Preparation method and application of zinc gallate catalyst for synthesizing carbon dioxide-based polycarbonate

Abstract

The invention discloses a preparation method and application of a zinc gallate catalyst for synthesizing carbon dioxide-based polycarbonate, and belongs to the technical field of catalysts.The zinc gallate catalyst is prepared through the steps that zinc salt and gallic acid (3, 4, 5-trihydroxybenzoic acid) are subjected to a reaction, low-carbon-number alcohol serves as a complexing agent, and a reaction solution is obtained; the copolymer can be applied to ring-opening copolymerization of carbon dioxide and epoxide, and a third monomer even a fourth monomer can be added on the basis to carry out ternary copolymerization and quaternary copolymerization to generate aliphatic polycarbonate with a multi-element structure. The activity of the zinc gallate catalyst for catalyzing ring-opening copolymerization of carbon dioxide and epoxypropane is larger than 900 g polymer / g catalyst, the content of carbonate units is larger than 96%, the selectivity is larger than 91%, the balance of the activity and the content of the carbonate units can be met, the synthesis process is simple, the reactant cost is low, and the zinc gallate catalyst is 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 zinc gallate catalyst for synthesizing carbon dioxide-based polycarbonate. Background Art

[0002] Carbon emissions caused by human activities are causing climate change. To prevent a global climate disaster, social life and industrial production based on fossil fuels must be transformed. The International Energy Agency (IEA) said that global carbon dioxide (CO2) emissions increased by 410 million tons in 2023, an increase of 1.1%, which also brought global carbon emissions to a new high of 37.4 billion tons in 2023. If global warming is to be limited to 2 °C, carbon dioxide emissions need to be kept below 17 billion tons per year by 2030. This is a challenging task given the current high annual emissions and the limited industrial application of carbon dioxide. To meet this challenge, it is crucial to develop new technologies that can convert large amounts of carbon dioxide into commercially valuable products. Replacing fossil fuel processes with sustainable carbon dioxide processes can play an important role in achieving carbon peak and carbon neutrality.

[0003] Using carbon dioxide as a carbon source in polymers has great potential for advancing sustainable chemistry because this method broadens the application of plastic products containing carbon dioxide. Polymers synthesized from carbon dioxide and epoxides are favored by scholars, and their polycarbonate chains contain a large amount of carbon dioxide. In addition, these polymers have a variety of commercial uses, such as coatings, adhesives, and mulch films. Based on these advantages, scholars have been working hard to develop effective catalysts.

[0004] In 1969, Inoue first reported a zinc-based catalyst synthesized from diethylzinc and water (Journal of Polymer Science Part B: Polymer Physics, 1969, 7(4): 287-292), with a catalytic activity of 13 g / g cat (g polymer / g catalyst). Subsequently, scholars have conducted extensive research on homogeneous and heterogeneous zinc-based catalysts to improve catalytic activity, increase carbonate content, and reduce the formation of byproduct cyclic carbonate (CPC). Although heterogeneous catalysts have economic advantages, the lack of understanding of their catalytic activity has hindered the development of efficient heterogeneous zinc-based catalysts. The most effective heterogeneous catalyst reported so far for the alternating synthesis of polycarbonate from propylene oxide (PO) and carbon dioxide is zinc glutarate (ZnGA), with an activity of 83 g / g cat (Catalysis Today, 2006, 115(1-4): 134-145). Scholars have conducted a lot of research to try to improve the catalytic activity of ZnGA, such as montmorillonite loading, MCM-41 molecular sieve loading, perfluorinated compound loading, or acid modification, sulfur dioxide modification, p-toluenesulfonic acid modification, etc. However, these methods are difficult to significantly improve its catalytic activity. There are many domestic patents on ZnGA, a large part of which come from Wang Xianhong's team at the Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, including CN105418907A, CN113683764A and CN112358607A. Taking CN105418907A as an example, although the highest number average molecular weight (Mn) of the product obtained by catalyzing CO2 / PO ring-opening copolymerization reaches 290×10 3 , but the highest catalytic activity is only 151 g poly / g cat. 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). Although the activity was significantly improved after activation, the carbonate unit content of the product dropped to 61% and the selectivity dropped to 82%. In summary, the low activity limits the large-scale industrial application of ZnGA.

[0005] Therefore, developing a heterogeneous zinc-based catalyst that can achieve a balance between catalytic activity and carbonate unit content is one of the unresolved problems in this field. Summary of the invention

[0006] In view of the deficiencies of the prior art, the present invention provides a preparation method and application of a zinc gallate catalyst for synthesizing carbon dioxide-based polycarbonate, which can realize the preparation of a zinc gallate catalyst using a low-carbon alcohol as a complexing agent by reacting a zinc salt with gallic acid (3,4,5-trihydroxybenzoic acid). When the zinc salt reacts with gallic acid, a layered structure can be formed, exposing the abundant Zn-OH active sites to epoxides and CO2. The increase in the number of active sites greatly improves the catalytic activity, and can take into account a higher carbonate unit content.

[0007] To achieve the above object, the present invention provides the following technical solutions: The present invention provides a method for preparing a zinc gallate catalyst for synthesizing a carbon dioxide-based polycarbonate, comprising the following steps: Dissolve gallic acid (3,4,5-trihydroxybenzoic acid) and zinc salt A in solvent B at a certain molar ratio to prepare a solution with a mass ratio concentration of 0.1-20%. Stir the mixture vigorously under nitrogen or inert gas atmosphere, gradually drop ammonia solution until the pH value is 10, and react for 0-6 h. Centrifuge the resulting slurry for 1-30 min at a speed of 1000-10000 rpm. Pour off the upper liquid, wash the gray precipitate in solvent B, and centrifuge for 1-30 min at a speed of 1000-10000 rpm. Centrifuge and wash several times until the pH value is 7. The gray solid precipitate obtained by centrifugation is dried under vacuum at 25-80 °C for 12-48 h, and the dried solid is ground into powder to obtain a zinc gallate catalyst.

[0008] Furthermore, the zinc salt A is one or more of zinc chloride, zinc bromide, zinc iodide, zinc acetate, zinc acetylacetonate, zinc trifluoromethanesulfonate, zinc benzoate, zinc nitrate and zinc sulfate.

[0009] Furthermore, the molar ratio of gallic acid to zinc salt is 1:0.5-3.

[0010] Furthermore, the solvent B is one or more of methanol, ethanol, ethylene glycol, isopropanol, n-butanol, isobutanol, and tert-butanol.

[0011] The present invention also provides the use of the zinc gallate catalyst prepared by the above method in synthesizing carbon dioxide-based polycarbonate, comprising the following steps: Before the start of the copolymerization reaction, clean the feed pipeline several times and dry the pipeline to remove residual solvent. Add zinc gallate catalyst with a mass of 0.01-10% of the mass of the reaction monomer epoxide into the autoclave, and then keep the reactor in a closed state. Heat the reactor to 60-100 °C. Then, very slowly introduce and discharge carbon dioxide, and continuously replace the air in the autoclave with carbon dioxide for 1-12 h. When the autoclave cools 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 a certain amount of reaction monomer epoxide, introduce carbon dioxide to maintain the pressure at 1-5 MPa, and react continuously for 12-72 h at a temperature of 50-100 °C and a stirring speed of 100-1000 rpm. After the reaction is completed, cool the reactor to 5-20 °C and slowly release the unreacted carbon dioxide. Then open the reactor, quickly take out a small amount of crude product sample and dissolve it in deuterated chloroform for further NMR characterization. Subsequently, a small amount of 5% hydrochloric acid in ethanol solution was added dropwise to the reactor to terminate the reaction. The crude reaction 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.

[0012] Compared with the prior art, the present invention has the following beneficial effects: The significant enhancement of the catalytic activity of the catalyst can be attributed to the disintegration of its layered structure during the polymerization reaction, which produces ultra-thin zinc gallate, which in turn exposes a large number of catalytically active zinc sites, including Zn-OH sites and unsaturated coordinated zinc sites. Similar to ZnGA, zinc gallate initiates the reaction through Zn-OH, which mainly activates PO, while the unsaturated coordinated zinc sites are responsible for activating CO2. The increase in ultra-thin layer active sites makes the polymerization of PO and CO2 more efficient while taking into account higher selectivity. DETAILED DESCRIPTION

[0013] 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.

[0014] 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.

[0015] 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.

[0016] 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.

[0017] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0018] Example 1: Preparation of zinc gallate catalyst Dissolve 1.14 g (6.7 mmol) of gallic acid and 4.87 g (13.4 mmol) of zinc trifluoromethanesulfonate in 50 mL of anhydrous methanol, stir the mixture vigorously under a nitrogen atmosphere, gradually drop a 3% aqueous ammonia solution until the pH value is 10, and react for 2 h. Centrifuge the resulting slurry for 8 min at 3000 rpm. Pour off the upper liquid, wash the gray precipitate in anhydrous methanol, and centrifuge for 8 min at 3000 rpm. Centrifuge and wash several times until the pH value is 7. The gray solid precipitate obtained by centrifugation is dried under vacuum at 60 °C for 24 h, and the dried solid is ground into powder to obtain the zinc gallate catalyst, which is sealed and stored in a desiccator.

[0019] Example 2: Synthesis of CO2-based polycarbonate using zinc gallate catalyst Before the start of the copolymerization reaction, the feed line was cleaned 3 times, and the line was dried to remove residual solvent. 4.4 mg of the zinc gallate catalyst prepared in Example 1 was added to the autoclave, and the reactor was then 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 reactor 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. The vacuum pump was turned on and the reactor was evacuated with a vacuum pump to a pressure of -0.1 MPa. Then 4.36 g of propylene oxide was injected with a disposable syringe, and carbon dioxide was introduced to maintain the pressure at 4 MPa, and the reaction was continued for 20 h at a temperature of 80 ° C and a stirring speed of 650 rpm. After the reaction was completed, the reactor was cooled to 15 ° C, and the unreacted carbon dioxide was slowly released. The reactor was then 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 was added dropwise to the reactor to terminate the reaction. The solid product weighed 4.356 g, and the catalytic activity was 990 g polymer / g catalyst. 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. The polymer carbonate unit content was 97%, the selectivity was 98%, and the molecular weight distribution index was 3.1.

[0020] Example 3: Synthesis of CO2-based polycarbonate using zinc gallate catalyst Before the copolymerization reaction begins, the feed line is cleaned 3 times, and the line is dried to remove residual solvent. 4.4 mg of the zinc gallate catalyst prepared in Example 1 is added to the autoclave, and then the reactor is in a closed state. The reactor is heated to 80 ° C. Then, carbon dioxide is introduced and discharged very slowly, and the air in the reactor is continuously replaced with carbon dioxide for 3 h. When the autoclave is cooled to room temperature, the entry and exit of carbon dioxide is stopped. Turn on the vacuum pump and evacuate the reactor with a vacuum pump at a pressure of -0.1 MPa. Then 4.36 g of propylene oxide is injected with a disposable syringe, and carbon dioxide is introduced to maintain the pressure at 4 MPa, and the reaction is continued for 20 h at a temperature of 70 ° C and a stirring speed of 650 rpm. After the reaction is completed, the reactor is cooled to 15 ° C, and the unreacted carbon dioxide is slowly released. Then the reactor is opened, and a small amount of crude product sample is quickly taken out and dissolved in deuterated chloroform for nuclear magnetic characterization. Subsequently, a small amount of 5% hydrochloric acid in ethanol solution is added dropwise to the reactor to terminate the reaction. The solid product weighed 2.244 g, and the catalytic activity was 510 g polymer / g catalyst. 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 at 50°C. The polymer carbonate unit content was 98%, the selectivity was 98%, and the molecular weight distribution index was 6.8.

[0021] Example 4: Synthesis of CO2-based polycarbonate using zinc gallate catalyst Before the start of the copolymerization reaction, the feed line was cleaned 3 times, and the line was dried to remove residual solvent. 4.4 mg of the zinc gallate catalyst prepared in Example 1 was added to the autoclave, and the reactor was then placed in a closed state. The reactor was heated to 90 ° C. Then, carbon dioxide was introduced and discharged very slowly, and the air in the reactor 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. The vacuum pump was turned on and the reactor was evacuated with a vacuum pump at a pressure of -0.1 MPa. Then 4.36 g of propylene oxide was injected with a disposable syringe, and carbon dioxide was introduced to maintain the pressure at 4 MPa, and the reaction was continued for 20 h at a temperature of 90 ° C and a stirring speed of 650 rpm. After the reaction was completed, the reactor was cooled to 15 ° C, and the unreacted carbon dioxide was slowly released. The reactor was then 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 was added dropwise to the reactor to terminate the reaction. The solid product weighed 5.236 g, and the catalytic activity was 1190 g polymer / g catalyst. 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. The polymer carbonate unit content was 97%, the selectivity was 92%, and the molecular weight distribution index was 2.5.

[0022] Example 5: Synthesis of CO2-based polycarbonate using zinc gallate catalyst Before the start of the copolymerization reaction, the feed line was cleaned 3 times, and the line was dried to remove residual solvent. 4.4 mg of the zinc gallate catalyst prepared in Example 1 was added to the autoclave, and the reactor was then 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 reactor 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. The vacuum pump was turned on and the reactor was evacuated with a vacuum pump at a pressure of -0.1 MPa. Then 4.36 g of propylene oxide was injected with a disposable syringe, and carbon dioxide was introduced to maintain the pressure at 3 MPa, and the reaction was continued for 20 h at a temperature of 80 ° C and a stirring speed of 650 rpm. After the reaction was completed, the reactor was cooled to 15 ° C, and the unreacted carbon dioxide was slowly released. The reactor was then 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 was added dropwise to the reactor to terminate the reaction. The solid product weighed 2.706 g, and the catalytic activity was 615 g polymer / g catalyst. 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. The polymer carbonate unit content was 97%, the selectivity was 98%, and the molecular weight distribution index was 7.6.

[0023] Example 6: Synthesis of CO2-based polycarbonate using zinc gallate catalyst Before the start of the copolymerization reaction, the feed line was cleaned 3 times, and the line was dried to remove residual solvent. 4.4 mg of the zinc gallate catalyst prepared in Example 1 was 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 reactor 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 at a pressure of -0.1 MPa. Then 13 g of propylene oxide was injected with a disposable syringe, and carbon dioxide was introduced to maintain the pressure at 4 MPa, and the reaction was continued for 20 h at a temperature of 80 ° C and a stirring speed of 650 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 was added dropwise to the reactor to terminate the reaction. The solid product weighed 6.2216 g, and the catalytic activity was 1414 g polymer / g catalyst. 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 at 50 ° C. The polymer carbonate unit content was 98%, the selectivity was 98%, and the molecular weight distribution index was 2.4.

[0024] It can be seen in the examples that the catalytic activity of zinc gallate catalyst under optimized reaction conditions far exceeds that of ZnGA, even reaching about 10 times that of the latter, and can achieve a balance between catalytic activity and carbonate unit content while taking into account higher selectivity.

[0025] 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 zinc gallate catalyst for synthesizing carbon dioxide-based polycarbonate, characterized in that: The following steps are involved: Dissolve gallic acid (3,4,5-trihydroxybenzoic acid) and zinc salt A in solvent B at a certain molar ratio to prepare a solution with a mass ratio concentration of 0.1-20%. Stir the mixture vigorously under nitrogen or inert gas atmosphere, gradually drop ammonia solution until the pH value is 10, and react for 0-6 h. Centrifuge the resulting slurry for 1-30 min at a speed of 1000-10000 rpm. Pour off the upper liquid, wash the gray precipitate in solvent B, and centrifuge for 1-30 min at a speed of 1000-10000 rpm. Centrifuge and wash several times until the pH value is 7. The gray solid precipitate obtained by centrifugation is dried under vacuum at 25-80 °C for 12-48 h, and the dried solid is ground into powder to obtain a zinc gallate catalyst.

2. The method for preparing a zinc gallate catalyst as claimed in claim 1, characterized in that The zinc salt A is one or more of zinc chloride, zinc bromide, zinc iodide, zinc acetate, zinc acetylacetonate, zinc trifluoromethanesulfonate, zinc benzoate, zinc nitrate and zinc sulfate.

3. The method for preparing a zinc gallate catalyst as claimed in claim 1, characterized in that The molar ratio of gallic acid to zinc salt is 1:0.5-3.

4. The method for preparing a zinc gallate catalyst as claimed in claim 1, characterized in that The solvent B is one or more of methanol, ethanol, ethylene glycol, isopropanol, n-butanol, isobutanol, and tert-butanol.

5. Use of the zinc gallate catalyst prepared by the method of claim 1 in the synthesis of carbon dioxide-based polycarbonate, characterized in that: The following steps are involved: Before the start of the copolymerization reaction, clean the feed pipeline several times and dry the pipeline to remove residual solvent. Add zinc gallate catalyst with a mass of 0.01-10% of the mass of the reaction monomer epoxide into the autoclave, and then keep the reactor in a closed state. Heat the reactor to 60-100 °C. Then, very slowly introduce and discharge carbon dioxide, and continuously replace the air in the autoclave with carbon dioxide for 1-12 h. When the autoclave cools 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 a certain amount of reaction monomer epoxide, introduce carbon dioxide to maintain the pressure at 1-5 MPa, and react continuously for 12-72 h at a temperature of 50-100 °C and a stirring speed of 100-1000 rpm. After the reaction is completed, cool the reactor to 5-20 °C and slowly release the unreacted carbon dioxide. Then open the reactor, quickly take out a small amount of crude product sample and dissolve it in deuterated chloroform for further NMR characterization. Subsequently, a small amount of 5% hydrochloric acid in ethanol solution was added dropwise to the reactor to terminate the reaction. The crude reaction 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.