Understanding the interaction between sodium dodecyl sulfate (SDS) and gas hydrates provides insight into the role of SDS in promoting gas hydrate formation. The aim of this study was to investigate the relationship between tetrahydrofuran (THF) hydrate induction and SDS adsorption at the hydrate/liquid interface. The adsorption behavior was studied by ζ-potential and pyrene fluorescence measurements. The negative charge of the hydrate particles remains constant at SDS concentrations of 0 to 0.17 mM. The ζ-potential becomes more negative as the SDS concentration increases from 0.17 to 3.4 mM. The micropolarity of the THF hydrate/ liquid interface decreases with increasing SDS concentrations, and then it remains almost unchanged at SDS concentrations above 0.17 mM. A monolayer of DSis completed at a SDS concentration of 0.17 mM. The reduction of induction time in the presence of SDS levels off at a SDS concentration of 0.17 mM. This provides strong evidence that the short induction is due to the adsorption of DSat the hydrate/liquid interface. The adsorption study of SDS on THF hydrates can be extended to other systems and we may screen suitable surfactants for accelerating or retarding gas hydrate formation.
The interaction between surfactants and hydrates provides insight into the role of surfactants in promoting hydrate formation. This work aims at understanding the adsorption behavior of sodium dodecyl sulfate (SDS) on cyclopentane (CP) hydrates and its derivative surfactant on tetrabutylammonium bromide (TBAB) hydrates. Cyclopentane (CP) is a hydrophobic former whereas tetrabutylammonium bromide (TBAB) is a salt that forms semiclathrate hydrates. The adsorption on these two hydrates was studied by zeta potential and pyrene fluorescence measurements. CP hydrates have a negative surface charge in the absence of SDS, and it decreases to a minimum as the SDS concentration increases from 0 to 0.17 mM. Then, it increases with further increased SDS concentration. The adsorption density of DS (-) on CP hydrates reaches a saturated value at 1.73 mM SDS. The micropolarity parameter of the TBAB hydrate/water interface starts to increase rapidly at 0.17 mM SDS and levels off at 1.73 mM SDS. The presence of Br (-) in TBAB hydrate suspensions could compete with TBADS (from association of DS (-) and TBA (+)) and DS (-) for the adsorption on the hydrate surface, but they have a much stronger affinity for the hydrates than does Br (-). From the fluorescence measurements, it was found that the micropolarity of the hydrate/water interface is mainly dependent on the polarity of hydrate formers.
This work presents the adsorption of an anionic surfactant, sodium dodecyl sulfate (SDS), and a cationic one, dodecyl-trimethylammonium bromide (DTAB), on cyclopentane (CP) hydrates. Adsorption isotherms were obtained by liquid−liquid titrations. Also, the adsorption was qualitatively studied by zeta potential measurements. The isotherm of both SDS and DTAB exhibits a two-plateau (L-S) type. The saturated adsorption amount in the first step (Langmuir type) is 0.01 and 0.03 mmol g−1 for SDS and DTAB, respectively. The Langmuir equilibrium constant is 1.17 mM−1 for SDS and 0.32 mM−1 for DTAB. The maximum adsorption amount of SDS in the second step (S type) is 2.5 times higher than that in the Langmuir step. The similar trend is observed for DTAB. SDS adsorption shifts the zeta potential from −60 to −90 mV in the first step, followed by a further 30 mV decrease as the adsorption approaches the second plateau. For DTAB, the zeta potential increases from −60 to 50 mV in the Langmuir step and then it approaches 90 mV in the second step. On the basis of these results, the role of surfactants in enclathration is discussed and the adsorption mechanism of surfactant on clathrate hydrates is also presented.
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