When mixed-gas hydrates are formed in a closed system, such as in a batch reactor, the gas-phase composition changes during formation due to a preferred enclathration of one of the guest molecules. To understand this complex process, we developed two numerical models that we compare to experimental data obtained for a methane + propane mixed-gas system. The models are thermodynamic yet include kinetic processes such as the gas-consumption and composition heterogeneity in the crystal. Because we can calculate the time evolution of the gas-phase composition during crystal growth, which is difficult to measure experimentally, we can show that the rate-determining process of methane + propane mixed-gas hydrate formation is the enclathration rate of propane.
Teraoka et al. (Mon,) studied this question.