KR100993011B1 - Gas-absorbing ionic liquids containing a fluoric group - Google Patents

Abstract

The present invention relates to a gas absorbent using a fluorine-containing ionic liquid, and more particularly, a cation and a 1,1 of dialkylimidazolium having an alkyl group of 1 to 6 carbon atoms and a fluorine-containing alkyl group of 2 to 3 carbon atoms. A fluorine-containing ionic liquid which absorbs carbon dioxide (CO ₂ ) or sulfur dioxide (SO ₂ ) composed of anions of 1, trifluoroacetate, and relates to a gas absorbent for exhaust gas purification.

In addition, the gas absorbent according to the present invention is less corrosive than the alkaline aqueous solution or organic solvent used as a conventional gas absorber and has a low vapor pressure so that there is no solvent loss and can stably absorb the gas without contaminating the separated gas with the absorbent vapor. have.

Fluorine, Ionic Liquids, Gas Absorbers

Description

Gas-absorbing ionic liquids containing a fluoric group}

The present invention relates to a gas absorbent using a fluorine-containing ionic liquid.

Absorption, adsorption, membrane, and deep cooling methods are used to separate environmentally harmful gases such as CO, CO ₂ , SO ₂ , and N ₂ O from chemical plants, power plants, and large boilers. In particular, when the concentration of the gas to be separated in the discharged gas is low and must be separated selectively, absorption or adsorption methods are frequently used. Absorption or adsorption methods can be selectively separated only some gas that is absorbed or adsorbed to the absorbent or adsorbent is widely used industrially, but there is a disadvantage that the periodic replacement is necessary because the absorbent and the adsorbent is chemically modified during the separation process. Therefore, it is advantageous to apply the solid adsorbent only in the case where the chemical modification of the adsorbent is small and the adsorbent replacement cycle is long and the useful gas is separated. On the other hand, the absorption method uses a liquid absorbent, so it is easy to replace the absorbent, and thus it is widely used for purifying a large amount of exhaust gas or separating gas. Generally, the absorbent used in the absorption method forms a chemical bond with the gas molecules to be separated, and when heat is applied, the bond with the gas is broken, the gas is removed and recovered, and the absorbent is regenerated. However, the problem that the absorbent is decomposed due to deterioration in this process, the absorption efficiency of the absorbent is reduced or corrosive due to the formation of the non-regeneration reaction product, the problem that the gas regenerated by the vapor pressure of the absorbent is contaminated As it is pointed out as a disadvantage, it is required to find a new absorbent having high thermal and chemical stability and low vapor pressure.

Recently, attempts have been made to overcome the drawbacks of existing absorbents by using ionic liquids which have no volatility and high thermal stability and maintain a liquid phase at low temperatures below 100 ° C. as absorbents. Ionic liquids are polar salt compounds composed of organic cations and organic or inorganic anions and have a property of dissolving polar gas molecules such as CO, CO ₂ , SO ₂ , and N ₂ O well. At this time, the solubility of the gas absorbed in the ionic liquid depends on the degree of interaction between the gas and the ionic liquid, and thus the polarity, acidity, Changing the basicity and nucleophilicity can control the solubility in a particular gas to some extent.

Conventional amine compounds such as ethanolamine, which is a chemical absorbent, have been mainly used for absorption separation of acidic gases, but they can be replaced by chemical absorbents due to decomposition of the absorbent during absorption and stripping and loss of the absorbent due to volatility of the absorbent. There is an active research on ionic liquid-based physical absorbents. Typical ionic quaternary in liquid ammonium, pyrrole lithium, blood rolryum, imidazolium, pyrazolium, triazolium, pyridinium, pyridinium Dodge titanium, pyrimidinyl titanium, organic cations containing nitrogen, and Cl ^-, Br ^-, I ^- such as a _{^{halogen, BF 4 -, PF 6 -}} , (CF 3 SO) 2 N -, CF 3 SO 3 -, MeSO 3 -, NO 3 -, CF 3 CO 2 -, CH 3 CO 2 - Compounds composed of anions such as these have been known, and especially when anions contain fluorine atoms, they have been reported to have a relatively high carbon dioxide absorption capacity.

Tetrafluoroborate (BF ₄ ^-), hexafluorophosphate (PF ₆ ^-) ionic liquid, but is has a high solubility in an acidic gas such as carbon dioxide and carbon disulfide mixture with an anion containing a fluorine atom such as Hydrogen is potentially hydrolyzed by the water contained in to generate hydrofluoric acid (HF), which makes it difficult to lose and regenerate ionic liquid as an absorbent.

Accordingly, the present inventors have conducted research to solve the above problems, and as a result, by combining a cation having an fluorine-containing alkyl group with an organofluorine anion, the absorption ability for carbon dioxide or sulfur dioxide is high, the absorption rate is high, and the thermal chemical stability is excellent and the room temperature is high. The present invention has been completed by developing a gas absorbent of an ionic liquid having an extremely low vapor pressure while maintaining a liquid phase in.

Accordingly, an object of the present invention is to provide a gas absorbent using an ionic liquid having a high absorption rate to carbon dioxide or sulfur dioxide but having a fast absorption rate, excellent thermal chemical stability, non-flammability, and maintaining a liquid phase at room temperature.

The present invention is composed by combining an alkyl group having 1 to 6 carbon atoms, a cation of dialkylimidazolium having a C 2 to 3 fluorine-containing alkyl group and a 1,1,1-trifluoroacetate (-OOCCF ₃ ) anion. The ionic liquid is characterized by a gas absorbent for purifying exhaust gas which absorbs carbon dioxide (CO ₂ ) or sulfur dioxide (SO ₂ ).

Hereinafter, the present invention will be described in more detail.

The present invention provides a combination of an alkyl group having 1 to 6 carbon atoms with a cation of dialkylimidazolium having a C 2 to 3 fluorine-containing alkyl group and a 1,1,1-trifluoroacetate (CF ₃ COO ⁻ ) anion. It relates to a fluorine-containing ionic liquid represented by the following formula (1) which can be used as a selective absorbent of carbon dioxide or sulfur dioxide gas;

[Formula 1]

In Formula 1, R represents an alkyl group having 1 to 6 carbon atoms, R _f represents a fluorine-containing alkyl group having 2 to 3 carbon atoms; Y _f ⁻ represents 1,1,1-trifluoroacetate (CF ₃ COO ⁻ ) anion.

Amine-based absorbents such as monoethanolamine, diethanolamine, and triethanolamine, which are currently widely used industrially, have weak alkalinity, and thus exhibit excellent performance in absorbing acidic gases such as carbon dioxide or sulfur dioxide. However, these amine-based absorbents have a problem of being lost due to the absorption of absorbents when they are degassed due to high vapor pressure, contamination of recovered gas with absorbents, and low thermal stability. The absorbent tended to be partially destroyed. Cations and Cl containing nitrogen ^{-, Br -, I -,} AlCl 4 -, BF 4 -, PF 6 -, (CF 3 SO) 2 N -, CF 3 SO 3 -, MeSO 3 -, NO 3 -, _{^{CF 3 CO 2 -, CH 3}} CO 2 - Among the salts combined with various anions, such as ionic liquids that maintain a liquid state even near room temperature, is known as a gas absorbent, various ionic liquids have been proposed as carbon dioxide and sulfur dioxide gas absorbers. However, the anion is ^{Cl -, Br -, I -} , AlCl 4 -, BF 4 -, PF 6 - ionic liquid having an inorganic halogen groups, such as are to be decomposed by moisture susceptible to moisture contained in the gas mixture It shows a tendency to have a problem of gradually falling gas absorption capacity. CF ₃ CO ₂ ^- by replacing the anion of an organic compound having a fluorine element, such as to enhance the susceptibility to water in the ionic liquid, but the carbon dioxide and sulfur dioxide is not absorbing power is not so high. In order to overcome this problem, the present invention is to provide an ionic liquid having excellent durability and good absorption of carbon dioxide and sulfur dioxide by converting at least one of two alkyl groups in a dialkylimidazolium cation into a compound containing fluorine. do.

In the present invention the ionic liquid is l, l, l-trifluoro by the following formula The fluorinated dialkyl having the same structure as the second microporous jolnyum (dialkylimidazolium) and the anion to cation developed acetate (trifluoroacetate, CF ₃ COO ^- ) Is a combination of

[Formula 2]

In Formula 2, R is an alkyl group having 1 to 6 carbon atoms, for example, methyl (CH ₃ ), ethyl (C ₂ H ₅ ), butyl (C ₄ H ₉ ), or hexyl (C ₆ H ₁₁ ), R _f is composed of a fluorine-containing alkyl group having 2 to 3 carbon atoms, such as tetrafluoroethyl (C ₂ HF ₄ ), chlorotrifluoroethyl (C ₂ ClHF ₃ ) or hexafluoropropyl (C ₃ HF ₆ ).

When absorbing carbon dioxide using the fluorine-based ionic liquid proposed in the present invention, the temperature is in the range of 0 to 80 ℃, preferably in the range of 20 to 50 ℃, the pressure is absorbed in the normal pressure (1 atm) to 30 atm, Again in the range of room temperature (20 ° C.) to 120 ° C., preferably in the range of room temperature to 80 ° C., the pressure is degassed to normal pressure. When absorbing carbon dioxide, the lower the temperature and the higher the pressure, the higher the carbon dioxide absorption. In particular, as the absorption pressure increases, the carbon dioxide absorption increases almost linearly. The fluorine-based ionic liquids show good absorption and fast absorption rates for carbon dioxide, and the absorption capacity is maintained as high as almost the first time even in repeated use. For example, absorption of carbon dioxide at 10 atmospheres and 30 ° C. using butylhexafluoropropylimidazonium trifluoroacetate reaches 90% of the apparent equilibrium value within 60 minutes, and the absorption amount of carbon dioxide reaches the apparent equilibrium value. Lower the pressure to normal pressure to degas at 30 ℃. Here, the apparent equilibrium value refers to the absorption value when the absorption amount no longer changes by measuring the absorption amount of carbon dioxide with time. When the absorption and degassing of carbon dioxide is completed once, the absorption and degassing are repeated five times, and the final absorption capacity is reduced to within 3% of the initial carbon dioxide absorption capacity. In addition, if the carbon dioxide pressure is increased to 20 atmospheres and absorbed at 30 ° C, it reaches 90% of the apparent equilibrium value within 45 minutes. When repeated, the final absorption capacity decreases by around 4% compared to the initial carbon dioxide absorption capacity. In contrast, in the case of using conventional amine compounds used as carbon dioxide absorbents, such as diethanol amine as an absorbent, the carbon dioxide is absorbed at 1 atm and 30 ° C. and degassed at atmospheric pressure and 150 ° C., under the same conditions. At twice absorption and degassing, the final absorption capacity is reduced by more than 16% compared to the initial absorption capacity. Therefore, by utilizing the fluorine-containing ionic liquid proposed in the present invention, carbon dioxide can be repeatedly absorbed, degassed and separated for much longer than conventional amine absorbents.

Connect the sealed container filled with a little water to the carbon dioxide supply part of the absorber used in the above, and pass the pressurized carbon dioxide at 30 ° C. and 10 atm through the gas layer of the sealed container, such as butylhexafluoropropyl. When the process of supplying and absorbing imidazonium trifluoroacetate and degassing at normal pressure is repeated five times, the final absorbed mole fraction value decreases by 9% compared to the initial carbon dioxide absorbed mole fraction value. By using the well-known butylmethylimidazonium tetrafluoroborate in ionic liquid as the absorbent, carbon dioxide pressurized to 10 atm in the same manner as above is absorbed at 30 ° C. through a gas layer of a container filled with water and degassed at atmospheric pressure. When the process is repeated five times, the final absorption mole fraction value is reduced by 15% compared to the initial carbon dioxide absorption mole fraction value. Therefore, the fluorine-based ionic liquid proposed in the present invention can be applied to the absorption, degassing, and separation of carbon dioxide repeatedly for a long time since the carbon dioxide absorption capacity is reduced by moisture than butylmethylimidazonium tetrafluoroborate.

On the other hand, when absorbing sulfur dioxide using the fluorine-based ionic liquid proposed in the present invention, the temperature is in the range of 0 to 80 ℃, preferably in the range of 20 to 50 ℃, the pressure is absorbed in the normal pressure to 8 atmosphere range, and again 100 The temperature is raised in the range of from 200 ° C., preferably in the range of 130 ° C. to 160 ° C., and the pressure is degassed to normal pressure. When absorbing, the lower the temperature and the higher the pressure, the better the sulfur dioxide absorption. The fluorine-based ionic liquid presented has good absorption of sulfur dioxide, but the absorption of the ionic liquid is partially lowered if the part is strongly bonded and used repeatedly. For example, when butylhexafluoropropylimidazonium trifluoroacetate is used to absorb sulfur dioxide at atmospheric pressure at 40 ° C., 90% of the apparent equilibrium is reached within 25 minutes, and the absorbed by the equilibrium equilibrium is at atmospheric pressure, 130 When degassing at 占 폚, absorbing and degassing again under the same conditions, is repeated five times, the final absorption mole fraction is reduced by 23% compared to the initial sulfur dioxide absorption mole fraction. In contrast, in the case of using diethanol amine as an absorbent, when absorbing sulfur dioxide at atmospheric pressure and 40 ° C, degassing at 150 ° C, and performing absorption and degassing under the same conditions, the second mole fraction of sulfur dioxide absorption was 90% of the initial stage. This decreases, making it almost impossible to recycle the absorbent. Therefore, the proposed fluorine-based ionic liquid can repeatedly absorb, degas and separate sulfur dioxide for a long time.

According to the present invention, a fluorine-based ionic liquid made by combining a dialkylimidazolium cation having one alkyl group having 2 to 3 carbon atoms containing fluorine and a 1,1,1-trifluoroacetate anion containing fluorine It has the property of absorbing acidic gases such as carbon dioxide and sulfur dioxide, and it is able to regenerate most of its functions by removing gases at low pressure and high temperature after absorption. It can be used as a separation medium, has almost no vapor pressure of its own, has good thermal stability, and has a merit of being hardly deformed by a small amount of moisture.

The present invention as described above will be described in more detail based on the following examples, but the present invention is not limited to these examples.

Example 1

100 mL stainless steel high pressure cell with glass lining of container part consisting of 1-butyl-3-hexafluoropropyl imidazonium cation and 1,1,1-trifluoroacetate anion 10 g of an ionic liquid ([BhFpIM] [FAc]) was charged and installed in an air circulating thermostat. Maintain the temperature of the thermostat at 30 ℃, measure the volume of gas part of the cell with high pressure nitrogen, and calculate the pressure of carbon dioxide so that the initial carbon dioxide pressure in the high pressure cell is 5 atm. After filling the cylinder with carbon dioxide, the connecting valve was opened to expand the gas into the high pressure cell. Over time, the degree of decrease in gas pressure was tracked and converted to gaseous equations to record the amount of carbon dioxide dissolved in the ionic liquid. In the same way, the initial pressure of carbon dioxide in the high pressure cell was calculated to be 10 atm, 20 atm, and 40 atm, respectively, and the pressure of the auxiliary cylinder was increased to supply carbon dioxide to the high pressure cell to measure the amount of carbon dioxide absorption according to the pressure. The amount of carbon dioxide dissolved in the ionic liquid was calculated by the mole fraction as shown in Equation 1 below. As illustrated in FIG. 1, the mole fraction of carbon dioxide absorbed in 1-butyl-3-hexafluoropropyl imidazonium trifluoroacetate increased in proportion to the increase in carbon dioxide pressure.

Example 2

1-ethyl-3-hexafluoropropyl imidazonium ([EhFpIM]) or 1-methyl-3-hexafluoropropyl imidazonium ([MhFpIM]) in the same device as in Example 1 above Fill the fluorine-based ionic liquid consisting of 1,1,1-trifluoroacetate ([FAc]) with an anion and measure the solubility of carbon dioxide at an absorption temperature of 30 ° C, an absorption pressure of 10 atm, 20 atm and 40 atm. It is shown in Table 1 below.

TABLE 1

Fluorine Ionic Liquid Type CO ₂ pressure
(atmospheric pressure) CO ₂ absorption
Mole fraction [BhFpIM] [FAc] 10 0.289 [BhFpIM] [FAc] 20 0.364 [BhFpIM] [FAc] 40 0.542 [EhFpIM] [FAc] 10 0.277 [EhFpIM] [FAc] 20 0.350 [EhFpIM] [FAc] 40 0.461 [MhFpIM] [FAc] 10 0.262 [MhFpIM] [FAc] 20 0.315 [MhFpIM] [FAc] 40 0.445

Example 3

In 1-butyl-3-tetrafluoroethyl imidazonium ([BtFeIM]), 1-butyl-3-chlorotrifluoroethyl imidazonium ([BCtFeIM]) in the same apparatus as in Example 1 above Fill a fluorine-based ionic liquid prepared by combining one selected cation with 1,1,1-trifluoroacetate ([FAc]) anion, and at an absorption temperature of 30 ° C., an absorption pressure of 10 atm, 20 atm and 40 atm. The solubility of carbon dioxide was measured and shown in Table 2 below.

TABLE 2

Fluorine Ionic Liquid Type CO ₂ pressure
(atmospheric pressure) CO ₂ absorption
Mole fraction [BtFeIM] [FAc] 10 0.150 [BtFeIM] [FAc] 20 0.289 [BtFeIM] [FAc] 40 0.428 [BCtFeIM] [FAc] 10 0.157 [BCtFeIM] [FAc] 20 0.265 [BCtFeIM] [FAc] 40 0.395

Example 4

1-Butyl-3-hexafluoropropyl imidazonium trifluoroacetate ([BhFpIM] [FAc]) and 1-ethyl-3-hexafluoropropyl imidazonium in the same apparatus as in Example 1 above Trifluoroacetate ([EhFpIM] [FAc]), 1-methyl-3-hexafluoropropyl imidazonium trifluoroacetate ([MhFpIM] [FAc]), 1-butyl-3-tetrafluoroethyl imitate 20 atm, 30, using dazonium trifluoroacetate ([BtFeIM] [FAc]), 1-butyl-3-chlorotrifluoroethyl imidazonium trifluoroacetate ([BCtFeIM] [FAc]), and the like. The apparent equilibrium value was measured by absorbing carbon dioxide at < RTI ID = 0.0 > C, < / RTI > When absorption and degassing of the first carbon dioxide is completed, absorption and degassing are repeated five times, and the change in mole fraction of carbon dioxide is compared, and is shown in Table 3 below. After five times of repeated absorption and degassing, the mole fraction of carbon dioxide absorption decreased to within 7%.

[Table 3]

Fluorine Ionic Liquid Type CO ₂ absorption mole fraction 1 time absorption 5 times absorption [BhFpIM] [FAc] 0.364 0.352 [EhFpIM] [FAc] 0.350 0.339 [MhFpIM] [FAc] 0.315 0.307 [BtFeIM] [FAc] 0.289 0.272 [BCtFeIM] [FAc] 0.265 0.248

Comparative Example 1

The experiment of absorbing carbon dioxide at 1 atm, 30 ° C. and degassing at atmospheric pressure at 150 ° C. using diethanol amine as an absorbent in the same manner as in Example 4 was repeated twice. In the first absorption, carbon dioxide was absorbed by 0.150 in the mole fraction of the solvent and 0.126 in the second mole fraction, which was more than 16% less than that in the first absorption.

Example 5

In the same device as in Example 1, a 50 cc high-pressure cylinder was installed at the end of supplying carbon dioxide, 10 cc of water was contained therein, and the carbon dioxide was installed to pass through the gas part before being supplied to the high-pressure cell. 10 g of 1-butyl-3-hexafluoropropyl imidazonium trifluoroacetate ([BhFpIM] [FAc]) was charged in a high-pressure cell, and the gas layer of a vessel containing water pressurized to carbon dioxide pressurized at 30 ° C. and 10 atm. After passing through the ionic liquid absorbent [BhFpIM] [FAc] was degassed at atmospheric pressure. The same absorption and degassing process was repeated five times to compare the absorption of carbon dioxide in the first absorption stage with the absorption in the fifth absorption stage. In this case, carbon dioxide was supplied with moisture about 1500 ppm (weight ratio). At the first absorption, the mole fraction of carbon dioxide absorption was 0.272 and 0.247 at the fifth absorption.

Comparative Example 2

10 g of 1,3-butylmethylimidazonium tetrafluoroborate ([BMIM] [BF ₄ ]) or butylmethylimidazonium trifluoroacetate ([BMIM] [FAc]) was charged into a high-pressure cell, Under the same conditions as in Example 5, the carbon dioxide was passed through a vessel containing water, absorbed into an ionic liquid, and degassed at atmospheric pressure. In the same way, the absorption and degassing process was repeated five times to compare the absorption of carbon dioxide in the first absorption stage with the absorption in the fifth absorption stage. In 1,3-butylmethylimidazonium tetrafluoroborate ([BMIM] [BF ₄ ]), the mole fraction of carbon dioxide absorption was 0.067 at the first absorption, but decreased to 15% at 0.057 at the fifth absorption. In the case of butylmethylimidazonium trifluoroacetate ([BMIM] [FAc]), the molar fraction of carbon dioxide absorption was 0.058 at the first absorption, but 0.050 at the fifth absorption, and the molar fraction of carbon dioxide was reduced by 14%.

Example 6

1-butyl-3-hexafluoropropyl imidazonium trifluoroacetate ([BhFpIM] [FAc]), 1-ethyl-3-hexafluoropropyl imidazonium trifluoroacetate in a 50cc cell made of Pyrex ([EhFpIM] [FAc]), 1-methyl-3-hexafluoropropyl imidazonium trifluoroacetate ([MhFpIM] [FAc]), 1-butyl-3-tetrafluoroethyl imidazonium trifluor 10 g of an ionic liquid, such as low acetate ([BtFeIM] [FAc]) or 1-butyl-3-chlorotrifluoroethyl imidazonium trifluoroacetate ([BCtFeIM] [FAc]), is filled and weighed at regular intervals. It was placed on a scale that could record changes. This was installed in a thermostatically controlled thermostat, and the apparent equilibrium value was determined by measuring the increase in weight of the ionic liquid absorbing sulfur dioxide over time while supplying sulfur dioxide as a gas at atmospheric pressure and 40 ° C. When the sulfur dioxide absorption reached equilibrium, the cell was heated to 130 ° C. and slowly supplied with nitrogen to degas the absorbed sulfur dioxide at normal pressure. When there was no further weight loss and the sulfur dioxide degassing was terminated, the same procedure as described above was repeated five times for absorbing and degassing sulfur dioxide in the ionic liquid. The sulfur dioxide absorption mole fractions of the first and fifth times were measured, and the sulfur dioxide absorption capacity of each step was compared, and the results are shown in Table 4 below.

[Table 4]

Fluorine Ionic Liquid Type SO ₂ absorption mole fraction 1 absorption 5 absorptions [BhFpIM] [FAc] 0.480 0.416 [EhFpIM] [FAc] 0.455 0.392 [MhFpIM] [FAc] 0.448 0.378 [BtFeIM] [FAc] 0.453 0.363 [BCtFeIM] [FAc] 0.436 0.354

Comparative Example 3

In the same manner as in Example 6, using a diethanolamine (diethanol amine) as an absorbent was repeated two times to absorb sulfur dioxide at atmospheric pressure, 40 ℃ and degassing at atmospheric pressure, 150 ℃. In the first absorption, the absorption mole fraction of sulfur dioxide was 0.448 and the second molar fraction was 0.039. The absorption capacity was reduced by 90% or more compared with the first absorption.

Comparative Example 4

10 g of 1,3-butylmethylimidazonium tetrafluoroborate ([BMIM] [BF ₄ ]) or 1,3-butylmethylimidazonium trifluoroacetate ([BMIM] [FAc]) in a high-pressure cell After charging, sulfur dioxide was absorbed into the ionic liquid under the same conditions as in Example 6 and degassed at atmospheric pressure. The absorption and degassing process was repeated five times in the same manner, and the sulfur dioxide absorption in the first absorption step was compared with the absorption in the fifth absorption step. Repetitive absorption and degassing do not significantly reduce the sulfur dioxide absorption capacity of 1,3-butylmethylimidazonium tetrafluoroborate, but the initial absorption capacity of sulfur dioxide is 0.313, which is low. The initial molar fraction of sulfur dioxide of 1,3-butylmethylimidazonium trifluoroacetate was high at 0.445, but the absorption capacity was rapidly decreased by repeated absorption and degassing.

TABLE 5

Fluorine Ionic Liquid Type
SO ₂ absorption mole fraction 1 absorption 5 absorptions [BMIM] [BF ₄ ] 0.313 0.298 [BMIM] [FAc] 0.445 0.304

1 is a graph showing the absorption amount of carbon dioxide according to the pressure of the ionic liquid used in Example 1.

Claims (3)

Cations of fluorine-containing dialkylimidazolium having an alkyl group having 1 to 6 carbon atoms and a fluorine-containing alkyl group having 2 to 3 carbon atoms at the same time; And An ionic liquid composed by combining anions of 1,1,1-trifluoroacetate (CF ₃ COO ⁻ ), the gas absorbent for exhaust gas purification characterized by absorbing carbon dioxide (CO ₂ ) or sulfur dioxide (SO ₂ ) . The method of claim 1, The fluorine-containing alkyl group is selected from tetrafluoroethyl (-CF ₂ CHF ₂ ), chlorotrifluoroethyl (-CClFCHF ₂ ) and hexafluoropropyl (-CF ₂ CHFCF ₃ ). The method according to claim 1 or 2, The ionic liquid 1-butyl-3-hexafluoropropyl imidazonium trifluoroacetate ([BhFpIM] [FAc]), 1-ethyl-3-hexafluoropropyl imidazonium trifluoroacetate ([EhFpIM] [FAc]), 1-methyl-3-hexafluoropropyl imidazonium trifluoroacetate ([MhFpIM] [FAc]), 1-butyl-3-tetrafluoroethyl imidazonium trifluoroacetate ([BtFeIM] [FAc]) or 1-Butyl-3-chlorotrifluoroethyl imidazonium trifluoroacetate ([BCtFeIM] [FAc]).

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