Characterization and Hydrogenation Removal of Acid-Soluble Oil in Ionic Liquid Catalysts for Isobutane Alkylation

Acid-soluble oil (ASO) was produced during isobutane alkylation catalyzed by chloroaluminate ionic liquids (CAILs). However, the ASO composition characterizations and deactivated CAIL regeneration pathway were not clarified. In this work, a series of characterizations (elemental analysis and infrared, ultraviolet, and mass spectroscopy) were performed to reveal the ASO composition. The result showed that ASO contained numerous conjugated cycloolefins with various alkyl substituents and a few O1–O5 compounds. The activity index (AI) value of fresh CAILs was 1.74 and decreased to 1.18 with the addition of 9.09 wt % ASO because the [Al2Cl7]− anion in CAILs was complexed by C═C and C═O bonds in ASO. The hydrogenation regeneration of deactivated CAILs on the Pd/C catalyst was studied. The AI value of regenerated CAILs increased to 1.45 because unsaturated bonds in ASO were hydrogenated to saturation. Recovery of unsaturated hydrocarbons followed the order benzene > 1-methylcyclopentene > pentamethylcyclopentadiene. This work demonstrated that low ASO recovery was attributed to the partial occupation of the π-electron of unsaturated bonds by the [Al2Cl7]− anion.