Column profile reactive systems

Figure 10.10 demonstrates the simulated and measured concentration profiles for the pilot column with the reactive section filled with catalytically active rings. In the simulations, four components, namely, methanol, isobutene, MTBE and 1-butene, were chosen to represent the chemical system under consideration. Here, segment 1 corresponds to the reboiler. A satisfactory agreement between calculated and measured values can be clearly observed. In Fig. 10.11, the simulation results for the column packed with MULTIPAK are shown. Here, 16 components are considered, and, again, the liquid bulk composition profiles agree well with the experimental data. 

Ciric and Gu (1994) present a MINLP-based approach for the design of RD columns for systems where multiple reactions take place and/or where reactive equilibrium or thermal neutrality caimot be assured. This method is based on the combination of a rigorous tray-by-tray model and kinetic-rate-based expressions to give basic constraints of an optimization model that minimizes the total annual cost. The major variables are the number of trays in the column, the feed tray location, the temperature and composition profiles within the column, the reflux ratio, the internal flows within the column and the column diameter. 

Very similar composition profiles are observed for the IPAc system and, again, most of the conversion takes place in the column base of the reactive distillation column (Fig. 7.13). The separation in the stripper is quite straightforward, and high purity IPAc can be achieved... 

Thus far, we have considered only the neat design. The excess reactant design may be preferable for systems with high TACs, especially for types I, II, and possibly IIIr. The motivation comes from the fact that some of the reactant concentrations are so low that a large reflux ratio and/or boilup ratio are required to achieved 95% conversion. We can refer to the composition profile of reactants A toward the column base and B toward the top in Figure 17.9 for type I. Other examples are reactant B in the reactive zone (Fig. 17.13) for type IIr and reactant A in the reactive zone (Fig. 17.17) for type III/. The excess reactant design is a simple means to achieve an improved reactant composition profile. 

Al-Arfaj and Luyben show the steady-state temperature profile in which a nonmonotonic temperature profile is observed. A local temperature minimum occurs on the lower feed tray because of the presence of a significant amount of light reactant A. This behavior is not uncommon for reactive distillation columns but is rarely seen in conventional distillation systems. 

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