Most structures found in textbooks or publications are hypothetic or proposed (average) structures, derived from bulk chemical analysis, such as NMR, MS, FT-IR, UV-vis, EPR, elemental analysis, or scattering techniques, etc. However, advanced characterization techniques revealed that petroleum is an extremely complex molecular mixture, containing at least hundreds of thousands of species. Therefore, a huge uncertainty could be expected in our current understanding on petroleum molecules. Recently, the molecular imaging noncontact AFM technique has been applied to characterize individual molecules in petroleum in real space, and a summary of some recent findings will be presented in this talk.<br/>Numerous novel polycyclic aromatic hydrocarbons (PAHs) have been discovered, with various degrees of condensation and substitutions by heteroatoms and aliphatic groups. Both alternant and nonalternant PAHs are present in the PAH structures, including benzenoids, and two types of five-membered ring structures. Few structures have been found to contain more than one PAHs so far. In order to address some long-standing questions regarding petroleum asphaltene structures, studied of model compounds have been conducted to shed light onto the structure of real petroleum molecules. In addition, recent applications to characterize petroleum pitch materials and decipher thermal reaction mechanism will be presented. Lastly, the advantages and challenges of applying nc-AFM will be discussed on characterizing petroleum mixtures, including representativeness of molecules, impact of sample preparation on structural integrity, and the identification of common features and reactive sites among diverse molecules. These new insights into petroleum molecules are poised to have a profound impact on the petroleum and energy industry by providing a foundation to study structure-reactivity relationships or other properties or behaviors.

Unlocking the value of petroleum through structure characterization with nc-AFM molecular imaging

ACS Fall 2021

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