A Scalable MicroChannel Technology

Honeycomb monoliths (Fig. 6.1) are structured catalyst supports consisting of parallel straight capillary channels. Nowadays, they are widely used for the catalytic exhaust converter in the automobile industry and end-of-pipe gas cleaning. The gas-only application of monoliths stems from the fact that the pressure drop is low using the surface area of the catalyst as a criterion, the pressure drop in a monolith is an order of magnitude lower than in randomly packed beds. The channels are about a millimeter in diameter, and on the wall (-100 pm) a wash-coat of catalytic material (-50 pm) is applied. 

Briefly, we have obtained hydrogenation rates for a-methylstyrene that were orders of magnitude higher than in typical packed beds [15], and we have obtained selectivities in the A - B C hydrogenation of benzaldehyde that were similar to values obtained in fine powder slurry reactors [16]. Monoliths have been 

Most of the gas-liquid applications of monoliths have used a heterogeneous catalyst (be it supported noble metals or immobihzed enzymes) on the channel walls. Here, we also consider the use of monohths without a catalyst on the walls in gas-liquid applications, i.e. homogeneously catalyzed liquid-phase reactions. The fluid mechanics of the system do not change appreciably by lethng the reaction take place in the liquid bulk instead of in a washcoat layer, and it is interesting to consider such reactions in a discussion of mass transfer and power-input requirement. Of course, the mass-transfer behavior does change by changing the locahon where the reaction takes place, and we will discuss gas-hquid reactors and gas-liquid-solid reactors separately. 

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