New sorbents for desulfurization by π-complexation: Thiophene/benzene adsorption

New sorbents for the desulfurization of liquid fuels were developed using π-complexation. Vaporphase adsorption isotherms were investigated to understand the interaction between benzene/ thiophene and various kinds of sorbents, including Ag-Y, Cu-Y, Na-Y, H-USY, Na-ZSM-5, activated carbon, and modified activated alumina. Compared to Na-Y, Cu-Y and Ag-Y adsorbed significantly larger amounts of both thiophene and benzene at low pressures, as a result of π-complexation with Cu⁺ and Ag⁺. Molecular orbital calculations confirmed that the relative strengths of π-complexation lie in the order thiophene > benzene and Cu⁺ > Ag⁺. The experimental heats of adsorption for π-complexation are in excellent agreement with theoretical molecular orbital predictions. Na-ZSM-5 and activated carbon could also adsorb small amounts of thiophene and benzene at low pressures. The sorbent capacities for thiophene at the low pressure of 2.3 x 10^-5 atm were 0.92 molecule/Cu⁺ and 0.42 molecule/Ag⁺ and followed the order Cu-Y and Ag-Y ≫ Na-ZSM-5 > activated carbon > Na-Y > modified alumina and H-USY. The separation factors of thiophene over benzene (at low concentrations of thiophene) calculated from pure component adsorption isotherms exhibited the trend Ag-Y > Na-ZSM-5 > Cu-Y ≈ activated carbon ≫ Na-Y ≫ H-USY ≈ modified activated alumina.