Static multiplicities in heterogeneous azeotropic distillation sequences

In this paper the results of a bifurcation analysis on heterogeneous azeotropic distillation sequences are given. Two sequences suitable for ethanol dehydration are compared: The 'direct' and the 'indirect' sequence. It is shown, that the two sequences, despite their similarities, exhibit very different static behavior. The method of Petlyuk and Avet'yan (1971), Bekiaris et al. (1993), which assumes infinite reflux and infinite number of stages, is extended to and applied on heterogeneous azeotropic distillation sequences. The predictions are substantiated through simulations. The static sequence performances are compared for minimal impurities in both products, where the direct sequence exhibits output multiplicity, while the indirect sequence exhibits state multiplicity. The latter multiplicity may be avoided by accepting a slightly increased impurity in the ethanol product. Copyright (C) 1998 IFAC.