A Theoretical Study of Sulfur Adsorption on Ion-Exchanged Mesoporous Y Zeolites

Zachary Blanchette, Kevin X. Lee, and Julia A. Valla

Fossil fuels contain sulfur, which releases SO_x when burned. The produced SO_x creates a major environmental problem as it contributes to acid rain and can harm the human respiratory system. To address this challenge, the Environmental Protection Agency (EPA) has released new regulations which require minimal amounts of sulfur in transportation fuels (diesel and gasoline). The conventional method to remove sulfur from transportation fuels is hydrodesulfurization, which requires high temperature and pressure and is incapable of removing refractory sulfur compounds. Adsorptive removal of sulfur using zeolite Y is a promising new technique for desulfurization. The introduction of mesoporosity in zeolites allow adsorption of refractory sulfur compounds at the internal active sites. Additionally, metals like Cu and Ce can be added to the zeolite extra-framework to increase selective adsorption.

Mesoporous Y zeolites were modified using desilication and surfactant assisted (SA) methods and were ion-exchanged with Cu or Ce to create the modified zeolites. Breakthrough experiments were conducted to determine the capacity for refractory sulfur compounds removal for the different metal-exchanged zeolites. The adsorptive capability of all zeolites tested was dibenzothiophene (DBT) > benzothiophene (BT) > thiophene (TP). CuSAY was shown the have the highest capacity for refractory sulfur removal due to strong Ï?-complexation interaction.

A computational analysis for the metal-exchanged zeolites was also performed to investigate the interaction strength between the sorbate and sorbent. Adsorption of thiophenic compounds on metal-exchanged zeolites was calculated using density functional theory (DFT) in Gaussian 09. For all calculations, an m062x method was used with 6-311G basis sets. The thiophenic compounds examined were TP, BT, and DBT. The metal-exchanged zeolite used was CuY. The adsorption capabilities of CuY were as follows: DBT > BT > TP. Additionally, the DFT results show that CuY exhibits a higher adsorption capability than the parent Y.

Literature

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Acknowledgment

 This work was supported by the American Chemical Society / Petroleum Research Foundation (PRF+ 55900-DN15).