Effect of catalyst shape and multicomponent diffusion flux models on intraparticle transport-kinetic interactions in the gas-phase Fischer-Tropsch synthesis

Abstract

Intraparticle Fischer-Tropsch (FT) transport-kinetics interactions for various Fe-based catalyst particle shapes (sphere, solid cylinder, hollow cylinder, 4-hole cylinder, modified 4-hole cylinder, and 7-hole cylinder) under typical gas-phase FT process conditions (T = 493–533 K, P = 25–30 bar, and H2/CO = 2) are investigated using different multicomponent diffusion flux models. A Fe-based microkinetic gas-phase FT model is used to describe the intrinsic reaction rates for all reactants and products. The Soave-Redlich-Kwong (SRK) EOS is used to describe the vapor-liquid equilibrium associated with the FT product distribution. The effect of process conditions and catalyst shape on the effectiveness factor, particle volume-averaged key component concentrations, liquid-to-vapor (L/V) ratios and diesel range concentration profiles, along with methane-based diesel selectivities, are presented. It is found that the solid cylinder has the highest volume-average diesel concentration (ca. 4.4 mol/m3 at T = 493 K and P = 25 bar) when compared to the other shapes. The hollow cylinder and 7-hole cylinder shapes have the lowest intraparticle liquid-to-vapor (L/V) ratio (ca. 0.004 at T = 493 K and P = 25 bar) and the highest effectiveness factor (η) of 0.35. Temperature-based diffusivity correlations do not consider the change in effective diffusivities of the species in the FT reaction network. The simulations show that the inclusion of Knudsen diffusion through the Wilke-Bosanquet and Dusty-Gas Models resulted in an intraparticle FT product distribution that closely approximate literature results.