Phase Equilibria and Spectroscopic Investigations of Binary (But-3-en-1-ol + CH₄) Clathrate Hydrate

Abstract

In this study, we discovered an agent called but-3-en-1-ol, which has the ability to form a hydrate structure II (sII) in the presence of methane (CH4). Our study involves studying the crystal structure, guest distribution, and phase equilibria of the (but-3-en-1-ol + CH4) hydrate. The 13C NMR solid-state spectra of the (but-3-en-1-ol + CH4) hydrate indicate the formation of the sII hydrate, with the CH4 molecules being encapsulated in both the large and small cages of the sII hydrate. The synchrotron powder X-ray diffraction pattern of the (but-3-en-1-ol + CH4) hydrate was analyzed via Rietveld analysis. Consequently, we assigned the crystal structure of the (but-3-en-1-ol + CH4) hydrate as the cubic Fd3̅m crystal structure, with a lattice constant measuring 17.2150 Å. In particular, we estimated the shortest distance between the but-3-en-1-ol molecule in the hydrate cages and an oxygen atom in the host water as 2.37 Å, leading us to conclude that the hydroxyl group of the but-3-en-1-ol molecule forms hydrogen bonds with the host water framework. Finally, we measured the thermodynamic stability to determine the phase equilibrium conditions of the binary (but-3-en-1-ol + CH4) hydrate and found that the equilibrium temperature conditions were slightly lower compared to those of pure CH4 hydrate.