| In this thesis a nonequilibrium (NEQ) cell model is developed to describe the dynamic operation of reactive distillation (RD) tray columns. The features of the model are: (1) use of the Maxwell-Stefan equations for describing mass transfer between fluid phases, (2) chemical reactions are assumed to take place only in the liquid phase, (3) coupling between mass transfer and chemical reactions within the diffusion layer is accounted for, and (4) the use of multiple well-mixed cells in the liquid and vapour flow directions accounts for staging in either fluid phase. When the chemical reactions are suppressed, the model describes the dynamic behaviour of conventional distillation columns. We demonstrate the utility of the dynamic NEQ cell model by means of several cases studies: (a) synthesis of methyl tert-butyl ether (MTBE), (b) metathesis of 2-propene, (c) hydration of ethylene oxide to ethylene glycol, and (d) distillation of methanol - iso-propanol - water.; An extensive model comparison between commonly used equilibrium models, nonequilibrium models and multiple cell models reveals a qualitatively different steady state behavior with regard to conversion and selectivity. Increasing mass transfer resistance tends to narrow the region of steady state multiplicity. The qualitatively differences of the model predictions are also reflected in their dynamic behavior. For a process exhibiting multiple steady states, the models can lead to qualitatively different responses to feed flow disturbances. Due to differences in the hold-up of packed and tray columns, the dynamic responses of an RD column are sensitive to the hardware choice. Furthermore, the introduction of staging in the liquid and vapour phases not only influences the steady state performance, by increasing reaction conversion and separation capability, but also has in significant influence on the column dynamics.; The overall conclusion of this thesis is that nonequilibriurn dynamic model, taking proper account interphase mass transfer and of liquid and vapour staging in a column, are essential for developing the proper description of RD column dynamics and for developing appropriate control strategies. |
