6142
Ind. Eng. Chem. Res. 2004, 43, 6142-6149
Desulfurization of Commercial Jet Fuels by Adsorption via π-Complexation with Vapor Phase Ion Exchanged Cu(I)-Y Zeolites Arturo J. Herna´ ndez-Maldonado and Ralph T. Yang* Department of Chemical Engineering, University of Michigan, Ann Arbor, Michigan 48109-2136
William Cannella ChevronTexaco Energy Research and Technology Company, Richmond, California 94802
Desulfurization of a commercial jet fuel by vapor phase ion exchange (VPIE) Cu(I)-Y adsorbents were studied in a fixed-bed adsorber operated at ambient temperature and pressure. When used with an activated alumina guard bed, Cu(I)-Y(VPIE) provides by far the best adsorption capacities. In general, the adsorbents tested for total sulfur adsorption capacity at breakthrough follow the order Selexsorb CDX < Cu(I)-Y(VPIE) < Selexsorb CDX/Cu(I)-Y(VPIE). The best adsorbent, Selexsorb CDX/Cu(I)-Y(VPIE) (layered bed of 25 wt % activated alumina followed by Cu(I)-Y), is capable of producing 38 cm3 of jet fuel per gram of adsorbent with a weighted average content of 0.071 ppmw-S. The sorbent is also capable of producing about 50 cm3 of jet fuel with a sulfur content of less than 1 ppmw-S. These low-sulfur fuels are suitable for fuel cell applications. Regeneration tests have shown the sorbent capacity can be fully recovered using calcination/reduction methods. Gas chromatography-flame photometric detection results show that the π-complexation sorbents selectively adsorb highly substituted benzothiophenes from jet fuel, which is not possible by using conventional hydrodesulfurization reactors. The high sulfur selectivity and high sulfur capacity of Cu(I)-Y(VPIE) were due to π-complexation. Introduction Due to worldwide environmental mandates, refiners are facing the challenge of producing increasingly cleaner fuels.1 In 1998, the European Union first mandated new sulfur specifications for drastically reduced levels that started to be phased in from the year 2000.2 Similar regulations were legislated in the U.S. and elsewhere soon after. The EPA Tier II regulations require reductions of sulfur in highway diesel from the current average of 500 ppmw to 15 ppmw by June 2006, and that in gasoline from 350 ppmw to 30 ppmw by January 2005.1 However, refinery pipelines would probably require even lower sulfur content in their fuels, below 10 ppmw, to compensate for possible contamination from the higher sulfur concentration of some products and the inherent measurement variability.3 For aviation fuels, the current maximum sulfur limit is 3000 ppmw,4 but regulation on this type of fuels is likely to become more stringent as governments continue to study sulfur emission sources around the globe. According to the U.S. Northeast States for Coordinated Air Use Management [NESCAUM], airports are major local sources of air pollution due to heavy emissions from aircraft.5,6 In 1999, NESCAUM reported SO2 emissions as high as 230 tons/year. These numbers are expected to keep climbing over the next few years and, thus, it will be imperative to produce ultralow sulfur jet fuels to help reduce emissions.7 Removal of sulfur-containing compounds is currently achieved by hydrodesulfurization (HDS), a catalytic process operated at elevated temperatures (300-340 °C) and pressures (20-100 atm of H2) by using Co-Mo/ * To whom correspondence should be addressed. Tel.: (734) 936-0771. Fax: (734) 764-7453. E-mail:
[email protected].
Al2O3 or Ni-Mo/Al2O3 catalyst.8 HDS is highly efficient in removing thiols, sulfides, and disulfides but is less effective for aromatic thiophenes and thiophene derivatives, especially those containing functional groups that hinder the sulfur atoms. Because of this problem, the sulfur compounds that remain in the transportation fuels are mainly thiophene, benzothiophene, dibenzothiophene, and their alkylated derivatives. To reduce the sulfur content to meet the new regulations, the reactor size needs to be increased by factors of 5-15.9 Furthermore, a severe hydrotreatment side effect will be a further reduction in the “natural” lubricity of the resulting fuel blend.10,11 As a result, refineries need to add certain additives to restore the original lubricity, this to avoid mechanical problems in engines. Future fuel cells will also require deeply desulfurized fuels, if at all possible with “zero” sulfur content.12 For example, methanol-based fuels for on-board fuel cell applications required the use of a fuel with sulfur content
