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Tailoring the porous structure of hollow fiber membranes for osmotic power generation applications via thermally assisted nonsolvent induced phase separation

Cho, Young Hoon, Kim, Sang Deuk, Kim, Jeong F., Choi, Hyeon-gyu, Kim, Youngmi, Nam, Seung-Eun, Park, You-In, Park, Hosik
Journal of membrane science 2019 v.579 pp. 329-341
artificial membranes, osmosis, osmotic pressure, power generation, separation
For osmotic power generation using the pressure retarded osmosis (PRO) process, mechanically robust membranes with high osmotic water flux are needed to obtain high power density from a given osmotic pressure difference. Particularly in the case of support-free hollow fiber membranes (HFMs), the pressure tolerance is a critical factor in maximizing power density when operating at high applied pressure with concentrated brine. Here, mechanically robust integrally-skinned asymmetric (ISA) HFMs were developed by combining the nonsolvent induced phase separation (NIPS) with the quenching, into a facile approach called the thermally assisted NIPS (T-NIPS) method, to tailor the membrane structure for PRO applications. The prepared T-NIPS membranes exhibited two distinct layers: a dense ISA outer layer and an isoporous inner layer. Compared to conventional NIPS HFMs, the T-NIPS HFMs showed much higher power density and collapse pressure, up to 5.5 W/m2 and 18 bar, respectively. The effect of pore forming agents on the membrane structure during the T-NIPS process, and on PRO performance, were studied. In addition, the power density and the pressure tolerance were further enhanced by optimizing the membrane dimensions and structure of the T-NIPS HFMs.