II International Symposium on Carbon for Catalysis ABSTRACTS

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polymer gas separation membranes, these have so far been largely unsuccessful due to the
mechanical properties of the hollow fibres and the problems of achieving very low levels of
defects. The nearest approaches have been hollow carbon fibres produced by the
carbonisation of hollow polymer fibres, first evaluated Koresh et al 6 and more recently by
Koros er al 7 , Linkhov et al 8 , Tanihara et al 9 , Barbosa-Coutinho et al 10 . and Sznejer at al 11 . The
membranes commonly used have in nearly all cases been asymmetric with a thin nanoporous
separating layer supported on a multilayer tubular support. The majority of this work has
been targeted at the zeolite systems largely because of the extent to which the pore size can in
theory be controlled but also due to the enhanced stability of the pore structure compared to
the nanoporous amorphous oxide membranes that are usually prepared by sol gel type
processes. Both systems are however complex and expensive to produce and the reliable
production of defect free systems is still difficult to achieve on an industrials scale.
The manufacturing problems, costs and instability of the oxide membranes nanopore
structures prompted the investigations into carbon membranes that commenced with the work
of Koresh et al in 1983. Whilst these involved the studies into hollow fibres mentioned above
they have largely been based on supported films and have encompassed a wide range of
supports and polymer precursors. The critical limitation in the production of these carbonceramic
composites is the shrinkage that the polymer undergoes during carbonisation which is
typically in excess of 50% volume. This can lead to severe stress cracking during the
pyrolysis process that becomes more severe as the film thickness increases. In the earlier
studies into this preparation route by Rao et al 12 this could only be overcome by the
deposition of multiple thin coats of the polymer precursor with a pyrolysis step between each
deposition. In these studies the thickness of the carbon film required to approach a defect
free membrane was also quite thick due to the pore structure of the ceramic support. Most of
the recent studies now utilise the graded ceramic supports that are used to prepare the zeolite
and amorphous oxide membranes. Whilst this leads to significant increases in cost it allows
the production of much thinner carbon films which then permits the use of a single coatpyrolyse
preparation. The group of Fuertes has been responsible for much of the published
work in this area and, whilst earlier papers covered a wide range of precursors, the more
recent papers have concentrated exclusively on phenolic resins derived carbons 13 , and on the
optimisation of the properties of these films through thermal and oxidative treatments 14,15 .
Whilst the preparative approach adopted by Fuertes et al is different to that used in MAST the
resulting membranes have similar properties. These studies have shown that phenolic resin is
uniquely versatile in the production of coated ceramic membranes and that the properties of
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