Investigations into extra-heavy crude oil pyrolysis under non-isothermal conditions: thermal characteristics, kinetics, and thermodynamic parameters

Abstract

This study comprehensively investigated the pyrolysis characteristics, kinetics, and thermodynamic parameters of extra-heavy oil through thermogravimetry (TG) experiments. The TG results revealed a two-stage pyrolysis process, consisting of light-temperature pyrolysis (LTP) and high-temperature pyrolysis (HTP), in which the HTP was the primary mass loss interval, contributing roughly 53.5% of mass loss from 370 to 500 °C. The pyrolysis kinetics were obtained using Ozawa-Flynn-Wall (OFW) and Friedman methods. The results revealed that the main pyrolysis reaction mechanism shifted from volatilization to thermal cracking while the conversion degree exceeded 0.35. The thermodynamic parameters, including enthalpy (ΔH), Gibbs free energy (ΔG), and entropy (ΔS), were also calculated. The thermodynamic features showed that the pyrolysis process absorbed large amounts of energy to change the main reaction mechanism in the range of α = 0.4–0.6, and altered from an organized to a disordered state due to the disruption of intramolecular structure induced by the formation of coke while the conversion degree exceeded 0.6. These findings have the potential to offer a thorough comprehension of the pyrolysis mechanism of extra-heavy oil.