Asphaltene Characterization during Hydroprocessing by Ultrahigh-Resolution Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

Asphaltenes have a significant impact on the hychoprocessing of residues because they adversely affect the overall rate of hydroprocessing reactions. They also act as coke precursors, leading to catalyst deactivation. Understanding the changes of asphaltenes upon conversion can provide essential clues to the development and optimization of residue conversion processes. In this work, we use ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry (positive-ion mode atmospheric pressure photoionization) to follow asphaltene changes during the hydroprocessing of a residue. Asphaltenes were extracted from the feed and from two different products sampled, at various times (lining the run. Results indicate that intensities for hydrocarbon classes and N-containing classes increase for the processed asphaltenes, while the abundance of S Classes decreases. Similar results are found when the number of peak assignments is compared. The average double-bond equivalent (DBE) increases as a function of time on stream, which is usually associated with cyclization and aromatization reactions. However, the disappearance of molecules with low DBE as well as molecules with large DBE points to preferential cracking/hydrogenation of molecules in both regions. A small decrease in average:, molecular sizes is observed as a function of time on stream. In general, molecular size distributions for different DBEs are: narrower for the products than for the feed. The distributions also point to the disappearance Of the largest molecules from the products in accordance with the,preferential cracking previously reported for large molecules under hydroprocessing conditions. Analyses of the more abundant classes revealed trends that vary depending upon the type of heteroatoms as well as their relative amount within the molecules.