Thermally Rearranged Nanofibrous Membranes for Membrane Distillation and Pressure Retarded Osmosis: Evaluation for Hybrid System

Abstract

We fabricated two types of thermally rearranged nanofibrous membranes (TR-NFM) to be applied to membrane distillation (MD) and pressure retarded osmosis (PRO) hybrid systems, respectively. Plasma-coated membranes (TR-NFM-Rx), where wetting problem were resolved, were prepared by the plasma treatment using c-C4F8 gas for MD application. Fluorinated thin-film composite membranes (TFC-NFM-Fx), where stable selective layer was formed based on enhanced hydrophilicity by the direct fluorination, were prepared for PRO application. MD-PRO hybrid system was operated using 3 M NaClaq as an operating solution at 70 oC, and theoretical performances of MD and PRO were calculated, based on intrinsic properties of TR-NFMs and transport parameters. TR-NFM-R50 showed excellent water flux of 54.5 L∙m-2∙hr-1 based on enhanced hydrophobicity, excellent thermal stability, porosity and pore connectivity in MD process. TFC-NFM-F5 showed an unprecedented power density of 120 W·m-2 at 27 bar by virtue of stably formed selective layer with highly robust and porous support layer in PRO process. To generate power sustainably in the hybrid system, pure water from MD was transferred to the PRO feed. Due to the excellent rejection and robust mechanical strength of TFC-NFM-F5 and superior water permeance of TR-NFM-R50, the hybrid system could be constructed efficiently. It was determined that the hybrid system using TR-NFM-R50 and TFC-NFM-F5 was stable for 40 hr at 27 bar, showing high and stable performances (90-100 W∙m−2) despite of slight performance reduction due to rust. This was the first attempt to configure the MD-PRO hybrid system using the TR-NFMs with high performance. Therefore, the developed TR-NFMs can be used as an attractive membrane in closed-loop MD-PRO hybrid system, and we identified its potential.