Molecular dynamic study on hydrogen production from unsymmetrical dimethylhydrazine in supercritical water

Supercritical water gasification technology has been proved to be an alternative to realize both resource utilization and harmless treatment. However, atomistic simulation should be investigated as a supplement to our previous experiment to fully understand the gasification mechanism process of unsymmetrical dimethylhydrazine (UDMH) in supercritical water. The degradation mechanism was studied with molecular dynamic using the DFT and ReaxFF combination method. Simulation under different temperatures was systematically discussed to investigate the product distribution. It was found that hydrogen yield dominates and the amount of methane and ammonia tend to decrease at high temperature. The degradation mechanism was also developed. There are two ways of UDMH's degradation: the bond breaking of carbon–nitrogen or nitrogen-nitrogen bond. High temperature favors the former while low temperature favors the latter. We also analyzed the source of product species and found that abundant free radicals resulted from high temperature is the main reason for the dominant hydrogen yield. The yield of methane is resulted from two competing mechanisms, whereas element nitrogen in unsymmetrical dimethylhydrazine is transformed to nitrogen and ammonia.