Abstract
Fischer-Tropsch synthesis has been investigated over a commercial type cobalt-based catalyst (20 %Co/0.5 %Re/γ-Al2O3) by varying the H2/CO ratio (2.55–1.12), CO conversion (15–75 %), reaction temperature (210 °C, 230 °C), and by adding water to the syngas. The experiments were conducted in a fixed bed reactor with the main purpose of obtaining experimental data to be used in the development and fitting of a mechanistic model. A positive effect of water on the catalyst activity was found for experiments with a H2/CO ratio higher than 1.7. Water was found to always increase the C5+ selectivity regardless of the H2/CO ratio. Increasing conversion led to increased C5+ selectivity. The selectivity to CO2 was significantly enhanced at higher conversions (high water partial pressure), particularly with the lowest H2/CO = 1.12, interpreted as the emergence of water-gas shift activity. Re-oxidation of cobalt, probably limited to small cobalt particles, is proposed as the main deactivation mechanism caused by water while a steeper deactivation curve was found for higher temperature, indicating that sintering also may play a role.
