Unveiling radical pathways in the pyrolysis of eugenol: Experimental and computational insights

Abstract

Understanding the lignin pyrolysis mechanism holds significant importance for enhancing thermochemical conversion processes and advancing the refinement of biofuels. In this paper, a mechanism study was conducted on the pyrolysis of eugenol within the temperature range of 450 to 750 °C, utilizing synchrotron photoionization mass spectrometry coupled with density functional theory. 5-allyl-2-hydroxyphenoxyl radical (m/z 149) and other major radicals were detected experimentally during eugenol pyrolysis for the first time. The cleavage of the O-CH3 bond was confirmed as the main initial unimolecular pyrolysis pathway compared with other hemolysis and isomerization reactions. Radical-assisted bimolecular reactions initiated by CH3 and H atoms, such as ipso substitution and abstraction reactions, were well discussed. Radical-assisted abstractions made the most contribution to the formation of main radicals and products at high temperatures. Furthermore, quinone-type products were determined and their formation pathways were discussed. This research provides insights into eugenol pyrolysis, shedding light on the fundamental mechanisms of thermochemical conversion of lignin.