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

Abstract

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.