(537f) Fractionation of An Oligomeric Pyrene Pitch Via Supercritical Extraction

Semi-continuous, packed-column supercritical extraction was investigated for the fractionation of a polycyclic aromatic hydrocarbon (PAH) pitch into its constituent oligomers.  The starting pitch had been produced by the catalytic polymerization of pure pyrene using AlCl₃.  Although neat supercritical toluene (Tc = 318.6 °C; Pc = 41.1 bar) was shown to be an effective solvent for the recovery of both monomer and dimer cuts in high purities, higher-oligomer solubilities in toluene are notoriously low.  However, the addition of N-methyl-2-pyrrolidone (NMP) as a co-solvent enhanced oligomer solubilities in the extractive, supercritical-solvent phase by a factor of 3, making possible the recovery of trimer and higher oligomers.  An unexpected benefit of the use of NMP is that it was found to suppress the condensation reaction between toluene and the pyrene oligomers that can occur in the extraction column at temperatures above 350 °C.  Apparently the NMP forms a Lewis acid-base complex with the AlCl₃ catalyst, preventing further reaction.  

In this talk, we demonstrate how pyrene dimer and trimer cuts can each be recovered from the starting pyrene pitch in good yields at purities exceeding 99%.  A supercritical co-solvent mixture consisting of 15 mol % NMP in supercritical toluene was found to be an effective solvent system for the desired separation.  The dramatically different properties from the starting mixture that the dimer and trimer each exhibit once they are isolated and obtained in high purity will also be shown.