High-pressure melting temperature measurements in mixtures relevant to liquefied natural gas production and comparisons with model predictions

Accurate melting point data were measured for hydrocarbon mixtures analogous to natural gas under high pressure at cryogenic temperatures using a customized differential scanning calorimeter. New melting temperatures are reported for two [methane (C1) + n-heptane (C7)] binary mixtures, two [methane + propane (C3) + n-heptane] ternary mixtures, and three multicomponent mixtures containing methane + ethane (C2) + propane + butane (C4) with a solute of either benzene (CBz) or para-xylene (Cp-xyl). These measurements were performed over temperatures ranging from 137.82 to 302.18 K and pressures between 11.12 and 34.5 MPa. The binary mixture results were consistent with the literature data, and comparisons with the predictions of models implemented in Multiflash and ThermoFAST software packages showed deviations ΔT = Tmeas - Tcalc around +5 and +3 K, respectively. Similar results were obtained for the ternary mixtures. For the multicomponent mixture containing benzene, the deviation for the model implemented in Multiflash increased to +9.4 K, while it remained at around +3 K for the model implemented in ThermoFAST. However, for the multicomponent with para-xylene, the melting temperature deviations for the Multiflash and ThermoFAST models both increased significantly to +21.5 and +13.7 K, respectively. The results suggest that for well-characterized multicomponent mixtures containing components that have been well studied, the models implemented in ThermoFAST can adequately predict the melting temperatures at high pressure. Nonetheless, improvements are still in need for mixtures containing freeze-out components such as para-xylene that have not yet been studied sufficiently.