ELECTROSYNTHESIS OF SODIUM HYDROSULFITE - II - THE EFFECT OF CATHODE MATERIAL

Sodium hydrosulfite is a major commodity reagent currently manufacture d mainly by chemical means. A new, lower cost, electrochemical pathway is being used in some cases. One of the key determinants in the marke tability of sodium hydrosulfite is the level of sodium thiosulfate in the product. At present, the level of thiosulfate from the electrochem ical process is higher than that from the chemical process. Here a cri tical evaluation is presented of cathode materials for the electrochem ical manufacture of sodium hydrosulfite nearly devoid of thiosulfate. It is demonstrated that the yield, selectivity, and efficiency of hydr osulfite and thiosulfate production depends upon the applied potential , pH of the feedstream, buffering capacity, and cathode material. Seve ral planar cathodes for the electrosynthesis of hydrosulfite have been critically evaluated. We demonstrate that five main process parameter s contribute to high hydrosulfite to thiosulfate ratios; NaHSO3 reacta nt concentration, feedstream pH, buffer capacity, cathode material, an d applied potential. By control of these parameters, we demonstrate th at hydrosulfite solutions devoid of thiosulfate can be electrochemical ly produced.