The large-scale commercial development of natural gas hydrate puts forward requirements for efficient gas storage. Solidified natural gas storage via clathrate hydrates presents an economically sound prospect and promising high energy density. Sodium dodecyl sulfate (SDS) is regarded as one of the most effective kinetic promoters for the rapid and high-efficient conversion of CH4 hydrate. However, the mechanism that SDS influences the formation of clathrate hydrate remains controversial. Considering the differences in hydrate film formation characteristics and single crystal structure may be important reasons for the influence of SDS on hydrate formation and different promotion effects, this study investigated, from mesoscopic to molecular scale, the effects of SDS and subcooling on the evolution of CH4 hydrate film. The experimental results showed that a competitive mechanism between SDS concentration and driving force on the CH4 hydrate formation may exist, which could dominate the growth mode of CH4 hydrate. In case of the influence of subcooling being greater, a complete CH4 hydrate film was formed. Once SDS concentration dominates hydrate growth, a non-aggregated CH4 hydrate film can be formed. The critical concentrations of SDS varied with different subcooling conditions so that only if the SDS concentration exceeded the critical point can the formation of CH4 hydrate be obviously accelerated. The results obtained in this study are of great significance to guide the selection of the optimal SDS concentration for the promotion of CH4 hydrate formation and provide insights for the method modification of SDS or other surfactants accelerating CO2 hydrate formation.
Keywords CH4 hydrate, SDS concentration, subcooling, non-aggregated hydrate film, competitive mechanism