Chemical desulfurization of coal with hydroiodic acid

A novel method for the chemical desulfurization of coal in relatively moderate conditions and short times is presented. Using concentrated hydroiodic acid as a desulfurizing agent and microwaves as the energy source, sulfate and pyritic sulfur are completely removed in 10 min. Moreover, for the low-rank coals studied, variable amounts of organic sulfur, up to 70% in 20 min, can be removed, for a total sulfur (organic + pyritic) elimination greater than 80%. The study of the process shows that time and temperature of the reaction are the main factors affecting the desulfurization process. Experiments with other acids and lower concentrations showed low yields, the special characteristics of the concentrated hydroiodic acid being the driving force of the reaction. Experiments carried out at different microwave power did not show any singular effect of the microwave irradiation on the removal of sulfur.