Characterization of large nonvolatile polyaromatic molecules by a combination of in-source pyrolysis and field desorption mass spectrometry

Nonvolatile hydrocarbon systems, such as those formed via molecular weight growth reactions in refinery processes, normally have a low H/C atomic rati os (<0.5) and high boiling/decomposition points (> 600 degreesC). These mat erials pose a great challenge to mass spectrometric analysis due to difficu lties in vaporization and ionization. In this work, the combination of In-S ource Pyrolysis Mass Spectrometry (ISPyMS) and Field Desorption Mass Spectr ometry (FDMS) were utilized to obtain compositional information for a nonvo latile organic deposit (foulant) generated by a hydrocracking process. A mi xture of polystyrene standards was also analyzed for reference purposes. FD MS yields intact molecular ions for the large polyaromatic systems (similar to 15 aromatic rings on average). ISPyMS, on the other hand, converts the large multi-core aromatic systems into relatively small single aromatic cor es that could be analyzed in detail. In this case, 28 aromatic cores contai ning short alkyl chains were identified by ISPyMS. Average foulant composit ion was projected on the basis of IsPyMS and FDMS data. The projected WC at omic ratio and aliphatic carbon/aromatic ratio match well with those measur ed by elemental analysis and solid-state C-13 NMR.