5 Hydrate Challenges for the Future: Reversible and Irreversible Thermodynamics

As we deplete the readily accessible natural gas reserves, we will encounter conditions that are both more remote and more severe. We will be challenged to explore deep ocean environments with higher pressures, permafrost environments with lower temperatures, and gases that were previously considered non-economical, such as those containing non-combustible components of nitrogen, carbon dioxide, and hydrogen sulfide. Such unusual conditions also stretch the applicability limits of hydrate phase equilibrium thermodynamics.

In addition to their terrestrial applications, hydrates are of concern in outer space. Miller ^[77] suggested hydrates' presence in comets, and on Jupiter, Mars, Neptune, Saturn, Uranus, and Venus. Recently, Loveday et al. ^[78] suggested that methane hydrate may be the dominant methane-containing phase in the nebula from which Saturn, Uranus, Neptune and their major moons, including an important role in formation models of Titan, Saturn's largest moon. The temperature, pressure, composition, and enthalpy ranges for space applications encompass and usually exceed those encountered on earth. However, for normal conditions, hydrate thermodynamic predictions now rest on a comparatively sound foundation, with an accuracy approaching that of measurements.

Yet, the largest future challenge goes beyond time-independent descriptions, to irreversible thermodynamics, or kinetics. We know very little about a kinetic mechanism founded on hydrate measurements. Due to the stochastic nature of nucleation, experimentalists have dealt with the deterministic growth process.

Kinetic measurements are changing from macroscopic to microscopic scales. Initially, kinetics consisted of macroscopic measurements of the fluid phases...