Competitive adsorption between SDS and carbonate on tetrahydrofuran hydrates

Sodium dodecyl sulfate (SDS) has been well known as a promoter for the formation of hydrates. However, the use of SDS to enhance the formation of CO(2) hydrates has not been effective. This work will present an idea of competitive adsorption that will provide insights into the nonpromoting effect of SDS under high carbonate concentrations. The competitive adsorption is studied between DS(-) monomers and carbonate ions on tetrahydrofuran (THF) hydrates. The adsorption is qualitatively investigated by using pyrene fluorescence measurements. The SDS concentration at which hydrophobic domains occur on the hydrate surface increases with the increased carbonate concentration and this trend is less dependent on the order of addition of these two species. This concentration is 0.17 mM at carbonate concentrations less than 2 microM and it shifts to 3.47 mM at carbonate concentrations higher than 2.5 microM. Thus, using carbonate with its concentration higher than 2.5 microM would be enough to displace the hydrophobic domains formed by SDS up to the solubility limit.