A molecular dynamics study of the diffusion of a hydrocarbon in AIPO 4-5 molecular sieve

Abstract

In this paper a computational study of the ethane diffusion in AIPO₄-5 molecular sieve by classical molecular dynamics techniques is
presented. Calculations were performed at different temperatures and loading of ethane  molecules per AIPO₄-5 framework conditions in the calculations were analyzed. According to the results of the simulations the molecular diffusion of ethane in a defect-free AIPO₄-5 crystal structure occurs via a normal regime and not as single-file diffusion in agreement with the quasi-elastic neutron scattering (QENS) experiments. The simulated activation energy for a particular loading of the ethane molecules is calculated . Moreover, the calculations performed in dynamical conditions show the influence of the framework vibrations on the molecular diffusion. Particulary, the framework vibrations can be a factor to take into account when the molecular dimensions are close to the channel diameter. However, according to our calculations this fact does not produce a qualitative change in the diffusion regime of the ethane molecules (with a molecular diameter ~3 .8 A) in the 12-member channel of the AIPO₄-5 unit cell.