SYNTHESIS GAS UTILIZATION FOR TRANSPORTATION FUEL PRODUCTION - Biomass as a Sustainable Energy Source for the Future - page 527

Gasoline
Diesel
…

Reining
and
upgrading

Fischer-
Tropsch
synthesis

Natural gas

Methanol

Methanol
synthesis

Dimethyl ether

Dehydration

Coal

Syngas
cleaning

Gasiication

Gasoline

Deoxygenation

Synthetic natural gas

Methanation

Biomass

Other
processes

FIGURE 17.1 Schematic overview of the main routes from syngas to synthetic fuels.

The overall scheme for the conversion of various feedstocks into liquid fuels is
referred to as

to liquid (XTL). Depending on the feedstock, the names gas
to liquids (GTL), coal to liquids (CTL), and biomass to liquids (BTL) are used for
the specific variants, with, respectively, gas, coal, and biomass as feedstock. It should
be noted here that there are also alternative routes that are not based on syngas, such
as pyrolysis discussed in Chapter 11. Using the production of syngas as an intermediate
step has the advantage that the process becomes insensitive to the composition of the
biomass feed. We will focus on the processing aspects of the various routes. Routes that
are still far from commercial implementation, such as the direct production of ethanol
from syngas, will not be treated. The most important route is the Fischer

“ anything ”

Tropsch syn-
thesis (FTS), which was already used as an example process in Chapter 7 on process
design. This process will be discussed in more detail in Section 17.2. Second, we will
discuss the production of SNG. Third, we will discuss the synthesis of methanol from
syngas and the possible follow-up step to DME. Finally, we will make a comparison of
the different routes, with respect to efficiency and economic potential.

-

17.2 FISCHER-TROPSCH SYNTHESIS

FTS is a series of reactions by which syngas is converted into hydrocarbons. FTS was
discovered by Franz Fischer and Hans Tropsch in the 1920s. During the Second
World War, it was used in Germany to produce transportation fuels from coal. After
the war, interest decreased: a fuel supply system based on crude oil was economically
more attractive than one based on coal in combination with FTS. In South Africa,
which has large coal reserves, an important reason for starting coal-based FTS was
the embargo against the Apartheid policies, which limited its access to crude oil,