Abstract: A membrane stack comprising the following components: (a) a first ion diluting compartment (D1); (b) a second ion diluting compartment (D2); (c) a first ion concentrating compartment (C1); (d) a second ion concentrating compartment (C2); and (e) a membrane wall (CEM1, mAEM, mCEM, AEM, CEM2) between each compartment and on the outside of the first and last compartment of the stack; wherein: (i) each membrane wall comprises a cation exchange membrane (CEM1, mCEM, CEM2) or an anion exchange membrane (mAEM, AEM) and the order of the cation and anion exchange membranes alternates from each wall to the next; (ii) the membrane walls (mAEM, mCEM) on each side of compartment (a) both have a higher monovalent ion selectivity than the corresponding membrane walls (AEM, CEM2) on each side of compartment (b); and (iii) the stack further comprises a means for communicating fluid between compartments (a) and (b).

Abstract: A membrane stack comprising the following components: (a) a first ion diluting compartment (D1); (b) a second ion diluting compartment (D2); (c) a first ion concentrating compartment (C1); (d) a second ion concentrating compartment (C2); and (e) a membrane wall (CEM1, mAEM, mCEM, AEM, CEM2) between each compartment and on the outside of the first and last compartment of the stack; wherein: (i) each membrane wall comprises a cation exchange membrane (CEM1, mCEM, CEM2) or an anion exchange membrane (mAEM, AEM) and the order of the cation and anion exchange membranes alternates from each wall to the next; (ii) the membrane walls (mAEM, mCEM) on each side of compartment (a) both have a higher monovalent ion selectivity than the corresponding membrane walls (AEM, CEM2) on each side of compartment (b); and (iii) the stack further comprises a means for communicating fluid between compartments (a) and (b).

Abstract: A process for preparing a membrane stack comprising the steps of: (i) interposing a curable adhesive between alternate anion exchange membranes and cation exchange; and (ii) curing the adhesive; CHARACTERIZED IN THAT said adhesive, when cured, has a Shore A hardness of less than 70 and an elongation at break of at least 50%.

Abstract: A disposable, crossflow membrane stack suitable for use in an ion exchange unit, the stack comprising alternate dilution compartments and concentration compartments, each compartment being defined by a flat cation-permeable membrane (2) and a flat anion-permeable membrane (1) and at least two edges along which the cation-permeable and an anion-permeable membranes are permanently secured together wherein the cation-permeable membranes and/or the anion-permeable membranes have a textured surface profile which keep said membranes apart and/or from touching each other and wherein the edges secured together define the direction in which liquid may flow through the compartments. Also claimed are ion exchange units comprising the stack, optionally comprising a quick-release securement means to allow facile attachment and release of modular units comprising the stacks.

Abstract: A process for preparing a membrane stack comprising the steps of (i) interposing a curable adhesive between alternate anion exchange membranes and cation exchange; and (ii) curing the adhesive; CHARACTERIZED IN THAT said membranes are in a swollen state when step (ii) is performed.

Abstract: An electrodialysis unit comprising at least two electrodialysis stacks (ED1 and ED2) connected in series, wherein: (a) stacks ED1 and ED2 comprise anion exchange membranes and cation exchange membranes; and (b) the anion exchange membranes in stack ED1 have a lower electrical resistance than the anion exchange membranes in stack ED2 and the cation exchange membranes in stack ED1 have a lower electrical resistance than the cation exchange membranes in stack ED2. Also claimed is a process for purifying liquids, e.g. for desalinating sea water or brackish water.

Abstract: A process for preparing a membrane stack comprising the steps of: (i) interposing a curable adhesive between alternate anion exchange membranes and cation exchange; and (ii) curing the adhesive; CHARACTERISED IN THAT said adhesive, when cured, has a Shore A hardness of less than 70 and an elongation at break of at least 50%.

Abstract: A process for preparing a membrane stack comprising the steps of (i) interposing a curable adhesive between alternate anion exchange membranes and cation exchange; and (ii) curing the adhesive; CHARACTERISED IN THAT said membranes are in a swollen state when step (ii) is performed.

Abstract: A disposable, crossflow membrane stack suitable for use in an ion exchange unit, the stack comprising alternate dilution compartments and concentration compartments, each compartment being defined by a flat cation-permeable membrane (2) and a flat anion-permeable membrane (1) and at least two edges along which the cation-permeable and an anion-permeable membranes are permanently secured together wherein the cation-permeable membranes and/or the anion-permeable membranes have a textured surface profile which keep said membranes apart and/or from touching each other and wherein the edges secured together define the direction in which liquid may flow through the compartments. Also claimed are ion exchange units comprising the stack, optionally comprising a quick-release securement means to allow facile attachment and release of modular units comprising the stacks.

Abstract: An electrodialysis unit comprising at least two electrodialysis stacks (ED1 and ED2) connected in series, wherein: (a) stacks ED1 and ED2 comprise anion exchange membranes and cation exchange membranes; and (b) the anion exchange membranes in stack ED1 have a lower electrical resistance than the anion exchange membranes in stack ED2 and the cation exchange membranes in stack ED1 have a lower electrical resistance than the cation exchange membranes in stack ED2. Also claimed is a process for purifying liquids, e.g. for desalinating sea water or brackish water.