Distribution of potassium during chemical activation of petroleum coke: Electron microscopy evidence and links to phase behaviour

Abstract

In this study, direct evidence for chemical penetration into petroleum coke particles during activation is presented. In addition, the porosity development was directly related to the sulphur loss and phase behaviour of the species present. Petroleum coke (petcoke, 6 wt.% sulphur) was activated with KOH and NaOH at temperatures between 400 and 800°C. The C-S bonds were broken before 400°C in the presence of KOH and before 500°C in the presence of NaOH. Electron microscopy analysis of cross-sectioned and ultramicrotomed samples revealed that sulphur was still present within the particles and that the hydroxide activation agents had penetrated to the centre of the particles (90–150 μm). After heating to 800°C and washing with a weak acid aqueous solution, essentially all the sulphur was removed, as was any remaining chemical agent. The characterization results, phase diagrams, and complementary experiments with carbonate chemical agents or steam suggest that, during heating, a molten phase formed around the petcoke particles. The composition of this molten phase changed as activation proceeded and both sulphur and ash components were liberated from the petcoke. This better understanding of the activation process will improve the efficiency of preparing activated carbon.