KR20130110358A - Immidazolium cation based ionic liquid for selective separation of carbon dioxide and its use - Google Patents

Abstract

PURPOSE: An imidazolium-based ionic liquid for isolating carbon dioxide is provided to have superior carbon dioxide absorbing ability and to easily separate absorbed carbon dioxide by heating. CONSTITUTION: An imidazolium-based ionic liquid compound has carbon dioxide absorption ability and is denoted by chemical formula 1. A carbon dioxide absorbing agent contains the compound. A method for isolating carbon dioxide from a gas mixture comprises the steps of: absorbing carbon dioxide from the gas mixture using the carbon dioxide absorbing agent; and deaerating the absorbed carbon dioxide.

Description

Imidazolium ionic liquid for selective separation of carbon dioxide and its use

The present application relates to ionic liquids based on imidazolium cations.

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.

Currently, chemical / physical carbon dioxide absorption processes are widely applied to natural gas, petroleum, and various chemical industries for the purpose of separating CO ₂ . 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 the absorption of CO ₂ is a mixed liquid solution of alkanolamines, in particular monoethanolamine (MEA), diethanolamine (DEA) and methyldiethanolamine (MDEA). It is to use. 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, the 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 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 imidazolium-based ionic liquid compound having a carbon dioxide absorption capacity represented by the following Formula 1,

[Formula 1]

X in the above formula^-[BF₄]^-, [PF₆]^-, [Tf₂N]^-, [TfO]^-, Or [DCA]^-ego,

R ¹ , R ² and R ³ are each a straight or branched chain alkyl or aryl group having 1 to 10 carbon atoms.

The present application also provides the ionic liquid imidazolium compound, wherein the imidazolium-based ionic liquid compound is represented by the following formula (2),

(2)

Wherein X ⁻ is [BF ₄ ] ⁻ , [PF ₆ ] ⁻ , [Tf ₂ N] ⁻ , [TfO] ⁻ , or [DCA] ⁻ .

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

The present application also includes the steps of absorbing carbon dioxide using a carbon dioxide absorbent according to the present invention in a gas mixture; And degassing the carbon dioxide absorbed by the carbon dioxide absorbent.

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

The present application also provides a method for separating carbon dioxide from a gas mixture, characterized in that the temperature when degassing the carbon dioxide is from room temperature to 80 ℃.

The imidazolium-based ionic liquid functionalized with ether of the present invention has excellent carbon dioxide absorption ability, and the absorbed carbon dioxide can be easily desorbed by heating, etc., 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.
Figure 3 shows [C ₂ Omim] [BF ₄ ], [C ₂ Omim] [PF ₆ ], [C ₂ Omim] [Tf ₂ N], [C ₂ Omim] [TfO] and [C ₂ ] absorbing carbon dioxide. Omim] [DCA] shows the FTIR spectrum of the ionic liquid.
FIG. 4 is ¹³ C spectra of different ionic liquids absorbing carbon dioxide: (a) [C ₂ Omim] [BF ₄ ], (b) [C ₂ Omim] [PF ₆ ], (c) [C ₂ Omim ] [Tf ₂ N], (d) [C ₂ Omim] [TfO] and (e) [C ₂ Omim] [DCA]
5 shows the carbon dioxide absorption mechanism of ether 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 having an ether group represented by Formula 1 below.

[Formula 1]

Wherein X ⁻ is [BF ₄ ] ⁻ , [PF ₆ ] ⁻ , [Tf ₂ N] ⁻ , [TfO] ⁻ , or [DCA] ⁻ , R ¹ , R ² and R ³ are each a straight or branched chain alkyl group or an aryl group having 1 to 10 carbon atoms.

     In one embodiment, the imidazolium-based ionic liquid having an ether group of the present application is represented by the following Chemical Formula 2.

(2)

Wherein X ⁻ is [BF ₄ ] ⁻ , [PF ₆ ] ⁻ , [Tf ₂ N] ⁻ , [TfO] ⁻ , or [DCA] ⁻ .

     The ether functionalized imidazolium based ionic liquids herein 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 ether functionalized imidazolium-based ionic liquid compound of Formula 1. Carbon dioxide absorbents of the present disclosure may include one or more ether functionalized imidazolium based ionic liquid compounds according to the present disclosure.

The ether functionalized imidazolium-based ionic liquid compound according to the present invention absorbs carbon dioxide 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. Thus, chemical absorption is generally advantageous for separating the carbon dioxide produced when fueling fossil fuels.

This is because isolated electron pairs of ether group oxygen atoms nucleophilic attack carbon atoms of CO ₂ to form carboxylic acids (see FIG. 5). That is, only one of the ionic liquid for a carbamate forming the first to react with CO _2: a 1 (molar ratio) mechanism is dominant, which is another ionic liquid and CO ₂ for the formation of carbamate conventional one In addition, it has the advantage of being different from the so-called 1: 2 mechanism of reaction.

More specifically, the amine reacts with carbon dioxide to form carbamate, which reacts with carbon dioxide: amine in a molar ratio of 1: 2 and when water is added, a carbonide is formed and the carbon dioxide: amine reacts in a 1: 1 molar ratio. . However, since the ether group oxygen atoms react with carbon dioxide and the carbon dioxide: ionic liquid reacts in a 1: 1 molar ratio, the carbon dioxide: ionic liquid, which is an absorption reaction of an ionic liquid with an existing amine group, reacts in a 1: 2 molar ratio. It is advantageous compared to that.

In addition, the 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 more than 0.9 mole fraction of carbon dioxide absorption. In the present invention, by replacing the ether group in the side chain of the cationic imidazole it was possible 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 imidazolium-based ionic liquid compound according to the present invention not only has excellent carbon dioxide absorbing ability, but can also perform degassing of the absorbed carbon dioxide at a relatively low temperature. Can be effectively used as.

In another aspect, the present invention relates to a carbon dioxide separation method using a carbon dioxide absorbent comprising an ether functionalized imidazolium-based ionic liquid compound of formula (1) in a gas mixture. The method includes absorbing carbon dioxide and degassing the carbon dioxide absorbed by the carbon dioxide absorbent. In the process for separating carbon dioxide from the gas mixture according to the invention, the preferred temperature when absorbing carbon dioxide is in the range from 0 ° C. to 80 ° C., in particular in the range from 20 ° C. to 60 ° C., and the preferred pressure is from atmospheric pressure to 80 atm. When absorbing carbon dioxide, the lower the temperature and the higher the pressure, the higher the amount of carbon dioxide absorption.

In the method for separating carbon dioxide from the gas mixture according to the present invention, the preferred temperature when degassing the absorbed carbon dioxide is in the range of 60 to 150 ° C., more preferably in the range of 70 to 130 ° C., and the preferred pressure is 20 pascal at atmospheric pressure. (Pa). In the method for separating carbon dioxide from the gas mixture according to the present invention, the gas mixture may be exhaust gases, natural gas, etc. discharged from chemical plants, power plants, large boilers, and the like.

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

Chloromethylmethylether (CH ₃ OCH ₂ Cl), 1-methylimidazole, diethylether, acetone, sodium tetrafluoroborate (NaBF ₄ ), magnesium sulfate (MgSO ₄ ), potassium hexa used in the examples herein Fluorophosphate (KPF ₆ ) _, lithium bis [(trifluoromethyl) sulfonyl] amide Li (Tf ₂ N), sodium trifluoromethylsulfonate Na (TfO), sodium dicyanamide (Na (DCA) Was purchased from Sigma-Aldrich and no further purification.

Synthesis of the ionic liquids of the present application using the method reported in the existing literature (LC Branco, JN Rosa, JJM ramos, CAM Afonso, Preparation and Characterization of New Room Temperature Ionic Liquids, Chem. Eur. J. 8 ( 2002) 3671-3677). However, 1-methyl to reduce the amount of residual halogen through 1.1 equivalent ratio of halogen (Cl or Br) exchange with NaBF ₄ , KPF ₆ , Li (Tf ₂ N), Na (TfO), Na (DCA) Imidazole and alkyl halides were alkylated.

Example  1-1 [ C ₂ Omim ] [ Cl ] Synthesis of

Chloromethylmethylether (70 mL, 0.93 mole) and 1-methylimidazole (50 mL, 0.63 mole) were each placed in a round bottom flask and kept at 80 ° C. with a reflux condenser for 24 hours. Stirred. The product was washed with diethyl ether (4x25ml) and then stirred under reduced pressure (0.5mmHg) at 80 ° C for 2 days. The result is a solid after cooling (82% yield) of about 3.46 μg (H₂O) ml^-One A slightly yellowish result was obtained, which contained some amount of moisture.

Example  1-2 [ C ₂ Omim ] [ BF ₄ ] Synthesis of

[C₂Omim] [Cl] (25.00 g, 0.15 mol) was placed in plastic Ellenmeyer (250 ml). Acetone (150 mL) was added to NaBF₄ After mixing with (19.00 g, 0.17 mol) and stirred at room temperature for 24 hours. The resulting sticky solid precipitate was purified by filtration and washed twice with acetone (2 × 100 ml). Among them, the organic layer was collected and dried (MgSO₄After filtering, solvent was removed in vacuo and a light brown liquid (89% yield) result was obtained (2.66 μg (H₂O) ml^-One (RTIL)).

Example  1-3 [ C ₂ Omim ] [ PF ₆ ] Synthesis of

[C ₂ Omim] [Cl] (25.00 g, 0.15 mole) was placed in a plastic Elenmeyer flask (250 mL). Acetone (150 mL) was mixed with KPF ₆ (31.00 g, 0.168 mole) and the mixture was stirred at room temperature for about 24 hours. The resulting sticky solid precipitate was purified by filtration and washing with acetone (2 × 100 ml). The organic layer was collected, dried (MgSO 4), filtered, and then removed in vacuo to give a dark brown liquid (90% yield) result (1.84 μg (H ₂ O) ml ⁻¹ (RTIL)). .

Example  1-4 [ C ₂ Omim ] [ Tf ₂ N ] Synthesis of

[C ₂ Omim] [Cl] (25.00 g, 0.15 mole) was placed in a plastic Elenmeyer flask (250 mL). Acetone (150 mL) was mixed with Li (Tf ₂ N) (49.00 g, 0.170 mole) and the mixture was stirred at room temperature for about 24 hours. The resulting sticky solid precipitate was purified by filtration and washing with acetone (2 × 100 ml). The organic layer was collected, dried (MgSO ₄ ), filtered, and removed in vacuo under a solvent to give a dark brown liquid (89% yield) of the product (2.21 μg (H ₂ O) ml ⁻¹ (RTIL) ).

Example  1-5 [ C ₂ Omim ] [ TfO ] Synthesis of

[C ₂ Omim] [Cl] (25.00 g, 0.15 mole) was placed in a plastic Elenmeyer flask (250 mL). Acetone (150 mL) was mixed with Na (TfO) (29.50 g, 0.171 mole) and the mixture was stirred at room temperature for 24 hours. The resulting sticky solid precipitate was purified by filtration and washing with acetone (2 × 100 ml). The organic layer was collected, dried (MgSO ₄ ), filtered, and then removed in vacuo to give a pale brown liquid (90% yield). Results (2.25 μg (H ₂ O) ml ⁻¹ (RTIL) ).

Example  1-6 [ C ₂ Omim ] [ DCA ] Synthesis of

[C ₂ Omim] [Cl] (25.00 g, 0.15 mole) was placed in a plastic Elenmeyer flask (250 mL). Acetone (150 mL) was mixed with Na (DCA) (15.00 g, 0.168 mole) and the mixture was stirred at room temperature for about 24 hours. The resulting sticky solid precipitate was purified by filtration and washing with acetone (2 × 100 ml). The organic layer was collected, dried (MgSO ₄ ), filtered, and then removed in vacuo to give a pale yellow liquid (88% yield). The result was 2.52 μg (H ₂ O) ml ⁻¹ (RTIL). ).

Example 2 Characterization of Synthesized Ionic Liquid

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 conversion yields are expressed in ppm based on TMS internal reference. The mass of the samples 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 in the ionic liquid was measured using Karl-Fischer titration (Mitsubishi Chem., Model CA-07). All salts were used after drying for about 24 hours at 70-100 ° C. under vacuum drying. TGA experiments were performed with a thermal analysis system (Mettler Toledo, Model: TGA / SDTA 85 1e). Samples were placed in an average 5 mg platinum pan and heated at a rate of 10 ° C./min from 30 ° C. to 100 ° C. under N ₂ flow conditions. The density of each of the liquid salts was measured three times for 1.0 mL samples at 25 ° C. Viscosity measurements were performed using a viscometer (Brookfield, model DV-III +) model and each 0.6 ml 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 ionic liquids could be transformed into the desired properties through slight modifications of the 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 action (dispersion, repulsion action). In the case of imidazolium ionic liquids, the longer the alkyl ring of the cation, the higher the van der Waals attraction force, which has a higher viscosity, whereas the charge delocalization of the anion tends to lower the viscosity as it weakens the hydrogen bond of the cation.

In addition, for anions with even charge distribution and flat shapes (eg, [F (HF) _2.3 ] ^- [53], [N (CN) ₂ ] ^- [47,48] and [C (CN) ₃ ] ^- ) Or having non-uniform anions (eg, [Al ₂ Cl ₇ ], [46] [(CF ₃ SO ₂ ) (CF ₃ CO) N] ^- , [50] _{and [(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 - Have a high viscosity or high melting point despite the weak organizing ability. It is proved that the viscosity of the ionic liquid is mainly determined by the anion. It was confirmed that the ionic liquid containing the [DCA]-anion had the lowest viscosity, and the ionic liquid containing the [PF6]-anion had the highest viscosity. However, many studies have already been carried out by many research groups to prove that cations in ionic liquids also affect viscosity. It was also confirmed that the alcohol functional group ionic liquids had a lower viscosity as compared to the ether functional ionic liquids. In the case of ether functional ionic liquids, ionic liquids having larger alkyl groups have a higher viscosity than those with smaller alkyl group sizes. Ether functional ionic liquids having [CF ₃ BF ₃ ] anions have a higher viscosity than those having [C ₂ F ₅ BF ₃ ] anions. This suggests that these ionic liquids have a lower viscosity than the series with [TfO]-anions. These results indicate that not only the anion's ability to organize but also its shape (symmetry) and size influence viscosity determination.

Example  3 carbon dioxide Absorption capacity  And mechanism identification

Adsorption isotherm measurements of carbon dioxide were measured at 30, 50 ° C. based on isotropic saturation techniques. The main components of the measuring device include a gas reservoir, a thermostat, a pressure gauge, an isochoric cell, a vacuum pump and a magnetic stirrer. The temperature was measured by calibrated platinum resistance thermometers in each cell's heating jacket and the margin of error was ± 0.1 ° C. The error of the experimental measured pressure was ± 0.001 bar. In the experiment, generally, about 2ml of ionic liquid was injected into the isotropic volume cell, the internal air was removed by using a vacuum pump, and CO ₂ was injected into the gas reservoir, and the ionic liquid was stirred. The system then reaches equilibrium for about two hours without pressure fluctuations. The weight of the cell was measured with an electronic balance (Sartorius BS224S) with an error range of ± 0.0001 g. The carbon dioxide absorption capacity of the ionic liquid was determined by the shifted quality of this iso volumetric 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. Ether functional ionic liquids showed a significantly higher CO ₂ absorption capacity. The CO ₂ absorption capacity of the ionic liquid increased with increasing pressure and decreasing temperature. As a result, the CO ₂ absorption capacity of the ionic liquid reached up to about 0.9 mol of CO ₂ per mol of the ionic liquid at 30 ° C. Absorption capacity of different anions showed that BF ₄ <DCA ~ PF ₆ ~ TfO <Tf ₂ N. In the case of the anion having a fluoroalkyl group, the highest CO ₂ absorption capacity is consistent with the previously reported results, and when the fluoroalkyl group is increased in quantity, the CO ₂ absorption capacity is also increased.

The interaction between various ionic liquids and CO ₂ was investigated using FT-IR. As a result, it was confirmed that the CO ₂ absorption of ether functional ionic liquid was a chemical reaction. The FT-IR spectrum of CO ₂ absorbed by the ionic liquid (FIG. 3) shows two points, 1700 cm ^-1 and 1405 cm ^-1 , corresponding to (= C = O _str ) and (-OH in plane _bend ) of the carboxylic acid. Showed a new peak.

¹³ C NMR spectrum of CO ₂ absorbed by the ether functional ionic liquid is shown in FIG. 4. NMR spectra of all ionic liquids showed new peaks around δ = 200-210 ppm. These peaks are caused by the carbonyl carbon atoms of the carboxyl groups formed after the CO ₂ uptake. It was confirmed that isolated electron pairs of ether group oxygen atoms nucleophilicly attacked carbon atoms of CO ₂ to form carboxylic acids. The detailed mechanism is shown in FIG. This confirms that the 1: 1 mechanism in which only one ionic liquid reacts with CO ₂ for the formation of one carbamate is dominant, which is another ionic liquid and CO ₂ for the formation of one conventional carbamate. Is different from the so-called 1: 2 mechanism in which it reacts further.

Also, the maximum CO ₂ absorption capacity at 30 ° C. and 1.6 bar pressure reached 0.9 mol CO ₂ per mol of the ionic liquid. Absorption capacity is affected by viscosity, and the viscosity of ionic liquid decreases considerably with increasing temperature. Another important phenomenon observed in the absorption reaction is that the viscosity of the liquid phase increases rapidly by the formation of hydrogen bonding networks. The viscosity factor in the absorption reaction can be reliably controlled by reducing the number of hydrogens on the anion capable of hydrogen bonding or by adding a specific organic solvent or water. This can achieve the desired absorbing effect of the ionic liquid.

Example  4 Ionic liquid  Thermal stability and reuse

In order to study the thermal stability of the ether functional ionic liquid, it was tested in a nitrogen atmosphere (flow rate 20ml / min), temperature rising rate 10 ℃ / min conditions using TGA. As a result of the experiment up to about 100 ℃, there was no noticeable mass loss, and it was confirmed that all ionic liquids were stable even under the experimental conditions of about 30 and 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 [C 2 Omim] [X] series and measured their CO ₂ uptake. The CO ₂ absorption capacity reached 0.9 mol CO ₂ per mole of ionic liquid at room temperature. 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 proved chemical reaction. The CO ₂ absorbed by the ionic liquid could be easily desorbed by heating or pressure swinging and used repeatedly. The ether functionalized ionic liquids of the present application have a high carbon dioxide capture capacity, as well as selectivity, thermal stability, and a long service life, and thus may be usefully used for CO ₂ capture.

Claims (7)

Imidazolium-based ionic liquid compound having a carbon dioxide absorption capacity represented by the following formula (1):

[Formula 1]
Wherein X ⁻ is [BF ₄ ] ⁻ , [PF ₆ ] ⁻ , [Tf ₂ N] ⁻ , [TfO] ⁻ , or [DCA] ⁻ ,
R1, R2 and R3 are each a straight or branched chain alkyl or aryl group having 1 to 10 carbon atoms.
The ionic liquid imidazolium compound according to claim 1, wherein the imidazolium-based ionic liquid compound is represented by the following Chemical Formula 2:

(2)
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 using the carbon dioxide absorbent according to claim 3 in the gas mixture; And
Degassing carbon dioxide absorbed by the carbon dioxide absorbent.
5. The method of claim 4, wherein the temperature at the time of absorbing the carbon dioxide is from 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.
5. The method of claim 4, wherein the temperature at which the carbon dioxide is degassed is from room temperature to 80 ° C.

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