Rectification nonadiabatic

Nonadiabatic rectification (thermal rectification, redistillation) is a thermally gentle separation process of high-boiling liquid mixtures, using a combination of partial distillation and partial condensation. The fractionator is a special thin-layer evaporator, with externally heated columns and an externally cooled rotor (Fig. 2-84). 

The vapor mixture, generated in a thin-layer or falling film evaporator, flows countercurrently in the fractionator, with the downward liquid reflux at the heated inner wall of the evaporator. By repeatedly vaporizing and condensing some of the 

Depending on the separation task, the fractionator may be operated only as an enrichment column, only as a stripping column or in a normal operating mode as shown in Fig. 2-84. 

The thin-layer evaporator is most effective when the ratio of the mass flows vaporized and condensed on the side is equal to 1 [2.136]. Therefore, the separation efficiency of the fractionator depends on how often the generated vapor mixture is condensed and revaporized in the unit. At infinite reflux ratio and at constant relative volatility a, the separation efficiency in the concentration range of interest is 

Number of theoretical stages per m of the fractionator height for mass and heat transfer of the fractionator (chosen upper limit of the dimensions of a thin-layer evaporator 850 nun diameter, 9 m height) 

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Rectification processes may be operated continuously and discontinuously. Under adiabatic conditions the process can be operated at normal pressure, underpressure, and overpressure. Azeotropic mixtures are treated using azeotropic or extractive rectification. For special cases nonadiabatic, thermal rectification is used. The operation conditions and the type of internals used in the rectification column depend on the behavior of the mixture during separation and the properties of the components present. 

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