A systematic approach to constructing dynamic models involving phase equilibrium is presented. The view appears to be widely held that the dynamic modelling of VLE systems invariably leads to an "index problem". We show that this in general is not the case if an appropriate model formulation is used. This is provided by our systematic procedure. Index problems do in general occur when a state variable is constrained by an implied control system. Some properties of such systems are discussed and it is shown that it may not in practice be useful to attempt the solution of intractable index problems, as these may differ substantially from the behaviour of an achievable control system. © 1991.
Ponton, J. W., & Gawthrop, P. J. (1991). Systematic construction of dynamic models for phase equilibrium processes. Computers and Chemical Engineering, 15(12), 803–808. https://doi.org/10.1016/0098-1354(91)80026-R