Single-pellet reactor

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.)...

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 ... 

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

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

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]. 

Gas-solid (catalytic) Differential reactor Integral reactor Mixed (Carberry) reactor Mic roreactor Fluid-bed reactor Single-pellet reactor (Chapter 7)... 

Gas-solid (reactant) Thermogravimetric apparatus Single-pellet reactor... 

Particle related parameters should be determined in a so-called single pellet reactor /20,21/ as shown schematically in Fig. 

Single pellet reactor for determination of effective pellet diffusivity under reaction conditions... 

E. Aust Diss. Univ. of Erlangen-Niirnberg 1986 /21/ J.R. Balder and E.E. Petersen Application of the single pellet reactor for direct mass transfer studies I and II, J.Catal.JJ ( 1968) 195-201, 202-210... 

To compare static and dynamic methods, in this study the second method (III in Table 3) was applied (Figure 5), using a gas, A gas offers the advantage that the particles can be used in their original shape and in the actual reaction mixture (e.g. as a single pellet reactor). 

The single pellet moment technique which was originally developed by Dogu and Smith (1975,1976) for the evaluation of diffusion and adsorption parameters in porous solids, was extended to reaction systems and used for the kinetic analysis of SO 2-activated soda reaction (Dogu et al, 1986). In this technique, an inert carrier gas (helium) flowed over two end faces of a cylindrical soda pellet placed into the single pellet reactor (Figure 11). 

Figure 11. Schematic diagram of single pellet reactor.

Of the two transfer coefficients for gas-phase catalytic reactions, the heat transfer coefficient is much more important than the mass transfer coefficient since the external mass transfer resistance can be neglected under realistic conditions. The heat transfer coefficient under reaction conditions may be determined using a single-pellet reactor. At steady state, one has ... 

C2H6 oxidation on Pt has been investigated" in a single-pellet reactor at temperatures between 400 and 500°C. The reaction exhibits electrophobic behavior for positive currents (Vwr > V r ) and electrophilic behavior for negative currents (Vwr < V r ) (Figs. 37 and 38). In the former case, p is up to 20 and A up to 3(X). In the latter case, p is up to 7 and A up to -100. The open-circuit kinetic behavior indicates that the catalyst surface is predominantly covered with oxygen and that the cov-... 

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