VHF EPR quantitation and speciation of organic sulfur in coal. Technical report, 1 March--31 May 1994

Abstract

The existence of free electrons in coals` natural state offers a great attraction for Electron Paramagnetic Resonance (EPR) analysis to aid in the study of the structure and composition of coal. This direct and non-destructive approach to coal analysis has been hindered by the problem of resolution using the conventional 9.5 GHz EPR spectrometers. In the past few years, the authors have developed techniques including W-band Very High Frequency EPR spectroscopy as a means of determining the quantity and structure of organic sulfur in native and desulfurized coals. The state-of-the-art 95 GHz (W-band) EPR spectrometer which they have constructed shows a well resolved spectrum including the interaction between unpaired electrons and the heteroatom like sulfur. The spectra also provide quantitative as well as qualitative information regarding different sulfur species. In this quarter, the authors have been concentrating their efforts on developing a new standard protocol in handling and preparing the coal samples for EPR measurements to provide a quantitative comparison between the EPR spectra of coal in the natural state and desulfurized. Sixteen new coal samples, both native and desulfurized, have been provided to us as well as to the University of Kentucky for analysis by XANES. These samples havemore » been run in both laboratories. The results from these samples, which were kept in an oxygen-free environment, are compared to those of 10 previous samples, which were air-oxidized. Significant differences in the EPR spectra of air-oxidized and oxygen free samples are noted; results from Kentucky are not yet available. Desulfurized samples show a significant decrease in organic sulfur as measured by the VHF-EPR method.« less