ADSORPTION OF CH4-CF4 MIXTURES IN SILICALITE - SIMULATION, EXPERIMENT, AND THEORY

Grand canonical Monte Carlo (GCMC) simulations of binary Lennard-Jones mixtures in the zeolite silicalite have been used to predict the adso rption of CH4 and CF4 mixtures as a function of gas phase composition, total pressure, and temperature. For single components and mixtures, predictions of adsorption isotherms and isosteric heats are in good ag reement with experiment at room temperature. Within the experimental p ressure range of 0 to 17 bar, the mixtures are well described by the i deal adsorbed solution (IAS) theory. For very high loading, deviations from IAS theory appear. The configurations generated in the simulatio n were used to calculate sorbate-zeolite interaction energy distributi ons for different types of siting locations within the zeolite pores. These distributions display a pore shape related energetic heterogenei ty in different regions of silicalite. Near saturation at a total load ing of 12 molecules per unit cell, the shape of the observed energy di stribution is relatively independent of the composition in the pore. N evertheless, the energetic heterogeneity is responsible for a mild seg regation in the adsorbed mixtures, with methane adsorbed preferentiall y in the silicalite zigzag channels and CF4 preferentially in the stra ight channels.