Characterisation of tars from the co-pyrolysis of waste lubricating oils with coal

Pyrolysis of a lubricating oil waste with or without coal yields important quantities of valuable products such as C-1-C-3 alkanes, C-2-C-4 olefins and BTX. However, information on molecular structures of tars obtained is only available in terms of analyses in the CC-MS ranges. This range corresponds to an upper limit of approximately 300 u; aromatics of mass greater than 300 u do not normally elute from high-temperature GC columns. For this reason, an oil tar, a coal tar and a tar obtained by the co-pyrolysis of the coal and oil (50:50 wt%) have been characterised by an array of techniques: probe-mass spectrometry (probe-MS) (to extend the range of mass to 600 u); size exclusion chromatography (SEC) in 1-methyl-2-pyrrolidinone (NMP) solvent; matrix-assisted laser desorption ionisation-mass spectrometry (MALDI-MS); and UV-fluorescence spectroscopy (UV-F) to provide specific information on chemical structures of products. Thin-layer chromatography (TLC) was also carried out for three samples of tar (from oil, coal and mixed oil/coal) and fractions recovered from the plates were analysed by other techniques: SEC, UV-F and probe-MS. In addition, the proportion of the tars amenable to gas chromatography was determined; CC-MS was used to determine the main components of each tar within the GC range. In summary, it can be concluded that Samca coal tar is mainly formed by large polynuclear aromatic ring systems, as well as by heterocyclic structures and alkyl or heteroatom substituents. The tar from the coal/oil mixture is much more similar to the tar from oil than to the tar from coal, reflecting the synergy in the co-pyrolysis reaction. (C) 2000 Elsevier Science Ltd. All rights: reserved.