Batch reactor heterogeneous catalytic

Design equation— ideal batch reactor— heterogeneous catalytic reaction (moles)... 

The most common heterogeneous catalytic reaction is hydrogenation. Most laboratory hydrogenations are done on liquid or solid substrates and usually in solution with a slurried catalyst. Therefore the most common batch reactor is a stirred vessel, usually a stirred autoclave (see Figure 2.1.1 for a typical example). In this system a gaseous compound, like hydrogen, must react at elevated pressure to accelerate the process. 

For heterogeneous catalytic reactions, the rate of reaction is often expressed as the number of moles of component reacting per unit time, per unit mass of catalyst. For a batch reactor... 

At this point we wish to turn to a brief discussion of the types of batch and flow reactors used in industrial practice for carrying out homogeneous fluid phase reactions. Treatment of heterogeneous catalytic reactors is deferred to Chapter 12. 

Heterogeneously catalyzed hydrogenation reactions can be run in batch, semibatch, or continous reactors. Our catalytic studies, which were carried out in liquid, near-critical, or supercritical C02 and/or propane mixtures, were run continuously in oil-heated (200 °C, 20.0 MPa) or electrically heated flow reactors (400 °C, 40.0 MPa) using supported precious-metal fixed-bed catalysts. The laboratory-scale apparatus for catalytic reactions in supercritical fluids is shown in Figure 14.2. This laboratory-scale apparatus can perform in situ countercurrent extraction prior to the hydrogenation step in order to purify the raw materials employed in our experiments. Typically, the following reaction conditions were used in our supercritical fluid hydrogenation experiments catalyst volume, 2-30 mL total pressure, 2.5-20.0 MPa reactor temperature, 40-190 °C carbon dioxide flow, 50-200 L/h ... 

The reports on catalytic isomerization using various zeolitic catalysts, in comparison to the conventional catalysts previously used, gives results of reactions carried out discontinuously in a batch reactor in liquid phase, as well as for those carried out continuously in a fixed bed reactor in the vapor phase. The results in the liquid phase over heterogeneous catalysts are summarized in Table 15.2. 

The simplicity and general utility of the Madon-Boudart criterion make it one of the most important experimental tests to confirm that kinetic data are free from artifacts. It can be used for heterogeneous catalytic reactions carried out in batch, continuous stirred tank, and tubular plug flow reactors. 

The catalytic behavior of enzymes in immobilized form may dramatically differ from that of soluble homogeneous enzymes. In particular, mass transport effects (the transport of a substrate to the catalyst and diffusion of reaction products away from the catalyst matrix) may result in the reduction of the overall activity. Mass transport effects are usually divided into two categories - external and internal. External effects stem from the fact that substrates must be transported from the bulk solution to the surface of an immobilized enzyme. Internal diffusional limitations occur when a substrate penetrates inside the immobilized enzyme particle, such as porous carriers, polymeric microspheres, membranes, etc. The classical treatment of mass transfer in heterogeneous catalysis has been successfully applied to immobilized enzymes I27l There are several simple experimental criteria or tests that allow one to determine whether a reaction is limited by external diffusion. For example, if a reaction is completely limited by external diffusion, the rate of the process should not depend on pH or enzyme concentration. At the same time the rate of reaction will depend on the stirring in the batch reactor or on the flow rate of a substrate in the column reactor. 

Different types of reactors are applied in practice (Figure 1.14). Stirred tank reactors (STR), very often applied for homogeneous, enzymatic and multiphase heterogeneous catalytic reactions, can be operated batchwise (batch reactor, BR), semi-batchwise (semibatch reactor, SBR) or continuously (continuous strirred tank reactor, CSTR)... 

The examples described in the previous paragraphs were all carried out as batch reactions. For practical applications in industry, however, the ideal process would involve a continuous-flow system in which the substrates are continuously fed into the reactor, where they react in the presence of the catalyst, and the products are collected at the other end. The catalyst remains in the reactor at all times. Such systems were previously exclusively applied for heterogeneous catalytic reactions. Nowadays, the use of SILP systems allows the desired homogeneous catalysts to be used in continuous flow. 

Often homogeneous or homogeneously catalyzed reactions but even heterogeneous catalytic reactions exist batch, tank, and tube reactors, three-phase reactors, bubble columns Columns and mixer-settler... 

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. 

FIGURE 8.3 Heterogeneous catalysis reactor types (a) fixed bed, (b) batch fluid bed, (c) slurry, (d) catalytic gauze, (e) trickle bed, (f) moving bed, (g) continuous fluid bed, and (h) transport line. 

For all the systems under consideration, rate equations have been developed using extensive experimental data obtained over a wide range of operating conditions. In evaluating the kinetics, the contributions of both homogeneous (non-catalytic) and heterogeneous reactions have been taken into account. Batch and fixed bed reactor models have also been developed, and the model predictions have been compared with... 

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