Two theoretical simulations of hydrocarbons thermal cracking: Reactive force field and density functional calculations

Abstract

The aim of this study was to simulate 1-methylnaphthalene (1-MNa) thermal cracking with the use of a new reactive force field, ReaxFF, and to compare it with experimental results of 1-MNa pyrolysis and density functional calculations. Thermal decomposition of polyaromatic compounds is important to understand the oils thermal cracking in geological reservoirs. Pyrolysis experiments and simulation provided useful information on the different mechanistic pathways prevailing at the low and high conditions. Using ReaxFF, a reactive simulation of 20 1-MNa was performed at 3800 K. The main molecules and radicals formed have been analyzed. The yield of molecular hydrogen was notably high compared with that experimentally found. Simulation of 1-MNa and radicals, hydrogen atoms or methylnaphthyl radicals, were also studied to enhance reactivity at lower T. In parallel, DFT calculations with B3LYP and BH&HLYP functionals were performed on the elementary processes that may occur preferentially at low or high-temperature and the rate constant of these elementary reactions were determined using Transition State Theory. These results were in good agreement with the ReaxFF results. Preferential initiation reactions at high-temperature were also investigated through the estimation of the global activation energy accounting for 1-MNa thermal cracking with the use of ReaxFF. Again, results obtained with ReaxFF were in good agreement with experiments and DFT studies.