Kinematic Study of Methane Hydrate Formation and Self-Preservation in the Presence of Functionalized Carbon Nanotubes

Transportation of natural gas in the form of gas hydrates is shown to have superiority, from economic, environment, and safety viewpoints, over liquefied natural gas (LNG), especially for transferring natural gas from stranded gas reserve. However, hydrate-based technology is still under development as there are still many technical challenges, including slow production rate and stability. In this study, the effect of various multiwall carbon nanotubes (MWCNTs) on the equilibrium phase boundaries, kinetics, and self-preservation of CH4 hydrates have been studied. The carboxylated carbon nanotubes (COOH-MWCNTs) and hydroxylated carbon nanotubes (OH-MWCNTs) along with pristine MWCNTs were chosen. The carbon nanotubes were suspended in a 0.03 wt % SDS aqueous solution, and the results were compared with the SDS aqueous solution at the same concentration of 0.03 wt % and with deionized water. The CH4 hydrate phase equilibrium and kinetic parameters of the CH4 hydrate formation, including induction time, the initial rate of the hydrate formation, gas uptake, storage capacity, water-to-hydrate conversion, half-completion time, t(50), and semicompletion time, t(95), have been studied. The results show that the nanofluids studied did not affect the equilibrium conditions of the CH4 hydrates. In addition, the 0.01 wt % COOH-MWCNTs mixed with 0.03 wt % SDS showed the best promotional effect. Furthermore, a comparison between the SDS and the COOH-MWCNTs (without the SDS stabilizer) at 0.03 wt % revealed that the SDS was a more effective CH4 promoter. However, the self-preservation phenomenon at atmospheric pressure was more pronounced in the presence of the COOH-MWCNTs compared to the SDS.