Studies and Discriminations of the Kinetic Models for the Iron-Based Fischer−Tropsch Catalytic Reaction in a Recycle Slurry Reactor

Abstract

The Fischer−Tropsch synthesis kinetic rates were studied by discussing the hydrogenation steps of the favored hydrogen-assisted CO dissociation mechanism and the surface site balance over an industrial iron-based catalyst. Their mathematical expressions are the two proposed models −rFT = (kFTPCOPH2α)/(kCOPCO + ∑i=1ixi) and −rFT = (kFTPCOPH2α)/((kCOPCO + ∑i=1ixi)2) in the literature. Unresolved relationships and differences between the two models are addressed here and analyzed specifically. When the significance of each of the terms in the two rival models is critically evaluated, both surface site balances of the two could be simplified to two involved terms: an adsorbed CO term and a vacant site term. Although the two models could hardly be distinguished from each other at the typical range of experimental conditions, further theoretical analyses and extrapolated experimental data favor the latter [its simplified form is −rFT = (kFTPCOPH20.5)/((1 + kCOPCO)2)]. These studies are helpful to understand the CO activation processes, and some contradictory conclusions and experimental phenomena in the literature can be explained consistently and reasonably.