GB1067500A - Electrodialysis - Google Patents

Abstract

<PICT:1067500/C6-C7/1> Fig. 1 shows an electrodialysis cell 3 wherein liquor to be electrodialyzed is fed to a frame 13 (a frame being a compartment between two membranes or between a membrane and an electrode), having on one side an anion concentrating frame 9 and on the other side a cation concentrating frame 17 (these three frames 9, 13, 17 together being referred to as a treating frame). Three similar treating frames (9, 13, 17) (9', 13', 17') and (9", 13", 17") are separated from one another by barrier frames 23, 23' through each of which is passed a barrier solution containing ions which aid the passage of electric current and which may be used in the desired operation, e.g. solutions containing H2SO4, H2SO3 or CH3COOH. Membrane 11 is non-selective, 15 is cation selective, 19 is anion selective and 25 is cation selective. Fig. 2 (not shown) illustrates an electrodialysis cell (103) similar to that of Fig. 1 but which differs in having three anion concentrating frames (109a, b, c) separated from one another and from a liquor frame (113) by non-selective membranes (111 a, b, c) which allow molecules to pass in their order of decreasing molecular weight. Treating frames, each comprising anion concentrating frames (109, a, b, c), a liquor frame (113) and a cation concentrating frame (117) are built up into a stack with barrier frames (123) interposed between treating frames and with an additional anolyte frame (106) adjacent the anode and a catholyte frame (146) adjacent the cathode. Spent sulphite liquor from paper making may be electrodialyzed; such liquor contains lignosulphonates of varying molecular weights, wood sugars, SO2 and basic ions such as Na+, Ca++, Mg++ and NH4+. Alternatively salt-protein systems such as milk, blood or whey may be electrodialyzed. Particular examples relating to both Figs. 1 and 2 are for electrodialysis of an ammonia base spent sulphite liquor having a solids content of about 10%. The solutions were circulated through their frames at such a rate as to establish turbulence.