Insight into Polyethylene and Polypropylene Pyrolysis: Global and Mechanistic Models

• Published in: Energy & fuels Vol. 35; no. 8; pp. 6765 - 6775
• Main Authors: Harmon, Rebecca E, SriBala, Gorugantu, Broadbelt, Linda J, Burnham, Alan K
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 15.04.2021; American Chemical Society (ACS)
• Subjects: Catalysis and Kinetics; Energy & Fuels; Engineering
• ISSN: 0887-0624; 1520-5029
• DOI: 10.1021/acs.energyfuels.1c00342

Pyrolysis of polyolefins has been proposed as a potential resource recovery strategy by converting macromolecules into valuable fuels and chemicals. Due to variations in possible backbone structures, chain-length distributions, and arrangements of pendant groups, their decomposition behavior via pyrolysis can be complex. In the present work, a review of historical data and empirical models for two distinct polyolefins, polyethylene (PE) and polypropylene (PP), is provided followed by a comparison to recent mechanistic models. The characteristic sigmoidal behavior of linear polymer decomposition is captured with global, lumped-species, and mechanistic models of high-density polyethylene. The PE model was extended to simulate PP using the same reaction families and reaction family parameters, but with distinct rate coefficients that accounted for the difference in the structure of PP with its pendant methyl groups compared to PE as manifested through heats of reaction embedded in the Evans–Polanyi relationship, E a = E 0 + γ×ΔH reacn. The change in structure and its associated kinetic parameters resulted in no sigmoidal conversion, consistent with experimental reports for atactic PP. This suggests that mechanistic modeling could be an important complement to global model studies to understand when other effects are at play in the pyrolytic decomposition of polymers such as PP.