Molecular Asphaltene Transformations during Aquathermolysis of Heavy Crude Oil: Analysis of the Literature Data

Despite the remarkable effort performed to understand the reaction mechanism of asphaltenes during aquathermolysis reaction, the knowledge level about their molecular structures and reaction pathways is still limited. This work thoroughly reviews and discusses experimental results reported from different samples of asphaltenes during the aquathermolysis reaction to obtain information about the elemental composition, functional groups, and average structural parameters using analytical characterization techniques, including elemental analysis, Fourier transform infrared spectroscopy, synchronous fluorescence spectroscopy, X-ray diffraction analysis, electron paramagnetic resonance spectroscopy, and nuclear magnetic resonance spectroscopy. By studying the structural changes of asphaltenes, theoretical support is provided for future research on the aquathermolysis of heavy crude oils in the presence and absence of various catalysts such as water-soluble, ionic liquids-based, mineral, and heterogeneous. Characterization analyses show that the changes in asphaltenes are strongly influenced by the operating conditions, catalyst type, and asphaltene structure. Certain catalysts and hydrogen donors provide a higher effect on asphaltenes and their functional groups that have been observed through changes in the molecular weight, aromaticity, and condensation as well as representative parameters of the aggregation state of asphaltene molecules.