Pyrolysis of petroleum sludge under non-isothermal conditions: Thermal decomposition behavior, kinetics, thermodynamics, and evolved gas analysis

Abstract

Pyrolysis of petroleum sludge is considered as a promising way for energy production from solid waste of petroleum refineries and the ability to predict the thermal decomposition behavior of such processes is necessary for modeling, optimization, and control of the pyrolysis reactors. Therefore, this work focused on developing and applying a systematic methodology for the calculation of kinetics and thermodynamics of the oil sludge pyrolysis and investigation of evolved gases. Thermograms at different heating rates demonstrated that the pyrolysis reactions could be considered under three zones; i) moisture and low molecular weight hydrocarbon volatilization, ii) active pyrolysis, and iii) high-temperature carbonization. During active pyrolysis, two decomposition stages were obtained by deconvolution using the Asym2sig function, which indicated the occurrence of multiple reactions. The average activation energies, calculated by the iso-conversional models, ranged in 106.3-112.7 kJ. mol- 1 and 200.9-207.6 kJ.mol-1 for the first and second pyrolysis stages, respectively. Flynn-Wall-Ozawa and Friedman models showed the best consistency between the experimental and predicted values. The average preexponential factors were estimated as 9.79 x 106 s-1 and 1.91 x 1012 s-1 for these subsequent sub-stages. Furthermore, enthalpy, Gibbs free energy, and entropy changes were estimated together with monitoring emission profiles of the released gases from the sludge during pyrolysis by coupling TGA with an FT-IR spectrometer. The reported kinetic, thermodynamic parameters and findings on evolved gases can expand the use of this residue in refinery applications, consisting of a great attempt toward its valorization.