Sorption of binary gas mixtures in zeolites

Abstract

The adsorption of pure CO2 and N2 gases, and their mixtures have been determined on a very high silica form of the zeolite ZSM-5 using a newly developed isosteric technique. Unlike more traditional methods, this method allows one to measure mixture isotherms at fixed sorbed phase composition. The shape of the mixture isotherms and the isosteric heats of sorption for the mixture have been identified as functions of the equilibrium gas phase composition, which itself is a temperature dependent function of the sorbed phase composition. None of the isotherms approached saturation at the temperatures and pressures used. The ratio of Henry's constants for the two pure gases gives a reasonable estimate of the separation factor measured experimentally. Selective sorption of CO2 is marked even at 70°C. Binary mixture sorption isotherms predicted from pure gas data using the ideal adsorbed solution (IAS) theory, are shown to be in close agreement with the experimental data.