Kinetic Modeling of the Thermal Degradation of the Vacuum Residual using the Starink Isoconversional Method

Abstract

The vacuum residue is a byproduct of the bottom stream of the Vacuum Distillation Unit, containing large hydrocarbon chains, and is primarily fed to conversion units for the production of light hydrocarbons such as fuels. Pyrolysis is a thermochemical process wherein the vacuum residue sample is subjected to an inert atmosphere or in the absence of oxygen, allowing for the thermal degradation of the vacuum residue sample to produce light hydrocarbons. Thermogravimetric analysis was performed on a sample of vacuum residue extracted from the bottom product of a Vacuum Distillation Unit located in Lima, Peru, to determine the kinetic triplet (Activation Energy, Pre-exponential Factor, and kinetic model). The activation energy was calculated using the Starink Isoconversional method, the pre-exponential factor was determined using the compensation effect, and the kinetic model was determined using the Master Plots method. Average activation energies of 59.75 kJ/mol and 125.25 kJ/mol were obtained in the conversion range of 0.05≤α≤0.50 and 0.50≤α≤0.95, respectively. The pre-exponential factor, within the same range, was found to be 1.25x10^5 min^-1 and 2.5x10^14 min^-1, respectively. Finally, the kinetic model was determined; for conversions between 0.50≤α≤0.70, the model is second-order (F2), while for conversions outside of this range, the kinetic model that best fits is Unidirectional Diffusion (D1).