Kinetic model for removing phosphorus and zinc from waste lubricating oil by pyrolysis

Abstract

The present study focused on the establishment of a kinetic model for the removal of phosphorus and zinc from waste lubricating oil by pyrolysis. Zinc dialkyl dithiophosphate (ZDDP) was used as the model compound for the analysis. The pyrolysis of ZDDP was evaluated at different temperatures by infrared (IR) and nuclear magnetic resonance (NMR) spectroscopy. Moreover, thermogravimetry (TG), derivative thermogravimetry (DTG), and differential scanning calorimetry (DSC) curves were used to investigate the thermal decomposition characteristics of ZDDP at different heating rates. The apparent activation energies at different conversion rates were calculated by the Kissinger–Akahira–Sunose (KAS) and Flynn–Wall–Ozawa (FWO) methods. Finally, the thermal decomposition mechanism at each stage was determined by a model-based approach. The results indicated that the thermal decomposition process of ZDDP could be described by a four-step thermal decomposition model. The average apparent activation energy calculated by the FWO method was 107.959 kJ mol−1, while that calculated by the KAS approach was 105.0681 kJ mol−1. Additionally, it was established that the decomposition induction stage (II), competitive reaction stage (III), and precipitation stage (IV) involved a power function model reaction (P4) mechanism, Avrami–Erofeev reaction (A3) mechanism, and Avrami–Erofeev reaction (A2) mechanism, respectively. Importantly, the predactyl factor A and reaction rate constant K were also obtained. The outcomes of this study provide a valuable basis for optimizing the process of industrial pyrolysis of waste lubricating oil.