Ionic liquids (ILs) with fluorinated anions can solubilize significant quantities of refrigerant gases. Previous studies by our research group indicate that the relative positions of the hydrogen atom and surrounding substituents (H, F, C) can significantly impact the solubility of hydrofluorocarbon (HFC) solute molecules in ionic liquids. In this presentation, we will investigate the role of atom substitution on the solubility of a series of difluoromethane molecules (CHF2-X) as a function of temperature and pressure in ionic liquids. Gas solubility and diffusion coefficient measurements, obtained using a state of the art Hiden gravimetric microbalance, will demonstrate the macroscopic phase behavior and transport properties of the hydrofluorocarbon – ionic liquid systems. This presentation will additionally discuss how these fundamental measurements can be used to design gas separation processes.