Sub-surface carbon dioxide reaction in anodes

Abstract

Formation of carbon dust in electrolysis is linked to reaction of the anodes with carbon dioxide. The general understanding is that the reaction takes place inside the anodes, below the bath surface and rather more toward the sides of the anodes than the bottom. Given this, a relevant question is the relative importance of transport through the anode compared to its intrinsic reactivity. To provide quantitative answers, a transport-reaction model has been developed. The key finding is that the extent of reaction is insensitive to the permeability. This is because the reaction produces two moles of CO for every mole of CO2 consumed, so that there is a net flow away from the reaction locale. Consequently, fresh reactant must be supplied by diffusion rather than convection. Since these two processes are governed by different material properties, this finding opens the possibility of new approaches to optimization of anode structure.