Influence of sodium chloride on the kinetics of methane hydrate formation in the presence of surfactant

Abstract

Hydrates have been identified as potential technologies for applications such as storage and transportation of natural gas and seawater desalination. These industrial applications are usually affected by the induction time and the growth rate of the hydrate. The addition of surfactants to the gas–water system can improve this effect. The formation of natural gas hydrate requires a lot of water, and the use of seawater can save a lot of freshwater resources. However, the presence of NaCl in seawater has an opposite effect on the formation of hydrates. This article focuses on the influence of NaCl and different types of surfactants on the conversion of water to hydrates, gas dissolution, nucleate growth and formation rate of methane hydrate. Measurements of surface tension and the number of particles in complex systems further explained how surfactants and NaCl affect the hydrate formation. The results indicate that low concentration of NaCl (50 mmol/L) and anionic surfactant can significantly increase the water–to–hydrate conversion and hydrate nucleation. It has been pointed out that although NaCl is called thermodynamic inhibitors, low concentrations of NaCl and surfactants can further promote hydrate formation. The novel mechanism insights have been discussed by which different concentrations of NaCl and surfactants affect the hydrate formation kinetics. Most natural gas hydrates are distributed deep in the seabed, and NaCl is the main component of seawater. Understanding the influence of NaCl on hydrates in the complex system can provide a theoretical basis for future hydrate research.