Polycyclic aromatic structure distributions by high-resolution mass spectrometry

Polycyclic aromatic compounds are an important component of many high-boiling petroleum products. A detailed analytical description of the polycyclic aromatic structure distribution is useful for assessing the exact effects of refining processes, such as solvent extraction and hydrotreating, that alter or remove these compounds. High-resolution, low-voltage mass spectrometry was used to characterize the clay gel aromatics fractions of a petroleum vacuum distillate and three lubricant base oils that are derived from it. Proprietary methods were used to extract and hydrotreat the distillate, and different levels of severity were employed. The measurements were made with a Kratos MS50 mass spectrometer, using Exxon proprietary computer programs for data analysis. The programs allow the determination of concentrations for as many as 5,000 individual carbon number homologues and over 100 compound types. The polycyclic aromatic structure distributions of the oils are defined by the use of Z-number terminology and side-chain carbon number distributions. Structures specifically identified are the most probable ones, although other isomers cannot be totally excluded from consideration.