NaOH Manufacturing Process

NaOH Manufacturing

Caustic soda (NaOH) available in solid flakes and liquid solution (different concentration. Caustic soda production is done by any one of the following manufacturing processes.

Method of Manufacture:

1.    Chemical: lime soda process,

2.    Electrochemical: chloro alkali process

§      Diaphragm Cell

§      Mercury Cell Process

§      Membrane Cell Process

Electrochemical Process

Castner-Kellner Cell (Mercury Cell Process)

Castner-Kellner process was developed in the mid 1800’s. The cell had a positive electrode and a negative electrode inside a tank. The reactions proceeded as follows:

1.  A sodium chloride brine (salt water) is put into the tank. 
2.  The positive electrode (Titanium anode) attracts the chloride away from the sodium. The chloride builds up and combines to form chlorine gas ( an excellent disinfectant)

Anode Reaction (oxidation: 

 2Cl- (aq)  = CL2 (g)+ 2e-

fig: mercury cell process

3         3. The water is broken apart with the negative electrode (Mercury cathode) into hydrogen ions) which form into hydrogen gas) and hydroxide ions.

           4. The negative electrode (Mercury electrode) attract sodium ions forming.

Cathode Reaction (reduction):

Na+(aq)  + e- = Na(s)

         5.Na(s) dissolves in the liquid mercury to form an amalgam, which is removed to the decomposer.

         6.In the decomposer the amalgam reacts with water to form sodium hydroxide, hydrogen gas and mercury.

                                              2Na/Hg + 2H2O(l) = 2Na+   +  2OH-  +  2Hg (l) 

 7. Sodium hydroxide solution and hydrogen gas are collected.