Effect of oxidative modification of coal tar pitch-based mesoporous activated carbon on the adsorption of benzothiophene and dibenzothiophene

Abstract

This work examines the effect of modification of coal tar pitch-based mesoporous activated carbon (MC) by HNO3 oxidation on the liquid-phase adsorption of benzothiophene (BT) and dibenzothiophene (DBT) in the model fuel oil. The pore structure and surface properties of the MC samples were characterized by N2 adsorption, SEM, FT-IR and Boehm titration. The results show that after oxidative modification, the specific surface area decreased, while the mesopore ratio and the density of the surface oxygen-containing groups increased remarkably. Moreover, the average pore sizes of MCs were not changed. The oxidative modification considerably enhanced the adsorption capacity toward BT and DBT by 1.3 times and 0.9 times, respectively. The improved adsorption performance upon the HNO3 oxidation can be attributed mainly to an increase in the acidic oxygen-containing functional groups. The higher the concentration of nitric acid and the oxidation temperature were, the more the amounts of surface acidic oxygen-functional groups were, and thus the higher the amounts adsorbed of BT and DBT on corresponding carbon were. The resulting oxidized MC afforded a maximum capacity of 53.0mg DBT and 32.8mg BT g−1 of MC follow saturation kinetics with respect to the total acidity on the surface of the MC. The competitive adsorption effects of naphthalene and phenanthrene against DBT on the oxidized MCs are obvious, and the effect of phenanthrene is greater than that of naphthalene. The MCs could be easily regenerated by washing with toluene. The regenerated adsorbent afforded 98%, 95% and 91% of the initial adsorption capacity after the first three regeneration cycles, respectively.