Diffusivity of Propylene in One-Dimensional Medium-Pore Zeolites
Zainab A. Alaithan, N. M. Harrison, Germán Sastre
Abstract
One-dimensional medium-pore zeolites are promising catalysts for propylene production from naphtha cracking due to their high selectivity. However, fast deactivation due to pore mouth blockage is preventing these catalysts from being widely used in commercial applications. In this study, we used molecular dynamics simulations to investigate the diffusion of propylene in three one-dimensional medium-pore aluminosilicate frameworks (ZSM-23, ZSM-22, ZSM-48) and also in a two-dimensional pore zeolite (ZSM-5) for the sake of comparison. The influence of several factors such as loading, temperature, pore diameter, and Al/H distribution were also investigated. Our results show that at high loading and high temperature, the diffusion of propylene deviates from the Arrhenius regime, and diffusivity remains constant with temperature due to the dominant effect of propylene-propylene interactions. Also, when loadings are compared “per accessible volume”, the self-diffusivity in one-dimensional pore zeolites is similar to that of two-dimensional pore zeolites. Finally, Al/H distributions do have an influence on propylene diffusion when H-protrusions into the channel contribute to strengthening proton-propylene interactions.