Comparison of equilibrium stage and nonequilibrium stage models for reactive distillation

For modelling reactive distillation columns, two distinctly different appro aches are available in the literature: (1) the equilibrium (EQ) stage model , in which the vapour and liquid phases are assumed to be in thermodynamic equilibrium, and (2) the nonequilibrium (NEQ) stage model in which the fini te mass transfer rates across the vapour-liquid interface are accounted for . In this paper, these two approaches are compared using two case studies: (a) synthesis of MTBE and (b) hydration of ethylene oxide to ethylene glyco l, It is shown that while the phenomena of multiple steady states is exhibi ted by both modelling approaches, the "window" in which these multiplicitie s occur is significantly reduced in the NEQ model. It is also shown that in actual column design, some of the steady states calculated by the EQ model cannot be realised due to e.g. flooding or weeping limitations on distilla tion trays. Another important conclusion that can be drawn from this work i s that the hardware design can have a significant influence on the conversi on and selectivity. It is concluded that for design of reactive distillatio n columns we must adopt the NEQ modelling approach. (C) 2000 Elsevier Scien ce S.A. All rights reserved.