9.4.2 Fischer-Tropsch Synthesis
Fischer-Tropsch (FT) synthesis, developed in the 1920s, is a highly successful
method for the production of liquid hydrocarbons from syngas. The FT process
can produce high-quality diesel oil from biomass or coal with no aromatics and
with a high Cetane number (>70). The composition of this product is very
similar to that of petrodiesel. Thus, it can be blended with petrodiesel or used
directly in an engine.
Biomass conversion with the FT process may have several additional advantages
because its gasification product typically contains H2 : CO ratio of about
unity, which is ideal for iron catalysts. Furthermore, biomass gasification products
contain CO2, which is beneficial for the production of liquid products
(Reed, 2002, p. 242). The absence of sulfur in biomass also helps most
catalysts.
The most successful and well-known use of FT synthesis is for the production
of liquid fuel from coal by SASOL in South Africa, where syngas produced
from coal is converted into petroleum products. The FT process is also useful
for conversion of biomass into liquid fuels and chemicals.
The FT reaction, which is typically carried out in the range 200 to 350 °C
and 20 to 300 atm (Reed, 2002, p. II–238), may be written as