Application of irreversible Thermodynamics to Distillation

The objective of this work is to compare three different ways of modelling tray distillation: The most common way that assumes equilibrium between the liquid and vapour phases at the outlets of each tray, and two more precise methods that use irreversible thermodynamics. Irreversible thermodynamics determine the driving forces and fluxes of a system in agreement with the second law. The most common method that uses irreversible thermodynamics is the Maxwell-Stefan approach. This method considers interdiffusion in the vapour and liquid film, and, most commonly, heat transfer separate from mass transfer. The mass transfer coefficients contain both hydrodynamic and mixture properties in this approach. The interface integrated approach includes the specific surface resistance, but no hydrodynamic effects. Both methods can include the Dufour/Soret effect. In this work, the three approaches are compared to each other, and to experimental data. We show that the methods using irreversible thermodynamics are superior to the method that assumes that the stage reaches equilibrium. The Soret effect must be included to have a good description of the heat flux.