Role of silanol groups on silica gel on adsorption of benzothiophene and naphthalene

Abstract

The adsorptive removal of sulfur-containing compounds such as thiophene derivatives from transportation fuels has received extensive attention because of its economic and environmental advantages compared to the hydrodesulfurization process. In our previous study, we suggested that the adsorption sites for benzothiophene and naphthalene on the silica surface consist of different types of silanol groups, and the removal of vicinal silanols from the silica surface should enable silica materials to adsorb benzothiophene selectively. In this study, an attempt is made to prove this hypothesis for the development of novel desulfurization sorbents. Heat treatment of silica gel was performed at different temperatures to remove vicinal silanol groups, and the adsorption capacities of benzothiophene and naphthalene were evaluated. The amount of naphthalene adsorbed on heat-treated silica gel decreased with increasing heat-treatment temperature, whereas the amount of benzothiophene adsorbed on silica gel treated at 873 and 1073 K showed only a slight decrease. Considering the heat treatment might lead to the removal of vicinal silanols due to dehydration of surface silanols, the results indicate that vicinal silanol groups were selective adsorption sites for naphthalene. Moreover, for binary-component systems, the adsorption capacities of benzothiophene and naphthalene were almost identical because of multilayer adsorption of naphthalene on adsorbed benzothiophene, and the adsorption capacities of benzothiophene for single- and binary-component systems were also identical. This suggests that the heat treatment of silica enables the selective removal of benzothiophene.