Fischer-Tropsch synthesis high temperature operation

Dr. Moeller A methanation plant does not have a problem of selectivity. Whether you operate at low or high temperature, when using a nickel catalyst you will form only methane and no higher hydrocarbon. But with the Fischer-Tropsch synthesis, you have a wide range of possible products which can be formed. If you want to have a certain product, you must keep your temperature at a certain constant value. 

The methanation reaction is a highly exothermic process (AH = —49.2 kcal/ mol). The high reaction heat does not cause problems in the purification of hydrogen for ammonia synthesis since only low amounts of residual CO is involved. In methanation of synthesis gas, however, specially designed reactors, cooling systems and highly diluted reactants must be applied. In adiabatic operation less than 3% of CO is allowed in the feed.214 Temperature control is also important to prevent carbon deposition and catalyst sintering. The mechanism of methanation is believed to follow the same pathway as that of Fischer-Tropsch synthesis. 

Change occurred in high-temperature Fischer-Tropsch reactor technology. The circulating fluidized bed Sasol Synthol reactors were replaced by fixed fluidized bed Sasol Advanced Synthol (SAS) reactors.44 This did not meaningfully affect the Fe-HTFT syncrude composition, but it reduced the operating cost of HTFT synthesis. 

Fischer-Tropsch Technology FTS can be carried out in several different reactor types fixed bed, fluidized bed, or slurry phase and at different temperatures. The high-temperature Fischer-Tropsch (HTFT) synthesis runs at 320°C-350°C, at which temperatures typically all products are in the gas phase [22], HTFT is operated in fluidized-bed reactors, with iron catalysts. Selectivities correspond to chain-growth probabilities in the range of 0.70-0.75 and are ideal for gasoline production, but olefins and oxygenates are formed as well and are used as chemicals. 

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