A support surface pore structure re-construction method to enhance the flux of TFC RO membrane

Abstract

In this work, a support surface pore structure re-construction method was developed to enhance the flux of thin film composite (TFC) reverse osmosis (RO) membrane. With this method, an aqueous solution of a suitable organic solvent with a certain content, i.e., re-construction agent, was used to swell the support for a period of time and then the swelled support was immersed in water to complete the whole surface pore structure re-construction process. Herein, dimethylacetamide (DMAc) was employed as the organic solvent. It was shown that under proper conditions (i.e., the organic solvent content of 30% v/v, the re-constructing agent contacting time less than 10s and re-constructing agent contacting temperature of 25 ± 5°C), the support surface porosity and surface pore density increased a lot with the support surface pore size increasing slightly. The statistical results (obtained from scanning electron microscope images) showed that at the optimal condition, the support surface porosity and surface pore density increased by 92% and 89%, respectively. The results of RO membrane permselectivity obtained using 2000ppm NaCl solutions and 1.55MPa transmembrane pressure showed that the support surface pore structure re-construction method could improve the flux by 50.5% at most (an increase from 44.0 to 66.2Lm−2h−1) without sacrificing the salt rejection (all the membranes had a similar and high rejection of 99.38%). Besides, a support surface pore structure re-construction mechanism was proposed, which showed that the support surface pore structure was mainly determined by the diffusion and coalescence of re-construction agent molecules, and polymer chains mobility. This work provides a facile and effective method for preparing TFC RO membranes with high performance.