A nonequilibrium stage model of multicomponent separation processes. Part III: The influence of unequal component-efficiencies in process design problems



The conventional equilibrium-stage model that uses a component-independent stage efficiency and a nonequilibrium-stage model, in which mass transfer rate equations are solved simultaneously with the stage conservation equations, are employed to solve four representative distillation design problems. There are large differences between the number of stages predicted by the two models for a specific separation of the more volatile component. The differences arise from two causes: the way in which the liquid phase resistances and equilibrium equations are used in the models, and the consequences of diffusional interaction effects. Neglect of the latter may lead to an underdesigned column; there is between a 9 and 15% difference in the stage requirements predicted by the nonequilibrium model with a rigorous mass transfer model and a nonequilibrium model which ignores interaction effects.