Molecular-Level Characterization of Refinery Streams by High-Resolution Mass Spectrometry

Compositional changes of hydrocarbon fractions affect the physical properties and performance for a specific application. Various techniques, such as liquid chromatography and nuclear magnetic resonance spectroscopy, are normally used for determination of hydrocarbon analysis in petroleum fractions. These techniques provide limited information regarding the hydrocarbon classes. Mass spectrometry offers a unique advantage over these techniques by providing detailed information on hydrocarbon classes present in samples. Commonly used methods in mass spectrometry provide 19, 22, and 33 classes of hydrocarbons in petroleum fractions. These methods are useful in understanding relative changes in composition in the samples during further processing in refineries. The major problem with these methods is validation of results, which poses a challenge to researchers. In the present study, a high-resolution mass spectrometry (HR-MS) technique has been optimized to characterize the petroleum fractions in terms of 33 hydrocarbon classes (HC33), comprising S classes of saturates, 13 classes of aromatics, and 15 classes of sulfur aromatics, for detailed hydrocarbon-type analysis. About 40 samples covering a wide range of petroleum streams, such as light cycle oil (LCO), clarified light oil (CLO), and vacuum gas oil (VGO), in the boiling range of 170-650 degrees C have been analyzed for 33 classes of hydrocarbons. To validate the results, a correlation of sulfur compounds by HC33 with the total sulfur content as determined by wavelength-dispersive X-ray fluorescence (WDXRF) has been carried out. The saturate content was determined using saturates, aromatics, resins, and asphaltenes (SARA) by thin-layer chromatography flame ionization detection (TLC-FID) and compared to that obtained by HC33 for the samples. Results obtained from HC22 and HC33 methods were also correlated through analysis of variance for saturate, aromatic, and sulfur aromatic classes. The observed F value for the groups is less than F critical, indicating there is no significant difference between the two methods. Further, on the basis of mass spectrometry analysis, a case study on the importance of detailed hydrocarbon-type analysis (33 classes) for problem solving in VGO hydroprocessing has been reported.