Molecular dynamics studies of straight-chain alkanes diffusion in SiO2 ceramic versus Bosanquet formula

Molecular Dynamics (MD) simulations were applied to calculate self-diffusion coefficients (Di ) and heats of adsorption for ethane, propane and n-butane. The simulations were done in temperature range of 300-525 K for various concentrations inside the pores of silicalite type zeolite. The calculated values of self-diffusion coefficients and heats of adsorption resulted from the current work were in better agreement with experimentally estimated values found in literature than those resulted from MD simulations reported by other authors.  For instance, at temperature of 300K and loading of 5 molecules/unit cell, self-diffusion coefficients of ,  and  cm2/s were calculated for C2H6, C3H8 and n-C4H10 respectively comparing to experimentally reported values of ,  and  cm2/s. At the same conditions, adsorption energies of 9.2, 11.48, and 13.66 kcal/mol were calculated for ethane, propane, and n-butane respectively, while the experimentally reported values found to be 6.93, 9.7 and 12.7 kcal/mol. Considerable differences between MD simulation calculated values of  and values obtained by well-known Bosanquet formula were detected which were mainly attributed to the error of Knudson formula in the case of significant adsorption, i.e. when the values of molecule–wall interactions are not negligible. The MD simulations showed that the diffusivities decrease when loadings increase and the heats of adsorption increase by molecular weights of hydrocarbons for all the adsorbates studied.