Robust outer-selective thin-film composite polyethersulfone hollow fiber membranes with low reverse salt flux for renewable salinity-gradient energy generation

Abstract

This study reports outer-selective thin-film composite (TFC) hollow fiber membranes with extremely low reverse salt fluxes and robustness for harvesting salinity-gradient energy from pressure retarded osmosis (PRO) processes. Almost defect-free polyamide layers with impressive low salt permeabilities were synthesized on top of robust polyethersulfone porous supports. The newly developed TFC-II membrane shows a maximum power density of 7.81 W m-2 using 1 M NaCl and DI water as feeds at 20 bar. Reproducible data obtained in the 2 nd and 3 rd runs confirm its stability under high hydraulic pressure differences. Comparing to other PRO membranes reported in the literature, the newly developed membrane exhibits not only the smallest slope between water flux decline and ΔP increase but also the lowest ratio of reverse salt flux to water flux. Thus, the effective osmotic driving force could be well maintained even under high pressure operations. For the first time, the effect of feed pressure buildup induced by feed flowrate was evaluated towards PRO performance. A slight increment in feed pressure buildup was found to be beneficial to water flux and power density up to 10.06 W m-2 without comprising the reverse salt flux. We believe this study may open up new perspectives on outer-selective PRO hollow fiber membranes and provide useful insights to understand and design next-generation outer-selective TFC hollow fiber membranes for osmotic power generation.

Evolution of micro-deformation in inner-selective thin film composite hollow fiber membranes and its implications for osmotic power generation

“…A similar phenomenon was also suggested as creeping behavior by Chen et al [33]. In addition, Zhang et al [28], Chou et al [20], Wan and Chung [34] and many others [26,27,32,35] observed that the water and salt permeability of TFC HF membranes varied significantly with an increase in hydraulic pressures possibly owing to the microstructure changes of the polyamide layer. However, to the best of our knowledge, there are no systematic and in-depth studies on (1) the micro-deformation of the TFC HF membranes under PRO operations and (2) the effects of the deformation evolution on PRO performance.…”

“…The innerselective TFC HF membranes are chosen because they currently display much higher power density than the outer selective TFC HF membranes [35][36][37]. The second objective is to examine the effects of micro-deformation on basic permeation properties such as A (water permeability), B (salt permeability) and S (structure parameter).…”

Cleaning strategies and membrane flux recovery on anti-fouling membranes for pressure retarded osmosis

“…[28,[44][45][46] Hollow fiber membranes were loaded in the active-facing-draw mode (i.e., the PRO mode) where the active layer faces the draw solution, a synthetic SWRO brine (0.81 mol/L NaCl at pH 5~6). A hydra cell pump (Minneapolis, MN) was used to recirculate the draw solution through the lumen side of the hollow fiber module, and a peristaltic pump (Cole-Palmer, Vernon Hills, IL) was employed to recirculate the feed solution through the shell side of the modules.…”

Estimation of phase separation temperatures for polyethersulfone/solvent/non-solvent systems in RTIPS and membrane properties

“…Commonly employed approaches include the addition of additives to the casting solutions or coagulations [14,15], the introduction of an extra process [16,17] and chemical modification [18,19].…”