Mechanistic Analysis of the Pyrolysis of Vegetable Glycerin: A Reactive Force Field–Molecular Dynamics Study

Christina AlGemayel1

Joseph Zeaiter1,Email

Soha Talih2,3

Najat A. Saliba3,4

Alan Shihadeh2,3

1Baha and Walid Bassatne Department of Chemical Engineering and Advanced Energy, American University of Beirut, Beirut 1107 2020, Lebanon.
2Department of Mechanical Engineering, American University of Beirut, Beirut 1107 2020, Lebanon.
3Department of Psychology, Virginia Commonwealth University Center for the Study of Tobacco Products, Richmond, VA 23284, United States.
4Department of Chemistry, American University of Beirut, Beirut 1107 2020, Lebanon.

 

Abstract

Vegetable glycerin (VG, C3H8O3) is a triol found as an additive in food, pharmaceutical, and vaping products. Studying the pyrolysis of VG with the resulting species and their rates of formation is crucial in further understanding the underlying effects on human health. In this paper, we utilize molecular dynamics (MD) and the reactive force field (ReaxFF) to investigate VG pyrolysis. VG decomposed at a rate of activation energy Ea  = 204.3 kJ/mol and pre-exponential factor A0 = 1.42E+14 s-1. The main products were formaldehyde (FA), acetaldehyde (Ace), propanal (PA), acrolein (Acr), and glyoxal (GA). Both MD concentration profiles and transition state searches showed that FA, followed by AA, were the favored products. VG underwent several cracking mechanisms, with the cleavage of the hydroxyl group from the middle carbon having the lowest energy barrier (ΔG = 259.97 kJ/mol). Longer-chained species formed via side reactions, resulting in methacrolein, crotonaldehyde, and pentanal, along with benzene and ethylbenzene intermediates. VG decomposition was found to be endothermic where the reaction rate increased with increasing system temperature. The Ea value for decomposition and formation reactions reached a threshold at a system density of 0.13 g/mL, while the collision factor generally increased.

Mechanistic Analysis of the Pyrolysis of Vegetable Glycerin: A Reactive Force Field–Molecular Dynamics Study