Control comparison of conventional and thermally coupled ternary extractive distillation processes

Abstract

Extractive distillation is widely used to separate binary mixtures with azeotropes that prevent separation in a single distillation column. The conventional binary extractive distillation configuration uses two columns with one key component going overhead in the extractive column and the other key component going either overhead or out the bottom of the solvent recovery column, depending on the effect of the solvent on the volatilities of the key components.Extractive distillation can also be applied to separate ternary mixtures with azeotropes. The conventional ternary extractive process requires three columns. Unconventional processes can also be used, such as thermally coupled sidestream/rectifier columns. Economic advantages of the thermally coupled process have been reported for some separations.The controllability of extractive distillation system for binary mixtures has been explored in many papers. The novel contribution of this paper is the exploration of the dynamic controllability of extractive distillation systems for a ternary mixture. The dynamics of a conventional three-column process are compared with a thermally coupled column/rectifier process.