Monte Carlo adiabatic simulation of equilibrium reacting systems: The ammonia synthesis reaction

We present an application of the recently developed Monte Carlo method for simulations at fixed total enthalpy [W. R. Smith, M. Lísal, Phys. Rev. E 66 (2002) 01114-1–01114-3], combined with the reaction ensemble Monte Carlo method, for the direct prediction of equilibrium reactive adiabatic processes. For the industrially important ammonia synthesis reaction in an adiabatic plug-flow reactor, we perform direct simulations of the equilibrium reaction temperature and the composition of the exit stream as a function of the temperature and pressure of the inlet stream. The chemical species of the system are represented by all-atom potentials with interaction parameters taken from the literature. The accuracy of the molecular model is validated by comparing simulation results with experimental data. We also compare the simulation results with a macroscopic thermodynamic model based on the Soave–Redlich–Kwong equation of state. The simulation results for the reaction conversion show very good agreement with available experimental data over a wide range of temperatures and pressures, whereas the corresponding results from the macroscopic thermodynamic model slightly deteriorate with increasing pressure. Based on these comparisons, the predicted values of the reaction temperature and composition of the exit stream from the simulations are more accurate than the corresponding predicted values from the macroscopic thermodynamic model.