Sodium Hypochlorite (NaOCl)
Sodium hypochlorite (soda bleach liquor) has largely replaced calcium hypochlorite (lime bleach liquor) in the paper and textile industries, due to its greater stability and comparatively better bleaching efficiency. NaOCl is always handled as a solution (15% is about maximum), and is usually generated on-site by passing chlorine into a solution of caustic soda, soda ash or a mixture of the two, or by electrolysis of an aqueous NaCl solution. The type and degree of excess alkalinity in the final soda bleach liquor should be considered when designing the piping system.		Specific gravities of soda bleach solutions Sodium hypochlorite solution Specific heats of sodium hypochlorite solutions
Sodium hypochlorite, although more stable than ClO 2, suffers from many of the same problems. Under certain conditions it will release free wet chlorine, making piping material choice critical. NaOCl also freezes at about 30°F (-1°C), necessitating line tracing to keep it a liquid. Tracing lines can be a problem if a system is shut down and the pipes remain hot. Electric tracing is usually recommended where there is a chance of the hypochlorite breaking down and releasing free chlorine. The chart below provides selection data for materials suitable for handling sodium hypochlorite. Sodium Hypochlorite (NaOCl) Concentrate - maximum use temperatures, 5% - 15% concentration 1If decomposition to free chlorine is possible PP should not be used. PVDF or PTFE resin is preferred material. 2PVDF should not be used if the pH is 11 or higher.