Novel membrane and device for direct contact membrane distillation-based desalination process

In the direct contact membrane distillation (DCMD) process for desalination, the water vapor flux is strongly affected by the hot brine heat transfer coefficient, conductive heat loss, and long-term flux decline due to membrane pore wetting/fouling, etc. The DCMD process has been explored here using porous hydrophobic polypropylene hollow fibers having three different dimensions and two different wall thicknesses. The outside surfaces of the fibers have been coated with a variety of microporous plasmapolymerized silicone-fluoropolymer coating. A large number of rectangular modules having the hot brine in cross flow over the outside of the fibers and cold distillate flowing in the tube side have been investigated for their DCMD performances with hot brine (1% NaCl) over a brine temperature range of 60-90 degreesC. The module MXFR 3 containing fibers with larger internal diameter (i.d.) and wall thickness, and having the best performance, was tested in a continuous DCMD run for 120 h with 85 degreesC brine flowing at a Reynolds number of 70. The remarkably high water vapor flux (41-79 kg/m(2.)h) obtained in such modules and the complete absence of pore wetting over 400 h of experiments without any module cleaning demonstrate the excellent DCMD potential of such hollow fiber membranes and modules.