Method for absorbing low-pressure CO2 based on ternary eutectic solvent

Abstract

The invention discloses a method for absorbing low-pressure CO2 based on a ternary eutectic solvent, the eutectic solvent is composed of a component A, a component B and a component C. The component A is a nitrogen heterocyclic organic matter, the component B is an organic alkali, the component C is water, in the eutectic solvent, the component A and the component C are hydrogen bond donors, and the component B is a hydrogen bond acceptor. The amido on the component A provides a reaction site for chemical absorption of CO2 and is a main absorbent; the component B is alkaline and has the effects of receiving protons and stabilizing a system; and the component C has the effects of promoting ion hydrolysis, reducing the viscosity of the system and maintaining the liquid state of the system. Under the synergistic effect of the three components, the ternary DESs show good absorption performance on low-pressure CO2.

Description

Technical Field

[0001] The present invention belongs to the field of gas absorption, and in particular relates to a method for absorbing low-pressure CO2 based on a ternary low eutectic solvent. Background Art

[0002] With the continuous use of fossil fuels, the content of carbon dioxide (CO2) in the atmosphere has increased year by year, leading to severe problems such as global warming, rising sea levels, and abnormal climate. To this end, the Intergovernmental Panel on Climate Change (IPCC) has issued a series of requirements to reduce carbon dioxide emissions to mitigate the greenhouse effect. CO2 capture and storage (CCS) is recognized as a very promising method to achieve this goal. At present, organic amine aqueous solutions are widely used in industry for chemical absorption of CO2. Under normal pressure, its absorption capacity of CO2 is as high as 0.12 g / g; however, this type of absorbent has the disadvantages of being corrosive, high cost, and easy to volatilize and cause secondary pollution. Therefore, the development of new green absorbents is of great significance for capturing CO2.

[0003] As a new type of green absorbent, deep eutectic solvents (DESs) have the advantages of simple synthesis, high atomic utilization, adjustable structure, and good stability, which provide the possibility for the development of green new CO2 capture technology. DESs are mixed by hydrogen bond acceptors (HBA) and hydrogen bond donors (HBD) in a certain molar ratio. Due to the hydrogen bonding between HBA and HBD, the melting point of DESs is lower than any of its components. There is no by-product in the synthesis process of DESs, and it can be used without separation after synthesis. In addition, the raw materials of DESs are easy to obtain and the cost is low. Therefore, DESs have been widely studied in CO2 absorption. In particular, in view of the efficient absorption performance of amine groups for CO2, many scholars have designed and synthesized a series of amine-functional DESs for CO2 capture and achieved good results. For example, Cao's group (Phys. Chem. Chem. Phys., 2015, 17, 27306-27316) found that at room temperature and pressure, [Bmim]Cl-MEA (1:3) DES absorbed 0.214 g / g of CO2. Li Shui'e (CN202210532653.9) designed and synthesized Im-MEA DESs for capturing CO2, with an absorption capacity of 0.27 ~ 0.33 g / g. However, since amine groups usually react with CO2 in a 2:1 stoichiometric ratio to generate carbamate (─NHCOO - ) and quaternary ammonium salts (─NH3 + ), so the molar ratio of amine organic matter to CO2 is usually lower than 0.5 mol / mol. - and NH3 +The formation of hydrogen bond networks between them leads to a sharp increase in viscosity, which is not conducive to the mass transfer rate of CO2 and the subsequent fluid transportation. In addition, most current studies only report the absorption performance of DESs for CO2 at normal pressure, while relatively few reports are on the capture effect of low-pressure CO2 (especially pressure below 0.1 bar). Therefore, how to achieve efficient absorption of low-pressure CO2 by functionalizing the structure of DESs is a hot topic in current research. Summary of the invention

[0004] Based on the above-mentioned problems of the prior art, the present invention proposes a method for absorbing CO2 based on a ternary low eutectic solvent, which greatly improves the absorption of low-pressure CO2 by utilizing a low eutectic solvent composed of three components.

[0005] To achieve the above object, the present invention adopts the following technical solution: A method for absorbing low-pressure CO2 based on a ternary low eutectic solvent, wherein the low eutectic solvent is composed of three components A, B, and C, wherein the component A is a nitrogen-containing heterocyclic organic substance, the component B is an organic base, and the component C is water. In the low eutectic solvent, the component A and the component C are hydrogen bond donors, and the component B is a hydrogen bond acceptor.

[0006] Preferably, in the method, the pressure of the CO2 is 0.01 ~ 0.1 bar.

[0007] Preferably, in the method, the temperature of the CO2 is 20 ~ 60°C.

[0008] Preferably, the method further comprises a desorption step after absorbing CO2.

[0009] Preferably, in the desorption step, the desorption temperature is 70-90° C., and the desorption time is 0.5-2 h.

[0010] Preferably, in the low eutectic solvent, the molar ratio of the A component to the B component is 1:0.5 to 1:3, and the mass fraction of the C component is 10% to 40%.

[0011] Preferably, the A component is selected from: Imidazole, pyrrole, 2-imidazolidinone, pyrazole, 4-chloroimidazole, 2-methylimidazole, 1,2,4-triazole, tetrazole or 2-pyrrolidone. Its structure is as follows:

[0012] .

[0013] Preferably, the B component is selected from: 1,8-diazabicyclo[5.4.0]undec-7-ene (CAS No.: 6674-22-2), 1,5-diazabicyclo[4.3.0]non-5-ene (CAS No.: 3001-72-7) or 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene (CAS No.: 84030-20-6). Its structure is as follows: .

[0014] Preferably, the deep eutectic solvent is prepared by the following method: The component A and the component B are uniformly mixed and heated to form a uniform and stable liquid, and then the component C is added and mixed uniformly to obtain the product.

[0015] The beneficial effects of the present invention are: The present invention utilizes a ternary low eutectic solvent to absorb low-pressure CO2. Compared with the applicant's prior art (Chinese patent CN113578018A), when DES reacts with CO2, the amine group (—NH) on the nitrogen-containing heterocyclic organic compound of component A preferentially reacts with CO2 to generate carbamic acid (RNCOOH, where R represents the rest of the heterocyclic ring). Due to the presence of H2O and organic bases in the system, carbamic acid (RNCOOH) is unstable in this environment. Under the action of H2O, it transfers proton H to the organic base (component B) to generate BH + , which itself becomes carbamate (RNHCOO - ), so the absorption system is stabilized. When CO2 is continuously introduced into the system, the carboxyl group of the carbamate group will continue to react with CO2 to form an intermediate (RNHCOOCOO - This intermediate is unstable and will be hydrolyzed under the action of H2O and the organic base of component B to release BH + and HCO3 - Ion pair, self-regenerating carbamate (RNHCOO - ) continues to cycle and absorb CO2. This increases the relative absorption of CO2 by the ternary low eutectic solvent. The amine group on component A provides the main reaction site for the chemical absorption of CO2 and is the main absorbent; component B is alkaline and has the function of receiving protons and stabilizing the system; component C has the function of promoting ion hydrolysis and transferring protons. In addition, after absorbing CO2, a large number of hydrogen bonds will be formed between the components of the system, causing the viscosity of the system to increase and may even turn into a solid state. Therefore, the addition of water also has the function of maintaining the liquid state of the system. The ternary low eutectic solvent proposed in the present invention has broad application prospects in the absorption of low-pressure CO2. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1This is a mechanism diagram of the CO2 absorption process of imidazole / 1,8-diazabicyclo[5.4.0]undec-7-ene / water DES in Example 1.

[0017] Figure 2 is the imidazole / 1,8-diazabicyclo[5.4.0]undec-7-ene / water DES with different CO2 contents absorbed in Example 1 13 C NMR spectrum.

[0018] Figure 3 FTIR spectra of imidazole / 1,8-diazabicyclo[5.4.0]undec-7-ene / water DES absorbing different amounts of CO2 in Example 1.

[0019] Figure 4 This is a photograph of the appearance of the DES system in Example 12 after absorbing CO2.

[0020] Figure 5 This is a picture of the appearance of the DES system after absorbing CO2 in Example 1. DETAILED DESCRIPTION

[0021] The technical solution of the present invention is further described below by means of specific embodiments, but the present invention is not limited to the following embodiments.

[0022] Example 1

[0023] Take imidazole as component A (0.094 mol, 6.4 g) and 1,8-diazabicyclo[5.4.0]undec-7-ene as component B (0.188 mol, 28.6 g), mix, stir and heat at a molar ratio of 1:2 (heating temperature is 75°C). After forming a uniform and stable mixed system (35 g), add C component H2O (15 g) to it, continue stirring and mixing, and a ternary low eutectic solvent with a water content of 30% can be synthesized. Weigh 1.5 g of the synthesized ternary low eutectic solvent into the absorption kettle, and then pass CO2 gas of different pressures into it and stir continuously, keeping the absorption temperature controlled at 30°C. After the reaction is balanced, the absorption amount of CO2 by the ternary low eutectic solvent is calculated according to the pressure change in the kettle. The calculation results are shown in Table 1: Table 1. Imidazole / 1,8-diazabicyclo[5.4.0]undec-7-ene / water DES absorption capacity for CO2

[0024] The above results show that even at extremely low pressures, the imidazole / 1,8-diazabicyclo[5.4.0]undec-7-ene / water DES has a very good absorption effect on CO2. When the pressure is only 0.01 bar, its relative absorption exceeds 0.5 mol / mol, and when the pressure rises to 0.1 bar, its relative absorption is even higher than 1 mol / mol. As mentioned above, since amine groups and CO2 usually react in a 2:1 stoichiometric ratio, the molar ratio of amine organic matter (such as imidazole) to CO2 is usually less than 0.5 mol / mol. However, with the addition of DBU and water, the absorption of DES exceeds this upper limit at extremely low pressures, indicating that the presence of DBU and water greatly promotes the absorption.

[0025] Regarding the CO2 absorption process of imidazole / 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) / water DES, the mechanism, such as Figure 1 As shown: First, when imidazole encounters CO2, the secondary amine group (R-NH) on it will react with CO2 to form carbamic acid (RNHCOOH). Carbamic acid (RNHCOOH) is unstable in this system, and its proton will be transferred to 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), thereby generating [DBUH + ][RNHCOO - ] This ion pair. When CO2 is continuously introduced, the carboxyl group on the carbamate group can continue to absorb CO2 due to its alkalinity, thereby generating RNHCOOCOO - Due to the presence of H2O in the system, the above intermediate is unstable and will undergo hydrolysis to generate RNHCOOH and HCO3 - RNHCOOH is unstable and transfers its proton to DBU, thereby generating [DBUH + ][RNHCOO - ] ion pair. With the increase of CO2 content, RNHCOO - The CO2 can be captured continuously and the above process is repeated. Therefore, there will be more HCO3 in the product. - Generation of.

[0026] To verify the above mechanism, the absorbents with different CO2 contents were characterized by NMR ( Figure 2 ) and infrared characterization ( Figure 3 ).Depend on Figure 2 It can be seen that after DES absorbs CO2, new signal peaks appear at δ = 165 ppm and 162 ppm. The peak at δ = 165 ppm belongs to RNHCOO -, while 162 ppm is caused by HCO3 - In addition, with the increase of CO2 absorption, RNHCOO - The peak height is getting lower and lower, while HCO3 - The peak height has increased significantly. This verifies the above mechanism. On the other hand, 175 ppm is the signal peak of 1C on DBU. As the CO2 absorption increases, the peak at 175 ppm gradually splits into two peaks. This is because the N next to 1C accepts the H proton of carbamic acid. This result is also consistent with the above mechanism.

[0027] according to Figure 3 As shown in the figure, when DES has not absorbed CO2, the -1 There is a signal peak at 1564 cm, which is generated by the NH stretching vibration on imidazole. However, as the CO2 absorption content increases, this signal peak gradually weakens and eventually disappears. This is due to the chemical interaction between the secondary amine group and CO2 to generate carbamic acid. At the same time, at 1564 cm -1 A new peak appears at - ). It is worth noting that this peak appears when the CO2 equilibrium partial pressure is only 0.012 bar. This indicates that when CO2 and DES first come into contact, CO2 and imidazole react to form carbamic acid. This is consistent with the above mechanism. At the same time, with the increase of CO2 solubility, the peak at 1390 cm -1 The signal peak at the position is becoming more and more obvious. This new peak is caused by HCO3 - This phenomenon indicates that HCO3 - It is gradually produced with the increase of CO2 concentration. This result is consistent with the above mechanism.

[0028] According to the above mechanism, it can be found that RNHCOO - After absorbing CO2, it is regenerated by hydrolysis, so that it can absorb CO2 again and achieve recycling. It is precisely because of its cyclic absorption that the relative absorption capacity of imidazole / 1,8-diazabicyclo[5.4.0]undec-7-ene / water DES absorbent for CO2 far exceeds 0.5 mol / mol.

[0029] Embodiments 2 to 9 Similar to Example 1, 1,8-diazabicyclo[5.4.0]undec-7-ene was used as component B, the type of component A was changed, and the absorption temperature, the molar ratio of components A to B (1:2) and the water content (30%) were kept unchanged. The calculation results of the absorption amount of CO2 by DESs under different CO2 partial pressures (Pe) are as follows (Table 2): Table 2. Effect of component A on CO2 absorption .

[0030] Embodiment 10-11 Similar to Example 1, imidazole was used as component A, the type of component B was changed, and the absorption temperature, the molar ratio of A to B, and the percentage of water were kept unchanged. The results of the absorption of CO2 by DESs at different CO2 partial pressures (Pe) are shown in the following table (Table 3): Table 3. Effect of component B on CO2 absorption

[0031] Embodiment 12-15 Similar to Example 1, imidazole was used as component A, 1,8-diazabicyclo[5.4.0]undec-7-ene was used as component B, the absorption temperature and the molar ratio of A to B were kept unchanged, and the percentage of water was changed. The calculation results of the absorption amount of CO2 by DESs under different CO2 partial pressures (Pe) are as follows (Table 4): Table 4. Effect of water (C component) content on the CO2 absorption performance of DESs

[0032] When there is no water in the system (Example 12), after CO2 is introduced, DES can only absorb CO2 in the initial stage. However, as the absorption process proceeds, the viscosity of the system increases sharply, causing the absorbent to change from liquid to solid (e.g. Figure 4 ), at this time, the time for absorption to reach equilibrium is greatly extended, and it is difficult to measure its specific absorption amount. After adding water to the system, the absorbent can still remain in a liquid state after absorbing CO2 (such as Figure 5 ), with moderate viscosity. It can be seen that the presence of water plays an important role in reducing the viscosity of the system and maintaining the liquid state of the system. In addition, when the water content is relatively low, the relative absorption of CO2 by DES is low (Examples 13 and 14). This is because the presence of water can promote the absorption of RNHCOOCOO - Hydrolysis of the intermediate to generate RNHCOO - Repeated absorption of CO2. However, when the water content is as high as 40%, although the relative absorption capacity of the absorbent increases, its absolute absorption capacity decreases significantly. This phenomenon is not conducive to practical industrial applications. Therefore, the comprehensive performance is relatively good when the water content is around 30%.

[0033] Embodiments 16 to 18

[0034] Similar to Example 1, imidazole was used as component A, 1,8-diazabicyclo[5.4.0]undec-7-ene was used as component B, the absorption temperature and the percentage of water were kept constant, and the molar ratio of A to B was changed. The calculation results of the absorption amount of CO2 by DESs at different CO2 partial pressures (Pe) are as follows (Table 5): Table 5. Effect of the molar ratio of components A and B on CO2 absorption

[0035] Embodiments 19 to 22

[0036] Similar to Example 1, imidazole was used as component A, 1,8-diazabicyclo[5.4.0]undec-7-ene was used as component B, and the molar ratio of components A and B and the percentage of water were kept unchanged. T ), under different CO2 partial pressures (Pe), the calculation results of the absorption of CO2 by DESs are as follows (Table 6): Table 6. Effect of temperature on CO2 absorption by DESs

[0037] According to the data in Table 6, it can be seen that with the increase of absorption temperature, the absorption capacity of the ternary DES for CO2 decreases significantly. This is consistent with the relationship between the solubility of most gases and temperature.

[0038] Embodiment 23

[0039] The imidazole (A) / 1,8-diazabicyclo[5.4.0]undec-7-ene (B) / water (C) DES in Example 1 is first subjected to a CO2 absorption reaction. After the absorption is completed, it is heated to 80°C. At this time, the absorbed CO2 will escape from the DES liquid phase. The escaped CO2 is extracted from the absorption kettle in batches to 0.01 bar by a vacuum pump for desorption, and the desorption takes 1 hour. After the desorption experiment is completed, the regenerated DES continues to absorb CO2 again at 30°C to test its absorption capacity for CO2. The absorption-desorption cycle is repeated 4 times, and the absorption results measured in each cycle are shown in Table 7: Table 7. Regeneration performance of DES (desorption temperature: 80 °C, desorption time: 1 h)

[0040]

[0041] Embodiments 24 to 27

[0042] Similar to Example 23, four cycles of absorption-desorption were conducted using imidazole (A) / 1,8-diazabicyclo[5.4.0]undec-7-ene (B) / water (C) DES, with the regeneration temperature and regeneration time changed. The absorption results are shown in the following table (Table 8): Table 8. Regeneration performance of DES under different regeneration conditions

[0043]

[0044] The above implementation cases are only some of the cases of the present invention. Of course, the present invention is not limited to the above cases, and there are related extensions and variations. All derivatives that can be directly derived or associated with the contents disclosed by ordinary technicians in this field should be considered as the protection scope of the present invention.

Claims

1. A method for absorbing low-pressure CO2 based on a ternary deep eutectic solvent, characterized in that: The low eutectic solvent is composed of three components A, B, and C, wherein the component A is a nitrogen-containing heterocyclic organic substance, the component B is an organic base, and the component C is water. In the low eutectic solvent, the components A and C are hydrogen bond donors, and the component B is a hydrogen bond acceptor.

2. The method according to claim 1, characterized in that The A component is selected from: Imidazole, pyrrole, 2-imidazolidinone, pyrazole, 4-chloroimidazole, 2-methylimidazole, 1,2,4-triazole, tetrazole or 2-pyrrolidone.

3. The method according to claim 1, characterized in that The B component is selected from: 1,8-diazabicyclo[5.4.0]undec-7-ene, 1,5-diazabicyclo[4.3.0]non-5-ene or 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene.

4. The method according to claim 1, characterized in that The pressure of the CO2 is 0.01 ~ 0.1 bar.

5. The method according to claim 1, characterized in that The temperature of the CO2 is 20 ~ 60°C.

6. The method according to claim 1, characterized in that The method also includes a desorption step after absorbing CO2.

7. The method according to claim 6, characterized in that In the desorption step, the desorption temperature is 70-90° C., and the desorption time is 0.5-2 h.

8. The method according to claim 1, characterized in that In the low eutectic solvent, the molar ratio of the A component to the B component is 1:0.5 to 1:3, and the mass fraction of the C component is 10% to 40%.

9. The method according to claim 1, characterized in that: The deep eutectic solvent is prepared by the following method: The component A and the component B are uniformly mixed and heated to form a uniform and stable liquid, and then the component C is added and mixed uniformly to obtain the product.

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