Mechanisms of dibenzothiophene removal influenced by fuel molecular structure: Carbon chain length, ester groups, unsaturation, and aromaticity

Adsorption desulfurization is extensively applied in fuel desulfurization, but variations in fuel composition can notably affect the performance of adsorbents, complicating the selection of optimal adsorption conditions. In this study, quantum chemistry and molecular dynamics methods were employed, with dibenzothiophene (DBT), a typical sulfide, serving as the target molecule. Seven alkanes, one aromatic hydrocarbon, eight saturated fatty acid methyl esters (FAMEs), and three unsaturated FAMEs were selected based on the main components of biodiesel and 0# diesel. Experimental data were combined with theoretical calculations to thoroughly investigate the influence of fuel composition on DBT removal. The results indicate that among the three key factors—carbon chain length, ester group structure, and unsaturation—the ester group structure has the most significant impact on DBT removal. Notable differences were observed in the DBT adsorption capacities of FAMEs (27.57 mg/g–33.66 mg/g) and alkanes (51.01 mg/g–59.66 mg/g), with the ester group enhancing the electrostatic interactions between the fuel and DBT. The larger carbon chain length restricts the movement of DBT, slightly reducing its removal efficiency in fuel. The DBT adsorption capacity of the adsorbent in methyl palmitoleate (28.93 mg/g) was higher than in methyl palmitate (27.57 mg/g), with a 4.70 % increase, suggesting that unsaturation in FAMEs may enhance DBT removal efficiency. Furthermore, the aromatic structures of both DBT and aromatic hydrocarbons lead to strong competitive adsorption, significantly reducing DBT adsorption capacity in toluene (5.89 mg/g) compared to alkanes and FAMEs. This study provides a theoretical foundation for the practical application of adsorbents in desulfurization processes across various fuel types.