Responses of azeotropes and relative volatilities to pressure variations

Mixtures with azeotropes cannot be separated by simple distillation since the vapor and liquid compositions are the same. One option to overcome this limitation is to vary the applied pressure to shift the azeotropic composition out of the range of a single column or use pressure-swing operation of two columns.

Because operating costs are highly sensitive to the pressure dependence of azeotropic compositions, reliable and accurate phase equilibrium thermodynamic property information is needed to computationally explore pressure variation for such processes. An analysis of property modeling has been done for the pressure sensitivity of azeotropic composition, and examples are given of modeling strategies for binary and ternary mixtures.

A quantitative criterion for the need to consider nonideality effects in both modeling and parameter regression has been established, based on similarity of mixture excess enthalpies and pure component enthalpies of vaporization.