Kelvin A. Pacheco and Reginaldo Guirardello
Optimization, Mathematical Modelling, Gibbs Energy Minimization, Fischer-Tropsch Synthesis
The Fischer-Tropsch Synthesis (FTS) is an important technology for gas-to-liquids conversion process, which allows the conversion of syngas, (CO and H2) produced from natural gas, coal, waste or biomass, in a mixture of hydrocarbons such as light olefins, alcohols and other products. The thermodynamic modelling of such system can be made by chemical and phase equilibrium employing the minimization of the Gibbs free energy. Thermodynamic equilibrium calculation can be computed as an optimization problem, given certain constraints. The present work investigated the phase and chemical equilibrium of Fischer-Tropsch process through the minimization of the Gibbs energy of the system, with the objective to determine the most thermodynamic favorable phases and compositions of the formed FTS products. The software GAMS is used to solve the proposed problem. The restrictions of non-negativity of the number of moles and the non-stoichiometric balance are used; thirty three possible chemical species (linear paraffins, linear alpha alkenes and alcohols besides carbon monoxide, carbon dioxide, water and hydrogen) were considered. The effects of temperature (300-900 K), pressure (1-30 bar) and H2:CO ratio (2:1 and 3:1) are evaluated.