Measurement of the vapour–liquid equilibrium of binary and ternary mixtures of CO2, N2 and H2, systems which are of relevance to CCS technology

Abstract

The p–T phase envelopes of four binary and two ternary mixtures of carbon dioxide (CO2), nitrogen (N2) and hydrogen (H2) have been reported at temperatures between 252 and 304K. The compositions of the binary mixtures are xN2=0.0201 and 0.0399 for CO2+N2 and xH2=0.0300 and 0.0499 for CO2+H2, respectively. For the two ternary mixtures of CO2+N2+H2, the compositions are xN2=0.020, xH2=0.030 and xN2=0.040, xH2=0.030. The experimental data show that the bubble-point pressures of the CO2-permanent gas mixtures increase substantially when adding only several percent (mole fraction) of N2, H2 or both in CO2. H2 has the largest effect on the bubble-point pressure. For a mixture with 5% H2 in CO2, the bubble-point pressure reaches 10.1MPa at 288.15K, corresponding to an increase of 99% from the vapour pressure of pure CO2. These vapour–liquid-equilibrium data have also been compared to those predicted using the GERG-2004 and Peng–Robinson (PR) equations of state. Between the two models, the PR equation of state gives the smaller deviations (2.5–4.2%) for the bubble-point lines of CO2+H2 when using temperature-dependent binary interaction parameters, while both models show excellent agreement (0.4–2.8%) between the experimental and predicted data for CO2+N2. We also successfully model the CO2+H2 data using molecular simulation.