Removal Mechanism of Thiophenic Compounds in Model Oil by Inorganic Lewis Acids

The adsorptive desulfurization ability of four inorganic Lewis acids (AlCl3, FeCl3, ZnCl2, and CuCl) for three thiophenic S-compounds, viz., 3-methylthiophene (3-MT), benzothiophene (BT), and dibenzothiophene (DBT), from their model oils were studied here experimentally at 290 K. The results were explained in terms of the theory of hard and soft acids and bases (HSAB) reasonably. The results show that AlCl3 has excellent removal ability for 3-MT with its adsorbance being 141.4 without toluene and 123.0 mgS/g with 25 wt % toluene. It is noteworthy that 3-MT is removed solely through complexing adsorption; in contrast, BT is adsorbed, accompanied with the formation of oil soluble BT oligomers under catalysis of AlCl3 which can promote the complexation greatly. Further, the addition of benzene and toluene can accelerate the desulfurization rate of 3-MT and BT due to the concentration of aromatics on the adsorbent and the oligomerization between BT and the aromatics.