Molecular behavior of CO2 hydrate growth in the presence of dissolvable ionic organics

Abstract Hydration-based techniques involve hydrate formation in complicated systems containing ions and organics. Consequently, it is necessary to understand the molecular behavior of hydrate nucleation and growth in such solutions. This work shows that the hydrate-growth rate in a system containing methylene blue molecules does not necessarily accelerate on increasing the subcooling. Unexpected amorphous cage clusters were observed at a lower temperature of 240 K. To the best of our knowledge, this is the first study to propose that these amorphous clusters act as mass transfer barriers disturbing the agglomeration of solutes. Herein, hydrate growth was accompanied with the exclusion of methylene blue molecules. Although methylene blue can instantaneously reside in the cavity a half-cage structure, they were subsequently replaced by CO2 molecules. Notably, chloride ions were observed to participate in cage building (42510, 512, and 51262 cages) by bonding with the oxygen atoms of the surrounding water molecules. This phenomenon shows an interaction between the methylene blue molecules and hydrate cages during the exclusion process. These results support the current understanding on hydrate formation in the presence of ion-containing organics and could help improve kinetics-dependent applications in separation process.