Investigation of pitch modification and its effect on anode properties: Effect of pitch type

Aluminium is produced by electrolysis using carbon anodes. These anodes are manufactured with dry aggregate (mainly calcined petroleum coke, butts, and rejected green and baked anodes) and coal tar pitch, which acts as a binder. Utilization of good quality anodes decreases the consumption of carbon and energy, hence the process cost as well as the emission of greenhouse gases (GHG). The interactions between coke and pitch play an important role in determining the anode quality. If they are compatible, pitch can penetrate into the pores of the coke particles as well as into the voids between the particles, resulting in denser anodes. One way to improve these interactions is to modify the chemical composition of pitch using an additive. The objective of this study is to investigate the effect of the pitch type on the effectiveness of pitch modification in improving the anode properties. Two types of pitch with different quinoline insoluble (QI) contents were used: one with high QI (HQI pitch) and the other with low QI (LQI pitch). They were modified using the same additive. The interactions between the pitches and the coke were studied by measuring the wettability of coke by the pitches. The pitch chemical composition was studied using FTIR and XPS. Then, anodes were produced and characterized. Their apparent density, electrical resistivity, air and CO2 reactivities, and permeability were compared. The results showed that the properties of anodes produced using modified HQI pitch were improved. Modifying LQI pitch did not significantly improve the anode properties.

Automated summary

Aluminium is produced by electrolysis using carbon anodes. The properties of anodes, such as density and resistivity, can be improved by modifying the pitch used as a binder. In this study, the effect of pitch type on the effectiveness of pitch modification in improving anode properties was investigated. High QI pitch showed improved properties when modified, while modifying low QI pitch did not significantly affect anode properties.