Porous hydrophobic/hydrophilic composite membranes preparation and application in DCMD desalination at higher temperatures

Abstract

In our previous studies [1,2], porous hydrophobic/hydrophilic membranes have been proposed for desalination by direct contact membrane distillation (DCMD). The membranes were prepared by the simple phase inversion technique from polymer solutions containing a hydrophilic polymer, a solvent, a non-solvent additive and a surface modifying macromolecule (SMM). Membranes of different pore sizes have been prepared using polyetherimide (PEI) as a host polymer. The membranes were characterized by various techniques including atomic force microscopy (AFM), gas permeation test, liquid entry pressure of water (LEPw) measurements, X-ray photoelectron microscopy and contact angle measurements. DCMD experiments were carried out using water and NaCl salt aqueous solutions at different feed and permeate stirring rates (0–740 rpm), feed temperature (25– 50°C), permeate temperature (15–40°C) and feed concentration (0–2 M). The temperature polarization coefficients and the permeability of the membranes were evaluated. The DCMD performance of the proposed hydrophobic/ hydrophilic membranes were similar to those of commercial polytetrafluoroethylene (PTFE) membranes (TF200 and TF450, from Gelman) and one of the membranes, prepared with 12 wt% PEI in the casting solution, showed DCMD fluxes higher than those of PTFE membranes. All tested membranes exhibited very high separation factors, >99.8%, when aqueous salt solutions were used as feed. It was concluded that the porous hydrophobic/hydrophilic composite membranes are promising in the field of membrane distillation because they combine a low resistance to mass transfer achieved by the diminution of the water vapor transport length through the hydrophobic thin-layer of the *Corresponding author.