Preparation method and application of composite catalyst for preparing carbon dioxide-based polycarbonate

Abstract

The invention discloses a preparation method and application of a composite catalyst for preparing carbon dioxide-based polycarbonate, and belongs to the technical field of catalysts, and the composite catalyst is a binary catalytic system obtained by combining double metal cyanide and activated zinc carboxylate according to a certain proportion. After zinc carboxylate is activated by water or ethanol, the catalytic activity is greatly improved. The activity of the composite catalyst for catalyzing ring-opening copolymerization of carbon dioxide and epoxypropane is greater than 1500g polymer / g catalyst, the number-average molecular weight of the obtained product polycarbonate is greater than 150,000, and the selectivity is greater than 98%. Compared with single use of double metal cyanide or zinc carboxylate, the composite catalyst has remarkable advantages, and is simple in synthesis process, relatively low in cost and very suitable for industrial production of carbon dioxide-based polycarbonate.

Description

Technical Field

[0001] The invention belongs to the technical field of catalysts, and in particular relates to a preparation method and application of a composite catalyst for preparing carbon dioxide-based polycarbonate. Background Art

[0002] As the main greenhouse gas, carbon dioxide is an abundant and cheap C1 resource. Considering the rapid development of industry and the increasingly serious problem of global warming, the fixation of carbon dioxide into chemical products has attracted widespread interest in academia and industry. With carbon dioxide as the main reaction raw material, the chemical products synthesized include urea, methanol, acrylate, dimethyl carbonate, cyclocarbonate and polycarbonate. Among them, the conversion of carbon dioxide into polycarbonate is a reaction with high atomic utilization rate. Some alkylene oxide monomers can be prepared by conversion from plant extracts and are renewable resources. Considering the non-renewable nature of petroleum resources, carbon dioxide-based polycarbonate has received increasing attention as a resource-renewable biodegradable material in recent decades. Compared with other biodegradable plastics, such as polylactic acid and polybutene-succinate, carbon dioxide-based polycarbonate has lower raw material costs and milder processing conditions, and has commercial potential in the field of packaging or agricultural films.

[0003] The copolymerization of carbon dioxide and epoxide can be traced back to 1969, when Inoue pioneered the use of diethyl zinc / water system to successfully catalyze the copolymerization of carbon dioxide / propylene oxide (CO2 / PO) to produce polycarbonate (Journal of Polymer Science Part B: Polymer Physics, 1969, 7(4): 287-292). The catalytic activity of this catalytic system was low, only 13.4 g polymer / g catalyst (g poly / g cat), and the carbonate unit content of the copolymer was 88%. With the gradual deepening of the catalyst structure and polymerization mechanism, many catalysts with excellent performance have been developed one after another.

[0004] Except for the newly discovered metal-free organoboron system in recent years, the catalysts used to catalyze the copolymerization of CO2 and epoxides are basically organometallic compounds and metal complexes. For commercial applications, the catalyst must be active, non-toxic and colorless in order to be retained in the resulting polymer product, which is one of the prerequisites for achieving continuous production. In these aspects, zinc has huge advantages over other transition metals. It not only has high catalytic activity, but is also an economical and environmentally friendly metal that can provide ions that will not produce colored polymer products. At present, the catalysts used in the CO2-to-aliphatic polycarbonate projects that have been industrialized in my country are mainly zinc catalysts.

[0005] The patents of metal-free organoboron catalysts in China mainly come from the team of Meng Yuezhong of Sun Yat-sen University, such as CN111378101A, CN113929890A and CN111333825A. Although the polypropylene carbonate (PPC) synthesized by this catalyst has a high glass transition temperature and high tensile strength, it generally has the disadvantage of being significantly lower in molecular weight than PPC synthesized by other catalysts. Taking CN111378101A as an example, the highest number average molecular weight (Mn) of the polymer synthesized by metal-free organoboron catalysis is only 102.8×10 3 In addition, the catalyst has a relatively low conversion rate for epoxides. At present, the industrialization of aliphatic polycarbonate using metal-free organic boron as a catalyst has not yet been realized. Lianxin Technology's Taixing 25,000 tons / year CO2-based biodegradable plastic project is under construction.

[0006] Double metal cyanide (DMC) catalyst was first reported by General Tire and Rubber Company in the United States in the 1960s. In 1983, Kruper et al. applied for a patent (US4500704A) on Zn3[Co(CN)6]2·DME·6H2O / ZnSO4 for catalytic CO2 / PO copolymerization. DMC catalyst synthesized by precipitation reaction of potassium hexacyanocobaltate (K3[Co(CN)6]) and excess zinc chloride (ZnCl2) is suitable for CO2 / PO copolymerization (AppliedCatalysis A: general, 2007, 325(1): 91-98).

[0007] Chinese patent application CN110964192A reported a mixed acid modified double metal cyanide catalyst. The catalyst of this invention has high activity and strong thermal stability, but the conversion rate (≤90%) and molecular weight (Mn is 60.5×10 3 ) and the proportion of by-product cyclic carbonate (CPC) (≥9%) are not ideal. CN114736365A reported the use of metal cyanide and water-soluble metal zinc salt solution in CO2 atmosphere to achieve catalyst powders with different sizes and uniform size. CN116410454A reported a surface organic double metal cyanide catalyst. Both can greatly improve the catalytic activity, but the molecular weight of the copolymer product (Mn < 200×10 3 ) still needs to be improved. Zn-Co DMC generally exhibits problems of low CO2 insertion rate and insufficient molecular weight in catalyzing CO2 / PO copolymerization.

[0008] Zinc carboxylates are traditional catalysts for CO2 / epoxide ring-opening polymerization. In 1981, Soga et al. prepared zinc dicarboxylic acid complexes for the first time by reacting zinc hydroxide or zinc oxide (ZnO) with dicarboxylic acids in toluene (Polymer Journal, 1981, 13(4): 407-410). Among them, zinc glutarate (ZnGA) showed the highest catalytic activity for CO2 / epoxide copolymerization. In 1999, Ree et al. investigated the effect of different zinc sources on ZnGA-catalyzed copolymerization (Journal of Polymer Science Part A: Polymer Chemistry, 1999, 37(12): 1863-1876). The results showed that ZnGA synthesized with ZnO as the zinc source had a relatively low surface area and high crystallinity. The yield of ZnGA was greater than 98%, the highest activity was 70.0 g poly / g cat, and the Mn of the product PPC was 210.0×10 3 In 2022, Jang et al. used H3[Co(CN)6] to activate 2D ZnGA, and the activity of ZnGA was increased to 855 g poly / g cat, which is the most active ZnGA system reported so far (Dalton Transactionsactions, 2022, 51(43): 16620-16627). The carbonate unit content of the product was 61%, and Mn was 72.6×10 3 , polymer selectivity is 82%, and glass transition temperature is 20 ℃. Although the activity is significantly improved, the carbonate unit content of the product is significantly reduced compared with the ZnGA catalyst before activation. It is worth noting that cyanide has a positive effect on the improvement of ZnGA activity.

[0009] There are many patents on zinc carboxylate systems in China, a large part of which comes from Wang Xianhong's team at the Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, such as CN105418907A, CN113683764A and CN112358607A. Taking CN105418907A as an example, the highest Mn of the product obtained by catalyzing CO2 / PO ring-opening copolymerization is 290×10 3 However, the highest catalytic activity is only 151 g poly / g cat. ZnGA has the problems of low activity and wide molecular weight distribution of products in catalyzing CO2 / PO copolymerization.

[0010] The combination of ZnGA and other catalysts can effectively improve the catalytic activity of ZnGA and improve product performance. China's patent application CN101979424A uses DMC and zinc carboxylate catalysts in a composite, trying to combine the advantages of the two catalysts. DMC catalyst can shorten the induction period of zinc carboxylate catalysts, improve catalytic efficiency, and increase the conversion rate of epoxides. The addition of zinc carboxylate catalysts can increase the molecular weight and CO2 insertion rate of the polymer product and reduce the generation of byproduct CPC. The catalytic activity of the composite system (<600 g poly / g cat) and molecular weight (Mn is 60.5×10 3 ) cannot yet meet the needs of industrial production. Summary of the invention

[0011] In view of the shortcomings of the prior art, the present invention provides a preparation method and application of a composite catalyst for preparing carbon dioxide-based polycarbonate, and the method can realize the preparation of a binary composite catalyst composed of a double metal cyanide and an activated zinc carboxylate. After the zinc carboxylate is activated with water or ethanol, the catalytic activity is greatly improved. The composite catalyst can realize the ring-opening copolymerization of carbon dioxide and propylene oxide with high activity to synthesize high molecular weight polypropylene carbonate.

[0012] To achieve the above object, the present invention provides the following technical solutions: The present invention provides a method for preparing a composite catalyst for preparing carbon dioxide-based polycarbonate, comprising the following steps: The soluble divalent metal halide salt M1X2 is prepared into a solution with a mass ratio concentration of 0.1~20%, and the solvent is a mixed solution of organic solvent B1 and water in a volume ratio of 1:1. It is heated to 30~60 ℃, and then the aqueous solution containing M2[M3(CN)6] is slowly added dropwise. After completion, it is vigorously stirred at 30~60 ℃ for 1~12 h. The obtained white suspension is redispersed in a solution of B1 and water (volume ratio of 1:1), and centrifuged for 1~30 min at a speed of 1000~10000 rpm. Adjust the volume ratio of B1 and water, gradually increase the proportion of B1, and centrifuge for 1~30 min at a speed of 1000~10000 rpm. Finally, the white precipitate is washed in pure B1, centrifuged for 1~30 min at a speed of 1000~10000 rpm, and the white precipitate obtained by centrifugation is dried under vacuum at 60~100 ℃ for 12~48 h. The dried solid is ground into powder to obtain a double metal cyanide catalyst. Carboxylic acid C is mixed with an equimolar amount of zinc oxide or zinc acetate to form a solution with a mass ratio concentration of 0.1-20%, and the solvent is organic solvent B2. The solution is heated to 50-100 °C, the rotation speed is 1000-4000 rpm, and the reaction is carried out for 6-24 hours. The obtained product is centrifuged at a speed of 1000-6000 rpm, and the white solid precipitate obtained by centrifugation is dissolved in organic solvent B1 for washing. After repeating the above step 3 times, the product is dried in a vacuum drying oven at 50-100 °C for 12-48 hours. The dried solid is ground into powder, dissolved in a certain amount of water or ethanol, and stirred into a slurry. Dry in a vacuum drying oven at 100-120 °C for 12-48 hours. The dried solid is ground into powder to obtain an activated zinc carboxylate catalyst. The synthesized double metal cyanide catalyst and the activated zinc carboxylate catalyst are mixed in a molar ratio of 1:1 to 50 to prepare a solution with a mass concentration of 0.1 to 20%, wherein the solvent is an organic solvent B2, and the solution is heated to 50 to 80 °C, stirred vigorously for 6 to 24 hours, and then centrifuged for 1 to 30 minutes at a speed of 1000 to 10000 rpm, and washed several times with organic solvent B1. The obtained white solid is dried in a vacuum drying oven at 80 to 100 °C for 12 to 48 hours. The dried solid is ground into powder to obtain the double metal cyanide / activated zinc carboxylate composite catalyst.

[0013] Furthermore, the metal M1 is one or more of zinc, cadmium, iron, cobalt, nickel, chromium and copper.

[0014] Furthermore, the metal M2 is one or more of potassium, sodium and lithium.

[0015] Furthermore, the metal M3 is one or more of iron, cobalt, nickel, manganese, molybdenum, chromium, tin, aluminum, vanadium, and copper.

[0016] Furthermore, the organic solvent B1 is one or more of acetone, methyl ethyl ketone, methyl propyl ketone, ethylene glycol, isopropanol, n-butanol, isobutanol, tert-butanol, glycol dimethyl ether, diglycol dimethyl ether, ethylene glycol methyl ether, or one or more of their derivatives.

[0017] Furthermore, the organic solvent B2 is one or more of cyclohexane, methylcyclohexane, toluene, polyether, polysulfide, polyethylene glycol, polypropylene glycol, polyethylene glycol-polypropylene glycol-polyethylene glycol, polyformaldehyde, polyester, polyamide, polyvinyl alcohol, or one or more of their derivatives.

[0018] Furthermore, the carboxylic acid C is one or more of succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, terephthalic acid, phthalic acid, isophthalic acid, or one or more of their derivatives.

[0019] The present invention also provides the use of the composite catalyst prepared by the above method in synthesizing carbon dioxide-based polycarbonate, comprising the following steps: Before the start of the copolymerization reaction, the feed pipeline was cleaned several times and the pipeline was dried to remove residual solvent. A composite catalyst with a mass of 0.01-5% of the mass of the reaction monomer epoxide was added to the autoclave, and then the reactor was kept in a closed state. The reactor was heated to 60-100 °C. Then, carbon dioxide was introduced and discharged very slowly, and the air in the autoclave was continuously replaced with carbon dioxide for 1-12 h. When the autoclave was cooled to room temperature, the entry and exit of carbon dioxide was stopped. The vacuum pump was turned on and the reactor was evacuated with a vacuum pump to a pressure of -0.1 MPa. Then a certain amount of reaction monomer epoxide was added, and carbon dioxide was introduced to maintain the pressure at 1-5 MPa. The reaction was continued for 12-36 h at a temperature of 50-100 °C and a stirring speed of 100-1000 rpm. After the reaction was completed, the reactor was cooled to 5-20 °C and the unreacted carbon dioxide was slowly released. Then the reactor was opened, and a small amount of crude product sample was quickly taken out and dissolved in deuterated chloroform for further nuclear magnetic characterization. Subsequently, a small amount of 5% hydrochloric acid in ethanol solution was added to the reactor to terminate the reaction. The crude product was dissolved in dichloromethane and then precipitated in ethanol to precipitate a white flocculent product. The product was allowed to stand for a period of time and the supernatant was removed. The product was placed in a vacuum drying oven and dried to constant weight under vacuum conditions at 50 °C.

[0020] Compared with the prior art, the present invention has the following beneficial effects: The zinc carboxylate catalyst is modified by water or ethanol to optimize the catalytic performance of zinc carboxylate. Taking zinc glutarate as an example, after being activated by water or ethanol, water or ethanol is a component of the zinc glutarate crystal, which plays an important role in its catalytic activity. The active center of zinc glutarate is Zn-OH species. The difference in activity between the zinc glutarate catalyst before and after activation in the ring-opening copolymerization experiment of carbon dioxide and propylene oxide is due to the fact that the introduction of water and ethanol reduces the particle size of the catalyst, increases the surface area of ​​the catalyst, the crystallinity of the catalyst and the number of Zn-OH species in the active center. A double metal cyanide catalyst is introduced into the activated zinc glutarate catalyst to synthesize a composite catalyst. The active centers of the two raw materials of the catalyst are both Zn-OH species. The composite catalyst is used to catalyze the ring-opening copolymerization of carbon dioxide and propylene oxide, with an activity greater than 1500 g polymer / g catalyst, and the number average molecular weight of the resulting polycarbonate is greater than 150,000, and the selectivity is greater than 98%. The method is simple and easy to operate, low cost, and has good experimental repetition stability, and is very suitable for industrial large-scale application of carbon dioxide-based polycarbonate. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0022] Figure 1 This is the XRD diagram of the double metal cyanide / activated zinc carboxylate (zinc glutarate with zinc acetate as the zinc source) composite catalyst provided in Example 1 of the present invention.

[0023] Figure 2 This is the infrared spectrum of the double metal cyanide / activated zinc carboxylate (zinc glutarate with zinc acetate as the zinc source) composite catalyst provided in Example 1 of the present invention. DETAILED DESCRIPTION

[0024] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0025] It should be understood that the terms described in the present invention are only for describing special embodiments and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. Each smaller range between the intermediate value in any stated value or stated range and any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0026] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0027] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to those skilled in the art. The present application description and examples are exemplary only.

[0028] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0029] Example 1: Preparation of double metal cyanide / activated zinc carboxylate composite catalyst 3.2348 g (49.0 mmol) of glutaric acid and 2.0343 g (50.0 mmol) of zinc oxide were added to a 250 mL Schlenk container, and 150 mL of toluene was added. The device was placed in an oil bath, the temperature was set to 70 °C, the speed was set to 1800 rpm, and the reaction was carried out for 15 h. The obtained product was centrifuged at a speed of 6000 rpm, and the white solid precipitate obtained by centrifugation was dissolved in acetone for washing. Repeat the above step 3 times. Finally, the product was dried in a vacuum drying oven at 80 °C for 30 h. The dried solid zinc glutarate (with zinc oxide as the zinc source) was ground into powder, dissolved in a certain amount of water, and stirred into a slurry. Dry in a vacuum drying oven at 120 °C for 30 h. Take the dried solid, that is, the activated zinc glutarate (with zinc oxide as the zinc source) catalyst, grind it into powder, and store it in a sealed desiccator.

[0030] 3.2253 g (49.0 mmol) of glutaric acid and 4.5922 g (50.0 mmol) of zinc acetate were added to a 250 mL Schlenk container, and 150 mL of toluene was added. The device was placed in an oil bath, the temperature was set to 70 °C, the speed was set to 1800 rpm, and the reaction was carried out for 15 h. The obtained product was centrifuged at a speed of 6000 rpm, and the white solid precipitate obtained by centrifugation was dissolved in acetone for washing. Repeat the above step 3 times. Finally, the product was dried in a vacuum drying oven at 80 °C for 30 h. The dried solid zinc glutarate (with zinc acetate as the zinc source) was ground into powder, dissolved in a certain amount of water, and stirred into a slurry. Dry in a vacuum drying oven at 120 °C for 30 h. Take the dried solid, that is, the activated zinc glutarate (with zinc acetate as the zinc source) catalyst, grind it into powder, and store it in a sealed desiccator.

[0031] Solution 1 was prepared by dissolving 10.1034 g potassium hexacyanocobaltate in 50 mL water. Solution 2 was prepared by dissolving 39.9835 g zinc chloride in a mixture of 100 mL water and 100 mL tert-butyl alcohol. Solution 1 was slowly added dropwise to solution 2 at 45 °C with vigorous stirring. After the addition was completed, the mixture was vigorously stirred at 45 °C for 6 h. The resulting white suspension was redispersed in a solution of tert-butyl alcohol and water (1:1 by volume) and centrifuged for 10 min at 6000 rpm. The volume ratios of tert-butyl alcohol and water were adjusted to 6:4, 7:3, 8:2, and 9:1, respectively, and centrifuged. Finally, the white precipitate was washed in pure tert-butyl alcohol and then centrifuged for 10 min at 6000 rpm. The white precipitate obtained by centrifugation was dried under vacuum at 80 °C for 30 h. 29.1147 g of white solid, namely double metal cyanide catalyst, was obtained, which was ground into powder and sealed in a desiccator.

[0032] 0.3005 g of double metal cyanide catalyst and 0.9005 g of zinc glutarate (with zinc oxide as zinc source) catalyst were introduced into a 250 mL round-bottom flask filled with 150 mL of toluene and stirred vigorously at 60 °C for 18 h. After that, the precipitate was centrifuged and washed three times with 100 mL of acetone. The resulting white suspension was dried in a vacuum oven at 100 °C for 30 h, and the dried solid was ground into powder to obtain a double metal cyanide / activated zinc carboxylate (zinc glutarate with zinc oxide as zinc source) composite catalyst, which was sealed and stored in a desiccator.

[0033] 0.3019 g of double metal cyanide catalyst and 0.9041 g of zinc glutarate (with zinc acetate as zinc source) catalyst were introduced into a 250 mL round-bottom flask filled with 150 mL of toluene and stirred vigorously at 60 °C for 18 h. After that, the precipitate was centrifuged and washed three times with 100 mL of acetone. The resulting white suspension was dried in a vacuum oven at 100 °C for 30 h, and the dried solid was ground into powder to obtain a double metal cyanide / activated zinc carboxylate (zinc glutarate with zinc acetate as zinc source) composite catalyst, which was sealed and stored in a desiccator.

[0034] The XRD pattern obtained in this embodiment is as follows Figure 1 As shown, the double metal cyanide / activated zinc carboxylate (zinc glutarate with zinc acetate as zinc source) composite catalyst exhibits a unique crystal structure, significant characteristic peaks (at 2θ=12.7, 22.5, 23.0, 13.3 and 18.1, etc.) and good crystallinity and crystal quality, indicating that the double metal cyanide catalyst was successfully introduced into the zinc glutarate catalyst, and the composite catalyst inherited the crystal structure of the double metal cyanide catalyst and the zinc glutarate catalyst.

[0035] The infrared spectrum obtained by the test in this embodiment is as follows Figure 2 As shown, at 1405 cm -1 、1585 cm -1 、1537 cm -1 、1447 cm -1 、2955 cm -1 、1720 cm -1 and 2200-2190 cm -1 At the same position, the double metal cyanide / activated zinc carboxylate (zinc glutarate with zinc acetate as zinc source) composite catalyst showed significant characteristic peaks. This shows that the composite catalyst has the characteristic functional groups of the double metal cyanide catalyst and the water-activated zinc glutarate catalyst. The double metal cyanide catalyst was successfully introduced into the water-activated zinc glutarate system, and the composite catalyst also inherited the characteristics of the water-activated zinc glutarate catalyst.

[0036] Example 2: Synthesis of CO2-based polycarbonate using double metal cyanide / activated zinc carboxylate composite catalyst Before the start of the copolymerization reaction, the feed pipeline was cleaned 3 times, and the pipeline was dried to remove residual solvent. Weigh 15 mg of the double metal cyanide / activated zinc carboxylate (zinc glutarate with zinc oxide as the zinc source) composite catalyst prepared in Example 1, add it to the autoclave, and then keep the reactor in a closed state. Heat the reactor to 80 ° C. Then, very slowly introduce and discharge carbon dioxide, and continuously replace the air in the autoclave with carbon dioxide for 3 h. When the autoclave is cooled to room temperature, stop the entry and exit of carbon dioxide. Turn on the vacuum pump and evacuate the reactor with a vacuum pump to a pressure of -0.1 MPa. Then add 20 mL of propylene oxide, introduce carbon dioxide to maintain the pressure at about 4 MPa, and react continuously for 24 h at 70 ° C and a stirring speed of 400 rpm. After the reaction is completed, the reactor is cooled to 15 ° C, and the unreacted carbon dioxide is slowly released. Then open the reactor, quickly take out a small amount of crude product sample and dissolve it in deuterated chloroform for nuclear magnetic characterization. Subsequently, a small amount of 5% hydrochloric acid in ethanol solution was added to the reactor to terminate the reaction. The product weighed 12.8625 g, and the catalytic activity was 857.5 g polymer / g catalyst. The crude product was dissolved in dichloromethane and then precipitated in ethanol to precipitate a white flocculent product. After standing for a period of time, the supernatant was removed. The product was placed in a vacuum drying oven and dried to constant weight under vacuum conditions at 50 °C. The number average molecular weight of the polymer was 111.3×10 3 , molecular weight distribution index is 3.1, carbonate unit content is 55.1%, selectivity is 96.9%, and glass transition temperature is 22 ℃.

[0037] Example 3: Synthesis of CO2-based polycarbonate using double metal cyanide / activated zinc carboxylate composite catalyst Before the start of the copolymerization reaction, the feed pipeline was cleaned 3 times, and the pipeline was dried to remove residual solvent. Weigh 15 mg of the double metal cyanide / activated zinc carboxylate (zinc glutarate with zinc acetate as the zinc source) composite catalyst prepared in Example 1, add it to the autoclave, and then keep the reactor in a closed state. Heat the reactor to 80 ° C. Then, very slowly introduce and discharge carbon dioxide, and continuously replace the air in the autoclave with carbon dioxide for 3 h. When the autoclave is cooled to room temperature, stop the entry and exit of carbon dioxide. Turn on the vacuum pump and evacuate the reactor with a vacuum pump to a pressure of -0.1 MPa. Then add 20 mL of propylene oxide, introduce carbon dioxide to maintain the pressure at about 4 MPa, and react continuously at 70 ° C and a stirring speed of 400 rpm for 24 h. After the reaction is completed, the reactor is cooled to 15 ° C, and the unreacted carbon dioxide is slowly released. Then open the reactor, quickly take out a small amount of crude product sample and dissolve it in deuterated chloroform for nuclear magnetic characterization. Subsequently, a small amount of 5% hydrochloric acid in ethanol solution was added to the reactor to terminate the reaction. The product weighed 25.9410 g, and the catalytic activity was 1729.4 g polymer / g catalyst. The crude product was dissolved in dichloromethane and then precipitated in ethanol to precipitate a white flocculent product. After standing for a period of time, the supernatant was removed. The product was placed in a vacuum drying oven and dried to constant weight under vacuum conditions at 50 °C. The number average molecular weight of the polymer was 231.5×10 3 , molecular weight distribution index is 2.4, carbonate unit content is 61.2%, selectivity is 98.7%, and glass transition temperature is 31 ℃.

[0038] Example 4: Synthesis of CO2-based polycarbonate using double metal cyanide / activated zinc carboxylate composite catalyst Before the start of the copolymerization reaction, the feed pipeline was cleaned 3 times, and the pipeline was dried to remove residual solvent. 8 mg of the double metal cyanide / activated zinc carboxylate (zinc glutarate with zinc acetate as the zinc source) composite catalyst prepared in Example 1 was weighed and added to the autoclave, and then the reactor was placed in a closed state. The reactor was heated to 80 ° C. Then, carbon dioxide was introduced and discharged very slowly, and the air in the autoclave was continuously replaced with carbon dioxide for 3 h. When the autoclave was cooled to room temperature, the entry and exit of carbon dioxide was stopped. Turn on the vacuum pump and evacuate the reactor with a vacuum pump to a pressure of -0.1 MPa. Then 20 mL of propylene oxide was added, and carbon dioxide was introduced to maintain the pressure at about 4 MPa, and the reaction was continued for 12 h at 70 ° C and a stirring speed of 400 rpm. After the reaction was completed, the reactor was cooled to 15 ° C and the unreacted carbon dioxide was slowly released. Then the reactor was opened, and a small amount of crude product sample was quickly taken out and dissolved in deuterated chloroform for nuclear magnetic characterization. Subsequently, a small amount of 5% hydrochloric acid in ethanol solution was added to the reactor to terminate the reaction. The product weighed 5.5696 g, and the catalytic activity was 696.2 g polymer / g catalyst. The crude product was dissolved in dichloromethane and then precipitated in ethanol to precipitate a white flocculent product. After standing for a period of time, the supernatant was removed. The product was placed in a vacuum drying oven and dried to constant weight under vacuum conditions at 50 °C. The number average molecular weight of the polymer was 144.5×10 3 , molecular weight distribution index is 2.2, carbonate unit content is 53.1%, selectivity is 98.2%, and glass transition temperature is 22 ℃.

[0039] Example 5: Synthesis of CO2-based polycarbonate using double metal cyanide / activated zinc carboxylate composite catalyst Before the start of the copolymerization reaction, the feed pipeline was cleaned 3 times, and the pipeline was dried to remove residual solvent. 8 mg of the double metal cyanide / activated zinc carboxylate (zinc glutarate with zinc acetate as the zinc source) composite catalyst prepared in Example 1 was weighed and added to the autoclave, and then the reactor was placed in a closed state. The reactor was heated to 80 ° C. Then, carbon dioxide was introduced and discharged very slowly, and the air in the autoclave was continuously replaced with carbon dioxide for 3 h. When the autoclave was cooled to room temperature, the entry and exit of carbon dioxide was stopped. Turn on the vacuum pump and evacuate the reactor with a vacuum pump to a pressure of -0.1 MPa. Then 20 mL of propylene oxide was added, and carbon dioxide was introduced to maintain the pressure at about 4 MPa, and the reaction was continued for 36 h at 70 ° C and a stirring speed of 400 rpm. After the reaction was completed, the reactor was cooled to 15 ° C and the unreacted carbon dioxide was slowly released. Then the reactor was opened, and a small amount of crude product sample was quickly taken out and dissolved in deuterated chloroform for nuclear magnetic characterization. Subsequently, a small amount of 5% hydrochloric acid in ethanol solution was added to the reactor to terminate the reaction. The product weighed 13.8664 g, and the catalytic activity was 1733.3 g polymer / g catalyst. The crude product was dissolved in dichloromethane and then precipitated in ethanol to precipitate a white flocculent product. After standing for a period of time, the supernatant was removed. The product was placed in a vacuum drying oven and dried to constant weight under vacuum conditions at 50 °C. The number average molecular weight of the polymer was 93.4×10 3 , molecular weight distribution index is 3.5, carbonate unit content is 58.3%, selectivity is 97.5%, and glass transition temperature is 26 ℃.

[0040] Example 6: Synthesis of CO2-based polycarbonate using double metal cyanide catalysts Before the start of the copolymerization reaction, the feed pipeline was cleaned 3 times, and the pipeline was dried to remove residual solvent. Weigh 3 mg of the double metal cyanide catalyst prepared in Example 1, add it to the autoclave, and then keep the reactor in a closed state. Heat the reactor to 80 ° C. Then, very slowly introduce and discharge carbon dioxide, and continuously replace the air in the autoclave with carbon dioxide for 3 hours. When the autoclave is cooled to room temperature, stop the entry and exit of carbon dioxide. Turn on the vacuum pump and evacuate the reactor with a vacuum pump to a pressure of -0.1 MPa. Then add 15 mL of propylene oxide, introduce carbon dioxide to maintain the pressure at about 4 MPa, and react continuously at 70 ° C and a stirring speed of 400 rpm for 8 hours. After the reaction is completed, the reactor is cooled to 15 ° C, and the unreacted carbon dioxide is slowly released. Then open the reactor, quickly take out a small amount of crude product sample and dissolve it in deuterated chloroform for nuclear magnetic characterization. Subsequently, a small amount of 5% hydrochloric acid in ethanol solution is added to the reactor to terminate the reaction. The product weighed 14.0 g, and the catalytic activity was 4666.7 g polymer / g catalyst. The crude product was dissolved in dichloromethane and then precipitated in ethanol to precipitate a white flocculent product. After standing for a period of time, the supernatant was removed. The product was placed in a vacuum drying oven and dried to constant weight under vacuum conditions at 50 °C. The number average molecular weight of the polymer was 69.9×10 3 , molecular weight distribution index is 1.9, carbonate unit content is 21.5%, selectivity is 96.5%, and glass transition temperature is 4 ℃.

[0041] Example 7: Synthesis of CO2-based polycarbonate using activated zinc carboxylate catalyst Before the start of the copolymerization reaction, the feed pipeline was cleaned 3 times, and the pipeline was dried to remove residual solvent. Weigh 125 mg of the activated zinc carboxylate (zinc glutarate with zinc acetate as the zinc source) catalyst prepared in Example 1, add it to the autoclave, and then keep the reactor in a closed state. Heat the reactor to 80 ° C. Then, very slowly introduce and discharge carbon dioxide, and continuously replace the air in the autoclave with carbon dioxide for 3 h. When the autoclave is cooled to room temperature, stop the entry and exit of carbon dioxide. Turn on the vacuum pump and evacuate the reactor with a vacuum pump to a pressure of -0.1 MPa. Then add 50 mL of propylene oxide, introduce carbon dioxide to maintain the pressure at about 4 MPa, and react continuously for 8 h at 70 ° C and a stirring speed of 400 rpm. After the reaction is completed, the reactor is cooled to 15 ° C, and the unreacted carbon dioxide is slowly released. Then open the reactor, quickly take out a small amount of crude product sample and dissolve it in deuterated chloroform for nuclear magnetic characterization. Subsequently, a small amount of 5% hydrochloric acid in ethanol solution was added to the reactor to terminate the reaction. The product weighed 3.8375 g, and the catalytic activity was 30.7 g polymer / g catalyst. The crude product was dissolved in dichloromethane and then precipitated in ethanol to precipitate a white flocculent product. After standing for a period of time, the supernatant was removed. The product was placed in a vacuum drying oven and dried to constant weight under vacuum conditions at 50 °C. The number average molecular weight of the polymer was 142.3×10 3 , molecular weight distribution index is 3.4, carbonate unit content is 92.5%, selectivity is 97.2%, and glass transition temperature is 40 ℃.

[0042] It can be seen in the examples that the molecular weight of the polymer obtained by using the composite catalyst is more than three times that of the single double metal cyanide catalyst, and the carbonate unit content is also increased from 21.5% to 61.2%. The composite catalyst used is the zinc glutarate catalyst reported by Jang et al. (Dalton Transactions, 2022, 51(43): 16620-16627, with a catalytic activity of 855 g poly / gcat, which is the most active zinc glutarate system reported so far. The carbonate unit content of the product is 61%, and the Mn is 72.6×10 3 , selectivity is 82%, glass transition temperature is 20 ℃), the catalytic activity of the composite catalyst can reach 2 times of the latter, the number average molecular weight of the product can reach 3 times of the latter, and the selectivity and glass transition temperature are also higher.

[0043] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for preparing a double metal cyanide / activated zinc carboxylate composite catalyst, characterized in that: The method comprises the following steps: preparing a soluble divalent metal halide salt M1X2 into a solution with a mass ratio concentration of 0.1-20%, wherein the solvent is a mixed solution of an organic solvent B1 and water in a volume ratio of 1:1, heating the solution to 30-60°C, and then slowly dropping an aqueous solution containing M2[M3(CN)6], and then vigorously stirring the solution at 30-60°C for 1-12 hours. The obtained white suspension is redispersed in a solution of B1 and water (volume ratio of 1:1), and centrifuged for 1-30 minutes at a speed of 1000-10000 rpm. The volume ratio of B1 to water is adjusted, the proportion of B1 is gradually increased, and the solution is centrifuged for 1-30 minutes at a speed of 1000-10000 rpm. Finally, the white precipitate is washed in pure B1, centrifuged for 1-30 minutes at a speed of 1000-10000 rpm, and the white precipitate obtained by centrifugation is dried at 60-100°C under vacuum for 12-48 hours. The dried solid is ground into powder to obtain a double metal cyanide catalyst. Carboxylic acid C is mixed with an equimolar amount of zinc oxide or zinc acetate to form a solution with a mass ratio concentration of 0.1-20%, and the solvent is organic solvent B2. The solution is heated to 50-100°C, the speed is 1000-4000 rpm, and the reaction is carried out for 6-24 hours. The obtained product is centrifuged at a speed of 1000-6000 rpm, and the white solid precipitate obtained by centrifugation is dissolved in organic solvent B1 for washing. After repeating the above step 3 times, the product is dried in a vacuum drying oven at 50-100°C for 12-48 hours. The dried solid is ground into powder, dissolved in a certain amount of water or ethanol, and stirred into a slurry. Dry in a vacuum drying oven at 100-120°C for 12-48 hours. The dried solid is ground into powder to obtain an activated zinc carboxylate catalyst. The synthesized double metal cyanide catalyst and the activated zinc carboxylate catalyst are mixed in a molar ratio of 1:1 to 50 to prepare a solution with a mass concentration of 0.1 to 20%, wherein the solvent is an organic solvent B2, and the mixture is heated to 50 to 80 °C, stirred vigorously for 6 to 24 hours, and then centrifuged for 1 to 30 minutes at a speed of 1000 to 10000 rpm, and washed several times with organic solvent B1. The obtained white solid is dried in a vacuum drying oven at 80 to 100 °C for 12 to 48 hours. The dried solid is ground into powder to obtain the double metal cyanide / activated zinc carboxylate composite catalyst.

2. The method for preparing the double metal cyanide / activated zinc carboxylate composite catalyst as claimed in claim 1, characterized in that The metal M1 is one or more of zinc, cadmium, iron, cobalt, nickel, chromium and copper.

3. The method for preparing the double metal cyanide / activated zinc carboxylate composite catalyst as claimed in claim 1, characterized in that The metal M2 is one or more of potassium, sodium and lithium.

4. The method for preparing the double metal cyanide / activated zinc carboxylate composite catalyst as claimed in claim 1, characterized in that The metal M3 is one or more of iron, cobalt, nickel, manganese, molybdenum, chromium, tin, aluminum, vanadium, and copper.

5. The method for preparing the double metal cyanide / activated zinc carboxylate composite catalyst as claimed in claim 1, characterized in that The organic solvent B1 is one or more of acetone, methyl ethyl ketone, methyl propyl ketone, ethylene glycol, isopropanol, n-butanol, isobutanol, tert-butanol, glycol dimethyl ether, diglycol dimethyl ether, ethylene glycol methyl ether, or one or more of their derivatives.

6. The method for preparing the double metal cyanide / activated zinc carboxylate composite catalyst as claimed in claim 1, characterized in that The organic solvent B2 is one or more of cyclohexane, methylcyclohexane, toluene, polyether, polysulfide, polyethylene glycol, polypropylene glycol, polyethylene glycol-polypropylene glycol-polyethylene glycol, polyformaldehyde, polyester, polyamide, polyvinyl alcohol, or one or more of their derivatives.

7. The method for preparing the double metal cyanide / activated zinc carboxylate composite catalyst as claimed in claim 1, characterized in that The carboxylic acid C is one or more of succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, terephthalic acid, phthalic acid, isophthalic acid, or one or more of their derivatives.

8. Use of the composite catalyst prepared by the method of claim 1 in synthesizing carbon dioxide-based polycarbonate, characterized in that: The following steps are involved: Before the start of the copolymerization reaction, the feed pipeline was cleaned several times and the pipeline was dried to remove residual solvent. A composite catalyst with a mass of 0.01-5% of the mass of the reaction monomer epoxide was added to the autoclave, and then the reactor was kept in a closed state. The reactor was heated to 60-100 °C. Then, carbon dioxide was introduced and discharged very slowly, and the air in the autoclave was continuously replaced with carbon dioxide for 1-12 h. When the autoclave was cooled to room temperature, the entry and exit of carbon dioxide was stopped. The vacuum pump was turned on and the reactor was evacuated with a vacuum pump to a pressure of -0.1 MPa. Then a certain amount of reaction monomer epoxide was added, and carbon dioxide was introduced to maintain the pressure at 1-5 MPa, and the reaction was continued for 12-36 h at a temperature of 50-100 °C and a stirring speed of 100-1000 rpm. After the reaction was completed, the reactor was cooled to 5-20 °C and the unreacted carbon dioxide was slowly released. Then the reactor was opened, and a small amount of crude product sample was quickly taken out and dissolved in deuterated chloroform for further nuclear magnetic characterization. Subsequently, a small amount of 5% hydrochloric acid in ethanol solution was added to the reactor to terminate the reaction. The crude product was dissolved in dichloromethane and then precipitated in ethanol to precipitate a white flocculent product. The product was allowed to stand for a period of time and the supernatant was removed. The product was placed in a vacuum drying oven and dried to constant weight under vacuum conditions at 50 °C.

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