Residue Curve Map for a Mixture of Three Alcohols; Nature of the Singular Points
This Demonstration plots the residue curve (RC) for a ternary mixture of alcohols: ethanol, -propanol, and -butanol. The blue arrows on the RC indicate how the composition in the still evolves with warped time. It is clear from the arrows that -butanol is a stable node (the arrows point to its vertex). On the other hand, -propanol is a saddle point (the arrows moves first toward and then away from its vertex). Finally, ethanol is an unstable node (all arrows diverge from its vertex). For this case, these results are obvious since (1) the mixture is ideal and (2) ethanol is the low-boiling component, -propanol is intermediate, and -butanol is the high-boiling component.
For more information, see
M. F. Doherty and M. F. Malone, Conceptual Design of Distillation Systems, New York: McGraw-Hill, 2001.