New combination of thermodynamic and kinetic promoters to enhance carbon dioxide hydrate formation under static conditions

Abstract

Gas hydrate based technologies have been considered as a promising novel approach for the capture of carbon dioxide from fuel and flue gas mixtures, sequestration of CO2, storage of cold energy, and desalination of seawater. However, the practical application of these technologies is restricted due to the slow kinetics of CO2 hydrate formation and the low conversion of water into hydrate, especially without stirring. In the presented work, the effect of the mixed additive of 1,1,1,2-tetrafluoroethane (CH2FCF3, R-134a) and sodium dodecyl sulphate (SDS) on the CO2 enclathration into hydrate is studied. The experiments were carried out with a gas mixture of 94 mol% CO2 + 6 mol% R-134a for pure water and 0.1 wt% SDS solution in an unstirred reactor. The addition of R-134a alone (without SDS) decreased the induction time but did not affect the hydrate growth kinetics or the water conversion into hydrate. The addition of SDS did not affect the induction time for the mixed CO2 + R-134a hydrate but decreased the induction time for the simple CO2 hydrate and increased both the hydrate growth rate and the water conversion. Visual observation of the hydrate formation for the CO2 + R-134a gas mixture revealed that, without SDS, the hydrate formation was limited by the lateral growth of the hydrate film at the gas-liquid interface. In the presence of SDS, the capillary-driven hydrate growth on the reactor walls was observed with the water conversion into hydrate of more than 90%. The possible mechanism for the joint effect of R-134a and SDS on the CO2 enclathration into hydrate was discussed.