Low-temperature oxidation of heavy crude oil characterized by TG, DSC, GC-MS, and negative ion ESI FT-ICR MS

Low-temperature oxidation (LTO) is of great significance for the subsequent oxidation reactions and oil recovery during in-situ combustion. The paper brings an in-depth analysis of crude oil LTO that is still not well understood. Firstly, one Xinjiang heavy oil was subjected to LTO reactions under different temperatures conducted in an oxidation reactor. The combustion behaviors of the oxidized oils were then investigated by thermogravimetry and differential scanning calorimetry. The Friedman and Ozawa-Flynn-Wall methods were adopted to perform combustion kinetic analysis of the oxidized oils. Subsequently, both gas chromatograph-mass spectroscopy and negative ion electrospray Fourier transform-ion cyclotron resonance mass spectrometry were introduced as a new route to investigate the compositional changes of crude oil caused by LTO. The condensation of aromatics as well as aromatization and condensation of other compounds was intensified from 40 to 200 degrees C. Chain saturated aliphatic, mono-cyclic, bicyclic, and tricyclic naphthenic acids were the main acidic components in the oxidized oils. The relative abundance of chain saturated aliphatic acids and O-1 species was decreased from 40 to 200 degrees C, whereas that of tricyclic naphthenic acids and O-3 species was increased. Finally, we summarized LTO reaction pathways of crude oil, which helped to understand LTO mechanisms. (C) 2020 Elsevier Ltd. All rights reserved.