Molecular Dynamics Simulation Study On Pyrolysis Of Light Hydrocarbon Molecules

Hydrocarbon molecules only contain carbon and hydrogen,which can provide a rich carbon source for the preparation of carbon materials.However,since the cracking process of hydrocarbon molecules is usually carried out under extreme conditions such as high temperature and high pressure.The cracking process is analyzed by experimental instruments,but there are still challenges in studying its detailed cracking mechanism.At present,the preparation process of carbon nanomaterials mostly has the presence of a metal catalyst to reduce the temperature required for the reaction,and the like,because the reaction process is rapid and complicated,the reaction mechanism is also not uniformly recognized by the researchers.The work of this paper mainly includes two parts:?1?Molecular Reactive Force-Field Simulations on the Methane PyrolysisIn this part,methane was selected as the research object.Two cubic cells with lengths of68.38 and 147.3?were constructed,each containing 1200 CH₄ molecules,which were simulated at 2500,3000 and 3500 K,for a total of six independent simulation system.By analyzing six sets of data,we found that a stable carbon nanocavities?CNC?was formed in the 3500K and 0.1g/cm3 systems.The process undergoes four stages:initial CH4 cracking,subsequent chain elongation and branching.cyclization and cycle condensation,and finally sheeting and curling.After these stages,a stable CNC with a diameter of 3.4 nm,923 C atoms and a small amount of H was obtained.?2?Molecular Dynamics Simulation Carburization of Fe Nanoparticles in Ethylene PyrolysisIn this part,we choose ethylene as a carbon source and a Fe nanoparticle as catalysts to study the carburizing mechanism of metals.Similarly,two cube models were constructed with side lengths of 71.96 and 155.04?,each containing 800 ethylene molecules and a Fe nanocluster composed of 339 iron atoms,simulated at 1500,2000 and 2500 K,respectively.By analyzing the calculation results,we found that the formation mechanism of iron carbide mainly follows the four steps:including chemisorption and dehydrogenation of C₂H₄ on the Fe nanoparticle,diffusion and polymerization of C₂H_x to form short carbon chains on the surface and in bulk of the particle,growth and branching of short chains,and chain crosslinking to longer chains and more branched chains.Our work provides deep insight into the earlier stages of the metal carburization.