Molecular simulation study on the evolution process of hydrate residual structures into hydrate

Abstract

The clathrate hydrate memory effect is a fascinating phenomenon with potential applications in CCUS, gas separation, and gas storage as it can accelerate the secondary formation of clathrate hydrate. However, the underlying mechanism of this effect remains unclear. To gain a better understanding of the mechanism, we conducted molecular dynamic simulations to simulate the initial formation and reformation processes of methane hydrate. In this work, we showed the evolution process of hydrate residual structures into hydrate cages. The simulation results indicate that the residual structures are closely related to the existence of hydrate memory effect, and the higher the contribution of hydrate dissociated water to the hydrate nucleation process, the faster the hydrate nucleation. After hydrate dissociation, the locally ordered structures still exist after hydrate dissociation and can promote the formation of cluster structures, thus accelerating hydrate nucleation. Additionally, the nucleation process of hydrate and the formation process of clusters are inseparable. The size of clusters composed of cup-cage structures is critical for hydrate nucleation. The residence time at high temperature after hydrate decomposition will affect the strength of the hydrate memory effect. Our simulation results provide microscopic insights into the occurrence of the hydrate memory effect and shed light on the hydrate reformation process at the molecular scale.