Understanding the Promotion of Solid Acid-Catalyzed Isobutane Alkylation with Butene by Hydrophilic/Hydrophobic Surface Modification

Abstract

The adsorption and diffusion behaviors of isobutane, 2-butene, and trimethylpentane (TMP) on the silica surface with various surface groups were investigated using molecular dynamics (MD) simulations in this work. A significant concentration gradient and density enhancement of isobutane and butene were observed on the silica surface due to their strong interaction with surface groups. The hydrophobic modification of the silica surface can improve the adsorption ratio of isoparaffin to olefins (I/O), further inhibiting the catalyst deactivation. However, the hydrophilic modification will increase the surface polarity and the interaction between propanesulfonic acid groups and butene, which is not beneficial for the alkylation reaction. The diffusion rate of molecules is affected by their size and follows the order of 2-butene > isobutane > TMP, while the difference between isobutane and 2-butene is the smallest in the hydrophobically modified system. Both surface modification and the presence of the C8 product will inhibit the diffusion and update rate of C4 hydrocarbons, while the increase in temperature will promote their diffusion. Hopefully, this work would bring deep insights into the countermeasures of solid acid deactivation.