The importance of variable compositions for the distillation sequence design of separating ternary azeotropes mixtures with heterogeneous region

During the synthesis of industrial compound methyl propionate (MePor), a complex ternary mixture (MePor/MeOH/H2O) would be formed which is characterized by dual binary azeotropes coupled with a liquid–liquid heterogeneous phase. While numerous studies have focused on the distillation sequence design, significant research gaps remain regarding to separation of MePor/MeOH/H2O under the variable feed compositions. Therefore, this study comparatively explored the heterogeneous extractive distillation (HED) processes across three feed regions based on the rigorous thermodynamic topology analysis of the azeotropic mixture. Within each region, two HED processes are respectively developed and optimized via the stochastic evolutionary algorithms to determine the optimal scheme. The design of pre-separation column along with the separation sequence of MePor/MeOH/H2O lead to the discrepancy in the indicators (total annual cost, CO2 emissions, process route index and thermodynamic efficiency) of two HED processes under three feed compositions. The integration of heat pump-assisted technique is further applied to enhance the economic, environmental and energetic performance for each optimal HED process. The results indicate that the superior separation sequences for the triangle region (i.e., 0.70MePor/0.15MeOH/0·.15H2O) and the quadrilateral region (i.e., 0.20MePor/0.666MeOH/0·.134H2O; 0.38MePor/0.37MeOH/0·.25H2O) are heat pump-assisted enhanced pre-separation process and direct extractive distillation process, respectively. In summary, this study addresses the limitation associated with fixed feed composition in the separation of conventional Serafimov’s 2.0.2b class mixtures, providing a methodological framework for determining the optimal HED process design in industrial implementations.