Patent GB-1416457-A (GB)
Title: Treatment of polymer membranes
IPC: B01D67/00
Filed: 1972-12-29
Abstract: 1416457 Permselective membranes E I DU PONT DE NEMOURS & CO 29 Dec 1972 [30 Dec 1971] 60205/72 Heading B5B [Also in Divisions B1 and C3] The solute rejection efficiency of a membrane of a substantially linear, aromatic, synthetic, organic nitrogen-linked condensation polymer of formula (-L-R-) n , wherein: (i) each -L-group is independently a linking group and at least 50% of the -L-groups contain a nitrogen atom in the polymer chain; (ii) each -R-group is independently an organic radical and at least 50% of the -R-groups contain a 5-member or 6-member ring subject to resonance bonding; (iii) the degree of polymerization is defined by n, an integer sufficiently large to provide film-forming molecular weight, is improved by contacting the membrane with an ether of formula weight greater than 400 and a ratio of carbon atoms to oxygen atoms between 2À5 ; 1 and 5 : 1. Preferably the polymer membrane is an aromatic polyamide, polyhydrazide or poly(amide-hydrazide). The ether may be of the formula wherein R is hydrogen, methyl or ethyl, and n is a number from 8 to 2000; (polyvinyl methyl ether) is preferred. Alternatively the ether may have the formula wherein R<SP>1</SP> is an aliphatic or aromatic radical; A is -O-, -S-, -NH-, -CONH-, -CO 2 -, or -PO 3 # ; x is a number sufficiently large to give a formula weight of more than 400; and a and b are one except where A is -PO 3  # a is one or two and b is one or two; and Q is hydrogen or methyl. The ether may also be one of the formula whereinR<SP>3</SP> is hydrocarbon radical; n is a number in the range 1 to 5; and x is a number sufficiently large to give a formula weight of more than 400; especially, R<SP>3</SP> contains 8 or 9 carbon atoms, n is one and x is between 5 and 20. Alternatively the ether may have the formula wherein Z is the residue of tetrahydrofuran, condensed tetrahydrofuran or tetrahydropyran; n is a number sufficiently large to give a formula weight of more than 400; R<SP>6</SP> is a straight or branched-chain saturated or unsaturated aliphatic radical of 10 to 18 carbon atoms; and p and q are independently numbers from 1 to 3 inclusive with the proviso that the sum of p and q is equal to the number of esterified and etherified hydroxyl groups in Z. In use, the membrane is suitably contacted with an aqueous solution of at least 5 parts per million of ether, e.g. by dipping. Thus the membrane may be assembled into a permselective separation apparatus and a solution of the ether containing 500 to 10,000 p.p.m. thereof passed through the apparatus to contact one surface of the membrane. The membrane may also be exposed to the ether under reverse osmosis conditions, the ether solution preferably containing 10 to 500 p.p.m. thereof. After its exposure to the ether, the membrane is desirably exposed to an aqueous medium at a temperature of 50‹ to 90‹ C. for a time sufficient to reduce the salt passage therethrough, suitably 2 to 24 hours. In examples, (i) a hollow fibre polyamide membrane is treated with an aqueous solution of an ethylene oxide-alkylamine condensation product; (ii) and (iii) similar membranes are treated with an aqueous solution of an octyl phenol-ethylene oxide condensation product; (iv) hollow fibre membranes as in (ii) are held overnight in water at up to 55‹ C. and then overnight at up to 55‹ C. in a solution of the condensation product of (ii); (v) and (vi) various polymers, including that of (ii) are cast from solution to form film membranes; (vii) hollow fibre membranes made as in (ii) are treated with a variety of ethers, including wetting agents available under the Trade Marks Igepal, Pluronic, Triton and Tetronic, (viii) a cast polyamide film membrane is treated with a poly(vinyl methyl ether); (ix) the hollow fibre membrane of (ii) is similarly treated; (x) hollow fibre membranes assembled as in (iv) are treated with a copolymer of methyl vinyl ether and ethyl vinyl ether; (xi) a cast polybenzimidazole film membrane is treated with a poly(vinyl methyl ether); (xii) the hollow fibre membrane assembled as in (iv) is treated with the reaction product of ethylene oxide with sorbitan monolaurate; (xiii) the hollow fibre membranes of (ii) are treated with the treating agent of (xii); (xiv) hollow fibre membranes assembled as in (vii) are treated with poly(vinyl methyl ether). Water flux and salt passage data are given for the treated and untreated membranes.