Probing interfacial behaviors of Brønsted acidic ionic liquids improved isobutane alkylation with C4 olefin catalyzed by sulfuric acid

Abstract

The interfacial microenvironments between catalysts and C4 hydrocarbons for the isobutane alkylation is of vital importance to producing high-quality alkylate. In the present work, the interfacial properties between Brønsted acidic ionic liquids (BILs)/H2SO4 and C4 mixtures, as well as between the cationic and anionic surfactants/H2SO4 and C4 mixtures were investigated using molecular dynamic (MD) simulations, in which BILs share different alkyl chain length on cations with or without a sulfonic acid group. It indicated both BILs and surfactants can enhance the H2SO4/C4 reactants interfacial properties and facilitate C4 reactants dissolution, contributing to a better catalytic performance. The enhancement of the interfacial properties can be ascribed into the stronger density enrichment and perpendicular behaviors of the longer alkyl chains at the interface. Compared to non-SFILs, sulfonic-acid-functionalized Brønsted acidic ionic liquids (SFILs) can facilitate a higher dissolution of isobutane in both bulk and interfacial regions, but result in a lower interfacial diffusion. In addition, the much stronger interfacial enrichment of surfactants without mixing with H2SO4 leads to a worse catalytic performance than BILs. However, the better mixing between BILs and H2SO4 leading to better catalytic performance suggests the important role of the BILs acting as phase transfer catalyst for the H2SO4-catalyzed alkylation.