Vacuum pyrolysis mass spectrometry of Pittsburgh No. 8 coal: comparison of three different, time-resolved techniques

Abstract

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 (10-2-104 K/s range) and sample size (2.5 X 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 " 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.to 5.0 X

Thermal Program Desorption Mass Spectrometry of PAHs from Mineral and Organic Surfaces

“…A higher temperature ramp rate did not allow time for the PAH molecular weight 178 (phenanthrene and anthracene) to show a desorption curve on a consistent basis with some of the materials tested. A shift toward higher peak temperatures for desorption response with increased heating rate has been described by Yun and Meuzelaar (1991). In that case, the PAH could be released at a slightly elevated temperature because there maybe insufficient time for temperature equilibration.…”

“…Various adaptations of thermal program desorption (TPD) techniques have been used in the past to study: desorption of gases from solid surfaces (Falconer and Madix, 1975;King, 1975), desorption of toluene from kaolin pellets (Keys and Silcox, 1994), pyrolysis of hydrocarbons from coal (Yun and Meuzelaar, 1991), estimation of PAH vapor pressures (Oja and Suuberg, 1997;Tesconi and Yalkowski, 1998), and desorption activation energies of trichloroethylene from silica gel (Farrell et al, 1999). Thermal desorption techniques have also been explored for their utility in detecting and quantifying organic contaminants in soil samples (Robbat et al, 1992).…”

“…The use of a direct insertion probe, which does not require transfer lines, with a mass spectrometer (MS) can allow measurement of the release of trace organics from very small samples. Direct probes have been used for the analysis of coal pyrolysis products by Yun and Meuzelaar (1991). To date, thermal desorption mass spectrometry with direct probes has been used for study of pyrolysis and as a means for inserting a sample into a mass spectrometer for compound identification.…”

Mass spectrometric profiling and pattern recognition

“…In several reviews, this extended research area has been summarized (4, [120][121][122][123]. Major areas of interest are fossil biomaterials such as coals, kerogens, bitumen and asphaltenes (11,77,78,120,(123)(124)(125)(126)(127)(128), and oil shales (122,125). Materials of recent geological history such as peat (129,130), soil humic acids, and soil organic matter (131)(132)(133) have also been investigated (134)(135)(136).…”

Preliminary Surface Structure Transition of Coal Particles during Prepyrolysis with CO2 Laser

“…Structural changes such as macromolecular relaxation and thermoplastic transitions in coal organic matters at temperature lower than 500 °C are important from the view of their utilization processes such as carbonization, gasification, liquefaction, and combustion. Studies based on 1 H NMR, , pyrolysis−mass spectrometry, , and field ionization mass spectrometry , have strongly suggested that a fundamentally different process is occurring at the low-temperature region in contrast to the ensuing pyrolytic process involving chemical decomposition. The committee for New Concepts on Coal Carbonization Control for Coke Production, the Iron and Steel Institute of Japan, has recently proposed a novel method comprising rapid preheating of coal up to around 450 °C and subsequent carbonization of coal softened.…”