|Fig: Manufacture of NaOH by Caster Kellener’s Process|
It consist mercury cathode cell which is a rectangular vessel divided into three compartments by a non-porous slate partition which do not touch the bottom of the cell. A layer of mercury seperates each compartments at the bottom of the cell. One end of the cell is pivoted and the rest of the part rests on an incentric wheel, which gives the rocking motion to the cell so mercury can circulate from one compartment to other.
The outer compartment of the cell consists of graphite as anode and filled with brine solution (28% NaCl) and the central compartment of the cell consists series of cylindrical iron rod as cathode and filled with water. The layer of mercury acts as cathode in outermost compartments, whereas anode in inner compartment due to induction. When we pass electricity through the brine solution as electrolyte, it gets ionized at outer compartment as follows:
NaCl ———–> Na++Cl–
Where Cl–oxidizes and evolved Cl2 which passes through outlet. Na+discharges at mercury cathode and forms sodium amalgam:
Na++e–+Hg ———-> NaHg
2Cl ————> Cl2
Due to rocking motion of the cell, NaHg flows towards central compartment and reacts with water:
NaHg+H2O ————> NaOH+Hg+H2
Hence, the amount of NaOH is about 20% in the cell. It is pumped and casted into pallets.