Modeling of Surface Structure of Supported Catalysts. Application to Deactivation of FT Reactors

Abstract

Water in Fischer−Tropsch synthesis (FTS) on supported cobalt catalysts is known to deactivate the catalysts. The deactivation involves the reoxidation of highly dispersed cobalt phase by water and water-induced sintering. In both cases, the dispersion state of the cobalt phase in the supported catalyst plays an important role. Therefore, the deactivation kinetics depends on the surface structure of the catalyst. Mathematical models are formulated to describe the deactivation behavior of cobalt catalyst pellets with the dependence on catalyst structure and reaction conditions. On the crystallite scale, a size-dependent deactivation model for individual metal particles is built; on the catalyst scale, the deactivation and growth (shrinking) of each individual metal crystallite in the pellet as well as the radial distribution for temperature and concentrations are accounted for using a population balance equation (PBE) coupled with intraparticle diffusion-reaction equations. The model is used for optimizatio...