The lighter oils originating from the lower parts of the distillation column, after passing through Hydrotreaters and the Fluid Catalytic Cracker (FCC), produce low-molecular-weight alkenes (butenes (C4), pentenes (C5), propene (C3H6)) and also isobutene (C4H10). The acid alkylation process converts these streams into alkylate, a high octane and clean burning gasoline blending component. Depending on the acid used, the process is called either SAA (Sulfuric Acid Alkylation) or HFA (Hydrofluoric Acid Alkylation).