1326489 Reverse osmosis membranes HERCULES Inc 27 Aug 1971 40433/71 Heading B5B [Also in Division B1] A reverse osmosis membrane comprises a sheet or hollow fibre of a cross-linked derivative of cellulose selected from: (a) hydroxyalkyl ethers of cellulose in which the hydroxyalkyl group has 2-6 C atoms; (b) mixed ethers of (a) in which the hydroxyalkyls contain an average of 2-6 C atoms; (c) mixed hydroxyalkyl-alkyl and mixed hydroxylalkyl-aralkyl ethers of cellulose in which the hydroxyalkyl group contains 2-6 C atoms, the alkyl group contains 1-6 C atoms and the aralkyl group contains 7-12 C atoms; (d) mixed hydroxy alkyl-aminoalkyl ethers of cellulose in which the hydroxyalkyl group contains 2-6 C atoms and the aminoalkyl group contains 2-10 C atoms; and wherein the degree of polymerization is from 25-5000, the degree of substitution is at least two. The derivatives are made by reacting cellulose with the appropriate epoxide (specified). Crosslinking may be effected with, e.g. dimethylolurea, ethylenedimethylolurea, hexamethylene diisocyanate, 2,4 - toluene diisocyanate, methylene bis - 4 - phenyl isocyanate, polymethylenepolyphenyl isocyanate, polyhydroxymethyl melamine, diglycidyl ether of bisphenol A or the triglycidyl ether of glycerol. Toluene sulphonic acid and dibutylin diacetate may catalize the cross-linking. The cross-linking may vary in amount through the membrane. If in the form of hollow fibres the membranes may be vacuum drying and extruding at 200 F. inlet temperature, 300 F. die temperature. The melt is extruded at a 2 : 1 compression ratio through a one hole die equipped with a pin for admitting nitrogen into the centre of the fibre during extrusion. If in sheet form the membrane is supported on a microporous substrate, e.g. of nylon cellulose acetate, P.V.C., nitrocellulose, metals, or P.T.F.E. The membrane may be multilayered. The substrate is pre-wetted before the membrane material is cast or laid upon it. The membranes are used for desalination of brackish or sea water or concentration of maple syrup, citrus juice, whey, coffee, soup, malt beverages or spent sulphite pulping liquors.