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

Haifa Shamseldin Mohamed Salim; Ibrahim Mohamed Ahmed; Mustafa Abbas Mustafa

doi:10.1021/acsomega.2c01871

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

ACS Omega. 2022 May 13;7(20):17472-17482. doi: 10.1021/acsomega.2c01871. eCollection 2022 May 24.

Authors

Haifa Shamseldin Mohamed Salim¹, Ibrahim Mohamed Ahmed², Mustafa Abbas Mustafa³

Affiliations

¹ Department of Basic Science and Engineering, Faculty of Engineering, University of Khartoum, P.O. Box 321, Khartoum, Sudan.
² Department of Chemistry, Faculty of Science, University of Khartoum, P.O. Box 321, Khartoum, Sudan.
³ Department of Chemical Engineering, Faculty of Engineering, University of Khartoum, P.O. Box 321, Khartoum, Sudan.

Abstract

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 O₂ to acids of multiple carboxylic and phenolic group (C _x H _y O₃ to C _x H _y O₁₅) 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 NO _x series indicates the presence of carboxylic carbazole acidic fraction. Low-temperature crude oil treatment at 200 °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 °C, the carboxylic acid intensity increases (O₂ classes), and thus, heating crude oil to 350 °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 °C, whereas there is an increase in TAN of 5% at 350 °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.