Process for the purification of salt-depleted solutions of the alkali metal chloride electrolysis employing a mercury cathode

Free chlorine concentration is reduced in a brine containing it by contacting the brine with a fluid hydrocarbon at a temperature of 50-100 DEG C. A major proportion of the chlorinated hydrocarbon may thereafter be separated from the brine. By the term brine an alkali metal chloride solution is intended. A major proportion of the free chlorine in the brine may initially be removed by vacuum distillation and the brine, whose salt content may be relatively low, may be obtained from alkali metal chloride electrolysis by the mercury process. The fluid hydrocarbon may be unsaturated aliphatic hydrocarbon such as ethylene, propylene or acetylene, a saturated aliphatic hydrocarbon such as methane, ethane, propane or butane, an aromatic hydrocarbon such as benzene, mixtures of hydrocarbons or residual gases containing hydrocarbons.