Diffusivity of Propylene in One-Dimensional Medium-Pore Zeolites

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.