Purificn. of chloride-contg. conc. aq. sodium hydroxide soln. - by treatment with basic ion exchanger

摘要

Chloride-contg. NaOH is purified by passing a conc. aq. soln. contg >=20 wt.% of the NaOH over a basic ion exchanger. The ion exchanger is then regenerated by diluting the conc. alkali in the exchanger bed to a concn.of 20 wt.% and separating the dil. alkali from the ion exchanger. The process is simple and economical and gives good reduction in chloride content of conc. NaOH solns. This allows the use of membrance cell electrolysis in the prodn. of NaOH in place of the previously used mercury process, which gives rise to environmentally polluting effluent streams. The membrance cell however gives NaOH solns. with a high chloride content (e.g. >=10000 ppm) which can cause stress corrosion and/or pitting corrosion of chrome nickel and austenitic stainless steels.