Sustainable Two-Column Design for the Separation of Ethyl Acetate, Methanol, and Water

This study investigates the design of a two-column distillation (TCD) process to separate a dilute ternary Ethyl Acetate (EtAc)-Methanol (MeOH)-water waste solvent into nearly pure components. The separation is complicated by the presence of a homogeneous EtAc-MeOH azeotrope and a heterogeneous EtAc-water azeotrope, creating a distillation boundary that divides the ternary composition space into two distinct regions. To address this, the proposed flowsheet incorporates liquid-liquid phase separation to cross the distillation boundary, enabling feasible separation. Additionally, the pressure sensitivity of the distillation boundary is exploited to reduce the recycle rate, enhancing energy efficiency. The basic TCD flowsheet consists of a decanter, a high-pressure simple column, and a low-pressure divided-wall column (DWC). Heat integration (HI) is achieved using external process-to-process heat exchangers and vapor recompression (VR)-driven reboilers. The resulting energy-efficient HIVR-TCD configuration is more cost-effective and energy-efficient than existing designs in the literature. Specifically, the total annualized cost (TAC) of the proposed HIVR-TCD process is 15.4% lower than the literature best design, with reductions in energy consumption and CO2 emissions of 34.3% and 31.4%, respectively, representing a significant improvement.