Fluid—solid reactions reactors

L. K. Doraiswany and M. M. Shamia, Heterogeneous Reactions, Hnaijses, Examples and Reactor Design, Vol. 2, Fluid—Fluid Solid Reactions, ]ohxi Wiley Sons, Inc., New York, 1984, pp. 299—300. 

Fixed-Bed Catalytic Reactors for Fluid-Solid Reactions... 

This chapter is devoted to fixed-bed catalytic reactors (FBCR), and is the first of four chapters on reactors for multiphase reactions. The importance of catalytic reactors in general stems from the fact that, in the chemical industry, catalysis is the rule rather than the exception. Subsequent chapters deal with reactors for noncatalytic fluid-solid reactions, fluidized- and other moving-particle reactors (both catalytic and noncatalytic), and reactors for fluid-fluid reactions. 

In a fixed-bed catalytic reactor for a fluid-solid reaction, the solid catalyst is present as a bed of relatively small individual particles, randomly oriented and fixed in position. The fluid moves by convective flow through the spaces between the particles. There may also be diffusive flow or transport within the particles, as described in Chapter 8. The relevant kinetics of such reactions are treated in Section 8.5. The fluid may be either a gas or liquid, but we concentrate primarily on catalyzed gas-phase reactions, more common in this situation. We also focus on steady-state operation, thus ignoring any implications of catalyst deactivation with time (Section 8.6). The importance of fixed-bed catalytic reactors can be appreciated from their use in the manufacture of such large-tonnage products as sulfuric acid, ammonia, and methanol (see Figures 1.4,11.5, and 11.6, respectively). 

A semicontinuous reactor for a fluid-solid reaction involves the axial flow of fluid downward through a fixed bed of solid particles, the same arrangement as for a fixed-bed catalytic reactor (see Figure 15.1(b)). The process is thus continuous with respect to the fluid and batch with respect to the solid (Section 12.4). 

Continuous reactors for fluid-solid reactions involve continuous flow for both fluid and solid phases. With the assumptions made in Section 22.2.1 about the fluid, we focus only... 

In this chapter, we consider reactors for fluid-solid reactions in which the solid particles are in motion (relative to the wall of the vessel) in an arbitrary pattern brought about by upward flow of the fluid. Thus, the solid particles are neither in ideal flow, as in the treatment in Chapter 22, nor fixed in position, as in Chapter 21. We focus mainly on the fluidized-bed reactor as an important type of moving-particle reactor. Books dealing with fluidization and fluidized-bed reactors include those by Kunii and Levenspiel (1991), Yates (1983), and Davidson and Harrison (1963). 

Doraiswamy, L.K. Sharma, M.M. Heterogeneous Reactions. Analysis, Examples, and Reactor Design. Fluid-Fluid-Solid Reactions, John Wiley New York, 1984 Vol. 2. 

The pulsed reactor consists of a fixed bed of catalyst pellets through which the reacting fluid moves in pulsating flow. Mass-transfer coefficients are increased because of the pulsating velocity superimposed on the steady flow. For viscous liquids, or any fluid-solid reaction system which has a high extemal-mass-transfer resistance, pulsation may be a practical way to increase the global reaction rate. Biskis and Smith measured mass-transfer coefficients for hydrogen in a-methyl styrene in pulsed flow and found increases up to 80% over steady values. Bradford" found similar results based on data for the dissolution of beds of j9-naphthoI particles in water. 

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