Model Development

Depending on the complexity, various combinations of models including reaction and mass transfer can be used to simulate reactive distillation (Fig. 3.5). The mass transfer can be described by either assuming an equilibrium or applying a kinetic model. By analogy, the reaction can be expressed as an established chemical equilibrium or with reaction kinetics. However, the complexity of the modeling is greatly increased if mass transfer and/or reaction kinetics are taken into account [8].

In the majority of cases the so-called equilibrium stage model is used for simulation of distillation without chemical reaction. This has also been shown to be useful in reactive distillation. The equilibrium stage model is a pragmatic approach suitable not only in the early stage of process development. In general, it is implemented in all current process simulators [9]. The mass-transfer stage model is recommended (e. g., RATEFRAC in AspenPlus) in the advanced stage of process development. Unfortunately, there are only few data available on suitable masstransfer kinetics. Furthermore, Higler et al. [10] have shown that small deviations (about +10 %) in the mass transfer coefficients cawed deviations in computed conversion of the same magnitude. This makes the application of these models fairly difficult. For this reason, the equilibrium stage model was used in this study.

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