Microwave-assisted removal of sulfur in large particle size coal by bromine water

Aiming at the difficulty of desulfurization of large-size and high-sulfur coal, especially organic sulfur, a new microwave-assisted bromine water removal method was proposed. In this experiment, Gaoyang (GY) and Shuiyu (SY) clean coal were used as research objects, bromine water was used as a solvent, and coal samples were irradiated with microwaves. The effects of coal sample type, particle size, microwave time, and reaction times on coal desulfurization are specifically studied. The results show that bromine water can effectively remove organic sulfur in coal. After 5 repeated reactions, the desulfurization rate of coal samples can reach 90%. In order to explore the change pattern of sulfur element form and content, X-ray photoelectron spectroscopy (XPS) was used to analyze the change of sulfur form in the solid phase (coal). Ion chromatography (IC) was used to analyze the form of sulfur in the liquid phase after the reaction. The results show that GY and SY clean coal have high organic sulfide sulfur content, of which thiophene is the main component, accounting for more than 70%, followed by sulfones and thiols. After the bromine water-microwave treatment, the content of thiol, thioether and thiophene on the coal surface decreased, and the sulfones increased. The thiol in coal was more easily removed than thiophene and sulfoxide, and the sulfur form gradually changed to a higher valence state during desulfurization. The results of ion chromatography identification showed that the filtrate contained a large amount of Br− and SO42− ions. Combining with the results of Fourier transform infrared spectrum (FTIR), the content of aliphatic hydrocarbon structure decreased, the oxygen-containing functional group increased, and bromine substituted groups appeared. It is speculated that the sulfur-containing bonds are broken in the microwave field and can be finally removed by HBrO oxidation to soluble sulfate.