Development of surface modifying macromolecule blended polyethersulfone membranes for vacuum membrane distillation

Abstract

Surface modifying macromolecule (SMM) has been developed aiming at the preparation of membranes with greater surface hydrophobicity and greater chemical resistivity at a lower cost than conventional hydrophobic membranes. Throughout the whole work in this study, the membranes, which contains SMM as an additive and PES as a base polymer, are called 'SMM blended PES membranes' or 'SMM modified PES membranes'. The objective of this study is the preparation of SMM blended membranes to be used for the removal of VOCs from their aqueous solutions by the membrane distillation process. In the first part of this work, a SMM, tSMM, was synthesized by a traditional method and the tSMM blended PES membranes were prepared to study the effects of tSMM on PES membranes by different methods; e.g. bubble-point method and gas permeation, pure water permeation (PWP), contact angle measurement, and X-ray photoelectron spectroscopy (XPS). In particular, based on the XPS results, the kinetics of surface migration of tSMM was studied. According to the results of experimental and theoretical studies, it was observed that the tSMM blended membranes prepared had a potential to be used in membrane distillation (MD), however to meet the requirement of MD membrane, relatively long evaporation time (over 10 minutes) and high evaporation temperature (110°C) should be needed during membrane preparations. In the second part of this work, a novel SMM, was designed and synthesized. Synthesized nSMMs from two different batches (nSMM1 and nSMM2) were characterized by GPC and the weight average molecular weight (Mw) of nSMM2 was about twofold of nSMM1. Furthermore, blended PES membranes were prepared and characterized. According to the results, the nSMM seems to be a better alternative to tSMM for membrane distillation, since a shorter period at room temperature was required for to migrate to the membrane surface. The ultrafiltration (UF) tests also gave the information on the effects of nSMM on PES membranes. nSMM was fully segregated to the surface of membrane forming a distinctive surface layer and this was observed from optical microscope and scanning electron microscopy (SEM) results. In the end of the second part, the nSMM blended PES membranes were successfully applied in vacuum membrane distillation (VMD) for the removal of ethanol from water.