BIFURCATION-ANALYSIS AND STEADY-STATE MULTIPLICITY OF MULTICOMPONENT, NONEQUILIBRIUM DISTILLATION PROCESSES

Steady-state multiplicity of multicomponent distillation processes is investigated by means of a continuous mass transfer model. As a first step towards the analysis of complex columns a single column section is considered. The structural properties of the steady-state concentration profiles in the limit of an infinite spatial domain are closely related to the global material balances of the column section. It is shown that there exists a direct relationship between multiple steady-state concentration profiles and multiple solutions to the global material balances. Multiplicity of the solution of the global material balances is investigated using the Newton polyhedron method. The theory is applied to ternary mixtures with an ideal vapour phase and an ideal as well as a non-ideal liquid phase. For the former system multiple solutions occur only on the boundaries of the concentration state space; the corresponding concentration profiles are therefore only of theoretical interest. In contrast, mixtures with a nonideal liquid phase-homogeneous as well as heterogeneous-are shown to reveal multiple steady states in various situations. The results of the theoretical investigations are confirmed by simulation.