Efficiency and Selectivity in the Chlorate Process
Time: Thu 2021-05-20 10.00
Subject area: Chemical Engineering
Doctoral student: Aleksandra Lindberg , Tillämpad elektrokemi
Opponent: Associate Professor Eva Blomberg, Yt- och korrosionsvetenskap
Supervisor: Professor Ann Cornell, Tillämpad elektrokemi; Susanne Holmin, Permascand AB
This licentiate thesis presents experimental studies concerning two parts of the electrochemical cell in the chlorate process: a cathode and an anode.
Newly synthesized MnOx electrodes were investigated for the cathodic reaction, hydrogen evolution reaction (HER) in the chlorate process. In industry addition of toxic and carcinogenic chromium (VI) as sodium dichromate provides high efficiency. Here undesirable addition of sodium dichromate was avoided while high cathodic efficiency was achieved. Cathodic efficiency and selectivity towards HER, achieved by the MnOx electrodes annealed at different temperatures, were measured by means of mass spectrometry (MS).
The second study investigated oxygen evolution in the chlorate process, which is an anodic side reaction. The evolution of oxygen decreases anodic efficiency and also presents a safety risk due to occurrence of HER in the undivided cell. We followed the amount of produced oxygen by two types of the electrode TiRu, similar to that industrially used, and synthesized TiRuSnSb, by means of MS. The produced oxygen amount was compared to the amount produced by Pt. To our best knowledge, this was the first study that successfully disentangles three different sources of oxygen with good time resolution. Oxygen is produced by homogenous hypochlorite decomposition, heterogeneously by different catalysts present in the electrolyte solution and anodically during the electrolysis i.e. electrochemically. Different electrode materials catalyzed hypochlorite decomposition differently and led to a different volume of oxygen produced.