Reactivity of Coke in Relation to Sulfur Level and Microstructure

Abstract

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.

An EXAFS and XANES Study of V, Ni, and Fe Speciation in Cokes for Anodes Used in Aluminum Production

“…So now there is the possibility to investigate how these particular metal species act to drive theair burn and carboxy reactions. While correlations have been established between the air reactivity or the carboxy reactivity and the V, Ni or Fe content (including with these cokes [33]) the detailed mechanisms of the reactions involving the metal compounds have not been established. If knowledge of the reaction mechanisms could be investigated, now that we know the identity of the metal compounds present in these materials, it may be possible to poison these metal sulfide "catalysts" to mitigate the negative effect of high metal impurity levels.…”

Optical and Electrochemical Characterisation of Carbon Anodes with Varying Porosity and Coke Quality

“…Furthermore, anodes from a pilot study using smaller grains (<2 mm) and varying coke quality (sulfur in 1.4-5.5 wt% range, anisotropic and isotropic cokes) were also investigated as part of this study. These are referred to as anodes P1-P5 (these cokes have been thoroughly investigated in [18][19][20], in these papers referred to as cokes A-E). Anode P1 is presented in Table 1, while relevant sulfur and microstructural properties of the cokes are presented as part of the results (Table 3).…”