KR20130136617A - Immidazolium cation based ionic liquid functionalized with acid for separation of carbon dioxide and its use - Google Patents

Abstract

Disclosed are immidazolium based ionic liquid functionalized with acid, and a method for the separation of carbon dioxide using the same. The immidazolium based ionic liquid functionalized with acid of the present invention has excellent carbon dioxide absorption ability, and the absorbed carbon dioxide is easily separated by heating. The immidazolium based ionic liquid is convenient to use, and can be used for collecting CO2 by having selectivity, thermal stability, repetitive usage capacity, and long usage lifetime.

Description

Immidazolium cation based ionic liquid functionalized with acid for separation of carbon dioxide and its use}

The present application relates to cation based imidazolium ionic liquids and uses thereof.

In recent years, the technology of separating CO ₂ from flue-gases is of increasing importance not only for academic and industrial reasons, but also for environmentally beneficial sustainable development. In the situation where coal, petroleum and natural gas are used as the main fuels, the production of CO ₂ is inevitable. Therefore, the development of economical CO ₂ separation and recovery technology is a key step for CO ₂ reduction.

Chemical absorption, physical absorption, or membrane separation are known as carbon dioxide separation and recovery techniques, and are widely applied to natural gas, petroleum, and various chemical industries for the purpose of CO ₂ separation, and chemical absorption is mainly used.

Physical absorption methods are mainly preferred when the concentration of acidic gases (H ₂ S, CO ₂ , SO ₂ ) in the gas stream is high. Physical absorbers are mainly used as non-reactive polar organic compounds with high affinity with acid gases. Typically methanol, propylene, carbonate, sulfonate, N-ponylpyrrolidone (NMP), etc. are mainly used for physical absorption. In the case of chemical absorption, it is generally used to remove residual acidic substances. Liquid solutions such as primary, secondary, tertiary, hindered amines and processed amines are most widely used. Hindered amines are often used for selective H 2 S removal in gases containing CO ₂ and H ₂ S.

Currently, the most representative method for CO ₂ absorption is chemical absorption using mixed liquid solutions such as alkanolamines, especially monoethanolamine (MEA), diethanolamine (DEA) and methyldiethanolamine (MDEA). It is a way. MEA-based technology can recover approximately 75-90% of CO ₂ and produce more than 99% of high concentrations of CO ₂ gas.

However, despite these high CO ₂ separation efficiencies of amine-based technologies, these techniques include constraints on the concentration of amines in solution due to problems such as device corrosion, removal of moisture from recovered gases, loss of absorbents due to volatility, and sulfur content in flue gases. It has problems such as deterioration of absorbent which can occur when regenerating with material or high heat, and oxidation of absorbent by combining with oxygen. There is therefore a need for the development of absorbents that are not volatile and non-corrosive, process economical and environmentally beneficial.

An alternative is the ionic liquid. Ionic liquids have large organic symmetric cations, such as quaternary ammonium, imidazolium, pyridinium, and phosphonium ions, and relatively small asymmetric structures Inorganic substances such as [Cl] ^- , [Br] ^- , [I] ^- , [BF ₄ ] ^- , [PF ₆ ] ^- , [Tf ₂ N] ^- , or [RCO ₂ ] ^- It consists of an anion comprised with organic substances, such as these. It is also called a "designer solvent" because of the ionic liquid's ability to convert into various properties through infinite combinations of cations, anions, and functional groups.

Korean Patent No. 0975897 discloses a carbon dioxide absorbent comprising a trialkoxyhydroxyphosphonium carboxylate-based ionic liquid. Korean Laid-Open Patent Publication No. 2011-0080004 discloses a carbon dioxide absorbent using an imazolium-based ionic liquid containing a fluorine-containing olefin. However, fluorine-containing ionic liquids can be expected to have high CO ₂ absorption, but they are difficult to biodegrade and are environmentally harmful. Based on the imidazolium cation, ionic liquid and [Cl] ^- , [BF ₄ ] ^- , [PF ₆ ] ^- , [CH ₃ SO ₃ ] ^- , [CF ₃ BF ₃ ] ^- , [C ₂ F ₅ BF _3] ^- but performed synthesis using anionic, stable also thermally hydrophilic properties with optimum properties in the carbon dioxide separation, and low melting point, low viscosity, as well as the need for a new ionic development of a liquid capable of repeated use Do.

The present invention has been made to solve the above problems, to provide an acid functionalized imidazolium-based ionic liquid that is thermally stable, long life, and can be repeatedly used at high temperature and reduced pressure conditions.

The present application provides an acid functionalized imidazolium-based ionic liquid compound [Cmmim] [X] having a carbon dioxide absorption ability represented by the following Chemical Formula 1,

[Formula 1]

Wherein X ^- is [BF ₄ ] ^- , [PF ₆ ] ^- , [Tf ₂ N] ^- , [TfO] ^- , [DCA] ^- , [Cl] ^- , [Br] ^- , [I] ^- , [ _{^{NO 3] -, [SO 4}} ] 2 -, [CF 3 COO] -, [CF 3 SO 2] -, [(CF 3 SO 2) 2 N] -, [SF 6] -, [(C 2 F ₅ ) ₃ PF ₃ ] ^- , [N (SO ₂ CF ₃ ) ₂ ] ^- , [CF ₃ SO ₃ ] ^- , [B (CN) ₄ ] ^- , [N (CN) ₂ ] ^- , [C (CN ) ₃ ] ^- , [SCN] ^- , [HSO ₄ ] ^- , [CH ₃ SO ₄ ] ^- , [C ₂ H ₅ SO ₄ ] ^- , [C ₄ H ₉ SO ₄ ] ^- , [C ₆ H ₁₃ SO ₄ ] ^- , [B (C ₂ O ₄ ) ₂ ] ^- , [CH ₃ SO ₃ ] ^- , [CH ₃ C ₆ H ₄ SO ₃ ] ^- , or [C ₄ F ₉ SO ₃ ] ^- .

The application also provides a carbon dioxide absorbent comprising an acid functionalized imidazolium-based ionic liquid compound according to the invention.

The present application also includes absorbing carbon dioxide in a gas mixture using the ionic liquid or carbon dioxide absorbent according to the present disclosure; And degassing the carbon dioxide absorbed by the carbon dioxide absorbent.

The present disclosure also provides a method for separating carbon dioxide from a gas mixture, after degassing, further comprising reusing the carbon dioxide absorbent.

      The present application also provides a method of separating carbon dioxide from a gas mixture, in which the carbon dioxide: ionic liquid reacts in a molar ratio of 1: 1 in the carbon dioxide absorption step in the degassing step.

The present application also provides a method for separating carbon dioxide from a gas mixture, wherein the temperature when absorbing the carbon dioxide is about 0 ° C to 80 ° C.

The present application also provides a method for separating carbon dioxide from a gas mixture, wherein the pressure when absorbing the carbon dioxide is about atmospheric pressure to about 60 atmospheres.

The present application also provides a method for separating carbon dioxide from a gas mixture, wherein the temperature when degassing the carbon dioxide is 60 ℃ to 150 ℃.

The imidazolium-based ionic liquid functionalized with the acid of the present invention has excellent carbon dioxide absorption ability, and the absorbed carbon dioxide can be easily desorbed through heating and the like, so that the ease of use, selectivity, thermal stability and repeated use and long use Its useful life makes it useful for CO ₂ capture.

1 is a graph showing the mole fraction (χ) of carbon dioxide at different temperatures of 30 ° C. according to the pressure of different ionic liquids.
FIG. 2 is a graph showing the molar fraction χ of carbon dioxide with pressure in different ionic liquids at 50 ° C.
3 shows FTIR of [Cmmim] [BF ₄ ], [Cmmim] [PF ₆ ], [Cmmim] [Tf ₂ N], [Cmmim] [TfO] and [Cmmim] [DCA] ionic liquids It shows the spectrum.
FIG. 4 is ¹³ C spectra of different ionic liquids absorbing carbon dioxide: (a) [Cmmim] [BF ₄ ], (b) [Cmmim] [PF ₆ ], (c) [Cmmim] [Tf ₂ N] , (d) [Cmmim] [TfO] and (e) [Cmmim] [DCA].
5 shows the carbon dioxide absorption mechanism of acid functionalized ionic liquids.
FIG. 6 is a graph showing the molar fraction (χ) of carbon dioxide with pressure measured using different ionic liquids regenerated at 30 ° C.

The present application relates to an imidazolium-based ionic liquid functionalized with an acid represented by the following formula (1).

[Formula 1]

Wherein X ^- is wherein X ^- is ^{_{[BF 4] -, [PF}} 6] -, [Tf 2 N] -, [TfO] -, [DCA] -, [Cl] -, [Br] -, [ _{^{I] -, [NO 3]}} -, [SO 4] 2 -, [CF 3 COO] -, [CF 3 SO 2] -, [(CF 3 SO 2) 2 N] -, [SF 6] -, [(C ₂ F ₅ ) ₃ PF ₃ ] ^- , [N (SO ₂ CF ₃ ) ₂ ] ^- , [CF ₃ SO ₃ ] ^- , [B (CN) ₄ ] ^- , [N (CN) ₂ ] ^- , [C (CN) ₃ ] ^- , [SCN] ^- , [HSO ₄ ] ^- , [CH ₃ SO ₄ ] ^- , [C ₂ H ₅ SO ₄ ] ^- , [C ₄ H ₉ SO ₄ ] ^- , [ C ₆ H ₁₃ SO ₄ ] ^- , [B (C ₂ O ₄ ) ₂ ] ^- , [CH ₃ SO ₃ ] ^- , [CH ₃ C ₆ H ₄ SO ₃ ] ^- , or [C ₄ F ₉ SO ₃ ] ^- a.

In one embodiment X ^- is [BF ₄ ] ^- , [PF ₆ ] ^- , [Tf ₂ N] ^- , [TfO] ^- , [DCA] ^- .

The acid functionalized imidazolium-based ionic liquids of the present disclosure have a low viscosity while maintaining a liquid phase at room temperature in combination with the anions used herein.

    Furthermore, the present application relates to a carbon dioxide absorbent using the acid functionalized imidazolium-based ionic liquid compound of Formula 1. The carbon dioxide absorbent of the present disclosure may include one or more acid functionalized imidazolium based ionic liquid compounds according to the present disclosure.

The carbon dioxide absorbent using the acid functionalized imidazolium-based ionic liquid compound according to the present invention absorbs it through a chemical bond with carbon dioxide. Absorbents for absorbing carbon dioxide are classified into chemical and physical absorbents. Since the chemical absorbent is absorbed by the chemical bond between the carbon dioxide and the absorbent, it is possible to absorb the carbon dioxide in a low range. However, since physical absorption is absorbed and regenerated by pressure, the gas to be separated must be accompanied by pressure. Therefore, chemical absorption is generally advantageous for separating the carbon dioxide produced when burning fossil fuels.

It was also confirmed that lone pairs of oxygen atoms nucleophilic attack carbon atoms of CO ₂ to form anhydrides. It has a 1: 1 mechanism by which one mole of CO ₂ reacts with one mole of ionic liquid. Generally, the reaction of amine (RNH ₂ ) with carbon dioxide forms carbamate (2RNH ₂ + CO ₂ = RNHCOO ^- .RNH ₃ ⁺ ), and the reaction of amine with carbon dioxide and water produces bicarbonate (2RNH ₂ + CO ₂ + H The ^{_{+ RNH 2) - 2 O =}} RNH 3 + .HCO 3. At this time, the reaction of the amine and carbon dioxide has the advantage that the carbamate is formed by the 2: 1 molar reaction with the amine and carbon dioxide to increase the reaction rate very much. However, since 1 mole of carbon dioxide is absorbed by 2 moles of amine, the amount of carbon dioxide absorbed per unit amine is low. However, since the ionic liquid and carbon dioxide have a 1: 1 molar reaction when the carbon dioxide is separated using an acid (-COOH) functional group, the absorption capacity of carbon dioxide per unit ionic liquid is much higher than that of the amine type.

In addition, the acid-functionalized imidazolium-based ionic liquid compound according to the present invention shows a much higher carbon dioxide absorption capacity than the organic solvent absorbent, and in one embodiment according to the present invention showed a carbon dioxide absorption amount of more than 0.9 mole fraction. In the present invention, the side chain of the cationic imidazole is substituted with a carboxyl group to directly react with carbon dioxide. Therefore, the conventional ionic liquid can separate the carbon dioxide by the physical force by the interaction of the cation and the anion, but in the present invention by adding a function that can separate the carbon dioxide by chemical bonding increases the carbon dioxide absorption capacity than conventional. I was. Therefore, when the imidazolium-based ionic liquid compound according to the present invention is used as an absorbent, the circulation rate of the absorbent can be lowered and the size of the device can be drastically reduced.

In addition, when the imidazolium-based ionic liquid compound according to the present invention is used as a carbon dioxide absorbent, there is almost no loss of the absorbent. Since the imidazolium-based ionic liquid compound according to the present invention is chemically stable, the loss of carbon dioxide absorbent by decomposition is very low. In addition, the imidazolium-based ionic liquid compound according to the present invention in the re-use experiment can be reused because the deterioration of carbon dioxide absorption is not observed even when repeated 10 times the absorption-degassing experiment. Therefore, the ionic liquid compound according to the present invention not only possesses excellent carbon dioxide absorption ability, but can also perform degassing of absorbed carbon dioxide at a relatively low temperature, and there is almost no decrease in absorption capacity even after repeated use, so that it can be effectively used as a carbon dioxide absorbent. Can be.

In another aspect, the present invention relates to a method for separating carbon dioxide using a carbon dioxide absorbent comprising an acid functionalized imidazolium-based ionic liquid compound of Formula 1 in a gas mixture. The method includes absorbing carbon dioxide using a carbon dioxide absorbent comprising an acid functionalized imidazolium-based ionic liquid compound of the present application and degassing carbon dioxide absorbed in the carbon dioxide absorbent.

In the method using the carbon dioxide absorbent according to the present application, a known process for separating carbon dioxide may be applied, for example "Energy saving in a CO2 capture plant by MEA scrubbing", chemical engineering research and design, 89, p1676-1683 (2011), "Stripper configurations for CO2 capture by aqueous monoethanolamine", chemical engineering research and design 89, p1639-1646 ( See 2011).

      Absorbing carbon dioxide in the absorption tower using, for example, a carbon dioxide absorbent according to the present invention in a gas mixture; Moving the absorbent absorbing the carbon dioxide to a degassing column; And degassing the carbon dioxide absorbed by the carbon dioxide absorbent in a degassing column.

The method according to the present application may further comprise the step of moving to an absorption tower to reuse the degassed carbon dioxide absorbent.

In the process for separating carbon dioxide from a gas mixture according to the invention, the preferred temperature when absorbing carbon dioxide is in the range of about 0 ° C. to about 80 ° C., in particular in the range of about 20 ° C. to about 60 ° C., and the preferred pressure is from atmospheric to about 80 atm, especially atmospheric to 60 atm. When absorbing carbon dioxide, the lower the temperature and the higher the pressure, the higher the amount of carbon dioxide absorption.

In the process for separating carbon dioxide from a gas mixture according to the invention, the preferred temperature when degassing the absorbed carbon dioxide is in the range of about 60 to about 150 ° C, more preferably in the range of about 70 to about 130 ° C, and the preferred pressure is Atmospheric pressure to about 20 Pascals (Pa). In the method for separating carbon dioxide from the gas mixture according to the present invention, the gas mixture includes a gas containing carbon dioxide generated when burning fossil fuel, for example, an exhaust gas discharged from a chemical plant, a power plant, a large boiler, Natural gas and the like may be used, but is not limited thereto.

Hereinafter, the present invention will be described in more detail by the following examples. However, the following examples merely illustrate the present invention, and the contents of the present invention are not limited by the following examples.

Example

Example  Synthesis of 1 ionic liquid

Monochloroacetic acid (ClCH ₂ COOH), 1-methylimidazole, acetonitrile, methanol, sodium tetrafluoroborate (NaBF ₄ ), magnesium sulfate used in the examples herein (magnesium sulfate (MgSO ₄ )), potassium hexafluorophosphate (KPF ₆ )) _, lithium bis [(trifluoromethyl) sulfonyl] amide Li (Tf) ₂ N)), sodium trifluoromethylsulfonate Na (TfO) and sodium dicyanamide (Na (DCA)) were purchased from Sigma-Aldrich and did not undergo further purification.

Hereinafter, the synthesis of the ionic liquids of the present application was performed using methods reported in the existing literature (Z. Fei, D. Zhao, TJ Geldbach, R. Scopelliti, PJ Dyson, Bracidic ionic liquids and their zwitterions: synthesis, characterization and pKa determination , Chemistry, A European Journal 10 (2004) 4886-4893).

However, the alkylation of 1-methylimidazole was carried out with a slight excess (equivalent ratio 1.1) of NaBF ₄ , KPF ₆ , Li (Tf ₂ N), Na (TfO) and Na ( DCA) to reduce the amount of halogen remaining. (Cl, Br) substitution was performed using an alkyl halide.

Example  1-1 [ Cmmim ] [ Cl ] Synthesis of

50 ml of acetonitrile were injected into a round bottom flask equipped with a reflux distillation, followed by additional injection of monochloroacetic acid (6.73 g, 0.10 mol) and 1-methylimidazole (12.3 g, 0.15 mol). Stir at 24 ° C. for 24 hours. The solvent was then removed while heating at 50 ° C. to 100 ° C. while applying a vacuum of 300 to 500 mmHg to the round flask. At this time, a slightly yellow substance [Cmmim] [Cl] was synthesized, the yield was 82%, and the water content was 3.66μg (H ₂ O) ml ^-1 (RTIL, romm temperature ionic liquid, ionic liquid to keep the liquid at room temperature Liquid).

Example 1-2 [Cmmim] [BF ₄ ] Synthesis of

[Cmmim] [Cl] (27.00 g, 0.15 mol) and NaBF ₄ (19.00 g, 0.17 mol) were placed in a 250 ml Elenmeyer flask, and 150 ml of methanol was added thereto and mixed. The mixture was stirred at room temperature for 24 hours. Subsequently, the generated ionic liquid containing impurities was filtered using a filter equipped with an aspirator, and then the filtered ionic liquid was washed twice with 100 ml of methanol. The washed ionic liquid was dried using MgSO 4. The dried ionic liquid was then filtered again using a filtration device equipped with an aspirator. Finally, the solvent was removed under vacuum, and a weak brown liquid ionic liquid (37.00 g, 91% yield) was obtained. The water content was 2.37 μg (H ₂ O) ml ⁻¹ (RTIL).

Example 1-3 [Cmmim] [PF ₆ ] Synthesis of

[Cmmim] [Cl] (27.00 g, 0.15 mol) and KPF ₆ (31.00 g, 0.17 mol) were placed in a 250 ml Elenmeyer flask, and 150 ml of methanol was added thereto and mixed. The mixture was stirred at room temperature for 24 hours. Subsequently, the generated ionic liquid containing impurities was filtered using a filter equipped with an aspirator, and then the filtered ionic liquid was washed twice with 100 ml of methanol. The washed ionic liquid was dried using MgSO 4. The dried ionic liquid was then filtered again using a filtration device equipped with an aspirator. Finally, after removing the solvent in a vacuum condition, a dark brown liquid ionic liquid (37.00g, 91% yield) was obtained, the water content was 1.92μg (H ₂ O) ml ^-1 (RTIL).

Example 1-4 [Cmmim] [NTf ₂ ] Synthesis of

[Cmmim] [Cl] (27.00 g, 0.15 mol) and Li (Tf2N) (48.80 g, 0.17 mol) were placed in a 250 ml Elenmeyer flask, and 150 ml of methanol was added thereto and mixed. The mixture was stirred at room temperature for 24 hours. Subsequently, the generated ionic liquid containing impurities was filtered using a filter equipped with an aspirator, and then the filtered ionic liquid was washed twice with 100 ml of methanol. The washed ionic liquid was dried using MgSO 4. The dried ionic liquid was then filtered again using a filtration device equipped with an aspirator. Finally, the solvent was removed in vacuo and a light brown liquid product (37.00 g, 91% yield) was obtained and the water content was 1.88 μg (H ₂ O) ml ⁻¹ (RTIL).

Example  1-5 [ Cmmim ] [ TfO ] Synthesis of

[Cmmim] [Cl] (27.00 g, 0.15 mol) and Na (Tf0) (29.24 g, 0.17 mol) were placed in a 250 ml Elenmeyer flask, and 150 ml of methanol was added thereto and mixed. The mixture was stirred at room temperature for 24 hours. Subsequently, the generated ionic liquid containing impurities was filtered using a filter equipped with an aspirator, and then the filtered ionic liquid was washed twice with 100 ml of methanol. The washed ionic liquid was dried using MgSO 4. The dried ionic liquid was then filtered again using a filtration device equipped with an aspirator. Finally, the solvent was removed in vacuo to yield a light brown liquid product (37.00 g, 91% yield) with a water content of 1.78 μg (H ₂ O) ml ⁻¹ (RTIL).

Example 1-6 Synthesis of [Cmmim] [DCA]

[Cmmim] [Cl] (27.00 g, 0.15 mol) and Na (DCA) (15.13 g, 0.17 mol) were placed in a 250 ml Elenmeyer flask, and 150 ml of methanol was added thereto and mixed. The mixture was stirred at room temperature for 24 hours. Subsequently, the generated ionic liquid containing impurities was filtered using a filter equipped with an aspirator, and then the filtered ionic liquid was washed twice with 100 ml of methanol. The washed ionic liquid was dried using MgSO 4. The dried ionic liquid was then filtered again using a filtration device equipped with an aspirator. Finally, the solvent was removed in vacuo to yield a light brown liquid product (37.00 g, 91% yield) with a water content of 1.86 μg (H ₂ O) ml ⁻¹ (RTIL).

Example  2 synthesized Ionic liquid  Characterization

¹ H and ¹³ C NMR spectra were measured using a Bruker Avance-700 FT NMR spectrophotometer, and [D ₆ ] acetone was used as the solvent. Chemical shift values are expressed in ppm based on the TMS internal specification. The mass of the sample was measured with a Hewlett Packard 1100 Series, Mass Spectrophotometer, Agilent 1200 Series. FT-IR spectra were measured with Thermo, Model: Nicolet 6700. Component elemental analysis (C, H, N) was performed using the Thermo Finnigan Flash EA-2000 Elemental Analyzer (EA). The water content of the ionic liquid was Karl-Fischer titration (Mitsubishi Chem., Model CA-07). All the salts used in the examples were heated at a temperature of about 70-100 ° C. under vacuum and used after drying for 24 hours. TGA experiments were performed using a thermal analysis system (Mettler Toledo, Model: TGA / SDTA 85 1e). The average sample weighed about 5 mg and was placed in a platinum pan and heated at an elevated temperature rate of about 10 ° C./min from 30 ° C. to 100 ° C. in an N ₂ atmosphere. The density of each liquid salt was measured three times for 1.0 mL of each sample at 25 ° C. Viscosity measurements were performed using a viscometer (Brookfield, model DV-III +) and 0.6 ml of each sample was measured at 10, 20 and 30 ° C, respectively. The results are in Table 1.

[Table 1]

In general, when the anions are the same, the density of the ionic liquid increases as the length of the cation's 1-alkyl (alkylether) ring decreases. The density of [C _m O _n mim] ⁺ based ionic liquids is slightly higher than similar [C _m mim] ⁺ based ionic liquids, for example (C ₂ O> C ₃ ), (C ₃ O> C ₄ )to be. On the other hand, when the cations are the same, the density increases in proportion to the size of the anion. The density trend of [C ₂ Omim] [X] measured by different anions is as follows.

Tf ₂ N ^{- _{> PF 6 -> TfO ->}} BF 4 -> Cl -> DCA -

[Tf ₂ N] ^- ionic liquids having an anion [DCA] ^- has a higher density compared to the ionic liquid having an anion. However, the ionic liquid containing _{[C 2 F 5 BF 3]} [Tf 2] - has substantially the same density and the ionic liquid. Based on these results, these ionic liquids could be transformed into the desired properties through slight changes of cations and anions.

The viscosity of an ionic liquid is strongly dependent on the type of anion and is basically determined by the tendency to form hydrogen bonds and the van der Waals interaction. In the case of imidazolium ionic liquids, the van der Waals attraction increases as the alkyl ring of the cation increases, whereas charge delocalization of the anion tends to decrease the viscosity as it weakens the hydrogen bond of the cation. Also, for anions with even charge distribution and flat shapes (eg, [F (HF) _2.3 ] ^- , [N (CN) ₂ ] ^- , [C (CN) ₃ ] ^- ), Having an anion (eg, [Al ₂ Cl ₇ ], [(CF ₃ SO ₂ ) (CF ₃ CO) N] ^- , _{[(CF 3 SO 2) 2} N] -) , while the density of ionic liquids exhibit a low tendency, high symmetry ^{_{(eg, BF 4 -, PF}} 6 -, AsF 6 -, SbF 6 -, TaF 6 -) It has a high viscosity or high melting point despite its weak organizing ability. These viscosity data are shown in Table 1.

When the anions are identical, the measured viscosity trends of ionic liquids for different cations are:

_{^{Cl -> PF 6 -> BF}} 4 -> TfO -> CF 3 BF 3> C 2 F 5 BF 3> Tf 2 N -> DCA -

These results demonstrate that the viscosity of the ionic liquid is mainly determined by the anion. [DCA] ^- ionic liquids with the anion showed the lowest viscosity, [PF6] ^- ionic liquid containing the anion was confirmed that with the highest viscosity.

Example  3 Measurement and mechanism of isothermal absorption curve of carbon dioxide

The isothermal adsorption curves of carbon dioxide were measured at 30 and 50 ° C. using an isochoric saturation technique. The main part of the measuring device is a gas reservoir, a thermostat, a pressure gauge, an isothermal cell, a vacuum pump, a magnetic stirrer. The experimental temperature was measured with a calibrated platinum resistance thermometer in the heating jacket of each cell, with an error range of ± 0.1 ° C. The error of the experimental measured pressure was ± 0.001 bar. In the experiment, about 2ml of ionic liquid was injected into the isochoric cell, and then the internal air was removed using a vacuum pump.₂After the injection, the ionic liquid was stirred. The system then assumed that equilibrium was reached after about two hours of no pressure fluctuations. The weight of the cell was measured with an electronic balance (Sartorius BS224S) and had an error range of ± 0.0001 g. The carbon dioxide absorption capacity of the ionic liquid was determined by the shifted quality of this isotropic cell.

The CO ₂ uptake mechanism was investigated via FTIR and ¹³ C NMR measurements of CO ₂ . The same apparatus was also used to characterize each material.

The results are in FIGS. 1 and 2. CO ₂ adsorption isotherms for the ionic liquids synthesized herein were measured at atmospheric pressure, 30 and 50 ° C. The acid functional ionic liquids according to the present application showed a considerably high CO ₂ absorption capacity. The CO ₂ absorption capacity of the ionic liquid increases with increasing pressure and with decreasing temperature. As a result, the CO ₂ absorption capacity of the ionic liquid reached 30 to about 0.9 mol CO ₂ per mol of the ionic liquid. Absorption capacity of different anions showed that BF ₄ <DCA ~ PF ₆ ~ TfO <Tf ₂ N. In the case of anions with fluoroalkyl groups, the highest CO ₂ absorption capacity is consistent with previously reported results, and if the fluoroalkyl group is increased in quantity, the CO ₂ absorption capacity also increases.

In addition, the interaction between the ionic liquid synthesized herein and CO ₂ was investigated using FT-IR. As a result, it was confirmed that the CO ₂ absorption of the acid functional ionic liquid was a chemical reaction. The FT-IR spectra of CO ₂ absorbed by the ionic liquid (Figure 3) are two 1825 cm ^-1 and 1758 cm ^-1 corresponding to (= C = O _str ) and (-OH in plane _bend ) of the carboxylic acid. At the point of showed a new peak. ¹³ C NMR spectrum of CO ₂ absorbed by the acid functional ionic liquid is shown in FIG. 4. NMR spectra of all ionic liquids showed new peaks around δ = 182,172 ppm. These peaks are generated by carbonyl carbon atoms of the carboxyl groups formed after CO ₂ uptake.

The results indicate that the carbon dioxide absorption reaction of the acid functional ionic liquid is a chemical reaction. It was confirmed that isolated electron pairs of acidic oxygen atoms nucleophilicly attacked carbon atoms of CO ₂ to form anhydrides. The detailed mechanism is shown in FIG. This confirmed that 1 mole of CO ₂ reacted with 1 mole of ionic liquid.

It has a 1: 1 mechanism by which one mole of CO ₂ reacts with one mole of ionic liquid. Generally, the reaction of amine (RNH ₂ ) with carbon dioxide forms carbamate (2RNH ₂ + CO ₂ = RNHCOO ^- .RNH ₃ ⁺ ), and the reaction of amine with carbon dioxide and water produces bicarbonate (2RNH ₂ + CO ₂ + H The ^{_{+ RNH 2) - 2 O =}} RNH 3 + .HCO 3. At this time, the reaction of the amine and carbon dioxide has the advantage that the carbamate is formed by the 2: 1 molar reaction with the amine and carbon dioxide to increase the reaction rate very much. However, since 1 mole of carbon dioxide is absorbed by 2 moles of amine, the amount of carbon dioxide absorbed per unit amine is low. However, since the ionic liquid and carbon dioxide have a 1: 1 molar reaction when the carbon dioxide is separated using an acid (-COOH) functional group, the absorption capacity of carbon dioxide per unit ionic liquid is much higher than that of the amine type.

Example  4 Ionic liquid  Thermal stability and reuse

In order to study the thermal stability of the acid functional ionic liquid, it was tested under nitrogen atmosphere (flow rate 20ml / min) and temperature increase rate 10 ℃ / min using TGA. There was no noticeable mass loss as a result of the temperature increase experiment to about 100 ℃, it was confirmed that all the ionic liquid is stable even under the experimental conditions of about 30, 50 ℃. In addition, in order to regenerate the ionic liquid saturated with CO ₂ , it was heated to 70 ° C. or the pressure was lowered to 20 Pa or less, and 10 cycles of each were carried out continuously. The results are shown in FIG. 6 and thereafter, there was no particular change in the CO 2 absorption capacity of the ionic liquid.

Here we synthesized and characterized hydrophilic and chemically / thermally stable [Cmmim] [X] series and measured their CO ₂ absorption capacity. The CO ₂ absorption capacity reached 0.9 mol CO ₂ per mole of ionic liquid at atmospheric pressure. The ionic liquid exhibiting the greatest CO ₂ absorption capacity has a [Tf ₂ N] anion because the fluoroalkylation of the Tf 2 N anion is the largest in comparison with other anions.

The absorption mechanism was confirmed using FT-IR and ¹³ C NMR, which proved a chemical reaction. The CO ₂ absorbed by the ionic liquid could be easily desorbed by heating or pressure swinging and used repeatedly. The acid functionalized ionic liquid of the present application can be usefully used for CO ₂ capture due to its high carbon dioxide capture ability, as well as selectivity, thermal stability and long service life.

Claims (10)

An acid functionalized imidazolium-based ionic liquid compound having a carbon dioxide absorption capacity represented by the following formula (I):
[Chemical Formula 1]

Wherein X ^- is [BF ₄ ] ^- , [PF ₆ ] ^- , [Tf ₂ N] ^- , [TfO] ^- , [DCA] ^- , [Cl] ^- , [Br] ^- , [I] ^- , [ _{^{NO 3] -, [SO 4}} ] 2 -, [CF 3 COO] -, [CF 3 SO 2] -, [(CF 3 SO 2) 2N] -, [SF 6] -, [(C 2 F 5 ) ₃ PF ₃ ] ^- , [N (SO ₂ CF ₃ ) ₂ ] ^- , [CF ₃ SO ₃ ] ^- , [B (CN) ₄ ] ^- , [N (CN) ₂ ] ^- , [C (CN) ₃ ] ^- , [SCN] ^- , [HSO ₄ ] ^- , [CH ₃ SO ₄ ] ^- , [C ₂ H ₅ SO ₄ ] ^- , [C ₄ H ₉ SO ₄ ] ^- , [C ₆ H ₁₃ SO ₄ ] ^- , [B (C ₂ O ₄ ) ₂ ] ^- , [CH ₃ SO ₃ ] ^- , [CH ₃ C ₆ H ₄ SO ₃ ] ^- , or [C ₄ F ₉ SO ₃ ] ^- . The acid functionalized imidazolium-based ionic liquid compound according to claim 1, wherein X ^- is [BF ₄ ] ^- , [PF ₆ ] ^- , [Tf ₂ N] ^- , [TfO] ^- , or [DCA] ^- . . A carbon dioxide absorbent comprising the imidazolium-based ionic liquid compound according to claim 1. Absorbing carbon dioxide from the gas mixture using an ionic liquid according to claim 1 or a carbon dioxide absorbent according to claim 3; And
Degassing carbon dioxide absorbed by the carbon dioxide absorbent. 5. The method of claim 4, wherein the method further comprises reusing the degassed carbon dioxide absorbent. The method of claim 4, wherein the carbon dioxide: ionic liquid reacts in a molar ratio of 1: 1 in the carbon dioxide absorption step. The method of separating carbon dioxide from a gas mixture according to claim 4, wherein the temperature when absorbing carbon dioxide is 0 ° C to 80 ° C.
5. The method of claim 4 wherein the pressure when absorbing carbon dioxide is from atmospheric pressure to 60 atmospheres. The method for separating carbon dioxide from a gas mixture according to claim 4, wherein the temperature at which the carbon dioxide is degassed is from room temperature to 150 ° C. 5. The method of claim 4, wherein the gas mixture is a gas mixture generated when burning fossil fuels.

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