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The microwave-assisted hydrogen peroxide-citric acid desulfurization of coal was optimized by response surface methodology, and the samples were characterized before and after desulfurization by proximate analysis, ultimate analysis, sulfur forms determination, X-ray diffraction (×RD), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (×PS), and scanning electron microscopy (SEM) and so on. The quantum chemical calculations were selected to investigate desulfurization mechanism of microwave-assisted hydrogen peroxide-citric acid, and data analysis shows that the citric acid dose is the main factor affecting the desulfurization rate. Under optimized conditions, the actual desulfurization rate can reach 72.23%, the sulfur removal rate of pyrite up to 92.19%. The mineral content of the coal sample was significantly reduced. The oxygen-containing functional groups in the coal sample increased, and more inorganic sulfur and sulfoxide in the low valence state were oxidized to sulfone and sulfate in the high valence state. The microwave effect of pyrite will react with hydrogen ions to produce Fe2+, Fe2+ and citric acid reaction to form a complex. Quantum chemical calculations prove that the addition of an applied electric field can reduce the energy required for the coordination reaction and facilitate the reaction. [ABSTRACT FROM AUTHOR]

In order to investigate the effect of visible light irradiation on oxidative desulfurization. Three kinds of coals (SM, YYH and GZ) and four sulfur model compounds were selected as research objects. The effects of different irradiation time (30, 60, 90 and 120 min) and light source power (150, 220 and 300 W) of coal desulfurization were investigated. The samples before and after desulfurization were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS). The results show that when coal:H2O2 = 1:5 (g:mL), light source power is 220 W and irradiation is 60 min, the desulfurization rate of SM, YYH and GZ can reach the maximum, which were 27.97%, 56.28% and 66.22%, respectively. According to the characterization of samples before and after desulfurization, it was found that the low-valence sulfur changes into the high-valence sulfur with a more stable structure through a certain transition state during the desulfurization process. Coal responds to visible light, which can promote the generation of electron–hole pairs in the system, so as to enhance the oxidative desulfurization ability of the system. Visible light irradiation can promote the production of strong oxidation active group HO·, thereby improving the desulfurization rate of coal. [ABSTRACT FROM AUTHOR]