Thermodynamics of Natural Gas Clathrate Hydrates

Natural gas will be the premium fuel for this century for three reasons (1) while we wish to use hydrogen as a fuel, we are economically restricted from obtaining it by reforming light hydrocarbons (with attendant inefficiencies) until we learn to efficiently electrolyze water, (2) gas bums cleanly, causes few pollution problems and, relative to oil or coal, produces less carbon dioxide, and (3) liquid fuels are better used as feedstocks for petrochemicals. 

Yet when we consider natural gas as a resource, we invariably find it associated with water. For example, when natural gas is produced from a Gulf of Mexico deepwater well, flowline design is driven by concurrent water production to prevent gas + water from combining into a solid clathrate hydrate, which blocks the pipeline. As a second example, when dead plant and animal matter decompose on the bottom of the ocean, they form methane, which combines with water to form a clathrate solid. The amount of enclathrated methane in the bottom of the ocean is between 10 and 10 m (STP) - two orders of magnitude greater than the conventional worldwide gas reserve. 

Important application questions arise due to the profusion of natural gas hydrates  

What defines economic flow assurance in deepwater energy production  

Is it possible that in situ gas hydrate reserves can be an economic energy resource  

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Answers to such difficult questions can be found in applied thermodynamics - in terms of measured, macroscopic values of pressures, temperatures, compositions, volumes, enthalpies, etc. This chapter provides an overview of natural gas clathrate hydrates - structures, phase diagrams, and thermodynamic predictions/measurements that guide our understanding in dealing with such questions. The hydrate historical perspective provides an example of how knowledge advances in a technical field. At the conclusion of the chapter, future thermodynamic challenges are presented. 

In this work, we have presented new experimental 3-phase H-Lw V (Hydrate - Liquid Water- Vapour) equilibrium data for methane and a natural gas clathrate hydrates in the presence of high concentrations of mono-ethylene glycol solutions, generated by a reliable fixed-volume (isochoric), step-heating technique. These data in addition to data from literature have been used to validate the predietive capabilities of a thermodynamic model presented in this work. 

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