Compact apparatus for rapid measurement of high-pressure phase equilibria of carbon dioxide expanded liquids

A new apparatus based on a synthetic method was developed for phase equilibrium measurements. The characteristic features of the apparatus are its light weight (ca. 288 g), variable-volume with a free piston, position sensing device for the piston, precise pressure and temperature control, and a window for visual observation. The inner volume of the cell can vary from 2.5 to 8.8 cm3. The cell was constructed from titanium so that the composition of the sample can be determined by direct weighing of the cell. The apparatus was designed for temperatures up to 473 K and pressures up to 25 MPa.To confirm the reliability of the apparatus, vapor–liquid equilibria of the carbon dioxide–methanol system were measured. The estimated uncertainties of temperature, pressure, and composition of carbon dioxide were less than ±0.05 K, ±0.02 MPa, ±0.20 wt%, respectively. Bubble-point pressures obtained in this work agreed well with the literature data. Bubble-point pressure data for carbon dioxide with acetone, methyl ethyl ketone (MEK), and methyl isobutyl ketone (MIBE) were measured at temperatures ranging from 313 to 353 K, and could be correlated well with the Peng–Robinson equation of state. The P–x diagrams at a given temperature for acetone, MEK, and MIBK binaries with carbon dioxide were found to be practically identical.