Insight into the catalytic behavior of ionic liquids and deactivation suppression technique in naphthalene alkylation

Lewis acidic ionic liquids as catalysts for alkylation reactions exhibited the potential for industrial application. Herein, the catalytic behavior of AlCl3-based ionic liquids with four organic ammonium salts was studied in the alkylation of naphthalene with n-octene for production of lubricating base oil, with special focus on the deactivation and recovery of ionic liquid. The Et3NHCl-AlCl3 ionic liquid exhibited better catalytic performance than others due to its stronger interaction with naphthalene, as evidenced by the adsorption test of naphthalene over ionic liquids. To understand the deactivation mechanism, the deactivated catalysts were extensively characterized by FT-IR and UV–vis. The protonation effect of ionic liquids on polyalkylation products in the presence of HCl was found to aggravate the deactivation of ionic liquid. The negative effect is easily reversed by the decompression treatment on the reaction system before catalyst recovery, this method markedly enhanced the cycling durability of ionic liquids for industrial application.