Indirect Liquefaction Fischer Tropsch Synthesis

Fischer-Tropsch synthesis is the conversion of carbon monoxide and hydrogen to liquid hydrocarbons and related oxygenated compounds over variously promoted group-VII catalysts and is defined by the reaction:

Fischer-Tropsch synthesis can, in principle, provide almost all hydrocarbons conventionally obtained from petroleum. The actual product mix depends on the temperature, pressure, CO/H2 ratio, and catalysts used, and there are several variants of the process. Table 5-9 illustrates how the product composition can be influenced [19], and Table 5-10 lists some technical information on three industrial processes [1].

Medium-pressure synthesis, conducted at 430 to 640°F and 5 to 50 atm over iron catalysts, yields mainly gasoline, diesel oils, and heavier paraffins [19]. The proportion of gasoline in the product mix increases, and gasoline quality improves as the hydrogen-to-carbon monoxide ratio in the feed gas is increased, and the overall product composition is influenced by the type of reactor: fixed catalyst beds or a fluid-bed reactor. High-pressure synthesis, conducted at 210 to 300° F and 50 to 1000 atm over ruthenium catalysts, furnishes mainly straight-chain paraffin waxes with molecular weights up to 105,000 and melting ranges up to 270 to 273°F; however, the formation of lower-molecular-weight hydrocarbons can be increased by increasing the proportion of hydrogen in the feed gas, raising the reaction temperature, and decreasing the pressure.

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