LANGMUIR CONSTANT COMPUTATIONS FOR GAS HYDRATE SYSTEMS

Gas hydrates are nonstoichiometric clathrate compounds, in which a gas molecule (guest) is trapped in a cage formed by surrounding hydrogen bonded water molecules (hosts). Natural gas hydrates are present in two types of structures, I and II, with each structure having two types of cavities, small and large. The computation of gas hydrate forming conditions requires the evaluation of the chemical potential of water in the hydrate phase. This potential is obtained through a statistical mechanics based model. This model requires the computation of an important quantity known as the Langmuir constant which is obtained from the evaluation of a multidimensional configurational integral. The technique of Metropolis Monte Carlo (MMCT method) has been applied to calcualte the Langmuir constant. In this work, the MMCT method for computing Langmuir constants is examined. It is shown that the MMCT method gives erroneous computed Langmuir constants owing to possible failure of certain assumptions made to obtain the Langmuir constants.