The pyrolysis of plastic

In recent years, more and more pictures of plastic waste accumulated in oceans, rivers and on land have been released in the media and have shocked people all over the world. It turns out that at least 14 million tons of plastic end up in the oceans every year. These debris are a direct consequence of the plastic pollution crisis that the world is going through. Indeed, the plastic production keeps increasing and there is no question of reversing the trend in the coming years although this would be the best solution. According to the Waste Framework Directive proposed by the European Commission, the best option would be to reduce the production of plastic. Actually, plastics are part of our daily lives and present several advantages compared to other materials that make them much more competitive: they are low cost, lightweight, durable and present interesting mechanical and physical properties. However, plastic materials are generally non-degradable and present a short first-use cycle. Concern has grown in the population in order to tackle these problems. Cleaning operations are popping up but it is not enough. This is the reason why scientists have re-evaluated the plastic waste management crisis. One solution is to place plastic materials into a circular economy so as to close the loop by recycling waste plastic. The present master thesis is part of a larger investigation subsidised by Interreg, based on the pyrolysis of plastic. Pyrolysis is a promising technology aimed at reducing plastic waste by recycling it chemically. It is based on the thermal degradation of the plastic feedstock by heating it at moderate to high temperatures in an oxygen-free environment. The content of this work is subdivided into four main parts. First of all, a literature study will allow to give a general overview of the various existing technologies to perform pyrolysis. The conventional method (e.g. thermal pyrolysis) will be presented, as well as novel promising routes (e.g. catalytic pyrolysis and pyrolysis-gasification) used to convert plastic chemically into targeted product fractions. Then, the focus will be put on the pyrolysis of polyethylene. Some important background will be provided, such as a distribution of products depending on temperature and a kinetic model, based on recent researches. The scene being set, the focus will be put on the simulation of two promising reactor technologies, namely spray towers and continuous stirred tank reactors. The performance of each reactor type will be analysed based on the resolution of continuity and heat equations. Concerning the spray towers, a sensitivity analysis will be performed in order to study the impact of several operating conditions on the product's yield. The main goal of this work is to study the competitiveness of the two aforementioned reactor types with regard to more advanced and effective technologies in such a way that further research can potentially emerge to definitely solve the plastic waste management crisis.