Process

 Manufacturing : 

  • Castner-Kellener Process – In this process the caustic soda is prepared by the electrolysis of aqueous NaCl. 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 divides each compartments at the bottom of the cell. One end of the cell is pivoted and the rest of the part rests on an in centric wheel, which gives the rocking motion to the cell so mercury can circulate from one compartment to other.
  • Castner-Kellener cell – It is a rectangular cell made up of steel. The inner walls of the tank is lined wih ‘ebonite’. Anode is titanium and mercury acts as cathode.
  • Ionization of NaCl – When the solution is subjected to electric discharge the NaCl disassociates into  ions, now the positive and negative charges migrates towards its respective electrodes. The sodium deposited at mercury forms sodium amalgam and the chlorine produces at the anode is removed from the top of the cell.
  • Reaction at cathod – 2Na++2e-→2Na  |  Na+Hg→Na/Hg           Reaction at anode – 2Cl-Cl2+2e- 
  • Metathesis reaction – By reacting sodium carbonate with calcium hydroxide, sodium hydroxide and calcium carbonate is produced. These products can be easily separated by filtration as calcium carbonate is not soluble whereas sodium hydroxide is highly soluble. The solution will then be purified, processed and standardized for industrial consumption.
  • Chloralkali process – With the electrolysis of sodium chloride solution, solid sodium hydroxide is manufactured and obtained with the evaporation of water. Chlorine gas is also produced as the main by-product. This is done through three main types of cell, mainly mercury cell, diaphragm cell and the membrane cell.
  • Formation of NaOH :

    Amalgam now passed to the other chamber known as ‘denuder’, where it is treated with water to produce NaOH, it is in liquid state.