The primary raw material for the chlor-alkali industry is saturated brine; however, as crude brine contains impurities such as silt, Ca²⁺, Mg²⁺, and Fe³⁺-rendering it far from meeting electrolysis requirements-it must undergo purification and refining.
There are two process routes for the dechlorination of lean brine. The first is the air stripping method; this method yields poor dechlorination results, and the waste chlorine gas recovered from the lean brine is of low purity. Consequently, it cannot be fed into the wet chlorine header for downstream processing and must instead be absorbed by circulating caustic soda solution to produce sodium hypochlorite. The second route is the vacuum dechlorination method, which offers superior performance; a vacuum system-powered by steam ejectors or vacuum pumps-extracts and separates free chlorine from the lean brine, directing the recovered gas into the wet chlorine header. The vacuum dechlorination process is recommended.