VACUUM PYROLYSIS MASS-SPECTROMETRY OF PITTSBURGH NO 8 COAL - COMPARISON OF 3 DIFFERENT, TIME-RESOLVED TECHNIQUES

Three different vacuum pyrolysis mass spectrometry techniques, viz., pyrolysis-field ionization mass spectrometry, thermogravimetry/low voltage electron ionization mass spectrometry, and Curie-point pyrolysis-low voltage electron ionization mass spectrometry, were used to analyze samples of Pittsburgh No. 8 coal obtained from the Argonne National Laboratory Premium Coal Sample Program. The primary objective was to assess the effects of differences in experimental techniques and conditions, e.g., with regard to heating rates, pyrolysis methods, and soft ionization procedures (FI vs low voltage EI) on the mass spectral patterns. A second objective was to further characterize and study the pyrolysis behavior of Pittsburgh No. 8 coal. The results indicate that the distribution and the type of the primary pyrolysis products are largely independent of marked differences in heating rate (10(-2)-10(4) K/s range) and sample size (2.5 x 10(-5) to 5.0 x 10(-2) g range) as well as overall vacuum pyrolysis MS configurations and conditions used. All three vacuum pyrolysis MS techniques produce remarkably similar mass spectral patterns when analyzing Pittsburgh No. 8 coal. The results show that Pittsburgh No. 8 coal contains a significant amount of low temperature (< 380-degrees-C) evolving "bitumen" consisting primarily of alkyl-substituted aromatic components. The bitumen evolution step is followed by partially overlapping "bulk pyrolysis" step characterized by the evolution of abundant hydroxy- and dihydroxy-substituted aromatic compounds, thought to be primarily derived from vitrinitic components. During the bitumen evolution step the average MW of the compounds increases with temperature while maintaining a relatively narrow distribution. By contrast, during the bulk pyrolysis step, the average MW tends to decrease while exhibiting a much broader distribution.