Management of Formation Kinetics and Energy Storage Capacity of Methane Hydrates via Ag-Modified Graphene Aerogel

The use of a fixed bed has emerged as an effective approach to enhance methane hydrate formation for energy storage. In this study, a novel fixed bed was developed by incorporating Ag nanoparticles, which could serve as hydrate nucleation sites to ultralight graphene aerogel (Ag@GA) and then evaluated in methane hydrate formation. The presence of Ag nanoparticles on the fixed bed enhanced the hydrate nucleation dramatically, which shortened the induction time from 775.3 ± 186.66 min without Ag nanoparticles to 0–15 min. With the increase in the initial pressure (5–8 MPa), the hydrate growth rate ascended gradually from 0.063 to 0.26 mol/min/L, while the mass storage capacity remained stable at a high level of 0.120–0.126 g/g. The temperature in the range 273.15–276.15 K did not produce an obvious influence on both the hydrate formation kinetics and methane storage efficiency. However, the concentration of the kinetic promoter (l-methionine) dominated the hydrate formation significantly, especially the hydrate growth rate and morphology. At a low l-Met concentration (1 g/L), hydrates formed majorly in the inner pores of the fixed bed with a high growth rate (0.27 mol/min/L), while with the l-Met concentration increased to 2, 3, and 4 g/L, hydrates tended to grow out of the fixed bed and accumulated on the top and lateral surface. The morphology of hydrates varied from acicular crystals to hydrate blocks, and the hydrate growth rate decreased to 0.099 mol/min/L and then increased to 0.17 and 0.25 mol/min/L. Moreover, the excellent cyclic performance of Ag@GA was confirmed in five cycles of hydrate formation and dissociation, in which the induction time was 0–8.3 min, the hydrate growth rate reached 0.254–0.263 mol/min/L, and the methane storage capacity was kept at 135–145 V/V. This study provides an effective pathway for the application of ultralight fixed beds in hydrate-based natural gas storage and transportation.