Analytical investigation of asphaltene cracking due to microwave and ultrasonic radiations: A molecular insight into asphaltene characterization and rheology

Abstract

Asphaltene is a fraction of crude oil that causes technical and environmental problems because of its instability and precipitation. Microwave and ultrasonic radiations have been proven to be efficient for oil viscosity reduction and removal of asphaltene precipitants. This research aims to investigate the alteration of the asphaltene molecular structure from a molecular point of view, as well as their rheological behavior, due to microwave and ultrasonic radiations. Nuclear Magnetic Resonance (NMR), Fourier Transformed Infrared (FTIR), Energy Dispersive X-ray (EDX) spectroscopies, and Elemental analysis were implemented to find the ultrasonic and microwave radiation effects on the molecular structure of two asphaltene samples. Based on the obtained results, the number of fused aromatic rings is reduced due to ultrasonic and microwave radiations, indicating aromatic core cracking. The number of aliphatic carbons is reduced, representing the aliphatic chain cracking. Besides, the increase in the aliphatic chain length, aside from aromatic core cracking, was a sign of the ring opening. The reduction of the polar groups, such as carbonyl, in the microwave-treated asphaltene, was explained by more vulnerability of materials with higher dielectric constants to the microwave. The ultrasonic radiation was more feasible for removing heavier elements, such as oxygen. The aggregation behavior of the untreated/treated asphaltenes was investigated through rheological tests. The viscosity of the oil sample bearing treated asphaltene was lower than the ones bearing crude asphaltene, representing reducing the ability for aggregation. Based on the structural parameters and chemistry of the treated asphaltenes, weakening of hydrogen bonding interaction and π- π stacking were recommended mechanisms for reducing asphaltene aggregation and oil viscosity. This research could be used to modify the asphaltene structure to hinder the technical and environmental issues, caused by the asphaltene precipitations.