Synergistic CH4 recovery and CO2 sequestration through amino acid-assisted injection in methane hydrate sediments

Abstract

Methane (CH4) hydrates exist on the seabed globally. This study explores the novel concept of methane recovery by CO2 exchange into CH4 hydrate through depressurization-assisted CO2 injection. For the first time, we demonstrate the effectiveness of CH4 recovery and CO2 sequestration using l-Leucine amino acid. Three different approaches of additive injection to assess feasible methane recovery were studied. The investigation focuses on the thermodynamic region between CH4 and CO2 phase equilibrium lines in the presence of 0.5 wt% leucine. The amino acid system shows a 5 % increase in CH4 recovery compared to the pure sediment system. Gas exchange kinetics suggest equilibration of released methane and injected CO2, prompting recrystallization into mixed hydrate. CO2 consumption correlates with initial CH4 hydrate conversion, with higher methane conversion resulting in lower CO2 intake. The amino acid system promotes quicker hydrate dissociation and greater stability of mixed hydrates, preventing induced melting during depressurization. Ex-situ Raman analysis performed after the CO2 exchange in 0.5 wt% Leucine system resulted in a four-wave number upward shift at 2919 cm−1 indicating partial distortion of small cages. The Large (L)/Small (S) cage intensity ratio of CH4 hydrate after swapping is 0.57, suggesting a 50 % methane replacement by CO2 with preferential CO2 occupying large cages.