Resolving hydrate inhibition mechanism: Interactions between kinetic hydrate inhibitors and CH4 bubble

The kinetic hydrate inhibitors (KHIs) are known as both economic and eco-friendly in preventing hydrate blockage. To date, two main inhibition hypotheses of KHIs have been proposed, in which the dominant interactions are KHIs-crystals and KHIs-aqueous, respectively. However, both hypotheses experience challenges as contrary phenomena are frequently observed. Herein, we find the extensively generated CH4 bubble in hydrate exploitation or natural gas transportation can greatly promote hydrate nucleation, thus, a new inhibition mechanism is proposed based on the interaction of KHIs-CH4 bubble. Specifically, PVCaps (one typical KHI) can absorb on CH4 bubble surface to mitigate CH4 dissolution, which thus i) reduces concentrations and accommodations of CH4 in aqueous, thereby mitigating the formation of hydrate embryo; ii) reduces CH4 transfer from bubble to embryo, thereby mitigating the growth of hydrate embryo. As both formation and growth of hydrate embryos are inhibited, the hydrate nucleation involves longer induction time and larger critical nucleus. Moreover, this new mechanism is found generic to other KHIs, in which the interaction strengths of KHIs-CH4 bubble can successfully explain the experimental inhibition efficiencies of PEO < PVP < PVCap < VIMA. Thus, the interaction of KHIs-CH4 bubble can act as the key criterion in screening and designing effective KHIs.