Molecular Dynamics Study of Combustion Reactions in Supercritical Environment. Part 3: Boxed MD Study of CH₃ + HO₂ → CH₃O + OH Reaction Kinetics

Abstract

The kinetics of reaction CH + HO → CHO + OH in supercritical carbon dioxide media at pressures from 0.3 to 1000 atm in the temperature range (600-1600) K was studied using boxed molecular dynamics simulations at QM/MM theory level with periodical boundary conditions. The mechanism of this process includes two consecutive steps: formation and decomposition of CHOOH intermediate. We calculated the activation free energies and rate constants of each step, then used Bodenstein's quasistationary concentrations approximation to estimate the rate constants of the reaction. On the basis of the temperature dependence of the rate constants, parameters in the extended Arrhenius equation were determined. We found that reaction rate of each step, as well as overall reaction, increases with increasing CO pressure in the system. The most effective zone for the process is T = 1000-1200 K, and the CO pressure is about 100 atm.

An Optimized Methane Reaction Model for Oxyfuel Combustion

“…Rate constants predicted by using the investigated models and measured experimentally are shown in Figure . Around 1000 K, the optimized rate constant of CH 3 + HO 2 = OH + CH 3 O shows improved agreement with the recent theoretical work of Panteleev et al while remaining close to the data of Hong et al The optimized rate constant of CH 3 + HO 2 = O 2 + CH 4 shows excellent agreement with the data of Hong et al…”

Molecular Dynamics of Combustion Reactions in Supercritical Carbon Dioxide. Part 5: Computational Study of Ethane Dissociation and Recombination Reactions C2H6 ⇌ CH3 + CH3

“…In our previous studies, we have modeled equation-of-state parameters, reduced combustion mechanism, and analyzed counterflow diffusion flame in sCO 2 environment. We also predicted the catalytic effects of the CO 2 molecule on potential energy surfaces (PESs) of several reactions by quantum chemical methods, − and used molecular dynamics (MD) methods to optimize force field parameters to describe transcritical phenomena in H 2 O/CO 2 mixtures, and predict rate constants of some combustion reactions in sCO 2 environment. − …”

“…To the best of our knowledge, this work represents the first theoretical investigation of the rate constant of and in extremely high pressure in sCO 2 environment. Instead of quantum mechanics/molecular mechanics (QM/MM) with semiempirical correction by London, Eyring, Polanyi, and Sato , used in our previous publications, − here, we applied the multistate empirical valence bond (MS-EVB) , method to obtain more accurate PES. MS-EVB reproduces the reactive potential surface in the transition-state and post-transition-state regions and bridges the gap between quantum and classical mechanics.…”

Molecular Dynamics of Combustion Reactions in Supercritical Carbon Dioxide. 6. Computational Kinetics of Reactions between Hydrogen Atom and Oxygen Molecule H + O2 ⇌ HO + O and H + O2 ⇌ HO2

“…As a part of our efforts to further develop this technology, we have modeled equation-of-state parameters, developed reduced combustion mechanism, and performed counterflow diffusion flame analyses in sCO 2 environment. We also developed the force field to describe water and carbon dioxide in a mixture supercritical state, investigated potential energy surfaces (PESs) of reactions with the existence of CO 2 by density-functional theory (DFT) calculation, − and predicted the rate constant k of several important combustion reactions in high pressure of CO 2 by molecular dynamics (MD) − and DFT simulations. , In this contribution, we report advances in computational methods of reaction rate prediction in supercritical CO 2 and apply these methods to study R1 and R2.…”

“…The results showed a 4-fold increase of the rate constant from room temperature to 350 °C. Based upon our previous supercritical CO 2 study, − gas-phase free energy is strongly perturbed by the environment. However, the rate constant of bimolecular R1 with more than one product is consistent with the gas-phase high-pressure limit because collisional repopulation of states depleted by the reaction is fast enough to maintain thermal equilibrium distribution of states …”