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Fischer Tropsch synthesis of syngas to liquid hydrocarbons 229

The addition of La 2 O 3 decreased the reducibility of Co species to enhance
their dispersion [87]. The addition of CeO 2 into cobalt catalysts could
alter the hydrocarbon productivity [100]. However, the selectivity toward
CH 4 and C 2 C 4 hydrocarbons increased significantly in the presence of
CeO 2 modifier [100]. The role of promoters, which were commonly
used in cobalt catalysts for FT synthesis, is reported in Table 7.3
[75,94,99,100].

7.4 Kinetic modeling of Fischer Tropsch synthesis

The kinetic modeling is a major challenge to describe the FT synthesis
due to the complexity of the reaction mechanism and the combination of
a number of steps, which results in empirical power-law expressions for
the kinetics. Several kinetic modeling studies were conducted using single
and bimetallic catalysts, including Co, Fe, Ni, and Ru. The selectivity of
FT products and its kinetics constitute two pillars in the reaction mecha-
nism. Among various studies investigated on product distribution and
reaction kinetics of the FT synthesis, continuous laboratory reactors were
used. Major studies were carried in atmospheric gas solid packed bed
reactors. Packed beds at high pressures were applied, but integral reactors
were not unsuitable for kinetic studies of the FT synthesis [17,101 104].
Continuous recycle reactors are also suitable for gas solid kinetic mea-
surements, such as spinning basket reactor and Berty reactor. Slurry phase
FT synthesis was carried out in slurry-phase reactors (SPRs), and continu-
ous process was carried out with constant gas phase, while batch process
was carried out in liquid phase [35,105 107].
FT synthesis kinetic modeling is a prerequisite for industrialization the
process, for process design, operation, and simulation [35,107]. The kinet-
ics of cobalt-based FT catalysts has been the subject of many researches in
the last decades. The kinetics of the FT synthesis has been studied exten-
sively to describe the reaction rate using a power law rate equation.
However, other rate equations are also applied, such as Langmuir
Hinshelwood Hougen Watson (LHHW) and Eley Rideal, based on a
reaction mechanism for the hydrocarbon formation [35,107]. Mostly, for-
mation of the monomer accrues during the rate-determining step and
conversion of syngas commonly varies due to monomer structure
[104,108 110]. The atomic mass balances of C, H, and O are essential to
see on reliability and stability FT synthesis. The kinetic and selectivity
models should be developed on the basis of an extensive experimental