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A tree-based kinetic Monte Carlo (kMC) model is presented that differentiates between 38 end-group pairs for isothermal degradation of poly­(styrene peroxide) (PSP). The binary trees allow for fast and accurate calculation of reaction probabilities, with mass-weighted binary trees for the accurate sampling of peroxide bond fissions and hydrogen abstractions along chains. The kinetic parameters are tuned via artificial neural networks (ANNs) to successfully predict literature experimental data, among other lumped product yields. ANNs are also utilized for sensitivity analysis to unravel the effects of individual reactions on the time evolution of experimental responses and other simulation outputs, including the variations of the chain length distributions of the macrospecies. PSP degradation is characterized by three stages of degradation considering both instantaneous and time-averaged concentrations. The first stage features rapid unzipping and results in the fast production of major products benzaldehyde and formaldehyde, the second stage features the most significant level of hydrogen abstractions involving PSP and other macrospecies types, and the third stage exhibits the consumption of the remaining peroxide bonds toward oligomeric species in a wide time frame until the degradation process is finalized by the depletion of peroxide bonds. This proof-of-concept study based on unprecedentedly detailed analyses of the chemistry via kinetic Monte Carlo paves the way to further improve our understanding of chemical recycling of solid plastic waste.

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Hydroxycinnamaldehyde monomers are important intermediates in the lignin biosynthesis and can be incorporated into plants in large quantities via genetic modification. They are also important products formed during pyrolysis or combustion of lignocellulose. In this work, the decomposition of three hydroxycinnamaldehyde model compounds, cinnamaldehyde, p-coumaraldehyde, and coniferaldehyde, was studied in a micropyrolysis reactor equipped with an online GC × GC-FID/TOF-MS coupled with a customized GC for the on-line analysis of all the pyrolysis vapors including permanent gases. The vaporization or sublimation process of these model compounds in the reactor was fitted well based on the experimental time-resolved data. The dominating initial decomposition pathways were elucidated from a first-principles based kinetic model and using rate of production analysis. For cinnamaldehyde (at 773-1123 K) and p-coumaraldehyde (at 873-1123 K), the concerted decarbonylation reactions in the condensed phase are determining the initial decomposition, with almost no contribution from radical chemistry. For coniferaldehyde (at 773-1023 K), the homolysis of O-methyl (O−CH3) bond initiates a radical chain mechanism at temperatures above 773 K, and the H-atom abstraction on the aldehyde group is the most dominant consumption pathway at high temperatures. The presence of methoxy groups on the aromatic rings accelerates the decomposition of hydroxycinnamaldehydes. Models that do not account for these important structural differences will have difficulties to predict the decomposition of real lignocellulosic biomass.

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