Design and fabrication of inner-selective thin-film composite (TFC) hollow fiber modules for pressure retarded osmosis (PRO)

• Semi-pilot-scale TFC-PES hollow fiber modules are fabricated.
• The modules have 30% structured packing and 50% random packing.
• Interfacial polymerization conditions are optimized for hollow fiber modules.
• The power densities of the hollow fiber modules are 19–20 W/m2 at 20 bar.
• Modules after repair show 91% of power density of intact modules.

Pressure retarded osmosis (PRO) is a promising technology to harvest the renewable osmotic energy from salinity gradients. There are great progresses in the fabrication of PRO membranes in the last decade. Thin-film composite (TFC) hollow fibers have been widely studied and demonstrated superior performance. However, the lack of effective TFC hollow fiber modules hinders the commercialization of the PRO technology. Knowledge and experiences to fabricate TFC hollow fiber modules remain limited in the open literature. In this study, we aim to reveal the engineering and science on how to fabricate TFC hollow fiber modules including the formation of inner-selective polyamide layers and the repair of leakages. TFC-PES hollow fiber modules with 30% and 50% packing densities have been successfully fabricated, showing peak power densities of 20.0 W/m2 and 19.4 W/m2, respectively, at 20 bar using 1 M NaCl solution and DI water as feeds. The modules may be damaged during handling and high pressure testing. The repaired modules have a power density of 18.2 W/m2, 91% of the power densities of the undamaged ones. This study would make up the gap between TFC membrane fabrication and TFC membrane module fabrication in the membrane industry.

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