Control of the maximum-boiling acetone/chloroform azeotropic distillation system

The literature contains a number of papers that study the control of azeotropic distillation systems. Both homogeneous and heterogeneous azeotropes have been considered, but all of the systems considered in these control papers deal only with minimum-boiling azeotropes. These azeotropes are caused by molecular repulsion between different types of chemical components and are more common than systems in which molecular attractions occur that result in maximum-boiling azeotropes. There appears to be no papers that study the control of this type of azeotropic system. This paper explores the design and control of the maximum-boiling azeotropic acetone/chloroform distillation system. The normal boiling points of the two pure components are 329.4 and 334.3 K, while the azeotropic boils at 337.6 K at 1 atm with a composition of 34.09 mol% acetone. A two-column extractive distillation process is used with dimethyl sulfoxide as the solvent. The two components are separated into 99.5 mol% pure products leaving in the distillate streams from two distillation columns. The solvent flowrate that minimizes total energy consumption is determined. A control structure that is capable of handling very large disturbances in throughput and feed composition is developed. The control of two tray temperatures in the extractive column is found to be necessary to handle feed composition disturbances.