Molecular insights into the wettability of antifreeze protein-adsorbed hydrate surface: Application to hydrate anti-agglomeration

Abstract

Adding kinetic inhibitors (KIs) to prevent hydrate formation or anti-agglomerate agents (AAs) adsorbed on hydrate crystals to suppress particle aggregation are both effective means to eliminate hydrate blockage in pressurized pipelines. Antifreeze proteins (AFPs) are representative KIs that hinder hydrate growth via the interfacial adsorption mechanism. This implies the possibility of interfacial modification and simultaneous anti-aggregation effects, which yet have not been explored. Here molecular dynamics (MD) simulations were employed to determine the possible anti-aggregation performance of AFP. Specifically, we identified larger contact angles, that is, the enhanced hydrophobicity, of AFP-adsorbed CH4 hydrate under the dodecane oil phase. This indicates the possible dual inhibition effects of AFP to ensure oil transportation. However, no significant effects of AFP on wettability were observed in the systems with the CO2 hydrate substrate or gas environment. This contrasting behavior was explained by the differences in the hydrogen-bonding formation and interaction strength between substrates and water droplets, which are strongly influenced by the charged residues of AFP. Additionally, we compared AFP with traditional surfactants and emphasized that the anti-aggregation abilities of additives are intricately linked to their functional group arrangements and inherent structures. Our work provides molecular-level guidance for designing effective hydrate inhibitors with dual performance to ensure flow assurance.