| Industrial processes, land use, and energy use, all release carbon dioxide (CO2) into the atmosphere the majority result from energy production and consumption. The consequences of an increasing global temperature include rising sea levels, flooding, drought, changing patterns of precipitation, and increases in infectious diseases. As populations and economies continue to grow and develop, CO2 emissions will continue to increase, dictating the future climate (warming) changes.Room-temperature ionic liquids (RTILs) are molten organic salts at ambient temperatures that possess a number of desirable properties such as, thermal and chemical stability, negligible vapor pressures, high CO2 solubility, and tunable chemistry. The versatile functionality of RTILs allows for their usage for gas separations as a bulk fluid, a supported liquid membrane, or as polymerized RTIL solid membrane. Gas separations in these materials are driven by large solubility differences between gases, rather than by diffusion differences. Therefore, it is important to investigate gas transport properties and selectivity in RTILs to better understand their gas separation potential.This dissertation research is focused on characterizing gas solubility, diffusivity, permeability, and ideal selectivities in bulk fluid RTILs. The results will be used to develop predictive capabilities for the design of membranes for specific gas separation applications. First, the effect of temperature on gas solubility in pure RTILs was investigated. A regular solution theory (RST) model was used to describe the gas solubility results at all temperatures. Second, the RST model was successfully extended to describe the gas solubility behaviors in mixtures of two RTILs and in benzyl-functionalized RTILs. A group contribution method approach was also applied to the functionalized RTILs studies. Oxygen transport properties in various RTILs were examined experimentally and theoretically. Next, density, viscosity, and conductivity measurements in pyrrolidinium and imidazolium-based RTILs were completed as function of temperature. Lastly, gas transport properties in both bulk fluid RTILs and polymerized solid membrane RTILs with analogous chemical structures were compared. Collectively, this research is aimed at characterizing physical properties of RTILs, characterizing gas transport properties in RTILs, and ultimately developing predictive criteria for RTIL membrane design for gas separation applications. |
