Diffusion and Adsorption of Benzene and Propylene in MFI, MWW and BEA Zeolites: Molecular Dynamics and Grand Canonical Monte Carlo Simulations
摘要
The diffusion and adsorption behaviors of benzene and propylene in zeolites MFI, MWW and BEA have been studied by molecular dynamics(MD) and grand canonical Monte Carlo(GCMC) simulations. The diffusion coef- ficients of benzene and propylene in MFI, MWW and BEA zeolites were calculated by simulating the mean-square displacements(MSD) at 298 and 600 K. Benzene and propylene showed the different adsorption rules in the channels of the three zeolites. For propylene, the molecular loadings decreased in the order: BEA(linear channel)>BEA (tortuous channel)>MFI(linear channel)>MWW(12-membered rings, 12MR channel)>MFI(tortuous channel)>MWW (10-membered rings, 10MR channel); for benzene, the molecular loadings decreased in the order: BEA(linear chan- nel)>BEA(tortuous channel)>MWW(12MR channel)>MFI(linear channel)>MFI(tortuous channel)>MWW(10MR channel). Besides, the adsorption isotherms of benzene and propylene in the three zeolites at 298 and 443 K were si- mulated. The results show that the different factors influenced the molecular adsorption at various temperatures and pressures, leading to the different rules for the adsorption of benzene and propylene molecules in the zeolites. At a low pressure, the unfavorable energy would make the loadings of propylene lower than those of benzene. When pressure was higher than 0.25 kPa, the adsorption of benzene in MFI would nearly reach saturation.