Semi-continuous, packed-column supercritical extraction (SCE) with toluene and toluene-NMP (N-methylpyrrolidone) mixtures was used to fractionate various polycyclic aromatic hydrocarbon (PAH) pitches into their constituent oligomers. In particular, the starting model pitch samples were produced by the catalytic polymerization of pure pyrene using AlCl3, or by thermal polymerization, with both being done at temperatures from 300-500 °C. Each sample was reacted for a different period of time to vary the oligomeric composition of the final pitch product, such that kinetic data on the pyrene polymerization process could be obtained.
SCE was used to separate each sample into its constituent oligomers, such that an oligmeric mass balance could be performed on the reacted pitch products. The co-solvent NMP provided enhanced solvent power for extracting the higher MW oligomers from the pitch; furthermore, NMP serves as a valuable suppressant of the condensation reactions that can occur between toluene and the pyrene oligomers at the elevated temperatures necessary for SCE, thus keeping product purities high.
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