Selective Adsorption for Removing Sulfur from Jet Fuel over Zeolite-Based Adsorbents S. Velu, Xiaoliang Ma, and Chunshan Song* Clean Fuels and Catalysis Program, The Energy Institute, and Department of Energy and Geo-Environmental Engineering, The Pennsylvania State University, 209 Academic Projects Building, University Park, Pennsylvania 16802 Adsorbents based on transition metal ion-exchanged Y zeolites (with Cu, Ni, Zn, Pd, and Ce ions) were synthesized and evaluated for the adsorptive desulfurization of a model jet fuel (MJF) and a real jet fuel (JP-8). Among the adsorbents tested, Ce-exchanged Y zeolites exhibited better adsorption capacity of about 10 mg of sulfur/g of adsorbent at 80 °C with a MJF containing 510 ppmw sulfur. The same adsorbent exhibited a sulfur adsorption capacity of about 4.5 mg/g for the real JP-8 jet fuel containing about 750 ppmw sulfur. Desulfurization of MJF under flow conditions at 80 °C showed a breakthrough capacity of about 2.3 mg/g of adsorbent. Ce-exchanged zeolites exhibited higher selectivity for sulfur compounds as compared to the selectivity of aromatics, for which a comparative study indicated that the sulfur compounds are adsorbed over Ce-exchanged Y zeolites via direct sulfur-adsorbent (S-M) interaction rather than via π-complexation. While the selectivity for 2-methyl benzothiophene (2-MBT) was higher in the static adsorption studies, the adsorption selectivity decreased in the order 5-methyl ben- zothiophene (5-MBT) > benzothiophene (BT) > 2-MBT under dynamic conditions. This trend was correlated to the electron density on sulfur atoms derived from computer-aided molecular orbital calculations. 1. Introduction Gasoline, jet fuel, and diesel fuel are the three major transportation fuels. Currently these fuels contain significant amounts of organic sulfur compounds, up to 300 ppmw in gasoline, 500 ppmw in diesel, and 3000 ppmw in jet fuel. 1 Combustion of these fuels in internal combustion engines emits SO x , a major air pollutant. Even at lower concentration, the SO x can poison the catalyst designed for exhaust gas treatment such as NO x reduction catalyst. To reduce emissions of environmen- tal pollutants, the U.S. Environmental Protection Agency (EPA) has announced new regulations that mandate refineries to reduce the sulfur level down to 30 ppmw in gasoline and 15 ppmw in diesel by 2006. 2,3 The removal of organic sulfur compounds from transporta- tion fuels is becoming a more and more important issue in recent years not only due to such stringent environ- mental regulations but also because of the possibility that these fuels can be re-formed on-board or on-site to produce hydrogen-rich gas as a fuel for fuel cells for mobile, portable, and stationary applications. 2-6 To re- form these liquid fuels for fuel cell applications, the sulfur level should be further reduced close to zero ppm because the presence of even traces of sulfur is a poison to the re-forming catalysts as well as electrode catalysts. Hydrodesulfurization (HDS) using NiMo/Al 2 O 3 and CoMo/Al 2 O 3 catalysts is the conventional process being employed in the refineries worldwide to remove sulfur compounds from the liquid fuels. 7 Recently, some new catalyst formulations have been developed to improve the HDS processes. 1 As but one example, Turaga and Song 8 have reported a novel CoMo/MCM-41 catalyst with improved catalytic performance for the hydrode- sulfurization of diesel and jet fuel feedstocks. However, the HDS process is highly inconvenient to produce ultra- clean (near zero sulfur) transportation fuels, especially for fuel cell applications, as it requires severe reaction conditions such as high temperature and high pres- sure. 1,2 Under these conditions, part of the olefins and aromatics contained in gasoline are saturated, and this decreases the octane number even for conventional engines. Furthermore, the current HDS process is effective to remove only the “easy sulfur” compounds that are present in the liquid fuels to some extent while it is difficult to remove the refractory sulfur compounds present in the diesel and jet fuel feedstock. A new method is therefore needed to remove refractory sulfur compounds from the liquid fuels in order to re-form them to produce hydrogen for fuel cell applications. On the other hand, the selective removal of refractory sulfur compounds is challenging, as they coexist with aromatic hydrocarbons that are present in high concentrations in the range 10-30 wt %. The new sulfur removal technology therefore should be selective for removing only the sulfur compounds without removing aromatic hydrocarbons. Several non-HDS-based desulfurization technologies such as adsorptive desulfurization, charge-transfer complex formation, extraction using ionic liquids, bio- catalytic treatment, etc. have been proposed recently for the desulfurization of liquid fuels. 1-3,9,10 Conoco Phillips Petroleum Company has recently commercialized a new process called S Zorb technology for the desulfurization of gasoline and diesel, and the process is based on reactive adsorption in the temperature range of 340- 410 °C under low H 2 pressure between 2 and 20 bar. 1,2,10 Among the new processes, the adsorptive desulfuriza- tion seems more promising for certain applications including on-site and on-board fuel cell systems because * To whom correspondence should be addressed. Tel.: (814)- 863-4466. Fax: (814)865-3248. E-mail: csong@psu.edu. 5293 Ind. Eng. Chem. Res. 2003, 42, 5293-5304 10.1021/ie020995p CCC: $25.00 © 2003 American Chemical Society Published on Web 09/19/2003