Polyethylene glycol-based halogen-free acidic deep eutectic solvents for removal of olefins from aromatics

Abstract

In this study, seven novel green acidic deep eutectic solvents (ADESs) based on polyethylene glycol (PEG) was successfully synthesized. Organic acids containing carboxylic acid and sulfonic acid functional groups were utilized as hydrogen bond donors (HBDs) for the synthesis. The formation mechanism of ADESs was elucidated through 1H NMR and FTIR spectroscopy, as well as density functional theory (DFT) calculations. Acetonitrile-IR spectroscopy was employed to investigate the acidity of the prepared ADESs, revealing the superior Lewis acidity of ADESs derived from carboxylic acid functional groups. The generation of Lewis acidic sites can be attributed to the hydrogen bonding interaction between the hydroxyl groups of PEG and the carboxylic acid functional groups, promoting the dissociation of carboxylic acid molecules. The obtained DES [PEG:2FA] and [PEG:2AA], with formic acid (FA) and acetic acid (AA) as HBDs, exhibited remarkable efficiency in removing olefins from aromatics under mild reaction conditions. GC–MS analysis of the reaction products confirmed the formation of alkylbenzenes, indicating the occurrence of alkylation reactions. Furthermore, a rational reaction mechanism was proposed to elucidate the reaction process of aromatics and olefins on acidic sites.