In situ Raman spectroscopic study of the pressure effect on the concentration of CO2 in water at hydrate-liquid water equilibrium up to 900 bar

• CO2 concentrations in water in equilibrium with hydrate were measured by Raman spectroscopy.
• The pressure effect was studied from 50 to 900 bar at 276.15, 280.15, and 285.15 K.
• CO2 concentration in equilibrium with hydrate decreases slightly with increasing pressure.

CO2 hydrate may form during the injection of CO2 into the submarine environment for CO2 storage or enhanced recovery of CH4 hydrate. The growth of CO2 hydrate in seawater is dependent on the concentration of CO2 in seawater in equilibrium with hydrate. However, such data are currently only available at pressures below 250 bar, and the pressure effect on the concentration of CO2 in water at hydrate-liquid water equilibrium still remains controversial. In this study, Raman spectroscopy was applied to measure the concentration of CO2 in water in equilibrium with hydrate from 276.15 to 289.05 K and from 30 to 900 bar. Our results show that the concentration of CO2 in water at hydrate-liquid water equilibrium increases with increasing temperature (∼0.081 mol/(kg K) on average), but decreases slightly with increasing pressure (−0.016, −0.021 and −0.034 mol/(kg·100 bar) at 276.15, 280.15 and 285.15 K, respectively). An equation that can well reproduce the current and previous measurements of CO2 concentration in water at hydrate-liquid water equilibrium was proposed.