The structural identification and guest compositions of the mixed CO 2 and N2 hydrates at low temperature conditions were investigated by both theoretical predictions and experimental measurements. From the model calculations, at very low temperatures, the highly CO 2-concentrated hydrates over 95 mol % CO2 on the basis of water-free concentration could coexist with the gas mixtures of low CO 2 concentrations in equilibrium. X-ray diffraction measurements of the hydrates formed with the gas mixture of 3.16 mol % CO2 and balanced N2 indicate that the formed hydrates at all conditions considered in this study were identified as structure I, whereas the model predicts a structural transition to structure II around 220 K. However, it was also found that the formed hydrate samples contain a considerable amount of hexagonal ice resulting from incomplete conversion of ice to the hydrates. The compositional analysis suggests that a favorable encaging of CO2 in the mixed hydrate can be obtained by the hydrate formation at low temperatures and relative amount of CO2 molecules in the mixed hydrates increases with a decrease of temperature.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films
- Materials Chemistry