Nucleation rate of gas hydrates

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Ice floats on liquid water because it is less dense than water. The hollow structure of ice can accommodate small gas molecules as guests in its cavities under low temperature high pressure conditions. These crystalline solids in which guest molecules are trapped by water molecules are called gas hydrates. Gas hydrates have potential applications in gas storage, carbon dioxide sequestration, gas separation and desalination. Gas hydrates also form the largest unconventional natural gas resources on earth. Formation of gas hydrates is a firstorder phase transition that starts with nucleation. Nucleation refers to the formation of a thermodynamically stable phase in the metastable parent phase and the process requires surmounting of an activation energy barrier. This activation process is intrinsically stochastic and is best described in terms of probability distributions. One would wish to facilitate nucleation when the formation of gas hydrate is desirable and suppress nucleation when it is undesirable. Understanding of nucleation is of interest to many in chemical and petroleum industry, as nucleation, while a benefit in many chemical processes, is a concern in flow assurance. In particular, there is interest in understanding the nucleation process to more effectively, cost-efficiently and safely prevent nucleation of gas hydrates in pipelines. A primary difficulty in the investigation of gas hydrate nucleation has been the inability of researchers to compare nucleation rates of gas hydrates across various systems of different scales and complexity, which in turn has been limiting the ability of researchers to study the nucleation process itself. Nucleation rate is equivalent to nucleation probability density per unit system size and per unit time, and allows scientifically meaningful comparisons of nucleation processes between various systems. Based on the cutting-edge technology we have been developing, we propose to establish a robust technology that can reliably determine the nucleation rates of a range of gas hydrates. We also propose to create a database of nucleation rates of gas hydrates under a broad range of conditions that start from the simplest case of single-component gas hydrates in pure water to progressively complex systems that involve mixed gas hydrates, solid walls and a range of chemicals. Systematic determination of nucleation rates will allow identification of physicochemical factors that have the greatest impact on nucleation of gas hydrates.