Maximizing octane savings in a catalytic distillation unit via a dual reactor polishing system

Abstract

Low sulfur gasoline blend stock is produced by a hydrodesulfurization process including at least two hydrodesulfurization reactors with hydrogen feeds and two finishing reactors arranged where the first polishing reactor converts both thiophenic compounds and mercaptans to hydrogen sulfide and hydrocarbons and the second polishing reactor uses a catalyst that has much less thiophenic conversion activity but is operated at a higher temperature to more substantially reduce the sulfur content of the gasoline present in the form of mercaptans. As the conversion of thiophenes to hydrogen sulfide is correlated to reducing octane number, using a second polishing reactor that has little activity for thiophene conversion also protects the high-octane species in the gasoline thereby minimizing octane loss while reducing total sulfur content to acceptable levels. The sulfur left in the gasoline is biased toward higher thiophene content and away from mercaptan content.