Structural elucidation of Argonne premium coals: Molecular weights, heteroatom distributions and linkages between clusters

摘要

The objective of this study is to create a statistically accurate picture of important structural features for a group of coals representing a broad rank range. Mass spectrometric techniques are used to study coals, coal extracts and chemically modified coals and extracts. Laser desorption mass spectrometry is used to determine molecular weight distributions. Desorption chemical ionization high resolution mass spectrometry provides detailed molecular information on compound classes of molecules is obtained using tandem mass spectrometry. These results are correlated with other direct studies on these samples such as solid NMR, XPS and X-ray absorption spectroscopy. From the complex sets of data, several general trends are emerging especially for heteroatom containing species. From a statistical point of view, heteroatoms must play important roles in the reactivity of all coals. Direct characterization of sulfur containing species in the Argonne coals has been reported from XANES analysis. Indirect methods used include: TG-FTIR and HRMS which rely on thermal desorption and pyrolysis to vaporize the samples. Both XANES and XPS data on nitrogen has been reported, but at this time, the XPS information is probably more reliable. Results from HRMS are discussed in this paper. Most other information on nitrogen is limited to analysis of liquefaction products. However, nitrogen can be important in influencing characteristics of coal liquids and as a source of NO(sub x)'s in coal combustion.