Simultaneous Extraction of Both Basic and Non-basic N-Compounds from Oil via Triethylene Glycol–Metal Complex Solvent: Performance and Behavior

Simultaneous extraction of basic and non-basic N-compounds from oil is still a big challenge. Triethylene glycol (TEG) encounters very weak Bronsted acidity. Its N-distribution coefficient [D-N, (mmol.g(Ex)(-1))/(mmol.g(Oil)(-1))] for the basic was below 7.0. In this work, metals dissolved in TEG can improve the Lewis acidity of the extractant and bring about the simultaneous removal. For example, D-N of TEG-Ag(I) can increase to 40.5 for quinoline and 57.9 for pyridine, respectively. For the non-basic, it still remained higher than 70.0. The promoted performance was ascribed to the improvement of extractive behavior of the basic. From TEG to TEG-Ag(I), first, the distribution of equilibrium N-concentrations between two phases was significantly changed from the straight line to the non-linear curve with the plateau. Second, the interaction type inside the system was optimized. The Ag(I)-based complexation coupled with the TEG-based H-bonding was identified. Third, the interaction intensity was increased as well. Ag(I) contributed much to reduction of Gibbs free energy change for the basic. Therefore, enhancing Lewis acidity of the extractant was a feasible way for the extraction of the N-compounds.