CO2 Capture in Alkanolamine-RTIL Blends via Carbamate

Article pubs.acs.org/est

CO2 Capture in Alkanolamine-RTIL Blends via Carbamate Crystallization: Route to Efficient Regeneration Muhammad Hasib-ur-Rahman and Faïçal Larachi* Department of Chemical Engineering, Laval University, Québec QC, G1 V 0A6 Canada S Supporting Information *

ABSTRACT: One of the major drawbacks of aqueous alkanolamine based CO2 capture processes is the requirement of significantly higher energy of regeneration. This weakness can be overcome by separating the CO2-captured product to regenerate the corresponding amine, thus avoiding the consumption of redundant energy. Replacing aqueous phase with more stable and practically nonvolatile imidazolium based room-temperature ionic liquid (RTIL) provided a viable approach for carbamate to crystallize out as supernatant solid. In the present study, regeneration capabilities of solid carbamates have been investigated. Diethanolamine (DEA) carbamate as well as 2-amino-2-methyl-1-propanol (AMP) carbamate were obtained in crystalline form by bubbling CO2 in alkanolamineRTIL mixtures. Hydrophobic RTIL, 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([hmim][Tf2N]), was used as aqueous phase substituent. Thermal behavior of the carbamates was observed by differential scanning calorimetry and thermogravimetric analysis, while the possible regeneration mechanism has been proposed through 13 C NMR and FTIR analyses. The results showed that decomposition of DEA-carbamate commenced at lower temperature (∼55 °C), compared to that of AMP-carbamate (∼75 °C); thus promising easy regeneration. The separation of carbamate as solid phase can offer two-way advantage by letting less volume to regenerate as well as by narrowing the gap between CO2 capture and amine regeneration temperatures.

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INTRODUCTION Anthropogenic industrial activities are causing serious increase in atmospheric concentration of greenhouse gases; and carbon dioxide, being the most important of these in perspective of its contributions toward global warming, is considered as the main cause of environmental problems in this regard.1−4 Major CO2 emission sources that offer potential capture convenience comprise fossil-fuel based power generation installations.5 Various measures are being explored to check CO2 emissions from large point sources into the atmosphere. These include physical/chemical sorption, membrane separation, and cryogenic distillation techniques. In industry, the most preferred gas absorption processes comprise alkanolamine based aqueous solvents executing absorber-stripper arrangements, and can principally be used for postcombustion CO2 capture.5−7 At temperatures around 40 °C aqueous solutions of primary and secondary amines, such as monoethanolamine (MEA), diethanolamine (DEA) respectively, are subjected to absorb CO2 through carbamate formation whereas tertiary amines, such as N-methyldiethanolamine (MDEA), along with water react with the sour gas to form ammonium bicarbonate. In case of primary/secondary amines, predominantly one mole of CO2 reacts with two moles of amine obeying the following mechanism (eqs 1 and 2):8,9 CO2 + RR′NH ⇌ RR′NH+COO−

However, in presence of water, tertiary amines react with CO2 in 1:1 molar ratio, as shown below (eqs 3 and 4): (3)

RR′R″N + H+ ⇌ RR′R″NH+

(4)

Then the regeneration of these solvents is carried out by heat stripping at temperatures in the range of 100−140 °C.5 In case of primary/secondary aqueous alkanolamines, the following regeneration mechanism (eqs 5 and 6) has been proposed:8,10 RR′NCOO− + H 2O ⇌ CO2 + RR′NH + OH−

(5)

RR′NH 2+ + OH− ⇌ RR′NH + H 2O

(6)

While regeneration of tertiary amines occurs as follows (eqs 7 and 8): HCO3− ⇌ CO2 + OH−

(7)

RR′R″NH+ + OH− ⇌ RR′R″N + H 2O

(8)

Nevertheless, there are many downsides of these CO2 capture systems like low gas loading, degradation/evaporation of amines, and corrosion of equipment.11−13 Higher regeneration energy

(1)

Received: Revised: Accepted: Published:

RR′NH+COO− + RR′NH ⇌ RR′NH 2+ + RR′NCOO− (2) © 2012 American Chemical Society

CO2 + H 2O ⇌ H+ + HCO3−

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June 21, 2012 August 15, 2012 September 10, 2012 September 10, 2012 dx.doi.org/10.1021/es302513j | Environ. Sci. Technol. 2012, 46, 11443−11450

Environmental Science & Technology

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requirement is one of the major drawbacks of aqueous alkanolamine based state-of-the-art technologies. In a power generation plant, up to 40% additional energy is required for carbon dioxide capture and storage (CCS). Out of this extra bite, roughly 50% is consumed in regeneration step alone.5 Recently, unique room-temperature ionic liquids (RTILs), owing to their tunable physicochemical characteristics, have been emerging as potential contenders for CO2 capture.6,14 In this context, thermally stable imidazolium based RTILs are being investigated extensively as prospective alternates.15−19 Pressure swing technique can be used to regenerate such solvents. However, like other physical solvents such as methanol, dimethyl ethers of polyethylene glycol (currently being used industrially as rectisol/selexol processes), these alone cannot be employed effectively for separating CO2 from flue gases with low CO2 partial pressures.20,21 Neither aqueous alkanolamines nor RTILs solely are proficient enough for economical CO2 separation. In search of an efficient CO2 separation process, various methodologies are being scrutinized. These include amino functionalized solid adsorbants, task specific ionic liquids, as well as supported ionic liquid membranes.14,22 Work has also been initiated to combine the advantages of RTILs with those of primary/secondary alkanolamines, and in this regard Camper et al. were the first to report MEA-carbamate precipitation in amineRTIL solution.23−26 In case of alkanolamine solvents, replacing aqueous phase with more stable room-temperature ionic liquid (RTIL) can avoid the corrosion and equilibrium limitation problems particularly arising due to the presence of water. More significantly, the presence of RTIL provides the favorable environment for CO2-captured product to crystallize out, thus making it possible to easily separate the solid carbamate from the liquid counterpart in addition to completing the reaction to its full stoichiometric potential. As CO2 is about 3 times more soluble (in terms of moles of CO2 per volume of the solvent) in imidazolium based RTILs than in water,17,27,28 this new approach of CO2 absorption in alkanolamine-RTIL mixtures can ensure greater mass transfer capacity thus compensating to a certain extent the downside posed by higher viscosity of the ionic liquids. The objectives of this study were to look for an apposite alkanolamine-hydrophobic RTIL combination that can (a) guarantee stoichiometric maximum CO2 loading by evading equilibrium constraints; (b) minimize stripping temperatures; (c) manage less volumes to regenerate through separation of CO2captured product thus letting ensue probable cut down of the gratuitously high regeneration energy to affordable limit. The overall concept has been envisaged in Figure 1. The current activity was focused on looking into the regeneration scenario of CO2 absorption process comprising AMP/DEARTIL blends. Single crystal X-ray diffraction technique and 13C NMR/FTIR analyses were employed to infer the nature of CO2-captured products and the regenerated amines. Whereas decomposition behavior of solid carbamates, obtained by bubbling CO2 through amine-RTIL blends containing either 2-amino2-methyl-1-propanol (AMP) or diethanolamine (DEA), has been investigated in detail using differential scanning calorimetry (DSC), thermogravimetry (TG), 13C NMR, and FTIR techniques.

Figure 1. The simplified process flow diagram of alkanolamine-RTIL based CO2 capture process.

Figure 2. CO2 absorption isotherm for alkanolamine-[hmim][Tf2N] systems obtained at atmospheric pressure and 35 °C temperature.

Figure 3. Evaporation profiles of amines (in amine-RTIL blends) at 35 °C under N2.

1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([hmim][Tf2N]: 99% purity). While carbon dioxide and nitrogen gases (≥99% purity) were obtained from Praxair Canada Incorporation. All the materials were used as received. Procedures and Techniques. CO2 Capture Studies. Gas absorption studies were carried out by thermogravimetric analyzer (Perkin-Elmer Diamond TG/DTA) under carbon dioxide atmosphere isothermally at 35 °C. For this purpose, 18 (±1) mg sample (amine-RTIL mixture) was loaded in an aluminum pan and placed in the analyzer under N2 atmosphere. Then the sample was exposed to pure CO2 to obtain CO2 uptake profile. Mass flow meters were used to adjust gas flow rates at 100 mL/min.

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EXPERIMENTAL SECTION Materials. 2-Amino-2-methyl-1-propanol (AMP: purum, ≥97.0%) and Diethanolamine (DEA: ACS reagent, ≥99.0%) were purchased from Sigma-Aldrich, and Triton X-100 (t-Octylphenoxypolyethoxyethanol, a nonionic surfactant) was obtained from EMD Chemicals. IoLiTec Inc. supplied RTIL, 11444

dx.doi.org/10.1021/es302513j | Environ. Sci. Technol. 2012, 46, 11443−11450


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Figure 4. Packing diagrams: (a) AMP-carbamate; (b) DEA-carbamate (reproduced with permission25).

rate of 5 °C per minute. 13C NMR and ATR-FTIR techniques were employed to confirm the likely regeneration mechanism.

Prior to gas absorption capacity measurements by thermogravimetric analyzer, alkanolamine-RTIL samples were prepared using Omni homogenizer (Omni International, Kennesaw, GA) fitted with rotor-stator generator. Fifteen wt% amine (AMP/ DEA) was mixed in [hmim][Tf2N]. Though, in case of DEA/ [hmim][Tf2N] blend, Triton X-100 surfactant was added to stabilize the homogeneity of the mixture. In order to get solid carbamates, CO2 was bubbled through 15 wt % amine-RTIL blends (without surfactant) at 35 °C along with continuous stirring for two hours. The suspension obtained as a result of carbamate crystallization was allowed to stand for 48 h to help the two phases settle apart. This enabled easy separation of supernatant crystals that were washed thoroughly with acetone, dried and stored at room temperature. Carbamate Characterization. To know the nature of the CO2-captured products (AMP-carbamate, DEA-carbamate), 13C NMR spectra were recorded on a Varian Inova Spectrometer (Palo Alto, CA) at a frequency of 100 MHz with proton decoupling, after dissolving the crystals in DMSO-d6 solvent (CND Isotopes, QC, Canada). Whereas a Nicolet Magna 850 spectrometer (Thermo Scientific, Madison, WI) equipped with high temperature Golden Gate ATR accessory was used to perform FTIR analysis, and Single crystal X-ray diffraction technique provided the detailed information about crystalline structures. Regeneration Behavior. Amine regeneration studies were carried out using thermogravimetric (TG) analyzer and differential scanning calorimetry (DSC). In case of TG analysis, 9 (±1) mg of ground carbamate sample was taken in an aluminum pan and the analysis was conducted using a heating rate of 5 °C per minute. The regeneration behavior of carbamates was studied under two different environments, that is, pure N2, and pure CO2. The onset temperature for carbamate decomposition under N2 atmosphere, at which gas evolution started, was detected by quadrupole mass spectrometer (Thermostar Prisma QMS200, Pfeiffer Vacuum GmbH, Asslar, Germany) coupled with thermogravimetric analyzer. The gas flow rate was maintained at 100 mL/min. To ensure the reproducibility, each experiment was repeated at least once. Differential scanning calorimetric analyses were performed using a Mettler-Toledo DSC1 (Columbus, OH) instrument. DSC scans were also managed at a temperature scan

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RESULTS AND DISCUSSION Maximum Gas Capture Capacity. CO2 absorption in AMP-RTIL and DEA-RTIL blends resulted in crystallization of the product. This development enabled the product (carbamate) to move out of the reaction phase and hence helped overcome the equilibrium limitation barrier thus not only allowing maximum CO2 loading but also enabling easy separation of the solid product.25 However, due to higher volatility of AMP,29,30 regarding AMP-RTIL combination, it was not possible to maintain the initial concentration of amine in AMP-RTIL blends. And so the CO2 capture capacity apparently appeared inferior to what the theoretical maximum would have been with respect to initial AMP concentration (Figure 2). The evaporation phenomenon was quite evident from the mass loss profile of AMPRTIL blend acquired under N2 atmosphere at 35 °C (Figure 3). In order to verify the CO2 capture capacity in case of AMPRTIL blend, the resulting AMP carbamate was titrated against 1 M HCl to release captured gas, using Chittick apparatus. This practice substantiated the 50 mol % absorption limit of CO2 (wrt AMP) in AMP-RTIL blend. The procedure has been described in the previous work.26 However, no detectable evaporation loss was observed in case of emulsified DEA-RTIL mixture under the specified conditions, and CO2 capture resulted in theoretical maximum mass uptake (0.5 mol of CO2 per mole of DEA, in accordance with the mechanism proposed by Caplow8). CO2 capture studies at ambient conditions using DEA/[hmim][Tf2N] emulsion has been discussed in our previous study.25 Nature of CO2-Captured Products. Single crystal structure determination confirmed the formation of carbamate product, originating from chemical interaction of CO2 with amine; both (AMP-carbamate and DEA-carbamate) possessing monoclinic crystal system with P21/n and Pn space groups respectively (Figure 4; see also Supporting Information (SI)). Appearance of additional 13C NMR signals at 162.59 ppm and 162.57 ppm, regarding corresponding CO2-captured products (AMP-carbamate and DEA-carbamate, respectively), also validated the CO2 absorption exclusively through carbamate formation. 11445



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Figure 5. (a) FTIR spectra, and (b) 13C NMR spectra: AMP (fresh amine), AMPC (AMP-carbamate) and RAMP (regenerated AMP).

molar ratio. DEA interacts with CO2 preferably through zwitterion mechanism yielding carbamate product in either case, regarding aqueous DEA or DEA-RTIL blends. The detailed description of crystal structure determination of AMP-carbamate is provided in the SI file, whereas single crystal X-ray diffraction study of DEA-carbamate has been discussed in the previous work.25 Regeneration Ability. Regeneration was brought about by thermal decomposition of carbamates at 110 °C that resulted in quick release of CO2 and corresponding alkanolamine (AMP/ DEA). 13C NMR as well as ATR-FTIR analyses of fresh and

These outcomes were further complemented by FTIR analysis (Figures 5 and 6). As is observed in case of aqueous AMP based CO2 separation processes, AMP being a sterically hindered amine favors CO2 absorption via bicarbonate formation owing to water involvement that can guarantee higher sorption capacity. On the other hand, in present work, absence of water prohibited the formation of bicarbonate species, limiting the gas capture capacity to 50 mol % of CO2. Thermogravimetric isotherms as well as Chittick apparatus measurements also confirmed the same outcome as CO2 capture capacity never exceeded 0.5 CO2/amine 11446



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Figure 6. (a) FTIR spectra, and (b) 13C NMR spectra of DEA (fresh amine), DEAC (DEA-carbamate) and RDEA (regenerated DEA).

at 162.59 ppm and 162.57 ppm (Figures 5b and 6b) confirmed the CO2 absorption via AMP-carbamate and DEA-carbamate formation. Two series of carbon signals (compared to one series for corresponding fresh amine) in the range of 20−80 ppm, one originating from protonated amine and the other from carbamate moiety, also complemented the findings. Besides, the identical nature of NMR spectra of fresh and regenerated amines ruled out any probability of degradation occurrence at least after single absorption/desorption cycle. FTIR analysis (Figures 5a, 6a) too revealed the same outcome. Amine (AMP/DEA) Regeneration Behavior. Under N2 atmosphere, decomposition of AMP-carbamate commenced

regenerated amines demonstrated the excellent regeneration ability of both AMP and DEA. Theoretically, the probable mechanism might comprise the following reactions (eqs 9 and 10) responsible for CO2 liberation during heat treatment. Δ

RR′NCOO− → RR′N− + CO2

RR′N− + RR′NH 2+ → 2RR′NH

(9) (10)

13

The FTIR as well as C NMR spectra of fresh/regenerated amines and relevant carbamates are shown in Figures 5 and 6. The emergence of respective carbon signals in 13C NMR spectra 11447



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Figure 7. DSC/TG profiles of AMP-carbamate: Thermal behavior observed under N2 atmosphere at heating rate of 5 °C.

Figure 9. QMS monitoring of carbamates’ decomposition by measuring positive ion current m/z = 44 (CO2) under N2 atmosphere (100 mL/ min flow rate) at 5 °C/min heating rate.

Figure 8. DSC/TG curves of DEA-carbamate: Thermal behavior under N2 atmosphere, using heating rate of 5 °C/min.

carbamate absorption peaks above 70 and 50 °C respectively (Figures S4 and S5 in SI). However under 100% CO2 atmosphere, the beginning of decomposition was delayed significantly (now starting at ∼65 °C) regarding DEA-carbamate (Figure 10). While apparent mass loss, observed under N2 atmosphere in case of AMP-carbamate below 75 °C (decomposition onset temperature), appears to have been suppressed under CO2 cover. This trend probably emerged due to the presence of one of the reactants (CO2) in excess. Concerning AMP-carbamate, the CO2 atmosphere would also have helped revert some proportion of free amine (stemmed from hydrolytic activity during sample preparation) to carbamate thus curtailing the evaporation occurrence. The observations stated above indicate that using RTIL, in place of water, can act as a suitable medium for carbamate crystal growth thus allowing easy recovery of lower density CO2captured product. This not only can provide feasible opportunity to regenerate solely active species but also can promise milder regeneration conditions. From regeneration capabilities of AMP-/ DEA-carbamates, it is quite obvious that DEA-RTIL blends can help improve the process efficiency more successfully, regarding regeneration energy penalty in particular. From perspective of amine evaporation loss, DEA-RTIL recipe is undoubtedly better option compared to AMP-RTIL combination.

around 75 °C with CO2 liberation, accompanied by simultaneous evaporation of amine (Figure 7). Whereas, DEA-carbamate started decomposing at much lower temperature (∼55 °C) and the transition was completed at about 70 °C, as is evident from TG/ DSC plots in Figure 8. In case of TG profile of AMP-carbamate, the weight loss can be seen originating much before the decomposition onset temperature. AMP-carbamate, owing to its unstable nature in humid air,31 most probably underwent hydrolysis to some extent generating free amine during sample grinding/mounting process; the evaporation of which resulted in mass loss as appeared in TG plot prior to the commencement of carbamate decomposition. To detect CO2 release, QMS was coupled with TG. The QMS signals showed the evolution of CO2 above 70 °C in case of AMP-carbamate, and around 55 °C in case of DEA-carbamate (Figure 9); thus complementing the TG/DSC analyses outcomes. The temperature was increased at the rate of 5 °C/min under N2 (100 mL/min flow rate) and continued until the positive molecular ion current intensity, originating from CO2+ (m/z = 44), reached the initial levels. Quite prolonged release of CO2, as appears in ion current versus time plots (obtained via QMS), might be due to the foaming buildup as well as slow heat transfer at lower temperatures (above decomposition point). Variations in ion current intensity possibly were fallout of change in foaming makeup with temperature. The foaming phenomenon was also observed during ATR-FTIR analysis while studying regeneration behavior. Thermal decomposition temperatures of both AMP-carbamate and DEA-carbamate were also verified through temperatureprogrammed FTIR analysis, revealing the disappearance of

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IMPLICATIONS In case of alkanolamine based gas capture systems; better efficiency can be attained by avoiding energy wastage during regeneration by targeting the active species (responsible for CO2 capture) alone; and for this purpose incorporation of thermally stable RTIL can provide with the prospect of CO2-captured product (carbamate) precipitation and thereby easy separation. When compared to aqueous alkanolamine based processes, 11448



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Figure 10. TG profiles of carbamates: Thermal behavior under CO2 atmosphere, using heating rate of 5 °C/min. (4) Pires, J. C. M.; Martins, F. G.; Alvim-Ferraz, M. C. M.; Simões, M. Recent developments on carbon capture and storage: An overview. Chem. Eng. Res. Des. 2011, 89, 1446−1460. (5) Metz, B., Davidson, O., de Coninck, H., Loos, M., Meyer, L., Eds. IPCC Special Report on Carbon Dioxide Capture and Storage, Prepared by Working Group III of the Intergovernmental Panel on Climate Change; Cambridge University Press: New York, 2005. (6) Brennecke, J.; Gurkan, B. Ionic liquids for CO2 capture and emission reduction. J. Phys. Chem. Lett. 2010, 1, 3459−3464. (7) Kittel, J.; Fleury, E.; Vuillemin, B.; Gonzalez, S.; Ropital, F.; Oltra, R. Corrosion in alkanolamine used for acid gas removal: From natural gas processing to CO2 capture. Mater. Corros. 2012, 63, 223−230. (8) Caplow, M. Kinetics of carbamate formation and breakdown. J. Am. Chem. Soc. 1968, 90, 6795−6803. (9) Danckwerts, P. V. The reaction of CO2 with ethanolamines. Chem. Eng. Sci. 1979, 34, 443−446. (10) Pei, Z.; Yao, S.; Jianwen, W.; Wei, Z.; Qing, Y. Regeneration of 2amino-2-methyl-1-propanol used for carbon dioxide absorption. J. Environ. Sci. 2008, 20, 39−44. (11) Knudsen, J. N.; Jensen, J. N.; Vilhelmsen, P.-J.; Biede, O. Experience with CO2 capture from coal flue gas in pilot-scale: Testing of different amine solvents. Energy Procedia 2009, 1, 783−790. (12) Chi, S.; Rochelle, G. Oxidative Degradation of Monoethanolamine. Ind. Eng. Chem. Res. 2002, 41, 4178−4186. (13) Soosaiprakasam, I.; Veawab, A. Corrosion and polarization behavior of carbon steel in MEA-based CO2 capture process. Int. J. Greenhouse Gas Control 2008, 2, 553−562. (14) Hasib-ur-Rahman, M.; Siaj, M.; Larachi, F. Ionic liquids for CO2 captureDevelopment and progress. Chem. Eng. Process. 2010, 49, 313−322. (15) Anthony, J.; Anderson, J.; Maginn, E.; Brennecke, J. Anion effects on gas solubility in ionic liquids. J. Phys. Chem. B 2005, 109, 6366−6374. (16) Anderson, J.; Dixon, J.; Brennecke, J. Solubility of CO2, CH4, C2 H6 , C2H4, O2, and N2 in 1-Hexyl-3-methylpyridinium bis(trifluoromethylsulfonyl)imide: Comparison to other ionic liquids. Acc. Chem. Res. 2007, 40, 1208−1216. (17) Bara, J.; Carlisle, T.; Gabriel, C.; Camper, D.; Finotello, A.; Gin, D.; Noble, R. Guide to CO2 separations in imidazolium-based roomtemperature ionic liquids. Ind. Eng. Chem. Res. 2009, 48, 2739−2751. (18) Bara, J.; Camper, D.; Gin, D.; Noble, R. Room-temperature ionic liquids and composite materials: Platform technologies for CO2 capture. Acc. Chem. Res. 2010, 43, 152−159. (19) Yokozeki, A.; Shiflett, M. Separation of carbon dioxide and sulfur dioxide gases using room-temperature ionic liquid [hmim][Tf2N]. Energy Fuels 2009, 23, 4701−4708. (20) Kohl, A. L.; Nielsen, R. B. Gas Purification, 5th ed.; Gulf Publishing Company: Houston, TX, 1997. (21) Gui, X.; Tang, Z.; Fei, W. CO2 capture with physical solvent dimethyl carbonate at high pressures. J. Chem. Eng. Data 2010, 55, 3736−3741. (22) Langeroudi, E. G.; Kleitz, F.; Iliuta, M. C.; Larachi, F. Grafted amine/CO2 interactions in (gas−)liquid−solid adsorption/absorption equilibria. J. Phys. Chem. C 2009, 113, 21866−21876.

carbamate crystallization in alkanolamine-RTIL systems is not only meant to lessen the quantity required to regenerate but also can help narrow the gap between capture and regeneration temperatures. Besides, with this strategy we may well overcome the difficulties being faced regarding gas loading restraints (due to corrosion/degradation detriments) in current alkanolamine based industrial processes.13,32 In general, a secondary alkanolamine blended with pertinent RTIL can be a better pick for CO2 capture as is evident from lower thermal stability of DEA-carbamate compared to that of AMP-carbamate. Since bringing about regeneration at lower temperature can help decrease the magnitude of solvent degradation, future work will be focused on amine degradation studies using alkanolamineRTIL based CO2 capture processes. Moreover, measures/conditions will be optimized to minimize foaming as well as evaporation phenomena.

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ASSOCIATED CONTENT

S Supporting Information *

X-ray crystallographic file (CIF format), crystal structure data of AMP-carbamate and FTIR spectra of respective carbamates obtained at different temperatures. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*Tel.: (418) 656-2131 x3566; fax: (418) 656-5993; e-mail: faical. [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS Financial support from FL Canada Research Chair “Green processes for cleaner and sustainable energy” and the Discovery Grant to F. Larachi from the Natural Sciences and Engineering Research Council (NSERC) are gratefully acknowledged. Prof. Siaj is acknowledged for AMP single-crystal measurements.

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REFERENCES

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(23) Camper, D.; Bara, J. E.; Gin, D. L.; Noble, R. D. Roomtemperature ionic liquid-amine solutions: Tunable solvents for efficient and reversible capture of CO2. Ind. Eng. Chem. Res. 2008, 47, 8496− 8498. (24) Huang, Q.; Li, Y.; Jin, X.; Zhao, D.; Chen, G. Z. Chloride ion enhanced thermal stability of carbon dioxide captured by monoethanolamine in hydroxyl imidazolium based ionic liquids. Energy Environ. Sci. 2011, 4, 2125−2133. (25) Hasib-ur-Rahman, M.; Siaj, M.; Larachi, F. CO2 capture in alkanolamine/room-temperature ionic liquid emulsions: A viable approach with carbamate crystallization and curbed corrosion behavior. Int. J. Greenhouse Gas Control 2012, 6, 246−252. (26) Hasib-ur-Rahman, M.; Bouteldja, H.; Fongarland, P.; Siaj, M.; Larachi, F. Corrosion behavior of carbon steel in alkanolamine/roomtemperature ionic liquid based CO2 capture systems. Ind. Eng. Chem. Res. 2012, 51, 8711−8718. (27) Al-Ghawas, H. A.; Hagewlesche, D. P.; Rulz-Ibanez, G.; Sandall, O. C. Physicochemical properties important for carbon dioxide absorption in aqueous methyldiethanolamine. J. Chem. Eng. Data 1989, 34, 385−391. (28) Crovetto, R. Evaluation of solubility data of the system CO2-H2O from 273 K to the critical point of water. J. Phys. Chem. Ref. Data 1991, 20, 575−589. (29) Klepacova, K.; Huttenhuis, P. J. G.; Derks, P. W. J.; Versteeg, G. F. Vapor pressures of several commercially used alkanolamines. J. Chem. Eng. Data 2011, 56, 2242−2248. (30) Nguyen, T.; Hilliard, M.; Rochelle, G. T. Amine volatility in CO2 capture. Int. J. Greenh. Gas Control 2010, 4, 707−715. (31) Jo, E.; Jhon, Y. H.; Choi, S. B.; Shim, J.-G.; Kim, J.-H.; Lee, J. H.; Lee, I.-Y.; Jang, K.-R.; Kim, J. Crystal structure and electronic properties of 2-amino-2-methyl-1-propanol (AMP) carbamate. Chem. Commun. 2010, 46, 9158−9160. (32) Rochelle, G. T. Thermal degradation of amines for CO2 capture. Curr. Opin. Chem. Eng. 2012, 1, 183−190.

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CO2 Capture in Alkanolamine-RTIL Blends via Carbamate

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