1989
DOI: 10.1021/ef00016a015
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Limitations of electron spin resonance spectroscopy in assessing the role of free radicals in the thermal reactions of coal

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Cited by 40 publications
(19 citation statements)
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“…For semicoke, the N g increases with an increase in temperature and reaches more than 1.5 × 10 19 spins/g semicoke at 550 °C. Fowler 12 reported that EPR changes in coal during the pyrolysis process were ascribed to the complex interplay between stable free-radical species. As the temperature increases, the strong bonds in oil shale molecule are broken to accelerate the forming rate of free radicals, resulting in an increase of N g in semicoke.…”
Section: Resultsmentioning
confidence: 99%
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“…For semicoke, the N g increases with an increase in temperature and reaches more than 1.5 × 10 19 spins/g semicoke at 550 °C. Fowler 12 reported that EPR changes in coal during the pyrolysis process were ascribed to the complex interplay between stable free-radical species. As the temperature increases, the strong bonds in oil shale molecule are broken to accelerate the forming rate of free radicals, resulting in an increase of N g in semicoke.…”
Section: Resultsmentioning
confidence: 99%
“…In 1989, using a simulation based on a conceptual model, it was proven that the Ng variation of coal was caused by complex interactions between steady-state and unsteady-state free radical species. However, the concentration of unsteady-state free radicals was too low to be detected with EPR . In 1992, Silbernagel and Gebhard reported that the Ng of free radicals increased after demineralization by either citric acid wash or HCl/HF treatments.…”
Section: Introductionmentioning
confidence: 99%
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“…The works that have been carried out include those on behavior of total radicals [8,9] and those on kinetic models [10,11]. However, because most of the radical reactions are too faster to be measured by ESR [12], ESR data show only stable radicals that are either poor in mobility or confined in rigid structures that constitutes steric hindrance to other radicals [7,13]. Therefore, many researchers doubted about the ESR's capability in monitoring the active radicals.…”
Section: Introductionmentioning
confidence: 99%
“…More free radicals were proposed to be present in the char matrix. However, many of the radicals generated during pyrolysis were hypothesized to be ESR silent [30] or to disappear from the char matrix after pyrolysis [31e34]. Kihedu et al [35] reported that free radicals produced during bond breaking in fuels with a high hydrogen level, may prevent repolymerization/cross-linking reactions by the hydrogen donor-acceptor mechanism and therefore decrease the char yield.…”
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confidence: 99%