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To establish the scope for applying gas chromatography–isotope ratio mass spectrometry (δ13C GC–IRMS) to molecular recognition problems in coal utilisation, 13C/12C isotope ratios were determined for n-alkanes and polycyclic aromatic hydrocarbons (PAHs) as a function of coal rank and process conditions. Six coals ranging from a lignite to a low volatile bituminous coal were subjected to chloroform extraction, fixed-bed pyrolysis under hydrogen pressure (hydropyrolysis) and fluidised-bed (flash) pyrolysis. No significant variations in the stable isotope ratios of n-alkanes were evident as a function of either rank or conversion regime. In contrast, the isotope ratios of PAHs show large variations with those for hydropyrolysis (–23 to –25‰) being similar to the bulk values of the initial coals and being isotopically heavier (less negative) than their fluidised-bed pyrolysis counterparts by 2–3‰. However, the PAHs from fluidised-bed pyrolysis, which resemble closely those obtained from high temperature coal carbonisation, are still heavier (by 2–3‰) than those from diesel particulates and coal gasification and combustion residues. This provides a firm basis for the source apportionment of airborne PAHs in the proximity of coking plants, particularly with no major variations in the PAH isotope ratios being found as a function of rank.
Six coals, ranging in rank from a lignite to a low volatile bituminous coal, were subjected to CHCl3 extraction, fixed-bed hydropyrolysis at 650°C and fluidised-bed pyrolysis at 900°C. The resulting tars and extracts were fractionated to yield aliphatic and aromatic fractions. The components of the fractions were separated by GC and their C-13/C-12 isotope ratios were determined by MS (details given). No significant variations in the isotope ratios of n-alkanes were found as a function of either coal rank or conversion process. In contrast, the isotope ratios of PAH showed large variations with processing conditions. Those from hydropyrolysis were isotopically heavier than their counterparts from fluidised-bed pyrolysis by 2-3%. No major variations in PAH isotope ratios were evident with increasing coal rank.
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