METHOD OF PRODUCING CAUSTIC SODA FROM ELECTROLYTIC ALKALI Russian patent published in 2011 - IPC C01D1/04 

FIELD: chemistry.

SUBSTANCE: invention can be used in producing caustic soda via diaphragm electrolysis. The method of producing caustic soda from electrolytic alkali involves evaporating alkali in two steps with intermediate separation of sodium chloride from the solution evaporated at the first step, and sodium chloride and sodium sulphate from the solution evaporated at the second step. Further, said salts are washed from caustic soda and mixed with water at 18-20°C. Sodium chloride is then separated from brine and cooled via self-evaporation at low pressure and extraction of mirabilite Na₂SO₄·10H₂O from brine with addition of water and separation of mirabilite from brine by filtratering. The alkali is evaporated to concentration which is 0.2-1% higher than concentration of the product solution. The solution evaporated at the second step after separation of salts is mixed with a circulating solution of caustic soda, flow rate of which is 2-5 times greater than that of the evaporated solution. The circulating solution is mixed with vapour from self-evaporation of brine while extracting mirabilite and cooled to temperature 30-35°C. Water fed for mixing with sodium chloride and sodium sulphate is cooled through heat exchange with brine obtained after separation from mirabilite.

EFFECT: invention enables to lower power consumption when extracting sulphates from the cycle of producing caustic soda and improves quality of caustic salt fed for electrolysis.

2 cl, 1 dwg, 1 tbl