Modification of biocoke destined for the fabrication of anodes used in primary aluminum production

Abstract

Calcined petroleum coke, recycled anodes and the coal tar pitch are the raw materials used to manufacture carbon anodes for aluminum production. In order to reduce greenhouse (GHG) emissions from the aluminum industry and to add a value to the residue of wood industry, a small part of the calcined petroleum coke, used for the production of carbon anodes, was replaced with biocoke produced from wood by-products. Since the addition of biocoke deteriorates the properties of carbon anodes, it was modified using an additive in order to assess if the modification can render biocoke more suitable for carbon anode production by modifying the surface chemistry of the biocoke.Three samples of biocoke, unmodified, modified using 3% additive and modified using 4% additive, were produced and studied before and after modification to identify its effect on biocoke properties. First, the chemical characterization was carried out using X-ray photoelectron spectrometry (XPS) to verify whether the functional groups were added to the biocoke surface during the modification. To study the influence of the biocoke modification on the biocoke/pitch interactions, the wettability of the unmodified and modified biocokes by the coal tar pitch, which is used as a binder in anodes, were measured using sessile-drop test. After, the laboratory scale anodes were produced and their green and baked densities, electrical resistivity, air and CO2 reactivities, and bending strength were measured. The results showed that the biocoke modification was effective. A number of new surface chemical groups were added to the biocoke coke surface. This improved the biocoke/pitch wettability, consequently affected the anode properties.