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Novel Membrane and Device for Direct Contact Distillation Based Desalination Process

New Jersey Institute of Technology, Newark New Jersey;
March 2001.

Report #87 - Abstract -

Direct contact membrane distillation (DCMD) and vacuum membrane distillation (VMD) of brine for desalination suffer from long-term flux decay due to membrane pore wetting and low water flux due to poor transport coefficients in the hot brine. Preliminary studies were carried out to address these problems. To prevent pore wetting, modules having an ultrathin microporous silicone coating on the surfaces of hydrophobic porous polypropylene hollow fibers were employed. Using a parallel flow Module 4 and high water velocity yielded a water flux of 15 kg/m2-h at 91oC in VMD. There was no pore wetting even after a cumulative experimental duration of 1000 hours. In DCMD and VMD, a radial cross flow module and uncoated fibers yielded low water vapor fluxes. A large rectangular module having fibers with a nonporous coating also yielded low water vapor flux in DCMD. Conductive heat loss was substantial in the fine fibers; the cross flow velocity was very small in the large module where hydrophobic fluoropolymer coating hindered water permeation much more than that in Module 4. Large fiber diameter and wall thickness, silicon coating, and higher cross flow velocity are expected to substantially enhance the water vapor flux.


For more information about the DWPR program, contact Kevin Price at: Bureau of Reclamation, 86-69000, PO Box 25007, Denver CO 80225; phone (303) 445-2260; or e-mail a message to MPrice@usbr.gov.