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

Abstract

The kinetic hydrate inhibitors (KHIs) are known to be both economical and eco-friendly in preventing hydrate blockages. 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 the concentrations and accommodations of CH4 in aqueous, thereby mitigating the formation of hydrate embryo; ii) decreases CH4 transfer from bubble to embryo, thereby mitigating the growth of hydrate embryo. As both the formation and growth of hydrate embryos are inhibited, the hydrate nucleation requires longer induction time and larger critical nucleus. Moreover, this new mechanism has been found to be applicable 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.