Pyrolysis of Asphaltenes Derived from Residual Oils and Their Thermally Treated Pitch

Abstract

Thermogravimetric analysis (TGA) was employed to investigate the thermal stability of asphaltenes at different environments (inert and oxidizing atmosphere) and identify their refractory nature. TGA and differential scanning calorimetry were carried out at a temperature range of 50-700 °C, for asphaltene samples obtained from atmospheric residues, vacuum residues (VRs), and aromatic petroleum pitch samples, which were obtained from the cracking of VRs at different temperatures. The TGA results clearly indicate that thermal degradation of asphaltene takes place in a single process that starts around 350 °C and ends at 500 °C, giving ash contents of less than 2%. The derivatives of the TGA for the asphaltene samples suggest that the weight loss of composite material took place in two steps. The first step corresponds to the degradation of aliphatic side chains or easily oxidized hydrocarbons, while the second step corresponds to the degradation of the aromatic sheets or the stacked layers. TGA of asphaltenes in oxidizing atmosphere showed considerable changes in heat flow due to the destructive oxidation of the asphaltene molecular structure. The thermal stability or refractory nature of these asphaltenes have been calculated as heat of energy or enthalpy of the molecule, which corresponds to the π-πinteraction between the aromatic ring, hydrogen bonding, and alkyl chain size of the asphaltene molecule.