BOUNDARY MODES IN A SINGLE FEED DISTILLATION COLUMN FOR THE SEPARATION OF AZEOTROPIC MIXTURES

Feasible separations of mixtures with saddle binary azeotropes in cont inuous fractional distillation are discussed. Singularities of the equ ation of pinch (constant-concentration) zones, as well as their influe nce on the form of profiles in the column, are studied. For a mixture with an outgoing saddle separatrix, the multiplicity of solutions of t he equation of pinch zones is shown to give rise to saddle-type points within the concentration simplex, which are limiting points for the s tage-by-stage sequence in the stripping section and represent the firs t boundary mode. An equation for the separatrix in the bifurcation set of parameters is derived. It is shown that possible bottom-product co mpositions are bounded by this separatrix and by the separatrix of the composition line of liquid-to-vapor equilibrium transitions. For the upper section, similar barriers for the class of mixtures in question can occur only at the boundary of the simplex. Mixtures with reverse d istillation lines have symmetrical singularities.