Substrate modifications and alcohol treatment on thin film composite membranes for osmotic power

Polyamide/polyacrylonitrile (PAN) composite membranes with enhanced mechanical properties and water permeability for osmotic power generation have been fabricated in this study. Osmotic power production via pressure retarded osmosis (PRO) process is emerging as one possible environmental friendly and renewable energy sources that utilizes salinity gradient across a semi-permeable membrane as the driving force. The major challenge in the PRO process is how to design the semi-permeable membrane with robust mechanical strength, superior structural stability, desirable water permeability and high salt rejection. This paper presents a fundamental study on the fabrication of polyamide-based thin film composite (TFC) membranes over a polyacrylonitrile (PAN) support for the PRO process. It is revealed that the mechanical strength, pore structure and hydrophilicity of the supporting layer can be tailored by increasing PAN concentration, pre-compressing the substrate and coating with polydopamine which later affects the formation of the polyamide layer and its performance. The post ethanol treatment can toughen the selective layer and simultaneously enhance its water flux and mechanical strength. The resultant membrane is able to harvest the osmotic energy of 2.6W/m² and withstand the hydraulic pressure of 10bar. In addition to having superior mechanical properties, alcohol treated membranes for high pressure PRO processes must have a balanced salt permeability and water permeability in order to maximize the osmotic power.