We recently proposed a novel cascading osmotically mediated reverse osmosis (COMRO) membrane technology for energy-efficient desalination of hypersaline brines. COMRO utilizes the innovative design of bilateral countercurrent reverse osmosis stages to lessen the transmembrane osmotic pressure difference, thus depressing the hydraulic pressure needed. In COMRO operation, membranes are challenged by the atypical working environments, including high pressures and high salinities. In this study, we experimentally investigate impacts of hydraulic pressures and salinities on structural and transport properties of thin-film composite polyamide membranes in high-salinity desalination using COMRO. Our study shows that raising the hydraulic pressure detrimentally affects the membrane water permeability, A. After the membrane is completely compacted, A remains constant under different pressures, and will gradually recover when the membrane is relaxed from pressurization. Our study also indicates that these changes in water permeability are governed by morphological changes in the active-support interlayer of the membrane. Membrane salt permeability, B, presents similar tendencies to A as hydraulic pressure changes. The membrane structural parameter, S, is demonstrated to be consistent at different salinities (0-293,000 ppm TDS). We found that salinities of up to 117,000 ppm TDS does not exhibit significant influence on membrane water permeability, whereas the salt permeability is substantially elevated when the salinity increases (up to 228,000 ppm TDS). This research systematically studies fundamental structural and transport properties of membrane under the high pressure and salinities in COMRO operations to advance the technology, and also provides insights into principal membrane transport mechanisms applicable for all osmotically-driven processes.

Structural and transport properties of membranes in high-salinity desalination using cascading osmotically mediated reverse osmosis

2019 Fall National Meeting

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