Consistent Description of Hydrogen Hydrates and of their Properties in Mixtures with Multiple Hydrate-Forming Components

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The aim of the proposed project is to develop a hydrate model, which accurately describes the formation of hydrogen hydrates in pure form and in mixtures with other hydrate forming components, and which is consistent to accurate empirical mixture models for the fluid phases. For this reason, a model that has been developed by the applicant and by groups cooperating with the applicant over the last few years needs to be extended substantially. For example, a quadruple occupation of cavities needs to be considered for hydrogen, while other hydrate formers do not show more than double occupation of cavities. The formation of hydrogen hydrate in mixtures with other hydrate forming components is particularly relevant. The model that has been developed by the applicant and cooperating groups accurately describes mixed hydrates in a purely predictive manner based on a linear mixing rule for a single substance specific parameter. However, this approach requires an identical structure of the models used for the different hydrate formers; this condition will not be fulfilled for hydrogen due to multiple occupation of small and large cavities. Therefore, a completely new approach for the description of mixed hydrates will become necessary. The fact that hydrogen forms sH hydrates in combination with certain promoters, while pure hydrogen forms sII hydrates, will require the adjustment of model parameters for hydrogen to data for competing hydrate formation from a mixture containing different hydrate formers – an approach that is numerically very demanding. New ways need to be established with regard to the adjustment of model parameter. However, if successful this new approach can be used to improve the description of phase equilibria of mixtures containing hydrates of certain other hydrate forming components as well. Finally, the kinetics of the hydrate formation process is particularly relevant for hydrogen hydrates. Based on the new hydrate model and on established approaches for the kinetics of hydrate formation, the kinetics will be described based on differences of the chemical potential of the involved phases. For a long time, the applicant closely cooperates with Dr. Václav Vinš from the Institute Thermomechanics of the Czech Academy of Sciences on the development of hydrate models. Dr. Vinš will be involved in the proposed project as Mercator Fellow.