Analysis of Design and Control of Reactive Thermally Coupled Distillation Sequences

This work presents a study of the production of ethyl acetate from ethanol and acetic acid through three reactive thermally coupled systems: a thermally coupled distillation sequence with a side stripper, a thermally coupled distillation sequence with a side rectifier and a Petlyuk-type column. Using the process simulators Aspen Plus (TM) and Aspen Dynamics (TM), a parametric study was carried out in order to understand the effect of the process variables on the production of ethyl acetate. In the first part of the study, we found that most of the water produced in the sterification reaction can be removed by the use of side columns coupled to a main column. This favors the production of ethyl acetate and only the ethyl acetate-water heterogeneous azeotrope is formed in the distillate product. A similar result was also found in the case of the dividing wall distillation column (Petlyuk-type column) i.e., the side stream product is mainly water. In addition, this distillation sequence required the lowest amount of energy, compared to the thermally coupled distillation with side columns. In the second part of the study, dynamic closed-loop responses were obtained for the most energy-efficient reactive distillation scheme (Petlyuk column). The results showed that with this complex scheme, one can achieve changes in the set point and also elimininate the effect of disturbances with only simple PI controllers tuned by the Ziegler and Nichols' method. From these results, one may conclude that thermally coupled distillation systems present significant advantages over the classical process used to produce ethyl acetate.