Gas Solubilities in Ionic Liquids: Experimental Measurements and Applications

Solvents play an extremely important role in many industrial processes, acting as a media for chemical reactions or for extraction of products. Typically, these solvents are volatile organic compounds or VOCs. As the VOCs volatilize, the risk of human exposure through inhalation is increased. VOCs have also been found to increase ozone depletion and smog formation. Therefore, it is important to find other solvents that still meet the needs of industry while limiting the environmental and health risks. Room temperature ionic liquids (ILs) have recently been getting attention as potential environmentally benign or 'green' solvents. Ionic liquids, organic salts that are liquids in their pure states at ambient conditions, have many properties that are similar to conventional organic solvents. But, many ILs also have the unique characteristic in that they exhibit a vanishingly low vapor pressure. This negligible volatility eliminates many of the concerns associated with traditional organic solvents by decreasing the risk of worker exposure and the loss of solvent to the atmosphere. The main objective of this research is to determine thermodynamic/phase behavior properties by studying the phase behavior of the ionic liquids with various gases and liquids to further develop the relationships between these properties and the molecular structure of these ionic liquids. Knowledge of these properties is necessary prior to design and development of industrially relevant processes using ILs. This work explores the solubility and associated thermodynamic properties, such as Henry's law constants, and enthalpies and entropies of absorption, of a variety of gases in various ionic liquids, mainly those with 1-n-butyl-3-methylimidazolium as the cation and [PF6], [BF4], and [Tf2N] as the anions. The gases considered range from simple nonpolar compounds to more complex polar gases capable of hydrogen bonding. Water vapor, carbon dioxide, and nitrous oxide show the strongest interactions with the ionic liquids, whereas gases like N2, O2 and Ar are only sparingly soluble. This work also shows ionic liquids have potential for use as a gas separation medium.