Molecular Mechanisms for Cyclodextrin-Promoted Methane Hydrate Formation in Water

Cyclodextrins were used as environmentally friendly additives to overcome the slow kinetics of hydrate formation that limited the industrial application of gas hydrate technology. Microsecond molecular dynamics simulations were performed to identify the degree and the underlying mechanisms of the cyclodextrin effects on the methane hydrate formation rate by the four-body order parameter and molecular configurations and to clarify the hydrate structure in the presence of cyclodextrin by face-saturated incomplete cage analysis. Overall results indicated that the addition of beta-cyclodextrin in water facilitatedthe hydrate growth rate, promoted the formation of thermodynamically stable hydrate structure, and enhanced the methane storage capacity. It highlighted the role of cyclodextrin to facilitate the formation of water channel bridging hydrate and water (at low ratio of gas to water) and to increase thezas water interfacial curvature (at high ratio of gas to water) on the accelerated kinetics of hydrate growth. The advantages of the cyclodextrin-promoted gas hydrate approach for gas storage were also highlighted by comparing it with the gas hydrate formation using other additives and the gas cyclodextrin complexation method.