A critical review of the kinetics and selectivity of the Fischer–Tropsch synthesis (FTS) is given. The focus is on reaction mechanisms and kinetics of the water–gas shift and Fischer–Tropsch (FT) reactions. New developments in the product selectivity as well as the overall kinetics are reviewed. It is concluded that the development of rate equations for the FTS should be based on realistic mechanistic schemes. Qualitatively, there is agreement that the product distribution is affected by the occurrence of secondary reactions (hydrogenation, isomerization, reinsertion, and hydrogenolysis). At high CO and H2O pressures, the most important secondary reaction is readsorption of olefins, resulting in initiation of chain growth processes. Secondary hydrogenation of α-olefins may occur and depends on the catalytic system and the process conditions. The rates of the secondary reactions increase exponentially with chain length. Much controversy exists about whether these chain-length dependencies stem from differe...

Kinetics and Selectivity of the Fischer–Tropsch Synthesis: A Literature Review

The Fischer-Tropsch synthesis is at the heart of the Biomass-to-Liquids (BTL) process. Feasibility studies published in open literature typically consider cobalt-based catalysts for the Fischer-Tropsch synthesis. Here, we present an overview on the history and development up until the present for both cobalt- and iron-based Fischer-Tropsch catalysts. The role of the support material and various other additives to the catalyst formulation are discussed in detail with regard to activity, catalyst deactivation, and selectivity. Tentative explanations for e.g. the observed size dependency in cobalt-based catalysts and phase transformations in iron-based Fischer-Tropsch catalysts are offered. The productivity of cobalt-based catalysts at high conversion level is currently higher than that of iron-based catalysts. Nevertheless, it is argued that iron-based catalysts may be an attractive option for the BTL-process, since it is much cheaper, impacting on the cost of the process due to inevitable process set-ups in industrial operation. Improvement of current iron-based catalysts is however desired.

Fischer‐Tropsch Catalysts for the Biomass‐to‐Liquid (BTL)‐Process

The characteristics of a slurry phase reactor are contrasted with those of a conventional tubular fixed bed reactor (TFBR) for the conversion of synthesis gas to long chain hydrocarbons. Hydrodynamic information needed for the design of a commercial scale slurry phase Fischer–Tropsch (FT) reactor were obtained from experiments carried out on a 1 m internal diameter pilot plant reactor. The kinetics, selectivities and deactivation mechanisms of Fe and supported Co FT catalysts are compared for both slurry phase and fixed bed operation. The combined advantages of the slurry phase reactor and a very active Co catalyst create the opportunity to convert remote natural gas to high quality middle distillates in a cost effective manner.

Low temperature Fischer–Tropsch synthesis from a Sasol perspective

Biomass-derived syngas production via gasification process and its catalytic conversion into fuels by Fischer Tropsch synthesis: A review

The kinetics of the gas–solid Fischer–Tropsch synthesis over a commercial Fe–Cu–K–SiO 2 catalyst was studied in a continuous spinning basket reactor. Experimental conditions were varied as follows: reactor pressure of 0.8–4.0 MPa, H 2 /CO feed ratio of 0.25–4.0, and space velocity of 0.5–2.0×10 −3  Nm 3  kg cat −1  s −1 at a constant temperature of 523 K. A number of Langmuir–Hinshelwood–Hougen–Watson type rate equations were derived on the basis of a detailed set of possible reaction mechanisms originating from the carbide mechanism for the hydrocarbon formation and the formate mechanism for the water gas shift reaction, respectively. 14 models for the Fischer–Tropsch reaction rate and two water gas shift reaction rate models were fitted to the experimental reaction rates. Bartlett’s test was used to reduce the set of Fischer–Tropsch rate equations to 3 models, which were statistically indistinguishable. It could be concluded that the reaction rate of the Fischer–Tropsch synthesis is controlled by the formation of the monomer species (methylene) by hydrogenation of associatively adsorbed CO, whereas the carbon dioxide formation rate (water gas shift) is determined by the formation of a formate intermediate species from adsorbed CO and dissociated hydrogen. Simulations using the optimal kinetic models derived showed good agreement both with experimental data and with some kinetic models from literature.

Carroll O. Bennett

Papers

Kinetics of the Fischer-Tropsch Reaction over Iron