Adsorption of Dibenzothiophenes on Nanoporous Carbons: Identification of Specific Adsorption Sites Governing Capacity and Selectivity

Adsorption of dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) from simulated diesel fuel with 20 ppmw total concentration of sulfur was investigated on polymer-derived carbon and its oxidized counterpart. The initial and exhausted carbons were characterized using the adsorption of nitrogen, thermal analysis, potentiometric titration. X-ray fluorescence (XRF), mass spectrometry (MS), and scanning electron microscopy (SEM). The selectivities for DBT and 4,6-DMDBT adsorption were calculated with reference to naphthalene. Both the capacity and selectivity for DBT and 4,6-DMDBT removal from model diesel fuel increase with an increase in the volume or pores similar in sizes to DBT molecules, which is about 7 angstrom. The specific geometry of those pores in relation to the sizes of DBT and 4,6-DMDBT causes their adsorption to be stronger than that of arenes. Functional groups present on the surface in larger pores (about 100 angstrom) contribute to adsorption via polar interactions. The oxidative effect of the carbon surface was also evidenced by the presence of sulfoxide in the surface reaction products.