A new methane hydrate decomposition model considering intrinsic kinetics and mass transfer

Kinetics of the hydrate decomposition is crucial for the industrial application of hydrate related technologies, but there still remains challenges for describing and modeling its microscopic mechanism. Based on the concepts and achievements published by the predecessors, a somewhat more realistic microscopic methane hydrate decomposition mechanism hypothesis is proposed, which consists of three steps: desorption step of gas molecules in the linked cages, collapse step of linked and basic cages, and diffusion step of gas molecules to the bulk phase. Afterwards, a new hydrate decomposition model considering intrinsic kinetics and mass transfer is established. We use Statistical Rate Theory to explain the desorption step of gas molecules in the linked cavities and Interface Response Function to explain the collapse step of linked and basic cavities, and Molecules Diffusion Theory is used to explain the diffusion step of gas molecules to the bulk phase. This model can characterize the effects of partially occupied linked cages and completely occupied basic cages on the hydrate decomposition and can analyze the differences in driving force between isothermal depressurization and isobaric heating decomposition quantitatively. The required unknown model parameters are extracted from the published experimental data. The model validation shows that the accuracy of this model is within acceptable range. According to the simulation results, we found how the desorption and collapse steps affect the intrinsic kinetics of hydrate decomposition on microscopic scope, and the influence of stirring rate on the mass transfer of hydrate decomposition are discussed. These findings are of great practical value to give a deeper understanding of hydrate decomposition kinetics, which can promote further engineering application of hydrate related technologies.