Processing of Primary Fischer-Tropsch Products - University of Alberta

increased, the overall distillate yield first increased, passed through a maximum
and subsequently decreased. The higher pressure inhibits secondary cracking and
lighter product formation. The pour points of diesels produced from this program
varied between -12~ and -37~ UOP reported that the FT Diesel derived was
of extremely high quality, with a very high Cetane number, which can be
blended with low-value refinery products such as light cycle oil to increase the
volume of the diesel pool. The hydrocracking catalyst used in this program was a
commercial sulphided catalyst designed for petroleum refining.
Keeping some differences in mind, comparable trends were reported
processing a comparatively light feed- it contained ca 61% wt of material
already in the distillates range [68]. The catalyst used was platinum (0.3 mass%)
on amorphous mesoporous silica-alumina. This program included testing over
the same pressure range (35 to 70 bar) at temperatures between 330-355~ The
degree of isomerisation in the hydrocracked products increased with an increase
in the conversion. As a consequence, the freezing point of the kerosene was a
very low -50~ and the pour point of the diesel -30~ remarkable figures
considering the high fraction of linear light species in the feed.
This approach of using a noble metal on amorphous silica alumina is
likely to be the preferred approach for maximum production of highly desirable
diesel blending material. It is likely that all the C14+ material will be treated
using such catalysts due to the enhancement in cold flow properties resulting
from the simultaneous isomerisation. A high blending Cetane value is retained
and very little of the diesel range material in the feed is degraded into naphtha
and kerosene.
There are many technology licensors for hydroconversion processes
including ChevronTexaco, UOP, IFP (Axens) and Haldor-Topsoe. Additionally
catalysts can be obtained from these companies as well as from Akzo Nobel,
Stid-Chemie and Axens among others.
6.2.2 Hydrotreating of FT paraffins
The quality of the primary FT products, both condensate and wax, can be
improved by hydrotreating as Sasol has been doing commercially for many
years. The primary objective of this process is to saturate olefins and oxygenates
to the corresponding paraffins. This hydrogenation results in a hydrocarbon
product that is stable when stored for long periods. Stability during storage is the
primary objective for the hydrogenation of the hydrocarbon condensate or
fractions thereof. In the case of LTFT wax, the resulting product has better
colour and stability. It is also possible, depending on the reaction conditions, to
transform some of the linear hydrocarbons into branched species. In this case the
crystallization temperature of the wax can also be influenced. These results are
similar to those attainable when hydrotreating petroleum wax in a similar way
[69]. However, as it was mentioned for hydrocracking, the required process
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