Structural Transition Studies in Methane + Ethane Hydrates Using Raman and NMR

Abstract

A bstract : Methane and ethane are each known to form structure I (sI) hydrates. However, Raman and NMR measurements made on hydrates formed from gas mixtures of methane (CH 4 ) and ethane (C 2 H 6 ) indicate that structure II (sII) forms in this system for certain gas compositions. Raman band frequencies for ethane obtained from different CH 4 + C 2 H 6 hydrates at 274.2 K indicate a change in hydrate structure from sI to sII between 72.2 and 75 mole% of CH 4 in the vapor. A significant increase in the amount of methane incorporated into the hydrate is observed with change in hydrate structure from sI to sII. Solid‐state 13 C CPMAS NMR measurements at 253 K confirm that CH 4 + C 2 H 6 gas mixtures can form sII hydrates at certain feed compositions.