Thermogravimetric determination of coke from asphaltenes, resins and sediments and coking kinetics of heavy crude asphaltenes

Thermal analysis of asphaltenes and resins from heavy crude was carried out to understand the way in which they decompose to form coke. Sediments extracted from hydrotreated crude were also analyzed. It was found that asphaltenes produced 47 wt.% of coke, resins 9 wt.% of coke, and sediments decompose quickly toward coke giving the highest yield (66 wt.%). In the case of asphaltenes and resins a free radicals based mechanism is operating when labile points in alkyl chains are broken leading to condensation reactions. Thermal analysis of sediments obtained from hydrotreated crude revealed that they have high tendency to form coke. A non-isothermal technique using various heating rates was applied to study kinetics of asphaltene cracking toward coke formation. An iso-conversional method based on Friedman's procedure was used to calculate the reaction kinetic parameters from thermogravimetric analysis during asphaltene cracking and a set of activation energies and pre-exponential factor was obtained as the reaction progresses. Activation energy ranged from 29.2 to 52.4 kcal/mol.