INFLUENCE OF PH ON THE OXYGEN ABSORPTION KINETICS IN ALKALINE SODIUM DITHIONITE SOLUTIONS

Results from experimental studies on the influence of pH within the alkaline range on sodium dithionite oxidation with molecular oxygen reveal that it is possible to follow the kinetics of the process by observation of the consumption of base needed to maintain a constant pH. Under the conditions studied (partial oxygen pressure higher than 20,260 N/m2, pH > 8, 295 K less-than-or-equal-to T less-than-or-equal-to 318 K, and a dithionite concentration higher than 0.01 M), absorption occurs by means of a reaction of zero order for oxygen and of 1.5 for dithionite while the apparent kinetic constant is independent of pH. Under these conditions the process is adequate for measuring interfacial areas in gas-liquid contactors and non-coalescent systems, although the high rate of reaction could be an important restriction for very efficient gas-liquid contactors, i.e. those with high values of a and k(l)o. The discrepancy among results found in bibliography seems to be due to: (a) dithionite decomposition when the pH is lower than 8 which takes place when the starting alkaline solution is not sufficiently concentrated or when the pH is not kept constant by the addition of base, (b) absorption does not occur in the fast reaction regime.