• carbonium pseudo ionic liquid;
  • softening hard acid;
  • Lewis acid;
  • complexation;
  • extractive desulfurization

Lewis hard acid AlCl3 was softened by some butyl halides forming highly polarized liquids. These liquids are similar to the ionic liquids (ILs) with metallic complex anion and varying composition, and thus termed here as carbonium pseudo ILs (CPILs). The CPILs, that is, t-C4H9Cl-AlCl3, n-C4H9Cl-AlCl3, and t-C4H9Br-AlCl3, show very strong desulfurization activity for various thiophenic compounds like 3-methylthiophene, benzothiophene, and dibenzothiophene. The above thiophenic compounds can be removed completely from model oils within 20 min by a very small amount of CPILs reactive extractant. The extractive mechanism is deemed as an acid–base complexation along with alkylation of the thiophenic compounds, and the Lewis acidity comes from both carbonium ion (borderline acid) and the dissolved AlCl3 (hard acid). The t-C4H9Cl-AlCl3 shows good selectivity for three thiophenic compounds even in toluene-containing system. Further, some CPILs show satisfactory desulfurization performance for the model gasoline that mimics the composition of real one. © 2012 American Institute of Chemical Engineers AIChE J, 59: 948–958, 2013