Thermodynamic Stability of Structure H Hydrates Based on the Molecular Properties of Large Guest Molecules

Kyoichi Tezuka,Saman Alavi,Ryo Ohmura,Amadeu K Sum,Tatsuhiko Taguchi

doi:10.3390/en5020459

Abstract

This paper report analyses of thermodynamic stability of structure-H clathrate hydrates formed with methane and large guest molecules in terms of their gas phase molecular sizes and molar masses for the selection of a large guest molecule providing better hydrate stability. We investigated the correlation among the gas phase molecular sizes, the molar masses of large molecule guest substances, and the equilibrium pressures. The results suggest that there exists a molecular-size value for the best stability. Also, at a given molecule size, better stability may be available when the large molecule guest substance has a larger molar mass.

Highlights

Clathrate hydrates are crystalline inclusion compounds consisting of hydrogen-bonded water molecules forming cages that contain guest molecules [1]
We study possible correlations between the thermodynamic stability of structure-H hydrates and the structure and functionality of a large group of chemical species of large molecule guest substance (LMGS)
To study correlations between the molecular size and thermodynamic stability, we use equilibrium pressure data of structure-H hydrates formed with methane and 20 different LMGSs, as reported in previous studies [8,9,10,11,12,13,14,15] and calculated from interpolation of the data at 276 K

Summary

Introduction

Clathrate hydrates are crystalline inclusion compounds consisting of hydrogen-bonded water molecules forming cages that contain guest molecules [1]. Structure-H hydrate forms with two different guest substances: one Energies 2012, 5 is a small molecule guest substance, such as methane, xenon, and the other is a relatively large molecule guest substance (LMGS). Phase-equilibrium conditions of structure-H hydrates are milder (i.e., higher temperature/lower pressure) than those of structure-I or structure-II hydrates formed only with a small molecule guest substance. The milder phase equilibrium conditions in the structure-H hydrate forming systems is favorable for new technologies utilizing hydrates for storage (methane [3] or hydrogen [4,5]), capturing carbon dioxide [6], highly efficient heat pumps [7], etc

Methods

Results

Conclusion