Trajectories of Thermodynamically Reversible Distillation

Although the thermodynamically reversible process of distillation is unrealizable, it is of great practical interest for the following reasons (1) it shows in which direction real processes should be developed in order to achieve the greatest economy, and (2) the analysis of this mode is the important stage in the creation of a general theory of multicomponent azeotropic mixtures distillation. 

First investigations of thermodynamically reversible process concerned binary distillation of ideal mixtures (Hausen, 1932 Benedict, 1947). Later works concerned multicomponent ideal mixtures (Grunberg, 1960 Scofield, 1960 Petlyuk Platonov, 1964 Petlyuk, Platonov, Girsanov, 1964). 

The analysis of the thermodynamically reversible process of distillation for multicomponent azeotropic mixtures was made considerably later. Restrictions at sharp reversible distillation were revealed (Petlyuk, 1978), and trajectory bundles at sharp and nonsharp reversible distillation of three-component azeotropic mixtures were investigated (Petlyuk, Serafimov, Avet yan, Vinogradova, 1981a, 1981b). 

Restrictions at nonsharp reversible distillation of three-component azeotropic mixtures were studied by Poellmann and Blass (1994). 

Trajectories of adiabatic distillation at finite reflux for given product points should be located in concentration space in the region limited by trajectories at infinite reflux and by trajectories of reversible distillation (Petlyuk, 1979 Petlyuk Serafimov, 1983). 

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Figure 2.10. A thermodynamically reversible distillation (a) an infinite column with heat input and output (segments with arrows) at any cross-section of column, (b) a trajectory of reversible distillation. Segments with arrows, liquid-vapor tie-lines for certain cross-section of column (little circles).

Significance of reversible distillation theory consists in its application for analysis of evolution of trajectory bundles of real adiabatic distillation at any splits. Numerous practical applications of this theory concern creation of optimum separation flowsheets determination of optimum separation modes, which are close to the mode of minimum reflux and thermodynamic improvement of distillation processes by means of optimum intermediate input and output of heat. 

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