Structure identification and dissociation enthalpy measurements of the CO2 + N2 hydrates for their application to CO2 capture and storage

• We examined the structure and dissociation enthalpies of CO2 + N2 hydrates.
• The μ-DSC provided reliable hydrate phase equilibrium data.
• The structural transition was not observed in the range of flue gas compositions.
• The ΔHd of CO2 + N2 hydrates increased with an increase of CO2 composition.

In this study, the mixed gas hydrates formed from the flue gas mixtures of CO2 + N2 have been investigated with a primary focus on the structure identification and the dissociation enthalpy measurements. The stability conditions of the CO2 + N2 gas hydrates are determined using an isochoric (PVT) method and a differential scanning calorimeter (DSC). It is found from the comparison of the hydrate phase equilibrium data measured using two methods that the DSC can be effectively used as an alternative method for measuring the stability conditions of the CO2 + N2 gas hydrates. The microscopic analyses, such as powder X-ray diffraction and Raman spectroscopy, demonstrated that the gas mixtures of CO2 + N2 form a structure I hydrate and that the structural transition does not occur in the range of the flue gas composition. To reveal the dissociation behavior of the mixed gas hydrates, the dissociation enthalpies of the CO2 + N2 gas hydrates have been measured using a micro-differential scanning calorimeter (μ-DSC). The dissociation heats of the CO2 + N2 gas hydrates increased with an increase of the CO2 composition in the hydrate phase. The experimental results obtained in this study provide the thermodynamic and physical background required to estimate the heat liberated or absorbed during hydrate formation and dissociation and to predict the operation conditions for the gas hydrate-based CO2 capture and storage process.