Pseudoideal points of vapor-liquid equilibrium diagrams and the role that they play in the evolution of binary azeotropes under temperature (pressure) variations

The notion of a pseudoideal point on the vapor-liquid equilibrium curve of a binary mixture is introduced. A mixture corresponding to the pseudoideal point composition is characterized by the equality of the activity coeffici ents of both components and an extremal excess Gibbs energy value. A thermo dynamic equation for the rate of pseudoideal point displacements under temp erature variations was obtained. It is shown that the pseudoideal point is passable (nonpassable) for azeotropes (with respect to composition) under e xternal parameter variations only in the presence (absence) of a Bankroft p oint on the temperature dependences of component vapor pressures.