Photocatalytic enhanced HO₂MMimHSO₄−H₂O₂ removal of organic sulfur from coal

Coal is considered one of the largest energy sources globally, but the sulfur in coal combustion seriously affects the efficient utilization of coal. Moreover, the sulfide produced by burning high sulfur coal is one of the leading causes of several diseases and environmental pollution. Incorporating photocatalytic oxidation into the extraction desulfurization system can significantly improve the efficiency of ionic liquid reactive extraction desulfurization. To further study the mechanism of desulfurization, experiment and computer simulation were used to analyze it. The experimental results show that coupling the photocatalytic reaction process and the ionic liquid extraction process can effectively remove organic sulfur in coal. The desulfurization rate of organic sulfur in the coal treated by HO₂MMimHSO₄–H₂O–H₂O₂–TiO₂（mass ratio 5∶5∶10∶4）can reach 12.40%. In addition, an appropriate amount of water can improve the desulfurization rate of coal, but an excessive amount of aqueous solution can reduce the concentration of hydrogen peroxide and the organic sulfur desulfurization rate in coal. Materials Studio analysis shows that the hydroxyl radical (·OH) generated by photocatalytic activity has strong oxidability, and the area near the oxygen atom of ·OH is electronegative, which is easy to form S=O double bond with the positively charged S atom in thiophene via electrostatic attraction. In addition, the addition of ionic liquid makes the original lowest vacant orbital on the thiophene ring disappear. Moreover, it lowers the energy level difference between the HOMO and the LUMO, making the reaction easier to proceed with. Using COSMO analysis, it is found that the five-member heterocyclic structure of imidazole in HO₂MMimHSO₄ formed bonds with thiophene and sulfone molecules through van der Waals forces; thus, sulfide was constantly extracted into the ionic liquid phase and that adding the oxidizer can make it easier for sulfone with higher chemical potential to enter the lower chemical potential ionic solution HO₂MMimHSO₄ than thiophene.