NAMS 2002 Workshop - ICOM 2008

Inorganic Membranes II – 5
Thursday July 17, 11:00 AM-11:30 AM, O’ahu/Waialua
Recent Developments on the Preparation and Modeling of Nanoporous
Silicon Carbide Membranes for Gas Separation Applications
R. Mourhatch (Speaker), University of Southern California, Los Angeles, Califorinia, USA -
mourhatc@usc.edu
B. Elyassi, University of Southern California, Los Angeles, Califorinia, USA
F. Chen, University of Southern California, Los Angeles, Califorinia, USA
M. Sahimi, University of Southern California, Los Angeles, Califorinia, USA
T. Tsotsis, University of Southern California, Los Angeles, Califorinia, USA
Silicon carbide (SiC) is a material with very attractive chemical and physical
properties, which have made it a great candidate for membrane applications,
especially those related to gas separation and hydrogen production. The focus of
the present paper is on using two different approaches to prepare asymmetric
nanoporous silicon carbide membranes which are applicable in reactive
separations involving the water-gas shift and methane steam reforming
reactions, where the membrane has to function in the presence of hightemperature
steam. The first approach for the preparation of SiC microporous
membranes, involves the pyrolysis of thin allyl-hydridopolycarbosilane (AHPCS)
films coated, using a combination of slip-casting and dip-coating techniques, on
tubular SiC macroporous supports. Combining slip-casting with dip-coating
significantly improved the reproducibility in preparing high quality membranes.
The membranes were studied for their transport characteristics, and steam
stability. In addition, a novel method, based on the use of sacrificial interlayers,
was also developed for the preparation of nanoporous SiC membranes, which
involves periodic and alternate coatings of polystyrene sacrificial interlayers and
SiC AHPCS layers on the top of slip-casted tubular SiC supports. Membranes
prepared by this technique exhibit single gas ideal separation factors of He and
hydrogen over Ar in the range of (176-420) and (100-200), respectively, with
permeances that are typically two to three times higher than those of SiC
membranes prepared previously by the more conventional techniques.
Preparation of asymmetric nanoporous SiC membranes is also carried out using
chemical-vapor infiltration/chemical-vapor deposition (CVI/CVD) techniques. We
have used macroporous SiC disks and tubes as supports, and tri-isopropylsilane
as the precursor. We have also developed two dynamic models to describe the
preparation and the transport characteristics of the membranes by the CVD/CVI
technique. First, a coarse-grained pore network model was developed for the
membranes, that provides accurate predictions for the ideal selectivities, as well
as the transport of binary gas mixtures. A continuum model of the CVD/CVI
membrane preparation process has also been developed, which is validated by
the results of a comprehensive experimental study. The results of the model