At the anode, chlorine ions discharge with evolution of chlorine gas. At the cathode, hydrogen is evolved and caustic soda is formed. The cation exchange is impermeable to the chloride ions and therefore the caustic soda produced contains only trace levels of sodium chloride. In mercury cell process, the liquid mercury cath ode forms amalgam with sodium. The amalgam is re moved from the cell and reacted with water in denuders to give caustic soda and hydrogen.
Chlorine is liberated at the anode.
Factors which were considered in the choice of process technology include flexibility of scaling capacity utilisation and environmental impact. Other factors considered were cell materials, power consumption and current effi ciency. Comparison of the key parameters of the three processes are shown in Table 2. Characteristics of the various process technologies. The various cells materials are specified in Table 2.