Groundnut-shell derived oxygen enriched mesoporous carbon adsorbent for removal of thiophenic sulfur compounds.

Abstract

In this work, groundnut shell-derived mesoporous carbons, synthesized by one-step carbonization at different temperatures in presence of potassium hydroxide, were used for desulfurization studies involving dibenzothiophene, benzothiophene and thiophene. The pore formation and corresponding surface area of synthesized mesoporous carbon was governed by carbonization temperature as it increased from 600 to 900 °C. The carbon synthesized at carbonization temperature of 800 °C, that is GN-800, showed highest surface area (1192 m²/g) and pore volume (0.58 cm³/g) amongst the all synthesized mesoporous carbons. For all the thiophenic sulfur compounds, the prepared mesoporous carbons exhibited improved adsorptive desulfurization performance as the adsorption temperature increased from 25 to 70 °C. The oxygen enriched adsorbents showed higher oxygen content and improved removal for all the thiophenic sulfur compounds. The oxygen enriched adsorbent, obtained by treatment with nitric acid (V) and carbonized at 800 °C, showed highest adsorptive desulfurization performance for all sulfur compounds. At 70 °C the removal for thiophene, benzothiophene and dibenzothiophene was 97.7, 93.8 and 90.2%, while the corresponding adsorption capacities were 58.7, 56.3 and 54.6 mg/g, respectively. For mesoporous carbonized carbons, the π-π interaction also contributed to adsorptive forces in addition to Van der Waals forces. For the oxygen enriched samples, additional acid-base interactions also contributed to adsorptive forces. The experimental data was best fitted to pseudo-second order kinetics model and Langmuir isotherm model. The adsorbent showed a slight drop in the removal percentage after five adsorption-regeneration cycles. The oxygen enriched groundnut shell derived mesoporous carbon was observed to have the potential to function as an excellent desulfurization adsorbent for producing clean fuel.