Dynamic study in enhancing the controllability of an energy-efficient double side-stream ternary extractive distillation of acetonitrile/methanol/benzene with three azeotropes

The exploration of control strategy for the double side-stream ternary extractive distillation (denoted as DSTED) process is essential because it has a significant potential for energy-saving. However, how to effectively control the energy-efficient DSTED process is a unique and complex issue due to the additional coupled variables of double side-streams. Consequently, in this study, control schemes of the energy-efficient DSTED process for separating acetonitrile/methanol/benzene with multi-azeotrope are investigated. Firstly, a dual-temperature control strategy is proposed based on the existing single temperature control with feedforward scheme. Temperature difference control strategy is then studied to effectively reduce the offset of product purities for the disturbances of feed composition. Following that, a double-temperature difference control strategy is studied to maintain the product purities. Finally, the comparisons of product purities and energy consumption are introduced to clearly assess the stability and controllability of the different temperature control structures. Dynamic performances show that the temperature difference control structure has the best performance facing the ±10% feed disturbances.