Sulfur reduction from fuels is an
essential assignment to perform
for environmentally friendly rules and a petroleum refining perspective.
Extractive desulfurization is a unique and promising technique to
attain prerequisites of legislative S-content (EURO VI/Bharat VI of
S < 10 ppm). Phosphonium ionic liquids are competent for S-extraction,
because of their pleasing green features and high production rate,
compared to imidazolium ionic liquids. The findings of this research
confirmed that trihexyl (tetradecyl) phosphonium bromide [THTDP]Br
appeared as an alluring solvent for S-removal. The Fourier transform
infrared (FTIR) spectroscopy, nuclear magnetic resonance (NMR), ultraviolet
(UV), X-ray diffraction (XRD), thermogravimetry/differential scanning
calorimetry (TG/DSC), and electron paramagnetic resonance (EPR) analysis
were discussed, with regard to molecular confirmations and compound
purity. Furthermore, [THTDP]Br physical properties were explored thoroughly.
The influence of various parameters, viz. temperature, S-compounds,
shaking time, and [THDTP]Br recycling, was systematically presented.
In extractive desulfurization, 88.5% dibenzothiophene removal was
achieved with a mass ratio of ionic liquid to fuel of 1:1 in 30 min
at 30 °C. Density functional theory (DFT) calculations are conducted
to probe the overlapping of molecular orbitals between [THTDP]Br and
various S-compounds. The energy band gap of [THTDP]Br and DBT is −5.74
eV and is found to be the lowest among the complexes. Without a significant
S-reduction, [THTDP]Br reclaimed up to 10 cycles. Also, S-removal
from gasoline and diesel with multistage extraction was examined.
This research provided noteworthy understandings of phosphonium ILs
as efficient extractants for extractive desulfurization.