Heterogeneous reactors types

Heterogeneous reactors contain more than one phase. Several heterogeneous reactor types are available due to various combinations of phases. 

Overall, tracers have been and continue to be used in all homogeneous and heterogeneous reactor types. They remain an irreplacable tool in scaleup and cold flow modeling on which all prudent design engineers rely. The broad spectrum of their use is illustrated by this review. 

Flow Reactors Fast reactions and those in the gas phase are generally done in tubular flow reaclors, just as they are often done on the commercial scale. Some heterogeneous reactors are shown in Fig. 23-29 the item in Fig. 23-29g is suited to liquid/liquid as well as gas/liquid. Stirred tanks, bubble and packed towers, and other commercial types are also used. The operadon of such units can sometimes be predicted from independent data of chemical and mass transfer rates, correlations of interfacial areas, droplet sizes, and other data. 

In any catalyst selection procedure the first step will be the search for an active phase, be it a. solid or complexes in a. solution. For heterogeneous catalysis the. second step is also deeisive for the success of process development the choice of the optimal particle morphology. The choice of catalyst morphology (size, shape, porous texture, activity distribution, etc.) depends on intrinsic reaction kinetics as well as on diffusion rates of reactants and products. The catalyst cannot be cho.sen independently of the reactor type, because different reactor types place different demands on the catalyst. For instance, fixed-bed reactors require relatively large particles to minimize the pressure drop, while in fluidized-bed reactors relatively small particles must be used. However, an optimal choice is possible within the limits set by the reactor type. 

Single-phase catalytic fixed bed reactors are the main reactor type used for large-scale heterogeneously catalyzed gas-phase reactions. Frequently, multitubular... 

In this chapter, we first cite examples of catalyzed two-phase reactions. We then consider types of reactors from the point of view of modes of operation and general design considerations. Following introduction of general aspects of reactor models, we focus on the simplest of these for pseudohomogeneous and heterogeneous reactor models, and conclude with a brief discussion of one-dimensional and two-dimensional models. 

Chapter 1 reviews the concepts necessary for treating the problems associated with the design of industrial reactions. These include the essentials of kinetics, thermodynamics, and basic mass, heat and momentum transfer. Ideal reactor types are treated in Chapter 2 and the most important of these are the batch reactor, the tubular reactor and the continuous stirred tank. Reactor stability is considered. Chapter 3 describes the effect of complex homogeneous kinetics on reactor performance. The special case of gas—solid reactions is discussed in Chapter 4 and Chapter 5 deals with other heterogeneous systems namely those involving gas—liquid, liquid—solid and liquid—liquid interfaces. Finally, Chapter 6 considers how real reactors may differ from the ideal reactors considered in earlier chapters. 

The monolithic stirrer reactor (MSR, Figure 2), in which monoliths are used as stirrer blades, is a new reactor type for heterogeneously catalyzed liquid and gas-liquid reactions (6). This reactor is thought to be especially useful in the production of fine chemicals and in biochemistry and biotechnology. In this work, we use cordierite monoliths as stirrer blades for enzyme-catalyzed reactions. Conventional enzyme carriers, including chitosan, polyethylenimine and different are used to functionalize the monoliths. Lipase was... 

Equation (45) can be solved by applying different photoreactor models. The literature reports several photochemical reactor models for both homogeneous and heterogeneous reactors [11,108,109]. In practice, annular photoreactors are often used (see Fig. 5) therefore, models for this type of reactor are considered here. For other types of reactors, attention should be given to other publications [109]. 

The different industrially established fixed-bed reactor configurations of the adiabatic, the multistage and the multitubular reactor types represent a mature and versatile class of reactors for heterogeneously catalyzed gas phase reactions. Companies specialized in their... 

The various mathematical techniques used to obtain MWD with different combinations of mechanisms in different reactor types are surveyed. As Wei and Prater (57) stated for heterogeneous catalysis, and Benson (6) for kinetics in general, the chief difficulties are not the solutions of the kinetic equations once the mechanisms and constants are known. The real problem is the application of solutions to experimental data to determine fundamental mechanisms and constants which may be useful under other conditions. Too few investigators have noted this. 

The aggregation of cells in suspension culture leads to a heterogeneous population that confound the analysis and operations of the reactor types mentioned above in many cases. For non-growth associated products, immobilization of cells provides a... 

Industrial catalytic reactors exhibit a great variety of shapes, types and sizes. It is not our aim here to discuss all possibilities a survey of the most important reactor types is given by Ullmann [1]. In general, heterogeneous catalytic reactors can be divided in two categories, depending on the size of the catalyst particles, large and small. 

The design of fuel elements depends on the type of reactor and on the operating conditions. Fabrication of fuel elements does not apply for homogeneous reactors in which the fuel is used in the form of a solution of uranyl sulfate or uranyl [ N] nitrate. In heterogeneous reactors, the fuel is applied in the form of metals or alloys or in the form of ceramic substances, such as UO2, UC or mixtures with other components. 

Heterogeneously catalysed reactions are two-, three-, or even more than three-phase operations. Solid catalyst and gaseous and liquid reactants are brought in contact to achieve the desired conversion. Some of the reactor types that are used are briefly presented here for background information with generalized remarks on their advantages and disadvantages. 

Multiphase reactions that occur in the presence of a heterogeneous catalyst can be realized using a variety of tubular reactor types that can be classified according to the state of motion of the catalyst. When the catalyst remains stationary inside the tube and has the shape of a... 

The discovery of solid catalysts led to a breakthrough of the chemical process industry. Today most commercial gas-phase catalytic processes are carried out in fixed packed bed reactors. A fixed packed bed reactor consists of a compact, immobile stack of catalyst pellets within a generally vertical vessel. On macroscopic scales the catalyst bed behaves as a porous media. The fixed beds are thus employed as continuous tubular reactors in which the reactive species in the mobile fluid (gas) phase are reacting over the catalyst surface (interior or exterior) in the stationary packed bed. Compared to other reactor types or designs utilizing heterogeneous catalysts, the fixed packed bed reactors are preferred because of simpler technology and ease of operation. 

The PTEF factor (PTEF= p = Qused/Qa) equates the used energy in the photochemical transfomiation and the photon energy absorbed by the photocatalyst. The PTEF is of general applicability with its application not being restricted to a specific chemical species, reaction order, reactor geometry or reactor type (i.e. homogenous or heterogeneous). 

It seems reasonable that one should achieve larger conversion for plug flow, relative to viscous flow, in any type of heterogeneous reactor with catalyst coated on the inner walls. Simulations in Figure 23-2 and Table 23-4 verify this expectation in channels with square cross section, first-order irreversible chemical reaction, uniform catalyst activity, and = 1. The comer regions are not problematic in plug-flow simulations because the momentum boundary... 

A chemical transition process is always characterized by its stoichiometry and its extent of reaction independent of the mode of process operation. The rate of change in extent, however, depends on the mode of process operation, on the reaction rate and, in the case of heterogeneous reactions, on the mass transfer. In order to account for the mode of operation appropriately, models are required for the different reactor types. This is all comprehensively described in the overall mass balance of the system. 

As must be evident from a previous section on classification, gas-liquid reactions can be carried out in a large number of reactor types. This is also true of other multiphase reactions in which a liquid phase is involved. For other reactions such as gas-solid, catalytic or noncatalytic, the choice of reactor is confined to a lesser number of variations. Therefore, although reactor choice is an important consideration for all reactions, particularly heterogeneous reactions, it is more so for gas-liquid, liquid-liquid, and slurry systems, all of which are widely used in industrial organic synthesis. We discuss below the cost minimization criteria for a rational choice of reactors for gas-liquid reactions. 

The latter model type describes the experimentally determined relations between dependent and independent variables with the help of statistical methods and neglects the known physicochemical relations. Such models are primarily used on reactor types difficult to describe deterministically. The cell models are composed of specific networks of mixing cells (e.g. stirred reactor cascades) or of combinations of mixing cells and transport cells (ideal tube reactors). The so-called continuum models, however, handle each phase as a continuum. The continuum models are further distinguished as homogeneous and heterogeneous reactor models. In the heterogeneous reactor model, the fluid phases and the solid phase (catalyst) are considered and mathematically described as individual items. 

Figure 11.2 Various reactor types (schematic) for heterogeneous catalysts and gaseous reactants.

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