Gas product distribution from polyethylene pyrolysis

The disposal of plastic waste is extensively studied nowadays. Of the treat ments available, thermal degradation is attracting great interest because i t offers the possibility of recovering energy and useful chemicals. PE pyro lysis has already been discussed in a previous paper [1] where the rate of decomposition of a sample was modeled using a detailed kinetic scheme. Its predictions were validated by thermogravimetric experimental results across wide operative pressure and heating rate ranges. The gas product distribut ion was derived from the random scission hypothesis. Thus, the ratio of alk ane, alkene and dialkene species was 1:2:1 and, within the same class of pr oducts, the distribution was equimolecular, except for those species which are more favored by allyl resonance. This paper aims to continue the previo us work in attempting to model gas products correctly. The principal improv ements made here are the introduction of backbiting reactions into the kine tic scheme to predict the larger amounts of selected products and the consi deration of the physical aspects of the degradation process. These phenomen a are responsible for the production rate and the distribution of volatiles . A simplified model of the in-depth mass transfer through bubble formation is presented which describes the degradation progress for a small-sized po lyethylene sample. The model predictions are compared with both the experim ental results of polyethylene pyrolysis performed under various temperature conditions and with thermogravimetric analysis. (C) 1999 Elsevier Science B.V. All rights reserved.