Carbon nanotubes serving as fixed and flowable beds for enhanced methane storage in hydrates

Achieving the rapid formation of methane hydrates together with high density is critical to utilize this hydrate-based energy storage technology. Herein, CNTs were adopted as the media for methane hydrate formation, which were designed as fixed or flowable beds by regulating the mass ratio between CNTs and reaction solution. The mobility of the reaction solution in the beds was confirmed as the most critical factor affecting the hydrate formation process. For flowable bed containing DI water, even though the initial hydrate growth rate was lower than that of fixed bed (R 30 of 0.53 ± 0.16 vs 1.60 ± 0.19 v/v·min −1 for CNTs-2) due to fewer hydrate nucleation sites, the higher mobility of reaction solution resulted in much higher water-to-hydrate conversion (methane storage capacity of 125.2 ± 4.0 vs 83.3 ± 4.5 v/v for CNTs-2). When Leucine was coupled, the flowable bed with high mobility of reaction solution exhibited extremely efficient enhancement of hydrate formation kinetics, which achieved the synergistic effects of Leucine and CNTs beds, combining the rapid hydrate formation (t 90 of 16.3 ± 0.63 min and methane storage capacity of 142.9 ± 3.4 v/v for CNTs-2) with high apparent density. Moreover, CNTs-2 bed with looser network structure and higher mobility of reaction solution performed much better than CNTs-1 bed, further verifying the significant role of the mobility of the reaction solution in achieving high-efficiency methane hydrate formation. In general, this work, for the first time, proposed the concept of flowable bed for methane hydrate formation and determined the significant role of mobility of reaction solution, providing important guidance for the industrial application of hydrate technology.