Phase Equilibria upon Denitrification of Liquid Fuels Using Imidazolium-Based Ionic Liquids: Experiment and Quantum Chemical Calculations

The interaction between pyrrole and pyridine with 1-ethyl-3-methylimidazolium ethyl sulfate ([EMIM]­[EtSO4]) was investigated using quantum chemical calculations, the conductor-like screening model for real solvent (COSMO-RS) approach, and experimental ternary liquid–liquid equilibrium (LLE) data. Geometry optimization was performed usign density functional theory (DFT) with B3LYP functional and 6-311+G* basis set for individual species and complexes of [EMIM]­[EtSO4] with pyrrole/pyridine. The amount of charge transfer in [EMIM]­[EtSO4] + pyrrole was found to be ∼20% greater than that in [EMIM]­[EtSO4] + pyridine, indicating that CH−π interaction was stronger with pyrrole. The more negative interaction energy for the complex [EMIM]­[EtSO4] + pyrrole implies that [EMIM]­[EtSO4] has a more favorable interaction with pyrrole than with pyridine. σ-profile analysis using COSMO-RS confirmed the pivotal role of the CH-π interaction between [EMIM]­[EtSO4] and pyrrole or pyridine. Ternary LLE experiments were performed at 298.15 K and atmospheric pressure to compare the extraction efficiency of pyrrole and pyridine from model diesel compound (n-hexadecane) using [EMIM]­[EtSO4]. The experimental data showed that [EMIM]­[EtSO4] had a higher extraction efficiency for pyrrole than for pyridine, hence validating the computational results. The experimental data were well-correlated by the NRTL model with an average root-mean-square deviation (RMSD) of 0.28%, and COSMO-RS gave excellent prediction of the LLE data, with an average RMSD of 0.99%.