The impact of SO2 on post combustion carbon dioxide capture in bed of silica sand through hydrate formation

Abstract

Hydrate crystallization technology is one of the novel approaches for capturing carbon dioxide from flue gases. The presence of impurities such as SO2, NO2, H2S can influence the CO2 hydrate formation process. In the present work the impact of SO2 on hydrate equilibrium was investigated using the isothermal pressure search method. The hydrate equilibrium shifted to low pressures and high temperatures in the presence of small amount SO2. For example the hydrate formation pressure shifted from 7.7MPa to 7.25MPa at 273.75K. In addition, the presence of SO2 enhanced the initial hydrate formation rate and final moles of gas consumed 16h after the hydrate nucleation. The CO2 and SO2 gases were preferentially incorporated into the hydrate phase. The presence of SO2 helps the thermodynamics and kinetics of the hydrate formation process. Therefore complete removal of this SO2 impurity is not necessary; in fact it aids both thermodynamically and kinetically for hydrate formation, which indeed is a positive factor for the capture and geological sequestration of CO2 in the form of hydrates. The addition of THF reduces the CO2/N2/SO2 hydrate formation conditions (from 7.25MPa to 0.15MPa at 273.75K), which is practically important for reducing high compression costs. Moreover, the presence of THF decreases the hydrate nucleation time but reduces the hydrate formation rate significantly.