Conceptual design of the gasification of plastic waste for the production of syngas or naphta: A circular approach from plastic waste to renewed polymers

Gasification and pyrolysis are thermochemical processes proposed for the transformation of different biomass substrates into different compounds. Syngas is the main product under harsh gasification conditions, while a liquid "naptha-like" mixture is reported under milder pyrolytic conditions. The conceptual design of different options for the valorisation of plastic wastes through either gasification and pyrolysis is the goal of this work, in which the pyrolysis of polyethylene is specifically addressed as a mean to recover a gaseous mixture (to be used as fuel or later recovered for its olefin content) and a liquid to be valorised as feed for steam cracking. Some of the challenges for the design of the plant and modelling of the reactor are highlighted. Namely, the kinetic description of the reaction is still not available and very strongly dependent on the feed nature. Furthermore, the stoichiometry of the reaction depends on the feed and on operating conditions, leading to widely variable products distributions. The apparent reaction stoichiometry and the relative kinetic equation should therefore be carefully assessed. The simulation of a rotary kiln reactor has been at last successfully accomplished.