Nonequilibrium cell model for multicomponent (reactive) separation processes

Abstract

A generic nonequilibrium cell model for multicomponent separation processes, including liquid-phase chemical reactions, was developed. Its important features include the use of Maxwell-Stefan equations to describe interphase mass transfer and the use of a multiple cell per stage approach to consider various mixing characteristics of vapor and liquid phases. A finite difference approach was used for solving the diffusion-reaction equations in each fluid phase to properly account for effects of reactions on mass transfer. The multiple cells per stage approach was adopted to take into account the effect of concentration and temperature profiles on a tray on the local reaction rates. The model was compared to several case studies by Kooijman (1995). Comparison of various flow models showed only minor differences between Kooijman's model and the nonequilibrium cell model. The differences were found only for cases in which the phases are assumed to be imperfectly mixed and to be caused by different ways of modeling the interface concentration profiles in various flow models. In addition, some calculations are described for reactive distillation operations described by Okasinski and Doherty (1998) and Marek (1956). These examples show that staging in both flow directions influences overall column performance considerably.