Reverse osmosis in high temperature applications

Abstract

Water purification using membrane technology is one of the most effective ways to remove contaminants from water. In desalination applications, reverse osmosis (RO) is regarded as a highly successful membrane technology and is widely used for water purification on a global scale. Thin film composite (TFC) membranes are the most common type of RO membranes in the market and has widespread use in commercial applications due to their high performance. However, these membranes have their drawbacks, which their maximum operating temperature is 45°C. Hence, RO is not suitable for high temperature applications. In this study, we explore the limitations and performance of commercial TFC RO membranes at high temperature (70°C) applications. This study consists of 2 parts, in both parts, 2000ppm NaCl feed solution were used throughout the whole experiment. In part 1 of the study, the TFC membranes were treated at 85°C and tested for their performance at room temperature at a transmembrane pressure of 4 bar. It was found that the heat-treated membranes did not recover their performance when compared to fresh membranes. In part 2, the TFC membranes were subjected to long term high temperature cycles and their performance at 70°C with a transmembrane pressure of 15 bar were monitored, at the end of each cycle, the performance at room temperature were also recorded. At 70°C, the salt rejection was low (mostly < 95.0%), however, the membrane maintained high salt rejection of 99.0% despite going through the high temperature cycle when tested at room temperature, and the salt rejection even improved from the initial salt of rejection of 97.6%. This could imply subjecting these membranes to high temperature at 70°C do not destroy them nor degrade their performance at room temperature. One advantage from this finding could be conducting short-term washing of membranes at 70°C, as washing at higher temperature than normal can speed up the cleaning process, increasing the up time for the RO plant.