Page 362 - Adsorbents - fundamentals and applications

DESULFURIZATION OF TRANSPORTATION FUELS 347

development would lead to a major advance in petroleum refining. However,
success would depend on the development of a highly selective sorbent with a
high sulfur capacity, because the commercial sorbents are not adequate for this
application.

10.7.1. Fuel and Sulfur Compositions

The compositions of transportation fuels vary widely depending on the crude
oils used, the refining process, the product demand, and the product specifica-
tions. The approximate compositions of gasoline, diesel, and jet fuel are given
in Table 10.12. Branched and n-alkanes are the main ingredients of these fuels,
typically 70–80%. The major alkane is n-hexane and the main branched alkanes
are C 5 and C 6 compounds. The aromatics are mainly benzene, toluene, xylenes,
and alkyl benzenes, totaling about 20–30%.
The sulfur compounds in transportation fuels can be analyzed with X-ray
fluorescence spectroscopy or by gas chromatography equipped with a capil-
lary column plus a flame photometric detector. The remaining sulfur compounds
after hydrodesulfurization (HDS) are mainly thiophene (T), benzothiophene (BT),
dibenzothiophene (DBT) and their alkylated derivatives. Figure 10.50 shows the
substitution positions of DBT. The alkylated derivatives with alkyl groups at the
4- and 6-positions are most difficult to remove and are referred to as refrac-
tory species. Ma et al. (2001) showed GC-FPD chromatograms of a sample each
of gasoline, diesel, and jet fuel, reproduced in Figure 10.51. The FPD detects
only sulfur compounds. The dominant sulfur compounds in the gasoline were
(in decreasing order) 3-MT, BT, T, 2-MT, and 2,4-DMT. Those in the diesel
were 4-MDBT, 4,6-DMDBT, 2,4,6-TMDBT, 3,6-DMDBT, DBT, 2,3,7-TMBT,
2,3,5-TMBT, 2,3-DMBT, and others. The sulfur compounds in the jet fuel were

Table 10.12. Typical compositions of transportation fuels
(vol %)
Gasoline a Diesel b Jet Fuel c

◦
Boiling range ( C) 40–204 232–350 330–510
Aromatics 30.5 17 18
Olefins 1.8 5 2
n-alkanes 17.3 — —
Branched alkanes 32 — —
Cycloalkanes 5 — —
Saturates — 78 —
Paraffins — — 60
Naphthenes — — 20
a Sciences International, Inc., “Toxicological Profile for Gaso-
line,” Report to Department of Health and Human Services,
June, 1995.
b Ma et al., 1994.
c Ma et al., 2002.