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Structuring zeolite bodies for enhanced heat-transfer properties

 
: Borchardt, L.; Michels, N.L.; Nowak, T.; Mitchell, S.; Perez-Ramírez, J.

:

Microporous and mesoporous materials 208 (2015), pp.196-202
ISSN: 1387-1811
English
Journal Article
Fraunhofer IZM ()

Abstract
The predominantly insulating nature of zeolites, as many classes of porous catalysts, can severely impair heat transfer and hence their performance in industrial processes. Strategies developed to engineer the thermophysical properties of technical zeolites for fixed-bed applications comprise the use of conductive secondary phases as structured catalyst supports or as inert diluents. However, the impact of integrating conductive additives into composite zeolite bodies (pellets, extrudates, or granules) has not been widely explored. Here, using a transient hot-plate technique to decouple the distinct contributions of porosity, sample hydration, and temperature, we quantify the impact of metallic (copper), ceramic (silicon carbide, aluminum nitride, boron nitride), and carbonaceous (graphite, carbon nanotubes) phases on the thermal conductivity of shaped zeolites at the body and packed-bed scales. The decisive role of particle morphology, dominating over the intrinsic conductivity of an additive, is corroborated through the three-dimensional reconstruction of data acquired by focused ion beam-scanning electron microscopy and Xray microtomography coupled with in-situ thermographic studies. In particular, the order-of-magnitude improvement evidenced on application of graphite sheets stems from the extended paths of low thermal resistance created in the millimeter-sized catalyst ensemble. Through the identification of structure-property relations, our approach provides new insights into the rational design of composite porous materials with enhanced heat-transfer properties.

: http://publica.fraunhofer.de/documents/N-343501.html