Isobaric heat capacities of liquefied natural gas (LNG) mixtures by differential scanning calorimetry at temperatures from 116 K to 150 K and pressures up to 6.90 MPa

The isobaric heat capacity (c_p) is a crucial thermodynamic property for LNG industries in process design and optimization. Reliable c_p results can be applied to validate and improve the equation of state performance under relevant industry conditions. Here, we report the results of c_p measurements performed for eight LNG mixtures between (116.3 to 150.3) K and pressures ranging to 6.90 MPa. The results achieved were compared against four thermodynamic models: the fundamental equation of state (EOS) for liquefied natural gas (EOS-LNG), the Peng-Robinson (PR) cubic EOS widely applied in process design, the Lee-Kesler-Plöcker (LKP) EOS, which is reliable for gas enthalpy computation, and the Statistical Associating Fluid Theory (SAFT)-γ Mie EOS integrating contributions from functional groups. The EOS-LNG, which is equivalent for the mixtures investigated in this work to the GERG-2008 Helmholtz equation of state, can satisfactorily compute all the measured heat capacities. The SAFT-γ Mie EOS exhibits excellent accuracy when the correct ideal gas heat capacity correlation is implemented. On the contrary, the PR and LKP EOS show systematic deviations as a function of density, which stem from poor residual heat capacity predictions for the pure constituents and binary mixtures.