 h, performing solid-liquid separation, washing the solid repeatedly with deionized water, and drying it under vacuum at 40 - 60 °C for 8 - 24 h to obtain a Salen complex. The solvent for dissolving 1,2-cyclohexanediamine is an ethanol aqueous solution (volume ratio of ethanol to water is 5:1), and the solvent for dissolving 5-carboxylsalicylaldehyde is absolute ethanol; the molar ratio of 1,2-cyclohexanediamine to 5-carboxylsalicylaldehyde is 1:1 - 1:5;

[0007] 2. The Salen complex and anhydrous chromium dichloride first react at room temperature in an N2 atmosphere in the presence of a solvent (tetrahydrofuran) for 24 h, and then react in an air atmosphere for another 24 - 48 h. After the reaction is completed, first add diethyl ether to the reaction product, and then sequentially add saturated ammonium chloride solution and saturated sodium chloride solution for extraction and washing until the inorganic phase is clear. Collect the inorganic phase and dry it under vacuum at 40 - 50 °C to obtain a Cr(III)-Salen ligand; the molar ratio of the Salen complex to anhydrous CrCl2 is 1:1 - 1:5;

[0008] 3. In the presence of a solvent (dimethylformamide - water mixture), the Cr(III)-Salen ligand reacts with cadmium dichloride at 80 - 100 °C for 3 - 5 days. After filtration and washing with absolute ethanol, it is vacuum dried at 40 - 50 °C to obtain the Cr(III)-Salen-MOF heterogeneous catalyst. The molar ratio of the Cr(III)-Salen ligand to CdCl₂ is 1:1 - 1:10.

[0009] Another object of the present invention is to provide the Cr(III)-Salen-MOF heterogeneous catalyst prepared by the above method.

[0010] Another object of the present invention is the application of the Cr(III)-Salen-MOF heterogeneous catalyst in the adsorption and catalytic copolymerization of SO₂ and epoxide (CHO). The copolymerization reaction is carried out in a heat-collecting heating magnetic stirrer of a dynamic copolymerization device. The catalyst and CHO are put into an absorption bottle on the heating magnetic stirrer in a molar ratio of 1:100 - 1:2000. Industrial waste gas of SO₂ with a volume concentration of 2 - 8% is introduced into the absorption bottle through an inlet pipe, and the gas flow rate is 20 - 60m 3 / min. The reaction is carried out at 50 - 90 °C for 2 - 10 h. After the tail gas is treated by condensation and reflux, it is discharged. After the crude product is dissolved in dichloromethane and purified by methanol precipitation, it is vacuum dried at 30 - 50 °C for 4 - 8 h to obtain the copolymer product PCS.

[0011] The catalyst prepared by the present invention has a periodic network structure. Each network structure can be regarded as a microreactor for the adsorption and catalytic copolymerization of SO₂ gas. The copolymerization reaction can be completed in a heat-collecting heating magnetic stirrer of a dynamic copolymerization device; the preparation method of the present invention is simple, with low energy consumption, and has the characteristics of being not easily deactivated and being easily separated and recovered.

[0012] Compared with the prior art, the present invention has the following advantages:

[0013] (1) The heterogeneous catalyst (Cr(III)-Salen-MOF) prepared by the present invention has a simple preparation method, easy operation, mild reaction conditions, low energy consumption, and is easily separated and recovered;

[0014] (2) The heterogeneous catalyst (Cr(III)-Salen-MOF) prepared by the present invention can directly control the gas flow rate of industrial waste gas of SO₂ by using a dynamic copolymerization device and effectively adsorb the SO₂ component in the waste gas. By copolymerizing with epoxide to form a polymer with high added value, the resource utilization of SO₂ is achieved, and green industrial production is easily realized;

[0015] (3) The present invention takes into account both the adsorption of SO₂ gas and the catalytic copolymerization with epoxide;

[0016] (4) The present invention can be widely applied to the copolymerization reaction of catalytic SO2 and epoxides. The conversion rate of CHO monomer is as high as 98.9%, the content of sulfite units is 78.8%, and the PCS selectivity can also be as high as 97.7%. Description of the Drawings

[0017] Figure 1 X-ray photoelectron spectroscopy (XPS) diagram of the catalyst prepared in Example 1;

[0018] Figure 2 1H NMR spectrum of the poly(ethylene sulfite) formed by the copolymerization of SO2 and cyclohexene oxide catalyzed by the catalyst prepared in Example 1 in CDCl3 solvent 1 spectrum;

[0019] Figure 3 FTIR spectrum of the poly(ethylene sulfite) formed by the copolymerization of SO2 and cyclohexene oxide catalyzed by the catalyst prepared in Example 1;

[0020] Figure 4 Results of single-factor investigation of the Cr(III)-Salen-MOF catalyst applied to the copolymerization reaction of SO2 and cyclohexene oxide;

[0021] Figure 5 Results of single-factor investigation of the Cr(III)-Salen-MOF catalyst applied to the copolymerization reaction of SO2 and cyclohexene oxide;

[0022] Figure 6 Results of single-factor investigation of the Cr(III)-Salen-MOF catalyst applied to the copolymerization reaction of SO2 and cyclohexene oxide;

[0023] Figure 7 Results of the Cr(III)-Salen-MOF catalyst catalyzing different epoxides. Detailed Embodiments

[0024] The following examples and drawings are used to further illustrate the present invention in detail, but the protection scope of the present invention is not limited to the described content. Any other changes, modifications, substitutions, combinations, simplifications, etc. made without departing from the spirit and principle of the present invention are regarded as equivalent replacement methods and should be included in the protection scope of the present invention.

[0025] Example 1: Preparation and Application of Cr(III)-Salen-MOF Catalyst

[0026] (1) 0.025 mol of 1,2 - cyclohexanediamine, 50 mL of ethanol and 10 mL of deionized water were successively added into a 200 mL three - necked flask. The flask was placed on a constant - temperature heating magnetic stirrer. A reflux condenser and a constant - pressure dropping funnel were respectively placed on the three - necked flask. 0.050 mol of 5 - carboxylsalicylaldehyde was dissolved in 40 mL of absolute ethanol and then poured into the constant - pressure dropping funnel. Stir and heat up. When the reaction temperature rises to 75 °C, the 5 - carboxylsalicylaldehyde - ethanol solution was added dropwise. After reacting for 2 h, stop heating and add 75 mL of deionized water to the three - necked flask. After standing, filter with a sintered glass funnel. The obtained precipitate was washed repeatedly with deionized water 5 times to remove the unreacted salicylaldehyde. Then it was placed in a vacuum drying oven at 50 °C and vacuum - dried for 12 h to obtain the Salen complex. Take 0.05 mol of the dried Salen complex, dissolve it in 25 mL of tetrahydrofuran (THF), and pour it into a 100 mL three - necked flask. The flask was placed on a magnetic stirrer. Nitrogen was introduced into the flask through a gas - inlet tube assembled on the flask to remove the interference of oxygen in the air and create an inert reaction environment. After nitrogen was introduced for 0.5 h, 0.05 mol of anhydrous chromium dichloride (CrCl2) (the molar ratio of Salen complex:CrCl2 is 1:1) was added. First, stir and react under anaerobic conditions at room temperature for 24 h, then change to air and continue to stir for 24 h to form an oxygen - adduct. After the reaction is completed, stop stirring and add ether to the three - necked flask. Then transfer it to a separating funnel and successively add saturated ammonium chloride solution and saturated sodium chloride solution for extraction and washing until the inorganic phase is clear to remove the unreacted substrates completely. The organic phase was placed in a vacuum drying oven to remove the unreacted CrCl2 oxidized by air, the just - added ether and the solvent THF. After vacuum - drying at 40 °C for 12 h, the Cr(III) - Salen ligand was obtained;

[0027] Take 0.01 mol of Cr(III) - Salen ligand and 0.01 mol of cadmium dichloride (CdCl2), dissolve them in a mixed solvent of 3 mL of DMF and 1 mL of deionized water. After mixing evenly, pour it into the polytetrafluoroethylene liner of a 10 mL hydrothermal reactor. The reactor was placed in a forced - air drying oven and reacted at 80 °C for 4 days. After the reaction is completed, the obtained crude product was washed repeatedly with absolute ethanol 5 times. Finally, it was vacuum - dried at 40 °C for 24 h to obtain the Cr(III) - Salen - MOF catalyst. The X - ray photoelectron spectroscopy diagram of the catalyst is shown in Figure 1 , from which the doublet peaks of the metal active center chromium element coordinated with the ligand located at 575.7 eV and 585.5 eV can be seen. This data is consistent with the data in the XPS database. Therefore, it can be proved that the metal chromium is coordinated successfully, indicating the successful preparation of the catalyst.

[0028] (2) Copolymerization Experiment of SO2 and Cyclohexene Oxide Catalyzed by Cr(III)-Salen-MOF Catalyst

[0029] The copolymerization experiment of SO2 and cyclohexene oxide was carried out in a dynamic copolymerization device. First, turn on the circulating water pump. Add 0.0465 g of Cr(III)-Salen-MOF catalyst and 10 mL of cyclohexene oxide (molar ratio of catalyst to cyclohexene oxide is 1:1000) into the absorption bottle in sequence. Place the absorption bottle on a heating magnetic stirrer with a collecting heat function, and make the catalyst and cyclohexene oxide evenly mixed under stirring. Set the reaction temperature at 70 °C. Open the pressure relief valve, and pass the industrial waste gas containing 2% (volume concentration) of SO2 through an electronic flow controller into the inlet pipe of the absorption bottle at a flow rate of 60 m 3 / min. Contact and react with the mixture of the catalyst and cyclohexene oxide in the form of bubbling. Under the action of the catalyst, cyclohexene oxide and SO2 carry out copolymerization reaction in the absorption bottle. After 6 h of reaction, stop the ventilation and end the reaction. The tail gas is discharged after being condensed and refluxed through a condenser tube to prevent the volatilization of epoxides. Then take out the absorption bottle. The obtained crude product is first dissolved in dichloromethane, and then the dissolved mixed solution is poured into a beaker. Add methanol to wash the by-product cyclic sulfite, and at the same time, a precipitate is generated. The obtained precipitate is vacuum dried at 40 °C for 6 h to obtain the copolymer product of SO2 and cyclohexene oxide, poly(cyclohexylene sulfite) (PCS). Using deuterated chloroform (CDCl3) as the solvent, nuclear magnetic resonance (NMR) characterization was carried out on the product ( Figure 2 ). Through the peak integration method, the monomer conversion rate of CHO, the content of sulfite units, and the selectivity of PCS were calculated according to the integral area. According to this algorithm, the monomer conversion rate of CHO was calculated to be 98.9%, the content of sulfite units was 78.8%, and the selectivity of PCS was 97.7%; The FTIR spectrum of poly(cyclohexylene sulfite) is shown in Figure 3 . It can be seen from the figure that the C-O bond at 838 cm -1 and the C-H bond at 2988 cm -1 disappeared, and new S-O, C-O-S, and S=O bonds at 726 cm -1 , 983 cm -1 and 1203 cm -1 were generated. Thus, it can be proved that poly(cyclohexylene sulfite) was formed.

[0030] At the same time, copolymerization reactions were carried out according to the molar ratios of catalyst:cyclohexene oxide of 1:100, 1:500, 1:1500, and 1:2000, and the results are shown in Figure 4 ;

[0031] (3) The copolymerization experiment of SO2 and cyclohexene oxide catalyzed by the Cr(III)-Salen-MOF catalyst in step (1) was the same as that in step (2), except that the reaction temperatures were 50 °C, 60 °C, 80 °C, and 90 °C. The results are shown in Figure 5 ;

[0032] (4) The copolymerization experiment of SO2 and cyclohexene oxide catalyzed by the Cr(III)-Salen-MOF catalyst in step (1) was the same as that in step (2), except that the reaction times were 2 h, 4 h, 8 h, and 10 h. The results are shown in Figure 6 ;

[0033] (5) The copolymerization reactions of SO2 with methyloxirane, epichlorohydrin, 1,2-epoxybutane, and styrene oxide catalyzed by the Cr(III)-Salen-MOF catalyst in step (1). The results are shown in Figure 7 . Example 2

[0034] (1) Preparation of the Cr(III)-Salen-MOF catalyst

[0035] Preparation of Cr(III)-Salen ligand: 0.05 mol of 1,2-cyclohexanediamine, 50 mL of ethanol and 10 mL of deionized water were successively added into a 200 mL three-necked flask. The flask was placed on a thermostatic heating magnetic stirrer, and a reflux condenser and a constant-pressure dropping funnel were respectively placed on the three-necked flask. 0.05 mol of 5-carboxyl salicylaldehyde (the molar ratio of 1,2-cyclohexanediamine to 5-carboxyl salicylaldehyde was 1:1) was dissolved in 40 mL of ethanol and then poured into the constant-pressure dropping funnel. Then, the temperature was raised and stirring was started. When the reaction temperature reached 70 °C, the 5-carboxyl salicylaldehyde / ethanol solution was added dropwise. After reacting for 3 h, heating was stopped, and 75 mL of deionized water was added to the three-necked flask. After standing, it was filtered with a sintered glass funnel. The obtained precipitate was washed repeatedly with deionized water 5 times to remove the unreacted salicylaldehyde. Subsequently, it was placed in a vacuum drying oven at 45 °C and vacuum dried for 18 h to obtain the Salen complex. 0.05 mol of the dried Salen complex was dissolved in 25 mL of tetrahydrofuran (THF) and then poured into a 100 mL three-necked flask. The flask was placed on a magnetic stirrer. Nitrogen was introduced into the flask through a gas pipe assembled on the flask to remove the interference of oxygen in the air and create an inert reaction environment. After nitrogen was introduced for 1 hour, 0.15 mol of anhydrous chromium dichloride (CrCl2) (the molar ratio of Salen complex to CrCl2 was 1:3) was added. It was first stirred under anaerobic conditions at room temperature for 18 h, and then air was used to continue stirring for 18 h to form an oxygen adduct. After the reaction was completed, stirring was stopped, and ether was added to the three-necked flask. Subsequently, it was transferred to a separating funnel, and saturated ammonium chloride and saturated sodium chloride solutions were successively added for extraction and washing until the inorganic phase was washed to clarity to remove the unreacted substrates. The organic phase was placed in a vacuum drying oven to remove the unreacted CrCl2 oxidized by air, the just-added ether and the solvent THF. After vacuum drying at 50 °C for 18 h, the Cr(III)-Salen ligand was obtained.

[0036] Preparation of Cr(III)-Salen-MOF catalyst: 0.01 mol of the prepared Cr(III)-Salen ligand and 0.05 mol of cadmium dichloride (CdCl2) (the molar ratio of Cr(III)-Salen ligand to CdCl2 was 1:5) were dissolved in a mixed solvent of 3 mL of DMF and 1 mL of deionized water. After mixing evenly, it was poured into the polytetrafluoroethylene inner liner of a 10 mL hydrothermal reaction kettle. The reaction kettle was placed in a forced-air drying oven and reacted at 90 °C for 3 days. After the reaction was completed, the obtained crude product was washed repeatedly with ethanol 5 times to remove the unreacted carboxylic acid. Finally, it was vacuum dried at 50 °C for 18 h to obtain the Cr(III)-Salen-MOF catalyst.

[0037] (2) Experiment on copolymerization of SO2 and epichlorohydrin catalyzed by Cr(III)-Salen-MOF

[0038] The copolymerization experiment of SO2 and epichlorohydrin was carried out in a dynamic copolymerization device. First, the circulating water pump was started. 0.0183 g of Cr(III)-Salen-MOF catalyst and 10 mL of epichlorohydrin (the molar ratio of catalyst to epichlorohydrin was 1:500) were successively added into the absorption flask. The absorption flask was placed on a heating magnetic stirrer with a collector, and the catalyst and epichlorohydrin were evenly mixed under stirring. The reaction temperature was set at 60 °C. The unprocessed industrial waste gas containing 5% SO2 was passed through an electronic flow controller and entered from the inlet pipe of the absorption flask at a flow rate of 40 m 3 / min. It contacted and reacted with the mixture of the catalyst and epichlorohydrin in the form of bubbling. Under the action of the catalyst, epichlorohydrin and SO2 underwent a copolymerization reaction in the absorption flask. After 8 h of reaction, the ventilation was stopped and the reaction ended. The tail gas was discharged after being condensed and refluxed by a condenser to prevent the volatilization of epoxides. Then the absorption flask was taken out. The obtained crude product was first dissolved in dichloromethane, and then the dissolved mixture was poured into a beaker. Methanol was added to wash the by-product cyclic sulfite, and at the same time, a precipitate was generated. The obtained precipitate was vacuum dried at 30 °C for 8 h to obtain the copolymer product PCS of SO2 and epichlorohydrin. The copolymer product was characterized by nuclear magnetic resonance (NMR) using deuterated chloroform (CDCl3) as a solvent. By the peak integration method, the monomer conversion rate of CHO in epichlorohydrin, the content of sulfite units, and the selectivity of PCS were calculated according to the integration area. According to this algorithm, the monomer conversion rate of CHO was 93.6%, the content of sulfite units was 68.2%, and the selectivity of PCS was 79.7%. Example 3

[0039] (1) Preparation of Cr(III)-Salen-MOF catalyst

[0040] Preparation of Cr(III)-Salen ligand: 0.025 mol of 1,2-cyclohexanediamine, 50 mL of ethanol and 10 mL of deionized water were successively added to a 200 mL three-necked flask. The flask was placed on a magnetic stirrer with constant temperature heating. A reflux condenser and a constant pressure dropping funnel were respectively placed on the three-necked flask. 0.100 mol of 5-carboxyl salicylaldehyde (the molar ratio of 1,2-cyclohexanediamine to 5-carboxyl salicylaldehyde was 1:4) was dissolved in 40 mL of ethanol and then poured into the constant pressure dropping funnel. Then the temperature was raised and stirred. When the reaction temperature reached 80 °C, the 5-carboxyl salicylaldehyde / ethanol solution was added dropwise. After reacting for 1 h, the heating was stopped, and 75 mL of deionized water was added to the three-necked flask. After standing, it was filtered with a sintered glass funnel. The obtained precipitate was washed repeatedly with deionized water 5 times to remove the unreacted salicylaldehyde. Subsequently, it was placed in a vacuum drying oven at 60 °C and vacuum dried for 8 h to obtain the Salen complex. 0.05 mol of the dried Salen complex was dissolved in 25 mL of tetrahydrofuran (THF) and then poured into a 100 mL three-necked flask. The flask was placed on a magnetic stirrer. Nitrogen was introduced into the flask through a gas pipe assembled on the flask to remove the interference of oxygen in the air and create an inert reaction environment. After nitrogen was introduced for 0.75 h, 0.10 mol of anhydrous chromium dichloride (CrCl2) (the molar ratio of Salen complex to CrCl2 was 1:2) was added. It was first stirred under anaerobic conditions at room temperature for 20 h and then stirred with air for another 20 h to form an oxygen adduct. After the reaction was completed, the stirring was stopped, and ether was added to the three-necked flask. Then it was transferred to a separating funnel, and saturated ammonium chloride and saturated sodium chloride solutions were successively added for extraction and washing until the inorganic phase was washed to clarity to remove the unreacted substrate completely. The organic phase was placed in a vacuum drying oven to remove the unreacted CrCl2 oxidized by air, the just-added ether and the solvent THF. After vacuum drying at 45 °C for 16 h, the Cr(III)-Salen ligand was obtained.

[0041] Preparation of Cr(III)-Salen-MOF catalyst: 0.01 mol of the prepared Cr(III)-Salen ligand and 0.03 mol of cadmium dichloride (CdCl2) (the molar ratio of Cr(III)-Salen ligand to CdCl2 was 1:3) were dissolved in a mixed solvent of 3 mL of DMF and 1 mL of deionized water. After mixing evenly, it was poured into the polytetrafluoroethylene liner of a 10 mL hydrothermal reaction kettle. The reaction kettle was placed in a blast drying oven and reacted at 100 °C for 3 days. After the reaction was completed, the obtained crude product was washed repeatedly with ethanol 5 times to remove the unreacted carboxylic acid. Finally, it was vacuum dried at 45 °C for 20 h to obtain the Cr(III)-Salen-MOF catalyst.

[0042] (2)Cr(III)-Salen-MOF Catalyzed Copolymerization Experiment of SO2 and Styrene Oxide

[0043] The copolymerization experiment of SO2 and styrene oxide was carried out in a dynamic copolymerization device. First, turn on the circulating water pump. Add 0.0119 g of Cr(III)-Salen-MOF catalyst and 10 mL of styrene oxide (the molar ratio of catalyst to styrene oxide is 1:1000) into the absorption bottle in sequence. Place the absorption bottle on a thermostatic heating magnetic stirrer to uniformly mix the catalyst and styrene oxide under stirring. Set the reaction temperature at 80 °C. Open the pressure relief valve and pass the untreated 8% SO2 industrial waste gas through the electronic flow controller at a flow rate of 20 m 3 / min into the absorption bottle through the inlet pipe, and contact and react with the mixture of the catalyst and styrene oxide by bubbling. Under the action of the catalyst, styrene oxide and SO2 undergo copolymerization reaction in the absorption bottle. After 4 h of reaction, stop the ventilation and end the reaction. The tail gas is discharged after being condensed and refluxed through a condenser to prevent the volatilization of epoxides. Then take out the absorption bottle. The obtained crude product is first dissolved in dichloromethane, and then the dissolved mixture is poured into a beaker. Add methanol to wash the by-product cyclic sulfite, and at the same time, a precipitate is generated. The obtained precipitate is vacuum dried at 50 °C for 4 h to obtain the copolymer product PCS of SO2 and styrene oxide. The copolymer product uses deuterated chloroform (CDCl3) as a solvent, and the product is characterized by nuclear magnetic resonance (NMR). Through the peak integration method, the monomer conversion rate of CHO in styrene oxide, the content of sulfite units, and the selectivity of PCS are calculated according to the integral area. According to this algorithm, the monomer conversion rate of CHO is 87.4%, the content of sulfite units is 60.8%, and the selectivity of PCS is 68.2%.

Claims

1. A preparation method of a Cr(III)-Salen-MOF heterogeneous catalyst, characterized in that: Using 1,2-cyclohexanediamine and 5-carboxylsalicylaldehyde as raw materials, a Salen complex was synthesized by reacting at 70 - 80 °C in the presence of a solvent; the Salen complex and anhydrous chromium dichloride were first reacted at room temperature under a N2 atmosphere in the presence of a solvent for 18 - 24 h, and then reacted for another 18 - 24 h under an air atmosphere to obtain a Cr(III)-Salen ligand. In the presence of a solvent, the Cr(III)-Salen ligand and cadmium dichloride were reacted at 80 - 100 °C for 3 - 5 days. After filtration and washing with absolute ethanol, it was vacuum dried at 40 - 50 °C to obtain a Cr(III)-Salen-MOF catalyst; The molar ratio of the 1,2-cyclohexanediamine to the 5-carboxylsalicylaldehyde is 1:1 - 1:5; the molar ratio of the Salen complex to the anhydrous chromium dichloride is 1:1 - 1:5; the molar ratio of the Cr(III)-Salen ligand to CdCl2 is 1:1 - 1:

10.

2. The Cr(III)-Salen-MOF heterogeneous catalyst prepared by the preparation method of the Cr(III)-Salen-MOF heterogeneous catalyst described in claim 1.

3. The application of the Cr(III)-Salen-MOF heterogeneous catalyst described in claim 2 in the adsorption-catalyzed copolymerization reaction of SO2 and epoxides.

4. The application according to claim 3, characterized in that: The epoxides include cyclohexene oxide, methyl epoxide, epichlorohydrin, 1,2-epoxybutane, and styrene oxide.

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