Effects of additive mixtures (THF/SDS) on carbon dioxide hydrate formation and dissociation in porous media

摘要

The characteristics and stability conditions of carbon dioxide (CO_2) hydrate formation are crucial for hydrate-based CO_2 capture and storage. The effects of a mixture of additives (THF/SDS) on CO_2 hydrate formation and dissociation in porous media have been investigated experimentally using a graphic method. The Gibbs phase rule is used to analyze the experimental p-T curves. Hydrate formation processes can be divided into two cases, depending on the CO_2 initial state. The experimental results showed that 1000mg/L SDS is the best additive and concentration for CO_2 hydrate formation among those studied in this investigation due to its shorter induction time and resultantly higher hydrate saturation than those of other concentrations. The presence of 3mol% THF dramatically decreased the hydrate phase equilibrium pressure. The hydrate equilibrium temperature is 291.55K in the aqueous phase with 3mol% THF and 0mg/L SDS, which is the highest equilibrium temperature at 3.04MPa observed in this investigation. The experimental results also showed that "pseudo-retrograde" behavior exists at nearly 3.00MPa with all SDS concentrations. An improved model is used to predict the phase equilibrium conditions for CO_2 hydrates in glass beads in the presence of THF, in which the mechanical equilibrium of force between the interfaces in a hydrate-liquid-vapor system is considered.