Reactivity of Coke in Relation to Sulfur Level and Microstructure

The quality of coke materials available for anodes for the aluminium industry is changing and industrial cokes with higher impurity levels are now introduced. The cokes in the anodes must meet specifications with respect to impurity levels to ensure proper operation in the electrolysis cells, and a desired quality of the aluminium metal. The presence of sulfur has been observed to reduce the CO₂ reactivity and a certain level of sulfur is therefore targeted in the anodes. In this work, the significance of varying sulfur and metal impurity content in industrial cokes were evaluated with respect to CO₂ reactivity, accessible surface area, pore size distribution, surface oxide groups and crystallite reactive edge planes. While relatively similar cokes are observed to give a lower reactivity with increasing sulfur content, cokes that have distinct differences in surface properties can have dissimilar reactivity despite identical sulfur content. Correlations between pore size distribution and presence of S-S bound sulfur, possibly condensed Sx, was also observed.