Biochar as an Additive to Modify Biopitch Binder for Carbon Anodes

Abstract

Looking for alternative materials to coal-tar pitch (CTP), as a binder in anode manufacturing, in aluminum production is of great interest. Such a material should be able to mitigate the cost and health issues without decreasing the carbon anode quality. Biopitch (BP) could be considered as a potential candidate. Previous studies show that biomass-based pitch has generally a low coking value compared to that of CTP, which might negatively affect its properties as a binder in carbon anodes. To increase its coking value, biopitch was modified by using additives. A solid bio-based material, namely, biochar, was considered as an additive. The prepared biopitch samples, containing different quantities of biochars, were analyzed for their softening point (SP), QI content, coking value (CV), molecular weight distribution, viscosity, surface tension, chemical groups, and surface composition, as well as their wettability with coke particles. The differences in texture and topography of different pitches, as well as the interface between pitch and aggregate particles in sessile drop after wettability test, were studied. The results revealed that increasing the quantities of biochars in biopitch increases their coking value, QI content, density, viscosity, and softening point. Furthermore, biochar addition only shows a minor influence on surface tension and molecular weight distribution of biopitch. An optimum amount (9.0 wt %) of biochar addition in biopitch could therefore be beneficial in anode formulation while using biopitch as a binder, compared to those of the reference anodes. The properties of the laboratory anodes (green/baked density, air/CO2 reactivity, compressive strength and electrical resistivity, carbon structure of the carbonized pitch) were investigated. Addition of biochar into biopitch could reduce the overall consumption of biopitch in the carbon anode formulation.

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