Study on the impact of various storage conditions on the free radical nature, stability and concentration of oil

Free radical oil stability at different storage conditions and durations and in various matrices is crucial for the oil industry and is not well established. In the current work, high-accuracy Electron Spin Resonance (ESR) spectroscopy was employed to investigate the factors influencing the persistent free radical content in oil by studying the solvent effects, the storage time effect and the storage temperature effect. Interestingly, differences in free radical content and types were detected across various solvents and storage durations, despite the absence of chemical reactions. It was found that the solvent dielectric properties were not correlated with the change in free radical spin content and the shift in free radical center. Spin concentration of the free radicals is influenced by the chemical nature of the solvent and oil–solvent interactions. Hydrogen-donning solvents such as tetralin resulted in the highest spin concentration at 1.66×10¹⁴ for room temperature, whereas dissolution in benzene exhibited an exceptional free radical stability. On another hand, electron-donating solvents reported the lowest spins with 3.29×10¹² spins/g oil for N-methylpyrrolidine at room temperature. This was interpreted in terms of free radical interactions between the oil and the different matrices at different conditions. In addition, lower storage temperatures significantly reduced the change in the g-factor compared to room temperature due to lower molecular motion and activity. The study has major implications for the oil industry as managing oil storage can play a significant role in slowing down their degradation, bringing important financial benefits to the industry.