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 tw o types of structures, I and II, with each structure having two types of cavities, small and large. The computation of gas hydrate forming c onditions requires the evaluation of the chemical potential of water i n the hydrate phase. This potential is obtained through a statistical mechanics based model. This model requires the computation of an impor tant quantity known as the Langmuir constant which is obtained from th e evaluation of a multidimensional configurational integral. The techn ique of Metropolis Monte Carlo (MMCT method) has been applied to calcu alte the Langmuir constant. In this work, the MMCT method for computin g Langmuir constants is examined. It is shown that the MMCT method giv es erroneous computed Langmuir constants owing to possible failure of certain assumptions made to obtain the Langmuir constants.