Effect of Organic Matters on CO2 Hydrate Formation in Ulleung Basin Sediment Suspensions

Marine sediment core samples collected from a gas hydrate deposit site (Ulleung Basin (UB), East Sea, Korea) were explored to identify the role of sediment organic matters (SOMs) on the formation of CO2 hydrate. Two distinct CO2 hydrate formation regimes (favorable (≤40 min) and unfavorable (>250 min)) were observed from the hydrate formation tests. CO2 hydrate induction time in UB sediment suspensions was approximately seven times faster than that in UB sediment suspensions without SOMs (baked UB), showing a direct influence of SOMs. Spectrometric and spectroscopic analyses confirmed the existence of different types of SOMs including nonhumic and humic substances in UB sediment samples. We found SOMs with aromatic ring structures in all sediment extracts and SOMs with amine and amide groups and lignin in alkaline extracts. SOMs were extracted from UB sediment core samples (1 g each). Measured CO2 hydrate induction times were different in baked UB sediment suspensions with different extracts of UB sediments. The experimental results demonstrated that SOMs can play a significant role to accelerate the formation of CO2 hydrate in UB sediment suspensions, suggesting that the gas hydrate deposit site at UB may be a proper place for CO2 sequestration as a form of CO2 hydrate.