GB910202A - Improvements in or relating to ion-exchange membranes - Google Patents

Abstract

A cellulose-containing membrane having ion-exchange properties comprises regenerated cellulose having incorporated therein an ion-exchanger, which may be an ion-exchange cellulose derivative, an ion-exchange resin, or both. Specified cellulose derivative ion-exchangers include (a) cation-exchangers:-sulphethoxy cellulose, cellulose phosphate, carboxymethyl cellulose, cellulose citrate, cellulose hydrogen phthalate and oxidized cellulose; (b) anion-exchangers:-amino-ethyl cellulose, amino-propyl cellulose, diethylaminoethyl cellulose, ecteola cellulose (a derivative made from epichlorhydrin, triethanolamine and cellulose), di-isopropylamino-ethyl cellulose, and triethylamino-ethyl cellulose. Specified resinous ion-exchangers include (a) cation-exchangers:-polystyrene sulphonic acid, phenol sulphonic acid-formaldehyde resins and polyacrylic acid; (b) anion-exchangers:-styrene polymers and amine/aldehyde condensates containing quaternary ammonium or amine groups as active groups. The membrane may also include synthetic fibres, e.g. glass, polyethylene, polyacrylate, polyamide, polyester or polyvinyl derivative fibres. In a preferred method, a solution of viscose is mixed with an ion-exchanger, the mixture formed into a film and the film treated to regenerate cellulose from the viscose to form the membrane. The ion-exchanger may be an ion-exchange cellulose derivative in sheet, fibre, thread, web, film, floc or powder form, an ion-exchange resin in particle or sheet form, or a mixture of ion-exchange cellulose derivative fibre or powder and ion-exchange resin particles, and synthetic fibres may be included in the ion-exchanger. In an alternative method, the ion-exchanger is preformed into sheet form, the sheet impregnated with viscose solution, and the impregnated sheet treated to regenerate the cellulose from the viscose to form the membrane. The ion-exchanger may be preformed into a sheet in paper form, and synthetic fibres, e.g. of glass, polyethylene, polyacrylate, polyamide, polyester, polyvinyl derivatives, polystyrene or polyacrylonitrile/polyvinyl copolymers, may be incorporated in the paper. Regeneration is preferably effected by treatment with a salt solution, e.g. ammonium sulphate, followed by dilute acid, e.g. sulphuric acid. Examples are given.