Catalytic plate cell reactor

Figure 12.10 Examples of structured catalytic reactors for kinetic measurements (a) annular reactor [47, 61] (b) plate cell reactor [75].

The catalytic plates are not completely accessible in the monolithic cross-flow structure, since a certain part of the plates is lost by contact with the corrugated interstitial planes of this structure. Moreover, the successful development in the preparation of thin, porous plates for electrochemical purposes created the idea that this preparation technique should also be used to produce permeable catalyst plates for cross-flow catalyst reactors. Instead of using these plates for the complicated cross-flow structure, the whole step was taken to using them in an electrochemical cell-like design of the reactor. The catalytic plates were thus mounted in a special rack like a filter press (Fig. 13), giving the so-called cell reactor [26]. 

As seen from Fig. 13, which gives a model unit of the laboratory cell reactor, this cell contains specially designed nets, to provide turbulence of the liquid flow. From the experimental result it was shown that the effectiveness factor was very high (up to 0.84) in experiments with plates with a very thin catalytic layer located close to the liquid side. In experiments with plates with a thick catalytic layer located in the middle of the plate, the effectiveness factor was very low (down to 0.02), and only a small part of the catalyst layer was utilized, since p-nitrobenzoic acid vanished in the plate after only 10% of the thickness of the catalytic layer had been passed in this particular run. 

A preferred embodiment of this concept is the catalytic plate reactor, which consists of catalytically coated metal plates so that exothermic and endothermic reactions take place in alternate channels. In addition to minimizing the heat transfer resistances, this reactor facilitates mass transfer to the catalytic surface by reducing the diffusion length. Catalytic plate reactors can find applications in steam reforming, dehydrogenation, and hydrocarbon cracking which are strongly endothermic processes. In recent years those reactors have received considerable attention as steam reformers for fuel cell applications. " ... 

Attenuated total reflection (ATR) is sometimes used to measure the infrared spectra of catalysts inside a reactor. The infrared light is coupled into an ATR crystal, which can be either a flat plate (e.g., the wall of a reactor) or a cylindrical rod (surrounded by catalyst particles). The evanescent wave that protrudes outside the crystal when the infrared beam reflects on the inside of its surface is used for the measurement. A review of ATR in catalysis has been published by Biirgi and Baiker [11], and a catalytic cell to apply the method in situ inside a catalyst bed reported by Moser and co-workers [12]. An example of ATR is discussed later in this chapter. 

Finally, possible causes for deactivation of catalytic membranes are described and severad aspects of regenerating catalytic membrane reactors are discussed. A variety of membrane reactor configurations are mentioned and some unique membrane reactor designs such as double spiral-plate or spiral-tube reactor, fuel cell unit, crossflow dualcompartment reactor, hollow-fiber reactor and fluidized-bed membrane reactor are reviewed. 

Electrochemical reactors are heterogeneous by their very nature. They always involve a solid electrode, a liquid electrolyte, and an evolving gas at an electrode. Electrodes come in many forms, from large-sized plates fixed in the cell to fluidizable shapes and sizes. Further, the total reaction system consists of a reaction (or a set of reactions) at one electrode and another reaction (or set of reactions) at the other electrode. The two reactions (or sets of reactions) are necessary to complete the electrical circuit. Thus, although these reactors can, in principle, be treated in the same manner as conventional catalytic reactors, detailed analysis of their behavior is considerably more complex. We adopt the same classification for these reactors as for conventional reactors, batch, plug-flow, mixed-flow (continuous stirred tank), and their extensions. 

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