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Natural gas containing trace amounts of water is frequently liquefied at conditions where aqueous solids are thermodynamically stable. However, no data are available to describe the kinetics of aqueous solid formation at these conditions. Here, we present experimental measurements of both solid formation kinetics and solid–fluid equilibrium for trace concentrations of (12 ± 0.7) ppm water in methane using a stirred, high-pressure apparatus and visual microscopy. Along isochoric pathways with cooling rates around 1 K·min–1, micron-scale aqueous solids were observed to form at subcoolings of (0.3–8.6) K, relative to an average equilibrium melting temperature of (253 ± 1.9) K at (8.9 ± 0.08) MPa; these data are consistent with predicted methane hydrate dissociation conditions within the uncertainty of both the experiment and model. The 36 measured formation events were used to construct a cumulative formation probability distribution, which was then fitted with a model from Classical Nucleation Theory, enabling the extraction of kinetic and thermodynamic nucleation parameters. While the resulting nucleation parameter values were comparable to those published for methane hydrate formation in bulk-water systems, the observed growth kinetics were distinctly different with only a small percentage of the water in the system converting into micron-scale solids over the experimental time scale. These results may help explain how cryogenic heat exchangers in liquefied natural gas facilities can operate for long periods without blockages forming despite being at very high subcoolings for aqueous solids.

In cryogenic liquefaction processes, CO 2 poses a solid-formation risk even in trace concentrations. We present solid-fluid equilibrium (SFE) data for CO 2 in liquid methane at CO 2 concentrations from (52 to 500) ppm, extending the available data and indicating that models tuned to existing data over predict the solubility of CO 2 at LNG storage temperatures ($112 K) by nearly a factor of 3. The new data are used to improve the SFE model in the ThermoFAST software package. The formation kinetics of CO 2 solids in liquid methane are elucidated at conditions relevant to cryogenic gas processing. Repeated, ramped-temperature formation measurements provide a statistical basis for quantifying solidification risk. Nucleation rates extracted from the ramped-temperature data, consistent with those measured at fixed temperature, were used to extract parameters describing CO 2 solid formation in methane.These results significantly improve the ability to predict CO 2 solid formation risk in cryogenic natural gas processing.