ROLE OF AZEOTROPY IN CHARACTERIZATION OF COMPLEX HYDROCARBON MIXTURESBY TRUE-BOILING-POINT DISTILLATION

True-boiling-point distillation is an efficient batch distillation bei ng one of the most commonly applied techniques to study the polydisper sity of complex hydrocarbon mixtures. True-boiling-point curves are ob tained by plotting the temperature at the top of the column versus the fraction of mass distilled. The name expresses the assumption that th e complex mixture is separated into its components according to their boiling points. However, in the case of azeotropy (e.g. between alipha tics and aromatics) this assumption is not correct. Therefore, based o n continuous thermodynamics, a method is developed for describing quan titatively the azeotropic effect. The method presumes distillation of pure compounds or of azeotropic mixtures (if the efficiency of the col umn is sufficiently large). It is demonstrated for mixtures consisting of a petroleum fraction (low in aromatics) and of alcohols. (C) 1997 Elsevier Science B.V.