Modelling of the pyrolysis of high density polyethylene: Product distribution in a fluidized bed reactor

Abstract

The increase in the generation of plastic wastes has triggered the study of different alternatives for their recovery. Pyrolysis appears to be an interesting alternative for the treatment of mixtures of different plastics. The development of a model that simulates polyethylene pyrolysis (one of the most abundant plastics) has been considered interesting in order to analyse the influence of the operation variables on the behaviour of the system. The existing models predict the generation of the main products, paraffins, olefins and diolefins, but not the influence of temperature and residence time on the product distribution. Neither is the formation of aromatics and polyaromatics included. The main objective of this work is the formulation and development of a model that predicts the product distribution obtained in the pyrolysis of polyethylene. In order to do this a mechanistic model has been developed based on a radical mechanism. This model uses a small number of elementary kinetic steps, including initiation, β-scission, H-abstraction, aromatization and radical combination. The results obtained have been validated with experimental results obtained in a fluidized bed reactor in which the pyrolysis process has been studied at different temperatures (640–700 °C) and residence times (0.8–2.6 s). The results show that the trends experimentally observed for the different temperatures and residence times studied are predicted.