Differences between Fisher–Tropsch synthesis of either gasoline or diesel based on changes of entropy and free energy

• Fisher–Tropsch synthesis of fuels is analyzed evaluating energy release as consequence of heat of reaction.
• Experimental products distributions obtained using different kinds of catalysts are compared.
• Prevision of energy management during Fisher–Tropsch synthesis is used as criterion for production objectives.
• Lighter liquid fuels, such as gasoline, are found to be more favoured to be produced than diesel.

Synthesis of liquid fuels, mainly gasoline and diesel, by Fisher–Tropsch reactions is a complex process. Prediction of products distribution as function of carbon number has been under discussion for many years and, currently, it has not been possible to perform without a comprehensive description of catalyst properties/formulation; therefore, usually experimental data are necessary to study this process. In this work, analysis of experimental data obtained from several literature references is performed by evaluating the total energy release, as consequence of heat of reaction, and entropy and free energy generated during the experiments. It is found that depending on the production objectives and the catalyst used, energy management during hydrocarbons synthesis, mainly paraffins and olefins, could be a criterion to decide how long the hydrocarbons chain should be. Additionally, since total Gibbs’ free energy becomes less negative as hydrocarbons are longer, it is assessed that production of gasoline and LP gas could be more attractive as target than production of diesel.

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