Adsorption of sodium dodecyl sulfate onto clathrate hydrates in the presence of salt

This work presents the effect of NaCl on the adsorption of sodium dodecyl sulfate (SDS) at the cyclopentane (CP) hydrate–water interface. The adsorption isotherms and the SDS solubility in NaCl solutions are obtained using liquid–liquid titrations. The solubility data are determined at typical hydrate forming temperatures (274–287 K) to ensure that the adsorption isotherms are obtained within SDS solubility limits in NaCl solutions. The isotherms show L–S (Langmuir–Step) type behaviors with 1 mM and 10 mM NaCl solutions while L type isotherm is determined for 25 mM NaCl solutions due to the low SDS solubility in this salt concentration. Zeta potentials of CP hydrate particles in the aqueous solutions support the shape of the adsorption isotherm with the 1 mM NaCl solution. The 1 mM NaCl case shows the highest SDS adsorption amount among the cases with 0 mM, 10 mM, and 25 mM NaCl solutions. In this case, the competition for adsorption between Cl− and DS− is not as strong compared to the 10 and 25 mM NaCl cases and the presence of Na+ ions may reduce the repulsion between DS− ions, which results in a higher adsorption of DS− ions and enhanced enclathration.

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► Understand the effect of salt on SDS adsorption and hydrate formation kinetics.
► Observe L–S type SDS adsorption isotherms in 1 mM/10 mM NaCl solutions.
► Determine SDS solubility at low hydrate-forming temperatures in the presence of NaCl.
► Understand competitive adsorption between DS− and Cl− onto hydrate particles.
► Firstly identify Cl− adsorption to hydrate particles via zeta-potential measurements.