Dissociation enthalpy of methane hydrate in salt solution

Abstract The dissociation enthalpy of methane hydrate is an important thermal parameter for hydrate-related work. In this paper, the dissociation enthalpies of methane hydrate in various salt solutions are calculated using the previously measured H-L W -V equilibrium data by the Clapeyron equation and the Clausius-Clapeyron equation, respectively. The calculated results by the Clapeyron equation do not show temperature dependence and the order of the dissociation enthalpy of methane hydrate in different salt solutions is 0.5NaCl>0.5MgCl 2 >0.5CaCl 2 > 1.0NaCl >1.0CaCl 2 >2.0NaCl>1.0MgCl 2 , the corresponding value of which is 52.6 ± 0.1 kJ/mol, 51.3 ± 0.3 kJ/mol, 50.4 ± 0.5 kJ/mol, 49.4 ± 0.3 kJ/mol, 46.0 ± 0.2 kJ/mol, 45.1 ± 0.2 kJ/mol and 44.0 ± 0.3 kJ/mol. Both the values and the errors calculated by the Clausius-Clapeyron equation are bigger than those by the Clapeyron equation. Moreover, the calculated values obtained by the Clausius-Clapeyron equation decrease with the temperature increase. Cations have less effect on the dissociation enthalpy than anions due to the different ability in affecting the ambient water networks. However, how the two effects (the colligative effect and the salting out effect) combine to influence the dissociation enthalpy of hydrate needs to be investigated further.