Reactors, batch classification

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. 

As noted in the Introduction, kinetic and design calculations for reactors require information on the rate of reaction and equations to describe the concentration and temperature within the reactor. Part I developed equations to describe the rate of a chemical reaction, and briefly discussed energy (temperature) effects and chemical equilibrium. The contents of Part I can be combined and the results applied to the three major classifications of reactors batch, tank flow, and tubular flow. These three classes of reactors are discussed in the subsections that follow. 

Nowadays it is sometimes argued that each chemical reactor is unique and a systematic classification of chemical unit operations makes little sense. However, a classification based on the nature of the way different phases/substances are brought into contact with one another tends to dominate hence there are packed, fluidised, and spouted bed reactors, bubble column reactors, batch stirred tank reactors, etcetera. 

A useful classification of lands of reaclors is in terms of their concentration distributions. The concentration profiles of certain limiting cases are illustrated in Fig. 7-3 namely, of batch reactors, continuously stirred tanks, and tubular flow reactors. Basic types of flow reactors are illustrated in Fig. 7-4. Many others, employing granular catalysts and for multiphase reactions, are illustratea throughout Sec. 23. The present material deals with the sizes, performances and heat effects of these ideal types. They afford standards of comparison. 

Classification of Processes and Reactors. Most styrene polymers are produced by batch suspension or continuous mass processes. Some are produced by batch mass processes. Mass in this sense includes bulk polymerization of the polymer... 

Equipment in which homogeneous reactions are effected can be one of three general types the batch, the steady-state flow, and the unsteady-state flow or semibatch reactor. The last classification includes all reactors that do not fall into the first two categories. These types are shown in Fig. 4.1. 

Figure 4.1 Broad classification of reactor types, a) The batch reactor, b) The steady-state flow reactor, (c), d), and (e) Various forms of the semibatch reactor.

The most obvious distinctions are between nonflow (batch) and continuous operating modes and between the kinds of phases that are being contacted. A classification of appropriate kinds of reactors on the basis of these two sets of distinctions is in Figure 17.7. 

The classification in Figure 5 serves the description of the reactors used. Here, two ideal contacting types are used, the plug flow mode and the ideally mixed mode, both for the fluid and the solid phase. By appi-cation of the design equations of these ideal reactor types the experimental results are interpreted in a straightforward manner. For two phases, two contacting types and two operation modes (batch and flow) eight combinations arise ... 

To guide the reactor selection process, Walas [7] has classified reactions according to the operating mode (batch or continuous), reactor type (tank, tank battery, tubular), flow type (back mixed, multistage back mixed), and the phases in contact. This reactor classification in Table 7.2 indicates if a particular reactor arrangement is commonly used, rarely used, or not feasible. 

In this section we focus on the three main types of ideal reactors BR, CSTR, and PFR. Laboratory data are usually in the form of concentrations or partial pressures versus batch time (batch reactors), concentrations or partial pressures versus distance from reactor inlet or residence time (PFR), or rates versus residence time (CSTR). Rates can also be calculated from batch and PFR data by differentiating the concentration versus time or distance data, usually by numerical curve fitting first. It follows that a general classification of experimental methods is based on whether the data measure rates directly (differential or direct method) or indirectly (integral of indirect method). Table 7-13 shows the pros and cons of these methods. 

We have based the classification firstly on the type of operation, viz., batch or continuous, and secondly, on whether a solid catalyst is present or not. This classification is not unambiguous. For instance, most continuous-flow reactors discussed in Sections 8.2.2 and 8.2.3 can also be operated in batch mode. 

Fig. 1 Multiple steady states and their classifications in a batch reactor with negligible reactant consumption. The solid line is the heat generation curve, with B = y = 3, and 6c = —1.75. The upper dashed line is the heat removal line with a = 0.968 and the lower dashed line is the heat removal line with a = 0.199. [Data from Eq. (3).]...

Another classification of a semibatch reactor is one in which a gas forms or a solid precipitates during the reaction. Here, also, a volatile product may be fractionated off continuously. An example is batch esterification with continuous distillation. An example of this type of reaction, which will be dealt with later in this text, is the esterification of ethyl alcohol with acetic acid to form ethyl acetate. 

The success of an ISPR process does not depend only on the chosen separation technique but also on the configuration of the bioreactor/separation units and mode of operation. Previous reviews have shown the various possible modes of operation (continuous, batch) and the use of a separation unit outside of the reactor or separation techniques that act right inside the fermenter [19,22,31]. Freeman and coworkers introduced a classification scheme for ISPR process based on batch/continuous operation and internal (within the reactor)/external (outside the reactor) removal of the product [3]. 

Reactors are the essential elements of any technological process and flow sheet connected with the chemical transformation of snbstances. Eqnipment efficiency in terms of reliability, susceptibility, production and economic efficiency, and ecological safety are very important for any successful technological process. Industrial chemical equipment is available in different shapes, which complicates their classification. Generally, they are divided into continuous or batch models, perfect mixing and plug flow reactors, or their empirical combinations. 

Transient reactor operation plays an increasingly important role in bioprocessing and has to some extent already been considered (classification, see Fig. 3.31 fed-batch culture, see Fig. 3.37 situation, see Fig. 4.4 guidelines to solution, see Sect. 4.2 and Fig. 4.5 structured cell model concept, see Fig. 4.7 application, see Chap. 6). Both balanced and frozen conditions have also been considered in Fig. 3.34. A biosystem is in balanced condition when the mechanism is fully adapted, as in a quasi-steady-state (if x ). All different equations can be reduced to algebraic equations. A biosystem is in frozen condition of the initial state (if x x ) and the mechanism may be neglected due to the fact that the slowest step is rate determining ( rds concept ). By this procedure, equations are reduced to parameters so that the number of equations is reduced (e.g., the case of dropwise addition of substrate). This is the case of steady state CSTR. 

Biohydrogen photo-bioreactors have been thoroughly analysed and revised for both microalgae (Posten, 2009) and photo-fermentative bacteria (Koku et al., 2003) cultivation. For a first rough classification, photo-fermentation can be lead out in batch or in continuous reactors, with the choice being determined by feed rate and type and biomass. 

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