NAMS 2002 Workshop - ICOM 2008

Desalination II – 3
Thursday July 17, 3:30 PM-4:00 PM, Honolulu/Kahuku
Fabrication of High Performance Dual Layer Hydrophilic-Hydrophobic
Hollow Fiber Membranes for Membrane Distillation Process
S. Bonyadi (Speaker), National University of Singapore, Singapore
T. Chung, National University of Singapore, Singapore - chencts@nus.edu.sg
Hydrophilic-hydrophobic composite membranes have been considered as
promising membrane configurations to be applied as membrane contactors,
especially for flux enhancement in membrane distillation (MD) process. While
there are several reports in the literature demonstrating the fabrication of these
types of membranes in flat sheet geometries, however, there is no such report in
case of hollow fibers. Furthermore, most of the proposed approaches are either
expensive or inefficient in controlling membrane properties such as porosity and
pore-size distribution. For the first time in this paper, co-extrusion has been
applied as a novel approach to fabricate dual layer PAN (hydrophilic) - PVDF
(hydrophobic) composite membranes. The effect of different non-solvents on the
morphology of the PVDF membranes was investigated and it was found that
weak coagulants such as water/methanol (20/80, w/w) can induce a three
dimensional porous structure on PVDF membranes with high surface and bulk
porosities, big pore size, sharp pore size distribution, high surface contact angle
and high permeability but rather weak mechanical properties. In order to enhance
the membranes mechanical properties, hydrophobic and hydrophilic clay
particles were incorporated into the outer and inner layer dope solutions,
respectively. It was also found that the incorporation of clay particles in the fibers
inner layer reduces the shrinkage and reduces the delamination between the two
layers considerably. The fabricated fibers were characterized through pore size
distribution, gas permeation, porosity and contact angle measurement tests.
Ultimately they were tested for desalination through a direct contact membrane
distillation process and fluxes as high as 47 kg/m 2 hr, were achieved at 90 ºC. By
carrying out some modifications on the fabricated fibers the obtained flux was
increased to 70 kg/m 2 hr at 86 ºC, which is a superior flux compared to all the
data reported in the literature for hollow fiber membranes so far. The details
regarding the conducted modifications are under review by the AIChE Journal.