Development of composite hollow fiber membranes with strong mechanical strength for PRO application

Pressure retarded osmosis (PRO) is one of the promising processes in catering large amount of renewable energy from salt and fresh waters, through utilization of osmotic driving force. A desirable PRO membrane should possess high water permeability as well as low salt permeability. Salt rejection level should be as high as possible, while maintaining low structural parameter to minimize the effect of internal polarization (ICP). The membrane should have high mechanical strength to resist the high pressure applied in the draw solution. In this study, the objective is to develop thin-film composite (TFC) hollow fiber membranes with high mechanical strength for PRO applications. TFC hollow fiber membranes were fabricated, characterized and evaluated for their PRO performances. Polyether sulfone (PES) and Polyetherimide (PEI) polymers were used to fabricate the substrates through non-solvent induced phase inversion (NIPS) method. Interfacial polymerization was used to fabricate polyamide active layer for all the membranes in this study. TFC-PEI membranes generally possessed higher mechanical strength than TFC-PES membranes, allowing higher pressure to be applied to produce more power output. Other than PRO test, TFC membranes in this report were tested for the repeatability of their performance as well as PRO performance under sustained high pressure for more than 20 hours to test their commercial viability. The best newly fabricated TFC hollow fiber membrane in this report achieved a power density of 14.8 W/m2 at operating pressure of 12.6 bar, and it is by a TFC-PEI hollow fiber membrane. This pressure applied was also tested to prove that the performance of the TFC-PEI membrane can sustain for the long-term operation run. Such test was not conducted before for previous PRO membranes studies according to author’s knowledge. Synthetic seawater brine (1.0 M NaCl) was used as draw solution and freshwater (DI water) as the feed solution. The TFC hollow fiber membrane also achieved good water flux of 41.3 L/m2.h and low specific salt flux value of 0.01 M. Despite the ability to sustain long term PRO operation, there are still room for improvement for the PRO performance of the TFC membranes to achieve higher power density and mechanical strength. Better long-term stability PRO performance test procedures should be implemented in future work as well to test for PRO membranes’ long term commercial application.Bachelor of Engineering (Environmental Engineering