Sorbate/sorbent phase transition during adsorption of p‐xylene in silicalite

An analytically solvable lattice model was used to study the difference in the physics of p‐xylene adsorption in ORTHO and PARA phases of silicalite. The model predicts that a phase transition of p‐xylene in the pore space does not necessarily require a silicalite‐phase transition. Conditions for the sorbate‐phase transition are identified. The sign of the sorbate‐sorbate interactions is critical to sorbate‐phase transition. It is suggested that although the sorbate‐ and sorbent‐phase transitions can be distinct events, there is strong coupling between the two. It is reasonable to suppose that the fluid‐phase change may drive the zeolite phase change. Finally, this equilibrium study suggests the possibility of hysteresis at higher coverages depending on the kinetics of adsorption.