GB1050831A - - Google Patents

Abstract

1,050,831. Dialysis stacks. AMERICAN MACHINE & FOUNDRY CO. May 22, 1963 [June 6, 1962], No. 20418/63. Heading B1X. [Also in Division C7] A dialysis stack comprises ion-selective membranes, e.g. alternating cationic- and anionic-selective membranes 30C, 30A, intercalated with first and second separators, each of said first separators 32, 33, or 36 having parallel straight grooves the axes of which are perpendicular to the end edge faces and each of said second separators 42 having sealing means along the parallel side edges, the end edge faces of both separators between any pair of ion-selective membranes being in contact so that the separators define fluid-treatment compartments having one end only open, the other end being closed except for said groove openings. The apparatus described is for electrodialysis. In order to produce separate concentrating and diluting streams, the grooves 34 in separator 32 communicating with concentrating compartments C are offset from the grooves 35 in separator 33 communicating with diluting compartments D and grooves 37 in separator 36 which drain anode-washing liquid, the outputs from the different sets of grooves 34, 35 being separately collected in channels 70, 71. The sides of the stack housing, which may be of aluminium, parallel to the flow of liquid have a clearance with the ionselective membranes and separators to form by-pass passages between fluid inlet 64 and the opposite outlet end of the cell to reduce the hydrostatic pressure across the cell and avoid cross-leakage between the dilute and concentrated streams. The by-pass liquid stream is collected by sections 78 of a trough 75 and may be re-circulated through the stack via a pipe 79. The separate dilute and concentrated streams in channels 70 and 71 are collected in corresponding troughs 72 and 73. The second separators 42 comprise sheets of mesh-like expanded plastics material, e.g. polypropylene, with the sealing edges formed by bonding to the edge of the sheet a filling material such as a cold-setting silicone rubber, while the first separators 32, 33, 36 act as gaskets which clamp the outlet ends of the ion-selective membranes. In a modification, the first and second separators are combined into a single sheet. The anode 45 which may be of platinum or platinized titanium foil or wire is spaced from the final cation-selective membrane 30C by a separator 46 which is thinner than the separator 42 and is spaced from the bottom plate of the stack housing by a non-selective membrane 41 and a polythene foam packing block. The anode washing fluid is collected from grooves 37 in separator 36 in a section 78 of the trough 75 and is drained away by pipe 76. The cathode 50 of stainless steel screen material is contained in a sealed bag 49 of anion-permeable material provided with catholyte inlet and outlet tubes 51, 53, the cathode lead passing through tube 51, the bag 49 being disposed between the last anionselective membrane 30A and a second polythene foam packing block.