Optimizing extractants selection for efficient separation of phenols and nitrogen-containing heteroaromatics using hydrogen bond interaction strategies

Focusing on the use of imidazolium ionic liquids and quaternary ammonium salts-based deep eutectic solvents for separation phenols and nitrogen-containing heteroaromatics, the role of heteroaromatics as specific sites for hydrogen bond-based separation has been investigated. These environmentally friendly solvents are known for their ability to form hydrogen bonds with heteroatoms, a key aspect in separation processes. We quantified the hydrogen bonds interaction energy to reach the threshold energy for efficient O-, N-heteroaromatics separation. This article provides an in-depth study of the structural nuances of different hydrogen bonding sites and their affinity properties, while conducting a comparative evaluation of the separation efficiency of ionic liquids and deep eutectic solvents from a thermodynamic perspective. Results showed that phenols with dual hydrogen bonding recognition sites were easier to separate than nitrogen-containing heteroaromatics. Imidazolium ionic liquids were more suitable for the extraction of non-basic nitrogen-containing heteroaromatics, and quaternary ammonium salts-based deep eutectic solvents are more effective for phenols and basic nitrogen-containing heteroaromatics, which was confirmed by Fourier transform infrared spectroscopy and empirical tests. Therefore, this study provides a theoretical basis for the strategy design and selection of extractants for the efficient separation of O-, N-containing aromatic compounds.