Composite catalyst for polycondensation of carbon dioxide and aliphatic dihydric alcohol and method for preparing low polycarbonate by using composite catalyst

Abstract

The invention belongs to the field of carbon dioxide conversion and organic catalysis, and particularly relates to a composite catalyst for polycondensation of carbon dioxide and aliphatic dihydric alcohol and a method for preparing low polycarbonate by using the composite catalyst. According to the preparation method disclosed by the invention, a binary composite catalytic system of organic alkali and carbodiimide condensing agent is adopted, so that carbon dioxide and aliphatic dihydric alcohol are subjected to dehydration polycondensation under relatively mild conditions to prepare low-polycarbonate, and the low-polycarbonate can be connected in series with other processes to prepare a carbon dioxide-based polymer with higher molecular weight. The method does not need to use an epoxy raw material monomer, and has the advantages of simple process, low cost, controllable molecular weight of the product, designable structure, high expected added value and excellent industrial prospect.

Description

Technical Field

[0001] The invention belongs to the field of carbon dioxide conversion and organic catalysis, and specifically relates to a composite catalyst for polycondensation of carbon dioxide and aliphatic diols and a method for preparing oligocarbonates. Background Art

[0002] As the global greenhouse effect continues to intensify, the capture, fixation and conversion of carbon dioxide has become a hot topic in current research. Among them, the conversion and utilization of carbon dioxide is the most critical link. At present, it is common to convert carbon dioxide into small molecules (such as methanol and dimethyl carbonate), and some routes have been successfully industrialized. However, due to its reaction inertness, carbon dioxide often requires harsh reaction conditions (such as high temperature and high pressure) to activate it before it can be converted into other target products, and most of them are low value-added products. This makes the conversion of carbon dioxide restricted by energy consumption, cost, safety and other aspects, making it difficult to promote.

[0003] Polymer materials are high value-added products, and are easy to store and transport, and have a wide range of uses. If carbon dioxide can be converted into polymers under mild conditions, it is of great significance for the development of high value-added carbon dioxide chemical conversion products. At present, carbon dioxide-based polymers are mainly polycarbonates, and high molecular weight, narrow distribution, and stereoselective polycarbonates can be obtained by ring-opening polymerization of carbon dioxide and alkylene oxide under a specific catalytic system. The patent application with publication number CN108395510A discloses an organic metal catalytic system, which has the functions of coordination polymerization and controlled radical polymerization, and can prepare carbon dioxide-based polycarbonate block copolymers. The patent application with publication number CN103524724A discloses a bimetallic catalyst, which can regulate the stereochemistry of carbon dioxide-based polycarbonate by adjusting the ligand to obtain optically active crystalline polycarbonate.

[0004] The carbon dioxide-based polymer catalytic systems reported above are all organic metal catalytic systems, with high preparation costs and harsh reaction conditions (no water and no oxygen), and the raw materials all use alkylene oxide compounds, the preparation process is highly dangerous, and it is difficult to apply on a large scale. At the same time, constrained by the molecular structure of epoxy compounds, the polycarbonate obtained by the ring-opening polymerization of carbon dioxide and alkylene oxide can only be polyethylene carbonate and its derivatives, and the molecular chain structure is not diversified enough, making it difficult to regulate the polymer properties. Aliphatic diols have rich substrate extensibility, low volatility and toxicity, and some can be prepared from sustainable resources. They are an ideal monomer raw material for preparing polycarbonate. How to develop a simple, efficient and low-cost catalytic system to enable carbon dioxide and aliphatic diols to achieve dehydration polycondensation under mild conditions to prepare aliphatic polycarbonates is of great significance for broadening the application scope and market of carbon dioxide-based polycarbonates and accelerating their industrialization process. Summary of the invention

[0005] In order to solve the problems of reliance on epoxy raw material monomers, high catalyst cost, harsh reaction conditions, and difficulty in large-scale production in the existing carbon dioxide polymerization conversion technology, the present invention discloses a type of composite catalyst, which mainly uses organic bases and carbodiimide condensation agents to obtain a binary composite catalytic system, so that carbon dioxide and aliphatic diols can be dehydrated and polycondensed under relatively mild conditions to prepare low-polycarbonate, and this oligomer can be connected in series with other processes to prepare carbon dioxide-based polymers with higher molecular weight. The method does not require the use of epoxy raw material monomers, has a simple process, low cost, controllable product molecular weight, designable structure, high added value, and has good industrial prospects.

[0006] In a first aspect, the present invention provides a composite catalyst for condensation polymerization of carbon dioxide and aliphatic diols, the composite catalyst comprising an organic base and a carbodiimide compound;

[0007] The organic base comprises at least one of N,N,N',N'-tetramethylethylenediamine (TMEDA), 4-dimethylaminopyridine (DMAP), 4-pyrrolidinylpyridine (PPY), 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), 1,5,7-triazabicyclo[4.4.0]decene-5-ene (TBD), 7-methyl-1,5,7-triazabicyclo[4.4.0]decene-5-ene (MTBD), 1,1,3,3-tetramethylguanidine (TMG), and 2-tert-butyl-1,1,3,3-tetramethylguanidine (t-Bu-TMG), preferably DBU, MTBD, and t-Bu-TMG. The structural formula of the above organic base is as follows: , , , , , , ,

[0008] Furthermore, the structural formula of the carbodiimide compound is: ; Among them, R is isopropyl or cyclohexyl, preferably isopropyl.

[0009] Furthermore, the structural formula of the aliphatic diol is selected from: , , One of; Among them, n=2, 3, 4, 5.

[0010] Furthermore, the molar ratio of the organic base to the carbodiimide compound is 1:1-180.

[0011] In a second aspect, the present invention provides a method for preparing a class of oligomeric polycarbonates, which specifically comprises the following steps: R1. Dehydration polycondensation of carbon dioxide and aliphatic diol: aliphatic diol, organic base and carbodiimide compound are placed in a pressure-resistant autoclave, heated in a carbon dioxide atmosphere under a certain pressure for dehydration polycondensation, and the reaction lasts for 6-24 hours; R2. After the reaction is completed, a post-treatment process can be performed to obtain a low-polycarbonate.

[0012] Furthermore, the post-treatment process is as follows: after the reaction in step R1 is completed, a solvent is added at -20-0°C to fully dissolve the oligomer, filtered, and the filtrate is acid-washed, dried, rotary evaporated and vacuum dried.

[0013] Furthermore, in step R1, the molar ratio of the aliphatic diol, the organic base, and the carbodiimide compound is 1:(0.005-0.5):(0.5-0.9).

[0014] Furthermore, in step R1, the reaction pressure is 0.5-5 MPa, and the reaction temperature is 80-150°C.

[0015] Furthermore, the solvent is selected from at least one of dichloromethane, chloroform, dichloroethane, tetrachloroethane, and methyl tert-butyl ether, preferably dichloromethane and dichloroethane. The amount of the solvent is 3-5 times the mass of the aliphatic diol feed.

[0016] The oligomeric carbonate obtained by the preparation method is an alcohol hydroxyl-terminated oligomer with a polymerization degree of 1-10.

[0017] Beneficial effects: The present invention provides a composite catalyst that can be used for the polycondensation of carbon dioxide and aliphatic diols. The monomers are carbon dioxide and aliphatic diols, and dehydration polycondensation can be achieved under relatively mild conditions to prepare oligocarbonates. The catalytic system of the present invention has low cost, green raw materials, simple process, and the oligocarbonate product can be combined with other processes to prepare products with higher added value such as high molecular weight polymers, and has great industrial prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is the oligocarbonate in Example 1 1 H-NMR spectrum. DETAILED DESCRIPTION

[0019] In order to more clearly understand the above-mentioned objectives, features and advantages of the present invention, the scheme of the present invention will be further described below. It should be noted that the embodiments of the present invention and the features in the embodiments can be combined with each other without conflict.

[0020] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein; it is obvious that the embodiments in the specification are only part of the embodiments of the present invention, rather than all of the embodiments.

[0021] The preferred embodiments of the present invention will be described in detail below in conjunction with examples. It should be understood that the following examples are provided only for the purpose of illustration and are not intended to limit the scope of the present invention. Those skilled in the art may make various modifications and substitutions to the present invention without departing from the purpose and spirit of the present invention.

[0022] Test instrument model: The nuclear magnetic resonance spectrometer used was Vaian DLG400 (Varian, USA).

[0023] Example 1 (substrate: 1,4-butanediol) 4.506g of 1,4-butanediol (50mmol), 0.0761g of DBU (0.5mmol) and 5.679g of diisopropylcarbodiimide (45mmol) were placed in a pressure autoclave, and high-purity carbon dioxide was charged into the autoclave to 1MPa, and then the pressure was released to normal pressure, and repeated three times. Then carbon dioxide was charged to 1MPa, and the reaction was heated to 130℃ for 24h. After cooling to room temperature, the pressure was released, and 15mL of dichloromethane was added to the system, filtered, and the filtrate was washed with 10mL of 1.0M hydrochloric acid and 10mL of deionized water, respectively, and then dried with anhydrous magnesium sulfate, filtered, rotary evaporated and vacuum dried at 50℃ for 12h to obtain a low molecular weight prepolymer.

[0024] The product was characterized by H NMR spectroscopy. Figure 1 .

[0025] Example 2 (substrate: 1,4-butanediol) 4.506g of 1,4-butanediol (50mmol), 0.0766g of MTBD (0.5mmol) and 5.679g of diisopropylcarbodiimide (45mmol) were placed in a pressure autoclave, and high-purity carbon dioxide was charged into the autoclave to 1MPa, and then the pressure was released to normal pressure, and repeated three times. Carbon dioxide was then charged to 1MPa, and the reaction was heated to 130℃ for 24h. After cooling to room temperature, the pressure was released, and 15mL of dichloromethane was added to the system, filtered, and the filtrate was washed with 10mL of 1.0M hydrochloric acid and 10mL of deionized water, respectively, and then dried with anhydrous magnesium sulfate, filtered, rotary evaporated and vacuum dried at 50℃ for 12h to obtain a low molecular weight prepolymer.

[0026] Example 3 (substrate: 1,4-butanediol) 4.506g of 1,4-butanediol (50mmol), 0.0856g of t-Bu-TMG (0.5mmol) and 5.679g of diisopropylcarbodiimide (45mmol) were placed in a pressure autoclave, and high-purity carbon dioxide was charged into the autoclave to 1MPa, and then the pressure was released to normal pressure, and repeated three times. Carbon dioxide was then charged to 1MPa, and the reaction was heated to 130℃ for 24h. After cooling to room temperature, the pressure was released, and 15mL of dichloromethane was added to the system, filtered, and the filtrate was washed with 10mL of 1.0M hydrochloric acid and 10mL of deionized water, respectively, and then dried with anhydrous magnesium sulfate, filtered, rotary evaporated and vacuum dried at 50℃ for 12h to obtain a low molecular weight prepolymer.

[0027] Example 4 (substrate: 1,6-hexanediol) 5.9085g of 1,6-hexanediol (50mmol), 0.0856g of t-Bu-TMG (0.5mmol) and 5.679g of diisopropylcarbodiimide (45mmol) were placed in a pressure autoclave, and high-purity carbon dioxide was charged into the autoclave to 1MPa, and then the pressure was released to normal pressure, and repeated three times. Then carbon dioxide was charged to 1MPa, and the reaction was heated to 130℃ for 24h. After cooling to room temperature, the pressure was released, and 15mL of dichloromethane was added to the system, filtered, and the filtrate was washed with 10mL of 1.0M hydrochloric acid and 10mL of deionized water, respectively, and then dried with anhydrous magnesium sulfate, filtered, rotary evaporated and vacuum dried at 50℃ for 12h to obtain a low molecular weight prepolymer.

[0028] Example 5 (substrate: 1,8-octanediol) 7.3115g of 1,8-octanediol (50mmol), 0.0856g of t-Bu-TMG (0.5mmol) and 5.679g of diisopropylcarbodiimide (45mmol) were placed in a pressure autoclave, and high-purity carbon dioxide was charged into the autoclave to 1MPa, and then the pressure was released to normal pressure, and repeated three times. Then carbon dioxide was charged to 1MPa, and the reaction was heated to 130℃ for 24h. After cooling to room temperature, the pressure was released, and 15mL of dichloromethane was added to the system, filtered, and the filtrate was washed with 10mL of 1.0M hydrochloric acid and 10mL of deionized water, respectively, and then dried with anhydrous magnesium sulfate, filtered, rotary evaporated and vacuum dried at 50℃ for 12h to obtain a low molecular weight prepolymer.

[0029] Example 6 (substrate: 1,10-decanediol) 8.714g of 1,10-decanediol (50mmol), 0.0856g of t-Bu-TMG (0.5mmol) and 5.679g of diisopropylcarbodiimide (45mmol) were placed in a pressure autoclave, and high-purity carbon dioxide was charged into the autoclave to 1MPa, and then the pressure was released to normal pressure, and repeated three times. Carbon dioxide was then charged to 1MPa, and the reaction was heated to 130℃ for 24h. After cooling to room temperature, the pressure was released, and 15mL of dichloromethane was added to the system, filtered, and the filtrate was washed with 10mL of 1.0M hydrochloric acid and 10mL of deionized water, respectively, and then dried with anhydrous magnesium sulfate, filtered, rotary evaporated and vacuum dried at 50℃ for 12h to obtain a low molecular weight prepolymer.

[0030] Example 7 (substrate: 1,4-cyclohexanedimethanol) 7.2105g of 1,4-cyclohexanedimethanol (50mmol), 0.0856g of t-Bu-TMG (0.5mmol) and 5.679g of diisopropylcarbodiimide (45mmol) were placed in a pressure autoclave, and high-purity carbon dioxide was charged into the autoclave to 1MPa, and then the pressure was released to normal pressure, and repeated three times. Then carbon dioxide was charged to 1MPa, and the reaction was heated to 130℃ for 24h. After cooling to room temperature, the pressure was released, and 15mL of dichloromethane was added to the system, filtered, and the filtrate was washed with 10mL of 1.0M hydrochloric acid and 10mL of deionized water, respectively, and then dried with anhydrous magnesium sulfate, filtered, rotary evaporated and vacuum dried at 50℃ for 12h to obtain a low molecular weight prepolymer.

[0031] Example 8 (substrate: 2,5-tetrahydrofuran dimethanol) 6.608g of 2,5-tetrahydrofuran dimethanol (50mmol), 0.0856g of t-Bu-TMG (0.5mmol) and 5.679g of diisopropylcarbodiimide (45mmol) were placed in a pressure autoclave, and high-purity carbon dioxide was charged into the autoclave to 1MPa, and then the pressure was released to normal pressure, and repeated three times. Then carbon dioxide was charged to 1MPa, and the reaction was heated to 130℃ for 24h. After cooling to room temperature, the pressure was released, and 15mL of dichloromethane was added to the system, filtered, and the filtrate was washed with 10mL of 1.0M hydrochloric acid and 10mL of deionized water, respectively, and then dried with anhydrous magnesium sulfate, filtered, rotary evaporated and vacuum dried at 50℃ for 12h to obtain a low molecular weight prepolymer.

[0032] Comparative Example 1 (substrate: 1,4-butanediol) 4.506g of 1,4-butanediol (50mmol) and 0.0761g of DBU (0.5mmol) were put into a pressure autoclave without carbodiimide. High-purity carbon dioxide was charged into the autoclave to 1MPa and then the pressure was released to normal pressure, which was repeated three times. Carbon dioxide was then charged to 1MPa and heated to 130℃ for 24h. After cooling to room temperature, the pressure was released and 15mL of dichloromethane was added to the system. The filtrate was filtered and washed with 10mL of 1.0M hydrochloric acid and 10mL of deionized water, respectively, and then dried with anhydrous magnesium sulfate, filtered and rotary evaporated. No polymer was obtained in the end.

[0033] Comparative Example 2 (substrate: 1,4-butanediol) 4.506g of 1,4-butanediol (50mmol) and 5.679g of diisopropylcarbodiimide (45mmol) were placed in a pressure autoclave without adding an organic base. High-purity carbon dioxide was charged into the autoclave to 1MPa and then the pressure was released to normal pressure, which was repeated three times. Carbon dioxide was then charged to 1MPa and heated to 130°C for 24h. After cooling to room temperature, the pressure was released and 15mL of dichloromethane was added to the system. The filtrate was filtered and washed with 10mL of 1.0M hydrochloric acid and 10mL of deionized water, respectively, and then dried with anhydrous magnesium sulfate, filtered, and rotary evaporated. No polymer was obtained in the end.

[0034] The above are only preferred embodiments of the present invention, and the protection scope of the present invention is not limited thereto. Any equivalent structure or equivalent process transformation made by using the specification of the present invention, or directly or indirectly applied in other related technical fields, are also included in the protection scope of the present invention.

Claims

1. A composite catalyst for the polycondensation of carbon dioxide and aliphatic diols, characterized in that: The composite catalyst comprises an organic base and a carbodiimide compound; The organic base is selected from at least one of N,N,N',N'-tetramethylethylenediamine, 4-dimethylaminopyridine, 4-pyrrolidinylpyridine, 1,8-diazabicyclo[5.4.0]undec-7-ene, 1,5,7-triazabicyclo[4.4.0]decene-5-ene, 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene, 1,1,3,3-tetramethylguanidine and 2-tert-butyl-1,1,3,3-tetramethylguanidine; The structural formula of the carbodiimide compound is: ； Wherein, R is isopropyl or cyclohexyl.

2. The composite catalyst according to claim 1, characterized in that The structural formula of the aliphatic diol is selected from: , , One of; Among them, n=2, 3, 4, 5.

3. The composite catalyst according to claim 1, characterized in that The molar ratio of the organic base to the carbodiimide compound is 1:1-180.

4. A method for preparing oligocarbonate using the composite catalyst according to any one of claims 1 to 3, characterized in that: The following steps are involved: R1. Dehydration polycondensation of carbon dioxide and aliphatic diol: aliphatic diol, organic base and carbodiimide compound are placed in a pressure-resistant autoclave, heated in a carbon dioxide atmosphere under a certain pressure for dehydration polycondensation, and the reaction lasts for 6-24 hours; R2. After the reaction is completed, a post-treatment process can be performed to obtain a low-polycarbonate.

5. The method for preparing oligocarbonate according to claim 4, characterized in that: In the step R1, the molar ratio of the aliphatic diol, the organic base and the carbodiimide compound is 1:(0.005-0.5):(0.5-0.9).

6. The method for preparing oligocarbonate according to claim 4, characterized in that: In the step R1, the reaction pressure is 0.5-5 MPa, and the reaction temperature is 80-150°C.

7. The method for preparing oligocarbonate according to claim 4, characterized in that: The post-treatment process is as follows: after the reaction in step R1 is completed, a solvent is added at -20-0°C to fully dissolve the oligomer, filtered, and the filtrate is acid-washed, dried, rotary evaporated, and vacuum dried.

8. The method for preparing oligocarbonate according to claim 7, characterized in that: The solvent is selected from at least one of dichloromethane, chloroform, dichloroethane, tetrachloroethane and methyl tert-butyl ether.

9. The method for preparing oligocarbonate according to claim 7, characterized in that: Calculated by mass fraction, the amount of the solvent used is 3-5 times the mass of the aliphatic diol feed.

10. The method for preparing oligocarbonate according to claim 4, characterized in that: The prepared oligocarbonate is an alcohol hydroxyl-terminated oligomer with a polymerization degree of 1-10.

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