ADSORPTION EQUILIBRIA OF METHANE AND TETRAFLUOROMETHANE AND THEIR BINARY-MIXTURES ON SILICALITE

Binary mixture adsorption isotherms of CH4 and CF4 on silicalite have been measured for different constant gas compositions at 298 K in the pressure range up to 1.7 MPa using a high-pressure microbalance. Addit ionally, the single-component adsorption isotherms were determined at 273, 298 and 323 K in the same pressure range. The gravimetric method proposed by Van Ness has been applied to obtain the compositions of th e adsorbed phase as a function of gas-phase composition and pressure. The experimental mixture adsorption equilibria are compared with predi ctions of the ideal adsorbed solution (IAS) theory and the multisite L angmuir (MSL) model based on the single-component adsorption isotherms only. Despite the fact that the molecules of CH4 and CF4 differ great ly in size, ideal behaviour of their adsorbate mixtures on silicalite is found over a large pressure range. This result is due to the high s urface homogeneity as well as the channel-like pore geometry of silica lite, where interactions between the adsorbate molecules can only occu r to a small extent. Thus, both the IAS theory and the MSL model achie ve a good description of the experimental data.