Pellet reactors

Faradaic efficiency, A, values up to 6 and rate enhancement, p, values of at least up to 13 were obtained in this study which was carried out at 50 atm pressure and using a 24-catalyst pellet reactor.16... 

Morbidelli M, Gavriilidis A and Varma A (2001) Catalyst Design Optimal Distribution of Catalyst in Pellets, Reactors, and Membranes, Cambridge University Press. 

The optimal distribution of silver catalyst in a-Al203 pellets is investigated experimentally for the ethylene epoxidation reaction network, using a novel single-pellet reactor. Previous theoretical work suggests that a Dirac-delta type distribution of the catalyst is optimal. This distribution is approximated in practice by a step-distribution of narrow width. The effect of the location and width of the active layer on the conversion of ethylene and the selectivity to ethylene oxide, for various ethylene feed concentrations and reaction temperatures, is discussed. The results clearly demonstrate that for optimum selectivity, the silver catalyst should be placed in a thin layer at the external surface of the pellet. 

Although this reaction network has been studied extensively, its mechanism is still under debate (10). In this study, a single-pellet reactor was used, and the pellet was prepared mechanically by pressing the active catalyst layer between two alumina layers. In this way a step-type catalyst pellet was produced, which approximated a Dirac-type catalyst distribution. 

Figure 1. Single-pellet reactor. (Reproduced with permission from ref. 9. Copyright 1992 AIChE.)...

The two-phase (gas-solid) continuous stirred-tank reactors are represented by laboratory reactors as, for instance, one-pass differential reactors, reactors with forced recirculation, one-pellet reactors, etc. The industrial applications are the fluidized beds.2 Table V presents a list of experimental studies along with a very brief description of each system studied. 

Fig. 4.2 Deactivation study of 29 catalysts in the multi-chamber pellet reactor of Senkan et al. [26].

Measurement of Reaction Kinetics and Effective Pellet Diffusivity in a Single-pellet Reactor... 

The isomerization of n-hexane at 453° C and a total pressure of 1.6 bars has been investigated by Christoffel and Schuler [15]. They used a single pellet reactor with a pellet thickness L of 6.22 xlO-3 m. The porous pellet material contained 0.35 wt % Pt on A O,. The flow rate along the pellet was so high that the observed conversion rate was independent of the flow rate. The partial pressure of n-hexane in the feed was varied between 15 and 160 mbar. The ratio of the n-hexane concentration in the space below the pellet CAb and in the gas mixture above the pellet CAj was found to be independent of Caj CaJCa, = 0.191. The apparent conversion rate was found to be proportional to the n-hexane concentration in the feed and to be represented by RA = 0.184x0 krnol m 3 s 1. From these results the following information can be obtained ... 

Knudsen number, modified for multicomponent systems length (thickness) of a catalyst pellet reactor length... 

Harold et al. [1989] have compared the predicted CNMMR performances based on the above two models with that calculated from a string of pellets reactor model. The string of pellets reactor is considered a prototype trickle-bed reactor. 

Example Tbe pellet reactor is shown in Fig. 11-8. The reaction gases were... 

Fig. 14-1 Stirred-tank single-pellet reactor for hydrofluorination of uranium dioxide...

M. Morbidelli, A. Gavriilidis and A. Varma, Catalyst design, optimal distribution of catalyst in pellets, reactors, and membranes , Cambridge University Press, Cambridge, UK (2001). 

Figure 23 NEMCA-induced compensation effect in the oxidation of CjHg on Pt/YSZ in a single pellet reactor r Is the applied overpotentlal. ...

Yamamoto, T. Ramanathan, K. Lawless, P. L. Ensor, D. S. Newsome, J. R. Plaks, N. and Ramsey, G. H. Control of volatile organic compounds by an ac energized ferroelectric pellet reactor and a pulsed corona reactor IEEE Trans. Ind. AppUcat, 1992, 28. 528-534... 

Where quicklime is purchased, its particle size and reactivity should be specified to ensure that it is compatible with the handling equipment and suitable for the type of slaker installed (see section 22.3). For pellet reactors, the solution rate of the milk of lime should be sufficient to prevent significant amounts of undissolved calcium hydroxide being carried out of the reactor by the flow of water. 

Experimental verification of the above concepts will be given in the following examples. Of course, praaical difficulties often prevent perfect agreement, and it is sometimes necessary to perform direct experiments with a catalyst pellet see Balder and Petersen [95] for a useful single-pellet-reactor technique and a review by Hegedus and Petersen [152]. 

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