Processing of Primary Fischer-Tropsch Products - University of Alberta

The optimum olefins yields obtainable from any naphtha depend on the
maximum cracking severity attainable at commercial conditions. This in turn
depends on the chemical composition of the naphtha and, up to certain extent, to
the physical configuration of the cracker unit. The former is evident in Figs. 11
and 12 which show the ethylene and commercial olefin yields at different
cracking severities for the synthetic and the two petroleum feedstocks.
It is of relevance to indicate that while this kind of performance was
directionally predictable, it was not fully quantified. Indeed, hydroprocessing has
been previously reported as a crucial pre-treatment stage to improve the
properties of FT naphthas for conversion to lower olefins. [86].
Table 14
Research performance comparison of the Sasol SPD TM naphtha
Typical Petroleum Typical Petroleum
Light Naphtha Heavy Naphtha
P/Emassratio 0.77 0.68 0.59 0.82 0.74 0.65
Sasol SPD TM Naphtha
523
0.71 0.59 0.50 0.40
Yield (wt %)
Ethylene 24.1 27.0 29.3 19.4 21.9 24.0 26.5 32.3 35.7 37.5
Propylene 18.7 18.4 17.2 16.0 16.1 15.5 18.8 19.1 17.8 15.0
1,3-Butadiene 4.0 4.2 4.4 3.8 4.1 4.3 2.9 3.8 4.2 4.2
Light Olefins 46.7 49.6 50.8 39.2 42.1 43.8 48.2 55.2 57.7 56.7
Other Olefins 8.2 6.9 5.4 8.3 7.3 6.1 9.9 8.4 6.2 4.1
Hydrogen 0.6 0.7 0.8 0.5 0.6 0.7 0.6 0.7 0.8 0.9
Methane 12.8 14.6 16.3 10.9 12.6 14.2 10.2 13.0 14.9 16.2
Other Paraffins 11.8 9.4 7.5 11.8 9.4 7.3 5.1 5.3 4.8 4.4
Alkynes 0.4 0.7 0.9 0.4 0.7 1.0 0.4 0.7 1.1 1.4
C5+ Liquids 19.4 18.1 18.2 28.8 27.2 27.0 25.7 16.9 14.4 16.3
Total Products 100 100 100 100 100 100 100 100 100 100
The coking rate for LTFT Naphtha under commercial conditions is
expected to be lower than that of conventional feeds, meaning that run lengths in
commercial steam cracking operations using LTFT Naphtha can be expected to
be longer than those expected using conventional naphthas at similar cracking
severities.