Experimental and Mechanistic Investigation of Amide-Based Deep Eutectic Solvents for Quinoline Extraction and Separation from Wash Oil

This study undertakes a comprehensive examination of the action mechanism of deep eutectic solvents (DESs) as extractants in the extraction and separation process of quinoline found in coal tar wash oil. This research is significant to the design, development, and high-value utilization of new extractants and wash oils. In this investigation, DESs were synthesized from amides, specifically acetamide, propionamide, and butyramide, in conjunction with lactic acid. The extraction and separation process of the DESs-quinoline-toluene system was scrutinized using a method that combines thermodynamic property prediction, experimental validation, and exploration of the action mechanism. The findings revealed that the Hansen solubility parameter (HSPs) theory effectively yielded solubility parameters of DESs and accurately forecasted the extraction efficiency and interaction type of quinoline. The HSP theory-based predictions for extraction efficiency were corroborated through liquid–liquid phase equilibrium experiments, in which the order of efficacy was observed as butyramide > propionamide > acetamide. This was further consolidated by quantum chemical analysis, which quantitatively unveiled the system's separation action mechanism from an atomic fragment perspective. It was established that hydrogen bonding significantly influences the quinoline extraction process and that the interaction between the DES system and quinoline is predominantly governed by multicenter hydrogen bonding, which results in atom-pair interactions of superior strength.