News and Views
Inorganic membrane reactors reviewed An article in the Journal of Membrane Science, (92, pp 1-28), reviews applications of inorganic m e m b r a n e reactors, in particular their application in high-temperature g a s - p h a s e reactions. The development of inorganic m e m b r a n e s , especially ceramic m e m b r a n e s having consistent quality a n d n a r r o w pore size distribution has lead to the application of m e m b r a n e s in these reactors. The use of m e m b r a n e s as chemical reactors in established a n d novel reactor systems is attractive b e c a u s e of increased conversions, better selectivity, milder operating conditions a n d decreased separation load. In the review, the most promising inorganic m e m b r a n e s developed so far are looked at - palladlum-based m e m b r a n e s , ceramic a n d glass m e m b r a n e s , solid oxide m e m b r a n e s a n d dense m e m b r a n e s supported on p o r o u s substrates. Palladium-based m e m b r a n e s are highly selective to oxygen, a n d have been u s e d with hydrogenation, dehydrogenation, dehydrogenation-oxidation a n d steam reforming reactions. Only recent applications are discussed in this paper, which includes the decomposition of hydrogen sulphide. It was concluded that the greatest difficulty in developing metal-based m e m b r a n e reactors is the difficulty in obtaining a thin m e m b r a n e with sufficient mechanical strength a n d satisfactory permeability. Applications of ceramic a n d glass m e m b r a n e s were looked at in some detail, including using the m e m b r a n e as a catalyst as wen as partitioning wall to separate the reactants, allowing controlled addition of one reactant. However, it was concluded that the fuU scale commercial application of composite ceramic m e m b r a n e reactors alone m a y have to wait for the development of techniques for obtaining even smaller pore structure, allowlng greater selectivity or some degree of molecular sieving. Solid oxide m e m b r a n e s have found applications in fuel cells, oxygen p u m p s , oxygen sensors a n d chemical reactions of various kinds. The two most significant areas of c u r r e n t research interests with these m e m b r a n e s are In the utilization of n a t u r a l gas to produce useful chemicals a n d in the generation of energy carriers in h i g h - t e m p e r a t u r e reactions. Methods of producing supported m e m b r a n e s were looked at, including electroless plating, chemical vapour deposition a n d s p r a y pyrolysis, along with surface modification techniques. Three classes of models to simulate the experimental reactors or to explore the operation of the system were examined. In all, the a u t h o r s looked at over 200 items in the literature, b u t concluded that in m a n y cases work reported so far seemed exploratory and tentative in
M e m b r a n e Technology No. 51
n a t u r e a n d m a n y of them failed to bring in new ideas or break new ground. In their opinion there was a need to obtain longer term d a t a in the laboratory units a n d move to piloting potential systems.
Further information from: A. Chakma, Department of Chemical and Petroleum Engineering, University of Calgary, Calgary, Canada T2N 1N4. Tel: +1 403 220 5752. Fax: +1 403 284 4852.
Sterilizable hollow-fibre m e m b r a n e for blood f i l t r a t i o n A honow-flbre m e m b r a n e which is clalmed to overcome m a n y of the problems c o m m o n l y encountered with similar p r o d u c t s used as artificial kidneys for blood purification h a s been developed by J a p a n e s e c o m p a n y Toyo Boseki Kabushiki Kalsha, based in Osaka. The polyamidimide hoUow-flbre m e m b r a n e (European p a t e n t 0 568 828) h a s appropriate water permeability a n d a high u r e a permeability, is sterflizable by g a m m a irradiation a n d steam, a n d does not induce i m m u n e reactions, the c o m p a n y says. The average micropore size is 1-20 nm. The m e m b r a n e also offers good processability (melt spinnability and solution spinnability) says the company, with excellent heat resistance, a n d physical a n d chemical stability. The polymer is formed b y the reaction of a n acid component, containing a trimellitic anhydride, with a diisocyanate component. Representative formulae for the c o m p o n e n t s are given in the p a t e n t application. Hollow fibres s p u n from the material have a n outer diameter of 237 ~m a n d are 18.5 ~ n thick. Besides the mechanical strength of the product, the thickness also affects the blood complement system a n d so a n y i m m u n e reaction.
Further Informatlon from: Toyo Bosekl Kabushlkl Kalsha, 2-2-8, Dojlmahama, Klta-ku, Osaka-shl, Osakafu, Japan. Tel: +81 6 348 3417. Fax: +81 6 348 3400.
MITI i n v e s t i g a t i n g C02 separation using ceramic films The J a p a n e s e Ministry of International Trade a n d I n d u s t r y (MITI) has b e g u n research a n d development