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

摘要：

选择性去除燃油中的硫化物对环境和人类健康具有重要意义。采用基于密度泛函理论（DFT）和含色散矫正的密度泛函理论（D-DFT）的方法，研究了多孔氮化硼（p-BN）及其空位缺陷对燃油中噻吩类硫化物及非硫化物的吸附行为及吸附选择性。结果表明：B—N极性键与硫化物极性分子之间的分子间力使p-BN能选择性去除燃油中的二苯并噻吩（DBT）；引入N、B空位缺陷后，缺陷能级与S原子形成化学相互作用并伴随电荷转移，进一步增强了p-BN对硫化物的吸附。通过对N、B空位缺陷形成能的计算，预测了合成含V_N、V_B的p-BN所需的化学条件：在富硼条件下，采用B₂H₄作为B源比采用B、α-B₁₂和BH₃等更有利于V_N的形成；而在富氮环境下采用N₂H₄作为N源比采用N₂、NH₃等更有利于V_B形成。为实验上有目的地合成高效吸附脱硫材料提供理论依据。

关键词: 计算化学, 吸附, 模拟, 多孔氮化硼, 燃油, 脱硫