Evaluation on the microwave-assisted chemical desulfurization for organic sulfur removal

Coal desulfurization is imperative to create clean coal and reducing harmful emissions during the combustion process. However, organic sulfur in coal is more difficult to remove than inorganic sulfur. Therefore, in this paper, a method of coal sample desulfurization using citric acid with microwave assisted was proposed, and experimental investigation was carried out. The influences of the particle size, reaction temperature, irradiation time, microwave power, and concentration of citric acid on desulfurization effect were studied and the corresponding optimal value was determined. The desulfurization effect was improved; the remove efficiencies of the total sulfur, organic sulfur and inorganic sulfur were 34.25%, 59.86% and 20.23%, respectively. In addition, XRD and FTIR were used to test and compare the coal samples before and after the experiment, and it was found that pyrite was transformed into H2S, S and the Fe2+ which was combined with citric acid to form a complex; The carbon-sulfur bond of sulfonate and the iron-sulfur bond of ferrous sulfide are both broken; Clean coal has a smoother surface. In general, microwave-assisted citric acid could potentially remove organic sulfur without any significant interference of the calorific value on coal. And compared with other desulfurizers, citric acid has the advantages of good desulfurization effect (especially organic sulfur), non-toxic, low corrosion and low cost, etc. The current research work may provide new routes and meaningful guidelines to pre-combustion desulfurization of coal