Desulfurization of diesel fuels by selective adsorption on activated carbons: Competitive adsorption of polycyclic aromatic sulfur heterocycles and polycyclic aromatic hydrocarbons

Adsorptive affinity of polycyclic aromatic sulfur heterocycles (PASHs) and polycyclic aromatic hydrocarbons (PAHs) on activated carbons and the effect of PAHs on the adsorption performance of PASHs were studied. Adsorptions of real and model diesels (MDs) containing aromatics and sulfur compounds over several activated carbons were conducted in both batch and fixed-bed adsorption systems. The adsorption results showed that adsorptive affinities of molecules with polycyclic aromatic skeleton structure are primarily governed by the π–π dispersive interaction between the aromatic rings and the graphene layers of activated carbons. In addition, the electron donor–acceptor mechanism also plays an important role for S-containing molecules. Furthermore, for effective adsorption of large molecules, not only the pore size of the adsorbent should be, at least, larger than the critical diameter of the adsorbate, but also the pore size should also be sufficiently large to reduce diffusional resistance during adsorption. Based on this studies, it can be concluded that the adsorption selectivity increases as follows: naphthalene < fluorene < dibenzothiophene < 4,6-dimethyl dibenzothiophene < anthracene < phenanthrene. The adsorption capacity of PASHs decreases significantly in the presence of PAHs as result of the adsorption competition due to similar structure, molecular diameter and adsorption mechanisms.