Highly-efficient separation of pyromellitic acid and trimellitic acid mixtures via forming deep eutectic solvents: Experiment and calculation

Pyromellitic acid (PMA) and trimellitic acid (TMA) are significant chemical raw materials and intermediates. They simultaneously exist in the industry processes of synthesis and are difficult to be separated. In this work, several kinds of biodegradable compounds were chosen as hydrogen bond acceptors (HBAs) to separate PMA and TMA mixtures from acetone solutions via forming deep eutectic solvent (DES). It has been found that all these compounds can separate PMA and TMA mixtures to obtain pure PMA or TMA. However, the interaction between HBAs and PMA or TMA is quite different. Choline chloride cannot extract TMA but can form a DES with PMA in acetone. Hexamethylenetetramine (HA) and L-carnitine (L-car) can form DESs with both PMA and TMA in acetone solution. But when L-car or HA is added, the extraction rate of PMA is larger than that of TMA until the extraction rate of PMA reach 100%, and pure TMA is left in the acetone solution. The selective separation mechanism was explored by infrared spectroscopy combined with quantum chemistry calculation, and the strength and site of the interaction between extractants with PMA and TMA were calculated.