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HistorY
The first application was soap
In antiquity the Egyptians were already using caustic soda to manufacture coarse soaps. For centuries, the main use remains the saponification of fatty acids.
Later, instead of extracting it, caustic soda was made from sodium carbonate. There was a long period of cottage-type production, as sodium carbonate was only to be found in a few natural deposits or in the calcination of marine plants. The quantities ofraw material were still too small for caustic soda to be manufactured economically.
Scientific Development
Research allowed man to produce caustic soda using processes which became ever more diverse and more efficient.
SOLVAY SETS UP THE BASIS FOR INDUSTRIALISATION:
- Caustic soda benefited from progress in the manufacture of sodium carbonate
In 1791, Leblanc invented a process for the production of sodium carbonate which was a major milestone in the evolution of commercial production.
However, this was superseded by Ernest Solvay who, in 1861, manufactured this same sodium carbonate using ammonia. His efficient production methodology overtook all other processes.
Producing sodium carbonate of such a high purity was not possible unit that time. The Solvay process gave a vigorous impulse to the consumer industries by providing unlimited quantities of sodium carbonate at a low cost.
Among these, the manufacture of caustic soda by the caustification of sodium carbonate was obviously the first beneficiary discovery.
- Caustic soda benefited from the mastery of electrolysis techniques
Towards the end of the 19th century, thanks to technological advances, another process for the manufacture of caustic soda, the electrolysis for a solution of sodium chloride, became feasible industrially.
Naturally, Solvay became interested inthe process and built its first electrolysis plant in 1898. Since then, this technique has been continuosly improved.
THE TECHNIQUES OF MANUFACTURE
ELETROLYSIS OF SODIUM CHORIDE
Sob o efeito de uma corrente elétrica que passe entre dois eletrodos (o ânodo e o cátodo), ocorre a dissociação das moléculas do cloreto de sódio e da água, o que produz cloro sobre o ânodo e hidrogênio e soda cáustica líquida sobre o cátodo.
EleCtriciTY
NaCl+H2O → Electricity → NaOH+1/2Cl2↑+1/2H2↑
This reaction takes place in equipment known as an electrolysis “cell”.
THERE ARE THREE TYPES OF CELL
The cell is fed with a punfied and concentrated brine. Uncer the effect of electric current, chlorine is released onto the anodes and the sodium forms na amalgam with the mercury on the cathode, which is drawn off from the cell.
Electrolytic decomposition of NaCl:
NaCl → Na++Cl-
2Cl-→ Cl2↑+2e
2Na++2e +2Hg→ 2NaHg
The amalgam is then introduced into a further cell, where it is decomposed by the water, with the formation of caustic soda and hydrogen.
The mercury is pumped out and returned to the first cell.
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