(134g) First Principles and Classical Simulations of Ionic Liquids for Carbon Dioxide Capture

Ionic liquids (IL) are promising materials for CO₂ capture due to their thermal and chemical stability. ILs have lower regeneration heat requirements compared with aqueous amine solutions because of their lower CO₂ absorption enthalpy (physical absorption). In addition, ILs have no measurable vapor pressure, and hence will not emit any volatile organic compounds. However, physisorption is not considered to be a viable approach, because the solubility and selectivity of CO₂ in ILs through physical absorption are too low at flue gas conditions. Functionalized ILs capable of specific reactions or interactions with CO₂ are designed to address the issues of solubility and selectivity at low partial pressures of CO₂. We are exploring ILs that can capture CO₂ through chemical interactions. Classical force fields can model the physical interaction between CO₂ and ILs fairly accurately, but they are not typically able to describe the bond breaking/forming events. Therefore, it is necessary to develop a new force field that can properly characterize the chemical interactions. ReaxFF is a very successful formalism for modeling chemical as well as physical interactions with an empirical approach. We are studying the IL [P(C₄)₄][Gly] that has the potential to chemically react with CO₂. Our aim is to develop accurate ReaxFF parameters to allow large-scale simulations of the thermodynamics and transport properties of CO₂/[P(C₄)₄][Gly] mixtures which likely involve chemical reactions. We use density functional theory (DFT) augmented with the van der Waals (vdW) interactions to explore the chemical and physical interactions between CO₂ and the functional group, [Gly]^-. Through first principles molecular dynamics, we have found there are different interaction sites for CO₂/[Gly]^-. One of these can be properly described by chemical binding, while another site could be classified as a quasi-chemical interaction. We also found that vdW interactions are important in determining the binding energies. We obtained several energy profiles along proposed reaction coordinates from our DFT calculations. We have also tested preliminary parameterizations of ReaxFF that are based on similar systems and have tested the validity of the parameterization against our DFT calculations.