Thin-film composite P84 co-polyimide hollow fiber membranes for osmotic power generation

A series of well-designed thin-film composite (TFC) hollow fiber membranes via dual-layer co-extrusion technology for pressure retarded osmosis (PRO) applications is reported in this work. By controlling the phase inversion process during spinning, we have molecularly engineered hollow fiber membranes with various structures, dimensions, pore characteristics, and mechanical properties as supports for the synthesis of TFC membranes. Under hydraulic tests, these hollow fiber membrane supports possess high burst pressures from 13 to 24bar. The TFC membranes fabricated by interfacial polymerization on the inner surface of the hollow fiber supports not only exhibit relatively high power densities of 5-12Wm^-2 but also display a superior tolerance to high pressures up to 21bar. The TFC membrane synthesized on a small dimensional hollow fiber support, which was spun from a P84 co-polyimide/ethylene glycol (EG)/N-methyl-2-pyrrolidinone (NMP) dope solution with a bore fluid of a water/EG/NMP mixture, shows the most impressive PRO performance (i.e., 12Wm^-2 at 21bar using water and 1M NaCl as feeds). Experimental results also suggest that inner-selective TFC hollow fiber membranes made from small dimensional fiber supports by means of delayed demixing during the fiber spinning are preferential for high pressure PRO processes. In addition, it was found that the flow rate of brine solutions plays a crucial effect on TFC membrane performance for osmotic power generation. By investigating the pressure drop as a function of flow rate, one may be able to choose appropriate PRO operation conditions to further ensure the sustainability of hollow fiber membranes for power generation.