Charcoal and Use of Green Binder for Use in Carbon Anodes in the Aluminium Industry

Abstract

Carbon anodes for aluminium production are produced from calcined petroleum coke (CPC), recycled anode butts and coal tar pitch (CTP). The CO 2 produced during anode consumption contributes to a substantial amount of the CO 2 footprint of this industrial process. Charcoal from wood has been suggested to partly replace coke in anodes but high porosity, low electrical resistivity and high ash content contributes negatively to final anode properties.In this work, charcoal from Siberian larch and spruce was produced by heat treatment to 800 °C, 1200 °C and 1400 °C and acid-washed with H 2 SO 4 . Acid-washing resulted in reduced metal impurity and the porosity decreased with increasing heat treatment. Pilot anodes were made from CTP, CPC with some additions of spruce and larch charcoal. Another set of pilot anodes were produced using a green binder. Compared to reference anodes, the CO 2 reactivity of anodes containing larch was less affected compared to anodes containing spruce. The green binder was found to be highly detrimental for the anodes' CO 2 reactivity properties. Electrochemical consumption increased for anodes containing both green binder, larch and spruce compared to the reference anode.

Continuous Calcination of Biocoke/Petcoke Blends in a Rotary Tube Furnace

“…While a small percentage of biocoke blending can significantly improve sustainability metrics, doing so will help to evaluate the optimal blending ratio(s) for physical property improvements. Although some studies blended biocoke into pilot anodes at 5−10 wt %, 17 we used 10 and 27 wt % blend ratios in order to account for extra volatile losses. We used the particle size distributions mentioned in order to flow coke properly with the smaller-scale equipment.…”

“…18 CO 2 reactivity, real density, and electrical resistivity also relate directly to the crystalline texture. The excessive porosity of most biochars also interferes significantly with the density and CO 2reactivity 17 requirements.…”

“…To resolve these issues, some have attempted to produce green coke from biomass. − Using biomass presents itself as an ideal solution due to the absence of sulfur, nickel, and vanadium, the most problematic CPC contaminants. Most attempts revolve around biomass pyrolysis, − which produces a solid biochar that, while rich in polyaromatic carbon, fails to provide adequate crystallinity. Biochar consists mostly of amorphous carbon, whereas the semicrystalline nature of CPC is perhaps the most critical property for anode success .…”

Progress on Biobased Industrial Carbons as Thermochemical Biorefinery Coproducts

“…They astutely noted that the high porosity of biocokes results in low densities, as well as a requirement for higher tar pitch percentages. Similarly to Monsen et al, Huang and co-workers , concluded that a 3 wt % blend of the biocoke fraction using fines could maintain acceptable anode properties, but blending 5 wt % of coke with biocoke significantly deviated from acceptable anode properties, including an increase of CO 2 reactivity beyond 25 mg/cm 2 h. Sommerseth et al went beyond mere testing of charcoal blends by increasing calcining temperatures to 1400 °C. This is beyond typical calciner temperatures, since it causes sulfur to escape quickly and thereby decreases density.…”

“…Similar to the previous studies incorporating biocoke, they used a higher percentage of pitch (here, biopitch) for biocokebased anodes. Sommerseth's biocoke anode study 77 utilized a green binder, although no details about the green binder are given; it was found that green binders were detrimental to the anode performance. In Hussein et al's biopitch synthesis, 89 differences in properties were attained when varying the heat treatment rates of the starting fast pyrolysis bio-oil.…”