Stability and cell distortion of sI clathrate hydrates of methane and carbon dioxide: A 2D lattice-gas model study

Abstract

Thermodynamic models of the stability of clathrate hydrates are important for different applications such as the storage, separation and transport of gases. The development of improved models relies on a better understanding of the relationships between the macroscopic stability of clathrate hydrates and their structure. In particular, lattice distortion is an important parameter that is difficult to incorporate in thermodynamic models of clathrate hydrates. In this work, a 2D lattice-gas model has been applied for the first time for the study of the stability and lattice distortion of sI clathrate hydrates of methane and carbon dioxide. Results show a direct relationship between cell distortion and cell occupancy: the minimum distortion is found at cell occupancies near 1. In addition, in the case of carbon dioxide hydrates, a complex behavior is observed due to the partial occupancy of small cavities by guest CO2 molecules. By relating lattice distortion with hydrate stability, phase diagrams can be calculated which are in qualitative agreement with experimental diagrams and with results of more complex simulation methods.