Heterogeneous monolith reactors

Du P, Cameiro JT, Moulijn JA, Mul G. A novel photocatalytic monolith reactor for multiphase heterogeneous photocatalysis. Applied Catalysis A General 2008 334 119-128. 

Classical heterogeneous catalytic reactor types used in various process technologies include packed beds, wall-catalyzed reactors, bubble columns, stirred tanks, risers, and fluidized beds. Monoliths and micro reactors have also made inroads in the last couple of decades. Novel designs attempt to... 

Monolith reactor model—For validation purposes, the kinetic models of the SCR catalyst [6] and of the PGM catalyst [18] were used to simulate catalytic activity runs over honeycomb monoliths coated with the SCR and the PGM component, respectively, of the studied ASC system. In the case of the SCR catalyst, the kinetics were implemented in a heterogeneous dynamic ID -I- ID model of a single monolith channel, accounting both for external (gas-solid) and internal (intra-porous) mass transfer resistances [12, 25, 26]. Model simulations... 

Control of emissions of CO, VOC, and NOj, is high on the agenda. Heterogeneous catalysis plays a key role and in most cases structured reactors, in particular monoliths, outperform packed beds because of (i) low pressure drop, (ii) flexibility in design for fast reactions, that is, thin catalytic layers with large geometric surface area are optimal, and (iii) attrition resistance [17]. For power plants the large flow... 

Most industrial catalysts are heterogeneous catalysts consisting of solid active components dispersed on the internal surface of an inorganic porous support. The active phases may consist of metals or oxides, and the support (also denoted the carrier) is typically composed of small oxidic structures with a surface area ranging from a few to several hundred m2/g. Catalysts for fixed bed reactors are typically produced as shaped pellets of mm to cm size or as monoliths with mm large gas channels. A catalyst may be useful for its activity referring to the rate at which it causes the reaction to approach chemical equilibrium, and for its selectivity which is a measure of the extent to which it accelerates the reaction to form the desired product when multiple products are possible [1],... 

The monolithic stirrer reactor (MSR, Figure 2), in which monoliths are used as stirrer blades, is a new reactor type for heterogeneously catalyzed liquid and gas-liquid reactions (6). This reactor is thought to be especially useful in the production of fine chemicals and in biochemistry and biotechnology. In this work, we use cordierite monoliths as stirrer blades for enzyme-catalyzed reactions. Conventional enzyme carriers, including chitosan, polyethylenimine and different are used to functionalize the monoliths. Lipase was... 

Then, a survey of micro reactors for heterogeneous catalyst screening introduces the technological methods used for screening. The description of microstructured reactors will be supplemented by other, conventional small-scale equipment such as mini-batch and fixed-bed reactors and small monoliths. For each of these reactors, exemplary applications will be given in order to demonstrate the properties of small-scale operation. Among a number of examples, methane oxidation as a sample reaction will be considered in detail. In a detailed case study, some intrinsic theoretical aspects of micro devices are discussed with respect to reactor design and experimental evaluation under the transient mode of reactor operation. It will be shown that, as soon as fluid dynamic information is added to the pure experimental data, more complex aspects of catalysis are derivable from overall conversion data, such as the intrinsic reaction kinetics. 

Figure 5 Product compositions and surface temperatures (upstream and downstream ends) for a 7-mm-Iong, 12-wt%-Pt extruded monolith (400 cells/in. ) at 2 5-sIpm total flow. The H2 and CO sclectivities are lower than those reported in previous experiments because the reactor was not insulated. A heterogeneous steady-state reaction is maintained for rich (> 12%) compositions, while at leaner compositions, a combination of heterogeneous and homogeneous reactions (a blue flame) is observed, with multiple ignited steady-states for compositions between 10 and 12% CH4. (From Ref. 7.)...

G. Wiessmeier, K. Schubert, D. Honicke, Monolithic microstructure reactors possessing regular mesopore systems for the successful performance of heterogeneously catalyzed reactions, in W. Ehrfeld (Ed.), Proceedings of the 1st International Conference on Microreaction Technology (IMRET 1), Springer, Berlin, 1997, p. 20. 

Along with the inclusion of heterogeneous metal catalysts in continuous flow reactors, numerous authors have evaluated the advantages associated with the incorporation of acid and base catalysts in these reaction systems, using a range of packed beds, monoliths, and wall-coated reactors. 

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. 

Combinatorial chemistry can perhaps help discover new catalyst formulations for reactions presently of particular interest, such as oxidations or ammoxidation, and generally all reactions of alkanes. Reactions traditionally made in different kinds of processes are frequently shown to be also activated by heterogeneous catalysts (e.g., epoxidations). Reactors of unexpected design allow surprisingly selective reactions (e.g., monoliths for the oxidative dehydrogenation of light alkanes). However, the distance often remains long between these discoveries and the manufacture of active and selective catalysts adequately structured for particular use in an industrial reactor inserted in an industrial plant. 

In conventional industrial multi-phase reactors, the heterogeneous catalyst can be organized as a packed (or fixed) bed of catalyst particles (e.g., in trickle-bed reactors or in submerged up-flow reactors), as catalyst particles suspended or fluidized in one of the two phases (in the hquid phase of a three-phase reactor, as for example in a slurry-stirred reactor and a slurry-bubbling reactor) or finally as a structured catalyst (e.g., monolith and membrane reactors). Structured catalysts are regular solid structures which reduce randomness through a well-defined structure and shape at a reactor level. The selection of the most appropriate traditional multi-phase... 

Catalytic monoliths are structured heterogeneous reactors. These two features require the consideration of the reaction-diffusion problem in the catalytic washcoat (the internal region), which can be designed with much more independence from the external domain, when compared to nonstructured reactors. In general, the operating conditions will be such that... 

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