(462g) Solubility and Diffusivity of Ammonia in Aprotic and Protic Ionic Liquids

Turnaoglu, T., University of Kansas
Shiflett, M. B., University of Kansas
Ionic liquids (ILs) are salts composed of discrete cations and anions with melting points below 100 °C and many are liquid at ambient temperature. Due to their negligible vapor pressure, nonflammability, relatively high thermal stability and excellent solvation potential, ILs have drawn broad attention in various applications including catalysis, gas separation, and heating/cooling cycles. Our motivation in this study is to replace water (high vapor pressure absorbent) with a feasible IL (negligible vapor pressure absorbent) in the ammonia-water absorption refrigeration cycle to reduce or eliminate separation costs. Therefore, we are thoroughly investigating the thermodynamic and kinetic properties of ammonia in aprotic ionic liquids (AILs) and protic ionic liquids (PILs). The major difference between AILs and PILs is that PILs have a proton available for hydrogen bonding due to the proton transfer from the acid to the base during formation. Therefore, PILs can be used to create hydrogen bonded network for ammonia which can result in exceptionally high ammonia sorption. The Vapor-Liquid-Equilibria (VLE) measurements were performed using advanced, fully automated and highly accurate magnetically coupled gravimetric microbalance (XEMIS, Hiden,Inc). Pressure-temperature-composition (PTx) data for NH3 in ILs at isothermal conditions up to 7 bar was correlated using the Peng-Robinson equation of state. In addition to thermodynamic analysis, to understand time dependent behavior of ammonia with ionic liquids, we applied a simplified diffusion model to ammonia absorption in ILs and ammonia desorption from NH3-IL mixtures. Findings on thermodynamic and kinetic behavior of NH3 and ILs in this study will contribute to the understanding of the interaction of ammonia and ionic liquids.