Using isothermal kinetic results to estimate kinetic triplet of pyrolysis reaction of polypropylene

Abstract

This paper describes how to estimate the Arrhenius parameters as well as the reaction model of the pyrolysis of polypropylene (PP) from isothermal kinetic results. We introduced a custom-made thermobalance that is able to record weight decrease with time under pure static condition. A best fit of experimental reduced-time-plot (RTP) to theoretical ones led to a conclusion that the pyrolysis reaction model and Arrhenius parameters of PP vary with reaction temperature. The pyrolysis reaction model of PP is accounted for by “Contracting Cylinder” model at lower-temperature reactions (683–693 K), whereas that of PP by “Avrami-Erofeev” model at higher-temperature reactions (728–738 K). Medium-temperature reactions (693–728 K) manifest the shift pattern of reaction model from “Contracting Cylinder” model to “Avrami-Erofeev” model. There is a critical temperature (705–720 K) that triggers the explosive generation of volatiles, leading to bubble nucleation and growth, simulating the “Avrami-Erofeev” model. The nth order model adopted by most previous studies appears to be inappropriate to represent the pyrolysis reaction model of PP. Consequently, the Arrhenius parameters derived from the assumption of nth order model would be improper as well.