Insights on the Solubility of CO 2 in 1‑Ethyl-3-methylimidazolium Bis(trifluoromethylsulfonyl)imide from the Microscopic Point of View Tuanan C. Lourenc ̧ o, † Mariny F. C. Coelho, † Teodorico C. Ramalho, ‡ David van der Spoel, § and Luciano T. Costa †, * † Instituto de Química, Universidade Federal de Alfenas, Rua Gabriel Monteiro da Silva, 700 Alfenas - MGCEP:37130-000, Brazil ‡ Departamento de Química, Universidade Federal de Lavras, Caixa Postal 3037, Lavras-MG, Brazil § Department of Cell and Molecular Biology, Uppsala University, Box 596, SE-75124 Uppsala, Sweden * S Supporting Information ABSTRACT: Emissions of greenhouse gases due to human activities have been well documented as well as the effects on global warming resulting from it. Efforts to reduce greenhouse gases at the source are crucial to curb climate change, but due to insignificant economic incentives to reduce usage of fossil fuels, not a lot of progress has been made by this route. This necessitates additional measures to reduce the occurrence of greenhouse gases in the atmosphere. Here we used theoretical methods to study the solubility of carbon dioxide in ionic liquids (ILs) since sequestration of CO 2 in ILs has been proposed as a possible technology for reducing the emissions of CO 2 to the atmosphere. Ionic liquids form a class of solvents with melting temperatures below 100 °C and, due to very low vapor pressures, which are not volatile. We have performed molecular dynamics (MD) simulations of 1-ethyl-3-methylimidazolium (C 2 mim) bis(trifluoromethylsulfonyl)imide (Tf 2 N) and its mixtures with carbon dioxide in order to investigate the CO 2 concentration effect on the CO 2 -cation and CO 2 -anion interactions. A systematic investigation of CO 2 concentration effects on resulting equilibrium liquid structure, and the local environment of the ions is provided. The Quantum Theory of Atoms in Molecules (QTAIM) was used to determine the interaction energy for CO 2 -cation and CO 2 -anion complexes from uncorrelated structures derived from MD simulations. A spatial distribution function analysis demonstrates the specific interactions between CO 2 and the ionic liquid. Our findings indicate that the total volume of the system increases with the CO 2 concentration, with a molar volume of CO 2 of about 0.038 L/mol, corresponding to liquid CO 2 under a pressure of 100 bar. In other words, the IL effectively pressurizes the CO 2 inside its matrix. The thermodynamics of CO 2 solvation in C2 min-Tf 2 N were computed using free energy techniques, and the solubility of CO 2 is found to be higher in this IL (-3.7 ± 1 kcal/mol) than in water (+0.2 kJ/ mol), predominantly due to anion-CO 2 interactions. ■ INTRODUCTION The carbon dioxide (CO 2 ) concentration in the atmosphere continues to increase, to a large extent due to anthropogenic sources like industrial activities, automotive vehicles, and forest- logging. Scott and co-workers noted in a recent review paper that a strong policy to implement carbon capture technologies is overdue, 1 and Ehrlich and Ehrlich even pose the question as to whether an impending collapse of civilization can be prevented. 2 Clearly, a combination of strong policy measures and technological innovations is needed, but a review by Li et al. shows that conventional tools are not efficient to remove greenhouse gases such as CO 2 and that new solutions are needed. 3 The authors highlighted that although carbon dioxide is the main source of climate change, it is also important for generating chemical compounds through synthesis. This suggests that by combining CO 2 capture with production of new compounds, an attractive route for realizing carbon capture may finally be in sight. 1,3 A number of experimental 4-6 and theoretical 7-9 studies have tackled the problem of CO 2 capture technology. 10,11 Initially, Ionic Liquids (ILs) were examined for use as low volatility “green” solvents, but other favorable properties such as thermal stability, the wide range of electrochemical windows, good ionic conductivity, low flammability and corrosivity, and very low vapor pressure 12 have stimulated researchers to consider ILs as multipurpose advanced materials. 13 ILs have a molecular architecture that allows one to change atoms or functional groups in order to modulate their properties, enabling the Received: January 22, 2013 Revised: May 24, 2013 Accepted: May 28, 2013 Published: May 29, 2013 Article pubs.acs.org/est © 2013 American Chemical Society 7421 dx.doi.org/10.1021/es4020986 | Environ. Sci. Technol. 2013, 47, 7421-7429