Thin-Film Composite Membranes for Osmotic Power Generation

Thin-Film Composite Membranes for Osmotic Power Generation  

Xue LI^a, Tai-Shung CHUNG ^{a, b,}*  

^aNUS Graduate School for Integrative Science and Engineering, National University of Singapore, Singapore 117456, Singapore

^bDepartment of Chemical & Biomolecular Engineering, National University of Singapore, Singapore 117576, Singapore ^*Corresponding Author's E-mail: chencts@nus.edu.sg   Keywords: Osmotic power generation; Thin-film composite membranes; Pressure retarded osmosis.     Abstract  

Pressure retarded osmosis (PRO) is a membrane-based technology that harvests the energy of mixing two solutions from different salinity and converts it to electricity with the aid of a semi-permeable PRO membrane and a hydro-turbine. In addition to utilize seawater and river water as the feed pair, the PRO process can use highly concentrated RO retentate and recycled municipal wastewater as the feed pair for power generation. By doing so, not only can the environmental issue such as the disposal of RO retentate be solved, but also produce much higher osmotic energy. Therefore, the development of PRO membranes for osmotic power generation will have repercussion effects on the production of both clean energy and clean water.

As the heart of PRO processes, more studies on PRO membranes are expected to further accelerate the process in the near future. The thin-film composite (TFC) membranes, a commonly used PRO membrane nowadays, consist of a TFC layer of cross-linked polymers which acts as the primary barrier to salt and is responsible for giving a reasonable selectivity. In PRO processes, the draw solutions are pressurized by high hydraulic pressures to later push the hydroturbine and convert osmotic power into electrical power. However, under high pressures, membranes inevitably lose selectivity because of deformation and damage of both TFC layer and supporting layer. In our work, a systematical investigation has been demostrated on the evolution of morphological deformation and membrane performance in terms of compacted structure, water flux, reverse salt flux, and power density as a function of hydraulic pressure for membranes used in high-pressure PRO processes. In addition, an insight to PRO membranes will be given on the effects of membrane modifications and post-treatments.

Acknowledgments

This research was funded under the project entitled “Membrane development for osmotic power generation, Part 1. Materials development and membrane fabrication” (1102-IRIS-11-01) and NUS grant number of R-279-000-381-279. This research grant is supported by the Singapore National Research Foundation under its Environmental & Water Technologies Strategic Research Programme and administered by the Environment & Water Industry Programme Office (EWI) of the PUB. Special thanks are due to Dr. Panu Sukitpaneenit, Dr. Sui Zhang, and Miss Xiuzhu Fu for their valuable suggestions and kind help.