Molecular Dynamics Insights into the Adsorption and Diffusion of Oil Shale Secondary Lysates in SBA-15 with Different Si/Al Ratios

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