Measurement and modelling of the vapor–liquid equilibrium of (CO2 + CO) at temperatures between (218.15 and 302.93) K at pressures up to 15 MPa

Abstract

Precise knowledge of vapor-liquid equilibrium (VLE) data of (CO2 + diluent) mixtures is crucial in the design and operation of carbon capture, transportation and storage processes. VLE measurements of the (CO2 + CO) system are reported along seven isotherms at temperatures ranging from just above the triple-point temperature of CO2 to 302.93 K and at pressures from the vapor pressure of pure CO2 to approximately 15 MPa, including near-critical mixture states for all isotherms. The measurements are associated with estimated standard uncertainties of 0.006 K for temperature, 0.009 MPa for pressure and 0.011x(1-x) for mole fraction x. The new VLE data have been compared with two thermodynamic models: the Peng-Robinson equation of state (PR-EOS) and a multi-fluid Helmholtz-energy equation of state known as EOS-CG. The PR-EOS was used with a single temperature-dependent binary interaction parameter, which was fitted to the experimental data. In contrast, EOS-CG was used in a purely-predictive mode with no parameters fitted to the present results. While PR-EOS generally agrees fairly well with the experimental data, EOS-CG showed significantly better agreement, especially close to the critical point.

Experimental density and an improved Helmholtz-energy-explicit mixture model for (CO2 + CO)

“…The mixtures were purchased from BOC who specified an expanded uncertainty in composition (k = 1.73) of 0.01x. Additionally, quantitative compositional analysis was carried out in our laboratory by means of a previously calibrated GC [27]. The mole fractions of the mixtures are presented in Table 1 together with their standard uncertainties.…”

“…Data sets that were used in the fitting process are specifically highlighted. The model was almost exclusively fitted to the VLE data from Souza et al [27] and the density data from this work. To fit the adjustable parameters of the mixture model, each experimental datum is individually weighted according to the property type, state region and the experimental uncertainty.…”

“…Fig. 5 presents comparisons between the available VLE data in the literature [26][27][28][42][43][44] and the new mixture model. The available data cover almost the full temperature range possible from just above the triple-point temperature of CO2 to just below the critical temperature of CO2.…”

“…However, two major deficiencies were identified: first, some binary systems present large regions without data; second, there are significant discrepancies between different data sources. Despite some recent improvements in the data situation, including Tsankova et al [21,22] and Løvseth et al [23] on (CO2 + Ar), Petropoulo et al [24] on (CO2 + CH4), and Tsankova et al [25], Westman et al [26] and Souza et al [27] on (CO2 + CO), these deficiencies remain.…”

“…The parameterization of this model was made possible by the availability of the new density measurements and the recently published VLE data of Souza et al [27].…”