Adsorption equilibria of methane and tetrafluoromethane and their binary mixtures on silicalite

Abstract

Binary mixture adsorption isotherms of CH ₄ and CF ₄ 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. Additionally, 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 the adsorbed phase as a function of gas-phase composition and pressure. The experimental mixture adsorption equilibria are compared with predictions of the ideal adsorbed solution (IAS) theory and the multisite Langmuir (MSL) model based on the single-component adsorption isotherms only. Despite the fact that the molecules of CH ₄ and CF ₄ differ greatly in size, ideal behaviour of their adsorbate mixtures on silicalite is found over a large pressure range. This result is due to the high surface homogeneity as well as the channel-like pore geometry of silicalite, where interactions between the adsorbate molecules can only occur to a small extent. Thus, both the IAS theory and the MSL model achieve a good description of the experimental data.