Dynamic behaviour of reactive distillation columns described by a nonequilibrium stage model

In this paper we develop a generic, dynamic, nonequilibrium (NEQ) stage mod el for reactive distillation (RD) columns. The main features of our model a re: (1) use of the Maxwell-Stefan equations for describing mass transfer be tween fluid phases,(2) solid catalysed reactions are treated using a pseudo -homogeneous liquid phase model with the appropriate pseudo-homogeneous kin etic expressions and (3) a comprehensive set of design correlations, for bo th trays (sieve, bubble caps) and packings (random dumped, structured), for hold-up and mass transfer have been incorporated into the software package following earlier work (Taylor et al., Comput. Chem. Eng. 18 (1994) 205), We report some interesting dynamic features of RE columns by examining the response of a column for methyl tert-butyl ether (MTBE) synthesis to pertur bations in the feed of methanol, iso-butene or n-butene. When operating at a high-conversion branch of the bifurcation diagram, small perturbations ar e shown to lead to a transition to a low-conversion branch. The NEQ model i s shown to be more susceptible to feed perturbations than a conventional eq uilibrium (EQ) model with constant component efficiencies. The differences between the dynamic behaviour of trayed and random-packed columns are also emphasised in this work. The dynamic behaviour of the column has been inter preted on the basis of the iso-butene recycle flow in the column. It has be en shown that the size type and duration of a feed perturbation causing a t ransition from one to another steady state depends on the model description , on the column configuration and an the residence time distribution along the column height. Experimental verification of the developed dynamic model is obtained by comparison with the experimental results, of Mohl et al. (C hem. Eng. Sci. 54 (1999) 1029) for synthesis of tertiary amyl ether (TAME). (C) 2001 Elsevier Science Ltd. All rights reserved.