ReaxFF molecular dynamics simulations of methane clathrate combustion

DS Bai and J Zhang, JOURNAL OF CHEMICAL PHYSICS, 160, 094710 (2024).

DOI: 10.1063/5.0189469

Understanding the ignition and dynamic processes for the combustion of hydrate is crucial for efficient energy utilization. Through reactive force field molecular dynamics simulations, we studied the high- temperature decomposition and combustion processes of methane hydrates in a pure oxygen environment. We found that at an ignition temperature of 2800 K, hydrates decomposed from the interface to the interior, but the layer-by-layer manner was no longer strictly satisfied. At the beginning of combustion, water molecules reacted first to generate OH center dot, followed by methane oxidation. The combustion pathway of methane is CH4 -> CH3 center dot -> CH3O center dot -> CH2O ->(HCO)-O-center dot -> HCOO center dot -> CO(CO2). During the combustion process, a liquid water layer was formed between melted methane and oxygen, which hindered the reaction's progress. When there is no heat resistance, oxygen will transform into radicals such as OH center dot and O-center dot, which have faster diffusion rates, allowing oxygen to conveniently cross the mass transfer barrier of the liquid water layer and participate in the combustion process. Increasing the amount of OH center dot may cause a surge in the reaction. On the other hand, when significant heat resistance exists, OH center dot is difficult to react with low-temperature hydrate components, but it can transform into O-center dot to trigger the oxidation of methane. The H-center dot generated has a sufficient lifetime to contact high- temperature oxygen molecules, converting oxygen into radicals that easily cross the water layer to achieve mass transfer. Therefore, finding ways to convert oxygen into various radicals is the key to solving the incomplete combustion of hydrates. Finally, the reaction pathways and microscopic reaction mechanisms of each species are proposed.

Return to Publications page