Enhanced adsorptive removal of thiophenic sulfur compounds by nitrogen-doped surfactant modified mesoporous templated carbons

Abstract

Adsorptive desulfurization is a greenway for sulfur removal from fossil fuels due to its ambient operating conditions and easy recyclable usage of spent adsorbent. This paper studied the effect of nitrogen doping in mesoporous templated carbon for the adsorptive removal of sulfur compounds from model fuel. The undoped and nitrogen-doped templated carbons were synthesized using alumina and surfactant-modified alumina as templates via the chemical vapor deposition method. Modification by nitrogen enhanced both the surface area and pore volume of templated carbon. The nitrogen-doped surfactant-modified alumina templated carbon, AS-N, showed the highest surface area of 1373 m2/g and pore volume of 1.15 cm3/g. The AS-N showed adsorptive removal of sulfur compounds (thiophene 92.15%, benzothiophene 82.90% and dibenzothiophene 82.38%) at 70 °C. This may be attributed to the highest surface area and presence of nitrogen (8.2 wt%), which improved the adsorption capability by increasing the π-π interaction between the sulfur compounds and carbon matrix. Further increase in nitrogen content in templated carbon enhanced the π-π interaction resulting in higher removal capacity. The AS-N-U adsorbent prepared in the presence of urea had 15.2 wt% nitrogen and showed enhanced removal of thiophene 97.7%, benzothiophene 92.4%, and dibenzothiophene 89.3%. The adsorptive desulfurization over AS-N-U for all sulfur compounds were best fitted to pseudo-second order kinetic model and Langmuir adsorption isotherm model. The templated carbon was regenerated successfully using the thermal regeneration process. After five adsorption-regeneration cycles, the removal efficiency was lowered only by 4–10% for all sulfur compounds.