As part of the process model, property models play a very important role in
the design of separation by distillation. This paper provides a systematic
analysis of the property models with special emphasis on relations between
separation task, equilibrium properties and energy consumption. The presen
ted analysis helps to establish the role of properties and the property mod
el in design of separation by distillation. Based on the roles of propertie
s and property models, a general guideline that serves as a useful roadmap
for design and analysis of various types of separation with distillation is
proposed. Finally, the roles and the guidelines are highlighted through si
mple illustrative examples.