Molecular-Level Investigation of Coal-Tar Pitch Treated with Air Bubbling Revealing the Restructure of Aromatic Compounds Via Radical Reactions

Air blowing is conventionally used to improve the properties of pitch via oxidation. Previous studies have shown that pitch modification by air blowing leads to a considerably higher carbon yield, without restricting the fluidity necessary for the impregnation of pitch. This is attributed to the dehydrogenative polymerization and cross-linking of aromatic molecules during the air-blowing process. However, in this study, during air-blowing experiments, samples with similar yields but higher softening points were obtained despite the absence of larger aromatic compounds. Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS) was used for the advanced analysis of pitch, enabling us to propose a more extended mechanism for the air-blowing procedure. The results show that air blowing does not simply induce polymerization by oxygen radicals, but converges aromatic compounds to more stable congeners through radical reactions. The data in this study show that the previously suggested mechanism is partially correct only for aromatic compounds with oxygen. We anticipate that these results will aid achieving a more complete understanding of the mechanism of coal-tar pitch reforming via air blowing. FT-ICR MS is also highlighted as a technique for further understanding traditional carbon materials, which are difficult to analyze because of their complexity.