Comparison Study on the Adsorption of CFC-115 and HFC-125 on Activated Carbon and Silicalite-1

The adsorption isotherms of CFC-115 (1-chloro-1,1,2,2,2-pentafluoroethane) and HFC-125 (1,1,1,2,2-pentafluoroethane) on Vruf activated carbon (Calgon Carbon Corp.; brand code, VRU-F) and silicalite-1 have been accurately measured at pressures up to 120 kPa and temperatures ranging from 273 to 348 K. The Toth or dual-site Langmuir (DSL) model appropriately describes the equilibrium data for the adsorptives CFC-115 and HFC-125 on Vruf carbon or silicalite-1, respectively. Because HFC-125 molecule has a higher packing efficiency in the pores of Vruf carbon, its saturation capacity extracted by the Toth model is higher than that for CFC-115. For CFC-115, a kink in the isotherm on silicalite-1 is observed at about 4 molecules (unit cell of silicalite-1 and the measured isotherms of CFC-115 for the first time show a second-step adsorption at loadings over 4 molecules (unit cell)(-1). This is ascribed to a large difference in the adsorption entropy between the molecular locations in the intersections and in the channels. The DSL model with fixed saturation capacities describes this behavior well. The mixture adsorption isotherms predicted by the ideal adsorbed solution theory show that both adsorbents could be industrially applicable in the separation of CFC-115 and HFC-125.