Anal. Chem. 1998, 70, 4743-4750
Resolution, Elemental Composition, and Simultaneous Monitoring by Fourier Transform Ion Cyclotron Resonance Mass Spectrometry of Organosulfur Species before and after Diesel Fuel Processing Ryan P. Rodgers,† Forest M. White,†,‡ Christopher L. Hendrickson, and Alan G. Marshall*,†
National High Magnetic Field Laboratory at Florida State University, 1800 East Paul Dirac Drive, Tallahassee, Florida 32310 Karin V. Andersen
Haldor Topsoe Research Laboratories, DK-2800 Lyngby, Denmark
Elemental compositional analysis of processed and unprocessed diesel fuels is obtained with a 5.6-T Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer coupled to an all-glass heated inlet system (AGHIS). High-resolution mass spectra of electron-ionized diesel fuel samples are obtained from as little as a 500-nL septum injection into the AGHIS, to yield ∼500 peaks over a range 90 < m/z < 300, with as many as seven peaks present at the same nominal mass. Molecular formulas (elemental compositions) are assigned from accurate mass measurement with an average error less than (0.5 ppm. Comparison of the raw and processed diesel spectra shows complete removal of the sulfurcontaining species except for dimethyldibenzothiophene and higher alkyl-substituted dibenzothiophenes. These results confirm prior reports of the resistance of these species to hydrotreatment due to steric hindrance of catalytic desulfurization arising from 4,6 dimethyl substitution. A simple liquid chromatographic separation to isolate N-, O-, and S-containing aromatics from processed diesel fuel simplifies the mass spectrum and extends the dynamic range of the analysis, making it possible to identify many nitrogen and oxygen homologues of the sulfur-containing species, as well as to confirm the presence of sulfur-containing species initially detected in the unfractionated processed diesel fuel. Hydrotreating is a fuel purification process which removes a number of heteroatoms (S, N, and O) and metals by saturation of the hydrocarbon feedstock and conversion (in the case of S) to an inorganic form such as H2S. Typical hydrotreating catalysts are alumina-supported molybdenum with either nickel or cobalt added to improve catalytic activity. In hydrotreating, sulfur is the † Member of the Department of Chemistry, Florida State University, Tallahassee, FL 32306. ‡ Present address: Department of Chemistry, University of Virginia, Charlotteville, VA 22901.
10.1021/ac980487i CCC: $15.00 Published on Web 10/08/1998
© 1998 American Chemical Society
most common target for removal due to its high abundance and propensity to produce, upon combustion, poisonous gases (SOx) which contribute to global pollution.1-3 In addition, sulfur compounds can poison expensive catalysts used in later processing. As a result, hydrodesulfurization is a very important process which accounts for ∼10% of the world market for catalysts.4 It is commonly used on a wide range of petroleum fractions for improving the quality of the final products, conversion of heavier feedstocks, and pretreating streams for other refinery processes. Several factors are driving current research interest in hydrotreating catalytic technology. Recent environmental legislation introduced in Europe, the United States, and Japan will lower the allowable sulfur content of commercial fuels to 100 000, in which ∆m50% is the mass spectral full peak width at half-maximum peak height) and mass accuracy (
