A novel preparation method for “small” eggshell Co/γ-Al2O3 catalysts: A promising catalytic system for compact Fischer–Tropsch reactors

Abstract

Due to the need of limiting pressure drop, and the consequent necessity of adopting “big” catalyst pellets, low-temperature Fischer–Tropsch synthesis in industrial fixed-bed reactors may suffer of strong intra-particle mass transport limitations, which are known to result in decreased CO conversion rate and C5+ selectivity. Upon decoupling the pellet diameter and the diffusive length, eggshell catalysts represent an engineering solution for the intensification of the Fischer–Tropsch reactors. In this work, preparation, characterization and testing of impregnated Co/γ-Al2O3 eggshell catalysts with sharply defined outer shell regions are reported. The method developed to impregnate the active phase only on the outer layer of the support is based on the “protection” of the inner pores of the support with an organic liquid and on the control of the contact time between the impregnating solution and the protected support. The method is particularly suitable to prepare “small” eggshell pellets, with diameters below 1mm, to be used in compact FT reactors. It is shown that 600μm pellets, with catalytically active layers 75μm thick, grant a remarkable combination of high CO conversion rate and high C5+ selectivity, thus resulting extremely interesting for operations in reactors 3–6m long.