Conversion Technologies 83
maximise its production [23]. Two reactions between syngas components can maximise
its formation: steam reforming and water-gas shift reaction. To maximise the relative
contentofhydrogeningaseousproducts,CO 2 is removed by adsorption on CaO [23].
Steam reforming
CH 4 +CO 2 ↔ 2H 2 +2CO
Water-gas shift reaction
CO+H 2 O↔H 2 +CO 2
Fischer–Tropsch process – Fischer–Tropsh synthesis (FTS) is one of the most
known applications of syngas. The technology was developed in Germany in the
1920s and is successfully utilised for large-scale synthesis of fuels and chemicals from
coal in South Africa. FTS allows the synthesis of numerous hydrocarbons from two
major constituents of syngas, hydrogen and carbon monoxide, in the presence of a
catalyst, usually iron or cobalt. The products from the FTS vary depending on the
catalyst formulation and process conditions [24]. Fundamental reactions of FTS are as
follows [24]:
Synthesis of paraffins
nCO+( 2 n+ 1 )H 2 ↔CnH 2 n+ 2 +nH 2 O
Synthesis of olefins
nCO+ 2 nH 2 ↔CnH 2 n+nH 2 O
Synthesis of alcohols
nCO+ 2 nH 2 ↔CnH 2 n+ 1 OH+(n− 1 )H 2 O
The flexibility of FTS in the production of various hydrocarbons makes it an excellent
platform for the production of renewable fuels and chemicals from biomass. Numer-
ous compounds such as gasoline, diesel oil, kerosene, olefins, alcohols, waxes and many
otherscanbesynthesisedusingthisroute[24].Thereare,however,twomajordraw-
backs that currently hinder the widespread utilisation of FTS for the synthesis of renew-
able fuels and chemicals. First, efficient production of chemicals through FTS requires
high-quality producer gas, free of tars and dust, and gas cleaning still remains one of
the bottlenecks of gasification process. Second, for the successful execution of FTS an
appropriate ratio of two gaseous substrates is required. The ratio of H 2 to CO should
be close to 2:1 for the successful synthesis. Although the exact composition of syngas
depends on a particular gasifier, biomass gasification usually produces gas with differ-
ent composition mostly due to high content of oxygen in the gasified biomass. In order
to successfully utilise FTS, the gas composition needs to be adjusted, which includes
removal of free methane and adjusting the content of hydrogen. Two reactions partic-
ularly useful for these purposes [23] are steam reforming and water-gas shift reaction.
Once these technical hurdles are resolved and costs of installations are brought down,
FTS can become one of the mainstream technologies in the synthesis of renewable fuels
and chemicals.
