Abstract
The synthesis of hydrocarbons (HC) from syngas (a mixture of hydrogen and carbon monoxide), commonly named Fischer-Tropsch synthesis (FTS), allows making valuable products from relatively cheap substrates, such as biomass, natural gas or coal. Furthermore, synthetic HC are reported to be useful, cleaner (lower in sulphur and heavier metals than crude oil), easier and cheaper to transport. FTS reaction is normally conducted on metal supported catalysts (Fe, Co and Ru) and the production of higher HC is directly related with the reaction conditions. In this work, optimization techniques are applied in Gibbs energy minimization method in a multiphase model that considers the potential formation of coke (S), a water phase (L1), an organic phase (L2) and a gas phase (V) (S+L1+L2+V model) to perform the thermodynamic characterization of FTS process. The software GAMS 23.2.1 and the solver CONOPT are used to solve the proposed problems. The restrictions of non-negativity of the number of moles and the stoichiometric balance are used. The effect of the catalyst is considered by restricting the products that can be formed, since the actual system is not in thermodynamic equilibrium. Twenty-three (23) compounds are selected to represent the possible products in FTS reaction, including aliphatic hydrocarbons in the range of C2-C20, H2O, H2, CO and CO2. The effects of reaction conditions are analyzed, effects of temperature (in the range of 350-550 K), pressure (in the range of 5-30 bar) and H2/CO ratio used in the feed (in the range of 1.0-2.0/0.5-1.0) are tested in terms of HC production and products composition. The reaction yields proved to be highly dependent on the reaction conditions; low temperature, high pressure and H2/CO molar ratio of 2.0/1.0 are achieved as the best conditions to promote HC production in FTS process.
