Thermogravimetric Determination and Pyrolysis Thermodynamic Parameters of Heavy Oils and Asphaltenes

Thermal analyses of Yarega heavy crude oil, its atmospheric residue, vacuum residue, and asphaltenes were carried out for a better understanding of the pyrolysis of high-molecular-weight hydrocarbons. The degree of influence of asphaltenes on the pyrolysis was determined. Kinetic and thermodynamic parameters of the pyrolysis were also investigated. Activation energy and pre-exponential factor were calculated. It was found that the degree of conversion depends on the average molecular weight of the liquid oil systems. The higher the molecular weight, the lower the final degree of conversion. It was determined that the activation energies of pyrolysis of the liquid oil systems are higher than those of the asphaltenes obtained from these systems. This process occurs due to deasphalting of the leaching of a solvate layer as a result of the existence of two phases (α-phase and β-phase). The β-phase is not soluble in the low-molecular-weight hydrocarbons but partially broken and converted into asphaltenes in the vacuum distillation. Images obtained by scanning electron microscopy showed that the asphaltenes size decreases with increase in density. Asphaltenes from heavy crude oil and atmospheric residue were found to have the highest strength and bond orders, and asphaltenes from vacuum residue have the highest strength of structure.