PVT Measurements of the H₂-CO₂-CH₄-CO-H₂O System at 740-939 K and 18.1-34.7 MPa with an Isochoric Apparatus and the Development of a Virial Equation of State

Modeling the pVT properties of hydrogen mixtures at high temperatures is significant for the development of relevant production and utility systems. In this work, pVT measurements are reported for the H2-CO2-CH4-CO-H2O system at 740-939 K and 18.1-34.7 MPa with an isochoric apparatus. The expanded relative uncertainty (k = 2) of density is less than 0.015. Based on the present and previous pVT data, a virial equation of state (EOS) has been developed at 720-939 K and up to 35 MPa for the quinary system with relative uncertainty (k = 2) at density less than 0.015. The thermal pressure coefficient of the quinary system was calculated from the virial EOS and the comparison with the experimental values indicated that changes in the specific volume and composition of the quinary system existed in each set of measurements. Isochoric heat capacity of the quinary system was also calculated and was compared with the GERG-2008 EOS. The calculated isochoric heat capacities agree with the GERG-2008 EOS within 1.75% above 873 K and up to 35 MPa, while at lower temperatures, the deviations become larger (up to 3.66%).