Page 228 - Synthetic Fuels Handbook

214 CHAPTER SEVEN

However, the decreasing availability and increased price of petroleum has been renewed
the worldwide interest in the production of liquid hydrocarbons from carbon monoxide and
hydrogen using metal catalysts, also known as Fischer-Tropsch synthesis.
In the last decades, the interest in Fischer-Tropsch synthesis has changed as a result of
environmental demands, technological developments, change in fossil energy reserves, and
high oil prices.
The Fischer-Tropsch process is a catalyzed chemical reaction in which carbon monox-
ide and hydrogen are converted into liquid hydrocarbons of various forms. Typical catalysts
used are based on iron and cobalt. The principal purpose of this process is to produce a
synthetic petroleum substitute for use as synthetic lubrication oil or as synthetic fuel.
The development of pressurized Fischer-Tropsch synthesis goes 80 years back, and
starts about 1925 in Germany when Prof. Franz Fischer, founding director of the Kaiser-
Wilhelm Institute of Coal Research in Mälheim an der Ruhr, and his head of department,
Dr. Hans Tropsch, applied for a patent describing a process to produce liquid hydrocarbons
from carbon monoxide gas and hydrogen using metal catalysts.
The experiments took place in Franz Fischer’s laboratory at the Kaiser Wilhelm Institute
for Coal Research, and the concept resulted in an industry which produced almost 4 million
barrels of synthetic fuel in 1945. At those times strategic reasons for liquid fuel production
from coal exceeded economic aspects. A good example is the “oil-age” from 1955 to 1970
with plenty of cheap oil supply and as a result only a marginal interest in Fischer-Tropsch
synthesis. High oil prices increase the focus at alternative fuels; likewise as carbon dioxide
concentration concern arises, being related to global warming, the focus at new technolo-
gies rises. Today the driving forces are environmental concern, but also higher oil price,
limited oil reserves, and increased focus at stranded gas.
The required gas mixture of carbon monoxide and hydrogen (synthesis gas) is created
through a reaction of coke or coal with water steam and oxygen, at temperatures over
900°C. In the past, town gas and gas for lamps were a carbon monoxide-hydrogen mixture,
made by gasifying coke in gas works. In the 1970s, it was replaced with imported natural
gas (methane). Coal gasification and Fischer-Tropsch hydrocarbon synthesis together bring
about a two-stage sequence of reactions which allows the production of liquid fuels like
diesel and petrol out of the solid combustible coal.
The Fischer-Tropsch synthesis took its first serious place in industry in 1935 at
Ruhrchemie in Oberhausen. By the beginning of the 1940s, some 600,000 t of liquid
hydrocarbons were produced per year in German facilities, made from coal using Fischer-
Tropsch synthesis. Licensed by Ruhrchemie, four facilities in Japan, as well as a plant in
France and in Manchuria, were in service. After World War II, competition from crude oil
made petrol production from coal unprofitable. The only new production facilities were in
South Africa, for political reasons, built starting in 1950 in Sasolburg.
The Fischer-Tropsch synthesis is, in principle, a carbon chain building process, where
methylene groups are attached to the carbon chain. The actual reactions that occur have
been, and remain, a matter of controversy, as it has been the last century since 1930s.
Even though the overall Fischer-Tropsch process is described by the following chemical
equation:
(2n+1)H + nCO → C H + nH O
2 n (2n+2) 2
The initial reactants in the above reaction (i.e., CO and H ) can be produced by other
2
reactions such as the partial combustion of a hydrocarbon:
C H (2n+2) + ½ nO → (n+1)H + nCO
2
n
2
For example (when n = 1), methane (in the case of gas to liquids applications):
2CH + O → 4H + 2CO
2
4
2