Modeling analysis of cobalt-based Fischer-Tropsch catalyst particles

The influences of particle size, shape and catalyst distribution on the reactivity and hydrocarbon product selectivity of a cobalt-based catalyst for Fischer-Tropsch synthesis were investigated in the present work. A self-consistent kinetic model for Fischer-Tropsch reaction proposed here was found to correlate experimental data well and hence was used to describe the consumption rates of reactants and formation rates of hydrocarbon products. The perturbed-chain statistical associating fluid theory equation of state was used to describe vapour-liquid equilibrium behaviour associated with Fischer-Tropsch reaction. Local interaction between intraparticle diffusion and Fischer-Tropsch reaction was investigated in detail. Results showed that in order to avoid the adverse influence of intraparticle diffusional limitations on catalyst reactivity and product selectivity, the use of small particles is necessary. Large eggshell spherical particles are shown to keep the original catalyst reactivity and enhance the selectivity of heavy hydrocarbon products. The suitable layer thickness for a spherical particle with diameter in 2 mm is nearly 0.15 mm. With the same outer diameter of 2 mm, the catalyst reactivity and heavy product selectivity of hollow cylindrical particles with a layer thickness of 0.25 mm is found to be larger than eggshell spherical particles. From the viewpoint of catalytic performance, hollow cylindrical particles are a better choice for industrial applications.