Effective Separation and Purification of Nitrogen-Containing Aromatics from the Light Portion of a High-Temperature Coal Tar Using Choline Chloride and Malonic Acid: Experimental and Molecular Dynamics Simulation

An effective deep eutectic solvent (DES) combined with column chromatography was designed for separating nitrogen-containing aromatics (NCAs) from the light portion (LP, which is petroleum ether-extractable portion) of a high-temperature coal tar. The total content of NCAs enriched with equimolar choline chloride (CC)/malonic acid mixture is much higher than that with other CC-based DESs. The maximum total recovery of NCAs is 57.2% with 1:2 of DES/LP mass ratio from the third run of extracting LP at 35 degrees C. The relative contents of carbazole, benzo[h]quinoline, and quinoline enriched by flash preparative chromatography are 93.3, 92.0, and 90.4%, respectively. In addition, the nonbonded interaction energy among the DESs, NCAs, and condensed arenes was calculated for demonstrating the difference in extract yield with diverse DESs. The reduced density gradient method proved that the typical hydrogen bonds, X-H...pi bonds (X denotes >C, >N, or -O), and van der Waals forces widely exist among the DESs and NCAs through molecular dynamics simulations.