Coal to liquids (CTL) and Biomass to liquids (BTL) plants produce, by gasification or pyrolysis, a synthesis gas rich in carbon monoxide. The H2:CO ratio is lower than that required for the stoichiometric conversion to paraffinic hydrocarbons. CTL and BTL plants may elect to use an iron based Fischer-Tropsch catalyst which readjusts the equilibrium and effectively converts part of the carbon monoxide to hydrogen, rejecting carbon dioxide in the process. However, if a cobalt Fischer-Tropsch catalyst is to be used the H2:CO ratio must first be adjusted to approximately 2:1.
The preferred way to adjust the stoichiometry is to shift all or part of the synthesis gas using a catalyst. Johnson Matthey manufacture a range of shift catalysts and is the leading supplier of sulphided or sour shift catalysts. This is the shift catalyst of choice for CTL and BTL plants in which the synthesis gas at this point are generally laden with sulphur and other impurities.
These catalysts have been widely used in substitute natural gas (SNG) or other coal based plants and have a long track record of efficient and robust operation.
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