Reconsideration of the micellization theory: Promotion or inhibition of gas hydrate formation for gas storage and flow assurance applications

Abstract

Micellization is one of the most challenging promotion mechanisms of surfactants for gas hydrate formation. Surfactants have been reported as the most efficient promoters for the formation of gas hydrates; however, their mechanism of action is not yet clear. The literature review reveals a major gap in the current knowledge for clarifying the effect of micellization on clathrate hydrate formation. Previous studies have mostly focused on hydrate formation in the presence of a special category of compounds that can form micelles, i.e., surfactants (in most cases, sodium dodecyl sulfate (SDS)). However, structures more complex than SDS have not been extensively studied. In other words, the changes in the surfactants’ molecular structure significantly alter their activity in the hydrate formation process. The current study aims to fill this gap by investigating a novel additive, i.e., waterborne polyurea/urethanes (WPUU), which can generate micelles at the hydrate forming temperature. The experimental results show that WPUUs have a surfactant property and form micelles at the hydrate forming temperature. Nonetheless, no promotion effect on methane hydrate formation was observed. The results of the molecular dynamic simulation confirm that WPUU inhibits gas hydrate formation due to its stronger proton-accepting hydrogen bond compared to water molecules. The results indicate that depending on the molecular structure of the additives, their micelles could have an inhibition effect on methane hydrate formation. Our findings present a molecular foundation to guide the molecular design of efficient hydrate inhibitors and promoters for flow assurance and gas storage applications. Moreover, they provide new insight into the inhibition mechanism of kinetic hydrate inhibitors.