Control of heat-integrated indirect triple-column extractive distillation for separating ternary azeotropic mixture tetrahydrofuran-ethyl acetate-water

Most of the design and control studies for extractive distillation of the ternary azeotropic separation today focus only on the direct sequence extractive distillation (DED) while the design study for indirect sequence extractive distillation (IED) is rarely reported. Furthermore, there is no control study that worked on the IED. To bridge this gap, we analyze the control performance of the heat-integrated (HI) IED, exemplified using the separation of tetrahydrofuran (THF)/ethyl acetate (EtAc)/water as a case study. A single point temperature control (TC) (CS 1), dual TC (CS 2), and feed forward dual TC (CS 3) are developed in this work and their performances in rejecting feed flow and composition disturbances are tested. Overall, CS 3 exhibits the best control performance in returning all the three products purities to a value close to the products specification and provides the lowest transient deviation under feed flow and composition disturbances. The CS 3 also provides the lowest sum of integral absolute error with respect to CS 1 and CS 2, further reflecting its dynamic superiority.