Abstract

In an electrolytic chlor-alkali cell, or bank of cells, having a plurality of electrolyte compartments containing electrode pairs (anodes and cathodes) and wherein a hydraulically-impermeable membrane separates the electrolyte compartments into catholyte portions and anolyte portions, said cell or cells being employed to produce chlorine at the anodes and caustic and hydrogen at the cathodes by the electrolysis of an aqueous alkali metal chloride electrolyte, improved operation is attained by flowing anolyte liquor from anolyte portion to anolyte portion, sequentially, while simultaneously, and in the opposite direction, flowing catholyte liquor from catholyte portion to catholyte portion, sequentially. The membrane substantially prevents Cl- from entering the catholyte liquor from the anolyte, and a high purity caustic, substantially free of salt, is produced.