VARIATIONS IN THE STABLE-ISOTOPE RATIOS OF SPECIFIC AROMATIC AND ALIPHATIC-HYDROCARBONS FROM COAL CONVERSION PROCESSES

To establish the scope for applying gas chromatography-isotope ratio m ass spectrometry (delta(13)C GC-IRMS) to molecular recognition problem s in coal utilisation,C-13/C-12 isotope ratios were determined for n-a lkanes and polycyclic aromatic hydrocarbons (PAHs) as a function of co al 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 fluid ised-bed (flash) pyrolysis, No significant variations in the stable is otope ratios of n-alkanes mere 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 parts per thousa nd) being similar to the bulk values of the initial coals and being is otopically heavier (less negative) than their fluidised-bed pyrolysis counterparts by 2-3 parts per thousand, However, the PAHs from fluidis ed-bed pyrolysis, which resemble closely those obtained from high temp erature coal carbonisation, are still heavier (by 2-3 parts per thousa nd) than those from diesel particulates and coal gasification and comb ustion residues. This provides a firm basis for the source apportionme nt of airborne PAHs in the proximity of coking plants, particularly wi th no major variations in the PAH isotope ratios being found as a func tion of rank.