Inhibition synergism of glycine (an amino acid) and [BMIM][BF4] (an ionic liquid) on the growth of CH4 hydrate

Abstract

This study examined the synergistic inhibition effect of glycine (an amino acid) and [BMIM][BF4] (an ionic liquid) on the thermodynamic phase equilibria and growth behaviors of CH4 hydrates. Hydrate phase equilibria indicated that there was no thermodynamic synergism of inhibitor mixtures on CH4 hydrates. Powder X-ray diffraction (PXRD) patterns demonstrated that the presence of inhibitor mixtures did not affect the structural characteristics of CH4 hydrates. However, the glycine (1.5 mol%) + [BMIM][BF4] (1.5 mol%) system showed significantly less growth of CH4 hydrate, less final gas uptake, and less conversion of water into hydrate than a pure water system. Time-dependent Raman spectra revealed that [BMIM][BF4] inhibited CH4 molecules from occupying small 5(12) cages at the initial stage of hydrate formation, whereas glycine was effective in preventing CH4 molecules from entering large 5(12)6(2) cages for the duration of hydrate formation. The cage-specific inhibition mechanism of the glycine and [BMIM][BF4] mixture had a synergistic effect, significantly reducing the growth of CH4 hydrate. The results of this study provide a better understanding of the inhibition mechanism and the synergistic potential of various inhibitors and could contribute to an expansion in the types of inhibitors that could be used for flow assurance in the pipelines of natural gas production and transportation.