Composite catalysts for the polycondensation of carbon dioxide with aliphatic diols and method for the preparation of oligocarbonates therefrom

Abstract

The application belongs to the field of carbon dioxide conversion and organic catalysis, and particularly relates to a kind of composite catalyst for carbon dioxide and aliphatic dihydric alcohol polycondensation and a method for preparing oligocarbonate by the composite catalyst.The application uses a binary composite catalytic system of organic base and carbodiimide condensing agent, to make carbon dioxide and aliphatic dihydric alcohol realize dehydration polycondensation under relatively mild conditions to prepare oligocarbonate, and the oligomer can be connected to other processes to prepare higher molecular weight carbon dioxide-based polymers.The method does not need to use epoxy raw material monomer, and has the advantages of simple process, low cost, controllable product molecular weight, designable structure, high expected added value and excellent industrialization prospect.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of carbon dioxide conversion and organic catalysis, and particularly relates to a kind of composite catalyst for carbon dioxide and aliphatic dihydric alcohol polycondensation and a method for preparing oligocarbonate thereof. BACKGROUND

[0002] With the increasing global greenhouse effect, carbon dioxide capture, fixation and conversion have become a hot research topic. Among them, the conversion of carbon dioxide is the most critical link. At present, carbon dioxide is converted into small molecules (such as methanol, dimethyl carbonate) and other substances, which is relatively common, and some routes have been successfully industrialized. However, due to the reaction inertness of carbon dioxide, it often needs to be activated under harsh reaction conditions (such as high temperature and high pressure) to be converted into other target products, and most of them are low value-added products. This makes the carbon dioxide conversion be restricted by energy consumption, cost, safety and other aspects, and it is difficult to promote.

[0003] Polymeric materials are high value-added products, and are easy to store, transport and have a wide range of applications. If carbon dioxide can be converted into polymers under mild conditions, it will have important significance for the development of high value-added carbon dioxide chemical conversion products. At present, carbon dioxide-based polymers are mainly polycarbonates. Polycarbonates with high molecular weight, narrow distribution and stereoselectivity can be obtained by ring-opening polymerization of carbon dioxide and alkylene oxide under a specific catalytic system. Patent application 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 copolymer. Patent application CN103524724A discloses a bimetallic catalyst, which can adjust the ligand to control the stereoisomer of carbon dioxide-based polycarbonate, and obtain optically active crystalline polycarbonate.

[0004] The above-mentioned carbon dioxide-based polymer catalytic system is an organic metal catalytic system, which has high preparation cost, harsh reaction conditions (water-free and oxygen-free), and uses alkylene oxide compounds as raw materials, which has high danger in the preparation process and is difficult to scale up. At the same time, due to the restriction of the molecular structure of the epoxy compound, the polycarbonate obtained by the ring-opening polymerization of carbon dioxide and alkylene oxide can only be polyethylene glycol carbonate and its derivatives, and the molecular chain structure is not diversified enough, which is difficult to control the performance of the polymer. Aliphatic dihydric alcohol has rich substrate expansion and low volatility and toxicity, and some can be prepared by sustainable resources, which is an ideal monomer raw material for preparing polycarbonate. How to develop a simple and efficient, low-cost catalytic system to make carbon dioxide and aliphatic dihydric alcohol dehydrate and condense under mild conditions to prepare aliphatic polycarbonate is of great significance to broaden the application range and market of carbon dioxide-based polycarbonate and speed up its industrialization process. SUMMARY

[0005] In order to solve the problems of the prior art, such as the dependence on epoxy monomers, high cost of catalysts, harsh reaction conditions and difficulty in large-scale production, a composite catalyst is disclosed, which is a binary composite catalyst system obtained by using an organic base and a carbodiimide condensing agent. The carbon dioxide and aliphatic diols are dehydrated and polycondensed under relatively mild conditions to prepare oligomeric carbonates. The oligomers can be connected to other processes to prepare higher molecular weight carbon dioxide-based polymers. The method does not require the use of epoxy monomers, is simple, low in cost, and has controllable molecular weight, designable structure and high added value, and has good industrialization prospects.

[0006] In a first aspect, the application provides a composite catalyst for the polycondensation of carbon dioxide and aliphatic diols, which comprises an organic base and a carbodiimide compound.

[0007] The organic base comprises at least one of N,N,N',N'-tetramethyl ethylenediamine (TMEDA), 4-dimethylaminopyridine (DMAP), 4-pyrrolidinyl pyridine (PPY), 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene (MTBD), 1,1,3,3-tetramethyl guanidine (TMG), and 2-tert-butyl-1,1,3,3-tetramethyl guanidine (t-Bu-TMG), preferably DBU, MTBD and t-Bu-TMG. The structure of the above-mentioned organic base is as follows:

[0008] 、 、 、 、 、 、 、

[0009] Further, the structure of the carbodiimide compound is as follows:

[0010] ;

[0011] wherein R is isopropyl or cyclohexyl, preferably isopropyl.

[0012] Further, the structure of the aliphatic diol is selected from one of the following:

[0013] 、 、 ​

[0014] wherein n = 2, 3, 4, 5.

[0015] Further, the molar ratio of the organic base and the carbodiimide compound is 1:1-180.

[0016] In a second aspect, the present application provides a preparation method of the oligocarbonates, which specifically comprises the following steps:

[0017] R1, carbon dioxide and aliphatic diols are subjected to dehydration polycondensation in a certain pressure of carbon dioxide atmosphere; R2, after the reaction, the oligocarbonates are obtained through a post-treatment process.

[0018] R2, after the reaction, the oligocarbonates are obtained through a post-treatment process.

[0019] Further, the post-treatment process is as follows: after the reaction in step R1, a solvent is added at -20-0°C to fully dissolve the oligomers, and then the filtrate is subjected to acid washing, drying, rotary evaporation and vacuum drying.

[0020] Further, in step R1, the molar ratio of the aliphatic diols, the organic base and the carbodiimide compound is 1:(0.005-0.5):(0.5-0.9).

[0021] Further, in step R1, the reaction pressure is 0.5-5 MPa, and the reaction temperature is 80-150°C.

[0022] Further, the solvent is selected from at least one of dichloromethane, trichloromethane, dichloroethane, tetrachloroethane and methyl tert-butyl ether, and preferably dichloromethane and dichloroethane. The amount of the solvent is 3-5 times the amount of the aliphatic diols.

[0023] The oligocarbonates obtained by the preparation method are alcohol-hydroxyl-terminated oligomers with a polymerization degree of 1-10.

[0024] Advantages:

[0025] The present application provides a composite catalyst which can be used for the polycondensation of carbon dioxide and aliphatic diols. The monomers are carbon dioxide and aliphatic diols, and the dehydration polycondensation can be realized under relatively mild conditions to prepare oligocarbonates. The catalyst system of the present application has low cost, green raw materials and simple process, and the oligocarbonates can be combined with other processes to prepare high molecular weight polymers and other products with higher added value, which has great industrialization prospect. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 The oligocarbonates prepared in Example 1 are analyzed by H-NMR. 1 H-NMR chart. DETAILED DESCRIPTION

[0027] In order to more clearly understand the above-mentioned objects, features and advantages of the present application, the schemes of the present application will be further described below. It should be noted that the embodiments of the present application and the features in the embodiments can be combined with each other without conflict.

[0028] In the following description, a large number of specific details are set forth in order to provide a thorough understanding of the present application, but the present application can also be implemented in other manners different from those described herein; obviously, the embodiments described in the specification are only a part of the embodiments of the present application, and not all the embodiments.

[0029] The preferred embodiments of the present application will be described in detail below with reference to the embodiments. It should be understood that the following embodiments are given only for the purpose of illustration, and are not intended to limit the scope of the present application. Those skilled in the art can make various modifications and replacements to the present application without departing from the spirit and principles of the present application.

[0030] Test instrument model: The model of the nuclear magnetic resonance spectrometer used is Vaian DLG400 (Varian, USA).

[0031] Example 1 (substrate: 1,4-butanediol)

[0032] 4.506 g of 1,4-butanediol (50 mmol), 0.0761 g of DBU (0.5 mmol) and 5.679 g of diisopropyl carbodiimide (45 mmol) were put into an autoclave, the autoclave was filled with high-purity carbon dioxide to 1 MPa, and then the pressure was released to normal pressure for three times. Subsequently, carbon dioxide was filled to 1 MPa, and heated to 130°C for 24 h. After cooling to room temperature, the pressure was released, and 15 mL of dichloromethane was added to the system, filtered, and the filtrate was washed with 10 mL of 1.0 M hydrochloric acid and 10 mL of deionized water, respectively, and then dried over anhydrous magnesium sulfate, filtered, rotary evaporated and vacuum dried at 50°C for 12 h to obtain a low molecular weight prepolymer.

[0033] The product was characterized by nuclear magnetic hydrogen spectrum, and the results are shown in Figure 1 .

[0034] Example 2 (substrate: 1,4-butanediol)

[0035] Into an autoclave, 4.506 g of 1,4-butanediol (50 mmol), 0.0766 g of MTBD (0.5 mmol), and 5.679 g of diisopropylcarbodiimide (45 mmol) were charged, and the pressure was released to the atmospheric pressure after the high-purity carbon dioxide was charged to 1 MPa for three times. Then, the carbon dioxide was charged to 1 MPa, and the reaction was performed at 130°C for 24 hours. After the cooling to the room temperature, the pressure was released, 15 mL of dichloromethane was added to the system, and the filtrate was washed with 10 mL of 1.0 M hydrochloric acid and 10 mL of ionized water, respectively, and dried with anhydrous magnesium sulfate. After the filtration, the rotary evaporation and the vacuum drying at 50°C for 12 hours were performed to obtain a low-molecular-weight prepolymer.

[0036] Example 3 (Substrate: 1,4-butanediol)

[0037] Into an autoclave, 4.506 g of 1,4-butanediol (50 mmol), 0.0766 g of MTBD (0.5 mmol), and 5.679 g of diisopropylcarbodiimide (45 mmol) were charged, and the pressure was released to the atmospheric pressure after the high-purity carbon dioxide was charged to 1 MPa for three times. Then, the carbon dioxide was charged to 1 MPa, and the reaction was performed at 130°C for 24 hours. After the cooling to the room temperature, the pressure was released, 15 mL of dichloromethane was added to the system, and the filtrate was washed with 10 mL of 1.0 M hydrochloric acid and 10 mL of ionized water, respectively, and dried with anhydrous magnesium sulfate. After the filtration, the rotary evaporation and the vacuum drying at 50°C for 12 hours were performed to obtain a low-molecular-weight prepolymer.

[0038] Example 4 (Substrate: 1,6-hexanediol)

[0039] Into an autoclave, 5.9085 g of 1,6-hexanediol (50 mmol), 0.0856 g of t-Bu-TMG (0.5 mmol), and 5.679 g of diisopropylcarbodiimide (45 mmol) were charged, and the pressure was released to the atmospheric pressure after the high-purity carbon dioxide was charged to 1 MPa for three times. Then, the carbon dioxide was charged to 1 MPa, and the reaction was performed at 130°C for 24 hours. After the cooling to the room temperature, the pressure was released, 15 mL of dichloromethane was added to the system, and the filtrate was washed with 10 mL of 1.0 M hydrochloric acid and 10 mL of ionized water, respectively, and dried with anhydrous magnesium sulfate. After the filtration, the rotary evaporation and the vacuum drying at 50°C for 12 hours were performed to obtain a low-molecular-weight prepolymer.

[0040] Example 5 (Substrate: 1,8-octanediol)

[0041] Into an autoclave, 7.3115 g of 1,8-octanediol (50 mmol), 0.0856 g of t-Bu-TMG (0.5 mmol), and 5.679 g of diisopropylcarbodiimide (45 mmol) were charged, and the autoclave was pressurized with high-purity carbon dioxide to 1 MPa, and the pressure was released to the atmospheric pressure three times. Subsequently, the autoclave was pressurized with carbon dioxide to 1 MPa, and the temperature was raised to 130°C, and the reaction was carried out for 24 hours. After the temperature was lowered to room temperature, the pressure was released, and 15 mL of dichloromethane was added to the system. The filtrate was washed with 10 mL of 1.0 M hydrochloric acid and 10 mL of ionized water, respectively, and dried over anhydrous magnesium sulfate. The filtrate was subjected to suction filtration, and distilled under reduced pressure, and dried at 50°C under vacuum for 12 hours to obtain a low-molecular-weight prepolymer.

[0042] Example 6 (Substrate: 1,10-decanediol)

[0043] Into an autoclave, 8.714 g of 1,10-decanediol (50 mmol), 0.0856 g of t-Bu-TMG (0.5 mmol), and 5.679 g of diisopropylcarbodiimide (45 mmol) were charged, and the autoclave was pressurized with high-purity carbon dioxide to 1 MPa, and the pressure was released to the atmospheric pressure three times. Subsequently, the autoclave was pressurized with carbon dioxide to 1 MPa, and the temperature was raised to 130°C, and the reaction was carried out for 24 hours. After the temperature was lowered to room temperature, the pressure was released, and 15 mL of dichloromethane was added to the system. The filtrate was washed with 10 mL of 1.0 M hydrochloric acid and 10 mL of ionized water, respectively, and dried over anhydrous magnesium sulfate. The filtrate was subjected to suction filtration, and distilled under reduced pressure, and dried at 50°C under vacuum for 12 hours to obtain a low-molecular-weight prepolymer.

[0044] Example 7 (Substrate: 1,4-cyclohexanedimethanol)

[0045] Into an autoclave, 7.2105 g of 1,4-cyclohexanedimethanol (50 mmol), 0.0856 g of t-Bu-TMG (0.5 mmol), and 5.679 g of diisopropylcarbodiimide (45 mmol) were charged, and the autoclave was pressurized with high-purity carbon dioxide to 1 MPa, and the pressure was released to the atmospheric pressure three times. Subsequently, the autoclave was pressurized with carbon dioxide to 1 MPa, and the temperature was raised to 130°C, and the reaction was carried out for 24 hours. After the temperature was lowered to room temperature, the pressure was released, and 15 mL of dichloromethane was added to the system. The filtrate was washed with 10 mL of 1.0 M hydrochloric acid and 10 mL of ionized water, respectively, and dried over anhydrous magnesium sulfate. The filtrate was subjected to suction filtration, and distilled under reduced pressure, and dried at 50°C under vacuum for 12 hours to obtain a low-molecular-weight prepolymer.

[0046] Example 8 (Substrate: 2,5-tetrahydrofuran dimethanol)

[0047] Into an autoclave, 6.608 g of 2,5-tetrahydrofuran dimethylol (50 mmol), 0.0856 g of t-Bu-TMG (0.5 mmol) and 5.679 g of diisopropyl carbodiimide (45 mmol) were put into the autoclave, and the pressure was released to normal pressure after the high-purity carbon dioxide was filled into the autoclave to 1 MPa for three times. Then, the carbon dioxide was filled to 1 MPa, and the reaction was carried out at 130°C for 24 h. After the pressure was released to normal pressure at room temperature, 15 mL of dichloromethane was added into the system, and the filtrate was washed with 10 mL of 1.0 M hydrochloric acid and 10 mL of deionized water, respectively, and then dried with anhydrous magnesium sulfate. After the filtration and rotary evaporation, the low-molecular-weight prepolymer was obtained by vacuum drying at 50°C for 12 h.

[0048] Comparative Example 1 (substrate: 1,4-butanediol)

[0049] Into an autoclave, 4.506 g of 1,4-butanediol (50 mmol) and 0.0761 g of DBU (0.5 mmol) were put into the autoclave without adding carbodiimide. The pressure was released to normal pressure after the high-purity carbon dioxide was filled into the autoclave to 1 MPa for three times. Then, the carbon dioxide was filled to 1 MPa, and the reaction was carried out at 130°C for 24 h. After the pressure was released to normal pressure at room temperature, 15 mL of dichloromethane was added into the system, and the filtrate was washed with 10 mL of 1.0 M hydrochloric acid and 10 mL of deionized water, respectively, and then dried with anhydrous magnesium sulfate. After the filtration and rotary evaporation, no polymer was obtained.

[0050] Comparative Example 2 (substrate: 1,4-butanediol)

[0051] Into an autoclave, 4.506 g of 1,4-butanediol (50 mmol) and 5.679 g of diisopropyl carbodiimide (45 mmol) were put into the autoclave without adding organic base. The pressure was released to normal pressure after the high-purity carbon dioxide was filled into the autoclave to 1 MPa for three times. Then, the carbon dioxide was filled to 1 MPa, and the reaction was carried out at 130°C for 24 h. After the pressure was released to normal pressure at room temperature, 15 mL of dichloromethane was added into the system, and the filtrate was washed with 10 mL of 1.0 M hydrochloric acid and 10 mL of deionized water, respectively, and then dried with anhydrous magnesium sulfate. After the filtration and rotary evaporation, no polymer was obtained.

[0052] The above merely describes the preferred embodiments of the present application, and is not intended to limit the protection scope of the present application. Any equivalent structure or equivalent flow transformation made according to the present application, or direct or indirect application in other related technical fields, is also included in the protection scope of the present application.

Claims

1. A method for preparing oligocarbonates, characterized in that, Includes the following steps: R1. Dehydration condensation of carbon dioxide and aliphatic diols: Aliphatic diols, organic bases, and carbodiimides are added to a pressure vessel and heated in a carbon dioxide atmosphere under a certain pressure for dehydration condensation for 6-24 hours. R2. After the reaction is completed, the oligocarbonate can be obtained through post-processing. The composite catalyst comprises organic bases and carbodiimide compounds; The organic base is selected from at least one of N,N,N',N'-tetramethylethylenediamine, 4-dimethylaminopyridine, 4-pyrrolylpyridine, 1,8-diazabicyclo[5.4.0]undec-7-ene, 1,5,7-triazabicyclo[4.4.0]decen-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 as follows: ； Wherein, R is isopropyl or cyclohexyl; The structural formula of the aliphatic diol is selected from: , , One of them; Where n = 2, 3, 4, 5; In step R1, the molar ratio of the aliphatic diol, organic base, and carbodiimide compound is 1:(0.005-0.5):(0.5-0.9).

2. The method for preparing oligocarbonate according to claim 1, characterized in that, In step R1, the reaction pressure is 0.5-5 MPa and the reaction temperature is 80-150℃.

3. The method for preparing oligocarbonate according to claim 1, characterized in that, The post-processing procedure is as follows: after the reaction in step R1 is completed, a solvent is added at -20 to 0°C to fully dissolve the oligomers, the mixture is filtered, and the filtrate is acid-washed, dried, rotary evaporated, and vacuum-dried.

4. The method for preparing oligocarbonate according to claim 1, characterized in that, The solvent is selected from at least one of dichloromethane, trichloromethane, dichloroethane, tetrachloroethane, and methyl tert-butyl ether.

5. The method for preparing oligocarbonate according to claim 1, characterized in that, The amount of solvent used, by mass fraction, is 3-5 times the mass of the aliphatic diol fed into the feed.

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

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