Page 264 - Lignocellulosic Biomass to Liquid Biofuels

220 Lignocellulosic Biomass to Liquid Biofuels

7.2 Fischer Tropsch chemistry and reaction

The FT chemistry is often regarded as the vital technological input for
converting syngas into liquid fuels in the range of C 1 C 100 [6,7,49]. Also
the FT reactions are considered as highly exothermic (Δ r H 2200 kJ/
mol) surface polymerization reaction. The reactants, gas mixture, absorb
and dissociate at the surface of the catalyst and react with chain initiator
[2,6]. The FT synthesis commonly contains the following reactions:

ð 2n 1 1ÞH 2 1 nCO-C n H 2n12 1 nH 2 O (7.1)

2nH 2 1 nCO-C n H 2n 1 nH 2 O (7.2)

Toward the synthesis of alkanes and alkenes, these are the end mole-
cules for FT process [Eq. (7.3)], where water is the main oxygenated
product.

2nH 2 1 nCO-C n H 2n12 O 1 n 2 1ð ÞH 2 O (7.3)
Moreover, the WGS reaction, shown in Eq. (7.4), also occurs over
most FT catalysts and is a reversible reaction, where CO 2 is fundamentally
produced with respect of CO by WGS reaction. Also, iron catalysts show
a key role in FT synthesis, which are used as a catalyst for WGS reaction
during FT synthesis.

CO 1 H 2 O-CO 2 1 H 2 (7.4)
In general, the chemical reactions of the FT synthesis are controlled
during the conversion of CO and H 2 . Moreover, the usage ratio signifi-
cantly depends on the extent of the other reactions and is influenced by
the WGS reaction. The WGS reaction arises simultaneously during FT
synthesis by reducing the usage ratio over the iron catalysts. This reaction
permits to use the H 2 /CO ratio less than 2.1 of syngas. Co catalysts show
low activity for the WGS reaction; therefore the scope of WGS reaction
is negligible.
Since the ideal case the syngas generated from biomass gasification and
subsequently undergoes FT synthesis, the reaction is as follows:
1
2C 1 O 2 1 H 2 O- 2 CH 2 21 CO 2 (7.5)
2
The yields of FT synthesis in an extensive variety of hydrocarbon pro-
ducts, such as conventional crude oil, could not refer to a pure product