Diffusion of a hydrocarbon mixture in a one-dimensional zeolite channel: an exclusion model approach

TL;DR

This study models hydrocarbon diffusion in zeolite channels using an exclusion lattice gas approach, explaining experimental desorption profiles and highlighting limitations of single-file assumptions.

Contribution

It introduces a simple lattice gas model with Monte Carlo simulations to analyze hydrocarbon diffusion in zeolites, incorporating temperature-dependent diffusion coefficients.

Findings

Model reproduces key features of experimental desorption profiles.

Cannot fully explain the higher propane current near the desorption peak.

Violation of strict single-file behavior affects diffusion dynamics.

Abstract

Zeolite channels can be used as effective hydrocarbon traps. Earlier experiments (Czaplewski {\sl et al.}, 2002) show that the presence of large aromatic molecules (toluene) block the diffusion of light hydrocarbon molecules (propane) inside the narrow pore of a zeolite sample. As a result, the desorption temperature of propane is significantly higher in the binary mixture than in the single component case. In order to obtain further insight into these results, we use a simple lattice gas model of diffusion of hard-core particles to describe the diffusive transport of two species of molecules in a one-dimensional zeolite channel. Our dynamical Monte Carlo simulations show that taking into account an Arrhenius dependence of the single molecule diffusion coefficient on temperature, one can explain many significant features of the temperature programmed desorption profile observed in experiments. However, on a closer comparison of the experimental curve and our simulation data, we find that it is not possible to reproduce the higher propane current than toluene current near the desorption peak seen in experiment. We argue that this is caused by a violation of strict single-file behavior.