A systematic entrainer screening and mechanism analysis method based on DFT for methanol/methyl propionate azeotrope separation

Abstract

The choice of entrainer is crucial for extractive distillation in azeotrope separation. A good entrainer improves efficiency and reduces costs, but traditional experimental screening is time-consuming. Existing computer aided methods, like the σ-profile method, don’t explain the interaction mechanisms between the entrainer and azeotropes. This work proposes a systematic approach using density functional theory (DFT) to evaluate the interaction energy differences, select the optimal entrainer, and determine the separation sequence. The molecular mechanism was analyzed using energy decomposition, intermolecular surface penetration, interaction region indicator and domain analysis, atoms-in-molecules theory, and extended transition state-natural orbitals for chemical valence. The methanol (MeOH)/methyl propionate (MP) system was used as a case study. Among various entrainers, 1-Butyl-3-methylimidazolium Bis(trifluoromethylsulfonyl)imide ([BMIM][NTf₂]) was found to the best. MeOH was first separated from the extraction column as a light component. Analysis showed that the interaction between [BMIM][NTf₂] and the azeotrope was primarily dominated by hydrogen bonds with dispersion interactions. The new method was validated against experimental data and proved to be more effective than the σ-profile method.