Raman Spectroscopic Study of the Effect of Aqueous Salt Solutions on the Inhibition of Carbon Dioxide Gas Hydrates.

We present an experimental Raman study on the thermodynamic inhibition effect of different salts (NaCl, KCl, MgCl2 and CaCl2 from 2.5 - 11 wt-%) on the formation of carbon dioxide gas hydrates. We performed the experiments in a high pressure vessel with two phases: A water-rich phase and a CO2 -rich phase. We investigated the changes the inhibitors induce in the water-rich phase before the onset of hydrate formation. This includes a study of the change in molar reaction enthalpy between strongly and weakly hydrogen bonded water and the decrease in solubility of carbon dioxide in water. Additionally, the growth mechanisms of carbon dioxide hydrates were investigated by determining the amount of solid hydrate formed and the reaction constant. The results show that the molar reaction enthalpy, the solubility of CO2 and the amount of solid hydrate formed can be correlated with the effective mole fraction, whereas the reaction constant is not affected by the addition of salts. The decrease of the molar reaction enthalpy can be directly correlated with the equilibrium temperature of the gas hydrates.