New Sorbents for Desulfurization by π-Complexation: Thiophene/Benzene Adsorption

New sorbents for the desulfurization of liquid fuels were developed using π-complexation. Vapor-phase 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 × 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.