The influence of SO2 and NO2 impurities on CO2 gas hydrate formation and stability.

The sequestration of industrially emitted CO(2) in gas hydrate reservoirs has been recently discussed as an option to reduce atmospheric greenhouse gas. This CO(2) contains, despite much effort to clean it, traces of impurities such as SO(2) and NO(2) . Here, we present results of a pilot study on CO(2) hydrates contaminated with 1% SO(2) or 1% NO(2) and show the impact on hydrate formation and stability. Microscopic observations show similar hydrate formation rates, but an increase in hydrate stability in the presence of SO(2). Laser Raman spectroscopy indicates a strong enrichment of SO(2) in the liquid and hydrate phase and its incorporation in both large and small cages of the hydrate lattice. NO(2) is not verifiable by laser Raman spectroscopy, only the presence of nitrate ions could be confirmed. Differential scanning calorimetry analyses show that hydrate stability and dissociation enthalpy of mixed CO(2)-SO(2) hydrates increase, but that only negligible changes arise in the presence of NO(2) impurities. X-ray diffraction data reveal the formation of sI hydrate in all experiments. The conversion rates of ice+gas to hydrate increase in the presence of SO(2), but decrease in the presence of NO(2). After hydrate dissociation, SO(2) and NO(2) dissolved in water and form strong acids.