Boron-doped activated carbon as efficient and selective adsorbent for ultra-deep desulfurization of 4,6-dimethyldibenzothiophene

Activated carbon was modified with varying concentrations (0.5–10 wt.%) of boric acid to make adsorbents with physico-chemical properties that are essential for the removal of bulky and recalcitrant 4,6-dimethyldibenzothiophene (4,6-DMDBT) from the model fuel via adsorptive desulfurization at room temperature. The features of boron-doped activated carbon adsorbents were examined in comparison with unmodified activated carbon using N₂ physisorption analysis, inductively coupled plasma-mass spectrometry, Raman spectroscopy, Fourier transform infra-red, temperature programmed desorption and scanning electron microscopy. Boron-doped adsorbents exhibited better adsorption capacity at low boron loadings of 0.5–2.5 wt.%, largely due to their preserved surface area compared to those with higher boron loadings (5–10 wt.%), and enhanced surface acidity, compared to the unmodified AC. Specifically, the adsorbent containing 1 wt.% of boron loading (1BDAC) gave the best adsorption performance of 85% (8.50 mg/g) in 100 ppmw-S containing 4,6-DMDBT within 5 min contact time. Furthermore, for the IBDAC sample, the effect of initial concentration, sorbent dosage, and selectivity were studied in the presence of naphthalene. Remarkable regeneration performance was exhibited by the 1BDAC adsorbent with only 7% loss in adsorption capacity after supplementary five-cycle regenerations. The kinetic studies showed that the adsorption followed a pseudo-second order model while isotherm data were well fitted by Freundlich isotherm. With an optimum boron loading of 1 wt.%, the boron-doped AC showed selectivity towards complex refractory organosulfur compound (4,6-DMDBT), which highlights its efficacy for significantly removing the compounds from the model fuel.