Effects of ionic surfactants on methane hydrate formation kinetics in a static system

Abstract

This paper reports an experimental study of the kinetics of methane hydrate formation in the presence of ionic surfactants with equal carbon chain length, such as sodium dodecyl sulfate (SDS), dodecylamine hydrochloride (DAH), dodecyltrimethylammonium chloride (DTAC) and N-dodecylpropane-1,3-diamine hydrochloride (DN2Cl). Methane hydrates were formed at 274K with incipient gas pressure of 15MPa in an unstirred isochoric/isothermal reactor containing aqueous solutions at different initial surfactant loadings. It was found that addition of DTAC had little effect on methane hydrate formation whereas SDS, DAH, and DN2Cl had pronounced promoting effects. This result coincides with the fact that the Krafft point of DTAC is below 273K and those of SDS, DAH, and DN2Cl are near room temperature. At a given initial surfactant loading, the effectiveness of the surfactants for reducing the induction time of methane hydrate formation followed the order of SDS>DAH>DN2Cl. SDS also gave higher hydrate growth rates than DAH and DN2Cl. At 1000 and 2000ppm, however, DN2Cl gave slightly higher final methane uptake than SDS. It was also found that during the nucleation or induction period, addition of SDS, DAH and DN2Cl instead of DTAC, considerably reduced methane mole fraction in the liquid phase. Possible promotion mechanisms of surfactants during the hydrate nucleation period were discussed.