Coke formation from heavy oil has been extensively studied and various kinetic models have been proposed in the literature. In this study, thermal behavior of crude oil and its asphaltene obtained from Fosterton field was investigated using thermogravimetric analysis. Non-isothermal pyrolysis experiments of whole oil and its asphaltene was performed in nitrogen atmosphere at different heating rates of 5, 10, 15 and 20 ?C/min. Although, much difference was not observed in the weight loss profile for whole oil and its asphaltene, the final amount of coke formed changes with the heating rate. Nonisothermal experiments were better described by Distributed Activation Energy Model (DAEM) compared to other applicable models. The non-isothermal pyrolysis kinetics of whole oil and its asphaltene were studied with DAEM equation. The activation energy for whole oil pyrolysis spreads over a range from 7 to 129 kJ/mol and the pre-exponential factor varies from 102 to 10 11 min−1. The asphaltene fraction separated from the oil has the activation energy from 50 to 183 kJ/mol and the pre-exponential factor ranges from 10 7 to 1014 min-1. Results from the kinetic analysis suggest that asphaltene requires more activation energy compared to the whole oil.
Thermal cracking of heavy oil feedstocks results in the formation of a wide range of gaseous, liquid and solid products. During pyrolysis, several reactions take place, which influence the overall kinetics and the resulting coke formation.
It is well known that thermal treatment of hydrocarbons follows a free radical mechanism, where cracking reactions take place in the initiation step, condensation and polymerization reactions comprise the final step [1]. The final step reactions explain the formation of products such as coke. Among the SARA fraction present in the whole oil, asphaltenes are precursors of coke formation. Asphaltenes are complex associated species typically isolated as a solubility class obtained by precipitation with a weak solvent [2]. Coke formations from both whole oil and its fractions like asphaltene have been extensively studied [3, 4]. However, the coke formation characteristics vary with the different sources of oil.
The kinetics of the thermal decomposition of various oil from different regions of the world, have been investigated and various suggestions as to the decomposition mechanism have been reported [5, 6]. Many thermogravimetric studies have been carried out under isothermal conditions, but this method involves some inaccuracies. It is more accurate to use a nonisothermal method to determine the kinetic parameters of the pyrolysis process, employing a TGA apparatus, with the sample heated at a constant rate and recording its weight change. This is mainly because of the shorter experimental time and the fewer encountered difficulties. But the principal reason for their popularity in the field of oil pyrolysis is that it more closely simulates the conditions expected in commercial scale. Thus, such a technique for determining the reaction kinetics, such as activation energy, has been preferred by many researchers [7–9]. Hence, the kinetics of thermal degradation of whole oil and its asphaltene from fosterton region can be obtained using a TGA apparatus.
