Impact of Different Surfactants and their Mixtures on Methane-Hydrate Formation

Gas hydrates can be used as a potential means for natural gas storage. Design of a gas-hydrate-based unit requires accurate knowledge of hydrate-formation kinetics especially in the presence of promoters. In this study, the effects of sodium dodecyl sulfate (SDS), hexa decyl trimethyl ammonium bromide (HTABr), polyoxy ethylene(20) cetyl ether (Brij-58) and mixtures of SDS with HTABr and Brij-58 have been investigated to determine their influence on the methane-hydrate-formation kinetics and thermodynamics. The study on the kinetics of hydrate formation is focused on the induction time and hydrate-formation rate. It is found that induction time of hydrate formation in the presence of a promoter is reduced considerably for each test compared with a pure water test. The minimum value of the induction time is found for a mixture of SDS (500 ppm) with HTABr (700 ppm). All of the surfactants and their mixtures can be designated as hydrate-formation promoters in the concentration ranges studied in the present work and can increase the hydrate-formation rate. SDS at a concentration of 500 ppm is determined to be the best hydrate-formation promoter among the surfactants tested. The percent conversion of methane to hydrate is increased in the presence of these surfactants at the end of hydrate formation. The maximum value of the conversion is observed for the 500 ppm concentration of SDS. The results demonstrate that these surfactants and their corresponding mixtures have no significant effect on the thermodynamics of methane hydrate formation.