Energy-efficient storage of methane in the formed hydrates with metal nanoparticles-grafted carbon nanotubes as promoter

Despite hydrate technology provides an economical and safe method to transport and store natural gas, the large-scale utilization is still restricted by the long hydrate formation process and low gas storage capacity. To address above problems, a novel nanopromoter was synthesized by electrostatic adsorption and in-situ reduction of silver or copper ions on the supports of oxidized carbon nanotubes (symbolized as metal@OCNTs). In the methane hydrate formation, with nanoparticles fraction varied from 0 to 100%, the methane consumption was improved from 44 mmol/mol water to 150 mmol.mol/water, among which Ag-grafted nanotubes performed better in accelerating hydrate formation. The increasing concentration of the nanopromoters led to reduced formation period to 125.1 min in 40 ppm Ag@OCNTs and 141.8 min in 40 ppm Cu@OCNTs. The optimum gas storage capacity was 153 V/V in 10 ppm Ag@OCNTs and 148.3 V/V in 20 ppm Cu@OCNTs. Moreover, the high methane recovery of 78.94% without foam generation was achieved during hydrate dissociation in the metals grafted carbon nanotubes nanofluids. Hence, the metal nanoparticles-grafted CNTs could facilitate both high storage capacity in the rapid hydrate formation and high methane recovery, which is of great significance to the application of hydrate-based technologies in efficient energy storage and utilization.