Oxidation thermolysis kinetics of asphaltenes with various chemical prehistory

Abstract

In this research, six various asphaltenes extracted from crude oil mixtures of three Russian refinery plants and some heavy residues of these plants were studied with applying thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) techniques. The kinetic experiments were performed at four various heating rates (5, 10, 15, 20 °C/min), all under air static atmosphere. The TGA data were transformed to conversions and first analyzed with the approved methods of Friedman, Ozawa-Flynn-Wall (OFW) and Kissinger-Akahira-Sunose (KAS). The results indicated of the complexity of decomposition-thermolysis process and a complicated and non-uniform dependency of the effective activation energy as a function of conversion, unique for each asphaltene studied. A kinetic model of two independent N-order reactions was proposed to make corresponding kinetic descriptions of complicated thermolysis reactions under non-isothermal conditions. The developed model was proved to be valid, and kinetic descriptions were obtained that fitted the experimental data. Activation energies for the first reaction and the second reaction were found to be in the interval 24–48 kJ/mol and 110–125 kJ/mol respectively (asphaltenes (1–3) extracted from the initial crude oil mixtures and pyrolysis resin). Activation energies for secondary asphaltenes (4–6) extracted from heavy refinery residues - 115–155 kJ/mol (1-st reaction) – 110–148 kJ/mol (2-nd reaction).