This research was conducted to investigate the pyrolysis behavior of crude oils and their fractions using differential scanning calorimetry and thermogravimetry. Experiments were performed at 10 °C/min heating rate under nitrogen atmosphere. An examination of the fractions of crude oils shows that pyrolysis mechanisms depend on the chemical nature of the constituents. A study of the weight loss properties of SARA constituents suggests that each fraction in whole crude oil follows its own reaction (distillation and cracking) pathway independent of the presence of other fractions.
This research is
intended to reveal the difference and connection
of oxidation behavior between crude oil and its SARA fractions. Thermogravimetry
(TG) and differential scanning calorimetry (DSC) techniques were used
to characterize oxidation behavior. The results showed that the oxidation
behavior of individual SARA components exhibited an obvious difference.
Saturates showed a weak high-temperature oxidation (HTO) region. Asphaltenes
generated more heat in HTO than in the low-temperature oxidation (LTO)
region. Aromatics showed intense exothermic activity in both LTO and
HTO regions. Heat release and mass loss showed a good correspondence
in the HTO region for all SARA fractions, which means heat release
and mass loss were caused by the same reaction mechanism that is believed
to be the coke combustion as it is the only significant reaction in
the HTO region. However, the good correspondence did not exist in
the LTO interval where the reactions are more complicated and a multiple-step
mechanism should be considered. In addition, it is not quite reasonable
to determine the reactivity of SARA fractions only by TG data as little
mass loss does not mean reactants are inactive. Kinetic parameters
of LTO and HTO reactions were determined by Friedman and Ozawa–Flynn–Wall
isoconversional methods. In general, for the crude oil and each fraction,
the activation energies of HTO were higher than that of LTO. The additivity
of DSC data could be applied quite well in the LTO region. However,
the predicted curve seriously deviated from the actual situation after
350 °C, which implies the exothermic reaction process of individual
components was influenced by the presence of other components. Nevertheless,
the total heat release of the measured and predicted values was similar,
which makes it possible to predict the heat effect of crude oil from
individual SARA components.
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