Salt splitting with radiation grafted PVDF membranes

Sulphonated PVDF cation-exchange membranes have been formulated for the splitting of sodium sulphate by electrohydrolysis. Three membranes with different degree of grafting were tested in a two-compartment membrane cell. The effect of flow rate, current density and salt concentration on the performance of each membrane is described. The different flow conditions in front of the membranes did not significantly affect the current efficiency. Productivity was greater at higher current densities, although a slight decrease in the current efficiency was observed. The SPVDF with a 22.7% degree of grafting performed slightly better than the other cation-exchange membranes. The new materials gave acceptable selectivity; low electrical resistance; and excellent chemical, thermal, and mechanical stability. They resulted in superior performance to the commercially available Nafion(R) 117, enabling an increase of approximately 20% in current efficiencies and sodium transport rates.