Characterization of Interactive Behavior between Bio-Pitch and Fine Calcined Petroleum Coke in a Hybrid Bio-Binder for Carbon Anodes.

The aluminum industry is looking to reduce its carbon footprint, and one possible pathway to achieve this goal is to switch from fossil to biomass carbon sources. Bio-pitch (BP) has shown potential to be used as the binder in carbon anodes, but it has a low coking value (CV). In our previous work, a hybrid bio-binder (HBB) was prepared when fine calcined petroleum coke (fine-CPC) between 0-30 wt % was added to bio-oil during its thermal treatment up to 180 °C to improve the CV of BP. Compared with BP, the CV of HBB increased monotonically with increasing concentration of fine-CPC to bio-oil, but the viscosity decreased when fine-CPC concentration was added between 5-10 wt %. This decrease in viscosity was unexpected, and the current work aims to explain this phenomenon. The possible phenomena were the activation of fine-CPC by bio-oil or the cracking of the bio-oil catalyzed by fine-CPC. Fine-CPC residues were solvent-separated from the BP phase in HBB for chemical and surface analysis, and the soluble phase of the BP was collected for molecular analysis. The results did not show an indication of the fine-CPC activation. The low concentrations of fine-CPC, along with the higher presence of low molecular weight compounds in the BP phase of HBB as revealed by liquid chromatography-mass spectrometry, suggest that the reduction of viscosity of HBB when fine-CPC was added to the bio-oil between 5-10 wt % results from the catalytic effect by fine-CPC. Understanding the reduction of viscosity with the addition of fine-CPC could be leveraged in the mixing process of raw materials for carbon anode formulation.