Processing of Primary Fischer-Tropsch Products - University of Alberta

Coke Oven
Gas
Coke
Steam
Coke Gasifier HzS Removal
Removal
l Fischer-Tropsch I
Synthesis I
I
Product
Separation
I
Figure 7 Typical process scheme of the 1935-1945 German FT plants
Light Gases
~- Naphtha
Kerosine
Gas Oil
Wax
" Heavy Oil
9 Tail Gas
L Reaction
Water
The first LTFT plants of Sasol included a more complex processing
scheme. The original concept, shown in Fig. 8, showed a high degree of
integration to maximize the benefits of the unique characteristics of the FT
products [3]. This process scheme included eight separate units. While its
objective was to produce fuels, gasoline and diesel, it also included the
production of LPG and hydrogenated waxes. The quality of the gasoline was by
improved by a Hot Refining step, a 400~ fixed catalyst bed treatment with two
objectives: (a) conversion of oxygenates to other hydrocarbon species and (b)
shifting the double bond in olefins to the centre of the molecule. Both changes
improved fuel stability and octane number of the synthetic naphthas. The diesel
was a blend of the straight run FT products and the cracked stock from the
Paraformer, a thermal cracker unit- therefore still containing some olefins and
oxygenates.
Table 8 presents the quality of a sample obtained and analysed by the
Allied forces after the war [78]. It is interesting to note that this straight run
synthetic diesel produced using a cobalt FT catalyst, contained aromatic species
and a significant amount of olefins.
With time the processing of the LTFT primary products became more
sophisticated. Most GTL technology licensors include different hydroprocessing
arrangements that eventually will lead to comparable distillates. Therefore, in
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