WO2011147033A2 - Compositions and methods for capturing carbon dioxide - Google Patents

Abstract

There are provided methods and compositions for capturing CO₂. The method can comprise contacting CO₂ with a composition comprising diethylenetriamine and at least one compound chosen from phosphonium-based ionic liquids, polymeric solvents, and mixtures thereof. These methods and composition are thus useful for capturing CO₂ in a given environment.

Description

COMPOSITIONS AND METHODS FOR CAPTURING CARBON DIOXIDE

CROSS-REFERENCE TO RELATED APPLICATION

[0001] The present application claims priority on U.S. provisional application No. 61/349,008 filed on May 27, 2010, which is hereby incorporated by reference in its entirety.

FIELD OF THE DISCLOSURE

[0002] The present disclosure relates to the field of carbon dioxide (C0₂) capture. In particular, this disclosure relates to methods for capturing C0₂. The disclosure also relates to compositions for capturing C0₂.

BACKGROUND OF THE DISCLOSURE

[0003] Currently there is a strong need to reduce carbon dioxide (C0₂) emissions. Although much of this reduction can be achieved through increases in efficiency, there is still a requirement for improved carbon capture methods as well as development of the subsequent sequestration technologies (Hermann, W.; Bosshard, P.; Hung, E.; Hunt, R.; Simon, A.J. An Assessment of Carbon Capture Technology and Research Opportunities. Stanford University Global Climate & Energy Project Technical Assessment Report. 2005, 1-20). Three methods appear promising for carbon capture. Firstly, C0₂ can be produced in a relatively pure form through the oxycombustion method (Favre, E.; Bounaceur, R.; Roizard, D. A hybrid process combining oxygen enriched air combustion and membrane separation for post-combustion carbon dioxide capture. Separation and Purification Technology 2009, 68, 30-36). In this method, capture of C0₂ is easy because it is the only gaseous product of the combustion process. Secondly, the precombustion method (Meis, N.N.A.H.; Bitter, J.H.; de Jong, K.P. Support and Size Effects of Activated Hydrotalcites for Precombustion C0₂ Capture. Industrial & Engineering Chemistry Research. 2010, 49, 1229- 1235; Agarwal, A.; Biegler, L.T.; Zitney, S.E. Superstructure-based Optimal Synthesis of Pressure Swing Adsorption Cycles for Precombustion C0₂ Capture. Industrial & Engineering Chemistry Research. 2010, 49, 5066-5079; Li, X.-S.; Xia, Z.-M.; Chen, Z.-Y.; Yan, K.-F.; Li, G.; Wu, H.-J. Gas Hydrate Formation Process for Capture of Carbon Dioxide from Fuel Gas Mixture. Industrial & Engineering Chemistry Research. 2010, 49, 11614-1 1619) involves separating fossil fuels into hydrogen and carbon dioxide before they are burnt. The fuel is converted into a synthetic gas "syngas" comprising carbon monoxide/dioxide and hydrogen/water. The "syngas" can be reacted with steam at high pressure (the water gas shift reaction) to produce a mixture with higher concentrations of C0₂ (35-45%) and hydrogen, from which the C0₂ can then be captured. Finally, C0₂ can be captured from flue gas (Hermann, W.; Bosshard, P.; Hung, E.; Hunt, R.; Simon, A.J. An Assessment of Carbon Capture Technology and Research Opportunities. Stanford University Global Climate & Energy Project Technical Assessment Report. 2005, 1-20). This method is more challenging because flue gas is a mixture of gases. Perhaps the simplest flue gas in existence is that obtained by the combustion of natural gas. Under dry conditions it contains ca. 1 1 % C0₂, 1 % 0₂, and 88% N₂ (Hesketh, H.E. Air Pollution Control; Michigan: Ann Arbor Science Publishers, Inc., 1979, pp 41-89). Other flue gases, particularly those from coal combustion, are typically contaminated with sulphur-containing compounds, mercury, and other by-products, thus making purification more challenging (Hesketh, H.E. Air Pollution Control; Michigan: Ann Arbor Science Publishers, Inc., 1979, pp 41-89).

[0004] Selectively capturing components of flue gases is technically demanding, but it is made easier if the gas of interest is a Lewis acid. Acidic gases, such as carbon dioxide and hydrogen sulphide, are easier to capture. Scrubbing technology using amines is well developed and extensively used in natural gas sweetening technologies (Huttenhuis, P.J.G.; Agrawal, N.J.; Hogendoorn, J.A.; Versteeg, G.F. Gas solubility of H₂S and C0₂ in aqueous solutions of /V-methyldiethanolamine. J. Petrol. Sci. Eng. 2007, 55, 122-134). Rochelle er al. have written extensively on the use of amines for C0₂ capture by gas scrubbing (Rochelle, G.T. Amine Scrubbing for C02 Capture. Science. 2009, 325, 1652-1654; Zhou, S.; Chen, X.; Nguyen, T.; Voice, A.K.; Rochelle, G.T. Aqueous Ethylenediamine for C02 Capture. ChemSusChem. 2010, 3, 913-918). One of the most common techniques utilizes monoethanolamine (MEA) in aqueous solution for carbon dioxide capture. MEA reacts to form a temperature sensitive carbamate composed of an ammonium cation and a carbamate anion (Scheme 1 a) (Tobiesen, F.A.; Svendsen, H.F.; Mejdell, T. Modeling of Blast Furnace C0₂ Capture Using Amine Absorbents. Ind. Eng. Chem. Res. 2007, 46, 7811-7819).

CO,

1 a © Θ H

,NH,

HO . NH₃ 0₂C-N,

HO OH MW = 61.08

Scheme 1 a: Reaction scheme showing the reaction stoichiometry of MEA (1 a) with C0₂

[0005] Ionic liquids have previously been recognized as useful materials for the separation of carbon dioxide from gas mixtures (Huang, J.; Ruther, T. Why are Ionic Liquids Attractive for C0₂ Absorption? An Overview. Aust. J. Chem. 2009, 62, 298-308). Perhaps this is best illustrated by the following four task specific onic liquids (TSILs) where either the cation (Bates, E.; Mayton, R.; Ntai, I.; Davis, J.H. C0₂ Capture by a Task-Specific Ionic Liquid. J. Am. Chem. Soc. 2002, 124, 926-927; Zhang, Y.; Zhang S.; Lu, X.; Zhou, Q.; Fan, W.; Zhang, X. Dual Amino-Functionalised Phosphonium Ionic Liquids for C0₂ Capture. Chem. Eur. J. 2009, 15, 3003-3011 ) or the anion (Zhang, J.; Zhang, S.; Dong, .; Zhang, Y.; Shen, Y. ; Lv, X. Supported Absorption of C0₂ by Tetrabutylphosphonium Amino Acid Ionic Liquids. Chem. Eur. J. 2006, 12, 4021 -4026; Gurkan, B.; de la Fuente, J.; Mindrup, E.; Ficke, L; Goodrich, B.; Price, E.; Schneider, W.; Brennecke, J. Equimolar C0₂ Absorption by Anion- Functionalized Ionic Liquids. J. Amer. Chem. Soc. 2010, 132, 21 16-21 17; Li, X.; Hou, M.; Zhang, Z.; Han, B.; Yang, G.; Wang, X.; Zou, L. Absorption of C0₂ by ionic liquid/polyethylene glycol mixture and the thermodynamic parameters. Green Chem. 2008, 10, 879-884) has been functionalised with a primary amine. The first such liquid, shown in Scheme 2a, contains an imidazolium cation and is reported to be very useful for carbon capture (Bates, E.; Mayton, R.; Ntai, I.; Davis, J.H. C0₂ Capture by a Task-Specific Ionic Liquid. J. Am. Chem. Soc. 2002, 124, 926-927). This TSIL demonstrates the concept of carbon capture very well, but as the authors describe in the original report, it suffers from high viscosity (Bates, E.; Mayton, R.; Ntai, I.; Davis, J.H. C0₂ Capture by a Task-Specific Ionic Liquid. J. Am. Chem. Soc. 2002, 124, 926-927) and tar formation (Camper, D.; Bara, J.E.; Gin, D.L.; Noble, R.D. Room-Temperature Ionic Liquid - Amine Solutions: Tunable Solvents for Efficient and Reversible Capture of C0₂. Ind. Eng. Chem. Res. 2008, 47, 8496-8498) during the capture reaction. Non-substituted phosphonium TSILs possessing amino-acid based anions (Zhang, J.; Zhang, S.; Dong, K.; Zhang, Y.; Shen, Y. ; Lv, X. Supported Absorption of C0₂ by Tetrabutylphosphonium Amino Acid Ionic Liquids. Chem. Eur. J. 2006, 12, 4021 -4026) (Scheme 2b) and amino-phosphonium substituted TSILs with amino-acid based anions (Zhang, Y.; Zhang S.; Lu, X.; Zhou, Q.; Fan, W.; Zhang, X. Dual Amino- Functionalised Phosphonium Ionic Liquids for C0₂ Capture. Chem. Eur. J. 2009, 15, 3003-3011) (Scheme 2c) have also been used to trap C0₂. Initial studies showed the latter capturing twice the amount of gas as the former (Zhang, Y.; Zhang S.; Lu, X.; Zhou, Q.; Fan, W.; Zhang, X. Dual Amino- Functionalised Phosphonium Ionic Liquids for C0₂ Capture. Chem. Eur. J. 2009, 15, 3003-3011). However, a more recent publication suggests that phosphonium based ionic liquids with amino acid derived anions can also capture carbon dioxide with a 1 :1 stoichiometry (Zhang, J.; Zhang, S.; Dong, K.; Zhang, Y.; Shen, Y. ; Lv, X. Supported Absorption of C0₂ by Tetrabutylphosphonium Amino Acid Ionic Liquids. Chem. Eur. J. 2006, 12, 4021-4026). On the whole, all of these capture systems appear to be robust, but are limited by the fact that the TSIL is both the capture material and dispersant. Finally, absorption of C0₂ by a TSIL synthesized from renewable materials, (2-hydroxyethyl)-trimethyl-ammonium (S)-2-pyrrolidine-carboxylic acid salt, [Choline][Pro], (Scheme 2d) in an ionic liquid/polyethylene glycol mixture ([Choline][Pro]/PEG200) has also been reported. Inclusion of PEG was found to enhance the kinetics of the absorption of C0₂ (Li, X.; Hou, M.; Zhang, Z.; Han, B.; Yang, G.; Wang, X.; Zou, L. Absorption of C0₂ by ionic liquid/polyethylene glycol mixture and the thermodynamic parameters. Green Chem. 2008, 10, 879-884).

Scheme 2: Task specific ionic liquids used in carbon capture

[0006] Rather than direct incorporation of amino-functionalized cations or anions, recent reports describe the use of imidazolium-based ionic liquids with amines added as the C0₂ capture reagents (Camper, D.; Bara, J.E.; Gin, D.L.; Noble, R.D. Room-Temperature Ionic Liquid - Amine Solutions: Tunable Solvents for Efficient and Reversible Capture of CO2. Ind. Eng. Chem. Res. 2008, 47, 8496-8498; Bara, J.E.; Carlisle, T.K.; Gabriel, C.J.; Camper, D.; Finotello, A.; Gin, D.L.; Noble, R.D. Guide to C0₂ Separation in Imidazolium- Based Room-Temperature Ionic Liquids. Ind. Eng. Chem. Res. 2009, 28, 2739-2751 ). These systems appear to work well, but it is important to note that they are based on imidazolium ionic liquids. Ramnial, T.; Taylor, S.A.; Bender, M.L.; Gorodetsky, B.; Lee, P.T.K.; Dickie, D.A.; McCollum, B.M.; Pye, C.C. Walsby, C.J.; Clyburne, J.A.C. Carbon-Centered Strong Bases in Phosphonium Ionic Liquids. J. Org. Chem. 2008, 73, 801-812 and others (Dupont, J.; Spencer, J. On the Noninnocent Nature of 1 ,3-Dialkylimidazolium Ionic Liquids. Angew. Chem. Int. Ed. 2004, 43, 5296 -5297) have reported extensively on the sensitivity of these materials. The C₂-H unit is extremely reactive, deprotonation requiring only mild bases such as 1 ,4- diazabicyclo[2.2.2]octane (DABCO) and 3-hydroxyquinuclidine, or amines, to initiate decomposition (Nair, V.; Bindu, S.; Sreekumar.V. N-Heterocyclic Carbenes: Reagents, Not Just Ligands! Angew. Chem. Int. Ed. 2004, 43, 5130-5135). Furthermore, it is well known that they react with oxygen (Islam, M.M.; Imase, T.; Okajima, T.; Takahashi, M.; Niikura, Y.; Kawashima, N.; Nakamura, Y.; Ohsaka, T. Stability of Superoxide Ion in Imidazolium Cation- Based Room-Temperature Ionic Liquids. J. Phys. Chem. A. 2009, 113, 912- 916), and they are more temperature sensitive than other ionic liquid alternatives (Fraser, K.J.; MacFarlane, D.R. Phosphonium-Based Ionic Liquids: An Overview. Aust. J. Chem. 2009, 62, 309-321). SUMMARY OF THE DISCLOSURE

[0007] According to one aspect of the present disclosure, there is provided a method for capturing C0₂, the method comprising contacting C0₂ with a composition comprising an amine chosen from diethylenetriamine, triethylenetetramine, dipropylamine, isopropylamine, propylamine, N- methyldiethanolamine, and mixtures thereof, and at least one compound chosen from phosphonium-based ionic liquids, polymeric solvents, and mixtures thereof.

[0008] According to another aspect of the present disclosure, there is provided a method for capturing C0₂, the method comprising contacting C0₂ with a composition diethylenetriamine and at least one compound chosen from phosphonium-based ionic liquids, polymeric solvents, and mixtures thereof.

[0009] According to another aspect of the present disclosure, there is provided a composition comprising an amine chosen from diethylenetriamine, triethylenetetramine, dipropylamine, isopropylamine, propylamine, N- methyldiethanolamine, and mixtures thereof, and at least one compound chosen from phosphonium-based ionic liquids, polymeric solvents, and mixtures thereof.

[0010] According to another aspect of the present disclosure, there is provided a composition comprising diethylenetriamine and at least one compound chosen from phosphonium-based ionic liquids, polymeric solvents, and mixtures thereof.

[0011] According to another aspect of the present disclosure, there is provided a method for using a composition as defined in the present disclosure. The method comprising contacting the composition with C0₂ so as to capture C0₂. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] In the appended drawings which represent various examples:

[0013] Fig. 1 is a thermogravimetric (TG) decomposition curve of an example of an adduct (DETA-C0₂ adduct) when heated at 5°C/min in a nitrogen atmosphere;

[0014] Fig. 2 is a mass spectrometry scan (44 amu) of the adduct of Fig. 1 monitored during its TG analysis showing release of carbon dioxide;

[0015] Fig. 3 shows a molecular structure (left) and a packing diagram (right) of the DETA-C0₂ adduct of Fig. ;

[0016] Fig. 4 is an infrared spectrum of the adduct of Fig. 1 ;

[0017] Fig. 5 is a plot of the vapour pressure as a function of the temperature (between 50 and 130 °C) in examples of compositions according to the present disclosure;

[0018] Fig. 6 is a plot of the vapour pressure as a function of the temperature (between 50 and 130 °C) in other examples of compositions according to the present disclosure;

[0019] Fig. 7 is a curve showing the vapour pressure as a function of time of an adduct comprising C0₂ and examples of compositions as defined in Fig. 5, wherein temperature was repeatedly increased and decreased (25 to 100 °C) during measurement;

[0020] Fig. 8 is a curve showing the vapour pressure as a function of time of an adduct comprising C0₂ and examples of compositions according to the present disclosure, wherein temperature was repeatedly increased and decreased (25 to 100 °C) during measurement;

[0021] Fig. 9 is a plot showing the vapour pressure as a function of time when capturing C0₂ from a flue gas mixture with an example of a composition according to the present disclosure;

[0022] Fig. 10 is a plot showing the vapour pressure as a function of time when capturing C0₂ from a flue gas mixture with another example of a composition according to the present disclosure; [0023] Fig. 11 are pictures showing stability of an example of a composition according to the present disclosure when being closed to the atmosphere and heated at approximately 100°C over one week;

[0024] Fig. 12 are pictures showing stability of another example of a composition according to the present disclosure when being closed to the atmosphere and heated at approximately 100°C over one week;

[0025] Fig. 13 is a plot showing the pH of a barium oxide solution as a function of the temperature, when heating an example of a C0₂ adduct according to the present disclosure. The C0₂ gas released by heating is carried into the barium hydroxide solution where changes in the pH are monitored;

[0026] Fig. 14 shows plots expressing the % of C0₂ remaining as a function of the temperature, for two different runs, when heating an example of a C0₂ adduct according to the present disclosure (as monitored by measuring the pH of a barium hydroxide solution (Fig. 13) into which the generated C0₂ is fed); and

[0027] Fig. 15 is a plot showing the average of the two runs (plots) illustrated in Fig. 14.

DETAILED DESCRIPTION OF THE DISCLOSURE

[0028] For example, diethylenetriamine can be present in the composition at a concentration of about 1 % to about 40 % v/v, about 2 % to about 30 % v/v, about 4 % to about 25 % v/v, about 5 % to about 20 % v/v, or about 6 % to about 15 % v/v.

[0029] For example, the at least one compound has an average heat capacity of about 1.0 to about 3.0 J/gK at 301 K, about 1.3 to about 2.3 J/gK at 301 K, about 1.5 to about 2.1 J/gK at 301 K, or about 1.6 to about 2.0 J/gK at 301 K.

[0030] For example, the composition can comprise diethylenetriamine and at least one phosphonium-based ionic liquids. [0031 ] For example, the at least one phosphonium ionic liquid can be chosen from tetradecyl(trihexyl)phosphonium chloride, tetradecyl(trihexyl)phosphonium decanoate, tetradecyl(trihexyl)phosphonium dicyanimide, tetradecyl(trihexyl)phosphonium bistriflamide, tetradecyl(trihexyl)phosphonium bromide, tetradecyl(trihexyl)phosphonium(bis 2,4,4-trimethylpentyl)phosphinate, triisobutyl(methyl)phosphonium tosylate, tributyl(methyl)phosphonium methylsulfate, tetradecyl(trihexyl)phosphonium hexafluorophosphate, tetradecyl(trihexyl)phosphonium tetrafluoroborate, tributyl(hexadecyl)phosphonium bromide, tetrabutylphosphonium bromide, tetrabutylphosphonium chloride, tetraoctylphosphonium bromide, tetraoctylphosphonium bromide, tetradecyl(tributyl)phosphonium chloride, ethyltri(butyl)phosphonium diethylphosphate, tetradecyl(tributyl)phosphonium dodecylsulfonate, tetradecyl(trihexyl)phosphonium dodecylsulfonate, and mixtures thereof.

[0032] For example, the at least one phosphonium ionic liquid can be tetradecyl(trihexyl)phosphonium chloride.

[0033] For example, the composition can comprise diethylenetriamine and at least one polymeric solvent.

[0034] For example, the at least one polymeric solvent can be chosen from poly(ethylene glycol) dimethyl ether, polydimethylsiloxane, a copolymer of phenylmethylsiloxane and dimethylsiloxane and a copolymer of diphenylsolizane, dimethylsiloxane, and mixtures thereof.

[0035] For example, the at least one polymeric solvent can be poly(ethylene glycol) dimethyl ether.

[0036] For example, the poly(ethylene glycol) dimethyl ether can have a MN of about 100 to about 700, of about 200 to about 600, of about 200 to about 300 or of about 500 to about 600.

[0037] For example, the composition can further comprise an amine chosen from triethylenetetramine, dipropylamine, isopropylamine, propylamine, N-methyldiethanolamine, and mixtures thereof.

[0038] For example, the composition can further comprise dipropylamine, isopropylamine, and propylamine. [0039] For example, wherein a precipitate is formed when contacting C0₂ with a composition comprising diethylenetriamine and at least one compound chosen from phosphonium-based ionic liquids, polymeric solvents, and mixtures thereof, the precipitate can comprise C0₂ and diethylenetriamine. The precipitate can comprise a diethylenetriamine-C0₂ adduct.

[0040] For example, the diethylenetriamine-CC>2 adduct can be :

[0041] For example, when a liquid is formed when contacting C0₂ with a composition comprising diethylenetriamine and at least one compound chosen from phosphonium-based ionic liquids, polymeric solvents, and mixtures thereof, the liquid can comprise an adduct comprising C0₂.

[0042] For example, the liquid can comprise a diethylenetriamine-C0₂ adduct.

[0043] For example, the method can further comprise releasing the captured CO2.

[0044] For example, the method can further comprise releasing the C0₂ comprised in the precipitate or liquid.

[0045] For example, CO2 can be released by heating the precipitate or liquid at a temperature of at least about 65 °C, at least about 70 °C, at least about 75 °C, at least about 80 °C, at least about 85 °C, at least about 90 °C, at least about 95 °C, at least about 100 °C, or at least about 105 °C.

[0046] For example, CO2 can be released by heating the precipitate or liquid at a temperature of about 70 °C to about 160 °C, about 75 °C to about 145 °C, about 80 °C to about 130 °C, about 90 °C to about 120 °C, or about 100 °C to about 110 °C.

[0047] For example, the compositions of the present disclosure can be used for capturing C0₂. For example, the composition can be used by contacting it with C0₂ so as to capture C0₂. For example, when a precipitate is formed when contacting C0₂ with the composition, the precipitate can comprise C0₂ and diethylenetriamine. The precipitate can comprise an diethylenetriamine-C0₂ adduct. The diethylenetriamine-C0₂ adduct can be :

[0048] As mentioned above, flue gas contains trace amounts of oxygen in a balance of C0₂ and nitrogen. Applicants' experience with non-volatile solvents and small molecule chemistry indicated that the presence of oxygen would prove to be a challenge for any carbon capture system in a non-volatile solvent. Thus, applicants have assessed the thermal stability of a series of phosphonium ionic liquids and polymeric solvents under both neutral and oxidative conditions. Using TGA, an onset of decomposition temperature as well as a useful working temperature range, or maximum operating temperature, was determined under neutral conditions (i.e. nitrogen atmosphere) for examples of ionic liquid and polymeric solvent investigated (see Table 1 below).

General experimentation

[0049] Materials and General Procedures

[0050] Some of the solvents used in the present disclosure, the phosphonium ionic liquids (see scheme 3 for illustrations of certain solvents tested), tetradecyl(trihexyl)phosphonium chloride, tetradecyl(trihexyl)phosphonium decanoate, tetradecyl(trihexyl)phosphonium dicyanimide, and tetradecyl(trihexyl)phosphonium bistriflamide, were all commercially available from Cytec Industries. Each ionic liquid was optionally purified and optionally dried before use according to the procedures described below.

[0051] The imidazolium ionic liquid, 1-butyl-3-methylimidazolium bistriflamide, was synthesized from 1-butyl-3-methylimidazolium chloride and bis(trifluoromethane)sulfonimide lithium salt as outlined in the synthetic procedure which follows. 1-butyl-3-methylimidazolium chloride was obtained from a fellow research laboratory at Saint Mary's University. The bis(trifluoromethane)sulfonimide lithium salt (99.95%) used was purchased from Sigma-Aldrich and was used as received.

Scheme 3: Molecular structures of examples of ionic liquids investigated.

[0052] Certain polymeric solvents used in the present disclosure (see scheme 4), poly(ethylene glycol) dimethyl ether (M_N = ~ 250 and ~ 500), copolymer (8-12% phenylmethylsiloxane)-(88-92% dimethylsiloxane), copolymer (18-22% diphenylsiloxane)-(78-82% dimethylsiloxane), and polydimethylsiloxane trimethylsiloxy terminated (one sample characterized with a Mw = - 770 and the other with a viscosity = 50 cSt), are all commercially available from Sigma Aldrich, Fluka, Alfa Aesar, and/or Gelest. All polymeric solvents were dried before use as described in the methods below.

poly

ethylene glycol) dimethyl

sample 1: _N = ~250 copolymer

sample 2: M_N = ~500 (8-12% phenylmethylsiloxane)-(88-92% dimethylsil

polyd

imethylsiloxane - trimethylsiloxy terminated

sample 1: M_w = 770 copolymer

sample 2: viscosity = 50 cSt (18-22% diphenylsiloxane)-(78-82% dimethylsiloxane)

Scheme 4 : Molecular structures of further examples of polymeric solvents investigated.

[0053] Samples of all ionic liquids and polymeric solvents were stored in both an argon atmosphere in an MBraun glovebox as well as in a bench top desiccator. All deionized water used was purified through reverse-osmosis (Milli-R012Plus, Millipore water purification system). Toluene used for azeotropic distillation was dispensed from an MBraun MB-SPS solvent purification system immediately before use. Schlenk techniques and a double manifold vacuum line were used for exhaustive evacuation to dry samples. C0₂ gas (Industrial Food Grade, 99.9%) was purchased from Praxair. Unless otherwise indicated all other solvents and reagents were obtained from commercial sources and used as received without further processing. [0054] Instrumentation

Thermogravimetric analysis was performed using a Mettler Toledo TGA/DSC 1 STAR^e System. Infrared (IR) spectroscopy was performed using potassium bromide salt plates in a Bruker Vertex 70 FT-IR with the percent transmittance values reported in cm^"1. Proton (¹H) and phosphorus (³ P) NMR spectra were recorded on a Bruker AVANCE-500 MHz spectrometer (500 MHz ¹H and 202.4 MHz ³¹ P) with chemical shifts reported in ppm. Chemical shifts of the ¹H spectra were referenced to the external standard tetramethylsilane (0.0 ppm) and the chemical shifts of the ³¹ P spectra were referenced to an external standard of 85% aqueous phosphoric acid (0.0 ppm). All NMR samples were run neat (i.e. solventless) in 8 inch long, 5 mm outer diameter Wilmad - Labglass NMR tubes by Katherine Robertson and Michael Lumsden of the Nuclear Magnetic Resonance Research Resource (NMR-3) at Dalhousie University.

[0055] Preparation of Solvents

[0056] Purification of Phosphonium Ionic Liquids (Ramnial, T.; Taylor, S.A.; Bender, M.L.; Gorodetsky, B.; Lee, P.T.K.; Dickie, D.A.; McCollum, B.M.; Pye, C.C.; Walsby, C.J.; Clyburne, J.A. J. Org. Chem. 2008, 73 (3), 801-812)

[0057] Purification of tetradecvKtrihexyQphosphonium chloride. A saturated aqueous sodium bicarbonate solution (35 mL) was added to tetradecyl(trihexyl)phosphonium chloride (200 mL) and the resulting pale yellow cloudy mixture was left to stir for 15 minutes. Slight foaming was observed. The mixture was then washed with water (5 x 100 mL) resulting in a biphasic system with water on the bottom and tetradecyl(trihexyl)phosphonium chloride on top. Attempts were made to wash tetradecyl(trihexyl)phosphonium dicyanimide with hexanes (1 x 50 mL); however, separation using a separatory funnel proved difficult and the hexanes had to be removed using rotary evaporation. Tetradecyl(trihexyl)phosphonium chloride was then dried by azeotropic distillation with toluene (3 x 50 mL) followed by exhaustive evacuation at approximately 60°C. ³¹P { H} NMR (202.4 MHz, neat) δ (ppm) 33.078. [0058] Purification of tetradecvKtrihexyDphosphonium decanoate. A saturated aqueous sodium bicarbonate solution (20 mL) was added to solid tetradecyl(trihexyl)phosphonium decanoate (86 g) and was heated to 30°C at which time a cloudy, liquidus mixture was obtained. Vigorous foaming occurred as the mixture was left to stir for 15 minutes. The mixture was then washed with water (5 x 100 mL) resulting in a biphasic system with water on the bottom and tetradecyl(trihexyl)phosphonium decanoate on top. Attempts were made to wash tetradecyl(trihexyl)phosphonium decanoate with hexanes (2 x 40 mL); however, separation using a separatory funnel proved difficult and the hexanes had to be removed using exhaustive evacuation. Tetradecyl(trihexyl)phosphonium decanoate was then dried by azeotropic distillation with toluene (2 x 30 mL) followed by exhaustive evacuation at approximately 60°C. ³ P {¹H} NMR (202.4 MHz, neat) δ (ppm) 33.526.

[0059] Purification of tetradecvKtrihexyDphosphonium dicvanimide. A saturated aqueous sodium bicarbonate solution (20 mL) was added to tetradecyl(trihexyl)phosphonium dicyanimide (120 mL) and the resulting pale yellow cloudy mixture was left to stir for 15 minutes. The mixture was then washed with water (5 x 100 mL) resulting in a biphasic system with water on the bottom and tetradecyl(trihexyl)phosphonium dicyanimide on top. Attempts were made to wash tetradecyl(trihexyl)phosphonium dicyanimide with hexanes (2 x 40 mL and 1 x 20 mL aliquots); however, separation using a separatory funnel proved difficult and the hexanes had to be removed using exhaustive evacuation. Tetradecyl(trihexyl)phosphonium dicyanimide was then washed with water again (3 x 40 mL), extracted, and then dried by azeotropic distillation with toluene (1 x 40 mL, and 1 x 20 mL aliquots) followed by exhaustive evacuation at approximately 60°C. ³¹ P {¹H} NMR (202.4 MHz, neat) δ (ppm) 33.359.

[0060] Purification of tetradecvKtrihexyDphosphonium bistriflamide. A saturated aqueous sodium bicarbonate solution (20 mL) was added to tetradecyl(trihexyl)phosphonium bistriflamide (120 mL) and the resulting cloudy mixture was left to stir for 15 minutes. The mixture was then washed with water (5 x 100 mL) followed by hexanes (3 x 40 mL) resulting in a three- phase system with the water layer on the bottom, the ionic liquid layer in the middle, and the organic (hexanes) layer on the top. After separation tetradecyl(trihexyl)phosphonium bistriflamide was dried by azeotropic distillation with toluene (1 x 40mL, and 2 x 20 mL aliquots) followed by exhaustive evacuation at approximately 60°C. ³¹P {¹H} NMR (202.4 MHz, neat) δ (ppm) 33.038.

[0061] Synthesis of 1-butyl-3-methylimidazolium bistriflamide

(Bonhote, P.; Dias, A.P.; Papageorgiou, N.; Kalyanasundaram, K.; Gratzel, M. Hydrophobic, Highly Conductive Ambient-Temperature Molten Salts. Inorg. Chem. 1996. 35, 1168-1 178)

[0062] Bis(trifluoromethane)sulfonimide lithium salt (14.64g, 51.00 mmol) was added to a solution of 1-butyl-3-methylimidazolium chloride (7.70g, 44.08 mmol) in water (70 mL) and stirred for 24 hours. The desired ionic liquid, 1-butyl-3-methylimidazolium bistriflamide, was extracted from the biphasic system using CH2CI2 (5 x 25 mL). The CH2CI2 layer was collected and subsequently washed with water (5 x 10 mL) to ensure complete removal of the chloride salt. The CH2CI2 layer was then dried over MgS0₄ and the solvent was removed via rotary evaporation followed by exhaustive evacuation at approximately 60°C.

[0063] Drying of Polymeric Solvents (Bender, M.L. A Survey of the Reactivity of Diphenylmagnesium in Polymeric Solvents. M.Sc. Thesis, Saint Mary's University, Halifax, NS, 2008)

[0064] Poly(ethylene glycol) dimethyl ether samples were dried through successive azeotropic distillations with toluene to remove residual water. All other polymeric solvent samples required additional steps of a saturated sodium bicarbonate rinse followed by a water rinse, in order to remove all of the acid from polymerisation, in addition to azeotropic distillation.

Thermoqravimetric Analysis

[0065] Onset of Decomposition Determination

[0066] To determine the onset of decomposition of the solvents under investigation a sample of each solvent was run on the TGA by raising the temperature gradually from 25 to 500°C at a rate of 5°C/minute. All samples were run using 100 μΙ_ aluminum crucibles with nitrogen as both the cell and purge gases with flow rates of 20 and 75 mUminute respectively. Initial sample weights were measured internally with the TGA balance. A step tangent method was used to determine the onset of decomposition using the STAR⁶ System evaluation software. The onset of decomposition was declared to be the point at which the sample lost 5% of its mass. All reported decomposition onset temperatures herein correspond to an inert atmosphere of nitrogen and a heating rate of 5°C/minute. The onset of decomposition under different conditions may vary.

[0067] Attempts were made to determine the onset of decomposition and maximum operating temperature of 1-butyl-3-methylimidazolium chloride, however, the extremely hygroscopic nature of ionic liquid lead to trouble with reproducibility in the thermogravimetric studies. An approximate onset of decomposition temperature of 164°C was determined leading us to believe that the maximum operating temperature of this ionic liquid is likely below 100°C; this is suggested by the large gap (~ 100°C) between the onset of decomposition temperatures and maximum operating temperatures determined for the other ionic liquids investigated herein.

[0068] TGA Decomposition Curves

[0069] TGA Decomposition Curves have been measured and the obtained results are summarized below in Table 2.

[0070] The TGA Decomposition curves can be found in Figures S3 to S13 of the supporting information section of Harper et al., Survey of Carbon Dioxide Capture in Phosphonium-Based Ionic Liquids and End-Capped Polyethylene Glycol Using DETA (DETA = Diethylenetriamine) as a Model Absorbent, Ind. Eng. Chem. Res. 2011 , 50, 2822-2830 and S1-S83, (published on February 2, 201 1) which is hereby incorporated by reference in its entirety.

[0071 ] Useful Working Temperature Range Determination

[0072] To determine the useful working temperature range of the solvents each was heated isothermally on the TGA for a period of 8 hours in a nitrogen atmosphere at varying temperatures just below the decomposition onset temperature. This procedure was performed systematically until a temperature was found at which the solvent lost less than 5% of its mass and hence was deemed thermally stable. Isothermal runs were terminated if 5% of the mass was lost before the 8 hour heating period was finished. The solvents examined are considered thermally stable only under the above stated conditions and therefore may not be stable if the conditions are changed (i.e. different atmosphere or length of isothermal period). Temperatures were raised gradually at a rate of 5°C/minute in order to reach the isothermal temperature desired. As before samples were weighed with the TGA and 100 μΐ aluminum crucibles were used along with nitrogen as both the cell and purge gases with the same flow rates as reported earlier. The step tangent method was used again in order to determine whether or not 5% of the mass was lost.

[0073] Isothermal TGA Plots

[0074] Isothermal TGA Plots have been measured and are illustrated in Figures S14 to S24 of the supporting information section of Harper et al. in Ind. Eng. Chem. Res. 2011 , 50, 2822-2830 and S1-S83 (previously cited).

[0075] Overall, the ionic liquids and polymeric solvents were determined to be less thermally stable than initially expected; many were only thermally stable up to a temperature which was 100°C lower than their corresponding decomposition onset temperature. Furthermore, the maximum operating temperatures are expected to lower with longer isothermal periods at high temperatures. Therefore, despite ionic liquids and polymeric solvents having no measurable vapor pressure at room temperature, thermogravimetric analysis revealed that the non-volatile solvents investigated herein do decompose and/or evaporate into volatile components upon prolonged heating at elevated temperatures.

[0076] Table 1 : Onsets of decomposition temperatures and maximum operating temperatures obtained for a series of ionic liquids and polymeric solvents in a neutral environment (N2 atmosphere).

[0077] ^*Onset of decomposition temperatures were defined as the temperature at which the solvent lost 5% of its mass while heating from 25 to 500°C at 5°C/min under a nitrogen atmosphere.

[0078] **Maximum operating temperatures correspond to the maximum temperature at which an isothermal heating period

[0079] Additionally, results showed that the lower molecular weight polymeric solvents are not as thermally stable as the higher molecular weight liquid polymers. Therefore, as polymer chain length increases, the thermal stability of the molecule also increases. This increase in stability is likely due to the higher temperatures needed to untangle the longer chained polymers and to break the additional chain interactions expected in the longer chained polymers to allow for decomposition and/or evaporation. Long-term Thermal Stability Testing

[0080] Observation of Colour Changes

Each solvent was heated for 7 days at 100°C under neutral and oxidative conditions. To induce neutral conditions the pure solvents were heated while sealed under argon using Schlenk techniques and a double manifold vacuum line (see Figure S25A of Harper et al. in Ind. Eng. Chem. Res. 2011 , 50, 2822-2830 and S1-S83 (previously cited)). Oxidative conditions were induced by leaving the pure solvents open to air (see Figure S25B of Harper et al. in Ind. Eng. Chem. Res. 2011 , 50, 2822-2830 and S1-S83 (previously cited)). All solvents were heated with a silicon oil bath on a VWR 720 Advanced hot plate/stirrer.

[0081] Pictures were taken of the solvents at room temperature before heating, as well as after 24, 48, 72, and 168 (i.e. 7 days) hours of heating (see Figures S26 to S36 of Harper et al. in Ind. Eng. Chem. Res. 2011 , 50, 2822- 2830 and S1-S83 (previously cited)) using a Canon EOS Rebel XT Digital SLR camera. The obtained results are summarized in Table 2 below.

[0082] Determining Cause for Colour Change

[0083] In an attempt to determine whether the solvents might be reacting with the oxygen or moisture (i.e. water) in the atmosphere to cause the colour changes observed tetradecyl(trihexyl)phosphonium chloride was heated under neutral conditions (i.e. sealed under argon on a Schlenk line) with the addition of deoxygenated water. The water was deoxygenated by having argon bubbled through it in a vial for several minutes in order to displace any atmospheric oxygen in the water. A needle was then used to obtain 1 mL of the deoxygenated water and transfer it to a Schlenk flask containing a sample of tetradecyl(trihexyl)phosphonium chloride sealed under argon. The resulting biphasic system was then heated for 7 days at 100°C and pictures were taken before, during, and after the course of the heating period as formerly described. [0084] Table 2: Colour changes observed on heating the selected ionic liquids and polymeric solvents in a neutral environment (A - argon atmosphere), an oxidative environment (B - air) and/or a neutral environment with the addition of deoxygenated water (C - argon atmosphere) for 7 days at 100°C.

[0085] All solutions remained clear, no precipitation or particulate material was observed, throughout the heating trials.

[0086] In addition to thermogravimetric analysis, long-term heating investigations were performed as seven-day heating experiments at 100°C under neutral (argon atmosphere) and oxidative (open to the atmosphere) conditions. These experiments were used in order to determine whether the solvents were decomposing or evaporating into volatile components at elevated temperatures. Overall, the ionic liquids were found to change colour, with the most extreme changes occurring under oxidative conditions (see Figures S26-S36 of Harper et al. in Ind. Eng. Chem. Res. 201 1 , 50, 2822- 2830 and S1-S83 (previously cited)) for the series of colour change photographs assembled for each solvent). This intense change in colour suggests, qualitatively, that the ionic liquids may be decomposing at high temperatures. The polymeric solvents, on the other hand, showed little or no colour change under both neutral and oxidative conditions; thus, the polymeric solvents appear to be evaporating as opposed to decomposing.

[0087] In addition infrared spectroscopy was performed on all samples before and after heating under the different conditions previously specified (see Figures S37 to S58 of Harper et al. in Ind. Eng. Chem. Res. 2011 , 50, 2822-2830 and S1-S83 (previously cited)).

[0088] IR spectroscopy performed on all ionic liquid and polymeric solvent samples before and after heating revealed an abundance of new peaks generated under oxidative conditions. Under neutral conditions, virtually no new peaks were seen. This suggests decomposition and/or evaporation into volatile components is likely to occur more rapidly in an oxidative environment. On the whole, the ionic liquids and polymeric solvents investigated herein appear to have better overall thermal stability in a neutral environment than an oxidizing environment.

[0089] ¹H and ³ P NMR spectroscopy was also performed on the ionic liquid samples after heating under each condition as well as on a pure sample before heating (see Figures S59 to S67 of Harper et al. in Ind. Eng. Chem. Res. 201 1 , 50, 2822-2830 and S1-S83 (previously cited)).

[0090] NMR spectroscopy was employed in an effort to determine the nature and structure of the coloured impurities generated in the ionic liquids upon heating. Proton (¹H) and phosphorus (³¹P) NMR spectra were obtained for each phosphonium ionic liquid sample before and after heating in both neutral and oxidative environments. Both the ¹H and ³ P NMR spectra obtained showed no changes between the samples before and after heating in either environment. ³¹ P NMR spectra revealed one sharp resonance peak at 32-33 ppm as expected (Ramnial, T.M. The Chemistry of Imidazolium Salts and Phosphonium-Based Ionic Liquids. Ph.D. Thesis, Simon Fraser University, Burnaby BC, 2006). Thus, the concentration of the coloured impurities seems to be too low for detection by NMR spectroscopy.

[0091] IR spectroscopy and ¹H NMR spectroscopy were also performed on both distilled and pure polyethylene glycol dimethyl ether (MN = ~ 250) to determine whether the polymeric solvent was decomposing or evaporating at elevated temperatures (see Figures S68 and S69 of Harper et al. in Ind. Eng. Chem. Res. 201 1 , 50, 2822-2830 and S1-S83 (previously cited)).

[0092] Polyethylene glycol dimethyl ether (M_N = ~ 250) was distilled at 150°C. IR spectroscopy and NMR spectroscopy performed on the distillate and the original polyethylene glycol dimethyl ether (MN = ~ 250) sample revealed that the two liquids were the same material. This supports the earlier proposal that polymeric solvents evaporate at elevated temperatures.

[0093] In order to investigate the drastic colour changes observed for the ionic liquids under oxidative conditions, and to determine if the solvents might be reacting with either oxygen or water from the atmosphere to cause decomposition, deoxygenated water was added to the ionic liquid tetradecyl(trihexyl)phosphonium chloride and heated under neutral conditions. The resulting colour change was found to closely resemble the colour change seen under neutral conditions, suggesting that atmospheric oxygen, and not water, may be causing the extreme colour changes observed. Therefore, the resulting colour change may result via 0₂ -> 0₂ ^" formation, a likely pathway of oxygen reactivity in ionic liquids (Nair, V.; Bindu, S.; Sreekumar.V. N- Heterocyclic Carbenes: Reagents, Not Just Ligands! Angew. Chem. Int. Ed. 2004. 43, 5130-5135). Furthermore, it was noted that th_e most drastic colour changes were observed in those ionic liquids containing the more strongly coordinating anions such as chloride versus more weakly coordinating anions. Thus, oxygen reactivity may be enhanced by strongly coordinating anions and reduced by weakly coordinating anions. Without wishing to be bound by this theory, Applicants speculate that 0₂, dissolved in the ionic liquid, may be more polarized and hence more reactive in more strongly coordinating ionic liquids.

Heat Capacity Measurements

[0094] The samples as submitted were moisture sensitive liquids. As a result, they had to be hermetically sealed in an aluminum pan before mounting on the calorimetry puck for heat capacity measurements. Hermetic aluminum pans were used as they isolate the sample from the atmosphere and the subsequent vacuum in the cryostat and they have the added benefit of being inexpensive. The samples were stable enough to be exposed to the atmosphere for a few minutes. This gave enough time to transfer them from the vial to the sample pan and hermetically seal the lid using the crimp. Large samples often have longer relaxation times and this can lead to lower heat capacity measurements. For these samples, it was found that using a mass of between 5 and 8 mg gave reproducible data with a good S/N ratio.

[0095] A commercial relaxation calorimeter from Quantum Design (Physical Property Measurement System) was used to measure the heat capacities of various ionic liquids over the specified temperature range, 298.15 to 373.15 kelvin. The two-tau method of heat capacity data analysis, which allows separately for relaxation of the temperature within the sample and within the addenda, was used. Due to the air sensitivity and liquid nature of the samples, the method used for data collection involved 4 separate runs. First, the background data (addenda) was collected. A very thin layer of Apiezon® H grease (ca. 1.5 mg) was spread over the platform (to provide a good thermal contact between the pan and platform in the following run) and data was collected. Then a second run, with the unsealed volatile pan added (and with a very thin layer of grease between the lid and pan lip for thermal contact), was collected; this gives the specific heat of the sample pan and grease. The third run was another addenda run (same as the first) and finally the fourth run added the sample pan (from run 2) with the sample sealed in it. With the data from runs 2 and 4, the specific heat of the pan and grease can be subtracted from the specific heat of the pan, grease and sample (i.e. 4-2) giving the specific heat of the sample. Table 3 summarizes the results obtained. Table 3: Specific heats of the ionic liquids measured.

(a) Values in the table were taken from references 7 (IL 1 and 2), 8 (IL 3, 5 and 6) and 9 (IL 4). Single density measurements at 298.1 K were all that were available for IL1 and IL2. These literature values were assumed to be close to the density of the experimental ILs at the lower temperatures (~300 K) measured. For the phosphonium ILs literature values allowed a linear regression of the data to be applied giving the following equations for density. IL3 p = 1.040 - 5.267 x 10^"4 x T (K); IL4 = 0.903 - 6.34 x 10^" x T (°C); IL5 p = 1.077 - 5.248 x 10^"4 x T (K); IL6 p = 1.230 - 6.002 x 10 x T (K). These equations were used to calculate the density of the ILs at the experimental temperature

CO? Capture

[0096] C0₂ Capture Experimental Procedure

[0097] 5, 10, and 20% v/v fractions of diethylenetriamine (DETA) were added to 5 mL of solvent [tetradecyl(trihexyl)phosphonium chloride OR polyethylene glycol dimethyl ether (M_N = - 250)]. The solution was then exposed to an atmosphere of C0₂ while swirling for 3 minutes. A gooey white precipitate was found to form in the solution upon exposure to C0₂. Overall, precipitate formation was observed to be more prevalent in the polymeric solvent solutions. After exposure to C0₂ the atmosphere in the flask was allowed to equilibrate with the atmosphere in the laboratory with the help of a Hagen Elite 802 Air Pump.

[0098] In addition, a solution of 10% DETA, 10% H₂0, and 5 mL of solvent [tetradecyl(trihexyl)phosphonium chloride OR polyethylene glycol dimethyl ether ( _N = ~ 250)] was also tested using the above described method.

[0099] Large scale reactions were also performed for 5, 10, and 20% DETA in addition to the 10% DETA/10% water mixture using 20 mL of solvent and the above described process.

[00100] DETA-CC-2 Adduct Formation and Data

[00101] A mixture of 10% DETA in tetradecyl(trihexyl)phosphonium chloride was prepared and exposed to pure C0₂ for 1 minute forming a gooey white precipitate. The flask was then heated in the microwave, capped and left sealed for over a week. The DETA/ionic liquid mixture was found to precipitate white-coloured plate-like crystals upon being left sealed under an atmosphere of C0₂. The DETA- C0₂ adduct once isolated was found to be extremely hygroscopic and temperature sensitive. Thermogravimetric studies (see Fig. 1 ) indicated that the adduct has an onset of decomposition temperature of 82°C (corresponding to 5% mass loss, at a heating rate of 5°C/min, and a nitrogen atmosphere). Furthermore, mass spectrometry studies demonstrated that the adduct releases C0₂ between the temperatures of 75 and 145°C (see Fig. 2). The crystal structure of the adduct was obtained and can be seen in Fig. 3. Mp: 132-136°C. Analysis: found for C₅H₁₃N₃0₂: C 39.88, H 9.75, N 27.96; calc: C 40.80, H 8.90, N 28.55. IR: 3360.78 (m, N-H stretch), 3248.33 (m, N-H stretch), 1649.06 (m, C=0 stretch), 1572.23 (m, N-H bend). C0₂ capture reactions

[00102] DETA formed clear smooth running solutions with both tetradecyl(trihexyl)phosphonium chloride (IL 101) and polyethylene glycol dimethyl ether, M_N = ~ 250 (PEG). The solutions are hygroscopic, and can absorb considerable water when exposed to air. Furthermore, they readily react with carbon dioxide, even in the atmosphere, at ambient pressure. Solutions containing upwards of 20 percent were prepared and left sealed. They maintained their integrity for weeks.

[00103] Upon exposure to carbon dioxide, the solutions react rapidly to form the carbamate zwitterionic material 1 b. This compound is a light fluffy white material which, when exposed to water, even in trace amounts, turns to a sticky gum. The absorption of carbon dioxide is a function of added amine and water as summarized in Table 4. It is important to note that one molecule of absorbent amine effectively binds 1 molecule of carbon dioxide.

[00 04] Table 4: C0₂ capture results averaged over 3 runs.

Exposure to C0₂ lasted for 3 minutes at ambient temperature and

[00106] Large scale reactions were also performed and broadly demonstrated that the C0₂ capture system reported herein is capable of scale-up (Table 5).

[00107] Table 5: C0₂ capture results for large scale reactions. Solvent: AM( >UNT MOLE IL101 or DETA H₂0 C 0₂ RATIO

SAMPLE PEG BO JND* C0₂ :

9 mmol g mmol g mmol g mmol DETA

5% DETA

IL 101 + DETA 18.28 35.20 1.17 11.34 0.28 6.36 0.56 :

1

PEG + DETA 21.03 1.14 11.05 0.54 12.27 1.11 :

1

10% DETA

IL 101 + DETA 18.25 35.14 2.05 19.87 0.37 8.41 0.42 :

1

PEG + DETA 20.50 2.02 19.58 0.85 19.31 0.99 :

1

20% DETA

IL 101 + DETA 18.27 35.18 3.94 38.19 0.35 7.95 0.21 :

1

PEG + DETA 20.60 3.87 37.51 0.59 13.41 0.36 :

1

10% DETA + 10 % Water

IL 101 + DETA 18.32 35.28 2.04 19.77 2.17 120.46 0.27 6.14 0.31 : + H₂0 1

PEG + DETA 20.40 2.03 19.68 2.16 119.90 0.72 16.36 0.83 : + t^G- 1

[00108] ^* Exposure to C0₂ lasted for 3 minutes at ambient temperature and pressure.

[00109] The reaction of DETA with C0₂ occurs rapidly. In one case, crystals of the adduct were isolated from the phosphonium ionic liquid, tetradecyl(trihexyl)phosphonium chloride, as white-coloured plates. Numerous adducts are possible (Hartono, A.; da Silva, E.F.; Grasdalen, H.; Svendsen, H.F. Qualitative Determination of Species in DETA-H₂0-C0₂ System Using ¹³C NMR Spectra. Ind. Eng. Chem. Res. 2007. 46, 249-254), however, under the conditions tested herein, only the zwitterionic adduct shown in Scheme 1b was formed.

MW = 103.17 Scheme 1 b: Reaction scheme showing the reaction stoichiometry of DETA (1 b) with C0₂

[001 10] The crystal structure of this adduct is shown in Fig. 3. Solution state spectroscopic data was difficult to obtain because the adduct was extremely insoluble, but elemental analysis and IR data are in accord with the crystallographic information. Notable IR spectral features include a broad amine N-H stretch peak at 3360 cm^"1, a sharp amine N-H stretch peak at 3248 cm^"1, and a sharp amine N-H bend peak at 1572 cm^"1. In addition, a C=0 stretch absorption at 1649 cm^'1 is present confirming the presence of C0₂ (see Fig. 4)

[0011 1] The adduct, shown in Fig. 3, is discrete but exhibits extensive intermolecular interactions within the layers forming 2d sheets. These sheets layer to form the crystal lattice and, on the microscopic level, are consistent with the plate structure of the crystalline material.

[00112] Thermogravimetric studies indicate that the adduct has an onset of decomposition temperature of 82°C (corresponding to 5% mass loss, at a heating rate of 5°C/min, and a nitrogen atmosphere). Furthermore, mass spectrometry studies demonstrate that the adduct releases C0₂ between the temperatures of 75 and 145°C. See Figs. 1 and 2 for the TGA and MS scans. As described above, at these temperatures the phosphonium ionic liquids are extremely stable, as are 1- butyl-3-methylimidazolium bistriflamide and the polymeric solvents explored by the stability study.

[00113] Finally, applicants also performed experiments to assess the specific heat of several of the more robust ionic liquids, including tetradecyl(trihexyl)phosphonium bistriflamide and tetradecyl(trihexyl)phosphonium decanoate. Consistent with expectations, the heat capacities for these two ILs were lower than that of water at 300 K; the values for the specific heats at 301 K were 1.58 and 1.97 J g^" K^"1.

[00114] Applicants have performed a survey of carbon dioxide capture in phosphonium-based ionic liquids and end-capped polyethylene glycol using DETA (DETA = diethylenetriamine) as a model absorbent. The carbon dioxide adduct of DETA forms readily in both ionic and polymeric media. Crystals of the adduct have been isolated and its X-ray crystal structure is reported. The material consists of discrete zwitterionic species that form a layered structure exhibiting extensive hydrogen bonds within the layers and minimal interactions between the layers. Applicants also described a study of the thermal stability of phosphonium ionic liquids and selected polymeric solvents under neutral and oxidizing conditions and showed that the presence of oxygen in the gas sample significantly affects the stability of the ionic liquid.

Mixtures of amines used for CO2 capture

Mixtures of Amines in IL 101 and PEG 200 and their Abilities to Capture C0₂

[00115] To begin this phase of the investigation, solutions of amines in either IL 101 or PEG 200 were prepared and observations recorded before and after the addition of C0₂. Each solution contained a 2:1 mixture of solvent to amine (by volume). C0₂ was bubbled into each solution for 3 minutes at ambient temperature and pressure. The observations are summarized in Tables 6 (IL 101) and 7 (PEG 200).

[00116] Table 6: Initial observations of solutions of amines in IL 101 , tetradecyl(trihexyl)-phosphonium chloride, before and after the addition of C0₂.

[00117] Table 7: Initial observations of solutions of amines in PEG 200, polyethylene glycol (Mw « 200), before and after the addition of C0₂.

[00118] Further tests have been made by using the general procedure described above. In these tests further amines have been added to the composition comprising diethylenetriamine and at least one compound chosen from phosphonium-based ionic liquids, polymeric solvents, and misxtures thereof. Six solutions comprising various amines in either an ionic liquid or polymeric solvent were prepared; three solutions in tridecyl(tetrahexyl)phosphonium chloride (IL 101) and three solutions in polyethylene glycol (MN = 200) (PEG 200). The amines used in the various samples are listed below.

[00119] Table 8: Abbreviations used for various amines and other compounds used in the present document.

DEA Diethanolamine

DETA Diethylenetriamine

DPA Dipropylamine

EA Ethanolamine

IPA Isopropylamine

MAE 2-(methylamino)ethanol

NMDEA N-methyldiethanolamine

PA Propylamine

TETA Triethylenetetramine

PEG Polyethylene glycol

IL 101 Tetradecyl(trihexyl)phosphonium chloride

Tetradecyl(trihexyl)phosphonium

IL 105 dicyanimide

Tributyl(methyl)phosphonium methyl

IL 108 sulphate

Tetradecyl(trihexyl)phosphonium

IL 109 bistriflamide

[BMIM][TFSI] l-butyl-3-methylimidazolium bistriflamide

[00120] The following table (Table 9) lists the compositions of each sample prepared. The "Volume of Solvent" column also shows which solvent was used in the sample, either PEG 200 (PEG) or IL 101 (IL).

[00121] Table 9: Parameters used for C0₂ capture tests made using various amines.

Sample Volume Volume Volume Volume Volume Volume Volume Volume

ID of of of of of of of of

Solvent DETA TETA DPA IPA PA NMDEA CHA

(mL) (mL) (mL) (mL) (mL) (mL) (mL) (mL)

1 8 (PEG) 4 N/A 4 N/A N/A N/A N/A

2 8 (PEG) 4 2 2 N/A N/A N/A N/A

3 8 (IL) 3 N/A 1.2 1.2 1.2 N/A N/A

4 8 (PEG) 3 N/A 1.2 1.2 1.2 N/A N/A 8 (IL) 2 N/A N/A N/A N/A 2 N/A

8 (IL) 2 N/A N/A N/A N/A 2 2

[00122] Gaseous carbon dioxide was then bubbled into each sample for three minutes at ambient temperature and pressure with light stirring. Samples ID Nos. 1 , 2, 4 and 5 all remained in the liquid phase after addition of CO2. Samples ID Nos. 3 and 6 both formed precipitates during the addition of C0₂. However, addition of approximately 1 ml_ of deionized water to Sample 6 dissolved the solid overnight and the solution separated into two layers (this was performed after the results were obtained). After the addition of C0₂, air was pumped into the flask using a syringe to displace excess C0₂. The mass of the solution was taken before and after the addition of C0₂ and the difference was taken to represent the mass of C0₂ bound. Very little change in mass occurred after several hours open to air. Each sample was tested in triplicate and the results are as follows.

[00123] Table 10: Results of CO2 capture tests made using various amines.

[00124] The results show that the most effective solution, Sample ID No. 4, binds 0.44 moles of C0₂ for every mole of DETA present in the solution, approaching a value of two DETA molecules for one CO2 molecule. [00125] Next, solutions of various combinations of amines, in one of IL 101 , PEG 200, PEG 400 or a deep eutectic (1 :2 ratio of choline chloride and urea) as the solvent, were prepared. Each formulation included some amount of DETA. C0₂ was bubbled into each of these prepared solutions for three minutes at ambient temperature and pressure and the solutions were left to sit closed to the atmosphere for several days, or until solid was observed in the flask. Of the dozens of solutions prepared, most formed a solid precipitate over the course of a few days, or during the addition of C0₂, however, many solutions did remain liquid. The solutions that remained liquid were tested for their ability to capture C0₂. They were remade and weighed before and after addition of C0₂. The difference in mass was taken to be the mass of C0₂ bound and an approximate ratio of C0₂ to DETA in the solution was calculated. The following table lists the composition of all tested solutions and the approximate ratio of C0₂ bound to the DETA present in solution. All solutions began as slightly yellow, transparent liquids and, with the exception of Sample ID No. 14, remained as a slightly foggy solution during the two- week storage period. Sample ID No. 14 was observed to remain as a clear liquid.

[00126] Table 11 : Composition of the liquid amine solutions after addition of C0₂.

[00127] Note: Only solutions that remained in the liquid phase after the two-week storage period are included. Solubility of the DETA-CO2 Adduct

[00128] The solubility of the DETA-C0₂ adduct was tested in a variety of solvents; milligram amounts of the adduct were added to approximately 10-20 mL of solvent in each case. The adduct was found to be insoluble in a deep eutectic solvent (choline chloride and urea), dichloromethane, hexanes, IL 101 , IL 105, IL 108, IL 109, isopropanol, methanol, PEG 400, PEG 200 and tetrahydrofuran.

Vapour Pressure Measurements of Solutions of DETA in IL 101 and PEG 200

[00129] Vapour pressure measurements were made on solutions of DETA in the chosen solvent (IL 101 (see Fig. 5) or PEG 200 (see Fig. 6)) held in an evacuated flask. The pressure and temperature were measured for every 5°C increment between 50- 130°C. This procedure was repeated for 0%, 10%, 20% and 100% solutions of DETA both in IL 101 and PEG 200. It was found that as the concentration of DETA increased so did the vapour pressure of the mixture at any given temperature. It was also found that IL 101 and PEG 200 both have negligible vapour pressures between 50-130°C, on the order of 0-1 kPa.

[00130] The vapour pressure of a 20% DETA solution in IL101 with added C0₂ was also measured as the temperature was repeatedly increased and decreased (see Fig. 7). The same procedure used for determining the vapour pressure of the DETA solutions was used for the temperature cycle tests. Rather than constant heating, the flask was heated to 100°C and then cooled in an ice bath to room temperature. This was repeated three times and the pressure was measured as a function of temperature.

[00131] As can be seen in Fig. 8, vapour pressure tests have also been made with (Sample ID No. 15) with C0₂.

C0₂ Capture Tests using a Flue Gas Mixture

[00132] For flue gas testing, a gas mixture from Praxair (11% C0₂, 1% 0₂ and

88% N₂) was utilized. The total volume of the test system was estimated to be 2.3 L.

Assuming ideality, there would be 0.103 mol of gas in the 2.3 L, 11% of which would be

C0₂ (0.01133 mol C0₂). If one mole of DETA binds one mole of C0₂, 0.01133 mol of

DETA would be needed to capture all the C0₂ present. Therefore a mixture of 2 mL

DETA (0.0185 mol) in 18 mL of IL 101 was used. After evacuation, the system was filled with the flue gas mixture and the pressure was measured as a function of time. As expected, the pressure in the flask decreased as the DETA present in the solution bound the free C0₂. Using the ideal gas law the expected pressure decrease was calculated to be ~12 kPa if all the C0₂ present was bound. In the case of the 10% DETA solution in IL 101 , a pressure drop of approximately 9 kPa was observed (see Fig. 9). A pressure drop of approximately 8 kPa was observed for one of the mixed amine solutions (Sample ID No. 15) which was also tested under the same conditions (see Fig. 10).

Thermal Stability Tests

[00133] Of key importance is an assessment of the long term stability of the solvent systems at temperatures relevant to the catch-and-release carbon system. Thermal stability tests were carried out on solutions of 20% DETA in various ionic liquids and polymeric solvents. These solutions were closed to the atmosphere and heated at approximately 100°C for seven days. Observations (including photographs) were made throughout the heating period. The solvents used were 1-butyl-3-methylimidazolium bistriflamide, tetradecyl(trihexyl)phosphonium chloride, tetradecyl-(trihexyl)phosphonium bistriflamide, tetradecyl(trihexyl)phosphonium dicyanimide, poly-(ethylene glycol) 200, poly(ethylene glycol) 400 and poly(ethylene glycol) 600. Overall, the systems with the higher MW PEGs or tetradecyl(trihexyl)phosphonium bistriflamide as the solvents appeared to be the most thermally stable. Examples are shown in Fig. 11 : 20% DETA in PEG 400 which showed relatively less decomposition and in Fig. 12 : 20% DETA in IL101 with relatively more decomposition observed.

ΔΗ_Γχη Determination for the DETA-C0₂ Reaction

[00134] Using a Dewar flask calorimeter, attempts have made to measure ΔΗ for the exothermic reaction between DETA and C0₂. C0₂ was added to the DETA in a Dewar flask until a constant temperature was attained. However, this determination proved difficult. Solutions of DETA in ionic liquids reacted with C0₂ with a large amount of foaming. This, in turn, greatly affected the temperature and mass readings so that the final results obtained were not entirely consistent. Since the reaction between DETA and C0₂ is very exothermic only small amounts of DETA were used. Taking the heat capacity of DETA to be 2.8 Jg^{"1 "1} and the heat capacity of the Dewar flask (determined by dissolution of sodium hydroxide in water) to be 52.81 JK^"1 the values shown in Table 12 were obtained. A total of 6 trials were run and the mean value for ΔΗ of the reaction was determined to be -150 kJ/mol with a standard deviation of ±23 kJ/mol. Attempts will be made to confirm these results using an alternative method.

[00135] Table 12: Estimated AH™ values for the reaction between DETA and C0₂.

Determination of the Temperature Required for 90% C0₂ Release using Titrimetric Methods

[00136] After preparing a solution of 20% DETA in tetradecyl(trihexyl)phosphonium chloride the adduct was prepared by bubbling C0₂ directly into the solution for approximately 10 minutes. A second flask was filled with 50mL of an aqueous barium hydroxide solution (prepared by a tenfold dilution of saturated barium hydroxide). The flasks were connected and purged for ten minutes with nitrogen gas. The adduct mixture was then heated at a rate of one degree per minute under constant nitrogen flow. The evolved C0₂ was carried into the barium hydroxide solution where the pH was monitored as a function of temperature. The pH decreased to a minimum at 135°C as the barium hydroxide was converted to insoluble barium carbonate by the evolved C0₂. Taking the minimum to occur when 100% of the possible C0₂ had been evolved from the adduct, the temperature of 90% release was found to be in the range 115-120°C (see Fig. 13).

[00137] This method for determination of CO2 release temperature was performed in duplicate yielding very similar results (see Fig. 14) and it was found that varying the rate of temperature increase had little effect on the overall result of the titration. The pH decrease amounts were converted to percentages and both runs were plotted on the same graph (see Fig. 15).

Competition between C0₂ and S0₂ for adduct formation

[00138] For the DETA-CO2 adduct melting began at approximately 115°C, with a colour change from off-white to yellow (the colour of liquid DETA). Continuous melting was observed between 120-127°C. The adduct was completely liquid at approximately 130°C. According to the barium hydroxide titration method, the temperature at which the C0₂ is fully evolved from the DETA-CO₂ adduct is approximately 135°C. In contrast, the solid product recovered from the reaction of DETA and S0₂ was observed to start melting at approximately 72°C with almost continuous melting until completely liquefied at 90°C, giving a clear and colourless liquid (note: This product was prepared by injecting SO₂ gas, generated from the reaction of 6M HCI with sodium bisulphate, into pure DETA to give a beige-pink coloured solid). At elevated temperatures above the melting point, some bubbling was observed in the range 140-170°C which may be attributed to additional dissolved SO2 escaping from the solution. After this point, decomposition to a dark brown liquid was observed in the range 170-185°C. This decomposition is not observed in the heating of the DETA-CO2 adduct. The lower SO₂ release temperature of the DETA-SO2 product, relative to that of the DETA-CO₂ adduct, suggests a weaker binding of S0₂ to DETA compared to C0₂.

[00139] The present disclosure has been described with regard to specific examples. The description was intended to help the understanding of the present disclosure, rather than to limit its scope. It will be apparent to one skilled in the art that various modifications may be made to the present disclosure without departing from the scope of the present disclosure as described herein, and such modifications are intended to be covered by the present document.

Claims

CLAIMS:

1. A method for capturing C0₂, said method comprising contacting C0₂ with a composition comprising diethylenetriamine and at least one compound chosen from phosphonium-based ionic liquids, polymeric solvents, and mixtures thereof.

2. The method according to claim 1 , wherein said diethylenetriamine is present in said composition at a concentration of about 2 % to about 30 % v/v.

3. The method according to claim 1 , wherein said diethylenetriamine is present in said composition at a concentration of about 4 % to about 25 % v/v.

4. The method according to claim 1 , wherein said diethylenetriamine is present in said composition at a concentration of about 5 % to about 20 % v/v.

5. The method according to any one of claims 1 to 4, wherein said at least one compound has an average heat capacity of about 1.3 to about 2.3 J/gK at 301 K.

6. The method of any one of claims 1 to 4, wherein said at least one compound has an average heat capacity of about 1.5 to about 2.1 J/gK at 301 K.

7. The method of any one of claims 1 to 4, wherein said at least one compound has an average heat capacity of about 1.6 to about 2.0 J/gK at 301 K.

8. The method of any one of claims 1 to 4, wherein said composition comprises diethylenetriamine and at least one phosphonium-based ionic liquids.

9. The method according to claim 8, wherein said at least one phosphonium ionic liquid is chosen from tetradecyl(trihexyl)phosphonium chloride, tetradecyl(trihexyl)phosphonium decanoate, tetradecyl(trihexyl)phosphonium dicyanimide, tetradecyl(trihexyl)phosphonium bistriflamide, tetradecyl(trihexyl)phosphonium bromide, tetradecyl(trihexyl)phosphonium(bis 2,4,4- trimethylpentyl)phosphinate, triisobutyl(methyl)phosphonium tosylate, tributyl(methyl)phosphonium methylsulfate, tetradecyl(trihexyl)phosphonium hexafluorophosphate, tetradecyl(trihexyl)phosphonium tetrafluoroborate, tributyl(hexadecyl)phosphonium bromide, tetrabutylphosphonium bromide, tetrabutylphosphonium chloride, tetraoctylphosphonium bromide, tetraoctylphosphonium bromide, tetradecyl(tributyl)phosphonium chloride, ethyltri(butyl)phosphonium diethylphosphate, tetradecyl(tributyl)phosphonium dodecylsulfonate, tetradecyl(trihexyl)phosphonium dodecylsulfonate, and mixtures thereof.

10. The method according to claim 8, wherein said at least one phosphonium ionic liquid is tetradecyl(trihexyl)phosphonium chloride.

11. The method of any one of claims 1 to 4, wherein said composition comprises diethylenetriamine and at least one polymeric solvent.

12. The method according to claim 11 , wherein said at least one polymeric solvent is chosen from poly(ethylene glycol) dimethyl ether, polydimethylsiloxane, a copolymer of phenylmethylsiloxane and dimethylsiloxane and a copolymer of diphenylsolizane, dimethylsiloxane, and mixtures thereof.

13. The method according to claim 11 , wherein said at least one polymeric solvent is poly(ethylene glycol) dimethyl ether.

14. The method according to claim 13, wherein said poly(ethylene glycol) dimethyl ether has an M_N of about 200 to about 600.

15. The method according to claim 13, wherein said poly(ethylene glycol) dimethyl ether has an M_N of about 200 to about 300.

16. The method according to claim 13, wherein said poly(ethylene glycol) dimethyl ether has an M_N of about 500 to about 600.

17. The method of any one of claims 1 to 16, wherein said composition further comprises an amine chosen from triethylenetetramine, dipropylamine, isopropylamine, propylamine, N-methyldiethanolamine, and mixtures thereof.

18. The method of any one of claims 1 to 16, wherein said composition further comprises dipropylamine, isopropylamine, and propylamine.

19. The method according to any one of claims 1 to 18, wherein a precipitate is formed when contacting C0₂ with a composition comprising diethylenetriamine and at least one compound chosen from phosphonium-based ionic liquids, polymeric solvents, and mixtures thereof, said precipitate comprising C0₂ and diethylenetriamine.

20. The method according to claim 19, wherein said precipitate comprises a diethylenetriamine-C02 adduct.

21. The method according to claim 20, wherein said diethylenetriamine-C0₂ adduct is :

22. The method according to any one of claims 1 to 18, wherein a liquid is formed when contacting C0₂ with a composition comprising diethylenetriamine and at least one compound chosen from phosphonium-based ionic liquids, polymeric solvents, and mixtures thereof, said liquid comprising an adduct comprising C0₂.

23. The method according to claim 22, wherein said liquid comprises a diethylenetriamine-C02 adduct.

24. The method of any one of claims 1 to 23, further comprising releasing said captured C0₂.

25. The method of any one of claims 19 to 24, further comprising releasing said C0₂ comprised in said precipitate or liquid.

26. The method according to claim 25, wherein said C0₂ is released by heating said precipitate or liquid at a temperature of at least about 65 °C.

27. The method according to claim 25, wherein said C0₂ is released by heating said precipitate or liquid at a temperature of at least about 70 °C.

28. The method according to claim 25, wherein said C0₂ is released by heating said precipitate or liquid at a temperature of at least about 75 °C.

29. The method according to claim 25, wherein said C0₂ is released by heating said precipitate or liquid at a temperature of about 70 °C to about 160 °C.

30. The method according to claim 25, wherein said C0₂ is released by heating said precipitate or liquid at a temperature of about 75 °C to about 145 °C.

31. A composition comprising diethylenetriamine and at least one compound chosen from phosphonium-based ionic liquids, polymeric solvents, and mixtures thereof.

32. The composition according to claim 31 , wherein said diethylenetriamine is present in said composition at a concentration of about 2 % to about 30 % v/v.

33. The composition according to claim 31 , wherein said diethylenetriamine is present in said composition at a concentration of about 4 % to about 25 % v/v.

34. The composition according to claim 31 , wherein said diethylenetriamine is present in said composition at a concentration of about 5 % to about 20 % v/v.

35. The composition of any one of claims 31 to 34, wherein said at least one compound has an average heat capacity of about 1.3 to about 2.3 J/gK at 301 K.

36. The composition of any one of claims 31 to 34, wherein said at least one compound has an average heat capacity of about 1.5 to about 2.1 J/gK at 301 K.

37. The composition of any one of claims 31 to 34, wherein said at least one compound has an average heat capacity of about 1.6 to about 2.0 J/gK at 301 K.

38. The composition of any one of claims 31 to 34, wherein said composition comprises diethylenetriamine and at least one phosphonium-based ionic liquids.

39. The composition according to claim 38, wherein said at least one phosphonium ionic liquid is chosen from tetradecyl(trihexyl)phosphonium chloride, tetradecyl(trihexyl)phosphonium decanoate, tetradecyl(trihexyl)phosphonium dicyanimide, tetradecyl(trihexyl)phosphonium bistriflamide, tetradecyl(trihexyl)phosphonium bromide, tetradecyl(trihexyl)phosphonium(bis 2,4,4- trimethylpentyl)phosphinate, triisobutyl(methyl)phosphonium tosylate, tributyl(methyl)phosphonium methylsulfate, tetradecyl(trihexyl)phosphonium hexafluorophosphate, tetradecyl(trihexyl)phosphonium tetrafluoroborate, tributyl(hexadecyl)phosphonium bromide, tetrabutylphosphonium bromide, tetrabutylphosphonium chloride, tetraoctylphosphonium bromide, tetraoctylphosphonium bromide, tetradecyl(tributyl)phosphonium chloride, ethyltri(butyl)phosphonium diethylphosphate, tetradecyl(tributyl)phosphonium dodecylsulfonate, tetradecyl(trihexyl)phosphonium dodecylsulfonate, and mixtures thereof.

40. The composition according to claim 39, wherein said at least one phosphonium ionic liquid is tetradecyl(trihexyl)phosphonium chloride.

41. The composition of any one of claims 31 to 34, wherein said composition comprises diethylenetriamine and at least one polymeric solvent.

42. The composition according to claim 41 , wherein said at least one polymeric solvent is chosen from poly(ethylene glycol) dimethyl ether, polydimethylsiloxane, a copolymer of phenylmethylsiloxane and dimethylsiloxane and a copolymer of diphenylsolizane, dimethylsiloxane, and mixtures thereof.

43. The composition according to claim 42, wherein said at least one polymeric solvent is poly(ethylene glycol) dimethyl ether.

44. The composition according to claim 43, wherein said poly(ethylene glycol) dimethyl ether has an M_N of about 200 to about 600.

45. The composition according to claim 43, wherein said poly(ethylene glycol) dimethyl ether has an MN of about 200 to about 300.

46. The composition according to claim 43, wherein said poly(ethylene glycol) dimethyl ether has an M_N of about 500 to about 600.

47. The composition of any one of claims 31 to 46, wherein said composition further comprises an amine chosen from triethylenetetramine, dipropylamine, isopropylamine, propylamine, N-methyldiethanolamine, and mixtures thereof.

48. The composition of any one of claims 30 to 45, wherein said composition further comprises dipropylamine, isopropylamine, and propylamine.

49. Use of the composition as defined in any one of claims 31 to 48 for capturing C0₂.

50. A method for using the composition of any one of claims 31 to 48, comprising contacting said composition with C0₂ so as to capture C0₂.

51. The method according to claim 50, wherein a precipitate is formed when contacting C0₂ with said composition, said precipitate comprising C0₂ and diethylenetriamine.

52. The method according to claim 51 , wherein said precipitate comprises an diethylenetriamine-C0₂ adduct. The method of claim 52, wherein said diethylenetriamine-C0₂ adduct

54. The method according to claim 50, wherein a liquid is formed when contacting C0₂ with said composition, said liquid comprising an adduct comprising C0₂.

55. The method according to claim 54, wherein said liquid comprises a diethylenetriamine-C0₂ adduct.

56. The method of any one of claims 50 to 55, further comprising releasing said captured C0₂.

57. The method of any one of claims 50 to 55, further comprising releasing said C0₂ comprised in said precipitate or liquid.

58. The method according to claim 57, wherein said C0₂ is released by heating said precipitate or liquid at a temperature of at least about 65 °C.

59. The method according to claim 57, wherein said C0₂ is released by heating said precipitate or liquid at a temperature of at least about 70 °C.

60. The method according to claim 57, wherein said C0₂ is released by heating said precipitate or liquid at a temperature of at least about 75 °C.

61. The method according to claim 57, wherein said C0₂ is released by heating said precipitate or liquid at a temperature of about 70 °C to about 160 °C.

62. The method according to claim 57, wherein said C0₂ is released by heating said precipitate or liquid at a temperature of about 75 °C to about 145 °C.

63. The method of any one of claims 1 to 30 and 50 to 62, wherein said composition is contacted with a flue gas comprising said C0₂.

64. A compound of formula :