Molecular Dynamics\nInsights into the Adsorption and\nDiffusion of Oil Shale Secondary Lysates in SBA-15 with Different\nSi/Al Ratios

As a critical aspect of catalytic processes, diffusion\nis indispensable\nfor understanding the mechanism of catalytic conversion. Herein, asphalt,\nmethane, and heptane were selected to represent the secondary pyrolysis\nreactants and products of oil shale, respectively. A molecular dynamics\nsimulation method was employed to investigate the adsorption and diffusion\nof oil shale secondary lysates in SBA-15 with different Si/Al ratios.\nThe results indicate that the diffusion coefficients of asphalt and\nits subfractions do not follow a linear relationship with increasing\naluminum content, revealing an optimal Si/Al ratio. Specifically,\nAl-SBA-15 zeolites with Si/Al ratios of 5 or 7 enhance the diffusion\nof asphalt and its subfractions. Conversely, the zeolite with a Si/Al\nratio of 4, despite having the highest aluminum content, does not\nfavor diffusion. Furthermore, aluminum content has minimal impact\non the isothermal adsorption of methane and heptane, but Al-SBA-15\nwith a Si/Al ratio of 5 facilitates better flow and diffusion of shale\noil and gas. Methane diffused ∼3-times faster than heptane,\nwith the diffusion coefficients being primarily influenced by the\nmolecular size. These findings provide crucial data for understanding\nthe mechanism of secondary cracking of oil shale within Al-SBA-15.