Binchotan charcoal as a renewable source for partial replacement of calcined petroleum coke in the aluminum industry

Abstract

Fossil-based materials have been used in the aluminum industry for many decades but cause major environmental impacts. The use of biomaterials can help to reduce these impacts. The aluminum industry uses calcined petroleum coke and coal tar pitch in carbon anode production, and the anodes act as chemical reducers and electrical conductors during the alumina electrolysis process. This work evaluated the partial replacement of calcined petroleum coke with binchotan charcoal, aiming at the production of carbon anodes. Binchotan was used because it is a type of charcoal characterized for showing high carbon content, high density, and low electrical resistivity. The study was carried out in partnership with an aluminum production company, which allowed the use of materials, methodologies, and equipment that are applied in conventional anodes. The literature review (Chapter 1) addresses concepts related to biomass, reduction processes, the origin, characteristics, and production process of binchotan charcoal. The materials characterization is in Chapter 2. Samples of binchotan charcoal were analyzed and compared to calcined petroleum coke. The following analyses were performed: proximate analysis, chemical composition, scanning electron microscopy and energy dispersive spectroscopy (SEM-EDS), Fourier-transform infrared spectroscopy (FTIR), thermogravimetry, density, higher heating value, electrical resistivity, and X-ray diffraction (XRD). Binchotan charcoal showed high carbon content and low ash content, but these values were better in coke. Analyzing the SEM images, a higher porosity was observed in binchotan charcoal. The thermal behavior was similar in all the materials, as were the FTIR spectra. The density of the coke was higher than that of the binchotan charcoal and the results of higher heating values were similar. Binchotan charcoal showed an electrical resistivity higher than petroleum coke. The XRD patterns were similar and showed the presence of graphite in the materials, with higher intensity in coke. In general, the properties of calcined petroleum coke were better than those of binchotan charcoal, although the results indicated that a replacement of small percentages would be feasible. The production of carbon anodes with the addition of binchotan charcoal is described in Chapter 3. The anodes were produced on a laboratory scale, replacing 1% and 3% of calcined petroleum coke with binchotan charcoal. The samples were analyzed by chemical composition, apparent density, mechanical strength, CO2 reactivity, and electrical resistivity. The obtained data was compared with an industrial reference standard. All the results were considered acceptable, suggesting that it is possible to make a partial substitution of calcined petroleum coke for binchotan charcoal. From a technical point of view, the addition of small percentages of binchotan charcoal in the carbon anodes proved to be viable.