Patent GB-1163686-A (GB)
Title: Heterogenous Ion Exchange Membranes.
Inventor: SCWACHULA GERHARD
IPC: C08J5/22
Filed: 1968-05-02
Abstract: 1,163,686. Ion exchange membranes. FARBENFABRIK WOLFEN, VEB. 2 May, 1968, No. 20895/68. Heading B1X. A heterogeneous ion exchange membrane comprises a condensed film made from an acetone-formaldehyde precondensate, the film containing at least one cation exchange-active and/or anion exchange-active material and being associated with a supporting fabric. The membrane, which preferably has a thickness of between 0.1 mm and 1 mm, may be a cation exchange membrane or an anion exchange membrane or, if the film contains both a cation exchange-active material and an anion exchange-active material, a bipolar ion exchange membrane. The membrane may be produced by forming an intimate mixture of an acetone-formaldehyde precondensate and at least one dustlike cation exchange-active and/or anion exchange-active material, applying the mixture and an alkaline catalyst to a supporting fabric, and condensing completely by the action of heat the substance applied to the fabric. The precondensate is produced from acetone and formaldehyde in a mole ratio preferably of between 1 to 1 and 1 to 5, most preferably of 1 to 2. As exemplified, the ion exchange-active material is sulphonated polystyrene crosslinked with 8% divinyl benzene (Example 1) from which material is produced a cation exchange membrane, an ammonium group-containing polystyrene cross-linked with, 5% divinyl benzene (Example 2) from which material is produced a strongly basic anion exchange membrane, styrene-divinyl benzene having a degree of cross-linking of 15% (Example 3) from which material is produced a strongly acidic cation exchange membrane, and acrylic acid-divinyl benzene having a degree of cross-linking of 10% (Example 4) from which material is produced a weakly acidic cation exchange membrane. The particle size of the ion exchange-active material preferably is less than 0.1 mm. The weight ratio of precondensate to ion exchange-active material preferably is between 60 to 40 and 30 to 70. The mixture of precondensate and ion ex change-active material also may contain a plasticizer which may be a compound containing primary hydroxyl groups, for example a polyalcohol, a polyester, a fatty alcohol, a polyether or a polyglycol having terminal hydroxyl groups. The catalyst may be used in the form of a solution the concentration of which preferably is from 10% to 50% by weight. Examples of suitable solutions are solutions of strong alkalis, for example sodium hydroxide, potassium hydroxide and tetraethyl ammonium hydroxide, in water or in an organic solvent, and alcoholic solutions of alkali metal alcoholates. The supporting fabric may be made from glass fibre, cotton, a polyamide, a polyester, polyvinyl chloride or polypropylene. The thickness of the fibre from which the fabric is made preferably is between 0.01 mm and 1 mm; the mesh size of the fabric preferably is between 0.1 mm<SP>2</SP> and 1 mm<SP>2</SP>. The mixture of precondensate and ion exchange-active material may be applied one or more times to the fabric which prior to such application may have been desized with a solvent, for example carbon tetrachloride. A non-porous ion exchange membrane is produced by condensing at a temperature of from 30‹C to 60‹C and using a non-porous dust-like ion exchange-active material and, as catalyst, either an alcoholic solution of an alkali metal hydroxide or a solution of an alkali metal alcoholate; a porous ion exchange membrane is produced by condensing either at a temperature of from 30‹C to 60‹C and using a porous dust-like ion exchange-active material and, as catalyst, an alcoholic solution of an alkali metal hydroxide or at a temperature of from 90‹C to 110‹C and using a non- porous dust-like ion exchange-active material and, as catalyst, an aqueous solution of an alkali metal hydroxide; a doubly porous ion exchange membrane is produced by condensing at a temperature of from 90‹C to 110‹C and using a porous dust-like ion exchangeactive material and, as catalyst, an aqueous solution of an alkali metal hydroxide. The ion exchange membranes are of use in the desalination of sea water and of brackish water, in the separation of electrolytes from industrial waste waters, in the deionisation of sugar juices, molasses, whey, glycerol and film emulsions, in the recovery of acids and salts from electrolysis and spinning baths, in the production and subsequent purification of organic acids, in the separation of anode and cathode chambers in electrolytic processes, in membrane electrodes as diaphragms and in fuel cells; bipolar ion exchange membranes may be used in rectifiers.