High temperature direct contact membrane distillation based desalination

Direct Contact Membrane Distillation (DCMD)-based desalination process is a thermally-driven separation process where a hydrophobic microporous membrane separates a hot brine feed and a cold distillate which condenses water vapor passing through the membrane pores from the hot brine solution. So far, DCMD has been explored by various researchers for hot brines and other aqueous solutions below 100°C. For feed solutions above 100°C, DCMD has an extra advantage over other conventional separation processes like reverse osmosis (RO) which requires cooling of the feed solution costing additional energy; further RO can not utilize the heat available in the feed solution. Produced water obtained from steam assisted gravity drainage (SAGD) process is one such example where DCMD can potentially be a very useful process. In this research, the DCMD technique is explored above 100°C for brine solutions containing 10000 ppm sodium chloride with porous flat sheet polytetrafluoroethylene (PTFE) membranes. This membrane has been also tested with saline feed containing 3000 ppm NaCl, 45 ppm phenol, 45 ppm cresol and 10 ppm naphthenic acid, simulating the composition of hot produced water obtained from the SAGD process. We will also report results from tubular/hollow fiber membranes for this application. Extensive results of water flux and desalting performance will be presented. The utility of existing models to predict water vapor flux will be explored.