Quantifying the Benefits of Membranes with Ultrahigh Vapor Permeability for Membrane Distillation

Abstract

Water reclamation from unconventional resources has attracted heightened interest worldwide. Membrane distillation (MD) is a promising technology for hypersaline wastewaters/brines reclamation. Since the key component in MD is the membrane, a myriad of research effort on MD has been devoted to developing MD membranes with ultrahigh vapor permeabilities. In this study, we perform a comprehensive analysis of the performance of practical MD operations to evaluate the benefits of developing MD membranes with ultrahigh vapor permeabilities. For coupon-scale MD operations (i.e., bench-scale systems), regardless of the membrane vapor permeability, the membrane vapor flux is limited by temperature polarization, and with the feed/distillate temperature of 60/20 °C under practical operating conditions, the membrane vapor flux can barely exceed 200 kg m–2 hr–1. For module-scale MD operations (i.e., large-scale systems), increasing the membrane vapor permeability by 15 folds only reduces the energy consumption by ∼26%, and despite the substantial saving of membrane area, the membrane cost needs to be considered. The results from our analysis demonstrate questionable benefits of membranes with ultrahigh vapor permeabilities in practical MD operations, casting doubt on the necessity of developing such membranes for MD applications. Last, we highlight the critical needs for robust MD membranes that can overcome challenges of membrane fouling, wetting, and scaling, shedding light on future MD membrane development.