Distribution of Sulfur during Solvent Extraction of Coals and Desulfurization of Extracted Product

Three kinds of coal with different ranks and sulfur contents were extracted using 1-methyl naphthalene at 350 degrees C. The sample coals were fractionated into three fractions: a solvent-soluble fraction, a deposited fraction from the solvent-soluble fraction at room temperature, and the solvent-insoluble fraction. The forms of sulfur in the raw coals and the extracted products were determined by X-ray adsorption near edge structure analysis. Most of the inorganic sulfur was transferred to the solvent-insoluble fraction and the organic sulfur was distributed among the three fractions. Interestingly, the solvent-soluble fraction contained organic sulfur without inorganic sulfur, and only thiophenic sulfur was detected independent of coal type. Because of the high selectivity of imidazolium type ionic liquid for thiophenic sulfur, dimethyl imidazolium methyl sulfate was applied to extract the sulfur contained in the solvent-soluble fraction. The extractive experiment using ionic liquid showed that the sulfur content decreased linearly with the number of extraction stages. A high extent of desulfurization was obtained with a high concentration of ionic liquid.