Removal intensification of basic and non-basic nitrides from liquid fuels by the optimization design of quaternary ammonium salt green solvents

Nitrogen compounds significantly affect the quality of oil products; therefore, the removal of these compounds from oil products has attracted significant attention. In this study, a novel method for separating nitrogen compounds from oil using quaternary ammonium salt (QAS) as an extractant to form deep eutectic solvents (DESs) with non-basic nitrides, interacting with basic nitrides was proposed. Based on the COSMO-SAC model, the possibility of nitrogen compounds acting as hydrogen-bond donors in oil was verified. The effects of four QAS types, agent oil ratios, reaction temperatures, and stirring times on the removal of nitrogen compounds in simulated oil, and the effects of the stripping agent type and recovery times on the recovery rate of QAS were investigated. The DESs were analyzed and characterized by Fourier-transform infrared spectroscopy. The results indicated that tetraethyl ammonium chloride (TEAC) was the best denitrogenation agent. When the stirring time was 8 min, the removal rate of the nitrogen compounds reached 92.62%. Simultaneously, the removal mechanism was studied at the molecular level using a quantum chemical calculation method. Ethyl acetate was used as the stripping agent. After five recovery cycles, the recovery rate of TEAC was 91.5%. This method demonstrates a high selectivity, rapid extraction efficiency, and high recovery efficiency. This study provides theoretical guidance for the efficient and green removal of nitrogen compounds from oil products.