Green and low-cost deep eutectic solvents for efficient extraction of basic and non-basic nitrides in simulated oils

The removal of nitrogenous compounds from fuel oil is essential to reduce NOx emissions and improve the quality of the oil. In the present work, a new method of nitrogen removal using deep eutectic solvents (DESs) as extractants is reported. Seven green and low-cost quaternary ammonium acidic DESs were prepared and used for the extraction of basic N-compounds (quinoline) and non-basic N-compounds (indole) in model oil. The results indicated that the structure of DESs has a profound effect on denitrification performance. Under the same conditions, DES composed of tetrabutylammonium bromide and formic acid ([TBAB:2FA]) showed the best denitrification performance and could effectively remove both basic and non-basic nitrogen compounds. The main experimental parameters such as the mass ratio of DESs to model oil, extraction temperature, time, initial concentration of N-compounds and water content when [TBAB:2FA] were used as extractants were investigated. Under the optimal conditions (initial N-compounds concentration of 200 ppm, DESs-oil mass ratio of 1:5, 30 °C, and 60 min of extraction), the extraction efficiency of quinoline and indole were 99.60% and 98.42%, respectively. In addition, the DESs were regenerated with deionized water. When reused four times, the denitrification capacity remained high. Finally, the mechanism of the extraction process was investigated by FT-IR spectroscopy. This research is expected to provide a theoretical reference for the removal of nitrogen compounds from fuel oil.