GB1013464A - Improvements relating to dialytic or electrodialytic cells - Google Patents

Abstract

In an electrodialysis cell which comprises a series of narrow compartments bounded on their major faces by ion-permeable or ion-selective membranes 16 and disposed within the open centres of spacers interposed between adjacent membranes, the membranes and spacers together forming a stack between end electrodes, and conduits 19 being formed through the cell by co-operating holes in the membranes and spacers, each spacer is formed of a pair of sheets 1, 11 mating face to face so that slots in the two sheets form passages leading from liquid supply and removal conduit-forming holes to each compartment, the slot 7 in one sheet merging into a hole 3 but being closed off from the open centre 2 at its inner end while the slot 11 in the other sheet merges into the open centre 21 but is closed off from the hole 31, and the construction is such that each face of the spacer makes continuous contact with the adjacent membrane over an area that lies between the open centre and the conduit-forming holes. Either each sheet is formed with two identical <PICT:1013464/C6-C7/1> <PICT:1013464/C6-C7/2> <PICT:1013464/C6-C7/3> slots arranged on opposite sides of the central opening so that two different sheets are used to form each spacer or each sheet may have slots 7 as in Fig. 1 on one side of the central opening and slots 11 as in Fig. 2 on the opposite side of the opening, one sheet being turned top to bottom relatively to the other to form the spacer. A thin gauze 18, e.g. of nylon, may be disposed between the portions of the sheets defining the passages to the conduits 19 if the compartments are filled with granular ion-exchange resin, the two sheets and the gauze of each spacer then being united into a single element. Normally one liquid flows through every alternate compartment of the cell and a different liquid through the other compartments and the pressure on the two liquids may differ without danger of leakage between the flow paths due to bowing of the membranes. The directions of liquid flow may be at right angles as in Specification 845,186, the holes 5, 6 and 51, 61 forming supply and withdrawal conduits for one of the liquids. Each sheet may be made up of a number of side-by-side pieces and the Specification also states that each spacer may be moulded as a single unit from a plastic such as polythene, polypropylene, or polyvinyl chloride without claiming such an arrangement. Specification 894,473 also is referred to.