Process for removing sodium chloride from aqueous caustic soda solutions

摘要

Sodium chloride is removed by osmosis from aqueous caustic soda by contact with a membrane constituted by a swellable synthetic resin, obtained by condensation of an aromatic amine, an aliphatic amino-compound and formaldehyde. The other side of the membrane is in contact with water or a pure dilute caustic soda solution. Aromatic amines referred to are meta-phenylene diamine, meta-xylidine, aniline and meta-toluidine. Aliphatic amino-compounds referred to are polyethylene polyamines, dicyandiamide, urea, guanidine and ethylene diamine. Preferably the resin employed is prepared by condensation of meta-phenylene diamine (1 mol.), polyethylene polyamine (0,5 mol.) and 1,5-2 mol. of formaldehyde, at 80 DEG -90 DEG C. in an atmosphere saturated with water vapour. The membranes formed may be reinforced with inert synthetic resins such as polyvinyl chloride or polyacrylonitrile, or with asbestos or glass. Examples refer to the use of membranes formed by impregnating a polyvinyl chloride or polyacrylonitrile fabric with a condensable mixture of meta-phenylene diamine and formaldehyde with dicyandiamide or polyethylene polyamine and thereafter effecting condensation in a water vapour atmosphere at 85 DEG C. Such condensation may be effected by passing the impregnated fabric over steam heated rolls in a water vapour atmosphere.ALSO:A dialysis membrane is formed by condensing an aromatic amine, an aliphatic amino-compound and formaldehyde, preferably at about 85 DEG C. in an atmosphere saturated with water vapour. Aromatic amines referred to are metaphenylene diamine, meta-xylidine, aniline and meta-toluidine. Aliphatic amino-compounds concerned are dicyandiamide, polyethylene polyamine, urea, guanidine and ethylene diamine. The membranes may be reinforced with asbestos or glass or inert synthetic resins such as polyvinyl chloride or polyacrylonitrile. Fabrics of the latter resins may be impregnated with a condensible mixture of meta-phenylene diamine and formaldehyde with dicyandiamide or polyethylene polyamine and the condensation thereafter effected by passing the so-impregnated fabric over steam heated rolls in a water vapour atmosphere, or by heating at about 85 DEG C. in water vapour.ALSO:A dialysis membrane is formed by impregnating a polyvinyl chloride or polyacrylonitrile fabric with a condensable mixture of metaphenylene diamine and formaldehyde with dicyandiamide or polyethylene polyamine, and thereafter effecting condensation at a temperature of about 85 DEG C. in an atmosphere saturated with water vapour. Such condensation may be effected by passing the impregnated fabric over steam heated rollers in a water vapour atmosphere.