Processing of Primary Fischer-Tropsch Products - University of Alberta

lower. A process scheme similar to that used with petroleum derived waxes and
suitable for the catalytic dewaxing of FT Wax is shown in Fig. 5.
Wax ..] Catalytic ~ Hydrofinishing |
"l Dewaxing Unit I I I
l
q
Vac.
Dist.
Figure 5 Process scheme for the production of synthetic base oils from wax
"l
I
Naphtha
Diesel
____~) Base Oils
.~ Heavy Base
Oil
The catalytic dewaxing route to lubricant base oils is becoming the
preferred processing option due to the lower capital and operating costs
compared to conventional solvent dewaxing. Recently introduced catalytic
dewaxing technology, e.g. ChevronLummus Global's ISODEWAXING and
ExxonMobil's MWI (Mobil Wax Isomerisation), makes converting FT wax to
base oils more economical than ever before.
6.3 Hydroprocesssing catalysts for LTFT primary products
6.3.1 Basic concepts
Although the type of hydrocracker feed from a FT process differs from the
normal refinery hydrocracker feed, e.g. VGO, the basic hydrocracking
mechanism is the same and standard hydrocracking catalysts can be used. As in a
refinery hydrocracking process, the choice of catalyst will depend on the
required product slate. When high middle distillate selectivity is desired
amorphous carriers would be chosen while, on the other hand, when maximum
kerosene and naphtha selectivity are wanted, a mixed zeolite/amorphous carrier
will probably be used.
Commercial hydrocracking catalysts are dual function catalysts,
containing a hydrogenation/dehydrogenation function, provided by the active
metal(s) and an acidic function derived from the carrier, typically amorphous
silica-alumina or crystalline silica-alumina, i.e. zeolites.
According to generally accepted hydrocracking theory, the active metal
sites promote dehydrogenation of the paraffins to olefins [76]. These are then
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