Removal of Branched Dibenzothiophenes from Hydrocarbon Mixtures via Charge Transfer Complexes with a TAPA-Functionalized Adsorbent

A direct grafting method has been demonstrated to successfully incorporate the π-acceptor, 2,4,5,7-tetranitro-9-fluorenylideneaminooxy propionic acid (TAPA), onto silica. Adsorption isotherms were measured for complexation of 4,6-dimethyldibenzothiophene (4,6-DMDBT) from n -heptane onto the TAPA-functionalized silica adsorbent. At 25 °C, maximum adsorption capacity was measured to be 58.6 mg/g for binding 4,6-DMDBT, which is 4-fold higher than that of the nonfunctionalized, bare silica sample with a surface area of 480 m 2 /g. The results from batch studies suggest that adsorption occurs via a 1:1 complexation between 4,6-DMDBT and TAPA. Adsorption isotherm data were collected at 0, 25, and 40 °C; these data were used to develop a relationship between the Henry’s constant for adsorption and temperature. The molar enthalpy of adsorption was calculated to be Δ H ads = −12.1 kJ/mol; this value is evidence for formation of π-electron acceptor−donor complexes.