Oxidation characteristics of heavy oil and its SARA fractions during combustion using TG-FTIR

The oxidation reactions between air and crude oils play a key role in in-situ combustion (ISC). This study is intended to explore the oxidation characteristics of one heavy oil and its SARA fractions by thermogravimetry associated with Fourier transform infrared spectroscopy (TG-FTIR). The results indicated the release behavior of typical evolved gases (hydrocarbons, CO2, CO, and H2O) during oxidation for the oil and its SARA fractions existed huge difference because of different structures and compositions. The heavy oil encountered appreciable weight loss at the low temperature oxidation (LTO) region where hydrocarbons, CO2, H2O, etc., were released. Quite a few coke could be formed from the LTO residue of heavy oil during fuel deposition (FD), thus resulting in a pronounced high temperature oxidation (HTO) stage characterized with apparent mass loss and one notably sharp peak of CO2. Saturates experienced a great amount of mass loss and release of hydrocarbons in the LTO regime. Aromatics showed obvious LTO and FD intervals in terms of mass loss and evolved gases, but its most of intermediate products during FD were evaporated with the temperature leading to the occurrence of weak HTO reactions. Resins was subjected to a small amount of mass loss and release of hydrocarbons and H2O in the LTO interval, and some of its intermediate products during FD formed coke through condensation reactions, which consequently led to a pronounced HTO stage. For asphaltenes, almost no hydrocarbons, CO2 and CO were released in the LTO region, and most of intermediate products at the initial FD stage condensed with each other to form coke. During HTO of asphaltenes, an extremely distinctive peak of CO2 and a small shoulder peak of CO and H2O were observed, verifying the occurrence of fierce combustion reactions.