Abstract:

Selective removal of sulfides in fuel oil is of great significance to the environment and human health. In this work, using density functional theory (DFT) with and without long-range dispersion correction via Grimme??s scheme (D-DFT), the adsorption behavior and adsorption selectivity of dibenzothiophene (DBT), n-hexadecane, and n-octane and toluene on the porous boron nitrides (p-BN) with/without vacancy defect have been studied. On perfect p-BN, the adsorption energy (E_ads) was calculated to be 1.395, 0.600 and 0.457 eV (PBE+D) for single DBT, n-hexadecane and n-octane molecules respectively, indicating that the adsorption of DBT on p-BN is highly preferred over n-hexadecane. The strong adsorption of DBT on p-BN was attributed to the intermolecular force that derived from the interaction between the B—N polar bond and the permanent dipole of DBT molecule. With the introduction of nitrogen (V_N) and boron (V_B) vacancy defects, the E_ads of DBT increased to 1.650 and 1.875 eV (PBE+D) and the E_ads of the n-hexadecane is only 0.400 and 0.600 eV (PBE+D), respectively. The electronic structure [calculations density of states (DOS), the highest occupied molecular orbital (HOMO), total charge density together with charge density difference, and Hirshfeld charges] reveal that the chemical interactions between the defect level and S atom in sulfide enhanced the adsorption of DBT molecule on p-BN. For practical application, other sulfur-containing organic compounds including 4,6-dimethyldibenzothiophene (4,6-DMDBT), thiophene (T), benzothiophene (BT) and carbide toluene in fuel oil are also considered and p-BN still tends to selectively adsorb sulfides from carbides preferentially, suggesting that p-BN with/without vacancy defect is promising for the removal of sulfur-containing organic compounds from fuel oil. Finally, the defect formation energies were estimated to evaluate the energetic stability of defective p-BN. The growth of V_N or V_B strongly depends on the chemical environment. Under boron-rich conditions, the use of B₂H₄ as the B source is more conducive to the formation of V_N than the use of B, α-B₁₂, and BH₃, etc. Contrastingly, the use of N₂H₄ as the N source in the nitrogen-rich environment is more beneficial to the formation of V_B than the use of N₂, NH₃. Our results provide a useful guidance for the design and fabrication of porous BN sorbent for sulfur-containing organic matter removing from fuel oil.

Key words: computational chemistry, adsorption, simulation, porous BN, fuel oil, desulfurization