NAMS 2002 Workshop - ICOM 2008

Membrane and Surface Modification II – 6
Thursday July 17, 5:00 PM-5:30 PM, O’ahu/Waialua
Hydrophobic Modified Ceramic Membranes for Gas Separation and
Desalination
S. Cerneaux (Speaker), Institut Européen des Membranes, Montpellier, France -
cerneaux@iemm.univ-montp2.fr
S. Condom, Institut Européen des Membranes, Montpellier, France
M. Persin, Institut Européen des Membranes, Montpellier, France
E. Prouzet, Institut Européen des Membranes, Montpellier, France
A. Larbot, Institut Européen des Membranes, Montpellier, France
Ceramic membranes are hydrophilic by nature since hydroxyl groups are present
both on the surface and within inner pores of membranes. Hence, this
characteristic is highly suitable to perform membranes surface modification to
confer them a specific affinity depending on the targeted applications. For water
treatment and desalination, attention has been focused on membranes showing
a hydrophobic feature as it yields to the formation of a repellent barrier for liquid
water transfer in Membrane Distillation (MD) processes, which are driven by a
temperature difference across hydrophobic membranes and only allow water
vapor permeation. In gas separation, these hydrophobic membranes are also of
great interest as perfluorinated chains used in this work are well known to have a
specific affinity for the CO2 gas molecules.
To post-functionalize zirconia, alumina and titania ceramic materials with different
pore diameters, perfluoroalkyl alkoxysilane molecules CnF2n+1(CH2)2Si(OR)3
were used. Materials were chemically modified by reaction of the different
fluorinated alkoxysilanes in alcoholic media for 4h and efficiency of grafting was
evaluated by FTIR, TGA and solid-state 29Si NMR for corresponding modified
powders. The influence of the perfluorinated chain length on the hydrophobic
stage of the modified membranes was further evidenced by measuring the water
liquid entry pressure and the wettability, water contact angles higher than 140°
being obtained for n=6 and n=8. The pore diameters of the modified membranes
need to be considered in desalination and liquid separations as they represent
the limiting factor for rejection rate and flux in desalination. Modified zirconia
membrane with pore diameters of 50nm yielded to the highest flux and rejection
rates higher than 99%, while working in Direct Contact Membrane Distillation.
Preliminary results in CO2 separation using hydrophobic zirconia membranes
showed that a pure gas selectivity of 3 for CO2 against N2 can be achieved with a
CO2 permeance of 0.2 m 3 (STP)/m 2 .h.bar.