desalination

Abstract

A membrane stack comprising the following components: (a) a first ion dilution chamber (D1); (b) a second ion dilution chamber (D2); (c) a first ion concentration chamber (C1); (d) a second ion dilution chamber (D2); Two ion concentration compartments (C2); and (e) membrane walls (CEM1, mAEM, mCEM, AEM, CEM2) between each compartment and on the outside of the first and last compartments of the stack, wherein: (i) Each membrane wall includes either a cation exchange membrane (CEM1, mCEM, CEM2) or an anion exchange membrane (mAEM, AEM), and the order of the cation exchange membranes and anion exchange membranes is alternate from each wall to the next; ( ii) the membrane walls (mAEM, mCEM) on each side of compartment (a) are more selective for monovalent ions than the corresponding membrane walls (AEM, CEM2) on each side of compartment (b); and (iii ) The stack further comprises means for transferring fluid between compartments (a) and (b).

Description

technical field [0001] The present invention relates to a membrane stack, an electrodialysis cell, an apparatus comprising at least two electrodialysis (ED) cells and a desalination method. Background technique [0002] The world's increasing population, diminishing water supplies, and droughts have led to increased demand for fresh water. A process known as electrodialysis ("ED") is known for converting saline water and providing drinking water. The method is especially useful in coastal areas where there is ample supply of salt water. The first commercial ED units were developed in the 1950s. Since then, improvements in ion-exchange membranes have led to significant advances in ED. [0003] An ED unit typically includes one or more membrane stacks. Each membrane stack includes an anode, a cathode, and a plurality of cell pairs through which a fluid passes. The cell pair includes an ion diluting chamber and an ion concentrating chamber. Each cell includes walls made o...

AI Technical Summary

Problems solved by technology

[0016] figure 2 A problem with the known ED units used in the EDM shown in is that it is difficult to produce drinking water from seawater at high yields due to the large concentration differences between the ion diluting and ion concentrating chambers

This results in high water loss due to osmotic transport of water molecules across the membrane wall from the ion diluting compartment to the ion concentrating compartment

figure 2 Another disadvantage of the known EDM unit shown is the need to supply sodium chloride solution (in the rightmost compartment), which leads to higher costs, not only concerning the required materials (ie sodium chloride) , but also involves additional energy due to the transport of sodium and chloride ions across the membrane wall

The requirement for a compartment dedicated to the supply of NaCl solution also reduces the desalination capacity of the EDM unit

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