Solvent-based recovery of high purity polysulfone and polyester from end-of-life reverse osmosis membranes

Abstract

A facile, solvent-based recycling method is presented to recover high value-added polymers from the end-of-life, Thin Film Composite (TFC) based Reverse Osmosis (RO) membrane modules. The presented recycling method involves the separation of the active polyamide (PA) top layer, polysulfone (PSf) middle support layer and the nonwoven polyester (PET) bottom layer of waste TFC-RO membrane sheets in dimethyl formamide (DMF). The TFC sheet that was obtained from the dismantled RO modules was allowed to delaminate by mixing into DMF, in which the nonwoven PET bottom layer and the active PA top layer immediately separated and remained insoluble, whereas the PSf middle layer completely dissolved. The intact, nonwoven PET sheets were collected from the mixture and purified by washing with DMF and water. Solid PSf product was obtained by precipitation in water from DMF solution, which was first filtered through 0.2 or 1.2 μm pore-size filter papers to exclude undissolved PA pieces. The obtained solid PSf product was further purified by chlorine treatment via an investigation of the chlorine treatment level on the color and molecular weight of the final PSf product. The chemical structure, purity and thermal properties of recovered PET and PSf products were verified using Fourier-Transform Infrared (FT-IR) spectroscopy, Differential Scanning Calorimetry (DSC) and Thermo-Gravimetric Analysis (TGA). The molecular weight analysis using Size Exclusion Chromatography (SEC) showed that the recovered PSf had similar molecular weight values to that of pristine, commercially available PSf product. The newly developed recycling process reported herein presents the recycling of end-of-life TFC sheets for the recovery of high purity PET and PSf products that can be readily reused.