Unimolecular decomposition of pentacyclic carbonates: a computational kinetic study

To develop chemical kinetic models for the pyrolysis and combustion of pentacyclic carbonates, including ethylene carbonate (EC), propylene carbonate (PC), 2,3-butylene carbonate (23BC), and 1,2-butylene carbonate (12BC), which are always focused on in the battery industry as representative solvents and alternative fuels, theoretical aspects of unimolecular decomposition reactions were studied. According to the calculations, CO₂, H₂, and CH₄ elimination channels and isomerization channels were found based on the potential energy surface of the unimolecular decomposition channels. These pentacyclic carbonates predominantly tend to eliminate CO₂, thereby generating aldehydes, ketones, and oxiranes. Among these exothermic pathways, the formation of aldehydes is generally more energetically favorable compared to the production of the other species. It is found that EC exhibits the slowest rate of CO₂ elimination to produce acetaldehyde. PC and 12BC demonstrate relatively higher rates of CO₂ elimination, which is attributed to the presence of a single substituent on the pentacyclic ring. However, a symmetric molecule structure (23BC) contributes to the formation of ketone rather than aldehyde due to the complex transition state. Moreover, the CO₂ elimination reactions exhibit insensitivity to pressure changes. This study identifies potential decomposition products during thermal runaway of cyclic carbonates and provides valuable insights for subsequent model development.