(154s) A Two-Stage Process and a Generalized Molecular-Level Kinetic Model for Polyolefin Pyrolysis: Low Molecular Weight Product Evolution

Industrialization and development of the global economy have boosted the production of plastics, leading to an explosive growth in the generation of plastic waste. As an undesired result, 6300 million metric tons of plastic waste has been generated globally between 1950 and 2015, 60% of which is polyolefin including polyethylene (PE), polypropylene (PP) and polystyrene (PS), which is one of the most urgent and difficult environmental challenges. In this work, the pyrolysis of PE and PP has been studied by a two-stage tube reactor to obtain high yield of light olefins. The maximum yield of light olefins of PE and PP pyrolysis are 76.1 wt% and 71.8 wt% at 800 °C, respectively. Comparing with the results of other literatures, the present study obtaines a high yield of light olefins and a lower yield of methane. In addition, probable mechanisms for the pyrolysis of PE and PP are proposed to reveal the interplay of reactions which can guide how to produce more light olefins and provide additional information regarding the molecular-level kinetic model. A simplified and generalized molecular-level kinetic model for describing the pyrolysis of polyolefin such as PE, PP and PS has been presented, avoiding the introduction of complex mathematical methods and extensive chemical databases to keep smooth calculation. The structure-oriented lumping (SOL) and Poisson distribution sre selected to transform the feedstock information into the mathematical matrix. The complex reaction network is constructed through automated generation, realizing quick analysis of the data and the delivery of the model parameters. For example, the automatic generated network for PS pyrolysis containing 3,008 substances and 15,025 reactions is partially visualized. Genetic algorithm is used to optimize the kinetic parameters. The model can be applied to predict the experimental data of various researches in the literature without adjusting the rules. Therefore, this work can provide guidance of the recycling and upcycling of plastic waste by analyzing key indicators and predict the impact due to changes in operating conditions from a viewpoint at molecular level.