High-Pressure Densities and Excess Molar Volumes for the Binary Mixture of Carbon Dioxide and Hydrogen Sulfide at T=343-397 K

A few studies have been carried out on the volumetric properties of binary systems of H2S + CO2, which are rich in CO2; however, no volumetric studies for acid gas fluids rich in H2S have been found in the open literature. Herein we report new high-precision density measurements for three compositions (x(CO2) = 0.09822, 0.26989, and 0.49556) for the CO2 + H2S binary system at T = 343-398 K and pressures up to p = 25 MPa. The measured mixture densities were compared to data from Stouffer et al. (J. Chem. Eng. Data 2001, 46, 1309-1318. DOI: 10.1021/je000182c.) and Nazeri et al. (Fluid Phase Equilib. 2016, 423, 156-171. DOI: 10.1016/j.fluid.2016.04.024.The measured density data showed agreement within ca. +/- 2% at high pressures and up to 4% in the vicinity of the critical point or high compressibility region. Additionally, we used our mixtures and interpolated pure fluid densities to calculate the excess molar volumes, to further ascertain the accuracy of the mixing coefficients provided by Kunz and Wagner (J. Chem. Eng. Data 2012, 57, 3032-3091. DOI: 10.1021/je300655b.). The comparison of the calculated and experimental molar volumes showed good agreement to within +/- 2 cm(3).mol(-1), especially in the high-pressure region. Within the study, we considered the COS formation from the reaction of CO2 + H2S, which was a potential explanation for measurement failure in previous studies. The measured equilibrium concentrations of COS were low and showed that the reaction of CO2 + H2S to form COS was not facile at the measured conditions.