(711a) Thin Film Composite Membranes for Reverse Osmosis Desalination

Desalination by reverse osmosis (RO) has become an important process to produce fresh water for domestic and industrial uses¹. We develop RO membranes using different polymeric materials as the selective layer in thin film composite (TFC) membrane structures. TFC structure is selected due to its low resistance to the water flow and ability to tailor the selective layer without affecting the porosity of the support². Cellulose acetate thin film composite (CA TFC) membranes were successfully made on microporous polymeric substrate by spin coating a dilute cellulose acetate solution. This membrane initially had low salt rejection (~ 60 %) and was later developed up to the level of a RO membrane (~ 90 % salt rejection) by treating in room temperature water baths. The pure water flux through these membranes showed a strong relationship with the time in the water bath. A significant decrease in the surface roughness of the cellulose acetate selective layer was also observed with the time in the water bath. Here the CA TFC membrane was successfully used as a model to investigate the effect of absorbed water on the evolution of the CA selective layer which is not directly observable with asymmetric CA membranes due to the complexity of the process. The surface of the CA TFC membrane was further treated with silver nanoparticles to incorporate anti-fouling properties. This treatment was found to reduce the bacterial adhesion by around 4 orders of magnitude. 

We also develop novel TFC RO membranes with polymers of intrinsic microporosity (PIMs) and polyamide for the selective layers. While having excellent salt rejection (> 95 %), these membranes open new pathways for developing chemical-resistant RO membranes. The effects of treatment methods in improving the flux of these RO membranes are also investigated.

References:

1. L. Greenlee, D. Lawler, B. Freeman, B. Marrot, and P. Moulin, Water res., 2009, 43, 2317-2348.

2. K. P. Lee, T. C. Arnot, and D. Mattia, J. Membrane Sci., 2011, 370, 1 – 22.