Methane Hydrate Formation Improved by Water-Soluble Carbon Nanotubes Via Π-Π Conjugated Molecules Functionalization

The carbon nanotubes (CNTs) have been reported as an efficient kinetic promoter for hydrate formation. However, their effects would be weakened by the severe aggregation of the hydrophobic nanotubes. In this work, the carbon nanotubes coated by pi-pi conjugated molecules of reactive red 195 (RR195) was prepared using method of either sonication or ball milling. These functionalized CNTs showed highly solubility and stability in aqueous phase. When the water-soluble coated CNTs (RR195@CNTs) was used in hydrate reaction system, the formation could finish within the shortest time of 203 +/- 20 min and the gas storage capacity was improved from 40 +/- 8 v/v in deionized water to the high value of 140 +/- 2 v/v in the RR195@CNTs dispersion. In comparison, the ball milling treated CNTs showed preferable promotion effect on both expediting hydrate formation and elevating the energy storage efficiency. Moreover, the sonication treated CNTs had only three times of favorable recycling uses, while seven cycles of hydrate formation-dissociation processes were achieved with the ball milling treated CNTs as promoter. Besides, the formed methane hydrates with RR195@CNTs as promoters generated no foams during the dissociation process, which was also welcomed in the actual hydrate-based natural gas release and utilization process.