Fossil energy quarterly report, October 9, 1979-December 31, 1979

Abstract

Conditions for the chemical desulfurization of fine-size coals by leaching with hot alkaline solutions containing dissolved oxygen under pressure were investigated further. It was confirmed through experiments conducted with a 1-liter autoclave that about 46% of the organic sulfur can be removed from Illinois No. 6 coal by a single alkaline leaching step. Benefits of acidic and alkaline leaching conditions were compared. At higher oxygen partial pressures (e.g., 200 psia) the removal of pyritic sulfur from Illinois No. 6 coal seems to be favored by oxydesulfurization in an acidic solution while the removal of organic sulfur is favored by oxydesulfurization in an alkaline solution. Treatment of coal with methyl iodide followed by extensive washing with a solvent to remove the reaction products was used to remove approximately one-half of the organic sulfur content in an Iowa high volatile bituminous coal. The pyritic and sulfatic sulfur content was not affected by the methyl iodide treatment. Washing the coal with solvent only did not produce any effect either. On the basis of chemical reactions reported in the literature, it is assumed that the reactive sulfur groups that were removed by this treatment may be organic sulfides or mercaptans. Subsequent leachings of the methyl iodide-treated coal under various conditions of oxydesulfurization did not reduce further the organic sulfur content. The inorganic sulfur content, however, was reduced by the oxydesulfurization steps. It can be assumed that all the reactive and accessible organic sulfur was removed by the methyl iodide treatment, and further chemical desulfurization was directed only against the inorganic sulfur. A laboratory study of various conditions for the froth flotation method of cleaning a high volatile bituminous coal from the Dahm mine in Marion County, Iowa, produced some unusual results.