Mechanism, Kinetics, and Thermodynamic Characteristics for the Demetallization of Used Lubricating Oil via Pyrolysis

This study analyzed the pyrolysis mechanism, developed a pyrolysis kinetic model, and determined the corresponding thermodynamic parameters for the removal of calcium from used lubricating oil using sulfurized calcium alkyl phenolate (T-115B) as a model compound. The pyrolysis process and products were evaluated by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. Visual inspection indicated that the removal of calcium from T-115B depended primarily on the destruction of micelles caused by the pyrolysis of compounds at high temperatures. The pyrolysis characteristics of T-115B at different heating rates were investigated by thermogravimetry and differential thermal analysis, which revealed two distinct pyrolysis phases. Thus, the pyrolysis mechanism can be described by a twostep model. The activation energy and thermodynamic parameters (?H, ?G, and ?S) were determined by applying the Kissinger-Akahira-Sunose, Flynn-Wall-Ozawa, Friedman, and Starink methods; the average activation energies for T-115B pyrolysis obtained using these methods were 115.80, 119.84, 124.96, and 116.14 kJ/mol, respectively. Further, both stages of the pyrolysis reaction followed Fn mechanisms with n = 1.39 in the first stage and n = 0.86 in the second stage. This study provides reliable and effective pyrolysis models along with kinetic and thermodynamic parameters to facilitate the largescale industrial application of used lubricating oil.