Chemical composition and molecular structure of asphaltene in Azerbaijani crude oil: A case study of the Zagli field

Abstract

The lack of information about the chemical composition and structure of asphaltenes in crude oil, which has a sufficient share in the economy of Azerbaijan, complicates its processing and use. As a first attempt, this research is devoted to the detailed analysis of the average molecular structure and properties of asphaltenes isolated from crude oil samples collected from the Zaglı oil field using the integrated application of high-sensitivity devices such as Nuclear Magnetic Resonance (NMR), Ultraviolet–Visible (UV–Vis), Fourier Transform Infrared (FTIR) spectroscopy, X-ray diffraction analysis, Elemental analysis, Scanning Electron Microscope (SEM), Differential Thermal Analysis (DTA), Dynamic Light Scattering (DLS). The average molecular formula of asphaltene monomer was determined to be C49.5H55O3.04N0.95S2. An island architecture with one polycyclic aromatic hydrocarbon (PAH) in each molecule of this compound is predominant. Amorphous asphaltene molecule contains vanadium-based porphyrins, –COOH group, disulfide (−S-S-) linkage. It was found that asphaltene of crude oil is stable up to 406 °C. The three-stage pyrolysis process in the temperature range of 406–818 °C resulted in the formation of 12.58 % coke. Due to the absence of free radicals in the range of 25–100 ℃, the asphaltene sample is dielectric. The decrease of monodispersity with particle growth in asphaltene compound in different solvents was analyzed by dynamic and static light scattering. The HOMO-LUMO energy gap of the asphaltene molecule was 2.666 eV, indicating high stability. The knowledge gained about the chemical composition and molecular structure of asphaltenes can help prevent problems arising in oil production and refining processes.