Off-Gas Analysis of Laboratory-Scale Electrolysis Experiments with Anodes of Various Compositions

The sulphur content of industrial anodes in the aluminium industry is usually between 1% and 2%. This sulphur is converted to different sulphuric gases which are released along with the other off gases from the cell. Although wet scrubbers in modern plants are capable of capturing the sulphur before it is released to the atmosphere, the equilibrium dynamics and production kinetics of the sulphurous gases are of vital interest in order to be able to predict acid dew point temperatures and other important parameters for the off gas suction system in a plant.Controlled potential electrolysis with on line gas analysis was utilized to study the compositions of gas species produced in a laboratory cell during regular electrolysis conditions and during anode effects. A three-electrode setup with an Al reference electrode was used to monitor the anodic voltage. The combination of mass spectrometry (MS) and Fourier-transform infrared spectroscopy (FTIR) was used to characterize the off gas.The dominant sulphur containing gas specie in the laboratory cell was COS. CS₂ was only observed during anode effect, along with small amounts of SO₂.