Synthesis of deep eutectic solvents based on triethylamine and organic acids and their application in fuel oil denitrogenation: A theoretical and experimental study

In this work, three deep eutectic solvents (DESs) triethylamine/formic acid ([Et3N/FA]), triethylamine/acetic acid ([Et3N/PA]), triethylamine/propionic acid ([Et3N/AA]) were synthesized and were used for extractive denitrogenation of model oil. Among them [Et3N/PA] exhibited reasonably high extraction efficiency for both indole and quinolone. Structure optimization, electrostatic potential analysis and reduced density gradient analysis were performed to explore the synthesis mechanism of DESs and extractive denitrogenation mechanism by DESs taking [Et3N/PA] as a representative. The structure of [Et3N/PA] were characterized by FTIR and NMR. Results indicate that both strong hydrogen bond and van der Waals are the major force for DESs synthesis. Both hydrogen bonds and van der Waals are responsible for indole removal, while only van der Waals is responsible for quinolone removal. The effect of factors on extraction efficiency was also investigated and results indicate that [Et3N]/[PA] has the advantages of short equilibrium time, ability to deal with fuel oils with a wide range of nitrogen contents, excellent performance near room temperature. The presence of olefins and aromatics in fuel oil has negligible negative influence on the extraction efficiency of indole and quinolone. Furthermore, [Et3N/PA] exhibits excellent regeneration performance. Consequently, [Et3N/PA] is a promising extractant for fuel oil denitrogenation.