Summarizing the above, there are at present two catalyst systems available for large — scale commercial plants — cobalt-based and iron-based — and two operating modes of the FT process — low and high temperature. The iron catalyst produces gaseous and gasoline range products when operated in the high-temperature range, usually in fluid catalyst bed reactors. In the low-temperature range, both iron and cobalt catalysts produce a large amount of high boiling, waxy products and straight-run diesel and naphtha. The wax is then upgraded to lower boiling range products and normally distilled to yield highly paraffinic, zero sulphur and zero aromatic middle distillate diesel fuels, with naphtha as a co-product. Typical carbon number distribution of HTFT and LTFT products is given in Table 19.3 (de Klerk, 2008).

As the focus of the BTL process, so far, has been to maximize the production of premium BTL-FT fuels, in this section, we will focus on the technologies for upgrading the FT waxes originating from the LTFT process mode to FT diesel and gasoline by hydrocracking and catalytic cracking, respectively. The upgrading of the FT naphtha co-product to gasoline will also be discussed.