Controlled autoxidation of HVGO to produce high-value carbon fibers precursors: the role of oxygen availability and naphthenic-aromatic hydrocarbons

This study investigated the application of heavy vacuum gas oil (HVGO) as a feedstock for high-value carbon fiber precursor production through controlled autoxidation. HVGO, initially had no asphaltenes, was subjected to varying oxidation conditions, such as blowing without mixing and bubbling with mixing at different temperatures with and without addition of tetralin (a naphthenic-aromatic hydrocarbon), to enhance its asphaltenes content and modify its physicochemical properties required for carbon fiber formation. The elemental analysis and physicochemical characterization of the HVGO samples after oxidation showed that the autoxidation significantly enhanced the asphaltenes content, with the highest asphaltenes yield of 47.2 wt. %, viscosity of 117.6 Pa.s, and softening point of 210 °C achieved after 72 hours at 190°C using 5% tetralin and air blowing without mixing. It also found that tetralin addition maintaining limited oxygen conditions would help to form heavier products, desirable as carbon fiber precursor. The melt spinning of the asphaltenes from oxidized HVGO with tetralin, provided green fibers with diameters of 70 µm and carbonized fibers with diameters of 40 to 50 µm, as detected by SEM imaging analysis. The mass residues of the oxidized HVGO samples and the carbon fibers were confirmed by TGA analysis. All these observations indicated that the controlled autoxidation, especially when tetralin was added, was a potential pathway to turn low-value HVGO into high-value carbon fiber precursors. Understanding the current research can also be applied to produce high-value carbon materials for CNT, graphene, and carbon materials for energy storage applications.