Total acid number (TAN) is an important property which impacts refinery safety and corrosion management. TAN is normally determined by nonaqueous titration (ASTM D 664). It is believed that naphthenic acids is the major determinant for TAN value especially in high acid crude oil. In recent years, electrospray ionization (ESI) coupled with Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) has been used to quantitatively characterize petroleum acids and rapid determination of TAN. In these studies, the models were solely based on the related abundance of naphthenic acids, other acidic compounds, like phenols, generally were ignored.<br/>In this paper, phenols extracted from the residue fluid catalytic cracking (RFCC)-derived light cycle oil (LCO) and naphthenic acids extracted from Canadian oil sands bitumen (VTB) were mixed into four samples with different ratio. The titration results, based on ASTM D 664-11a, indicates that the phenols does contribute to TAN. However the contributions of phenols to TAN on same molar concentration is much less than the naphthenic acids, only about one twentieth. The naphthenic acids is the major determinant for TAN in crude oil, especially in high TAN crude oil. But in low TAN crude oil, if the concentration of phenols is much higher than the naphthenic acids, they could be the major determinant on the TAN value.<br/>The naphthenic acids, phenols and stearic acid (C18D35O2H) solutions were mixed and detected by ESI FT-ICR MS. The proportions of phenols, naphthenic acids and stearic acid in the six samples were consistent, but gradually increased with concentration. The relative abundance of naphthenic acids and stearic acid was constant in different concentration. But the relative abundance of phenols was gradually increased with the increasing of concentration. The response of the phenols is much lower than the naphthenic in the ESI FT-ICR MS. The response of the phenols per molar is about one twentieth to thirtieth of that of the naphthenic acids. In the mass spectra of some low TAN crude oil, the relative abundance of phenols is higher than the naphthenic acids. This suggests that the concentration of the phenols is much higher than the naphthenic acids. It also indicate that why using the related abundance of naphthenic acids to predict the TAN were not working well with low TAN crude oils.

Contribution to the total acid number of petroleum phenols and its response in electrospray mass spectrometry analysis

253rd National Meeting (2017)

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