Separation of Methyl Ethyl Ketone/Methanol Azeotrope via Extractive Distillation with Ionic Liquids: Mechanism Analysis and Process Intensification

Methyl ethyl ketone (MEK) and methanol (MeOH) are byproducts obtained during the destructive distillation of wood, forming an azeotrope that is challenging to separate using conventional distillation. Three ionic liquids (ILs) ([N 2222 ][Ac], [HMMIM][Ac], and [N 4441 ][Ac]) are selected as entrainers for separating the MEK/MeOH azeotrope via extractive distillation. The separation mechanisms of three ILs are analyzed using four quantum chemical computational methods: molecular dynamics simulations combined with density functional theory calculations, van der Waals surface penetration analysis, independent gradient model based on Hirshfeld partition analysis, and atoms in molecules analysis. The results indicate that [N 2222 ][Ac] exhibits the best separation performance. Three ILs extractive distillation processes are developed, employing multiobjective optimization and multicriteria decision-making to obtain the optimal solution. The eco-indicator 99 (EI99) framework is utilized for life cycle assessment. The results indicate that the [N 2222 ][Ac] process exhibits the lowest total operation cost (TOC), total annual cost (TAC), CO 2 emissions ( E CO2 ), and EI99 points, as well as the highest extraction efficiency. Flash vapor circulation heat pump (FVCHP) is implemented to intensify the [N 2222 ][Ac] process. FVCHP-assisted [N 2222 ][Ac] process achieves a TOC reduction of 49.6%, a TAC reduction of 11.9%, an E CO2 reduction of 62.7%, and an EI99 points reduction of 71.6%. This study encompasses multiple perspectives, including separation mechanisms, process scale performance, and life cycle assessment, providing a systematic evaluation approach for the application of ILs in azeotropic separations.