Robust Flowsheet Synthesis for Ethyl Acetate, Methanol and Water Separation

This work presents a robust flowsheet design for the recovery and purification of waste solvent streams containing ethyl acetate (EtAc), methanol (MeOH), and water. Separation of this mixture is challenging due to the presence of two azeotropes: a homogeneous EtAc-MeOH azeotrope and a heterogeneous EtAc-water azeotrope. These azeotropes create a distillation boundary that divides the ternary composition space into two distinct regions, making separation via conventional distillation difficult. Additionally, the wide variability in waste solvent compositions requires a versatile design, as flowsheets optimized for dilute mixtures may not be feasible for concentrated ones. The key to this design is using a liquid-liquid extractor (LLX) with recycled water as the solvent, ensuring the mixture remains within the liquid-liquid equilibrium (LLE) split region, which facilitates spontaneous separation across the distillation boundary and promotes energy-efficient separation. The raffinate composition lies near the EtAc-water edge in the EtAc-rich region and is stripped to recover pure EtAc, while the extract phase is processed to yield pure MeOH and water. Converged designs are developed for equimolar, EtAc-rich, MeOH-rich, and water-rich compositions, with the proposed robust structure validated for all four compositions. This study represents a significant advancement in sustainable solvent recovery by eliminating the need for separate designs tailored to specific compositions, offering a unified, robust solution for separating various solvent feed mixtures.