Simple process design calculations have been done using the process synthesis concepts, basic thermodynamics and simple Fischer-Tropsch (FT) synthesis flowsheet models to see if the probability of chain growth or alpha value has any effect on the overall carbon efficiency of the FT synthesis process design in order to compare possible alternatives.

Two process configurations, namely; once-through and recycle processes, were compared and the results show that for a fixed production rate of liquid fuels at 100% CO conversion, the carbon efficiency for the process with a recycle stream is higher than the once-through process. However, if the aim is to use a low temperature FT synthesis catalyst in order to maximize diesel production by hydrocracking the waxes, it was found that there should be an optimal alpha value above which the cost of hydrocracking very heavy waxes into diesel becomes very costly. At alpha values beyond 0.7, the incorporation of wax hydrocracking in the two processes drops carbon efficiency, thereby making it uneconomical to produce very long chain hydrocarbons.