Multiple Steady States in Heterogeneous Azeotropic Distillation
In this article we study multiple steady states in ternary heterogeneous azeotropic distillation. We show that in the case of infinite reflux and an infinite number of trays one can construct bifurcation diagrams on physical grounds with the distillate flow as the bifurcation parameter. Multiple steady states exist when the distillate flow varies non-monotonically along the continuation path of the bifurcation diagram. We show how the distillate and bottom product paths can be located for tray or packed columns, with or without decanter and with different types of condenser and reboiler. We derive a necessary and sufficient condition for the existence of these multiple steady states based on the geometry of the product paths. We also locate in the composition triangle the feed compositions that lead to these multiple steady states. We show that the prediction of the existence of multiple steady states in the case of infinite reflux and an infinite number of trays has relevant implications for columns operating at finite reflux and with a finite number of trays.
We acknowledge gratefully the financial support of the Donors of the Petroleum Research Fund administered by the American Chemical Society and of the I.S. Latsis Foundation. We also thank Prof. Seider (University of Pennsylvania, Philadelphia) and Prof. Michelsen (Danish Technical University, Lyngby) for providing us thermodynamic subroutines.