ReaxFF molecular dynamics simulations of non-catalytic pyrolysis of triglyceride at high temperatures

Abstract

In order to investigate the initiation mechanisms associated with the pyrolysis of triglyceride that could potentially be used as petrochemical replacements, we carried out 500 ps molecular dynamics simulations employing the ReaxFF reactive force field using tripalmitin as the model molecule at 1500 and 2000 K. We find that the primary decomposition reactions of tripalmitin initiate with the successive scission of the alkyl-oxygen bond to form three straight chain C₁₆H₃₁O₂˙ (RCOO˙) radicals and C₃H₅˙ radical. The deoxygenated alkyl chain is produced through the decarboxylation of the RCOO˙ radical with concurrent production of CO₂. The resulting alkyl and C₃H₅˙ radicals further undergo recombination and decomposition to yield mainly alkanes and alkenes, with the actual product distribution being dependent on reaction temperature. β-Scission plays an important role in alkyl chain decomposition with a concomitant release of C₂H₄. Compared to 1500 K, this reaction is accelerated at 2000 K. In addition, the formation of cyclic hydrocarbon is also observed at 2000 K. As opposed to previous proposed Diels–Alder reactions or intramolecular cyclizations of alkenyl radicals mechanisms, it is found that cyclopentane could be produced by intramolecular cyclization of a biradical.