Theoretical investigation of the interaction between aromatic sulfur compounds and [BMIM]+[FeCl4]− ionic liquid in desulfurization: A novel charge transfer mechanism

•A coordination structure has been found in extractive desulfurization by using [BMIM]+[FeCl4]− ionic liquid.•Interaction energy and extraction selectivity follow the order: TS < DBT ≈ BT.•The alkyl group for TS and BT may improve the interaction energy and extraction selectivity.•NBO results show that the mechanism of this extractive desulfurization is determined by charge transfer.

In this work, interaction nature between a group of aromatic sulfur compounds and [BMIM]+[FeCl4]− have been investigated by density functional theory (DFT). A coordination structure is found to be critical to the mechanism of extractive desulfurization. Interaction energy and extractive selectivity follow the order: thiophene (TH) < dibenzothiophene (DBT) ≈ benzothiophene (BT). Alkylation of TH or BT (e.g. 3-methylthiophene, and 3-methylbenzothiophene) leads to a stronger interaction with ionic liquid, but steric hindrance effects of some alkylic derivatives (e.g. 2,7-dimethylbenzothiophene) lead to a weaker interaction with ionic liquid. The mechanism of extractive desulfurization is attributed to the charge transfer effect. During extractive desulfurization, electrons on aromatic sulfur compounds transfer into the Lewis part of ionic liquid, namely, [FeCl4]−. Furthermore, it is better to consider the Lewis acidity of Fe-containing ionic liquid by the whole unit (such as [FeCl4]− and aromatic sulfur compounds (X)) rather than only Fe or S atom.

Graphical abstractDesulfurization of aromatic sulfur compounds is attributed to a coordination interaction by [BMIM]+[FeCl4]− ionic liquid. The interaction energy and selectivity is linearly related to the amount of charge transfer between them.Figure optionsDownload full-size imageDownload high-quality image (146 K)Download as PowerPoint slide