Exact statistical mechanical one-dimensional lattice model of alkane binary mixture adsorption in zeolites and comparision with Monte-Carlo simulations

Adsorption isotherms obtained by Monte-Carlo simulation for ethane–methane mixtures in the zeolite silicalite show a highly unusual structure with a shoulder at low coverage and adsorption preference reversal at high pressures whose interpretation is uncertain. To understand this behaviour an exact calculation of the statistical mechanics of a lattice model of alkane mixture adsorption in zeolites has been undertaken. The lattice model reproduces all of the novel features of the Monte-Carlo isotherms, allowing us to infer that these unusual characteristics arise from a combination of molecular reorientation of ethane molecules, and displacement of ethane by methane at higher pressures.