An ionic liquid composite activated carbon fiber absorbent for air CO2 capture and its application

Abstract

The present invention discloses an ionic liquid composite activated carbon fiber absorbent for air CO2 capture and its application. The absorbent of the present invention uses activated carbon fiber (ACF) as the base material. After the base material is modified by a surfactant, it is then loaded with an ionic liquid. In the present invention, the activated carbon fiber is first modified with a surfactant to fill the pores of the activated carbon fiber with the surfactant. Subsequently, the ionic liquid with a relatively high viscosity is impregnated into the pores of the activated carbon fiber rich in the surfactant. The surfactant can eliminate or reduce the surface tension between the ionic liquids, so that the ionic liquids with high viscosity will not stick to each other and block the pores of the carbon fiber, but will form a uniform liquid film extending on the large specific surface area of the activated carbon fiber. The large gas-liquid contact area enables the adsorbent to have a high capture capacity for CO2 gas at a low concentration of about 400 ppm in the air.

Description

Technical Field

[0001] The invention belongs to the technical field of gas separation, and in particular relates to an ionic liquid composite activated carbon fiber absorbent for capturing CO2 from air and an application thereof. Background Art

[0002] Carbon capture, utilization and storage (CCUS) technology is a cutting-edge technology for mitigating greenhouse gas emissions that has been recognized internationally in recent years. There are many methods for CO2 capture, including solvent absorption, adsorption separation, membrane separation, and cryogenic liquefaction separation (Energy & Fuels, 2018, 32 (7): 7727-7733). Among them, direct air capture (DCA) technology has no geographical restrictions and can place the capture point and storage point in one place, reducing transportation costs. It can also solve the emission problems of many CO2 distribution sources such as transportation and construction industries, and can also avoid the impact of high concentrations of pollutants (such as NOx, SOx, etc.) in flue gas on the performance of adsorbents / absorbents. It is a carbon capture technology with great development prospects (Chemical Industry Progress, 2024.1-19, 1000-6613).

[0003] Among them, the solvent absorption method is a relatively mature CO2 capture method. At present, the most widely used method in industry is the amine method, which mainly uses aqueous amine solutions such as ethanolamine (MEA), diethanolamine (DEA), and methyldiethanolamine (MDEA) as absorbents to capture and separate CO2 (Separation and Purification Technology, 2021(2):119181.). However, the amine method has problems such as high solvent volatility, high loss, and high regeneration energy consumption, which makes it difficult to meet the needs of green and sustainable development. Therefore, the development of efficient, low-energy, and green CO2 capture and separation technologies has become a hot topic in international research.

[0004] Ionic liquids (ILs) are organic salts composed entirely of anions and cations, and have the characteristics of low vapor pressure, good gas solubility and adjustable structure. Conventional ionic liquids absorb CO2 mainly through physical interactions such as electrostatic force, van der Waals force, hydrogen bond, etc. between anions and cations and CO2, so the solubility of CO2 is relatively limited under low partial pressure. In order to improve the CO2 absorption performance, a series of amino, carboxylic acid, nitrogen heterocyclic and other functional ionic liquids have been developed successively (RSC ADVANCES, 2013, 3 (36): 15518-15527.), and these functional ionic liquids have more advantages in CO2 absorption performance, and can even achieve equimolar or supermolar absorption. The imide functional ionic liquid tributyl quaternary ethylphosphonimide salt ([P 4442[Suc]) showed the highest absorption capacity (Angewandte Chemie, 2017, 56(43): 13293-13297.), at 20°C and 0.1MPa, the absorption capacity of pure CO2 was 1.87 mol CO2 / mol IL, and the absorption capacity at 10% CO2 concentration could reach 1.65 molCO2 / mol IL; Patent CN112892160B reported a phase change CO2 absorbent of AEP / n-propanol aqueous solution, with an absorption load of 1.26 mol / mol at 10% CO2 concentration at 40°C. However, the viscosity of ionic liquids is relatively high. In particular, during the absorption process, the ionic liquids and the CO2 system form a complex hydrogen bond network structure, which leads to a sharp increase in viscosity, affecting mass transfer and limiting their application in absorption separation (Science China: Chemistry, 2014, 44(6): 1050-1057). Other organic solvents need to be added to enhance absorption or separation. Patent CN111871152A reports a functionalized ionic liquid: tetraethylenepentamine-5-aminoimidazole-4-carboxamide salt, and organic solvents n-propanol (NPA) and ethylene glycol (EG) are added to [TEPAH][AICA] for compounding. The obtained [TEPAH][AICA] / NPA / EG solution has an absorption load of 1.78 mol / mol for a CO2 concentration of 10% at 40°C; the [TEPAH][CPL] / EG / DGDE solution prepared by patent CN115945034A has an absorption load of 1.86 mol / mol for a CO2 concentration of 15% at 40°C.

[0005] The above-mentioned ionic liquids, although having a large absorption capacity, have the disadvantages of complex preparation, becoming sticky after absorption, slow absorption / analysis rate, and long absorption time, which hinder their large-scale application. In addition, the ionic liquids that are not easily volatile are matched with some volatile organic solvents (such as adding ionic liquids to organic solvents n-propyl alcohol NPA or diethylene glycol dimethyl ether DGDE reported in patents CN110339672A, CN111871152A, and CN115945034A for compounding), although the absorption effect is enhanced, these solvents still have a certain vapor pressure, and long-term use requires the addition of organic solvents.

[0006] In summary, ionic liquids have the advantages of designable structure, adjustable performance and good stability. They are chemical absorbents with relatively promising development prospects in CO2 capture technology. Currently, most ionic liquids only increase the absorption capacity by compounding with organic solvents, and do not fully utilize ionic liquids fundamentally.

[0007] The present invention aims to develop an ionic liquid composite activated carbon fiber absorbent that is highly effective in capturing CO2 from air. The activated carbon fiber (ACF) with a large specific surface area, fast adsorption speed, few impurities, and abundant micropores is first modified with a surfactant, and then the prepared ionic liquid is impregnated into the activated carbon fiber (ACF) with an equal volume of ethanol. The surfactant reduces or eliminates the surface tension of the ionic liquid, prevents the ionic liquid from agglomerating, and allows it to fully spread or extend in the pores of the activated carbon fiber (ACF) and form a liquid film, increasing the gas-liquid contact interface, so that the absorbent has a very high adsorption capacity and adsorption efficiency. This increases the diversity of the subsequent adsorption material construction and provides new ideas for the industrial application of capturing carbon dioxide from air. Summary of the invention

[0008] In view of the shortcomings of ionic liquids, such as complex preparation, stickiness after absorption, slow absorption / analysis rate, and long absorption time, the purpose of the present invention is to provide an ionic liquid composite activated carbon fiber absorbent for air CO2 capture and its application, by first modifying activated carbon fiber (ACF) with a large specific surface area, fast adsorption rate, few impurities, and rich micropores with a surfactant, and then impregnating the prepared ionic liquid into the activated carbon fiber (ACF) with an equal volume of ethanol. The surfactant reduces or eliminates the surface tension of the ionic liquid, prevents the ionic liquid from agglomerating, and allows it to fully spread or extend in the pores of the activated carbon fiber (ACF) and form a liquid film, increasing the gas-liquid contact interface, so that the absorbent has a very high adsorption capacity and adsorption efficiency. It increases the diversity of the construction of subsequent adsorption materials and provides new ideas for the industrial application of air capture of carbon dioxide.

[0009] The technical solution adopted by the present invention to solve its technical problem is:

[0010] The ionic liquid composite activated carbon fiber absorbent for air CO2 capture uses activated carbon fiber ACF as a base material. The base material is modified by a surfactant and then loaded with an ionic liquid to form the absorbent.

[0011] Furthermore, the ionic liquid includes but is not limited to: one or more of tetraethylenepentamine-imidazole, tetraethylenepentamine-glycine, tetraethylenepentamine-bistrifluoromethanesulfonimide, tetraethylenepentamine-2-methylimidazole, tetraethylenepentamine-4-hydroxypyridine, tetraethylenepentamine-tetrafluoroboric acid, and tetraethylenepentamine-hexafluorophosphoric acid.

[0012] Furthermore, the surfactant includes, but is not limited to: one or more of polyoxyethylene sorbitan laurate (Tween 20), polyoxyethylene sorbitan monopalmitate (Tween 40), polyoxyethylene sorbitan monostearate (Tween 60), polyethylene glycol (PEG), N-methylpyrrolidone (NMP), cetyltrimethylammonium chloride (CTAC), betaine (Betaine), and sodium methyl ester sulfonate (MES).

[0013] Furthermore, the preparation method of the ionic liquid includes the following differences:

[0014] The first step is to mix tetraethylenepentamine and a compound containing a corresponding anionic group in a molar ratio of 1:1-3, and the mixed solution is heated in a water bath at 60-80°C and stirred at a speed of 500-2000 r / min for 6-12 hours; the compound containing a corresponding anionic group is one or more of imidazole, glycine, bistrifluoromethanesulfonimide, 2-methylimidazole, 4-hydroxypyridine, tetrafluoroboric acid, and hexafluorophosphoric acid;

[0015] Step 2: After the first step of the reaction is completed, the unreacted raw materials in the ionic liquid are removed by reduced pressure distillation, and then the product is placed in a vacuum drying oven at 60-80°C and dried for 6-15 hours to remove residual moisture, thereby obtaining the corresponding ionic liquid.

[0016] Furthermore, the preparation method of the ionic liquid composite activated carbon fiber absorbent comprises the following steps:

[0017] 1) Soaking the activated carbon fiber in 1-2 mol / L sodium hydroxide solution for 6-12 hours to remove impurities such as contamination layer and oxidation layer on the surface of the activated carbon fiber, filtering out, washing with deionized water until neutral, and then drying;

[0018] 2) dissolving a surfactant in ethanol to prepare a surfactant solution, placing the activated carbon fiber dried in step 1) in the surfactant solution, soaking for 6-12 hours, and then drying to obtain surfactant-modified activated carbon fiber;

[0019] 3) The solution prepared by dissolving the ionic liquid in ethanol is impregnated onto the surfactant-modified activated carbon fiber, and then blow-dried under a nitrogen flow at 60-80°C.

[0020] Furthermore, in step 2), the concentration of the surfactant solution is 0.5-1 mol / L, and the liquid-solid ratio of the surfactant solution to the activated carbon fiber is 50-150 ml: 1 g.

[0021] Furthermore, in step 3), the mass concentration of the ionic liquid prepared in ethanol to form a solution is 20-60%, preferably 30-40%, and the impregnation ratio of the ethanol solution of the ionic liquid to the surfactant-modified activated carbon fiber is 5-20:1.

[0022] The present invention also provides the application of the ionic liquid composite activated carbon fiber absorbent for efficiently adsorbing and capturing CO2 in the air, and the application method is: the concentration of CO2 in the air is below 400ppm, the adsorption pressure is normal pressure, and the adsorption temperature is 20-60°C. The absorption rate of the absorbent of the present invention is significantly improved compared with conventional ionic liquids.

[0023] Compared with the prior art, the present invention has the following advantages:

[0024] (1) High absorption capacity. The ionic liquid composite activated carbon fiber absorbent described in the present invention is highly effective for capturing CO2 in the air. First, the activated carbon fiber is modified with a surfactant so that the pores of the activated carbon fiber are filled with the surfactant. Then, the ionic liquid with high viscosity is impregnated into the pores of the activated carbon fiber rich in the surfactant. The surfactant can eliminate or reduce the surface tension between the ionic liquids, so that the ionic liquids with high viscosity will not adhere to each other and block the pores of the carbon fiber, but will form a layer of uniform liquid film extending on the large specific surface of the activated carbon fiber. The large gas-liquid contact area enables the adsorbent to have a high efficiency in capturing CO2 gas at a low concentration of about 400ppm in the air. Different from adding an organic solvent to compound an ionic liquid, the present invention fundamentally overcomes the problem of increased viscosity after traditional ionic liquid absorption by forming a liquid film on a material with a large specific surface area, which is conducive to industrial promotion.

[0025] (2) High adsorption rate. The surfactant modification allows the ionic liquid to evenly form a liquid film on the activated carbon fiber. When a low-concentration CO2 gas flow passes through, due to the CO2 concentration difference on both sides of the liquid film, CO2 will spontaneously penetrate and diffuse. In addition, the amino-based ionic liquid has a strong ability to capture CO2, so it can efficiently capture CO2 molecules in each passing gas flow, achieving high efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a conceptual diagram of the absorption of ionic liquid composite activated carbon fiber absorbent used for air CO2 capture;

[0027] Figure 2 It is a breakthrough curve of ionic liquid composite activated carbon fiber absorbent used for air CO2 capture at 40°C;

[0028] Figure 3It is an ionic liquid composite activated carbon fiber absorbent used for air CO2 capture, and the absorption capacity of air-captured carbon dioxide at 40°C with different ionic liquid loadings;

[0029] Figure 4 This is an adsorption rate diagram of CO2 captured from air by an ionic liquid composite activated carbon fiber absorbent at 40°C.

[0030] Figure 5 It is a static adsorption capacity curve of an ionic liquid composite activated carbon fiber absorbent used for air CO2 capture under different CO2 partial pressures.

[0031] Figure 6 It is an N2-BET adsorption curve of an ionic liquid composite activated carbon fiber absorbent and original activated carbon fiber used for air CO2 capture.

[0032] Table 1 is a table showing the adsorption capacity of different ionic liquid composite activated carbon fiber absorbents for capturing carbon dioxide from air at 40°C.

[0033] Table 2 is a table of N2-BET adsorption data of ionic liquid composite activated carbon fiber absorbent and original activated carbon fiber applied to air CO2 capture. DETAILED DESCRIPTION

[0034] The present invention will be further described below in conjunction with specific embodiments, but the protection scope of the present invention is not limited thereto.

[0035]

Instrument test

[0036] <Dynamic adsorption test>

[0037] Beijing Huayun GXH-3010F portable infrared gas analyzer is used to detect the carbon dioxide concentration. It uses non-dispersive infrared (non-dispersive infrared principle) to selectively absorb infrared rays of the measured gas to provide real-time feedback of CO2 concentration data, and draws a penetration curve to integrate and calculate the adsorption capacity.

[0038] <Static adsorption test>

[0039] CO2 static adsorption: Using BET instrument at 20°C, N2 as the power gas and CO2 as the analytical gas. Using a fully automatic specific surface and porosity analyzer (brand: 3-Flex), the static adsorption capacity curves under different CO2 partial pressures were obtained.

[0040] N2 static adsorption: The specific surface area of ​​the material was measured using the size of nitrogen molecules at a temperature of 77K. The adsorption / desorption curve and pore size distribution curve were obtained using a fully automatic specific surface and porosity analyzer (3-Flex). The specific surface area and pore volume of the material were calculated using Brunauer-Emmett-Teller (BET), T-Plot and Density functional theory (DFT) algorithms.

[0041] [Example]

[0042] <Example 1>

[0043] This embodiment relates to the preparation of an ionic liquid composite activated carbon fiber absorbent for use in capturing CO2 from air.

[0044] Example 1.1

[0045] This embodiment relates to a method for preparing an absorbent using tetraethylenepentamine-imidazole as an ionic liquid and polyethylene glycol as a surfactant, comprising the following steps:

[0046] In the first step, tetraethylenepentamine (TEPA) and imidazole (IM) were weighed in a molar ratio of 1:2, the raw materials were mixed and reacted at 60°C for 6 hours under stirring at a speed of 1000 r / min;

[0047] The second step is to distill the reacted ionic liquid under reduced pressure at 70° C. for 4 hours to a constant weight to remove unreacted raw materials in the ionic liquid, and then dry it under vacuum at 70° C. for 12 hours to remove moisture, and finally obtain the ionic liquid tetraethylenepentamine-imidazole ([TEPA][IM]2) for standby use;

[0048] In the third step, 2 g of activated carbon fiber was soaked in 100 ml of 1 mol / L sodium hydroxide solution for 12 h, filtered out, washed with deionized water until neutral, and then vacuum dried at 70 °C for 12 h;

[0049] Step 4: Use polyethylene glycol as a surfactant and dissolve it in ethanol to prepare a surfactant solution with a concentration of 0.5 mol / L, place the dried activated carbon fiber in 300 ml of the surfactant solution, soak it for 12 hours, and then vacuum dry it at 70°C for 12 hours to obtain a polyethylene glycol surfactant-modified carbon fiber;

[0050] Step 5: Dissolve the ionic liquid tetraethylenepentamine-imidazole in ethanol to prepare a solution with a mass concentration of 40%, and impregnate an equal volume of the carbon fiber modified with polyethylene glycol surfactant (the impregnation ratio of the solution to the carbon fiber is about 9:1), and then blow dry under a nitrogen flow at 80°C, recorded as PEG-[TEPA][IM]2-ACF.

[0051] Example 1.2

[0052] This embodiment relates to a method for preparing an absorbent using tetraethylenepentamine-glycine as an ionic liquid and hexadecyltrimethylammonium chloride as a surfactant, comprising the following steps:

[0053] In the first step, tetraethylenepentamine (TEPA) and glycine (Gly) were weighed in a molar ratio of 1:1, the raw materials were mixed and reacted at 60°C for 6 hours under stirring at a speed of 1000 r / min;

[0054] The second step is to distill the reacted ionic liquid under reduced pressure at 70° C. for 4 hours to a constant weight to remove unreacted raw materials in the ionic liquid, and then dry it under vacuum at 70° C. for 12 hours to remove moisture, and finally obtain the ionic liquid tetraethylenepentamine-glycine ([TEPA][Gly]) for standby use;

[0055] In the third step, 2 g of activated carbon fiber was soaked in 100 ml of 1 mol / L sodium hydroxide solution for 12 h, filtered out, washed with deionized water until neutral, and then vacuum dried at 70 °C for 12 h;

[0056] Step 4: Use hexadecyltrimethylammonium chloride as a surfactant and dissolve it in ethanol to prepare a 0.5 mol / L surfactant solution, place the dried activated carbon fiber in 300 ml of the surfactant solution, soak it for 12 hours, and then vacuum dry it at 70°C for 12 hours to obtain a carbon fiber modified with hexadecyltrimethylammonium chloride surfactant;

[0057] Step 5: Dissolve the ionic liquid tetraethylenepentamine-glycine in ethanol to prepare a solution with a mass concentration of 40%, and impregnate an equal volume of the solution onto the carbon fiber modified with the hexadecyltrimethylammonium chloride surfactant (impregnation ratio is about 9:1), and then blow dry under a nitrogen flow at 80°C, recorded as CTAC-[TEPA][Gly]-ACF.

[0058] Example 1.3

[0059] This embodiment relates to a method for preparing an absorbent using tetraethylenepentamine-2-methylimidazole as an ionic liquid and N-methylpyrrolidone as a surfactant, comprising the following steps:

[0060] In the first step, tetraethylenepentamine (TEPA) and 2-methylimidazole (2-MI) were weighed in a molar ratio of 1:1, the raw materials were mixed and reacted at 60° C. for 6 hours under stirring at a speed of 1000 r / min;

[0061] The second step is to distill the reacted ionic liquid under reduced pressure at 70° C. for 4 hours to a constant weight to remove unreacted raw materials in the ionic liquid, and then dry it under vacuum at 70° C. for 12 hours to remove moisture, and finally obtain the ionic liquid tetraethylenepentamine-2-methylimidazole ([TEPA][2-MI]) for standby use;

[0062] In the third step, 2 g of activated carbon fiber was soaked in 100 ml of 1 mol / L sodium hydroxide solution for 12 h, filtered out, washed with deionized water until neutral, and then vacuum dried at 70 °C for 12 h;

[0063] Step 4: Use N-methylpyrrolidone as a surfactant and dissolve it in ethanol to prepare a 0.5 mol / L surfactant solution, place the dried activated carbon fiber in 300 ml of the surfactant solution, soak for 12 hours, and then vacuum dry at 70 ° C for 12 hours to obtain N-methylpyrrolidone surfactant-modified carbon fiber;

[0064] Step 5: Dissolve the ionic liquid tetraethylenepentamine-2-methylimidazole in ethanol to prepare a solution with a mass concentration of 40%, and impregnate an equal volume of the solution onto the carbon fiber modified with N-methylpyrrolidone surfactant (the impregnation ratio is about 9:1), and then blow dry under a nitrogen flow at 80°C, which is recorded as NMP-[TEPA][2-MI]-ACF.

[0065] Example 1.4

[0066] This embodiment relates to a method for preparing an absorbent using tetraethylenepentamine-4-hydroxypyridine as an ionic liquid and Tween 60 as a surfactant, comprising the following steps:

[0067] In the first step, tetraethylenepentamine (TEPA) and 4-hydroxypyridine (4-Pyr) were weighed in a molar ratio of 1:1, the raw materials were mixed and reacted at 60°C for 6 hours under stirring at a speed of 1000 r / min;

[0068] The second step is to distill the reacted ionic liquid under reduced pressure at 70° C. for 4 hours to a constant weight to remove unreacted raw materials in the ionic liquid, and then dry it under vacuum at 70° C. for 12 hours to remove moisture, and finally obtain the ionic liquid tetraethylenepentamine-4-hydroxypyridine ([TEPA][4-Pyr]) for standby use;

[0069] In the third step, 2 g of activated carbon fiber was soaked in 100 ml of 1 mol / L sodium hydroxide solution for 12 h, filtered out, washed with deionized water until neutral, and then vacuum dried at 70 °C for 12 h;

[0070] Step 4: Use Tween 60 as a surfactant and dissolve it in ethanol to prepare a 0.5 mol / L surfactant solution, place the dried activated carbon fiber in 300 ml of the surfactant solution, soak it for 12 hours, and then vacuum dry it at 70°C for 12 hours to obtain a carbon fiber modified with Tween 60 surfactant;

[0071] Step 5: Dissolve the ionic liquid tetraethylenepentamine-4-hydroxypyridine in ethanol to prepare a solution with a mass concentration of 40%, and impregnate an equal volume of the solution onto the carbon fiber modified with Tween 60 surfactant (impregnation ratio is about 9:1), and then blow dry under a nitrogen flow at 80°C, recorded as Tween60-[TEPA][4-Pyr]-ACF.

[0072] The absorption concept diagram of ionic liquid composite activated carbon fiber absorbent used for air CO2 capture is shown in the figure Figure 1 The adsorption capacity data of different surfactant and ionic liquid loadings are shown in Table 1.

[0073] Example 1.5

[0074] In the first step, tetraethylenepentamine (TEPA) and imidazole (IM) were weighed in a molar ratio of 1:2, the raw materials were mixed and reacted at 60°C for 6 hours under stirring at a speed of 1000 r / min;

[0075] The second step is to distill the reacted ionic liquid under reduced pressure at 70° C. for 4 hours to a constant weight to remove unreacted raw materials in the ionic liquid, and then dry it under vacuum at 70° C. for 12 hours to remove moisture, and finally obtain the ionic liquid tetraethylenepentamine-imidazole ([TEPA][IM]2) for standby use;

[0076] The third step is to mix equal volumes of n-propanol and ethylene glycol (volume ratio V1 / V2=50 / 50, calculated based on 100 parts of n-propanol and ethylene glycol in total) as a solvent, and then add ionic liquid tetraethylenepentamine-imidazole ([TEPA][IM]2) to the solvent, wherein the concentration of the ionic liquid tetraethylenepentamine-imidazole ([TEPA][IM]2) is 0.75 mol / L, to obtain a functionalized ionic liquid / organic solvent composite system [TEPA][IM]2 / NPA / EG;

[0077] The detailed preparation method can refer to [TETAH][2-MI] / NPA / EG in patent CN110339672A.

[0078] Example 1.6

[0079] This embodiment relates to a method for preparing an absorbent using tetraethylenepentamine-imidazole as an ionic liquid and polyethylene glycol as a surfactant, the difference being that water is used instead of ethanol as a solvent, and the method comprises the following steps:

[0080] In the first step, tetraethylenepentamine (TEPA) and imidazole (IM) were weighed in a molar ratio of 1:2, the raw materials were mixed and reacted at 60°C for 6 hours under stirring at a speed of 1000 r / min;

[0081] The second step is to distill the reacted ionic liquid under reduced pressure at 70° C. for 4 hours to a constant weight to remove unreacted raw materials in the ionic liquid, and then dry it under vacuum at 70° C. for 12 hours to remove moisture, and finally obtain the ionic liquid tetraethylenepentamine-imidazole ([TEPA][IM]2) for standby use;

[0082] In the third step, 2 g of activated carbon fiber was soaked in 100 ml of 1 mol / L sodium hydroxide solution for 12 h, filtered out, washed with deionized water until neutral, and then vacuum dried at 70 °C for 12 h;

[0083] Step 4: Use polyethylene glycol as a surfactant and dissolve it in ethanol to prepare a surfactant solution with a concentration of 0.5 mol / L, place the dried activated carbon fiber in 300 ml of the surfactant solution, soak it for 12 hours, and then vacuum dry it at 70°C for 12 hours to obtain a polyethylene glycol surfactant-modified carbon fiber;

[0084] Step 5: Prepare a solution of ionic liquid tetraethylenepentamine-imidazole with water at a mass concentration of 40%, and impregnate an equal volume of the carbon fiber modified with polyethylene glycol surfactant (the impregnation ratio of the solution to the carbon fiber is about 9:1), and then blow dry under a nitrogen flow at 80°C, recorded as PEG-[TEPA][IM]2-ACF(H2O).

[0085] <Example 2>

[0086] This embodiment relates to a test of the absorption capacity of an ionic liquid composite activated carbon fiber absorbent for carbon dioxide in the air that is highly effective in capturing CO2 from the air.

[0087] At 40°C, take 1g of PEG-[TEPA][IM]2-ACF, CTAC-[TEPA][Gly]-ACF, NMP-[TEPA][2-MI]-ACF and Tween60-[TEPA][4-Pyr]-ACF in Example 1, respectively, put them into U-shaped tubes and place them in a water bath at 40°C, and then use a 5L / min air pump (air concentration is about 400ppm) to directly extract CO2 from the air. The airflow is then connected to the sample tube and then to the three-way valve, and then to the carbon dioxide infrared detector with a self-priming flow rate of 1L / min (excess gas flows out from the other outlet of the three-way valve) until the carbon dioxide infrared detector shows absorption saturation. The tail gas outlet of the instrument is connected to a rotor flowmeter to detect the terminal flow, and the adsorption capacity is calculated based on the inlet and outlet flow rates of the gas. The penetration curve results of air capture of CO2 at 40°C are as follows: Figure 2 shown.

[0088] Through integration, it can be seen that the adsorption capacities of PEG-[TEPA][IM]2-ACF, CTAC-[TEPA][Gly]-ACF, NMP-[TEPA][2-MI]-ACF and Tween60-[TEPA][4-Pyr]-ACF are 1.79 mol / kg, 1.29 mol / kg, 1.6 mol / kg and 1.43 mol / kg, respectively, all of which have relatively high adsorption capacities. This indicates that compared with other air capture adsorption materials, the method of forming a layer of ionic liquid film on the surfactant-modified activated carbon fiber in the present invention has significant advantages in air capture.

[0089] <Example 3>

[0090] This embodiment relates to an investigation of different ionic liquid loading amounts in an ionic liquid composite activated carbon fiber absorbent that is highly effective in capturing CO2 from air.

[0091] The absorbent was prepared according to the method of Example 1.1, except that "in the fifth step, the mass concentration of the ionic liquid tetraethylenepentamine-imidazole in the ethanol solution was replaced with 0, 20%, 40%, 60% and 100%", and other conditions remained unchanged. Finally, PEG-[TEPA][IM]2-ACF absorbents prepared from [TEPA][IM]2 ethanol solutions of different concentrations (0, 20%, 40%, 60% and 100%) were obtained, i.e., PEG-[TEPA][IM]2-ACF absorbents at different ionic liquid loadings were obtained.

[0092] At 40°C, 1g of the EG-[TEPA][IM]2-ACF prepared from [TEPA][IM]2 ethanol solutions of different concentrations (0, 20%, 40%, 60% and 100%) was taken, placed in a U-shaped tube and placed in a 40°C water bath, and then a 5L / min air pump (air concentration of about 400ppm) was used to directly extract CO2 from the air. The airflow was then connected to the sample tube and then to the three-way valve, and then to the carbon dioxide infrared detector with a self-priming flow rate of 1L / min (excess gas flows out from the other outlet of the three-way valve) until the carbon dioxide infrared detector shows absorption saturation. The tail gas outlet of the instrument was connected to a rotor flowmeter to detect the terminal flow, and the adsorption capacity was calculated based on the inlet and outlet flow rates of the gas. The adsorption capacity of PEG-[TEPA][IM]2-ACF absorbents with different ionic liquid loadings for capturing carbon dioxide from air at 40°C is shown in the following figure. Figure 3 shown.

[0093] From the results, it can be seen that when the ionic liquid is not loaded, the base material itself hardly adsorbs or has difficulty in adsorbing low-concentration and high-velocity carbon dioxide in the air; when the loading is too large, excess ionic liquid will cause pore blockage, and the overall adsorption capacity presents a volcano-shaped curve, among which the adsorption capacity of the absorbent for carbon dioxide under a 40% concentration of [TEPA][IM]2 load is relatively the highest for this adsorbent material.

[0094] <Example 4>

[0095] This embodiment relates to an investigation of different ionic liquid loading amounts and different surfactant modifications in an ionic liquid composite activated carbon fiber absorbent that is highly effective in capturing CO2 from air.

[0096] The absorbent was prepared according to the method of Example 1.1, except that "in the fifth step, the mass concentration of the ionic liquid tetraethylenepentamine-imidazole in the ethanol solution was replaced with 20%, 40% and 60%", and other conditions remained unchanged. Finally, PEG-[TEPA][IM]2-ACF absorbents prepared from [TEPA][IM]2 ethanol solutions of different concentrations (20%, 40% and 60%) were obtained, i.e., PEG-[TEPA][IM]2-ACF absorbents at different ionic liquid loadings were obtained.

[0097] Similarly, referring to the methods of Example 1.2, Example 1.3 and Example 1.4, CTAC-[TEPA][Gly]-ACF, NMP-[TEPA][2-MI]-ACF and Tween60-[TEPA][4-Pyr]-ACF absorbents were prepared at different ionic liquid concentrations (20%, 40% and 60%).

[0098] In addition, referring to the method of Example 1.1, the surfactant was replaced with Tween 20, Betaine or MES at the same concentration, and absorbents at different ionic liquid concentrations (20%, 40% and 60%) were prepared respectively.

[0099] At 40℃, take 1g of the above different absorbents, put them into a U-shaped tube and place them in a 40℃ water bath, then use a 5L / min air pump (air concentration is about 400ppm) to directly extract CO2 from the air, and then connect the airflow to the sample tube and then the three-way valve, and then connect to the carbon dioxide infrared detector with a self-priming flow rate of 1L / min (excess gas flows out from the other outlet of the three-way valve) until the carbon dioxide infrared detector shows absorption saturation. The tail gas outlet of the instrument is connected to a rotor flowmeter to detect the terminal flow, and the adsorption capacity is calculated based on the inlet and outlet flow of the gas. The adsorption capacity of different absorbents for air capture of carbon dioxide at 40℃ is shown in Table 1.

[0100] Table 1

[0101]

[0102] <Example 5>

[0103] This embodiment relates to a test of the absorption rate of carbon dioxide in the air by an ionic liquid composite activated carbon fiber absorbent which is highly effective in capturing CO2 from the air.

[0104] At 40°C, take 1g of PEG-[TEPA][IM]2-ACF in Example 1, ionic liquid organic solvent composite solution [TEPA][IM]2 / NPA / EG, and prepare [TEPA][IM]2 ionic liquid (wherein the mass of the effective ingredients of [TEPA][IM]2 ionic liquid is the same), respectively, put them into U-shaped tubes and place them in a water bath at 40°C, and then use a 5L / min air pump (air concentration is about 400ppm) to directly extract CO2 from the air. The airflow is then connected to the sample tube and then to the three-way valve, and then to the carbon dioxide infrared detector with a self-priming flow rate of 1L / min (excess gas flows out from the other outlet of the three-way valve) until the carbon dioxide infrared detector shows absorption saturation. The tail gas outlet of the instrument is connected to a rotor flowmeter to detect the terminal flow, and the adsorption capacity is calculated based on the inlet and outlet flow of the gas. Different time periods are integrated separately to represent the adsorption rate, and a scatter plot is drawn. The adsorption rate diagram of air capturing CO2 at 40°C is shown in the figure. Figure 4 shown.

[0105] As can be seen from the figure, although the organic solvent compounding alleviates the impact of viscosity to a certain extent, its fundamental improvement is not obvious. When the ionic liquid is impregnated onto the surfactant-modified activated carbon fiber, the initial adsorption rate is significantly improved, and the adsorption capacity is also slightly improved.

[0106] <Example 6>

[0107] This embodiment relates to the determination of the static adsorption capacity of a solid-phase ionic liquid membrane that is efficiently applied to capture CO2 from air.

[0108] At 20°C, 0.2-0.3 g of the PEG-[TEPA][IM]2-ACF sample in Example 1 was taken, N2 was used as the power gas, and CO2 was used as the analysis gas. The static adsorption capacity curves under different CO2 partial pressures were obtained using a fully automatic specific surface area and porosity analyzer (brand: 3-Flex). The results are shown in Figure 5 shown.

[0109] At 77K, 0.2-0.3g of unloaded fresh activated carbon fiber and the PEG-[TEPA][IM]2-ACF sample in Example 1 were taken respectively, and the specific surface area of ​​the material was measured using the size of nitrogen molecules. The adsorption or adsorption / desorption curve was obtained using a fully automatic specific surface and porosity analyzer (3-Flex). The specific surface area and pore volume of the material were calculated using the Brunauer-Emmett-Teller (BET), T-Plot and Density functional theory (DFT) algorithms. The results are shown in Figure 6 , pore volume and pore volume are shown in Table 2.

[0110] Table 2

[0111] ACF <![CDATA[PEG-[TEPA][IM]2-ACF]]> <![CDATA[Total specific surface area (m 2 / g)]]> 1476 2160 <![CDATA[Micropore specific surface area (m 2 / g)]]> 1412 2031 <![CDATA[Mesoporous specific surface area (m 2 / g)]]> 64 129 <![CDATA[Pore volume (cm 2 / g)]]> 0.59828 0.920405

[0112] From the analysis of the chart, it can be seen that compared with the original activated carbon fiber, the pore volume (especially the micropore volume) and pore volume of the activated carbon fiber modified by liquid membrane are increased. The larger micropore specific surface area and pores are conducive to the transmission of CO2 gas molecules in the adsorbent pores, thereby increasing the adsorption capacity.

[0113] <Example 7>

[0114] This embodiment involves an investigation into the preparation of different solvents for an ionic liquid composite activated carbon fiber absorbent that is highly effective for air CO2 capture.

[0115] At 40°C, 1g of PEG-[TEPA][IM]2-ACF in Examples 1.1 and 1.6 were taken respectively. The difference was that Example 1.1 used ethanol as solvent, while Example 1.6 used water as solvent. Therefore, they were named PEG-[TEPA][IM]2-ACF(EG) and PEG-[TEPA][IM]2-ACF(H2O), respectively. Then, they were respectively loaded into U-shaped tubes and placed in a 40°C water bath. Then, a 5L / min air pump (air concentration of about 400ppm) was used to directly extract CO2 from the air. The airflow was then connected to the sample tube and then to the three-way valve, and then to the carbon dioxide infrared detector with a self-priming flow rate of 1L / min (excess gas flowed out from the other outlet of the three-way valve) until the carbon dioxide infrared detector showed absorption saturation. The tail gas outlet of the instrument was connected to a rotor flowmeter to detect the terminal flow, and the adsorption capacity was calculated based on the inlet and outlet flow rates of the gas.

[0116] Through integration, we can know that the adsorption capacity of PEG-[TEPA][IM]2-ACF(EG) and PEG-[TEPA][IM]2-ACF(H2O) are 1.79 mol / kg and 1.57 mol / kg respectively. Using water as solvent reduces the absorption capacity by about 12%. Compared with water, ethanol has the advantages of lower density, high solubility with different solvents, lower specific heat, lower boiling point, and lower latent heat of vaporization. In addition, ethanol as solvent is easy to evaporate quickly, which can load ionic liquid into the absorbent faster.

[0117] The contents described in this specification are merely an enumeration of implementation forms of the inventive concept, and the protection scope of the present invention should not be regarded as being limited to the specific forms described in the embodiments.

Claims

1. An application of an ionic liquid composite activated carbon fiber absorbent for efficiently adsorbing and capturing CO2 in the air, characterized in that: The absorbent is made of activated carbon fiber ACF as a base material, and the base material is modified by a surfactant and then loaded with an ionic liquid to form the absorbent; The surfactant is at least one of polyethylene glycol and N-methylpyrrolidone; The method for modifying activated carbon fiber ACF with a surfactant comprises the following steps: 1) Soak the activated carbon fiber in 1-2 mol / L sodium hydroxide solution for 6-12 hours, filter it out, wash it with deionized water until it is neutral, and then dry it; 2) dissolving a surfactant in ethanol to prepare a surfactant solution, placing the activated carbon fiber dried in step 1) in the surfactant solution, soaking for 6-12 hours, and then drying to obtain the surfactant-modified activated carbon fiber; In step 2), the concentration of the surfactant solution is 0.5-1 mol / L, and the liquid-solid ratio of the surfactant solution to the activated carbon fiber is 50-150 ml: 1 g; The steps of loading the ionic liquid on the surfactant-modified activated carbon fiber are as follows: dissolving the ionic liquid in ethanol to prepare a solution, impregnating the solution on the surfactant-modified activated carbon fiber, and then drying the solution under a nitrogen gas flow at 60-80° C.; The mass concentration of the solution formed by preparing the ionic liquid in ethanol is 20-60%, and the impregnation ratio of the ethanol solution of the ionic liquid to the activated carbon fiber modified by the surfactant is 5-20:

1.

2. The use according to claim 1, characterized in that The ionic liquid includes one or more of tetraethylenepentamine-imidazole, tetraethylenepentamine-glycine, tetraethylenepentamine-bistrifluoromethanesulfonimide, tetraethylenepentamine-2-methylimidazole, tetraethylenepentamine-4-hydroxypyridine, tetraethylenepentamine-tetrafluoroboric acid, and tetraethylenepentamine-hexafluorophosphoric acid.

3. The use according to claim 2, characterized in that The preparation method of the ionic liquid comprises the following steps: The first step: tetraethylenepentamine and a compound containing a corresponding anionic group are mixed in a molar ratio of 1:1-3, and the mixed solution is heated in a water bath at 60-80°C and stirred at a speed of 500-2000 r / min for 6-12 hours; the compound containing a corresponding anionic group is one or more of imidazole, glycine, bistrifluoromethanesulfonimide, 2-methylimidazole, 4-hydroxypyridine, tetrafluoroboric acid, and hexafluorophosphoric acid; Step 2: After the first step of the reaction is completed, the unreacted raw materials in the ionic liquid are removed by vacuum distillation, and then the product is dried to remove residual water to obtain the corresponding ionic liquid.

4. The use according to claim 1, characterized in that The mass concentration of the ionic liquid in ethanol to form a solution is 30-40%.

5. The use according to claim 1, characterized in that The concentration of CO2 in the air is below 400ppm, the adsorption pressure is normal pressure, and the adsorption temperature is 20~60℃.

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