TABLE OF CONTENTS The packed-bed reactors discussed in Chapters 9 and 10 are multiphase reactors, but the solid phase is stationary, and convective flow occurs only through the fluid phase. The reaction kinetics are pseudohomogeneous, and components balances are written only for the fluid phase.
Chapter 11 treats reactors where mass and component balances are needed for at least two phases and where there is interphase mass transfer. Most examples have two fluid phases, typically gas-liquid. Reaction is usually confined to one phase, although the general formulation allows reaction in any phase. A third phase, when present, is usually solid and usually catalytic. The solid phase may be either mobile or stationary. Some example systems are shown in Table 11.1.
| Reaction | First phase | Second phase | Third phase |
|---|---|---|---|
| Phenol alkylation | Phenol | Gaseous alkenes | None |
| Refinery alkylation | Liquid alkanes (e.g., isobutane) | Gaseous alkenes (e.g., 1-butene) | HF or H 2SO 4 |
| Aerobic fermentation | Water+organic carbon source | Air | Bacteria |
| Anaerobic fermentation | Water+sugar | Carbon dioxide | Yeast |
| Fluidized catalytic cracking (FCC) | Heavy oils, C 18+ | Fluidized catalyst particles | None |
| Trickle-bed hydrocracking | Refinery residues, C 30+ | Hydrogen | Stationary catalyst particles |
When two or more phases are present, it is rarely possible to design a reactor on a strictly first-principles basis. Rather than starting with the mass, energy, and momentum transport equations, as was done for the laminar flow systems in Chapter 8, we tend to use simplified flow models with empirical correlations for mass transfer coefficients and interfacial areas.
