Thermal Rate Constants and ReaxFF MD simulation of the Pyrolysis of n-Heptane

The pyrolysis mechanism and kinetics of n-Heptane are investigated by using statistical-theoretical methodology and reactive molecular dynamics (ReaxFF MD) simulation. Firstly, we studied the temperature and pressure dependence rate constants of pyrolysis of n-Heptane in detail. The pyrolysis mechanism includes the important P-reaction, β-scission reaction and H-atom abstraction reaction, consisting of 22 species, 28 reactions and 25 transition states. The energy barrier and geometrical parameters of transition states have been calculated at a high level of CCSD (T)/6-311G (d, p)//B3LYP/6-311G (d, p). The temperature-dependent rate constants for individual reaction have been obtained in the temperature range of 200-3000 K using variational transition state theory and Rice–Ramsperger–Kassel–Marcus theory. The pressure dependence rate constants have been treated by one-dimensional master equation calculations at different pressure as well as high-pressure limit. Three-parameter fittings of the calculated rate constants are given at several different pressures. Secondly, we carried out molecular dynamics (MD) simulation employing the ReaxFF reactive force field. We found the initiation mechanism of decomposition of n-Heptane involve the cleavage of C-C bond, resulting in the formation of smaller radicals. The free radical chain mechanism of pyrolysis of hydrocarbons can be proved from the MD result. ReaxFF MD leads to good agreement with experiment for the product distribution as a function of conversion of reactant. Moreover, based on the first-order kinetic analysis of n-Heptane, we calculate an activation energy of 51.19 kcal/mol, which is consisted with the experimental result. Besides, temperature-dependent MD simulations give the detailed pyrolysis distributions of n-Heptane at high temperature and the temperature influences on the kinetics mechanism of pyrolysis of n-Heptane.The pyrolysis mechanism and kinetics of n-Heptane are investigated by using statistical-theoretical methodology and reactive molecular dynamics (ReaxFF MD) simulation. Firstly, we studied the temperature and pressure dependence rate constants of pyrolysis of n-Heptane in detail. The pyrolysis mechanism includes the important P-reaction, β-scission reaction and H-atom abstraction reaction, consisting of 22 species, 28 reactions and 25 transition states. The energy barrier and geometrical parameters of transition states have been calculated at a high level of CCSD (T)/6-311G (d, p)//B3LYP/6-311G (d, p). The temperature-dependent rate constants for individual reaction have been obtained in the temperature range of 200-3000 K using variational transition state theory and Rice–Ramsperger–Kassel–Marcus theory. The pressure dependence rate constants have been treated by one-dimensional master equation calculations at different pressure as well as high-pressure limit. Three-parameter fittings of the calculated rate constants are given at several different pressures. Secondly, we carried out molecular dynamics (MD) simulation employing the ReaxFF reactive force field. We found the initiation mechanism of decomposition of n-Heptane involve the cleavage of C-C bond, resulting in the formation of smaller radicals. The free radical chain mechanism of pyrolysis of hydrocarbons can be proved from the MD result. ReaxFF MD leads to good agreement with experiment for the product distribution as a function of conversion of reactant. Moreover, based on the first-order kinetic analysis of n-Heptane, we calculate an activation energy of 51.19 kcal/mol, which is consisted with the experimental result. Besides, temperature-dependent MD simulations give the detailed pyrolysis distributions of n-Heptane at high temperature and the temperature influences on the kinetics mechanism of pyrolysis of n-Heptane