Characterization of Acid-Soluble Oxidized Asphaltenes by Fourier Transform Ion Cyclotron Resonance Mass Spectrometry: Insights on Oxycracking Processes and Asphaltene Structural Features

The dissolution of organic matter into water via oxidative processes, named oxycracking, has been practiced for a long time for the removal of organic pollutants, in which oxygen induces breakage and functionalization of organic molecules. Recently, oxycracking has been explored as an alternative approach to handling the increased amount of solid residues produced in oil sands upgrading activities that involve carbon rejection in solvent deasphalting units. This study uses an asphaltene-rich feedstock, operationally known as petroleum pitch, isolated from an Athabasca bitumen vacuum residue, which was submitted to oxycracking reactions at 200 and 220 °C. The feed and water-soluble fractions isolated at pH 1, termed acid-soluble oxidized asphaltenes (ASOA), were analyzed by ultrahigh-resolution mass spectrometry [Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS)] using electrospray and atmospheric pressure photoionization ion sources. FTICR-MS analysis revealed extensive oxidation of all compound classes originally present in the asphaltene-rich feed. Double bond equivalent (DBE) distribution plots show that sequential carboxylation (formation of a carboxyl group) occurs progressively with an increasing reaction temperature, leading to the incorporation of up to 15 oxygen atoms per molecule, whereas simultaneous decarboxylation reactions produce a CO₂-rich gas phase. ASOA samples also show lower overall carbon number distributions than the asphaltene feed, which is direct evidence of C–C bond cleavage during the oxycracking process. In addition, molecular fragments detected in ASOA after carbon–carbon bond cleavages showed not only lower carbon numbers but also lower DBEs per molecule, consistent with a more dominant archipelago architecture for the parent asphaltene molecules