Stofftransport in mikro‐ und mesoporösen Materialien

Mass Transfer in Micro‐ and Mesoporous Materials Mass transfer in micro‐ and mesoporous materials is of crucial relevance for their practical application to separation and catalysis, since the mobility of adsorbed molecules ultimately limits the rate of the overall processes. Diffusion, i.e. the irregular thermal motion of the molecules, is the dominating process. Diffusion measurements are therefore indispensable for the evaluation of the quality parameters of porous materials. Being able to directly follow the diffusion path of the molecules, microscopic techniques hold a key position among the various methods of diffusion measurement. Besides their fundamentals, the contribution describes the application of these techniques to the investigation of structure‐mobility relations in zeolites and in mesoporous materials of type MCM‐41. As features of particular technological relevance, the phenomena of correlated diffusion anisotropy, of single‐file diffusion, and of molecular traffic control are discussed in detail.     

Gekoppeltes Berechnen von Blasengrößenverteilungen und Strömungsfeldern in Blasensäulen

Coupled Calculation of Bubble Size Distribution and Flow Fields in Bubble Columns In this paper the use of computational fluid dynamics (CFD) for the calculation of flow fields in bubble columns is explained. The local bubble size distribution is considered with the aid of a simplified balance equation for the average bubble volume in bubbly flow. Models are developed for the rate of bubble break‐up and coalescence based on physical principals. The flow fields in cylindrical bubble columns without internals are calculated using the Euler‐Euler method. The small and large bubble fraction are considered as pseudo‐continuous phases in addition to the liquid phase. The calculated flow fields are characterised by several large scale vortices. The local volume fractions of gas and liquid are very inhomogeneous and highly time dependent. The calculated volume fractions, velocities and bubble size distributions agree well with experimental results for bubble columns up to 0.3 m in diameter.     

Messverfahren zur Bestimmung des Staubungsvermögens von dispersen Pulvern

Dustiness Measuring Methods of Disperse Powders Industrial handling of bulk materials, for example to store, convey, mix, fill etc. often leads to dust emissions. Generated dust is closely related to health hazards and environmental pollution and often leads to fires and explosions. The dust liberation property of powders depends on a multitude of variables and also on the method and intensity of stressing. The present paper describes further developed resp. used dustiness measuring methods. It also describes particle measurement techniques and summarizes the measurement methods systematically.     

Molekularsieb‐Membranen für industrielle Anwendungen – Probleme,Fortschritte, Lösungen

Molecular Sieve Membranes for Industrial Applications – Problems, Advances, Solutions Molecular sieve membranes are characterised by their high thermal and chemical resistance and by their monodisperse micropore system. Mixtures can be separated according to molecular size as well as according to adsorptive interactions and diffusion differences. This paper outlines techniques for reproducible production of large area membranes together with methods for their regeneration and repair. Typical separations demonstrate the efficiency of these membranes. Potential application fields can be deduced from developmental trends.