Experimental Study on Organic Sulfur Removal in Bituminous Coal by a 1-Carboxymethyl-3-methyl Imidazolium Bisulfate...

In order to improve the total sulfur removal rate in coal combustion, an acidic ionic liquid (IL) 1-carboxymethyl-3-methylimidazolium hydrogen sulfate ([HOOCCH₂mim][HSO₄]) as the extractant combined with the oxidant 30% hydrogen peroxide (H₂O₂) was applied to reduce the total sulfur content, and its microscopic mechanism of desulfurization was analyzed. The experimental results show that the desulfurization rate of the [HOOCCH₂mim][HSO₄]-H₂O₂ (1:10) solution was 45.12% and the organic sulfur removal rate was 16.26%, which were significantly higher than those of only H₂O₂ or pure [HOOCCH₂mim][HSO₄]. Fourier-transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy analyses showed that the mercaptan -SH and disulfide -S-S- in coal decreased after being treated with IL-H₂O₂. In particular, the results of FTIR spectroscopy indicated that the relative proportion of -S-S-and -SH treated with IL-H₂O₂ (1:10) decreased by 31.9 and 27.2%, respectively, compared with that of a pure IL. This is due to H₂O₂ oxidation; -SH and -S-S- were oxidized to sulfoxide and then the sulfoxide transferred from the coal phase to the IL phase, which improved organic sulfur removal from coal. Therefore, the combination of an ionic liquid and H₂O₂ could increase the total desulfurization rate. In addition, the thermogravimetric analysis of coal is divided into four different stages; the weight loss during the combustion stage and the residues show that the IL-H₂O₂ could improve the coal combustion because of good previous swelling and destruction of bridge bonds and hydrogen bonding of coal. Besides, the fewer residues in IL-H₂O₂-treated coals also indicate that a less amount of inorganic substance is left in coal after IL-H₂O₂ desulfurization, which is consistent with the desulfurization results.