Reactions and Reactors

Carberry and Varma (eds.). Chemical Reaction and Reactor Engineeting, Dekker, 1987. 

For complex reac tions and with multistage CSTRs, more than three steady states can exist (as in Fig. 23-17c). Most of the work on multi-phcities and instabilities has been done only on paper. No plant studies and a very few laboratoiy studies are mentioned in the comprehensive reviews of Razon and Schmitz Chem. Eng. Sci., 42, 1,005-1,047 [1987]) and Morbidelli et al. (in Carberry and Varma, Chemical Reaction and Reactor Engineering, Dekker, 1987, pp. 973-1,054). 

Shinnar, R., Use of Residence and Contact Time Distributions in Reactor Design, Chapter 2, pp. 63-149 of Chemical Reaction and Reactor Engineering, Carberry, J. J. and Varma, A., Eds., Marcel Dekker, New York, 1987. 

Chemical Reaction and Reactor Engineering, edited by J. J. Carberry and A. Varma... 

REACTION AND REACTOR PARAMETERS USED IN THE COMPUTER SIMULATION... 

Whatever the nature of the reaction, the choice of catalyst and the conditions of reaction can be critical to the performance of the process, because of the resulting influence on the selectivity of the reaction and reactor cost. 

Aspects of the various factors affecting performance in the types of reactions and reactors considered in Chapter 9 and in this chapter are summarized in Figure 22.1. 

Carberry, J.J., and Arvind Varma (editors), Chemical Reaction and Reactor Engineering, Marcel Dekker, New York, 1987. 

A runaway reaction and reactor explosion occurred in a resins production facility that killed one worker and injured four others. To control the reaction rate, an operating procedure called for the slow addition of one of the raw materials to the reactor. The runaway was triggered when the raw materials and catalysts were improperly charged to the reactor simultaneously, followed by heat addition. 

In the rest of this book we will apply these ideas to increasingly complex situations, so that by the last chapter you should have seen all the ideas necessary to deal with these reactions and reactors. More important, these ideas should permit you be able to understand the even more complex reactions and reactors that you will have deal with to develop new processes for future technologies. 

In the 1930s it was discovered that the pyrolysis of alkanes produced large quantities of olefins. This pyrolysis process is not very selective, but the costs of separation were cheaper, and scaleup was simpler and safer in making ethylene rather than acetylene so during the 1940s ethylene and other small olefins replaced acetylene as the major building block in chemical synthesis. We will consider the reactions and reactors used in olefin synthesis from alkanes in the next chapter. 

Note This is a prototype of polymerization reactions and reactors that will be considered further in Chapter 11. 

This seems to be a simpler set of equations than the differential equations of the PFTR, but since the PFTR equations are first-order differential equations, their solutions must be unique for specified flow, reaction, and reactor parameters, as we discussed in the previous chapter. This is not necessarily tme for the CSTR. 

After reactivity and selectivity, the next complication we encounter with all catalytic reactions is that there are essential transport steps of reactants and products to and from the catalyst. Therefore, in practice catalytic reaction rates can be thoroughly disguised by mass transfer rates. In fact, in many industrial reactors the kinetics of individual reactions are quite unknown, and some engineers would regard knowledge of their rates as unimportant compared to the need to prepare active, selective, and stable catalysts. The role of mass transfer in reactions is therefore essential in describing most reaction and reactor systems, and this will be a dominant subject in this chapter. 

We will not attempt to discuss polymers or their properties in any detail in this chapter because this would require several complete courses for comprehensive coverage. Our interest is in polymerization rates and polymerization reactors. These topics are simple extensions of our previous discussion of other reactions and reactors with some important differences. We wiU only attempt to describe polymers and polymerization in sufficient detail to introduce the notation of polymers and some of the issues arising in polymerization process. 

In this chapter we have examined the reactions and reactors used in polymerizing monomers. In many situations the production of monomers from feedstocks, the polymerization, and the forming of the polymer into products are done in the same chemical plant. In some cases the monomer is too reactive to be shipped to a polymerization plant (isocyanates, for example), and in some cases the producer does not want to be dependent on monomer suppliers. 

In parallel with this development, we discuss the chemical and petroleum industries and the major processes by which most of the classical products and feedstocks are made. We begin in Chapter 2 with a section on The Real World, in which we describe the reactors and reactions in a petroleum refinery and then the reactions and reactors in making polyester. These are all catalytic multiphase reactors of almost unbelievable size and complexity. By Chapter 12 the principles of operation of these reactors will have been developed. 

---