Abstract
AbstractSodium dithionite was generated by electroreduction of sulphur dioxide on a graphite fibre mat cathode in a continuous ‘flow‐by’ trickle‐bed electrochemical reactor. Reactor performance was measured with respect to variation of the feed catholyte NaOH concentration [0.5‐1.0 mol/L], feed gas SO2 concentration [4‐40 vol%], product catholyte pH [2.4‐12.0] and applied current [10‐50 A (0.4‐2.0 kA/m2)]. Product catholyte temperature was in the range 18 to 30°C. With product catholyte pH between 2.4 and 6.9, dithionite was generated at current efficiency from 42 to 100%, concentration from 0.05 to 0.78 mol/L, yield from SO2 up to 69% and specific energy from about 2 to 5 kWh/kg Na2S2O4. Current efficiency fell with increasing current and rose with increasing gas load. High levels of thiosulphate [0.07‐0.3 mol/L] and sulphide [0.01‐0.13 mol/L] measured in the product catholyte would compromise the use of this process in commercial applications such as brightening wood pulp.
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