7-Ethyl-2-methyl-1,2,3,4,4a,9,9a,10-octahydroanthracene
H 2
C
Saturation reactions of aromatic compounds proceed sequentially
The saturation reactions are exothermic and reversible. These reactions consume
hydrogen (not shown) but also improve the quality of the diesel fuel by increasing
the cetane number; therefore, they are not necessarily undesirable, and distillate
hydrotreater pressures and catalyst choices are sometimes dictated by the desire
to achieve a given cetane number. Additionally, there is evidence that aromatics
may inhibit the desulfurization of the most difficult, sterically hindered
dibenzothiophenes, sulfur species (Jones et al. 2004).
Feedstocks
Feed to a distillate hydrotreating unit may be any blend or combination of straightrun distillate (SRD), coker distillate (LCGO), and light cycle oil (LCO).
Straight-run distillate is, as the name implies, derived from the distillation of
crude oil and is the cut obtained crude column, boiling in the range of ~300
F to
~730
F. Straight-run distillates are characterized by high API gravities, in the
range of 28–32 and sometimes higher and low levels of sulfur (0.5–1.5 wt%),
nitrogen (40–100 wppm), and aromatics (usually <20 wt% total).
Coker distillates, while boiling in the same range as straight-run distillates, are
derived from coking operations and differ from straight-run distillates in that they
contain greater amounts of sulfur (up to 2.5–3.0 wt are possible), higher levels of
nitrogen (500–1,500 wppm), and somewhat higher aromatics content. The additional feature that sets them apart is the presence of olefins (typically measured as a
bromine number) with a bromine number of 10–30. Due to the olefin content and
the higher aromatics content of coker distillates, their processing in a hydrotreater is
388
P. Kokayeff et al.
H 2
C
Saturation reactions of aromatic compounds proceed sequentially
The saturation reactions are exothermic and reversible. These reactions consume
hydrogen (not shown) but also improve the quality of the diesel fuel by increasing
the cetane number; therefore, they are not necessarily undesirable, and distillate
hydrotreater pressures and catalyst choices are sometimes dictated by the desire
to achieve a given cetane number. Additionally, there is evidence that aromatics
may inhibit the desulfurization of the most difficult, sterically hindered
dibenzothiophenes, sulfur species (Jones et al. 2004).
Feedstocks
Feed to a distillate hydrotreating unit may be any blend or combination of straightrun distillate (SRD), coker distillate (LCGO), and light cycle oil (LCO).
Straight-run distillate is, as the name implies, derived from the distillation of
crude oil and is the cut obtained crude column, boiling in the range of ~300
F to
~730
F. Straight-run distillates are characterized by high API gravities, in the
range of 28–32 and sometimes higher and low levels of sulfur (0.5–1.5 wt%),
nitrogen (40–100 wppm), and aromatics (usually <20 wt% total).
Coker distillates, while boiling in the same range as straight-run distillates, are
derived from coking operations and differ from straight-run distillates in that they
contain greater amounts of sulfur (up to 2.5–3.0 wt are possible), higher levels of
nitrogen (500–1,500 wppm), and somewhat higher aromatics content. The additional feature that sets them apart is the presence of olefins (typically measured as a
bromine number) with a bromine number of 10–30. Due to the olefin content and
the higher aromatics content of coker distillates, their processing in a hydrotreater is
388
P. Kokayeff et al.