Method for synthesizing carbonate by absorbing and in-situ converting CO2 with a non-halogen ionic liquid

Abstract

The present invention discloses a method for constructing an ionic liquid structure containing non-halogen weak basic sites to absorb and in-situ catalytically convert CO2 and synthesize cyclic carbonates under mild conditions. Ionic liquids with quaternary phosphonium salt cations / imidazole cations and different weak base anions are used as absorbents and catalysts. Gaseous CO2 is first absorbed and captured, and then in-situ catalytically converted into cyclic carbonates under mild conditions without gas pressure. The method of the present invention can simply and quickly synthesize a series of ionic liquids with non-halogen weak basic anions, avoid the generation of halogenated alcohols, has the characteristics of integration of CO2 absorption activation-catalytic conversion, wide substrate applicability, realizes the resource utilization of renewable carbon under pressureless and mild conditions, and provides a feasible solution for industrial conversion.

Description

Technical Field

[0001] The present invention relates to the field of green synthesis of simply and rapidly synthesizing non-halogen weak basic ionic liquids for CO2 absorption-in-situ catalytic conversion. Specifically, by changing the structures of cations and anions, the nucleophilicity and stability of ionic liquids are regulated to achieve the absorption of CO2 by weak basic ionic liquids under mild conditions and the in-situ catalytic conversion thereof to realize the method for synthesizing cyclic carbonates without pressure from low-concentration CO2. Background Art

[0002] CO2 is the main component of greenhouse gases. With the consumption of fossil fuels, its continuous accumulation has brought many environmental and social problems. At the same time, CO2 is also a renewable C1 resource with rich reserves, wide sources, non-toxic, harmless, cheap and easily available. Utilizing it resourcefully can achieve the conversion of inorganic carbon into high-value-added chemicals. However, at present, the main method for large-scale treatment of CO2 is to absorb, capture and store it (CCS), which requires too much energy input and cannot effectively utilize this C1 resource. Moreover, CO2 molecules have thermodynamic stability and kinetic inertness, and their reactivity is relatively low when participating in reactions, requiring high energy input. Therefore, activating CO2 absorption and then performing in-situ catalytic conversion is one of the efficient and mild conversion strategies. This method can bypass the storage step, avoid excessive energy consumption in the subsequent process of CCS, and is also conducive to realizing the integration of CO2 absorption-in-situ conversion and gently preparing cyclic carbonate compounds.

[0003] Cyclic carbonates are classic organic solvents and intermediates, and are classic electrolyte solutions. Driven by the new energy field, their demand has increased rapidly. Traditional methods for synthesizing cyclic carbonates include phosgene method, urea alcoholysis method, transesterification method, etc., all of which have disadvantages such as large pollution, complex reaction processes, harsh conditions, high costs, and more by-products. The direct cycloaddition synthesis method of CO2 has 100% atom utilization rate, but this traditional process uses catalytic systems such as organic complexes (Green Chemistry, 2020, 12, 1514 - 1539, CN 104327036A), metal salts (Journal of Organic Chemistry, 1993, 58, 6198 - 6202), halogen-containing ionic liquids (ACS Sustainable Chemistry & Engineering 2019, 7, 16674 - 16681, CN108586343A), etc., and there are problems such as harsh reaction conditions and unavoidable halogenated by-products. In addition, for the mild conversion system of low-concentration CO2, its substrate applicability still needs to be improved (Science China Chemistry, 2017, 60, 958 - 963). Therefore, improving the structure and performance of the catalyst, designing and constructing weak basic sites of ionic liquids, and improving the absorption and catalytic performance of ionic liquids, so as to realize a new process for the absorption-in-situ conversion synthesis of cyclic carbonates under mild conditions, has important scientific and industrial significance. Summary of the Invention

[0004] In view of the problems that more halogenated by-products will be generated during the catalytic process of halogen ionic liquids and the reaction conditions are harsh during the direct conversion of gaseous CO2, a series of ionic liquid structures containing non-halogen weak basic sites are constructed in the present invention, and the structures and performances of the absorption and catalytic systems are improved, avoiding excessive energy input, realizing the integration of CO2 absorption activation and catalytic conversion under green and mild conditions, and having high industrial value.

[0005] To achieve this purpose, the present invention adopts the following technical solutions:

[0006] In the first aspect, a series of weak basic ionic liquids of the present invention include the following several cationic structures:

[0007]

[0008] Among them, the conditions to be satisfied are that m is any integer from 0 to 16, and n is any integer from 1 to 14; the chain length of the group connected to the nitrogen atom of the imidazole ring can be controlled, and the chain tail can be different groups, such as methyl, hydroxyl, amino, mercapto, sulfonic acid group, carboxyl group, etc.; for quaternary phosphonium salt cations, alkyl groups, aryl groups, heterocyclic groups, etc. with different chain lengths can be selected.

[0009] A series of weakly basic ionic liquids of the present invention include the following anion structures:

[0010]

[0011] The anions of a series of weakly basic ionic liquids may include imide anions, cyano-substituted anions, pyrimidine / pyridine anions. The R, R 1 , R 2 groups carried by imide ionic liquids are mainly alkyl groups, aryl groups, amino groups, hydroxyl groups, etc., and the R groups of cyano-substituted ionic liquids are mainly alkyl groups, aryl groups, N / O heteroatom groups, etc.

[0012] A series of weakly basic ionic liquids prepared by the present invention are in a viscous or solid state at room temperature, have good thermal stability, almost no vapor pressure, and a thermal decomposition temperature of about 270 °C, and can be used as excellent catalysts for catalyzing the cycloaddition reaction of CO2.

[0013] The present invention designed and synthesized novel imide-based, pyrimidine / pyridine-based, and cyano-substituted nitrogen / carbon negative ionic liquids, which are synthesized conveniently, the catalytic reaction is mild and efficient, the weakly basic sites have low requirements for equipment, taking into account both activity and stability, and avoiding side reactions and by-products brought about by the presence of halide ions.

[0014] In a second aspect, the present invention also provides a method for synthesizing cyclic carbonates by using a weakly basic ionic liquid to catalyze CO2, and the method uses the catalyst described in the first aspect.

[0015] 1. Using a non-halogen weakly basic ionic liquid as a catalyst to catalyze CO2 gas to prepare cyclic carbonates, and the reaction general formula is:

[0016]

[0017] wherein R is a straight-chain or branched alkyl group of substituted or unsubstituted C1-C 20 , a cycloalkyl group of substituted or unsubstituted C3-C 20 , a heterocycloalkyl group of substituted or unsubstituted C3-C 20 , or an aryl group of substituted or unsubstituted C6-C 20 of one kind.

[0018] Preferably, the preparation method includes the following steps:

[0019] Under the conditions of using a non-halogen weakly basic anion ionic liquid as a catalyst, the molar fraction of the epoxide is 1-10 mol%, the reaction pressure is 0.5-4 MPa, and the reaction temperature is 60-140 °C, the cycloaddition reaction of CO2 and the epoxide is carried out for 0.5-12 h to synthesize ethylene carbonate.

[0020] 2. Using non-halogen weak basic ionic liquids as absorbents to directly absorb CO2, and under the conditions of no gas pressure and no additional catalyst added, the cycloaddition reaction is carried out in situ to synthesize cyclic carbonates. The general reaction formula is:

[0021]

[0022] where R is a straight-chain or branched alkyl group with substituted or unsubstituted C1-C 20 a cycloalkyl group with substituted or unsubstituted C3-C 20 a heterocycloalkyl group with substituted or unsubstituted C3-C 20 or an aryl group with substituted or unsubstituted C6-C 20 one of them.

[0023] Preferably, the preparation method includes the following steps:

[0024] The non-halogen weak basic anionic ionic liquid absorbs 100 mL / min CO2 at room temperature by solvent dilution. After the absorption reaches equilibrium, an equimolar amount of epoxide is added. Without pressure, the reaction temperature is 30 - 60 °C, and the reaction time is 8 - 24 h. The absorbed CO2 and the epoxide undergo a cycloaddition reaction to synthesize the corresponding cyclic carbonate. The solvent of the absorption and conversion system is ethylene glycol and polyethylene glycols.

[0025] The beneficial effects of the present invention are as follows: The non-halogen weak basic ionic liquid designed and synthesized in the present invention can absorb and capture CO2 and catalyze its in-situ conversion, realizing the green resource utilization process of low-concentration CO2 to cyclic carbonates under mild conditions, and has the advantages of simple synthesis, high absorption-catalytic activity and integration, and the system does not contain metals and halogens. The target product cyclic carbonate has mild reaction conditions and high selectivity, conforms to the principle of green economy and environmental protection, and has broad application prospects in electrolyte solvents, catalytic reactions, and as separation and extraction media, etc. Specific Embodiments

[0026] The technical solutions of the present invention will be further described below through specific embodiments. However, the present invention is not limited to the following examples.

[0027] Exemplarily, an ionic liquid with a phosphonium salt cation and an imide anion can be synthesized through the following steps:

[0028] Add an aqueous solution of tetraalkylphosphonium hydroxide (4 mmol) to a 100 mL single-neck round-bottom flask equipped with a magnetic stirrer, add 15 mL of absolute ethanol, and then add imide (4 mmol) to the flask. Place it in a water bath and stir the reaction mixture at room temperature for 24 h. After the reaction is completed, rotary evaporate for 2 h and then vacuum dry for 12 h to finally obtain the product.

[0029] Exemplarily, an ionic liquid with imidazole cation and imide anion can be synthesized through the following steps:

[0030] First, prepare the bromide salt of hydroxyimidazole. Mix bromoethanol (0.01 mol) and 1-methylimidazole (0.011 mol) in toluene (20 mL), and heat the mixture at 110 °C for 24 h. After the reaction is completed, remove toluene by rotary evaporation, and wash with ethyl acetate to form a white solid. Finally, vacuum dry 1-hydroxyethyl-3-methylimidazolium bromide for 12 h. Subsequently, add potassium hydroxide (0.02 mol), 1-hydroxyethyl-3-methylimidazolium bromide (0.02 mol), and dichloromethane (25 mL) to a round-bottom flask, and stir the mixture at room temperature for 24 hours. After the reaction is completed, filter the mixed solution under reduced pressure to obtain a precipitate, and then wash with ether. Vacuum dry for 10 h to obtain 1-hydroxyethyl-3-methylimidazolium hydroxide salt. Dissolve 1-hydroxyethyl-3-methylimidazolium hydroxide salt (0.01 mol) and imide (0.01 mol) in absolute ethanol, and stir at room temperature for 24 h. After the reaction, wash with chloroform after rotary evaporation, and vacuum dry for 24 h to finally obtain the product.

[0031] Exemplarily, an ionic liquid with phosphonium salt cation and pyrimidine / pyridine anion can be synthesized through the following steps:

[0032] Add an aqueous solution of tetraalkylphosphonium hydroxide (4 mmol) to a 100 mL single-neck round-bottom flask equipped with a magnetic stir bar, add 15 mL of absolute ethanol, then add pyrimidine / pyridine (4 mmol) to the flask, place it in a water bath, and stir the reaction mixture at room temperature for 24 h. After the reaction is completed, perform rotary evaporation under reduced pressure and then vacuum dry for 12 h to finally obtain the product.

[0033] Exemplarily, an ionic liquid with imidazole cation and pyrimidine / pyridine anion can be synthesized through the following steps:

[0034] First, prepare the bromide salt of hydroxyimidazole. Mix bromoethanol (0.01 mol) with 1-methylimidazole (0.011 mol) in toluene (20 mL), and heat the mixture at 110 °C for 24 h. After the reaction is completed, remove toluene by rotary evaporation and wash with ethyl acetate to form a white solid. After drying 1-hydroxyethyl-3-methylimidazole bromide in a vacuum drying oven, add potassium hydroxide (0.02 mol), 1-hydroxyethyl-3-methylimidazole bromide (0.02 mol) and dichloromethane (25 mL) to a round-bottom flask, and stir the mixture at room temperature for 24 h. After the reaction is completed, filter the mixed solution under reduced pressure to obtain a precipitate, and then wash with ether and vacuum dry for 10 h to obtain 1-hydroxyethyl-3-methylimidazole hydroxide salt. Dissolve 1-hydroxyethyl-3-methylimidazole hydroxide salt (0.01 mol) and pyrimidine / pyridine (0.03 mol) in absolute ethanol, and then stir the mixture at room temperature for 24 h. After the reaction, vacuum dry for 24 h to finally obtain the product.

[0035] Exemplarily, an ionic liquid with a phosphonium salt cation and a cyano-substituted anion can be synthesized through the following steps:

[0036] Add an aqueous solution of tetraalkylphosphonium hydroxide (4 mmol) to a 100 mL single-neck round-bottom flask equipped with a magnetic stir bar, add 15 mL of absolute ethanol, and then add a cyano-substituted carbanion and nitrogen anion precursor (4 mmol) to the flask. Place it in a water bath and stir the reaction mixture at room temperature for 24 h. After the reaction is completed, perform rotary evaporation and then vacuum dry for 12 h to finally obtain the product.

[0037] Exemplarily, an ionic liquid with an imidazole cation and a cyano-substituted anion can be synthesized through the following steps:

[0038] First, prepare the bromide salt of hydroxyimidazole. Mix bromoethanol (0.01 mol) with 1-methylimidazole (0.011 mol) in toluene (20 mL), and heat the mixture at 110 °C for 24 h. After the reaction is completed, remove toluene by rotary evaporation and wash with ethyl acetate to form a white solid. Finally, vacuum dry 1-hydroxyethyl-3-methylimidazole bromide for 12 h. Add potassium hydroxide (0.02 mol), 1-hydroxyethyl-3-methylimidazole bromide (0.02 mol) and dichloromethane (25 mL) to a round-bottom flask, and stir the mixture at room temperature for 24 h. After the reaction is completed, filter the mixed solution under reduced pressure to obtain a precipitate, and then wash with ether and vacuum dry for 10 h to obtain 1-hydroxyethyl-3-methylimidazole hydroxide salt. Dissolve 1-hydroxyethyl-3-methylimidazole hydroxide salt (0.01 mol) and a cyano compound (0.01 mol) in acetone and stir at room temperature for 48 hours. Remove the solvent by rotary evaporation and vacuum dry for 24 h to finally obtain the product.

[0039] In each embodiment of the present invention, the yield of the product is quantitatively determined by a 7890A-FID gas chromatograph produced by Agilent Technologies. Description of the Drawings

[0040] Figure 1 For the imidazole-based quaternary phosphonium salt ionic liquid catalyst [P 4444 + [Suc - synthesized in the present invention, 1 1H NMR spectrum (600 MHz, CDCl3);

[0041] Figure 2 For the pyrimidine-based quaternary phosphonium salt ionic liquid catalyst [P 4444 + [2,4-Oym-5-Ac - synthesized in the present invention, 1 1H NMR spectrum (600 MHz, CDCl3);

[0042] Figure 3 For the cyano-based quaternary phosphonium salt ionic liquid catalyst [P 4444 + [Malon - synthesized in the present invention, 1 1H NMR spectrum (600 MHz, CDCl3).

[0043] Example 1

[0044] Add 1 g of ethylene oxide (EO) and 0.3 mmol of an ionic liquid with a quaternary phosphonium cation and an imide anion to the reaction kettle. Charge an appropriate amount of CO2 at room temperature and close the gas inlet valve of the reactor. Place the reaction kettle in an automatic temperature-controlled heating furnace. To prevent the carbonylation reaction from being too violent in the initial stage, adjust the pressure of the reaction kettle to 0.5 MPa first. After the temperature reaches the target temperature, adjust the pressure of the reaction kettle to 3 MPa and react at 110 °C for 4 h. After the reaction is completed, cool the reaction kettle to room temperature, collect the gas phase and the reaction solution respectively, and perform conversion and selectivity analysis using a gas chromatograph. The yield of ethylene carbonate as the product is 92.4 - 98.2%, and the selectivity is 93 - 95%.

[0045] Example 2

[0046] Add a certain amount of ionic liquid catalyst with phosphonium salt cation and imide anion and triethylene glycol to the reactor liner. After sealing, fill with CO2 at 100 mL / min at room temperature, weigh every 5 minutes. When the weight no longer increases, that is, the absorption equilibrium is reached. Then add ethylene oxide, put it into the reactor, adjust the reactor temperature to 60 - 80 °C, react for 4 - 8 h. After the reaction, cool the reactor to room temperature, take out the reaction solution, and analyze the yield of ethylene carbonate by NMR. The yield of the product ethylene carbonate is 50 - 80%, and the selectivity is 95 - 98%.

[0047] Example 3

[0048] The difference from Example 1 is that the ionic liquid used is an ionic liquid with phosphonium salt cation and pyrimidine anion, and other conditions remain unchanged.

[0049] For the product ethylene carbonate obtained in Example 3, the yield of the product ethylene carbonate is 91 - 93%, and the selectivity is 93 - 95%.

[0050] Example 4

[0051] The difference from Example 1 is that the ionic liquid used is an ionic liquid with phosphonium salt cation and cyano anion, and other conditions remain unchanged.

[0052] For the product ethylene carbonate obtained in Example 4, the yield of the product ethylene carbonate is 91 - 93%, and the selectivity is 93 - 95%.

[0053] Example 5

[0054] The difference from Example 1 is that the epoxide used is propylene oxide, and other conditions remain unchanged.

[0055] For the product propylene carbonate obtained in Example 5, the yield of the product propylene carbonate is 91 - 93%, and the selectivity is 95 - 98%.

[0056] Example 6

[0057] The difference from Example 1 is that the epoxide used is epichlorohydrin, and other conditions remain unchanged.

[0058] For the product allyl chloroformate obtained in Example 6, the yield of the product propylene carbonate is 94 - 96%, and the selectivity is 95 - 98%.

[0059] Example 7

[0060] The difference from Example 1 is that the epoxide used is styrene oxide, and other conditions remain unchanged.

[0061] For the product styrene carbonate obtained in Example 7, the yield of the product propylene carbonate is 85 - 88%, and the selectivity is 95 - 98%.

[0062] Example 8

[0063] The difference from Example 2 is that the epoxide used is propylene oxide, and other conditions remain unchanged.

[0064] The product obtained in Example 8 is propylene carbonate, and the yield of propylene carbonate is 50 - 78%, and the selectivity is 95 - 98%.

[0065] Example 9

[0066] The difference from Example 2 is that the epoxide used is epichlorohydrin, and other conditions remain unchanged.

[0067] The product obtained in Example 9 is allyl chloroformate, and the yield of propylene carbonate is 55 - 82%, and the selectivity is 95 - 98%.

[0068] Example 10

[0069] The difference from Example 2 is that the epoxide used is styrene oxide, and other conditions remain unchanged.

[0070] The product obtained in Example 10 is styrene carbonate, and the yield of propylene carbonate is 40 - 65%, and the selectivity is 95 - 98%.

[0071] Example 11

[0072] The difference from Example 6 is that the temperature used is 60°C and the reaction is carried out for 12 hours, and other conditions remain unchanged.

[0073] The product obtained in Example 11 is allyl chloroformate, and the yield of propylene carbonate is 96 - 98%, and the selectivity is 97 - 98%.

[0074] The applicant declares that the above - mentioned is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any modification, equivalent replacement, improvement, etc. made by any person skilled in the art within the technical scope disclosed by the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing cyclic carbonates by catalyzing CO2 with a non-halogen weak basic ionic liquid, characterized in that: Using a non-halogen weak basic ionic liquid as a catalyst to catalyze the gas CO2 to prepare cyclic carbonates, the reaction general formula is: wherein R is a straight-chain or branched-chain alkyl group having 1 to 20 carbon atoms, a cycloalkyl group having 3 to 20 carbon atoms, a heterocycloalkyl group having 3 to 20 carbon atoms, or an aryl group having 6 to 20 carbon atoms; Under the conditions of using a non-halogen weak basic ionic liquid as a catalyst, the molar fraction of the epoxide being 1-10 mol%, the reaction pressure being 0.5-4 MPa, and the reaction temperature being 60-140 °C, carry out the cycloaddition reaction of CO2 and the epoxide for 0.5-12 h to synthesize the corresponding cyclic carbonate; The cation structure of the non-halogen weak basic ionic liquid is: The quaternary phosphonium salt cation is a tetrabutyl quaternary phosphonium salt cation; The anion of the non-halogen weak basic ionic liquid is a malononitrile anion.

2. The non-halogen weak basic ionic liquid according to claim 1, characterized in that: The preparation method of the non-halogen weak basic ionic liquid includes reacting a quaternary phosphonium hydroxide salt with a proton-containing anion precursor to obtain the non-halogen weak basic ionic liquid.

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