Sustainable Extractive Distillation Process for Separating n -Hexane/Ethyl Acetate/Ethanol Azeotropic Mixtures: Molecular Mechanism Insights and Multiobjective Optimization

The separation of the n-hexane/ethyl acetate/ethanol (HE/EA/EtOH) azeotropic mixture is a critical challenge in chemical industrial processes due to the complex thermodynamic behavior of this ternary system. This study developed an efficient, intrinsically safe, and ecologically sustainable extractive distillation (ED) process for this system. First, candidate entrainers were screened via residue curve mapping and toxicity assessment; quantum chemical calculations (σ profile) and molecular simulations were further employed to elucidate the underlying intermolecular weak interactions governing separation performance. Results demonstrated that EtOH exhibits strong hydrogen bond donor capacity with entrainers N-methyl-2-pyrrolidone (NMP) and dimethyl sulfoxide (DMSO), whereas HE predominantly interacts with these entrainers via dispersion forces due to the absence of hydrogen bond-forming ability. Hydrogen-bond energy analysis verified that NMP exhibits superior separation performance for the HE/EA system, while DMSO is more efficient for EA/EtOH separation. Subsequently, three ED processes using DMSO (ED-DMSO), NMP (ED-NMP), or their mixture (ED-MIX) as the entrainer were conceptualized and optimized via multiobjective optimization using total annual cost (TAC), CO2 emissions (ECO2), and process risk index (PRI) as sustainability performance metrics. The results indicate that ED-DMSO achieved the lowest TAC (28.05 × 105 $/year) and ECO2 (1407.58 kg-CO2/h); in contrast, ED-NMP yielded the lowest PRI (4.18), attributed to the narrower flammability limit of NMP as compared with DMSO. Ecologically, ED-DMSO and ED-MIX reduced Eco-indicator 99 by 39.86 and 47.28% compared to ED-NMP, respectively. Notably, ED-MIX integrated the advantages of both entrainers, achieving an optimal trade-off among economic viability, environmental footprint, ecological sustainability, and intrinsic safety. Thus, ED-MIX is identified as the optimal sustainable process for HE/EA/EtOH separation.