Simulation and optimization of pre-concentration extractive distillation for the separation of acetonitrile-n-propanol-water ternary azeotropic system
The separation of multicomponent azeotropic mixtures remains a persistent challenge in industrial wastewater treatment due to complex phase equilibrium behavior involving minimum/maximum boiling azeotropes and liquid-liquid phase separation. Pharmaceutical wastewater often contains a ternary mixture of acetonitrile, n-propanol, and water, which exhibits significant non-ideality and multiple azeotropic points, including binary azeotropes for acetonitrile-water, n-propanol-water, and acetonitrile-n-propanol pairs, as well as a ternary azeotrope. This study conducted a comprehensive investigation encompassing thermodynamic modeling, solvent screening, process design, and multi-objective optimization. A reliable thermodynamic framework was established using an activity coefficient model (NRTL), validated against experimental data. Systematic analysis of vapor-liquid equilibrium diagrams identified ethylene glycol as the optimal extractant due to its superior selectivity. Three distinct separation processes were developed: a conventional three-column distillation sequence (TCED), a four-column pre-concentration extractive distillation configuration (FCED), and an innovative three-column integrated pre-concentration extractive distillation system incorporating a thermally coupled column (TCED-IDC). Multi-objective optimization using the improved nondominated sorting genetic algorithm (NSGA-II) targeted total annualized cost (TAC), CO2 emissions (ECO2), and thermodynamic efficiency (η), subject to stringent purity constraints (≥99.9 wt% for products and ≥99.99 wt% for extractant recycle). The integrated three-column configuration achieved 41.2% lower TAC, 50.4% lower CO2 emissions, and 102% higher thermodynamic efficiency compared to the conventional TCED process. This integrated pre-concentration extractive distillation process is established as an industrially viable, energy-efficient solution for acetonitrile-n-propanol-water separation, aligning with green chemistry principles.