Experimental and modeling studies of quadricyclane and 2-ethylnorbornane pyrolysis from atmospheric to high pressure

Abstract

To improve the understanding of cyclopentadiene-based high-density liquid hydrocarbon fuels combustion chemistry, the pyrolysis experiments of 1,3-cyclopentadiene (c-C5H6), quadricyclane (QC) and ethylnorbornane (EthNB, reported in our recent work: Wang et al.,2020), were performed in a flow reactor at atmospheric and high pressure over 348–1173 K. The mole fraction profiles of products in three fuels pyrolysis were obtained using online GC–MS/FID. Based on theoretical calculations and literature research, a universal kinetic model (397 species and 1522 reactions) of QC and EthNB, incorporating the sub-mechanisms of c-C5H6 and polycyclic aromatics, was constructed in this work. It was validated against the present data and pyrolysis data of c-C5H6 as well as norbornane in literature with reasonable reproducibility. The rate of production analysis shows that the retro-Diels-Alder reaction to c-C5H6 plus C2H2 is always the dominant path to 2,5-norbornadiene (NBD, the only isomer product of QC) consumption at atmospheric and high pressures, whereas the contribution of isomerization to 1,3,5-cycloheptatriene increases with the increasing pressure and is almost equal to that of the former at high pressure and low conversion. The aromatics formation channels in QC pyrolysis are affected by the presence of C2H2 and different from those of c-C5H6 pyrolysis, especially under high pressure. For EthNB decomposition, the open-ring and H-abstraction reactions play a dominant role. The C2-C6 alkene products are formed via the decomposition of ethylnorbornyl radicals and the further reactions of these alkenes are the precursors of aromatics in EthNB pyrolysis. Although QC and EthNB have a similar U-shaped carbon skeleton structure, the difference is that the former has an extra four-membered ring with more strain energy, which leads a lower initial decomposition temperature. Similarly, the extra CC double bonds, in NBD compared to EthNB, result in more c-C5H6 and C2H2 formation and further increase the growing tendency of initial PAH.