Initial pyrolysis of perhydroacenaphthene conformers: A multi-scale simulation and experimental analysis

Abstract

The enduring quest for a fuel that embodies both high density and superior heat sink capacity has been a long-standing goal within the scientific community. Perhydroacenaphthene (PHAN) fuels, characterized by five-membered ring structure that enhances density, also serve as hydrogen donors to inhibit coking, showcasing significant potential in fuel applications. Given their "strain-free" cyclic configuration, PHAN fuels manifest diverse conformations like chair, boat, and twist, among others, each influencing fuel properties and subsequently affecting pyrolysis process and the utilization of heat sink. In this work, leveraging the five preferred PHAN conformers substantiated by experiments, we embarked on a comprehensive investigation into their microstructures, properties, pyrolysis behavior, and initial pyrolysis mechanisms combining with molecular simulation and experimental analysis. Among them, interaction region indicator (IRI) analysis was employed to elucidate the differences in density. Upon this foundation, taking trans-trans-trans and cis-cis-cis PHAN with minimum and maximum density as models, the effects of different conformations on the initial pyrolysis reaction were explored by micro-pyrolysis system attached to an online GC-MS/FID strategy. It was found that compared to the trans-trans-trans conformation, the cis-cis-cis conformation manifested superior initial pyrolysis activity and more substantial heat sink capacity. Moreover, upon delving into the reaction mechanism and microkinetic analysis, it became evident that the favored initial reaction type of PHAN pyrolysis was H-abstraction reaction, and cis-cis-cis PHAN presented a lower barrier and a faster reaction rate than trans-trans-trans. Additionally, in conjunction with the calculation of free energy barrier and reaction heat of numerous reactions, the kinetic and thermodynamic dominances for the initial pyrolysis pathways of trans-trans-trans and cis-cis-cis PHAN were identified. Finally, utilizing intermolecular interaction energy (ΔE), independent gradient model based on Hirshfeld partition (IGMH) and Xiamen energy decomposition analysis (XEDA), the microscale justification for cis-cis-cis PHAN conformation displaying superior initial pyrolysis activity was further unveiled. This endeavors pioneer innovative pathways for the directional development and application of PHAN conformers.