Phase-equilibrium measurements with a novel multi-purpose high-pressure view cell: CO2 + n-decane and CO2 + toluene

• Novel high-pressure view cell with a variable volume was built.
• The performance of the cell was tested using different experimental techniques.
• CO2 + n-decane and CO2 + toluene served as test systems to measure phase equilibria.
• Excellent agreement with literature data was shown.
• New isotherm for CO2 + toluene system at 343 K was measured.

The development and evaluation of a new apparatus for the determination of high-pressure phase equilibria is presented. With this very versatile apparatus different experimental methods can be applied: the synthetic-visual, the synthetic-nonvisual, the synthetic-isothermal and the analytical-isothermal method. It allows visual observation of the entire content of the equilibrium cell whereby the apparatus can be used with a fixed volume or with a variable volume using a membrane bellows. Considering the advantages and drawbacks of the different experimental methods, this apparatus allows the use of a suitable method or a combination of methods according to the needs of the system under investigation and the specific experimental conditions (pressure, temperature, composition, slope of phase boundaries …). The apparatus was evaluated using different methods with binary systems for which sufficient data in the literature were available: CO2 + n-decane (319 K ≤ T ≤ 355 K; 1.7 MPa ≤ p ≤ 12.7 MPa) and CO2 + toluene (303 K ≤ T ≤ 343 K, 1.1 ≤ p ≤ 11.5 MPa). Additionally, new data for the CO2 + toluene system were determined. The Soave–Redlich–Kwong and the Peng–Robinson equations of state with quadratic mixing rules were used to correlate the phase behavior. The measured equilibrium data for both test systems were compared with calculated data and with experimental data from the literature, and good agreement was found.