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Abstract:
Reactive distillation columns that are designed to exploit differences in reactivity can exhibit extremely high selectivities for separating close-boiling mixtures. When the reaction product is not needed itself it can be split back. This leads to coupled reactive distillation columns for reactive separations (see figure). In many such separation systems, olefins are to be separated by performing an addition reaction to a double bond. Whenever this is the case, water is often deemed to be the ideal reactant because of its price, availability and ease of disposal. In some cases the resulting product alcohol is even valued directly as a product. The reaction of water with olefins in a reactive distillation column is difficult however because of the simultaneous liquid-liquid phase splitting. This additional phenomenon makes the simulation of such systems extremely costly with respect to computation time. Also for many systems little experimental data is available on reaction kinetics over the whole range of concentrations including the phase splitting region. Experimental Parameter Identification and Model Validation: An efficient rigorous mathematical model for a reactive distillation column with phase splitting is currently under development at the MPI Magdeburg. As a model reaction the hydration of cyclohexene to cyclohexanol was chosen because of its extreme phase splitting behavior and because cyclohexanol is a valued intermediate in nylon production. To adapt this model to the system under consideration a complete set of thermodynamic and reaction kinetic parameters is needed. For this reason an effort is currently under way to measure such a complete set of data. To measure the necessary parameters a VLE apparatus (FISCHER, 250 Pa - 0.3 MPa temperatures up to 250°C), a stirred batch reactor (1.5 liters, pressure up to 1 MPa, temperatures up to 200°C) and a continuously operated CSTR (100 ml, pressures up to 6 MPa, temperatures up to 250°C) have been set up. To allow for the validation of column simulations a reactive distillation column in miniplant scale is also available (1 kPa - 1.5 Mpa, temperatures up to 300°C, Katapak S).
