Dynamic membranes
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Date
1975-08-20
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Publisher
Institution of Chemical Engineers
Abstract
Dynamic membranes are formed when water containing membrane-forming additives is circulated under pressure over a porous surface to deposit a thin membrane layer at the interface. In-situ procedures of this type have the potential advantage that membranes may be removed when performance becomes unsatisfactory and replaced without disassembly of equipment. Dynamic membranes are capable of a very high flux and, compared to conventional film membranes, hold promise of providing more economic processing, particularly for the high-fouling feeds often found in waste water treatment. Kraus, Johnson and co-workers at the Oak Ridge National Laboratory have investigated a range of ion exchange membranes dynamically prepared from organic polyelectrolytes including poly-acrylic acid, polyvinyl sulphonic acid, polyvinyl pyridine, and humic acid, and from inorganic polyelectrolytes formed from solutions of hydrolysable metal ions. It is also sometimes possible to form such membranes from polyelectrolytes already present in waste waters such as sewage.
Because their rejection properties are based upon relatively long-range coulombic forces, ion-exchange
membranes have the potential to function with a more open structure than that required of neutral membranes and hence to allow a greater flux. Conventional ion-exchange membranes, when manufactured with sufficient strength for reverse osmosis applications, are too impermeable. The dynamic technique provides a method for forming very thin ion-exchange membranes which are capable of use at high pressure and which have a very high flux. The performance of these membranes, as with other ion-exchange membranes, deteriorates with increasing feed concentration and the presence of polyvalent counter-ions. Their usefulness for single-stage seawater desalination thus appears doubtful, but they have promise for waste water treatment, where very high salt rejection is not always required. Dynamic membranes have also been formed from a range of neutral additives including hydroxyethyl cellulose, polyvinyl pyrrolidone and polyethylene oxides.4 Although often successful in removing large molecules by ultrafiltration, the salt rejection of these membranes is poor, usually less than 30 per cent. Neutral membranes are difficult to prepare by this technique because polymer additives which are soluble enough to form dynamic membranes are too hydrophilic to form membranes of low enough water content for good salt rejection. Whilst exhibiting poor salt rejection in their neutral form, dynamic ion-exchange membranes can still act as ultrafiltration membranes.
Description
Physical copy held by ANSTO Library at DDC 628.4/7
Keywords
Membranes, Additives, Pressure range, Waste water, Water treatment, Ion exchange materials
Citation
Evans, J. V. (1975). Dynamic membranes. Paper presented to the Third National Chemical Engineering Conference: Treatment, recycle and disposal of wastes, Mildura, Victoria, 20-23 August 1975, (pp. T193- T195).