l-Methionine modified active ice enables ultra-rapid methane hydrate kinetics for solidified natural gas storage

Abstract

Hydrate-based solidified natural gas (SNG) technology offers significant potential due to its high volumetric density and inherent safety. However, the slow kinetics of CH₄ hydrate formation from conventional gas–liquid systems has long limited its large-scale application. Herein, we report a green approach by introducing an environmentally benign amino acid, L-methionine (L-Met), to synthesize active ice for ultra-rapid CH₄ hydrate kinetics. Active ice modified by optimal 0.3 wt% L-Met enabled a high CH₄ uptake of 156.05 V_g/V_w and a record-high growth rate with a t₉₀ of 3.33 min, representing one of the fastest CH₄ hydrate formation rates to date. Cryogenic scanning electron microscopy revealed that 0.3 wt% L-Met modified active ice exhibited a well-connected porous structure with open pore size ranging from 7 to 17 μm, whereas both pure ice and high-dose L-Met modified active ice both exhibited a compact morphology with closed pores. We employ both in situ Raman and Fourier transform infrared spectroscopy to examine the micro-kinetics and reveal for the first time the strong correlation between ultra-rapid CH₄ hydrate kinetics and the partially ordered hydrogen bond network in active ice. High-dose L-Met modified active ice reduced the hydrogen bond ordering, while pure ice increased the rigidity of the ordered hydrogen bond. The combination of the designed partially ordered hydrogen bond network and the observed porous structure of the active ice collectively promoted the ultra-rapid formation of CH₄ hydrate for effective natural gas storage. Our study provides molecular-level insights into the mechanism of L-Met modified active ice in promoting CH₄ hydrate formation and develops an energy-efficient route for SNG technology.