Quaternary Ammonium Salts-Based Deep Eutectic Solvents: Utilization in Extractive Desulfurization

In this work, three deep eutectic solvents (DESs) were synthesized and further used in extractive desulfurization (EDS). Three DESs were synthesized by the thermal method using choline chloride (ChCl), tetrabutylammonium bromide (TBAB), and tetramethylammonium chloride (TMAC) as hydrogen bond acceptors (HBAs) and ethylene glycol (EG) as a hydrogen bond donor (HBD). The thermal properties of DESs and their individual components were determined via differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) coupled with Fourier transform infrared spectroscopy (TGA-FTIR). The DESs were further utilized in the extraction of sulfur-based model oil (500 mg.L-1 sulfur content as a dibenzothiophene (DBT) dissolved in isooctane). The maximum sulfur extraction efficiency of 81.2% was achieved using TBAB/2EG as DES at optimized operating conditions, i.e., contact time of 30 min, temperature at 25 degrees C, the volumetric ratio of DES to fuel being 1.2:1, and stirring speed of 350 rpm. The recyclability of DES without regeneration caused a decrease in extraction efficiency, which was regained after regeneration. The pseudo first-, second-, and nth-order models represented the EDS kinetics. The interaction between the components during the synthesis and after regeneration was confirmed by FTIR and H-1 NMR. Gas chromatography with flame ionization detection (GC-FID) analysis showed negligible loss (1.5%-2.5%) of DES during regeneration.