GB845544A - Improvements in and relating to the concentration of solutions - Google Patents

Abstract

845,544. Electrodialysis. PERMUTIT CO. Ltd. May 23, 1957 [May 30, 1956], No. 16748/56. Drawings to Specification. Class 41. A process for concentrating an aqueous solution of a non-electrodialisable substance, i.e. a non-electrolyte or an electrolyte having ions too large to pass readily through membranes used in an electrodialytic process, e.g. diptheria antitoxin solutions or sugar solutions, comprises adding to the solution an electrolyte. e.g. sodium chloride, of which the ions at least of one sign are water-bearing, i.e. carry water molecules with them through the membranes during electrodialysis, and electrodialysing the solution to remove the water-bearing ions and some water. The electrodialysis may be carried out by placing the solution in, or passing it through, the centre compartment of a three compartment cell in which an anionic permselective membrane bounds the anode compartment and a cationic permselective membrane bounds the cathode compartment. If desired, one of the membranes may be replaced by a non-selective membrane, e.g. of regenerated cellulose. The added electrolyte should be one in which the cations and/or anions are hydrated in aqueous solution, and preferably are inorganic, univalent ions. The process is applicable to the concentration of aqueous solutions which contain a non-aqueous liquid, so long as the amount of liquid present is not such as to reduce the degree of hydration to a point where satisfactory concentration is unobtainable, e.g. a solution containing up to 50 % alcohol may be concentrated by the process. In a specific embodiment, 400 gms. sodium chloride where added to 4À5 litres of sugar solution which was circulated at 1 litre per minute through the alternate compartments of a multicompartment cell having alternate anionic and cationic permselective membranes, a 1 % sodium chloride solution being passed in counter-current through the remaining compartments. A current of 4 amps was passed for 4¢ hours to raise the concentration from 20 % w/w to 40 % w/w. Some or all of the anionic, or alternatively, of the cationic permselective membranes, may be replaced by non-selective membranes.