DESIGN OF TAME REACTIVE DISTILLATION SYSTEMS

In this chapter we take a look at an important example of a reactive distillation column operating in a plantwide environment. The reactive column is part of a multiunit process that includes other columns for recovery of one of the reactants. The process may give the impression that the reactive column is not operating in neat mode because of the need for reactant recovery. We will show that this is really not the case. The recovery of reactant is made necessary by the presence of azeotropes that unavoidably remove one of the reactants from the reactive column. 

2M1B + MeOH TAME 2M2B + MeOH TAME 2M1B 2M2B 

This system is fundamentally a ternary system with inerts. The heavy component is TAME, which leaves the reactive distillation column in the bottoms. 

The process flowsheet has a prereactor, a reactive distillation column, and a methanol recovery section. A methanol recovery section is required because the inert C5 components coming in with the reactive isoamylenes in the C5 fresh feed form azeotropes with methanol. The result is that a signifleant amount of methanol is present in the distillate from the 

Reactive Distillation Design and Control. By William L. Luyben and Cheng-Ching Yu Copyright 2008 John Wiley Sons, Inc. 

---

DESIGN OF TAME REACTIVE DISTILLATION SYSTEMS TABLE 8.10 Stream Information for Columns C2 and C3... 

The TAME reactive distillation system with a two-column methanol recovery system was successfully simulated in Aspen Dynamics. The system features two recycles (methanol and water) and three feedstreams (C5, methanol, and water). The system is essentially a ternary system with inerts, but the complex vapor-liquid equilibrium results in the formation of azeotropes that result in losses of methanol out of the top of the reactive column with the inerts. Therefore, a methanol recovery system must be included in the plant design and control. 

In Chapter 8 we explored the steady-state design of the TAME reactive distiUalion system. The reactive column is part of a multiunit process that includes other columns for recovery of the methanol reactant. The recovery is necessary because the presence of methanol/C5 azeotropes unavoidably removes methanol from the reactive column in the distillate stream. The economics of two alternative methanol recovery systems were evaluated in Chapter 8. In this chapter the dynamic control of the process is studied, and an effective plantwide control structure is developed. The process has three distillation columns one reactive column, one extractive distillation column, and one methanol/water separation column from which methanol and water are recycled. 

FTocesses for the production of tertiary amyl methyl ether (TAME) Brockwell et ah, Hyd. Proc., 70(9), 133 (1991)]. Highly endothermic reactions may require intermediate reboilers. None of these heat management issues preclude the use of reactive distillation, but must be taken into account during the design phase. Comparison of heat of reaction and average heat of vaporization data for a system, as in Fig. 13-97, gives some indication of potential heat imbalances [Sundmacher, Rihko, and Hoffmann, Chem. Eng. Comm., 127, 151 (1994)]. The heat-neutral systems [-AH (avg)]... 

Sundmacher and Qi (Chapter 5) discuss the role of chemical reaction kinetics on steady-state process behavior. First, they illustrate the importance of reaction kinetics for RD design considering ideal binary reactive mixtures. Then the feasible products of kinetically controlled catalytic distillation processes are analyzed based on residue curve maps. Ideal ternary as well as non-ideal systems are investigated including recent results on reaction systems that exhibit liquid-phase splitting. Recent results on the role of interfadal mass-transfer resistances on the attainable top and bottom products of RD processes are discussed. The third section of this contribution is dedicated to the determination and analysis of chemical reaction rates obtained with heterogeneous catalysts used in RD processes. The use of activity-based rate expressions is recommended for adequate and consistent description of reaction microkinetics. Since particles on the millimeter scale are used as catalysts, internal mass-transport resistances can play an important role in catalytic distillation processes. This is illustrated using the syntheses of the fuel ethers MTBE, TAME, and ETBE as important industrial examples. 

---