A DFT Study of the Extractive Desulfurization Mechanism by [BMIM]⁺[AlCl₄]⁻ Ionic Liquid

Abstract

In this work, the interaction nature between [BMIM](+)[AlCl4](-) ionic liquid (IL) and aromatic sulfur compounds (thiophene, benzothiophene, and dibenzothiophene) has been studied by means of density functional theory (M06-2X functional) combined with an implicit solvation model. Although [BMIM](+)[AlCl4](-) is a metal-containing IL, its extractive desulfurization mechanism is different from other metal-containing ILs but similar to non-metal-containing ILs. Important reactions involved in extractive desulfurization (EDS) were systematically studied. Our results have demonstrated that both the cation and the anion play important roles in EDS. On the basis of the structure analysis, reduced density gradient analaysis (RDG), and energy decomposition analysis, [BMIM](+) cation affords a π-π interaction while [AlCl4](-) anion provides a hydrogen bonding interaction. Electrostatic potential analysis implies the dominant π-π interaction and hydrogen bonding interaction are driven by electrostatic interaction between IL and aromatic sulfur compounds. Interaction energy between [BMIM](+)[AlCl4](-) and thiophene (TH), benzothiophene (BT), and dibenzothiophene (DBT) follows the order TH < BT < DBT. Moreover, Al-containing IL with a high molar ratio of AlCl3 ([BMIMCl]/2[AlCl3]) has also been studied. Results show that [Al2Cl7](-) species will be formed with excess AlCl3. However, the [Al2Cl7](-)-based IL cannot improve the EDS performance. Improvement of EDS performance with a high molar ratio of AlCl3 is credited to the Lewis acidity of AlCl3. Charge analysis reveals that there is no obvious charge transfer during the reaction, which is different from Fe-containing ILs as well as solid sorbents. In addition, CH-π interaction is not important for the current system.

The selectivity for sulfur removal from oils: An insight from conceptual density functional theory

“…For EDS, researchers proposed that hydrogen bonding interactions, π‐π interactions, as well as CH‐π interactions were the main interactions in EDS (Figure d). Our previous work have shown that the essence of those interactions probably arise from electrostatic interaction between solvents and aromatic sulfur compounds …”

“…Generally speaking, the selectivity for sulfur removal may depend on different physical properties of sulfides for different desulfurization methods but not only depend on the electron density of S atom. For example, in ADS and EDS, the mechanisms show that the selectivity may be determined by the properties of whole molecules but not the electron density of S atom . To find out the relationship between physical properties of sulfides and the selectivity, we have systematically explored this issue by using CDFT for the first time.…”

Vibrational analysis and formation mechanism of typical deep eutectic solvents: An experimental and theoretical study

“…It is well known that electrostatic potential (ESP) analysis, as a reflection of electron density, is significant for noncovalent interaction systems. [58][59][60] For noncovalent interaction systems, van der Waals interactions, hydrogen bonding interactions and other interactions may coexist. All of them or just a few kinds of noncovalent interaction may play important roles in the weak interaction for different noncovalent systems.…”

The CO2 Absorption in Flue Gas Using Mixed Ionic Liquids

“…All calculations were carried out by the Gaussian 16 program [30]. For IL calculations, Li et al [31] suggested that the density function of the Minnesota family [32] (e.g., M06-2X) with a diffusion function basis set (e.g., 6-311++G(d,p)) might give reasonable results. If dispersion-corrected density functionals (e.g., gd3bj, DFT-D3) were used, more reliable results could be obtained [33].…”