Influences of large molecular alcohols on gas hydrates and their potential role in gas storage and CO2 sequestration

Abstract

In this study, the influences of large molecular alcohols (LMAs) including pinacolyl alcohol (PCA) and tert-amyl alcohol (tAA) on thermodynamic phase behaviors and structural characteristics of CH4 and CO2 hydrates were investigated for their potential use in gas storage and CO2 sequestration. The experimentally measured hydrate phase equilibria demonstrated that CH4 hydrates were stabilized in the presence of PCA and tAA. 13C NMR and Raman spectroscopy confirmed sH hydrate formation from both CH4+PCA+water and CH4+tAA+water systems, resulting from the enclathration of LMAs in the large 51268 cages. The sH hydrate formation of the CH4+PCA+water system was also confirmed by an endothermic dissociation thermogram from a differential scanning calorimeter (DSC). In contrast with CH4 hydrates, the addition of both PCA and tAA to CO2 hydrates resulted in thermodynamic inhibition. Through Raman and powder X-ray diffraction (PXRD) analyses, both CO2+PCA and CO2+tAA hydrates were characterized as sI hydrates, indicating that LMAs simply inhibit the formation of CO2 hydrates without being captured in the hydrate lattices. Therefore, PCA and tAA are expected to function as thermodynamic promoters which reduce the hydrate forming pressure in natural gas storage applications, while they can serve as thermodynamic inhibitors which prevent CO2 hydrate formation in pipelines for CO2 transportation to sequestration sites.