Laminated PTFE membranes to enhance the performance in direct contact membrane distillation for high salinity solution

Due to the excellent performance in treating high salinity brines, membrane distillation (MD) has been widely employed in desalination, brine treatment and wastewater purification. Commercial hydrophobic membranes were limited by wetting and fouling over time. Herein, we reported a simple and practicable method to improve the stability performance of thin polytetrafluoroethylene (PTFE) membranes by laminating PTFE flat sheet membranes. A NaCl solution with a concentration of 3.26 mol/L was utilized as a model high salinity brines. Results indicated that single-layered PTFE flat membrane did show high flux, but salt leakage occurred in a few days caused by the contaminants leached from the tubing and connections. By simply laminating two pieces of PTFE membranes, a double-layered membrane showed a very stable performance for nearly one month at a rather high flux of 30 kg/m(2)-h. Air pockets between two sheets of PTFE membranes were observed during operation resulting in flux fluctuation. Interestingly, these air pockets coincidently avoided the close contact of the flat sheets, thus reduced overlapped pores which causing extra mass transfer resistance. Experimental verification of the reduced pore size and flux due to layer overlap. Proper module design would realize this laminated membrane as a potential stable MD membrane for treating high salinity water.