Dibenzothiophene adsorption onto carbon-based adsorbent produced from the coconut shell: Effect of the functional groups density and textural properties on kinetics and equilibrium

Abstract

The aim of this work was to evaluate the effect of the acidic surface oxygenated groups and textural properties onto the adsorbent surface towards dibenzothiophene removal. The samples were prepared from an activated carbon derived from coconut shell (AC), by oxidative (ACO) and thermal (ACT) treatments. Morphological and chemical analyses were performed to characterize the adsorbents. The adsorption experiments were carried out in batch and closed system. The Langmuir isotherm model was used to describe equilibrium data, while kinetic data were described by the Homogeneous Surface Diffusion Model. The characterization results indicated that the adsorbents are predominantly microporous materials with effective surface area higher than 750 m2 g−1 (AC = 753 m2 g−1, ACT = 802 m2 g−1, ACO = 755 m2 g−1). It was observed a decrease in the amount of oxygenated functional groups in the ACT (310 µmol g−1) in relation to AC (738 µmol g−1), while for the ACO this amount was increased (2630 µmol g−1). The insertion of oxygenated functional groups on the adsorbent’s surface promoted an increment of density of sites (AC = 0.98 µmol m−2, ACT = 0.38 µmol m−2, ACO = 3.48 µmol m−2) what, consequently, led to the enhancement of the adsorption capacity. Also, the oxidative treatment provided a more favorable mass transfer kinetics with an increase of 89% enhancement for the diffusivity coefficient. These results indicate that an increase of effective specific surface area and acidic oxygenated groups can improve the adsorption performance of the carbon-based adsorbents for desulfurization purposes.