Cross flow reactors

Fig. 8. Combined flow reactor models (a) parallel flow reactors with longitudinal diffusion (diffusivities can differ), (b) internal recycle—cross-flow reactor (the recycle can be in either direction), comprising two countercurrent plug-flow reactors with intercormecting distributed flows, (c) plug-flow and weU-mixed reactors in series, and (d) 2ero-interniixing model, in which plug-flow reactors are parallel and a distribution of residence times dupHcates that...

However, many reactions of commercial interest have chemistry, mechanical, or system requirements that preclude the use of cross-flow reactors. Processes cannot use a cross-flow orientation primarily because of high temperatures and the need to internally recuperate heat such as steam methane reforming (SMR) [12, 13] and oxidation reactions [14]. Counter- and coflow devices require a micromanifold to dehver sufficiently uniform flow to each of the many parallel channels. 

Reactor 24 [R 24] System with Series of Micro Mixers-Cross-Flow Reactor Modules... 

Reactor type System with series of micro mixers-cross-flow reactor moldules Number of reaction channels 169... 

Cross-flow reactors are fed continuously with streams of components of the reaction mixture whereby some components are introduced at the inlet, while others are introduced at other locations. The reaction mixture flows out continuously from the end of the reaction zone. A cascade of CSTRs with additional feeds to individual reactors represents a cross-flow reactor system. Cross-flow reactors are also operated at steady-state conditions ... 

OA2 > CMI, am > am Concentration of B should be minimized. Dosing of B into the reaction mixture containing A is advantageous. A semibatch reactor or a cross-flow reactor is recommended. 

A special type of cross-flow reactor was developed in the laboratories of Vogt [16] to handle continuous gas / liquid reactions. The challenge in the reactor design was to combine efficient gas-liquid mixing, liquid level control in the reactor, turbulent flow across the membrane, and efficient gas-liquid separation to avoid gas contacting the membrane, which would lead to a shunt of gas. The total internal volume should not... 

In the cross-flow reactor a species B is introduced at several places in a reactor while species A is introduced at the entrance as sketched in Figure 4-16. What might be the benefits on selectivity and in autocatalytic reactions by this flow situation ... 

Figure 4-16 Cross-flow reactor in which a species B is introduced at several points in the reactor.

Fig. 1.24. Performance of cross-flow reactors with five equidistant feed points Parallel reactions A + B -> P > kPCACB...

Figure 10.18 Gas-liquid flow in section of cross-flow reactor [De Vos and Hamrin, 1982]...

Permeable walls are also used in cross-flow reactors. The concept behind the cross-flow reactors is, however, somewhat wider than the principles of devices presented heretofore. Cross-flow involves two different fluids flowing perpendicularly to or from each other in a process apparatus. The streams can be separated by a permeable wall or can be combined without such a wall. Cross-flow reactors of various kinds are presented in Chapter 20 of this book. 

Cross-Flow Reactors with Permeable Walls... 

Figure 1 Possible cross-flow reactor systems consisting of tubular reactors. (From Ref. 1.)...

Tn the multitubular cross-flow reactor, one or more baffles are used to force the coolant to flow across the tubes, and some parallel flow arises where the coolant flow direction reverses. 

In addition to the above cross-flow reactors of extended definition, the block of thin-walled spiral-tubular-membrane catalyst reactor and the double-spiral coiled-plate-membrane reactor may be included [30-33]. 

II. SURVEY OF CROSS-FLOW REACTORS WITH SEPARATING WALLS IN REGARD TO THEIR FUNCTION AND APPLICABILITY... 

Examples of different cross-flow reactors are shown in Table 1, where different characteristics such as separating wail material, type of transport through the wall, and model reactions studied arc given. As seen from Table 1 the reactors may be divided into five groups with respect to their fields of application ... 

In all these fields the traditional cross-flow reactor is represented. This reactor consists of a great number of parallel porous plates separated from each other by corrugated planes or by a similar regular structure, giving rise to a compact system of parallel closed channels, with only entrance and exit openings perpendicular to the main flow direction (cf. Fig. 3). The parallel-channel system of this traditional cross-flow reactor is arranged so that the inflows of the two fluids are separated 90°. This means that the two fluids will not be mixed in the same channels and the fluids will penetrate the plane plates from different sides. The fluids can meet only inside the porous catalytic plates where the reactions proceed. 

Table 1 Examples of Cross-Flow Reactors with Separating Walls Between the Fluids... 

Catalytic cross-flow reactor Calcium aluminum silicate H2 diffusion in liquid-filled pores Hydrogenation of p-nitrobcnzoic acid Pd-coated monolith wall 60 ... 

The goal of using solid-state electrolytic reactors is not only to generate electrical power, but also to combine this with an industrially important catalytic reaction, such as dissociation of oxygen-containing compounds like NO [40,41], quantitative oxidation of NH3 to NO [42-44], oxidation of SO2 [45], and methanol [46], ethylene epoxidation [46], or Fischer-Tropsch synthesis [47]. The cross-flow reactor used in this type of study (Fig. 10) [48,49] has a solid electrolyte consisting of yttria-doped zirconia. The plates are electrically connected in series, with a varying number of plates in parallel. The oxidant flow channels... 

The three kinds of reactors already described in this section are all traditional cross-flow reactors with permeable plates or membranes. The electrochemical filter-press cell reactors used, e.g., for electrosynthesis, are equipped with cation-selective membranes to prevent mixing of the anolyte and the catholyte. These cell reactors are therefore good examples of the extended type of cross-flow reactors according to the definition transferred from the filtration field. The application of the electrochemical filter-press cell reactor technique... 

Even if the monolithic catalyst reactor is a well-accepted alternative to the trickle bed, it cannot be the ideal final option. In such an alternative, the two phases have to be separated, and therefore the cross-flow reactor may have all the qualifications of an ideal option. 

The key problem of the cross-flow reactor is not how to construct an effective separation of the two flowing phases. It is instead connected with how to design the porosity and location of the catalytic active zones of the separating walls so that the transport resistance across the wall does not limit the conversion and the selectivity of the chemical reactions. Palladium-alloy membranes, or thin films of these alloys on porous ceramic tubs, seem to have the potential to be good solutions of the separating-wall problem for cross-flow reactors used for hydrogenation reactions. 

Deactivation of the catalyst is always an industrially important problem. For fixed-bed reactors, to which class the cross-flow reactors also belong, catalyst poisoning is a particularly delicate matter, since the reactivation is often complicated and expensive. Some poisoning effects may be difficult to explain and understand, and this of course causes extra uncertainty. One example of such poisoning was the observation by Amor and Farris [33] that a special deactivation effect appeared in liquid-phase hydrogenation of toluene using a spiral tubular membrane reactor. Toluene was not hydrogenated at all over the palladium foil used. This phenomenon and reactivation of the catalyst have recently been studied by Ali et al. [56]. 

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