Abstract
This work aims to study the CO-CO2 gas composition at low potentials and low current densities in cryolite melt with relatively low alumina content (≤2 wt%). There is a scarcity of data in the literature regarding the low current density region and also for bath low in alumina. The experimental setup was constructed to minimize the back reaction as well as the Boudouard reaction. For potentials up to 1.55 V and corresponding current densities up to 0.07 A cm−2, it was found that CO is the dominant product. Between 1.55 and 1.65 V (corresponding current density region 0.07 to 0.2 A cm−2), CO2 becomes the dominant gas product. These potential values are probably slightly large due to suspected Boudouard reaction between CO2 and carbon particles in the melt formed by disintegration of the graphite anode. The results are discussed in relation to the literature data and thermodynamic calculations.
Highlights
The electrochemical anode gas product in industrial aluminum electrolysis is CO2, and some CO is produced electrochemically
For Setup 1, the CO(1%)/CO2(2%)/N2(balance) gas introduced at the bottom of the furnace and passed on the outside of the graphite crucible on its way mixture was introduced at the bottom of the furnace and passed on the outside of the graphite through the furnace
Pure nitrogen gas was flushed through the analyzer and the furnace before and after the mixture
Summary
The electrochemical anode gas product in industrial aluminum electrolysis is CO2 , and some CO is produced electrochemically. The amount of electrochemically produced CO is difficult to determine since there are several chemical reactions where CO2 is converted to CO. The anode gas from the industrial cells contains a considerable amount of CO, where most of the CO is formed by the back reaction between dissolved anodic and cathodic products, CO2 (diss.) and. The nature of the dissolved aluminum is still not completely resolved, and in the industrial electrolyte composition, sodium-containing species are dominant. Sodium dissolves in the electrolyte in the form of free Na, while dissolved aluminum is probably present as the monovalent species AlF2 − , which, by anodic oxidation, becomes AlF4 −
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