PROCESS FOR SYNTHESIZING ZWITTERIONIC BASES, ZWITTERIONIC BASES, PROCESS FOR CAPTURING CO2 AND USE

Abstract

The present invention relates to a process for capturing CO2 on a large scale using aqueous solutions of zwitterionic bases by contacting a gas stream containing one or more acid gases with said solutions. The internal salts obtained in the present invention have the advantage of not being volatile, being less susceptible to chemical and thermal decomposition, and also have lower absorption enthalpy. The present invention can be used in various industry sectors, such as in the energy sector, for capturing CO2 from exhaust gases, in the chemical sector, for removing CO2 from the gas streams of catalytic processes in which the CO2 can poison the catalysts, and, in particular, in the oil and gas sector, for purifying natural gas.

Claims

1- A process of synthesis of zwitterionic bases, characterized in that it comprises three steps: a) First step: promoting the reaction between a compound of the hydroxy-benzaldehyde type with a primary amine to form the corresponding imine, followed by the cyclization reaction of this imine, by adding an ammonium salt and a vicinal dialdehyde, for obtaining a compound of the 2-(hydroxy-phenyl)-imidazole type, in the presence of a solvent, at temperatures between ?10? C. and 80? C. for times between 10 minutes and 24 hours; b) Second step: promoting the N-alkylation reaction between the compound of 2-(hydroxy-phenyl)-imidazole type obtained in the previous step and an alkylating agent to form a 2-(hydroxy-phenyl)-imidazolium salt, in the presence of solvent, at temperatures between 40? C. and 100? C. and in reaction times between 10 minutes and 24 hours; c) Third step: promoting the deprotonation of the phenolic OH group of the 2-(hydroxy-phenyl)-imidazolium salt, obtained in the second step, through the reaction of an aqueous solution of this component with a strongly basic ion exchange resin, which results in the formation of the inner or zwitterionic salt of the 2-(oxy-phenyl)-imidazolium type in a time of up to 60 minutes and temperatures between 10? C. and 80? C.

2- The process according to claim 1, characterized in that the compound of the hydroxy-benzaldehyde type contains at least one hydroxyl group in its aromatic ring and the other substituents of the benzene ring are hydrogen, alkoxy groups containing between 1 and 10 carbons, halides, phenyl or alkyl group or containing between 1 and 10 carbons.

3- The process according to claim 2, characterized in that the compound of the hydroxy-benzaldehyde type is 3-hydroxy-benzaldehyde or 4-hydroxy-benzaldehyde.

4- The process according to claim 1, characterized in that the primary amine has the general formula R1-NH.sub.2 in which the radical R1 comprises an alkyl, aryl, alkylether or alkylalcohol group containing between 1 and 10 carbons.

5- The process according to claim 4, characterized in that the primary amine is methylamine.

6- The process according to claim 1, characterized in that the primary amine is in a proportion of 0.5 to 2 equivalents in relation to the compound of the hydroxy-benzaldehyde type.

7- The process according to claim 1, characterized in that the ammonium salt has the general formula (NH.sub.4).sub.nY, where Y comprises the bromide, chloride, sulfate, acetate, carbonate and bicarbonate anions; n has a value of 1 or 2.

8- The process according to claim 1, characterized in that the ammonium salt is in a proportion of 0.3 to 2 equivalents in relation to the compound of the hydroxy-benzaldehyde type.

9- The process according to claim 1, characterized in that the dialdehyde is glyoxal or its analogues with alkyl, aryl, alkylether or alkylalcohol substituents containing 1 to 10 carbons.

10- The process according to claim 1, characterized in that the dialdehyde is in a proportion of 0.5 to 2 equivalents in relation to the compound of the hydroxy-benzaldehyde type.

11- The process according to claim 1, characterized in that the solvent of the first step is water, acetonitrile, ethyl acetate, aliphatic alcohols containing from 1 to 10 carbons in the alkyl chain or a mixture of these in any proportion in the amount of 1 to 100 times the mass of the compound of the hydroxy-benzaldehyde type.

12- The process according to claim 11, characterized in that the solvent is an amount of 10 times the mass of the compound of the hydroxy-benzaldehyde type.

13- The process according to claim 1, characterized in that the alkylating agent has the general formula R9-X, in which R9 comprises an alkyl, arylalkyl, alkylether or alkylalcohol group containing between 1 and 10 carbons, and the X group comprises a halide, alkylsulfonate and alkylsulfate group, in which the alkyl group has between 1 and 5 carbons.

14- The process according to claim 13, characterized in that the alkylating agent is iodomethane or methanesulfonyl chloride.

15- The process according to claim 1, characterized in that the second step occurs at a temperature of 70? C., under stifling for 1 hour.

16- The process according to claim 1, characterized in that the solvent of the second step is water, acetonitrile, ethyl acetate, aliphatic alcohols containing from 1 to 10 carbons in the alkyl chain or a mixture of these in any proportion in the amount of 1 to 20 times the mass of the compound of the hydroxy-benzaldehyde type.

17- The process according to claim 16, characterized in that the solvent is an amount of 5 times the mass of the compound of the hydroxy-benzaldehyde type.

18- The process according to claim 1, characterized in that the third step occurs at a temperature of 30? C. and under stifling for 10 minutes.

19- Zwitterionic bases, as obtained in the process of claim 1, characterized in that they present in their structure an imidazolium cation covalently linked, through carbon C-2, to a phenolate anion, represented by the general formula: ##STR00013## wherein the R.sub.1 and R.sub.9 substituents comprise the alkyl, aryl, alkylether or alkylalcohol group containing 1 to 10 carbons; the R.sub.7 and R.sub.8 substituents of the imidazolium cation comprise hydrogen or alkyl, aryl, alkylether or alkylalcohol groups containing 1 to 10 carbons; and the R.sub.2, R.sub.3, R.sub.4, R.sub.5 and R.sub.6 substituents of the benzene ring are independent of each other and comprise the O.sup.? group, hydrogen, hydroxyl, alkoxy groups containing between 1 and 10 carbons, halide, phenyl or alkyl group containing between 1 and 10 carbons, and, necessarily, one of the substituents of the benzene ring is the O.sup.? group.

20- The zwitterionic bases according to claim 19, characterized in that they are solids soluble in water and polar organic solvents, such as alcohols, polyalcohols, acetonitrile and acetone.

21- A CO.sub.2 capture process, using zwitterionic base solutions as defined in claim 19, characterized in that it promotes the contact, under sorption conditions, of a gaseous stream containing acidic gases with a zwitterionic base sorbent solution for the removal of, at least, part of these acidic gases, obtaining a purified gaseous stream and a solution with sorbed acidic gases; and, in parallel, it promotes the regeneration of the sorbent solution, under desorption conditions, to obtain a zwitterionic base solution and a stream of acidic gases.

22- The CO.sub.2 capture process according to claim 21, characterized in that the gaseous feed stream is composed of a gaseous mixture containing one or more acidic gases, such as carbon dioxide and hydrogen sulfide.

23- The CO.sub.2 capture process according to claim 21, characterized in that the zwitterionic base is an inner organic salt formed by the covalent association of a quaternary ammonium cation, quaternary phosphonium, pyridinium, pyrrolidinium or imidazolium, with the phenolate anion.

24- The CO.sub.2 capture process according to claims 21 to 23, characterized in that the zwitterionic base containing the quaternary ammonium cation has the formula: ##STR00014## wherein R.sub.1, R.sub.2 and R.sub.3 comprise the alkyl, aryl, alkylether or alkylalcohol groups containing between 1 and 10 carbons; and PhO.sup.? represents the phenolate anion with substituents, independent of each other, comprising hydrogen, halides, phenyl, alkoxy containing between 1 and 10 carbons or alkyl containing between 1 and 10 carbons.

25- The CO.sub.2 capture process according to claims 21 to 23, characterized in that the zwitterionic base containing the quaternary phosphonium cation has the formula: ##STR00015## wherein R.sub.1, R.sub.2 and R.sub.3 comprise the alkyl, aryl, alkylether or alkylalcohol groups containing between 1 and 10 carbons; and PhO.sup.? represents the phenolate anion with substituents, independent of each other, comprising hydrogen, halides, phenyl, alkoxy containing between 1 and 10 carbons or alkyl containing between 1 and 10 carbons.

26- The CO.sub.2 capture process according to claims 21 to 23, characterized in that the zwitterionic base containing pyridinium has the formula: wherein R.sub.1, R.sub.2, R.sub.3, R.sub.4 and R.sub.5 comprise hydrogen and alkyl, aryl, alkylether or ##STR00016## alkylalcohol groups containing between 1 and 10 carbons; and PhO.sup.? represents the phenolate anion with substituents, independent of each other, comprising hydrogen, halides, phenyl, alkoxy containing between 1 and 10 carbons or alkyl containing between 1 and 10 carbons.

27- The CO.sub.2 capture process according to claims 21 to 23, characterized in that the zwitterionic base containing the pyrrolidinium cation has the formula: ##STR00017## wherein R.sub.1, R.sub.2, R.sub.3, R.sub.4 and R.sub.5 comprise hydrogen and alkyl, aryl, alkylether or alkylalcohol groups containing between 1 and 10 carbons; and PhO.sup.? represents the phenolate anion with substituents, independent of each other, comprising hydrogen, halides, phenyl, alkoxy containing between 1 and 10 carbons or alkyl containing between 1 and 10 carbons.

28- The CO.sub.2 capture process according to claims 21 to 23, characterized in that the zwitterionic base containing the imidazolium cation has the formula: ##STR00018## wherein R.sub.1, R.sub.2, R.sub.3 and R.sub.4 comprise hydrogen and alkyl, aryl, alkylether or alkylalcohol groups containing between 1 and 10 carbons; and PhO.sup.? represents the phenolate anion with substituents, independent of each other, comprising hydrogen, halides, phenyl, alkoxy containing between 1 and 10 carbons or alkyl containing between 1 and 10 carbons.

29- The CO.sub.2 capture process according to claim 21, characterized in that the zwitterionic solution is a solution of 1,3-dimethyl-2-(3-oxyphenyl)-imidazolium or 1,3-dimethyl-2-(4-oxy-phenyl)-imidazolium inner salt.

30- The CO.sub.2 capture process according to claim 21, characterized in that the zwitterionic solution uses as solvent water, methanol, ethanol, isopropanol, aliphatic alcohol having from 1 to 18 carbons in the alkyl chain, diols having from 2 to 5 atoms of carbon or polyols having from 3 to 6 carbon atoms, ethylene glycolmonoalkylethers of the formula H(OCH.sub.2CH.sub.2)nOR.sub.2, where n varies from 1 to 4 and R.sub.2 consists of an alkyl group containing from 1 to 12 carbons, ionic liquids functionalized with the hydroxyl group or mixtures thereof.

31- The CO.sub.2 capture process according to claim 21, characterized in that the absorption condition is: concentration of the zwitterionic base solution between 0.5 M and 5 M, temperature between 0? C. and 60? C. and pressure between 1 and 150 bar absolute (100 kPa and 15 MPa).

32- The CO.sub.2 capture process according to claim 21, characterized in that the zwitterionic solution of the absorption step presenting a temperature of 40? C. and pressure between 1.3 and 3 bar absolute (130 and 300 kPa).

33- The CO.sub.2 capture process according to claim 21, characterized in that the desorption condition being: temperature between 60? C. and 150? C. and a pressure between 0 and 10 bar absolute (1 MPa).

34- The CO.sub.2 capture process according to claim 33, characterized in that the zwitterionic solution of the desorption step presents a temperature of 100? C. and a pressure of 1 absolute bar (100 kPa).

35- A use of the co t capture process, as defined in claim 21, characterized in that it is applied in industrial segments, such as in the energy sector to capture CO.sub.2 from exhaust gases, in the chemical sector to remove CO.sub.2 from process gaseous streams catalysts in which CO.sub.2 can poison the catalysts and especially in the oil and gas sector for the purification of natural gas.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The present invention will be described in more detail below, with reference to the attached figures which, in a schematic way and not limiting the inventive scope, represent examples of its embodiment. In the drawings there are:

[0025] FIG. 1 illustrating developed inner salts: A) 1,3-dimethyl-2-(3-oxy-phenyl)-imidazolium and B) 1,3-dimethyl-2-(4-oxy-phenyl)-imidazolium;

[0026] FIG. 2 illustrating the first step of the synthesis of the 1,3-dimethyl-2-(3-oxy-phenyl)-imidazolium (synthesis of 1-methyl-2(3-hydroxy-phenyl)-imidazole) inner salt;

[0027] FIG. 3 illustrating the second step of the synthesis of the 1,3-dimethyl-2-(3-oxy-phenyl)-imidazolium inner salt (synthesis of 1,3-dimethyl-2(3-hydroxy-phenyl)-imidazolium iodide);

[0028] FIG. 4 illustrating the ESI(+)MS spectrum of the 1,3-dimethyl-2(3-hydroxy-phenyl)-imidazolium iodide precursor for the synthesis of the 1,3-dimethyl-2-(3-oxy-phenyl)-imidazolium inner salt, where there are represented the simulated spectrum at the top and below the experimentally obtained spectrum;

[0029] FIG. 5 illustrating the third step of the synthesis of the 1,3-dimethyl-2-(3-oxy-phenyl)-imidazolium inner salt (synthesis of the 1,3-dimethyl-2-(3-oxy-phenyl)-imidazolium inner salt);

[0030] FIG. 6 illustrating the NMR spectrum of .sup.1H NMR (400 MHz, D.sub.2O) of 1,3-dimethyl-2-(3-oxy-phenyl)-imidazolium inner salt;

[0031] FIG. 7 illustrating the .sup.13C NMR spectrum (100 MHz, D.sub.2O) of 1,3-dimethyl-2-(3-oxy-phenyl)-imidazolium inner salt;

[0032] FIG. 8 illustrating the infrared spectrum of 1,3-dimethyl-2-(3-oxy-phenyl)-imidazolium inner salt;

[0033] FIG. 9 illustrating the first step of the synthesis of the 1,3-dimethyl-2-(4-oxy-phenyl)-imidazolium (synthesis of 1-methyl-2-(4-hydroxy-phenyl)-imidazole) inner salt;

[0034] FIG. 10 illustrating the second step of the synthesis of the 1,3-dimethyl-2-(4-oxy-phenyl)-imidazolium inner salt (synthesis of 1,3-dimethyl-2-(4-hydroxy-phenyl)-imidazolium iodide);

[0035] FIG. 11 illustrating the third step of the synthesis of the 1,3-dimethyl-2-(4-oxy-phenyl)-imidazolium inner salt (synthesis of the 1,3-dimethyl-2-(4-oxy-phenyl)-imidazolium inner salt);

[0036] FIG. 12 illustrating the NMR spectrum of .sup.1H NMR (400 MHz, DMSO-d.sub.6) 1,3-dimethyl-2-(4-oxyphenyl)-imidazolium inner salt;

[0037] FIG. 13 illustrating the .sup.13C NMR spectrum (100 MHz, DMSO-d.sub.6) 1,3-dimethyl-2-(4-oxy-phenyl)-imidazolium inner salt;

[0038] FIG. 14 illustrating the infrared spectrum of 1,3-dimethyl-2-(4-oxy-phenyl)-imidazolium inner salt;

[0039] FIG. 15 illustrating the experimental apparatus for sorption tests, where there are represented the following items: 401CO.sub.2 cylinder; 402CO.sub.2 reservoir with monitored pressure; 403valve for pressure control in the sorption vessel; 404jacketed sorption vessel; 405purge valve; 406purge gas; 407thermostatic bath to control the temperature of the process; 408magnetic stirrer; 409Field Logger pressure recorder; and 410computer for data storage and processing;

[0040] FIG. 16 illustrating the UV-VIS spectra of the aqueous solution of the 1,3-dimethyl-2-(3-oxy-phenyl)-imidazolium inner salt, solution after absorption and after desorption;

[0041] FIG. 17 illustrating the recyclability of the aqueous solution of 1,3-dimethyl-2-(3-oxy-phenyl)-imidazolium, where the reaction conditions are: 5 mL of solution with a concentration of 1 M, absorption temperature of 40? C. and pressure of 1.3 bar absolute (130 kPa); desorption temperature of 100? C. and atmospheric pressure; absorption values determined through the pressure drop in the reservoir and expressed in moles CO.sub.2 per moles of absorbent; mean represents mean absorption value from cycles 2 to 27?standard deviation.

[0042] FIG. 18 illustrating the recyclability of the aqueous solution of 1,3-dimethyl-2-(4-oxy-phenyl)-imidazolium, where the reaction conditions are: 5 mL of solution with a concentration of 1 M, absorption temperature of 40? C. and pressure of 1.3 bar absolute (130 kPa); desorption temperature of 100? C. and atmospheric pressure; absorption values determined through the pressure drop in the reservoir and expressed in moles CO.sub.2 per moles of absorbent; mean represents mean absorption value from cycles 2 to 17?standard deviation;

[0043] FIG. 19 illustrating the recyclability of the commercial MDEA/Piperazine aqueous solution, where the reaction conditions are: 5 mL of MDEA/piperazine/water 40%:10%:50% solution, absorption temperature of 40? C. and pressure of 1.3 bar absolute (130 kPa); desorption temperature of 100? C. and atmospheric pressure; absorption values determined through the pressure drop in the reservoir and expressed in moles CO.sub.2 per moles of absorbent; mean represents mean absorption value from cycles 1 to 26?standard deviation;

[0044] FIG. 20 illustrating the experimental apparatus for estimating the enthalpy of absorption, where there are represented the following items: 301O.sub.2 cylinder; 302CO.sub.2 reservoir with monitored pressure; 303CO.sub.2 admission valve in the sorption vessel; 304sorption vessel; 305pressure transducer to monitor the pressure in the CO.sub.2 reservoir; 306pressure transducer to monitor the pressure of the sorption vessel; 307Field Logger pressure data recorder; 308computer for storing and processing data; 309thermostatic bath to control the temperature of the system; 310isochoric balance chamber; 311vacuum pump; and 312syringe for adding the sorbent solution;

[0045] FIG. 21 illustrating the process of absorption of acidic gases using zwitterionic bases, where there are represented the following items: 101gaseous feeding; 102absorption unit operating at T.sub.1, P.sub.1; 103purified gaseous stream; 104zwitterionic solution rich in absorbed acidic gases; 105desorption unit operating at T.sub.2, P.sub.2; 106gaseous stream rich in CO.sub.2 and/or other acidic gases; and 107regenerated zwitterionic solution;

[0046] FIG. 22 illustrating the family of inner salts of the present invention with predictable effect for acidic gas capture processes from the mere direct extrapolation of the state of the art;

[0047] FIG. 23 illustrating the process of synthesis of zwitterionic bases of the present invention;

[0048] FIG. 24 illustrating the family of inner salts obtained by the process of synthesis of zwitterionic bases of the present invention;

[0049] FIG. 25 illustrating the ionic liquids used as a solvent of general formula A.sup.+Z.sup.? for preparing the solutions of zwitterionic bases of the present invention;

[0050] FIG. 26 illustrating an embodiment of acidic gas absorption process using zwitterionic bases for the purification of natural gas, where there are represented the following items: 201gas feed; 202absorption unit at T.sub.1, P.sub.1; 203purified gaseous stream; 204zwitterionic solution rich in absorbed acidic gases; 205desorption unit operating at T.sub.2, P.sub.2; 206gaseous stream rich in CO.sub.2 and/or other acidic gases; 207regenerated zwitterionic solution; 208reboiler; and 209heat exchanger.

DETAILED DESCRIPTION OF THE INVENTION

[0051] The process of synthesizing zwitterionic salts according to the present invention is characterized by comprising three very simple steps that occur successively promoting reactions between its components in the liquid phase, in the presence of solvent, under mechanical stifling, under pressure atmospheric and at temperatures between ?10? C. and 100? C., typically between 0? C. to 70? C.

a) First Step

[0052] The first step is characterized by promoting the reaction between a compound of the hydroxy-benzaldehyde type with a primary amine of general formula R1-NH.sub.2 for the formation of the corresponding imine, followed by the cyclization reaction of this imine, in the presence of a salt of ammonium and a vicinal dialdehyde, to obtain a compound of the 2-(hydroxy-phenyl)-imidazole type, according to Step 1FIG. 23.

[0053] The first step is characterized by occurring at temperatures that can vary between ?10? C. and 80? C., typically 0? C. to 40? C. and reaction times between 10 minutes and 24 hours, typically 24 hours.

[0054] The first step is characterized by the reaction product of the 2-(hydroxy-phenyl)-imidazole type being purified by simple techniques of precipitation, crystallization and/or filtration followed, or not, by washing and/or evaporation of the solvent.

[0055] The compound of the hydroxy-benzaldehyde type is characterized by containing, in its aromatic ring, at least one hydroxyl group and the other substituents of the benzene ring being hydrogen, alkoxy groups containing between 1 and 10 carbons, halides, phenyl or alkyl group or containing between 1 and 10 carbons, with 3-hydroxy-benzaldehyde and 4-hydroxy-benzaldehyde being typically used.

[0056] The primary amine of general formula R1-NH.sub.2 is characterized in that the radical R1 comprises an alkyl, aryl, alkylether or alkylalcohol group containing between 1 and 10 carbons, typically methylamine, and in that being used in the proportion of 0.5 to 2 equivalents to benzaldehyde, typically 1.05 equivalents.

[0057] The ammonium salt is characterized by having the general formula (NH.sub.4).sub.nY, where Y comprises the bromide, chloride, sulfate, acetate, carbonate and bicarbonate anions; n has a value of 1 or 2 and, because this salt is used in a proportion of 0.3 to 2 equivalents relative to the benzaldehyde, typically 0.75 equivalents.

[0058] Dialdehyde is characterized by being typically glyoxal and can also be analogues of glyoxal with alkyl, aryl, alkylether or alkylalcohol substituents containing 1 to 10 carbons and for being used in the proportion of 0.5 to 2 equivalents in relation to benzaldehyde, typically 1 equivalent.

[0059] The solvent used in the first step comprises water, acetonitrile, ethyl acetate, aliphatic alcohols containing from 1 to 10 carbons in the alkyl chain or a mixture of these in any proportion in the amount of 1 time to 100 times the mass of benzaldehyde, typically 10 times.

[0060] The purification of the reaction products of the first step is characterized by using water, acetonitrile, ethyl acetate, aliphatic alcohols containing from 1 to 10 carbons in the alkyl chain or a mixture of these in proportions suitable for, under temperatures of ?10? C. to 30? C., typically 0? C., the precipitation or crystallization of compounds of the 2-(hydroxy-phenyl)-imidazole type is carried out followed by removal of the solvent by filtration or simple decantation, being recommended to wash the product with the same solvent and evaporating the residual solvent under reduced pressure.

b) Second Step

[0061] The second step is characterized by promoting the N-alkylation reaction between the compound of the 2-(hydroxy-phenyl)-imidazole type obtained in the previous step and an alkylating agent of general formula R9-X to form a salt of 2-(hydroxy-phenyl)-imidazolium, in the presence of solvent, according to Step 2FIG. 23.

[0062] The second step is characterized by occurring at temperatures that can vary between 40? C. and 100? C., typically 70? C., and reaction times between 10 minutes and 24 hours, typically 1 hour.

[0063] The second step is characterized in that the reaction product of the 2-(hydroxy-phenyl)-imidazolium salt type precipitates as it is formed and is removed from the reaction mixture by filtration or decantation followed by washing and evaporation of the residual solvent under reduced pressure.

[0064] The alkylating agent of general formula R9-X is characterized in that R9 comprises an alkyl, arylalkyl, alkylether or alkylalcohol group containing between 1 and 10 carbons, and the X group comprises the halide, alkylsulfonate and alkylsulfate group, in which the alkyl group has between 1 and 5 carbons, typically iodomethane or methanesulfonyl chloride.

[0065] The solvent used in the second step comprises water, acetonitrile, ethyl acetate, aliphatic alcohols containing from 1 to 10 carbons in the alkyl chain or the mixture of these in appropriate proportions in the amount of 1 time to 20 times the mass of the compound of 2-(hydroxy-phenyl)-imidazole type, typically 5 times.

c) Third Step

[0066] The third step is characterized by promoting the deprotonation of the phenolic OH group of the 2-(hydroxy-phenyl)-imidazolium salt, obtained in the previous step, through the reaction of an aqueous solution of this component with a strongly basic ion exchange resin, which results in the formation of the inner or zwitterionic salt of the 2-(oxy-phenyl)-imidazolium type, as shown in Step 3FIG. 23.

[0067] The third step is also characterized in that the reaction between the 2-(hydroxy-phenyl)-imidazolium salt and the ion exchange resin occurs by simply mixing and stifling these components for periods of up to 60 minutes, typically 10 minutes, or by passing a solution of the 2-(hydroxy-phenyl)-imidazolium salt through a fixed or fluidized bed column of resin at temperatures between 10? C. and 80? C., typically 30? C.

[0068] Furthermore, the third step is characterized in that the aqueous solution containing the product is separated from the ionic resin by filtration or simple decantation and the reaction product, inner salt of the 2-(oxy-phenyl)-imidazolium type, is isolated by simple evaporation of the solvent under reduced pressure and temperatures between 10? C. and 80? C., typically 40? C.

[0069] The zwitterionic bases obtained in the synthesis process disclosed herein have as their main structural characteristic the presence of an imidazolium cation covalently linked, through carbon C-2, to an oxy-phenyl group, having as possible substituents of the imidazolium ring, R.sub.7 and R.sub.8, hydrogen or alkyl, aryl, alkylether or alkylalcohol groups containing 1 to 10 carbons; and as substituents on the benzene ring, necessarily an O.sup.? group, the others being hydrogen, hydroxyl, alkoxy groups containing between 1 and 10 carbons, halide, phenyl or alkyl group containing between 1 and 10 carbons, as shown in FIG. 24.

[0070] The zwitterionic bases obtained in the synthesis processes are neutral compounds that have opposite charges in different regions of their structure and can also be called inner salts or hybrid salts.

[0071] The zwitterionic bases obtained in the synthesis processes are solids soluble in water and polar organic solvents, such as alcohols, polyalcohols, acetonitrile and acetone.

[0072] Unlike most traditional zwitterions, which are amphoteric amino acids, the main property of zwitterionic bases is precisely the fact that they are basic inner salts, and have relatively high basicity, typical of the phenolate group, and may vary depending on the substituents of the benzene ring.

[0073] The zwitterionic bases have a unique characteristic for the process of capturing acidic gases, the fact that both they and their acid-conjugates are organic salts, therefore, non-volatile.

[0074] The key aspect of the zwitterionic bases disclosed herein is the presence of a phenolate group covalently linked to an imidazolium cation to form a basic salt with good solubility in water and polar solvents.

[0075] The process for capturing acidic gases through zwitterionic base solutions comprises contacting, under sorption conditions, a gaseous stream containing one or more acidic gases with a zwitterionic base sorbent solution for the removal of at least part of the acidic gases, and obtaining a purified gaseous stream and a solution with sorbed acidic gases; and the regeneration of the sorbent solution, under desorption conditions, to obtain a zwitterionic base solution and a stream of acidic gases.

[0076] FIG. 21 illustrates in a simplified way the continuous cyclic process of purification of a gaseous stream using solutions of zwitterionic bases. The feed stream 101 enters the sorption unit 102, which contains the zwitterionic base solution and whose temperature is controlled by heat extraction. In the sorption unit, the gaseous stream comes into contact with the zwitterionic base solution under temperature and pressure conditions (T1 and P1) so that at least part of the acidic gases contained in the feed stream is absorbed by the zwitterionic base solution, generating a purified gaseous stream 103 and a solution rich in sorbed acidic gases 104, which is conducted to the desorption unit 105. In the desorption unit, acidic gases are desorbed from the solution through appropriate temperature and pressure conditions (T2 and P2) generating a gaseous stream rich in acidic gases 106 and the regenerated zwitterionic base solution 107.

[0077] Conventional equipment can be used for the various functions necessary for the process of capturing acidic gases by solutions of zwitterionic bases, such as, for example, to control the gaseous flow, to promote contact between the gas and the sorbent solutions, for pumping the solutions between the sorption and desorption units, to promote heat exchanges between the process streams in such a way as to obtain an efficient cyclic process of capturing acidic gases.

[0078] FIG. 26 shows an embodiment of the cyclic capture process of acidic gases by solutions of zwitterionic bases in which heat exchangers are used between the sorption tower (scrubbing) and the desorption tower (stripping). This process is particularly suitable for the purification of natural gas. The stream of natural gas 201 containing acidic gases, especially CO.sub.2 or H.sub.2S, comes into contact with the zwitterionic base solution in a sorption tower 202, under temperature and pressure conditions (T.sub.1 and P.sub.1) typical for sorption, giving rise to the gaseous stream of purified natural gas 203 and a stream of saturated solution of acidic gases 204. The saturated solution of acidic gases is pumped to the regeneration (or desorption) tower, in which it is subjected to a temperature and pressure condition (T.sub.2 and P.sub.2), which favors the desorption of acidic gases generating a gaseous stream rich in acidic gases 206 and the regenerated zwitterionic base solution. The temperature in the regeneration tower is maintained by reboiler 208, which heats the regenerated zwitterionic base solution. A part of the regenerated solution 207 that passes through the reboiler is sent back to the sorption tower and another part returns to the desorption tower to maintain the temperature. The regenerated solution stream 207 exchanges heat by heating the solution stream saturated in acidic gases through heat exchanger 209.

[0079] The absorption step of the process promotes the direct or indirect contact, by means of contact membranes, of the gaseous feed stream, with zwitterionic solutions without concentration between 0.5 M and 7 M, temperatures (T.sub.1) between 0? C. to 60? C. and pressures (P.sub.1) between 1 and 150 bar absolute (100 kPa and 15 MPa), typically 40? C. and 1.3 bar to 3 bar absolute (130 kPa to 300 kPa).

[0080] The desorption step of the process promotes the regeneration of zwitterionic solutions by heating the solution rich in acidic gases at temperatures (T.sub.2) greater than the absorption temperature (T.sub.1) and/or through the use of pressures (P.sub.2) lower than the absorption pressure (P.sub.1), the desorption temperatures (T.sub.2) being between 60? C. and 150? C. and the desorption pressures between 0 and 10 bar absolute (1 MPa), typically 100? C. and 1 bar absolute (100 kPa).

[0081] The process feed gaseous stream can be composed of any gaseous stream or gaseous mixture containing one or more acidic gases, such as carbon dioxide and hydrogen sulfide, in concentrations of 5% to 90%, typically streams of natural gas containing from 1% to 20% CO.sub.2.

[0082] The zwitterionic solutions used in the capture process are any of those in which the zwitterionic base is dissolved in water, methanol, ethanol, isopropanol or other hydrocarbon, aliphatic alcohol having from 1 to 18 carbons in the alkyl chain, diols having from 2 to 5 carbon atoms or polyols having from 3 to 6 carbon atoms, ethylene glycol monoalkylethers of the formula H(OCH.sub.2CH.sub.2).sub.nOR.sub.2, where n varies from 1 to 4 and R.sub.2 consists of an alkyl group containing from 1 to 12 carbons or ionic liquids functionalized with the hydroxyl group as well as mixing these solvents in appropriate proportions, typically water, ethylene glycol, glycerol and ionic liquids functionalized with the hydroxyl group.

[0083] Ionic liquids functionalized with the hydroxyl group are compounds with the general formula A.sup.+Z.sup.?, wherein A.sup.+ represents a quaternary ammonium cation, an imidazolium cation, a pyridinium cation, a pyrrolidinium cation or a phosphonium cation, and Z.sup.? represents susceptible anions to form a liquid salt with these cations at the absorption temperature.

[0084] The cations of ionic liquids include derivatives of the imidazolium cation, the pyridinium cation, the pyrrolidinium cation, the quaternary phosphonium cation or the quaternary ammonium in which, as shown in FIG. 25, the R.sub.21, R.sub.2, R.sub.23, R.sub.24, R.sub.25 and R.sub.26 substituents are H, alkylalcohols, alkylether, aryl or alkyl containing between 1 and 10 carbons in each of these groups, typically 1,2-dimethyl-3-(3-hydroxypropyl)-2,3-imidazolium.

[0085] The anions of ionic liquids include chloride, bromide, iodide, perchlorate, nitrate, tetrafluoroborate, tetrachloroborate, hexafluorophosphate, trifluoromethanesulfonate, bis(trifluoromethanesulfonyl)imidate, typically NTf.sub.2.sup.? and PF.sub.6.sup.?.

[0086] From the mere direct extrapolation of the results disclosed herein, in particular, the results of example 3, example 4, example 5 and example 6 and example 7, it can be concluded that the zwitterionic bases have a predictable effect for capturing acidic gases and that have in their structure an organic cation covalently linked to a phenolate anion; therefore, the process of capturing acidic gases described herein is characterized by the zwitterionic base being an organic compound formed by the covalent association of quaternary ammonium, quaternary phosphonium, and pyridinium cations, pyrrolidinium or imidazolium with substituents, independent of each other, comprising hydrogen and alkyl, aryl, alkylether or alkylalcohol groups containing between 1 and 10 carbons, with the phenolate anion with substituents, independent of each other, comprising hydrogen, halides, phenyl, alkoxy containing between 1 and 10 carbons or alkyl containing between 1 and 10 carbons, according to FIG. 22, typically the zwitterionic bases are 1,3-dimethyl-2-(4-oxy-phenyl)-imidazolium and 1,3-dimethyl-2-(3-oxy-phenyl)-imidazolium.

[0087] The use of solutions, especially aqueous solutions, of the inner salts called herein zwitterionic bases, object of the present invention, minimizes the main intrinsic inconveniences of large-scale CO.sub.2 capture processes based on aqueous solutions of ethanolamines, as follows: [0088] I) The problems resulting from the loss of mass of the absorbents during the process, such as the increase in costs related to their replacement and the greater operational complexity, are completely solved by the fact that both the absorbent agents and the absorption products are ionic species and, therefore, have negligible vapor pressure; [0089] II) The problems related to thermal and mainly chemical decomposition are minimized by the innovative use of the phenolate functional group in substitution of the amino group, which completely eliminates the decomposition via the formation of carbamates; [0090] III) The costs associated with the energy expenditure of the process are minimized, as estimates suggest that the enthalpy of absorption using aqueous solutions of the inner salts described herein are about 20% lower than the enthalpy of absorption of aqueous solutions of MDEA; [0091] IV) The process embodiment in which ionic liquids are used as solvents also eliminates energy losses resulting from solvent evaporation in the desorption process.

[0092] The zwitterion solutions containing the phenolate group, especially aqueous solutions, can be used in gas washing or scrubbing equipment, that is, in conventional equipment intended for the absorption of acidic gases by liquids.

[0093] Therefore, in addition to the various technical advantages, this technology is easy to implement, as it allows already-existing CO.sub.2 absorption plants that use aqueous alkanolamine solutions, in particular, in CO.sub.2 and H.sub.2S removal plants from natural gas, are converted into absorption plants by zwitterionic base solutions without all the equipment having to be replaced, requiring only small adaptations, for example, to adjust the energy demand of the process.

EXAMPLE

[0094] For this work, the following tests were carried out, which represent examples of embodiment of the present invention.

Example 1: Synthesis of 1,3-dimethyl-2-(3-oxy-phenyl)-imidazolium inner salt (FIG. 1-A)

[0095] The synthesis of 1,3-dimethyl-2-(3-oxy-phenyl)-imidazolium inner salt is carried out in three steps. In the first step, 1-methyl-2(3-hydroxy-phenyl)-imidazole is obtained, as shown in FIG. 2.

[0096] In a reaction flask, methylamine (40% aqueous solution, 3.3 g; 42 mmol) was added over a solution of 3-hydroxy-benzaldehyde (4.88 g; 40 mmol) in 20 mL of methanol at room temperature. The exothermic reaction causes a slight heating of the reaction mixture and, then, the precipitation of the corresponding imine is observed. The suspension was stirred for another 10 minutes and then ammonium carbonate (2.88 g, 30 mmol) was added. The resulting mixture was cooled to 0? C. using an external ice-water bath. Glyoxal (40% aqueous solution, 5.8 g; 40 mmol) dissolved in 15 mL of CH.sub.3OH was added slowly and under stirring. The reaction mixture was stirred for another 30 minutes at 0? C., generating a gradual dissolution of the solids. The ice bath was removed and the reaction was stirred for another 24 hours at room temperature, observing the precipitation of the desired reaction product. At the end, 15 mL of water were added to the suspension, the solid was filtered in a B?chner funnel, icy washed with CH.sub.3OH/H.sub.2O 1:1 and dried under reduced pressure. 2.69 g of a slightly yellowish solid were obtained (38.6% yield).

[0097] In the second step of the synthesis, 1,3-dimethyl-2(3-hydroxy-phenyl)-imidazolium iodide is obtained, as shown in FIG. 3. In a Schlenk flask, 40 mL of acetonitrile, 1-methyl-2-(3-hydroxy-phenyl)-imidazole (6.20 g; 35.6 mmol) and iodomethane (7.60 g; 53.4 mmol). The flask was closed with a rubber septum and the suspension was heated to 70? C., under stirring with the aid of a magnetic bar, for 1 hour. The solvent in the resulting brownish solution was evaporated to give a solid which was washed with ethyl acetate and then dried under reduced pressure. 10 g of brownish solid were obtained (88.9% yield) according to the ESI(+)-MS spectrum, as illustrated in FIG. 4.

[0098] In the third step of the synthesis, the 1,3-dimethyl-2-(3-oxy-phenyl)-imidazolium inner salt is obtained, as shown in FIG. 5. In a test tube, there was measured the volume of 14 mL of the ion exchange resin Ambersep 900 OH. The resin was washed three times with distilled water. Next, the resin was added to a solution of 1,3-dimethyl-2-(3-hydroxy-phenyl)-imidazolium iodide (3.16 g, 10.0 mmol) in 10 mL of water. The reaction remained under stirring at room temperature in a beaker for 10 minutes. After this time the ion exchange resin was separated by filtration, and the water in the solution was evaporated under reduced pressure, resulting in 1.8 g of a hygroscopic brown solid (96% yield). The 1 H NMR, .sup.13C NMR, infrared spectra are presented, respectively, in FIG. 6, FIG. 7, and FIG. 8.

Example 2: Synthesis of 1,3-dimethyl-2-(4-oxy-phenyl)-imidazolium (FIG. 1-B)

[0099] The synthesis of 1,3-dimethyl-2-(4-oxy-phenyl)-imidazolium inner salt is carried out in three steps. In the first step, 1-methyl-2-(4-hydroxy-phenyl)-imidazole is obtained, as shown in FIG. 9.

[0100] Into a reaction flask, there was added at room temperature methylamine (40% aqueous solution, 3.30 g; 42 mmol) over a solution of 4-hydroxy-benzaldehyde (4.88 g; 40 mmol) in 30 mL of methanol. The reaction mixture warms up a little and is stirred for another 10 minutes. After that time, ammonium carbonate (2.88 g; 30 mmol) was added and to the resulting suspension there was added glyoxal (40% aqueous solution, 5.80 g; 40 mmol) dissolved in 15 mL of CH.sub.3OH, slowly and under stirring. After the addition, the reaction mixture was stirred for another 2 hours at room temperature and then 60 mL of water were added, observing the precipitation of the desired reaction product. The solid was filtered on a B?chner funnel, cold washed with CH.sub.3OH/H.sub.2O 1:1 and dried under reduced pressure. 1.57 g of a slightly yellowish solid were obtained (22.5% yield).

[0101] In the second step of the synthesis, 1,3-dimethyl-2-(4-hydroxy-phenyl)-imidazolium iodide was obtained, as shown in FIG. 10. In a Schlenk flask, 12 mL of acetonitrile, 1-methyl-2-(3-hydroxy-phenyl)-imidazole (1.04 g; 6.00 mmol) and iodomethane (1.28 g; 9.00 mmol). The flask was closed with a rubber septum and the suspension was heated at 70? C., under magnetic stirring, for 1 hour. After this period, 5 mL of ethyl acetate was added and the resulting solid was filtered, washed with ethyl acetate and dried under reduced pressure. 1.65 g of brownish crystals were thus obtained (87% yield).

[0102] In the third step of the synthesis, the 1,3-dimethyl-2-(4-oxy-phenyl)-imidazolium inner salt was obtained, as shown in FIG. 11. In a test tube, there was measured the volume of 14 mL of the ion exchange resin Ambersep 900 OH. The resin was washed three times with distilled water. Then, the resin was added to a solution of 1,3-dimethyl-2-(3-hydroxy-phenyl)-imidazolium iodide (3.16 g; 10 mmol) in 10 mL of water. The reaction remained under stirring at room temperature in a beaker for 10 minutes. After this time, the ion exchange resin was separated by filtration, and the water in the solution was evaporated under reduced pressure, resulting in 1.8 g of a highly hygroscopic brownish solid (96% yield). The .sup.1H NMR, .sup.13C NMR and infrared spectra are presented respectively in FIG. 12, FIG. 13 and FIG. 14.

Example 3: CO.SUB.2 .absorption by aqueous solutions of the 1,3-dimethyl-2-(3-oxy-phenyl)-imidazolium and 1,3-dimethyl-2-(4-oxy-phenyl)-imidazolium inner salts at low pressure determined through the pressure drop in the CO.SUB.2 .reservoir

[0103] The laboratory tests of absorption and desorption of CO.sub.2 of the solutions of the inner salts were carried out in an experimental apparatus that allows the temperature and pressure of the sorption vessel to be kept constant while the pressure drop in a CO.sub.2 reservoir is monitored for determining the amount of gas absorbed, as shown in FIG. 15.

[0104] To carry out the test, the reservoir with calibrated volume 402 is previously filled with CO.sub.2 contained in the cylinder 401. The pressure control valve 403 is adjusted to maintain the pressure of the sorption vessel at 1.3 bar absolute (130 kPa) during the absorption test. The temperature of the sorption vessel 404 is adjusted by circulating, in its jacketed wall, thermal fluid from the thermostatic bath 407 to the absorption temperature (T1), typically 40? C. Then, 5 mL of 1 M aqueous solution of 1,3-dimethyl-2-(3-oxyphenyl)-imidazolium or 1,3-dimethyl-2-(4-oxy-phenyl)-imidazolium inner salt is added to the reaction vessel. The system was purged with CO.sub.2 for 5 seconds by opening purge valve 406, and the reservoir 402 was refilled with CO.sub.2 at 4 bar absolute (400 kPa). The absorption process begins when the magnetic stirrer 408 is activated and, from then on, the pressure drop in the CO.sub.2 reservoir is monitored to determine the number of moles of CO.sub.2 consumed. The pressure is monitored through a transducer installed in the CO.sub.2 reservoir coupled to a recorder 409 and a computer 410 for data processing. For the calculations, the ideal gas equation of state and the previously calibrated volume of the reservoir were considered. The end of absorption was considered when the reservoir pressure as a function of time remained at an unchanged level for at least 10 minutes.

[0105] At the end of the absorption step, the sorption vessel 404 was opened and the temperature of the thermostatic bath 407 adjusted to the desorption temperature (T2), typically 100? C. The system was kept under stifling for 30 minutes to regenerate the zwitterionic solution. With the aim of validating the method and obtaining a parameter for comparison, the absorption test was carried out with the commercial mixture MDEA/piperazine/water normally used in industrial CO.sub.2 absorption processes (Input 1, Table 1). It is important to point out that the tested salts present absorption at wavelengths in the UV-VIS region typical of phenolic decompositions. The wavelengths before and after absorption differ, as shown in FIG. 16, suggesting that these systems can be monitored by UV-VIS spectroscopy.

TABLE-US-00001 TABLE 1 Sorption tests of aqueous solutions of inner salts. ? Pressure Absorption drop by .sup.13C HCO.sub.3.sup.? After absorption NMR desorption (moles.sub.CO2/ (moles.sub.CO2/ (Percentage of Input Absorbent moles.sub.salt) .sup.b moles.sub.salt) .sup.c desorption) .sup.d 1 MDEA/piperazine/ 0.66 0.64 <0.3 (>95%) water(40%/ 10%/50% by mass) .sup.e 2 [00001] 0.88 ? 0.06 0.91 0.18 ? 0.3 (80%) 3 [00002] 0.69 ? 0.09 0.81 ? 0.05 <0.3 (>95%) .sup.a Reaction conditions: 5 mL of solution with a concentration of 1 mol/L, temperature of 40? C. and pressure. Mean of at least two analyses ? standard deviation. .sup.b Absorption values expressed in moles CO2 per moles of absorbent obtained by pressure measurements of 1.3 bar (130 kPa). .sup.c Absorption values expressed in moles CO.sub.2 per moles of absorbent obtained by quantitative .sup.13C NMR. .sup.d Desorption percentage = (1-(HCO.sub.3.sup.? equivalents after desorption at 100? C. for 30 minutes / .sup.13C NMR absorption))*100. .sup.e CO.sub.2 absorption in relation to the number of moles of MDEA + moles of piperazine.

Example 4: Recyclability of aqueous solutions of 1,3-dimethyl-2-(3-oxy-phenyl)-imidazolium and 1,3-dimethyl-2-(4-oxy-phenyl)-imidazolium inner salts

[0106] The recyclability of aqueous solutions of the new developed absorbents was tested in cyclic tests of absorption followed by desorption. These tests were carried out in the same experimental apparatus used in Example 1 and shown in FIG. 15. The results of these tests are shown in Table 2 and detailed in FIG. 17, FIG. 18 and FIG. 19.

TABLE-US-00002 TABLE 2 Recyclability tests. ? Mean Absorption Number of Value .sup.b Input Absorbent tested cycles (moles.sub.CO2/moles.sub.salt) 1 MDEA/Piperazine/water 26 0.57 ? 0.04 .sup.c (40%/10%/50% by mass) 2 [00003] 27 0.58 ? 0.04 .sup. 3 [00004] 17 0.58 ? 0.08 .sup. .sup.a Reaction conditions: 5 mL of solution with a concentration of 1 mol/L, absorption temperature 40? C., and pressure of 1.3 bar (130 kPa), desorption temperature 100? C., atmospheric pressure (30 min.). .sup.b Absorption values determined through the pressure drop in reservoir and expressed in moles CO.sub.2 per moles of absorbent. Mean represents mean absorption value of the cycles ? standard deviation. .sup.c moles of CO.sub.2 per total moles of amines (MDEA + piperazine) MDEA/piperazine/water 40%:10%:50% solution.

Example 5: CO.SUB.2 .absorption by aqueous solutions of the 1,3-dimethyl-2-(3-oxy-phenyl)-imidazolium inner salt determined using the .SUP.13.C nuclear magnetic resonance spectroscopy technique

[0107] The capture of CO.sub.2 by zwitterionic solutions of the 1,3-dimethyl-2-(3-oxy-phenyl)-imidazolium inner salt was also studied through quantitative analyses of .sup.13C. This analysis methodology was described by SIMON, N. M. et al. Carbon dioxide capture by aqueous ionic liquid solutions, ChemSusChem, v. 10, p. 4927-4933, 2017 and allows to directly quantify both the chemisorption and the physisorption of CO.sub.2 in the solutions.

[0108] To carry out this experiment, a syringe pump coupled to a zirconia NMR tube installed in an NMR spectrometer was used. The syringe pump allows CO.sub.2 pressure control during experiments. The results were analyzed considering the proportion between the integrals of the signals corresponding to the dissolved CO.sub.2 and the bicarbonate formed in relation to the integral of the methyl carbons of the zwitterion. The results are presented in Table 3.

TABLE-US-00003 TABLE 3 CO.sub.2 absorption determined using .sup.13C NMR with pressure variation during spectra acquisition. .sup.a Gauge Physisorption Chemisorption pressure (moles.sub.CO2/ (moles.sub.CO2/ Absorbent (bar - ? 0.1 MPa) moles.sub.SALT) moles.sub.SALT) [00005] 10 20 33 40 0.07 0.13 0.25 0.27 0.99 1.01 1.01 0.99 .sup.a Reaction conditions: 0.5 mL of solution with a concentration of 2.2 mol/L (1.1 mmol of the inner salt, dissolved in 0.5 mL of D20), absorption temperature 40? C. The NMR spectra were obtained in a Bruker-400-Avance-IIIHD NMR equipment operating at a frequency of 100 MHz for .sup.13C equipped with a 5 mm probe with direct detection, with field gradient in z and thermostated via BCU-xtreme with constant temperature and spectral window from ?15 ppm to 235 ppm. Used syringe pump: Xtreme-10 syringpump - deadalus innovation.

Example 6: CO.SUB.2 .absorption by solutions of the 1,3-dimethyl-2-(3-oxy-phenyl)-imidazolium inner salt in protic solvents

[0109] One of the main advantages of the CO.sub.2 capture process using zwitterionic solutions is that the zwitterionic bases are not volatile. On the other hand, a fraction of the solvent (usually water) can be lost by evaporation and during the desorption step, which represents energy losses in the process and the need of replacing this solvent. The cyclic CO.sub.2 capture processes with the inner salts disclosed in the present discovery can also be carried out using non-aqueous solvents to minimize, or even eliminate, such mass losses in the desorption step. Alcohols, diols, polyols and ionic liquids functionalized with a hydroxyl group are solvents that, when combined with zwitterionic bases, are capable of reversibly absorbing CO.sub.2 through the formation of the respective alkyl carbonates. In Table 4, some examples of absorption in non-aqueous systems are presented. n-propanol, n-butanol, ethylene glycol or glycerol are alternative solvents with boiling points of 97.0? C., 117.7? C., 197.6? C. and 290? C., respectively. On the other hand, the 1,2-dimethyl-3-(3-hydroxypropyl)-imidazolium bistrifluoromethylsulphonylimidate ionic liquid is a solvent with negligible vapor pressure and represents a totally ionic system for CO.sub.2 capture in which there is certainly no loss of mass by evaporation.

TABLE-US-00004 TABLE 4 CO.sub.2 absorption through solutions of 1,3-dimethyl-2-(3-oxy-phenyl)- imidazolium inner salt in different protic solvents. .sup.a Pressure drop Absorption by Percentage absorption (mol.sub.CO2/ .sup.13C NMR of Absorbent Solvent mol.sub.SALT) .sup.b (mol.sub.CO2/mol.sub.SALT) .sup.c desorption .sup.d [00006] [00007] [00008] [00009] [00010] 0.74 0.67 0.68 ? 0.86 0.66 0.73 0.83 >95% >95% >95% >95% [00011] 0.64 ? ? .sup.a Reaction conditions: 5 mL of solution with a concentration of 1 mol/L, temperature of 40? C. and pressure. Mean of at least two analyses ? standard deviation. .sup.b Absorption values expressed in moles CO.sub.2 per moles of absorbent obtained by pressure measurements of 1.3 bar (130 kPa). .sup.c Absorption values expressed in moles CO.sub.2 per moles of absorbent obtained by quantitative .sup.13C NMR. .sup.d Desorption percentage = (1-(HCO.sub.3.sup.? equivalents after desorption at 100? C. for 30 minutes /.sup.13C NMR absorption))*100.

Example 7: Estimation of the enthalpy of absorption in aqueous solutions of the 1,3-dimethyl-2-(3-oxy-phenyl)-imidazolium inner salts

[0110] The experimental apparatus shown in FIG. 20 was used to determine the global equilibrium constants of the absorption process at temperatures of 10? C., 20? C., 30? C., 40? C., 50? C. and 60? C. The balance chamber 310 keeps all its components submerged in water with a temperature at the analysis temperature, controlled by the thermostatic bath 309. The reservoir 302 is filled with CO.sub.2 from the cylinder 301 with the pressure measured by the pressure transducer 305. The sorption vessel 304 is then evacuated with the aid of a vacuum pump 311 and the zwitterionic-based sorbent solution is injected, through a septum located in the upper part of the sorption vessel, with the aid of a syringe 312. Then, the sorption vessel is pressurized with CO.sub.2 through the brief opening of the valve 303. Finally, the pressure drop in the sorption vessel is monitored from the pressure transducer 306, which sends the data to the recorder 307 and the data is processed in the computer 308. Enthalpy of absorption of inner salts was determined using the same methodology reported by GABRIELSEN, J. et al. Model for estimating CO.sub.2 solubility in aqueous alkanolamines, Industrial & Engineering Chemistry Research, v. 44, p. 3348-3354, 2005 to estimate the heat of absorption of CO.sub.2 by aqueous solutions of alcoholamines. Table 5 shows the experimental results of the enthalpy of absorption of a commercial MDEA/piperazine/water mixture and for an aqueous solution of the 1,3-dimethyl-2-(3-oxy-phenyl)-imidazolium inner salt.

TABLE-US-00005 TABLE 5 Estimation of enthalpy of absorption. Estimated Enthalpy of Input Absorbent Absorption (kJ/mol) 1 MDEA/Piperazine/water ?45.0 (40%/10%/50% by mass) 2 [00012] ?36 ? 0.8 .sup.a Reaction conditions: 0.5 mL of solution with a concentration of 1 Mol/L, absorption temperature between 10? C. and 60? C. Equilibrium pressure between 0.9 bar and 1.4 bar absolute (90 a 140 kPa).

[0111] It should be noted that, although the present invention has been described in relation to the attached drawings, it may undergo modifications and adaptations by technicians skilled on the subject, depending on the specific situation, but provided that within the inventive scope defined herein.