The Evolution of the Distillate Fractions of Heavy Oil During Low Temperature Oxidation Process

Heavy oil was divided into different pseudo-components according to their boiling ranges through real-boiling point distillation process, and the oxidation products for pseudo-components with boiling range higher than 350 °C were systematically investigated during low temperature oxidation (LTO). The kinetic cell (KC) experiments were conducted under different ambient pressure conditions and temperature regions, and the oxidation products were characterized using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). The changes of molecular weight, functional groups and polar atomic ratio of the compounds could be calculated during the LTO process. The results indicate that the LTO process contains two kinds of reactions happening at different temperature regions and were detected to occur both sequentially and simultaneously in different pseudo-components. The oxygen addition and cracking reactions typically occur in the temperature intervals of 140-170 °C and 180-220 °C respectively at the given heating rate of 3.83 °C/min, and the pseudo-components of 420-450 °C and 500+ °C are the main contributors involved in thermal cracking reaction. FT-ICR-MS analysis results show that the polar components are susceptible to be oxidized through oxygen addition with 1O or 2O atoms and then part of them are crack into low molecule weight compounds and generate COx through decarbonation process in even higher temperature regions. Components with the mass-to-charge ratio in the region of 250-450 Da mainly evaporate in the temperature regions of 25-150 °C, which results in the fraction losing. Considering the gas-liquid multi-phase reaction, the pseudo-components with low boiling range distributed on the surface of liquid film are prone to generate high molecular weight compounds through the oxygen addition. Then the fractions of high boiling range might be changed into greater molecular weight through oxygen addition, which continue to endure further cracking process to generate lower molecular weight varying in the region of 200-400 Da. N1O3 and N1O4 containing-compounds were determined by high resolution mass spectra, which were generated through oxygen addition of basic N1-containing compounds. The evolution of the pseudo-components is disclosed in this study, which is helpful to obtain a better understanding of the LTO mechanism of the heavy oil.