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.
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