A Molecularly Validated GPC Calibration Curve for Petroleum Pitch

A GPC/SEC calibration curve for petroleum pitches has been developed to replace the almost 50-year-old curve of Greinke and O’Connor (1980) still in general use today. The molecular standards selected for calibration were based on actual molecules recently imaged in M-50 petroleum pitch by ExxonMobil–Princeton researchers via noncontact atomic force microscopy (nc-AFM). Because the phenyl-chain oligomers that are key to G&O’s calibration curve were discovered to be absent in petroleum pitch, we replaced them with existing PAH standards congruous with imaging to the extent possible. In addition, pyrene dimer and trimer were synthesized in-house to serve as standards because pyrene-based molecules comprised more than 40% of the imaged structures. Pyrene oligomers were generated via the catalytic polymerization of pyrene, followed by supercritical toluene column extraction to isolate the pure dimer (400 Da) and trimer (598 Da) species. The proposed, molecularly validated calibration curve not only has a significantly higher R2 (0.975 vs G&O’s 0.875), but its molecular weight range has also been extended from 350 to 600 Da. Thus, this range now encompasses trimer species identified in petroleum pitches.