Coal Desulfurization by Microwave Irradiation and Sodium Hydroxide Leaching

The effect of microwave power, treatment time, NaOH mass fraction and mass ratio of solution to coal on the removal of organic sulfur in Xinyu coal from Shanxi province was studied, and change of functional groups and contents of different forms of sulfur after microwave irradiation were also characterized. Compared with single treatment respectively, microwave irradiation combined with NaOH treatment can remove much more organic sulfur in coal. Under the optimum conditions of microwave power of 385 W, treatment time of 30 min, NaOH mass fraction of 10% and the mass ratio of solution to coal of 10:1, the desulfurization rate can reach up to 62.66%. Diffraction intensities of different forms of sulfur in coal decreased obviously after microwave irradiation, and the diffraction intensities of aliphatic structure were also weakened. The difficulties of organic sufur removal of different forms followed the order: thioalcohol and thioether < sulfone < sulfoxide < thiophene. The removal rate of thioalcohol and thioether can reach up to 89.87% under the optimum conditions mentioned above, and that of sulfone, sulfoxide and thiophene were 79.74%, 44.30% and 14.07%, respectively. The mechanism of microwave desulfurization is mainly due to that the microwave can promote the reaction between organic sulfur and NaOH, and can also promote the cleavage of C-S band directly.