Thermogravimetric analysis was used to study the pressure effect on the activation energy during asphaltene gasification. The experiments were carried out under steam atmosphere at different pressures (1−80 bar) and temperatures (100−900 °C). The measured values of the total mass loss of asphaltenes are pressure dependent. They increase with rising pressure. Kinetic parameters were determined using a first-order kinetic model and integral method with thermogravimetric analysis data. The activation energy was found to vary from 189.6 to 130.4 kJ/mol and frequency factor from 4.1 × 10 10 to 1.2 × 10 6 min −1 . A decrease of both parameters was observed with an increasing pressure. Coke produced during the gasification is obviously characterized by the bigger pore size and weaker mechanical strength as the pressure increases from 1 to 80 bar. The structure of the produced coke becomes more crumbly with raising pressure. The formation of spherical carbon particles with a radius of around 5 μm was observed at high pressure (20−80 bar). The elemental composition of these particles is roughly equal: C (∼97%), S (∼2%), and O (∼1%).
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.
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