Compositional Analysis of High-TAN Sudanese Crude Oil Using High-Resolution Mass Spectrometry and Study of the Effect of Temperature and Catalyst on Acidic Composition

Sudanese Fula crude oil, from the western region, is considered highly viscous and acidic and contains high amounts of heteroatoms (N and O) but a low sulfur content. This work presents an original and comprehensive analysis of its molecular composition in addition to an investigation of the effect of temperature and catalyst on the treatment of the acid fraction. The analysis was performed using a high-resolution Fourier transform mass spectrometer and Orbitrap-Elite with different ionization methods. The results reveal that the Fula crude oil contains a high abundance of nitrogen composition homologue classes N[H], NO2[H], and NO[H]. Their hydrocarbon composition includes low to high aromatic hydrocarbons. The number of oxygen classes varies from acids containing monocarboxylic acids of O-2 to acids of multiple carboxylic and phenolic group (CxHyO3 to CxHyO15) classes, which indicate a high content of acidic moiety of 0.765%. In addition to oxygen classes, the acidic fraction that is present as a NOx series indicates the presence of carboxylic carbazole acidic fraction. Low-temperature crude oil treatment at 200 degrees C decreases the intensity of acids. No significant reduction to low masses was observed; however, there was a clear reduction to high masses. At a high temperature of 350 degrees C, the carboxylic acid intensity increases (O2 classes), and thus, heating crude oil to 350 degrees C is unfavorable as it increases the amount of monocarboxylic acids, which are primarily responsible for corrosion in refinery units. Predicted TAN values of residual samples show a reduction in TAN of 62% using thermal treatment at 200 degrees C, whereas there is an increase in TAN of 5% at 350 degrees C. A great reduction in acidity results from catalytic treatment with a transition metal catalyst of cobalt and iridium complex. A reduction in all acidic oils is observed; however, the greater reduction is found in mono- and dicarboxylic acids. Catalytic treatment is shown to result in an 85% reduction in predicted TAN values.

Automated summary

Sudanese Fula crude oil from the western region is highly viscous and acidic, with high amounts of heteroatoms and low sulfur content. The molecular composition and treatment of the acid fraction are influenced by temperature and catalyst. Thermal treatment at 200 degrees C reduces acidity, while catalytic treatment with transition metal catalyst results in a significant reduction in acidic oils.