GB858076A - Fluid fractionation by electrodialysis - Google Patents

Abstract

858,076. Electro-dialysis of liquids. KOLLSMAN, P. Sept. 25,1958, No.30657/58. Class 41 Liquids including ionic and non-ionic mixtures, but excluding colloids are separated into their components by electro-dialysis using ion exchange permselective membranes whereby ions of one charge pass through the membrane, and the others build up a concentrated mixture at the membrane surface, and due to the influence of gravity, the components separate into layers with the lighter components at the top, which are then drawn off from the individual levels, The membranes may be anionic or cationic, and are selected in accordance with the ions to be separated, the cell compartments may be filled with porous granular material e.g. another ionic material which preferentially absorbs or transports a selected ion. The liquid preferably flows horizontally, to promote maximum separation under gravity. Fig. 1 shows a horizontal cross section of a suitable apparatus consisting of main cell compartments 44 bounded by membranes 23... 29, with guard cells 12, 13 flanking the main cells, the end sections 15, 16 containing the anode and cathode respectively. The sidewalls of the main cells communicate with a supply chamber 39 and exit-chamber 49, through screens 45, 47. The liquid mixture to be separated is supplied through one or more inlets 42, which also supplies the guard chambers 12, 13, An electrolyte is also fed to the electrode chambers. Liquid flows uniformly into the cells 14 where it is subjected to the electric field generated between electrodes 16, 17, and the ions concentrated at the membranes flow slowly towards the chamber 49 forming under the action of gravity, layers of different components at different levels. These are drawn off through a series of exit pipes arranged vertically of which one only 54 is shown. Several modifications of the apparatus are described, in which the floor of the main cells is sloping downwards to the exit chambers; in which the liquid flows in the same direction as the electric field; and in which the ionic membrane is arranged is a spiral, regarded in plan, with an inner cylindrical electrode, and an outer cylindrical electrode surrounding the spiral. For Examples, (1) a solution of KF, Na Cl and Li Cl is treated using an anion permeable membrane. The Li component is drawn off at the top, the Na is the central exits, while the K component concentrates at the bottom, (2) using fullers earth as an inert cell filler, and using potassium chloride solution in the electrode compartments, a mixture of 50:50 acetane and benzene separates into 62 % acetone at the top and 62% benzene at the bottom (3) sea water is separated into a top outflow containing about 1/3 the salt content of the bottom outflow. Reference is made to separating mixtures of salts of different dissociation e.g. sodium chloride or acetate, borax; boric acid, acetic acid; sugar solutions; mixtures of alcohol or acetone with water or benzene or other hydrocarbons.