Classification of Chemical Reactors

In many instances, the overall reaction rate is determined by the diffusion rate of reactants into the interior of the pore, and the diffusion of the product out of the pore. 

Each of these reaction categories has its features and characteristics that should be described quantitatively. 

Chemical reactors are commonly classified by the three main charateristics  

Geometric configuration (e.g., tubular, agitated tank, radial flow) 

Contacting patterns between phases (e.g., packed bed, fluidized bed, bubble column) 

---

Another classification of chemical reactors is according to the phases being present, either single phase or multiphase reactors. Examples of multiphase reactors are gas liquid, liquid-liquid, gas solid or liquid solid catalytic reactors. In the last category, all reactants and products are in the same phase, but the reaction is catalysed by a solid catalyst. Another group is gas liquid solid reactors, where one reactant is in the gas phase, another in the liquid phase and the reaction is catalysed by a solid catalyst. In multiphase reactors, in order for the reaction to occur, components have to diffuse from one phase to another. These mass transfer processes influence and determine, in combination with the chemical kinetics, the overall reaction rate, i.e. how fast the chemical reaction takes place. This interaction between mass transfer and chemical kinetics is very important in chemical reaction engineering. Since chemical reactions either produce or consume heat, heat removal is also very important. Heat transfer processes determine the reaction temperature and, hence, influence the reaction rate. 

A brief classification of chemical reactors is presented in Table 1.1. The classification is mainly based on the number of phases present in the reactor. This classification is very natural, as the character of reactive phases to a large extent decides the physical configuration of reactor equipment. 

A useful classification of types of chemical reactors is in terms of their concentration patterns. Certain limiting or ideal types are represented by Figure 4.1 which illustrates batch reactors, continuous stirred tanks and tubular flow reactors. This chapter is concerned with the sizes, performances and heat effects of these ideal types. They afford standards of comparison and are often as close enough to the truth as available information allows. 

Table LI Classification of Chemical Reactions Useful in Reactor Design...

The many attractive featuies of membrane reactors described in the previous section underscore the potential of these reactors in organic chemical technology and synthesis. A broad classification of these reactors is given in Table 24.1 and sketches of a few specific ones are given in Figure 24.2. 

Design and operation of chemical reactors in a chemical industry profoundly influence the impact that the industry may have on the surrounding environment. Understanding different types of reactions and characterising their kinetic behaviour are important for optimal design and operation of chemical reactors. This chapter outlines the basic principles of chemical kinetics, methods of obtaining rate equations for different types of reactions, principles of catalysis and kinetics of catalytic reactions. A brief introduction on the types and classification of reactors is presented in this chapter. 

Gives a brief introduction to classification and the various types of chemical reactors... 

Chapter 2 covers the basic principles of chemical kinetics and catalysis and gives a brief introduction on classification and types of chemical reactors. Differential and integral methods of analysis of rate equations for different types of reactions—irreversible and reversible reactions, autocatalytic reactions, elementary and non-elementary reactions, and series and parallel reactions are discussed in detail. Development of rate equations for solid catalysed reactions and enzyme catalysed biochemical reactions are presented. Methods for estimation of kinetic parameters from batch reactor data are explained with a number of illustrative examples and solved problems. 

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. 

Classification of the many different encapsulation processes is usehil. Previous schemes employing the categories chemical or physical are unsatisfactory because many so-called chemical processes involve exclusively physical phenomena, whereas so-called physical processes can utilize chemical phenomena. An alternative approach is to classify all encapsulation processes as either Type A or Type B processes. Type A processes are defined as those in which capsule formation occurs entirely in a Hquid-filled stirred tank or tubular reactor. Emulsion and dispersion stabiUty play a key role in determining the success of such processes. Type B processes are processes in which capsule formation occurs because a coating is sprayed or deposited in some manner onto the surface of a Hquid or soHd core material dispersed in a gas phase or vacuum. This category also includes processes in which Hquid droplets containing core material are sprayed into a gas phase and subsequentiy solidified to produce microcapsules. Emulsion and dispersion stabilization can play a key role in the success of Type B processes also. 

Ideal reactors can be classified in various ways, but for our purposes the most convenient method uses the mathematical description of the reactor, as listed in Table 14.1. Each of the reactor types in Table 14.1 can be expressed in terms of integral equations, differential equations, or difference equations. Not all real reactors can fit neatly into the classification in Table 14.1, however. The accuracy and precision of the mathematical description rest not only on the character of the mixing and the heat and mass transfer coefficients in the reactor, but also on the validity and analysis of the experimental data used to model the chemical reactions involved. 

Chemical reactors intended for use in different processes differ in size, geometry and design. Nevertheless, a number of common features allows to classify them in a systematic way [3], [4], [9]. Aspects such as, flow pattern of the reaction mixture, conditions of heat transfer in the reactor, mode of operation, variation in the process variables with time and constructional features, can be considered. This work deals with the classification according to the flow pattern of the reaction mixture, the conditions of heat transfer and the mode of operation. The main purpose is to show the utility of a Continuous Stirred Tank Reactor (CSTR) both from the point of view of control design and the study of nonlinear phenomena. 

Chemical reactors vary widely in shape and in the mode of operation. Consequently, there are various ways of classifying them. The first classification is based on the number of the... 

A wide variety of names are used in the electronic industry for various types of reactors, but two broad classifications of reactors based on the means by which the molecular species are delivered to the substrate are useful direct line-of-sight impingement and diffusive-convective mass transfer. The term chemical vapor deposition (CVD) has been used generally to describe... 

A huge number of publications meanwhile have included the term micro reactors and their applications [9] and some attempts were made to maintain order in the field, e.g. by sorting from the point of design and manufacturing issues [5, 13], by a classification of unit operations [14] or by sorting of the chemical reactions performed [15]. The latter becomes more common than the others, but a generic look seems to be necessary. 

Classification by End Use Chemical reactors are typically used for the synthesis of chemical intermediates for a variety of specialty (e.g., agricultural, pharmaceutical) or commodity (e.g., raw materials for polymers) applications. Polymerization reactors convert raw materials to polymers having a specific molecular weight and functionality. The difference between polymerization and chemical reactors is artificially based on the size of the molecule produced. Bioreactors utilize (often genetically manipulated) organisms to catalyze biotransformations either aerobically (in the presence of air) or anaerobically (without air present). Electrochemical reactors use electricity to drive desired reactions. Examples include synthesis of Na metal from NaCl and Al from bauxite ore. A variety of reactor types are employed for specialty materials synthesis applications (e.g., electronic, defense, and other). 

There are various types of electrochemical reactor5,6 the classification is similar to that used for other chemical processes. The three basic types of electrochemical reactor are shown in Fig. 15.1 ... 

Some possible subdivisions of the field are listed in Table I. We can characterize the type of polymerization process—i.e., mass, suspension, emulsion, etc.—and the type of reactor and how it is operated. The chemical classification of the reaction affects the mathematics as well as the product. The last distinction is between the rate of product formation and the distribution of the products obtained. 

At the basic level CVD reactors fall into two classifications—open and closed reactor systems. In the closed CVD system the precursors are loaded into the CVD chamber together with the specimens to be treated. The system is then closed and the temperature increased to initiate the chemical process. The process continues for a time sufficient to produce the required effect. The temperature is then reduced to ambient so that the reactor may be opened and the specimens removed. This reactor design is frequently used for the purification of metals and chromizing parts. The dominant type of CVD reactor is the open type. Flowing precursors continuously enter this reactor and the gaseous by-products of the chemical process are continuously removed from the reactor (usually with a vacuum pump) and appropriately treated for discharge into the environment. 

When chemical reactors have more than one phase, the problem increases in complexity because the reaction and mass transfer processes interact and another time constant is introduced. The interaction is governed by the relative rates of the reaction and mass transfer. In some cases, chemical reactions are mass transfer rate controlled (very fast chemical reactions) and in others, they are reaction kinetics controlled (very slow chemical reactions) however, in reality very few reactions strictly fit this classification. Thorough discussions of this problem are given in Refs. . Classifications of the relative contributions of mass transfer and reaction kinetics in heterogeneous systems... 

---