(642d) Adsorption Behaviors of Sodium Dodecyl Sulfate Onto Clathrate Hydrates in Electrolyte Solutions

Zhang, J., The City College of New York
Lee, J. W., The City College of New York

Clathrate Hydrates are ice-like non-stoichiometric crystalline compounds where water molecules (host molecules) form cages that trap low molecular weight molecules (guest molecules). Clathrate hydrates have attracted lots of attention since the discovery of large reserves of natural gas hydrates in oceanic deposits and permafrost areas because of the potential of methane hydrate as an energy resource. On the other hand, synthetic methane hydrates provide a promising gas storage capacity with 170 vol./vol. of hydrates.  Both methane recovery from the hydrate deposits and methane storage in hydrate forms require solid understanding of hydrate formation kinetics. Gas hydrate formation is slow due to the diffusion limitation of guest molecules into a liquid-solid growth front but this can be subdued by mechanical agitation and by addition of a small amount of surfactant. Sodium dodecyl sulfate (SDS) has been shown to be a potent surfactant for improving hydrate formation kinetics of low molecular weight hydrocarbon guest molecules like methane but the mechanism by which SDS improves the kinetics of hydrate formation is not well understood. The adsorption of SDS on cyclopentane hydrate-water interface was reported to be a main factor for the enhanced kinetics and possible orientations of SDS molecules at the hydrate-water interface are proposed [1]. Another study observed a marked increase in hydrate formation when 20 ppm SDS in 1 mM NaCl solution was used for a methane-cyclopentane (CP)-water hydrate system. However, the effect of salt on SDS adsorption was not clearly understood.  It was not also understood as to why the highest enclathration rate was observed for the case of 1 mM NaCl and how this is related to the SDS adsorption behavior. In this presentation, we try to understand the adsorption behaviors of SDS at CP hydrate-water interface in NaCl solutions by determining SDS adsorption isotherms and SDS solubility. Zeta potentials of CP hydrate particles will be shown to serve as backup data for the adsorption isotherm.

Literature Cited:

[1] C. Lo, J.S. Zhang. A. Couzis, P. Somasundaran, J.W. Lee.  J. Phys. Chem. C 114 (2010) 13385–13389.

[2]  S. Zhang, J. A. Salera, J. W. Lee. Ind. Eng. Chem. Res.  49 (2010) 8267-8270.