Patent GB-1350343-A (GB)
Title: Preparation of anisotropic semi-permeable membranes of polyaryl ether/sulphones
IPC: C08L81/06
Filed: 1972-05-23
Abstract: 1350343 Anisotropic semi-permeable membranes RHONE-POULENC SA 23 May 1972 [24 May 1971] 24263/72 Heading B5B [Also in Division B1] An anisotropic semi-permeable sulphonated polyaryl ether/sulphone membrane is made by casting a solution of the polymer on a support, immersing the supported film in a coagulating bath and recovering the membrane produced, in which process: (a) the sulphonated polyaryl ether/sulphone used possesses between 0À3 and 2 meq./g. of sulphonic acid groups (defined to include alkali metal and alkaline earth metal salts thereof), and a reduced specific viscosity of between 40 and 200 cm<SP>3</SP>/g. (measured as a 2g./l solution in dimethyl-formamide at 25 C.; (b) the concentration of the casting solution is between 5 and 60% w/v of solution; (c) the coagulation bath comprises, per 100 parts of water, 5 to 100 parts of a salt formed by an anion of a strong inorganic acid and a metal cation and 1 to 120 parts of a solvent for the polymer; (d) the temperature of the coagulation bath is between - 30 and + 30 C.; (e) the period of immersion in the coagulation bath is between 30 seconds and 60 minutes; (f) the immersion in the coagulation bath is preceded by gelling the polymer layer. The sulphonated polyaryl ether/sulphone may contain a plurality of units of the formula and, optionally, units of the formula in which each of E, G, and G 1 , which may be identical or different, is an aromatic group at least one of which comprises, as a substituent, one or more sulphonic acid groups (as hereinbefore defined), the number of sulphonic acid groups attached to each aromatic group being the same or different; each of E<SP>1</SP>, G<SP>1</SP> and G 1 , which may be identical or different, are the same as E, G and G 1  except that they do not contain sulphonic acid groups; each of Q and Q 1 , which may be identical or different, represents a substituent which is inert to sulphonation reactions, e.g. an alkyl radical of 1 to 4 carbon atoms or a halogen atom; each of Q 2  and Q 3 , which may be identical or different, represents an electronattracting group, e.g. a nitro, phenylsulphone, alkylsulphone, trifluoromethyl, nitroso or pyridyl group; each of r, s, t, and u, which may be identical or different, is 0 or an integer from 1 to 4, at least one of them being less than 4; m is 0 or 1; and R represents a valency bond or a radical selected from -CO-, -O-, -SO 2 - and divalent organic hydrocarbon radicals; e.g. an alkylene, alkylidene, cycloalkylene or arylene radical of less than 7 carbon atoms. E, G and G 1  may each represent a p-phenylene radical at least one of which carries one or more sulphonic acid groups; E<SP>1</SP>, G<SP>1</SP> and G<SP>1</SP> 1 , each represent a p-phenylene radical r, s, t and u may be 0, m may be 1 and R represent The casting solution may contain one or more solvents for the polymer which are aprotic polar solvents, e.g. dimethyl formamide, 0 to 50% based on the total weight of the liquids, of a different solvent or swelling agent for the polymer, of boiling point less than 90 C., e.g. dichloromethane, and 0 to 10% based on the total weight of the liquids, of a non-solvent for the polymer, e.g. water. The amine salt or quaternary ammonium salt may be a salt formed by an anion of a strong inorganic acid and a cation derived from an amine or a quaternary ammonium cation, or an ammonium salt produced by reacting a carboxylic polyacid or a carboxylic hydroxyacid with a polyamine or a quaternary ammonium cation. A salt derived from lactic acid and diethylenetriamine is preferred. The concentration of the casting solution may be between 30 and 55% by weight, and the solution may be cast on to a support which is covered by a woven, non-woven or knitted fabric, which may be of vegetable origin such as cotton or of synthetic origin such as polyamide or polyester, which fabric becomes incorporated in the membrane. Coagulation may be effected at from - 20 to + 20 C. for between 10 and 30 mins. The membrane may be heat-treated, suitably for 1 to 60 mins. with an aqueous solution of an inorganic salt especially sodium nitrate at a temperature of 100 to 150 C. Dehydration of the membrane may also be effected suitably with a compound or mixture of compounds containing at least one alcoholic -OH group for between 10 seconds and 24 hours at a temperature of between 20 and 80 C. The membranes may be used, e.g. for desalination in conventional apparatus. Details of salt rejection tests are given.