Thermogravimetric studies on pyrolysis and combustion behavior of a heavy oil and its asphaltenes

A thermogravimetric analyzer (TGA) was used to obtain information on the pyrolysis and combustion behavior of both crude oil (Neilburg) and its asphaltenes, each mixed with reservoir sand. Of all the saturate, aromatic, resin, and asphaltene fractions, asphaltenes contribute the most to the formation of coke (fuel). Temperature-ramped as well as the isothermal pyrolysis experiments on whole oil and asphaltenes were analyzed to determine the temperature at which coke formation was maximized. Furthermore, isothermal combustion curves for coke derived from whole oil and asphaltenes were obtained to provide reliable data for calculating the kinetics of the reactions. The classical Arrhenius model was applied, and the activation energy for the combustion of coke formed from pure asphaltenes and from the whole oil was calculated. The results showed that the Arrhenius model fitted the data well in the entire range of temperatures the experiments were conducted. The source material for the coke led to modest differences in its reactivity. The observed activation energy for asphaltenes was 117.7 kJ/mol, and for the whole oil it was 129.5 kJ/mol, which indicates that they were in close agreement. Also, the combustion of coke from asphaltenes showed a reaction order of 0.4 at 375 degrees C, which gradually increased to 0.9 at 525 degrees C. For whole oil, it increased from 0.5 at 375 degrees C to 0.7 at 500 degrees C.