Acid base interaction and its influence on the adsorption kinetics and selectivity order of aromatic sulfur heterocycles adsorbing on Ag-Al2O3

Adsorptive desulfurization is a promising technology to provide sulfur free fuels for fuel cell based power units. In this work the adsorption kinetics of three different aromatic sulfur heterocycles was studied for Ag-Al2O3. The influence of individual as well as competitive adsorption on the selectivity order was investigated by equilibrium and breakthrough experiments. In these experiments a jet-A1 fuel enriched with benzothiophene (BT), dibenzothiophene (DBT), and 4,6-dimethyldibenzothiophene (4,6-DMDBT) was used. The adsorption of aromatic sulfur heterocycles on Ag-Al2O3 proceeds via three different adsorption mechanisms. Within these mechanisms the π-interaction (π-Ag) and the direct sulfur-silver interaction (S-Ag) are significantly stronger in comparison to the acid base interaction (S-H). The results showed that the π-Ag and S-Ag interactions are the major adsorption mechanisms in the first stage, where film-diffusion limits the adsorption rate. In the second stage, the S-H interaction plays only an important role for BT, where intraparticle diffusion is the rate controlling step. The overall selectivity order was found to be BT > DBT > 4,6-DMDBT in the case of competitive adsorption for both equilibrium and breakthrough performance. The S-H contribution was related to incorporation of silver into blank γ-alumina, which significantly increased the overall acidity of the adsorbent.