Methane hydrates with a high capacity and a high formation rate promoted by biosurfactants

Dry Water as a Promoter for Gas Hydrate Formation: A Review

Applications of clathrate hydrate require fast formation kinetics of it, which is the long-standing technological bottleneck due to mass transfer and heat transfer limitations. Although several methods, such as surfactants and mechanical stirring, have been employed to accelerate gas hydrate formation, the problems they bring are not negligible. Recently, a new water-in-air dispersion stabilized by hydrophobic nanosilica, dry water, has been used as an effective promoter for hydrate formation. In this review, we summarize the preparation procedure of dry water and factors affecting the physical properties of dry water dispersion. The effect of dry water dispersion on gas hydrate formation is discussed from the thermodynamic and kinetic points of view. Dry water dispersion shifts the gas hydrate phase boundary to milder conditions. Dry water increases the gas hydrate formation rate and improves gas storage capacity by enhancing water-guest gas contact. The performance comparison and synergy of dry water with other common hydrate promoters are also summarized. The self-preservation effect of dry water hydrate was investigated. Despite the prominent effect of dry water in promoting gas hydrate formation, its reusability problem still remains to be solved. We present and compare several methods to improve its reusability. Finally, we propose knowledge gaps in dry water hydrate research and future research directions.

Study on the kinetic characteristics of gas hydrate in the dioctyl sodium sulfosuccinate system

Surfactants promote the production of hydrates, which provide a possibility for the industrialization of hydrate technology. In this paper, methane and CO₂ hydrate formation experiments were carried out, respectively, with surfactant-dioctyl sodium sulfosuccinate (DSS) using a visual experimental apparatus at a constant pressure. This study explored the influence of the surfactant dosage, experimental pressure, and subcooling temperature on the dynamic characteristics of hydrate formation. The results indicated that a small amount of surfactant had a significant promotion effect on the formation of hydrate, i.e., 600 mg L⁻¹ DSS shortened the induction time of methane hydrate by 60 times and that of CO₂ hydrate by 2.4 times, while it increased the formation rate by 3.4 times. Due to the weak acidity of the CO₂ solution, the effect of DSS on CO₂ hydrate formation was significantly reduced. The DSS concentration had a limited effect on changing the rate of the gas storage capacity of the two hydrates. Compared with other surfactants reported in the literature, DSS showed a better promotion effect on hydrate formation. This study reveals the mechanisms of interfacial tension reduction and the promotion of hydrate growth adhering to the wall using a surfactant with a double-chain structure, which further enriched the hydrate-promoting mechanism, and provides experimental data and a theoretical research basis for the study of kinetic characteristics of hydrates in surfactant systems.

Surfactants promote the production of hydrates, which provide a possibility for the industrialization of hydrate technology.

Biopromoters for Gas Hydrate Formation: A Mini Review of Current Status

Gas hydrates have promising application prospects in the fields of future energy sources, natural gas storage and transportation, CO2 capture and sequestration, gas separation, and cold energy. However, the application of hydrate technologies is being restricted due to the slow formation rate of gas hydrates. Kinetic promoters have been receiving increased attention, given that they can improve the hydrate formation rate with very small doses and do not affect gas storage capacity. However, most kinetic promoters are non-renewable, petrochemical-derived, non-degradable materials, inevitably leading to resource waste and environmental pollution. Biopromoters, derived from biomass, are renewable, biodegradable, environmentally friendly, non-toxic (or low toxic), and economically feasible. This mini review summarizes the current status of already discovered biopromoters, including lignosulfonate, amino acid, biosurfactant, and biological porous structures, which have the potential to replace petrochemical-derived promoters in hydrate technologies. Finally, future research directions are given for the development of biopromoters.

Biosurfactant as a Promoter of Methane Hydrate Formation: Thermodynamic and Kinetic Studies

Natural gas hydrates (NGHs) are solid non-stoichiometric compounds often regarded as a next generation energy source. Successful commercialization of NGH is curtailed by lack of efficient and safe technology for generation, dissociation, storage and transportation. The present work studied the influence of environment compatible biosurfactant on gas hydrate formation. Biosurfactant was produced by Pseudomonas aeruginosa strain A11 and was characterized as rhamnolipids. Purified rhamnolipids reduced the surface tension of water from 72 mN/m to 36 mN/m with Critical Micelle Concentration (CMC) of 70 mg/l. Use of 1000 ppm rhamnolipids solution in C type silica gel bed system increased methane hydrate formation rate by 42.97% and reduced the induction time of hydrate formation by 22.63% as compared to water saturated C type silica gel. Presence of rhamnolipids also shifted methane hydrate formation temperature to higher values relative to the system without biosurfactant. Results from thermodynamic and kinetic studies suggest that rhamnolipids can be applied as environment friendly methane hydrate promoter.

Methane storage in tea clathrates

Methane can be stored in tea clathrates, that is kinetics of methane clathrate formation can be significantly accelerated (90% saturation uptake in 20 min) by ingredients (polyphenols and saponins) in tea infusions with a volumetric capacity of up to 172 v/v.