Alleviation of Foam Formation in a Surfactant Driven Gas Hydrate System: Insights via a Detailed Morphological Study

Abstract

Surfactants such as sodium dodecyl sulfate (SDS), which are used as kinetic hydrate promoters in various hydrate based technological applications, are facing a serious roadblock toward their commercial utilization as a result of the excessive amount of foam generation, particularly during hydrate dissociation. One of the approaches to alleviate this foam formation is the use of various antifoaming agents which may be employed in combination with surfactants. The possibility of using one such antifoaming agent, a silicone based polymeric surfactant, for hydrate based methane storage, has been explored in the current work through a detailed morphological study. Investigations on the morphology of hydrate formation and dissociation reveal the strong antifoaming activity of the silicone based compound and the optimal ratio in which it should be mixed with a surfactant, specifically SDS, in order to effectively alleviate unwanted foam formation. Further, kinetic data reveal that the generally observed kinetic promotion of methane hydrate formation in the presence of SDS is not affected by the addition of antifoam thus underlining the cause for the antifoam's free and possible use in various hydrate based technological applications.

Amino Acids as Kinetic Promoters for Gas Hydrate Applications: A Mini Review

“…Following the initial work by Sa and coauthors, ,, as curiosity around amino acids grew for their potential as benign bioadditives for gas hydrate research, their unique structural makeup, a mix of both hydrophilic and hydrophobic function groups, drew particular attention owing to the high degree of similarity with the chemical structure of surfactants, traditionally the most used class of KHPs. In addition to being toxic synthetic chemicals, the use of surfactants also poses a problem of excessive foam generation, especially during hydrate dissociation, making these additives difficult to handle and unviable for repeat utilization. − Biosurfactants such as Surfactin, which have been proposed to circumvent the issue of chemical toxicity, are cumbersome to produce and present the same challenge of foam generation as conventional synthetic surfactants. , Thus, there was an urgent need to identify a class of additives that may be able to replace synthetic surfactants as competent KHPs, enduring across various gas hydrate systems and engaging through a clean mode of operation (no foam formation), in addition to being inherently ecofriendly and nontoxic entities. As we see in the upcoming sections, amino acids (hydrophobic ones in particular) fit the bill perfectly in this regard, delivering the desired kinetic promotion performance through a clean mode of action, i.e., with no accompanying foam generation whatsoever.…”

Strength and Deformation Behaviors of Methane Hydrate-Bearing Marine Sediments in the South China Sea during Depressurization

“…The enhancement amplitudes of hydrate on the strength characteristics of sediments are dominated by its morphology. , Different hydrate morphologies were gradually found due to the gas source conditions when they form . The hydrates formed from a segregated gas source always present sheet, bedded, or nodular morphologies, , which are basically part of the host particles. The hydrates formed from a disseminated gas source present pore spacing, frame supporting, grain enveloping, and cementing morphologies as well as strengthen and stiffen the sediments due to hydrate saturation. , …”

Carboxylate Surfactants as Efficient and Renewable Promoters for Methane Hydrate Formation

“…Methane hydrate is an ice-like compound formed by a methane molecule at the center of a cage crystal and water molecules around through van der Waals forces with a nonstoichiometric mole ratio. , Theoretically, one volume of water could store 172 volumes of methane in maximum for methane hydrate, and it could be formed under mild conditions, for example, 2 °C and 6 MPa. , Therefore, it has been regarded as a potential compound to store methane. Nevertheless, surfactants as promoters are crucial to synthesis of methane hydrate, which can reduce the surface tension of an aqueous solution and thus facilitate the diffusion of methane from a gas phase to a liquid phase and have been proved to be excellent promoters for methane hydrate formation. − Among the surfactants, sodium dodecyl sulfate (SDS) and sodium dodecyl sulfonate (AS) are better choices because of a faster formation rate and higher storage capacity. − However, during the dissociation of the hydrate, both the surfactants suffer from generation of large quantities of foam, leading to loss of surfactants and pollution in the pipeline and further affecting the recycling of the surfactants. − …”