Electrodialytic production of gas-free sodium hydroxide based on Donnan breakdown

Abstract

An approach to generating high purity NaOH solutions in a continuous flow system by electrodialytic means is described. Sodium hydroxide of ordinary purity flows along one side of a perfluorinated cation exchange membrane; this channel also contains a noble metal anode. Sodium ions from this donor channel are elctrodialyzed across the membrane into a flowing water receptor channel, bounded on the other side by an identical membrane. This membrane is in intimate contact on its far side by a perforated inert plate, beyond which the cathode is located. Water flows through the cathode channel. The restrictor plate causes the accumulation of high concentrations of NaOH on the electrode side of the cathode membrane, resulting in its eventual Donnan breakdown and passage of cathodically generated OH - through it to the central channel. From the purity of the H + -exchanged conductance of the NaOH solution generated, it is estimated that the generated product is at least an order of magnitude purer in terms of carbonate contamination relative to the feed NaOH solution. The pure NaOH generated is directly fed into a high pressure pump and used for anion chromatography.