Comparative study on polymer membranes for reverse osmosis

• Main Author: Ng, Elane Yi Ting.
• Other Authors: Loo Sun Sun Leslie
• Format: Final Year Project
• Language: English
• Published: 2009
• Subjects: DRNTU::Engineering::Chemical engineering::Polymers and polymer manufacture
• Online Access: http://hdl.handle.net/10356/16577
• Institution: Nanyang Technological University

In this review of “Comparative study on polymer membranes for reverse osmosis”, two major categories of reverse osmosis membranes namely asymmetric and thin-film composite membranes were discussed. Two common polymer materials used to manufacture reverse osmosis membranes are cellulose acetate and polyamide. Understanding the chemical structures of the reverse osmosis membranes is very important as they affect the membrane performance in terms of salt rejection and water flux. Thin-film composite polyamide membranes (TFC, PA) can operate at larger pH variations from pH 3 to pH 11 and at lower pressure compared to cellulose acetate (CA) membranes which have to operate at narrower pH range and higher pressure. However, the shortcomings of these (TFC, PA) membranes are that they are prone to bio-fouling and oxidation by chlorine. (TFC, PA) membranes being less hydrophilic tend to attract bacteria to adhere to membrane surface and using chlorine to disinfect the feed water may also damage the membrane. In contrast, CA membranes are more tolerant to chlorine exposure and more resistant to bio-fouling due to its more hydrophilic property. Chlorine resistance (TFC, PA) membranes were manufactured using secondary diamines and nitration of the membranes. These methods were based on the theory of ring chlorination in (TFC, PA) membranes by making the ring less electron rich so as to prevent chlorination and hence improving chlorine tolerance. One method to manufacture fouling resistance (TFC, PA) membranes is to graft the membranes with hydrophilic polymer chains and the other is to introduce isocyanato group (NCO) into acyl chlorides.