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NAMS 2002 Workshop - ICOM 2008

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Hybrid Membranes – 2<br />

Thursday July 17, 3:00 PM-3:30 PM, Wai’anae<br />

Hollow Fillers For Flux Enhancement In Mixed Matrix Membranes<br />

K. Vanherck (Speaker), Katholieke Universiteit Leuven, Heverlee, Belgium<br />

S. Aldea, Katholieke Universiteit Leuven, Heverlee, Belgium<br />

A. Aerts, Katholieke Universiteit Leuven, Heverlee, Belgium<br />

J. Martens, Universiteit Leuven, Heverlee, Belgium<br />

I. Vankelecom, Katholieke Universiteit Leuven, Heverlee, Belgium -<br />

ivo.vankelecom@biw.kuleuven.be<br />

Mixed matrix membranes (MMMs), consisting of an organic polymer (bulk phase)<br />

and inorganic particle phases (dispersed phase), have the potential to combine<br />

high selectivities with high membrane fluxes. Zeolites and carbon molecular<br />

sieves have been most attractive as inorganic fillers in MMMs because their very<br />

defined pore structure increases the selectivity. Zeolite-filled<br />

polydimethylsiloxane (PDMS) membranes have already been developed for gas<br />

separation, pervaporation, and nanofiltration. PDMS is known to be a chemically<br />

and thermally stable polymer, but the excessive swelling and resulting selectivity<br />

loss in certain organic solvents (e.g. toluene, DCM,&) limits its utility in these<br />

solvents. The incorporation of zeolites reduces PDMS swelling via extra crosslinking,<br />

without lowering the intrinsic fluxes. In previous research, composite<br />

membranes were prepared with a PDMS top layer filled with zeolites ZSM-5 and<br />

USY. Top layer thicknesses of approximately 8µm could be obtained, giving a<br />

92% rejection for Wilkinson Catalyst in toluene at a permeability of 1,07 l/m² bar<br />

h. Since a zeolite-filled PDMS top layer requires a certain minimal thickness to<br />

remain free of defects, it is not easy to obtain higher fluxes.<br />

To lower the minimal thickness of a zeolite-filled PDMS toplayer, two strategies<br />

were explored in this research. Firstly, zeolites with a smaller crystal size, nanosized<br />

silicalite-1 (NS), were used as fillers. Secondly, the incorporation in PDMS<br />

of micron-sized hollow spheres (HS) with a zeolite shell was investigated. Hollow<br />

spheres with a shell consisting of nano-sized silicalite crystals and a diameter of<br />

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