SULFUR REMOVAL FROM COAL BY ANALYTICAL-SCALE SUPERCRITICAL-FLUID EXTRACTION (SFE) UNDER PYROLYSIS CONDITIONS

Sulfur removal methods were developed using analytical-scale supercrit ical fluid extraction (SFE) under pyrolysis (450-degrees-C) conditions on a bituminous coal sample (IBC-101) obtained from the Illinois Basi n 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 supercriti cal CO2 (40.53 MPa) under pyrolysis-SFE conditions. Using on-line SFE gas chromatography-mass spectrometry (SFE-g.c.-m.s.), the major organi c sulfur forms removed by pyrolysis-SFE were identified as alkyl-thiop henes (C0-C5). When phosphoric acid was added to the coal prior to pyr olysis-SFE, about 80% of the total sulfur was removed from both coals regardless of whether the sulfatic sulfur, or both the sulfatic and py ritic sulfur, were removed (by HCl and HNO3 extraction, respectively) prior to pyrolysis-SFE. These results demonstrate that the major fract ion of sulfatic, pyritic and organic sulfur were extracted in the pres ence of phosphoric acid. In contrast, pyrolysis-SFE with CO2-methanol appears to preferentially extract organic sulfur species, since only a bout 60% of the total sulfur was removed from the raw coal by pyrolysi s-SFE using CO2 modified with 10% methanol, while about 80% of the tot al sulfur was extracted if the sulfatic and pyritic sulfur were remove d prior to extraction.