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A detailed kinetic model describing the consumption of key components and product distribution in the Fischer–Tropsch synthesis (FTS) over a 20%Co/0.5Re γ‐Al2O3 commercial catalyst is developed. The developed model incorporates the H2O‐assisted CO dissociation mechanism developed by Rytter and Holmen and a novel approach to product distribution modeling. The model parameters are optimized against an experimental dataset comprising a range of process conditions: total pressure 2.0–2.2 MPa, temperature 210–230°C, CO conversion range of 10%–75% and feed with and without added water. The quality of the model fit measured in terms of mean absolute relative residuals (MARR) value is 23.1%, which is comparable to literature reported values. The developed model can accurately describe both positive and negative effects of water on the rate kinetics, the positive effect of water on the growth factor, temperature and syngas composition on the kinetics and product distribution over a wide range of process conditions, which is critical for the design and optimization of the Fisher–Tropsch reactors. [ABSTRACT FROM AUTHOR]

The evaluation of the Fischer-Tropsch experiment with H 2 /CO = 2.13 at 210 °C with changes in CO conversion and water addition. [Display omitted] • Co-based catalyst developed WGS activity at low H 2 /CO ratio. • Water has a positive effect on C 5+ selectivity for all H 2 /CO ratios. • Re-oxidation of cobalt is proposed as the main deactivation mechanism caused by water. Fischer-Tropsch synthesis has been investigated over a commercial type cobalt-based catalyst (20 %Co/0.5 %Re/γ-Al 2 O 3) by varying the H 2 /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 H 2 /CO ratio higher than 1.7. Water was found to always increase the C 5+ selectivity regardless of the H 2 /CO ratio. Increasing conversion led to increased C 5+ selectivity. The selectivity to CO 2 was significantly enhanced at higher conversions (high water partial pressure), particularly with the lowest H 2 /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. [ABSTRACT FROM AUTHOR]

The effect of K on 20%Co/0.5%Re/γ-Al2O3 Fischer–Tropsch catalysts with two different cobalt particle sizes (small, in the range 6–7 nm and medium size, in the range 12–13 nm) was investigated. The catalyst with the smaller cobalt particle size had a lower catalytic activity and C5+ selectivity while selectivities towards CH4 and CO2 were slightly higher than over the catalyst with larger particles. These effects are ascribed to lower hydrogen concentration on the surface as well as the lower reducibility of smaller cobalt particles. Upon potassium addition all samples showed decreased catalytic activity, reported as Site Time Yield (STY), increased C5+ and CO2 selectivities, and a decrease in CH4 selectivity. There was no difference in the effect of potassium between the sample with small cobalt particles compared to the sample with medium size particles). In both cases the specific activity (STY) fell and the C5+ selectivity increased in a similar fashion. [ABSTRACT FROM AUTHOR]