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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]

The desulfurization effect of Ningxia Shuangma coal (SM) with an acetic acid-hydrogen peroxide system assisted by microwave, ultrasonic and ultraviolet light was compared. The results show that microwave-assisted desulfurization has the best effect. When the microwave power is 900W, the irradiation time is 5 min, and the volume ratio of acetic acid to hydrogen peroxide is 1:10, the desulfurization rate can reach 55.82%. Moreover, microwave-assisted desulfurization can effectively improve the removal effect of organic sulfur. XRD, XPS, SEM and other characterization showed that microwave assisted can effectively reduce the mineral content, expose more sulfur-containing groups, and improve the desulfurization effect. The desulfurization rate of three sulfur-containing compounds is: dibenzyl sulfide > diphenyl sulfoxide > benzothiophene. With the increase of intensity of the applied electric field, the C–S bond gets easier to fracture, the applied electric field can reduce the reaction energy barrier, is a benefit to the reaction. [ABSTRACT FROM AUTHOR]

To research the efficient and economical desulfurization of Lingshi high sulfur coal (LS), the influence of acid and alkaline additives on an ultraviolet (UV) light oxidation desulfurization system was assessed. Sodium hydroxide (NaOH) and oxalic acid (OA) were selected as the alkaline and acid additives, respectively, to investigate whether acid and alkaline additives could promote oxidative desulfurization in the UV–H2O2 system. The coal samples were investigated via scanning electron microscopy (SEM), Brannuer–Emmett–Teller analysis (BET), contact angle analysis (CA), Fourier transform infrared spectroscopy (FTIR), X-ray diffractometry (XRD), and X-ray photoelectron spectroscopy (XPS). In addition, the desulfurization mechanism, including sulfur removal, sulfur conversion, and change of coal surface morphology on the reaction, was investigated. The results demonstrated that the surface morphology and the pore structure in coal improved; the wettability and oxygen-containing functional groups increased after the action of NaOH and OA, which indicated that the oxidation was enhanced during the reaction. This study proved that strong oxidation promoted the efficient removal of sulfur from coal samples, where NaOH reacted strongly with pyrite, and OA influenced the removal of organic sulfur, which played a directional desulfurization effect. [ABSTRACT FROM AUTHOR]