Basic Reaction Engineering Aspects

some basic terms of chemical reaction engineering will be discussed before introducing the field of enzyme reactors. For further reading, textbooks are available (12°-1261. 

The mode of reactor operation can be classified as batchwise or continuous . Batch reactions are started by filling a reactor with the reaction mixture and stopped after reaching the desired conversion. A steady state is only reached at equilibrium conversion of the reaction. A typical batch reactor is represented by the stirred tank reactor. 

Continuous reactions are characterized by a continuous substrate feed and product output. A residence time of the reaction mixture within the total reactor volume V can be defined by Eq. (55)  

After a certain time a steady state will be reached within the reactor, meaning that concentrations of substrates and products do not change. Typical continuous reactors are the plug flow reactor (PFR) and the continuous stirred tank reactor (CSTR). A comparison of these different reactor types is given in Fig. 7-22. 

The differences between the reactors may be described by showing concentration profiles of substrate and product as a function of reactor position and time respectively. 

---

Dente and Ranzi (in Albright et al., eds.. Pyrolysis Theory and Industrial Practice, Academic Press, 1983, pp. 133-175) Mathematical modehng of hydrocarbon pyrolysis reactions Shah and Sharma (in Carberry and Varma, eds.. Chemical Reaction and Reaction Engineering Handbook, Dekker, 1987, pp. 713-721) Hydroxylamine phosphate manufacture in a slurry reactor Some aspects of a kinetic model of methanol synthesis are described in the first example, which is followed by a second example that describes coping with the multiphcity of reactants and reactions of some petroleum conversion processes. Then two somewhat simph-fied industrial examples are worked out in detail mild thermal cracking and production of styrene. Even these calculations are impractical without a computer. The basic data and mathematics and some of the results are presented. 

Instabilities can arise from interplay of quite normal reaction kinetics with other rate processes such as heat transfer or control systems. Such situations are well understood and covered in standard texts. Therefore, emphasis here is on behavior produced by vagaries of multistep kinetics, an aspect given short shrift in today s reaction-engineering education. However, easily understood examples with normal kinetics are included to illustrate basic principles. 

K.S. Gandhi, R. Kumar, and D. Ramkrishna. Some basic aspects of reaction engineering of precipitation processes. Ind. Eng. Chem. Res., 34(10) 3223-... 

One of the most important areas for application of concepts discussed in the previous section is the selection of polymerization reactors. The properties of polymers depend on their molecular weight distribution (M WD) and so the design should ultimately use this as its basis. The subject is a vast one, and so only the basic concepts will be briefly discussed. Several excellent reviews now exist, covering various aspects of the area from a chemical reaction engineering viewpoint see Shinnar and Katz, Keane, and Gerrens, [18, 19, 20]. The latter presents a masterful survey of the effects of the choice of reactor type. 

Presently, 90% of the large and middle-size production processes in the chemical industry are based on catalysis. In the comprehensive effort aiming at the development of new catalytic processes, catalyst preparation constitutes just one part amid other contributions. But this part led to conspicuous innovation, and this because the chemical engineering aspect of catalyst industrial development was considered simultaneously with the basic science aspects and the development of the whole process. This remark fully justifies the ambition of the special symposium The Science and Engineering of Catalyst Preparation. It also justifies the fact that the selection of topics in the present contribution was essentially not influenced by fashion. In our opinion, the word engineering, when catalyst preparation is considered, should certainly apply to the unit operations of catalyst manufacture. But it should also point to the comprehensive approach that includes the first steps in the discovery of an interesting catalytic reaction as well as the industrial process development. With that in mind, one must conclude that the most promising avenue is to... 

From reaction engineering point of view it is not only the single parameter, i.e. the ratio of catalyst amount to mass of the reactor or the mass specific activity of the catalyst which determines the choice. It is often a combination such as the product flow per reactor mass which is a major parameter since it combines the activity of the catalyst with the occupied volume ratio of the catalyst inside the microreactor. In the following subsections the headings refer basically to the items in Table 1 - except for the latter issue - and details the individual aspects. 

Main Aspects and Basic Definitions of Chemical Reaction Engineering... 

The transition state theory provides a useful framework for correlating kinetic data and for codifying useful generalizations about the dynamic behavior of chemical systems. This theory is also known as the activated complex theory, the theory of absolute reaction rates, and Eyring s theory. This section introduces chemical engineers to the terminology, the basic aspects, and the limitations of the theory. 

One feature that distinguishes the education of the chemical engineer from that of other engineers is an exposure to the basic concepts of chemical reaction kinetics and chemical reactor design. This textbook provides a judicious introductory level overview of these subjects. Emphasis is placed on the aspects of chemical kinetics and material and energy balances that form the foundation for the practice of reactor design. 

Chapters 3 to 7 treat the aspects of chemical kinetics that are important to the education of a well-read chemical engineer. To stress further the chemical problems involved and to provide links to the real world, I have attempted where possible to use actual chemical reactions and kinetic parameters in the many illustrative examples and problems. However, to retain as much generality as possible, the presentations of basic concepts and the derivations of fundamental equations are couched in terms of the anonymous chemical species A, B, C, U, V, etc. Where it is appropriate, the specific chemical reactions used in the illustrations are reformulated in these terms to indicate the manner in which the generalized relations are employed. 

In the first section of this book, the brief introduction about biochemical engineering is given in chapter 1. The second chapter deals with basics of enzyme reaction kinetics. The third chapter deals with an important aspect in enzyme bioprocess i.e. immobilization of enzyme and its kinetics. Chapter 4 is concerned about the industrial bioprocess involving starch and cellulose. 

---