Sulfur removal from coal by analytical-scale supercritical fluid extraction (SFE) under pyrolysis conditions

Abstract

Sulfur removal methods were developed using analytical-scale supercritical fluid extraction (SFE) under pyrolysis (450 °C) conditions on a bituminous coal sample (IBC-101) obtained from the Illinois Basin Coal Sample Program (IBCSP) and on physically cleaned Indiana No. 3 coal samples from AMAX Research and Development Center. Approximately one-half of the total sulfur was removed from IBC-101 using supercritical CO 2 (40.53 MPa) under pyrolysis-SFE conditions. Using on-line SFE gas chromatography-mass spectrometry (SFE-g.c.-m.s.), the major organic sulfur forms removed by pyrolysis-SFE were identified as alkyl-thiophenes (C 0-C 5). When phosphoric acid was added to the coal prior to pyrolysis-SFE, about 80% of the total sulfur was removed from both coals regardless of whether the sulfatic sulfur, or both the sulfatic and pyritic sulfur, were removed (by HCl and HNO 3 extraction, respectively) prior to pyrolysis-SFE. These results demonstrate that the major fraction of sulfatic, pyritic and organic sulfur were extracted in the presence of phosphoric acid. In contrast, pyrolysis-SFE with CO 2-methanol appears to preferentially extract organic sulfur species, since only about 60% of the total sulfur was removed from the raw coal by pyrolysis-SFE using CO 2 modified with 10% methanol, while about 80% of the total sulfur was extracted if the sulfatic and pyritic sulfur were removed prior to extraction.