Structural transition and phase behavior of N2 gas hydrates with pinacolyl alcohol and tert-amyl alcohol

The influences of large molecular alcohols (LMAs) (pinacolyl alcohol (PCA) and tert-amyl alcohol (tAA)) on N-2 hydrate were examined with a primary focus on the hydrate phase equilibria and structural transition. The four-phase (H-L-w-L-LMA-V) equilibria of the N-2 + PCA + water and N-2 + tAA + water systems were experimentally measured in order to determine the thermodynamic stability conditions of the N-2 hydrates with LMAs. The H-L-w-L-LMA-V curves of both N-2 + PCA and N-2 + tAA hydrates were significantly shifted to more thermodynamically stable regions. Powder X-ray diffraction (PXRD) and Raman analyses verified that the structure of N-2 hydrates with LMAs was transformed from the original structure of sII to sH (P6/mmm) as a result of the inclusion of LMAs. In addition, the formation of sH hydrate from the N-2 + PCA + water system was further verified using an endothermic dissociation thermogram from a high pressure micro-differential scanning calorimeter (HP mu-DSC) by confirming the appearance of three distinct peaks that correspond to ice, sII hydrate, and sH hydrate. Therefore, the experimental results that were obtained in this study are expected to be informative for understanding the roles of LMAs in affecting the macroscopic hydrate phase behavior and microscopic hydrate structure. (C) 2015 Elsevier B.V. All rights reserved.