Concentration effect of kinetic hydrate inhibitor on hydrate formation and inhibition

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Kinetic hydrate inhibitor (KHI) is an eco-friendly and promising technology for hydrate blockage issue in natural gas pipelines, but it remains unclear of how KHI performance would vary at different subcooling and concentration. In this study, the influence of KHI on the kinetics of methane - propane hydrate formation was evaluated with a wide range of subcooling (5–20 ℃) and concentration (100–51000 ppm) conditions, by characterizing the pressure evolution, average hydrate growth rate and hydrate volume fraction. The results put forward a ‘concentration effect’ concept that represented the nonmonotonic relationship between the performance and concentration of KHI, where KHI obtained higher inhibition performance with either relatively low or high concentration, but became almost ineffective at the intermediate concentration zone. Two hypotheses were then proposed to reveal its internal mechanisms, including the ‘weakened adsorption’ hypothesis and the ‘competition’ hypothesis. Results further demonstrated that the above concentration effect became less obvious when the experimental conditions were more contributory for fast hydrate formation, such as the enhanced subcooling and stirring speed. In addition, the universality of concentration effect was preliminarily verified, which was not restricted by the type of KHI or the selected experimental system. To the best of our knowledge, such concentration effect was for the first time systematically investigated and reported in this study, which highlighted the possibility of flexibly selecting the appropriate KHI concentration based on the practical driving force for hydrate formation.