ISOCHORIC PVT AND PHASE-EQUILIBRIUM MEASUREMENTS FOR CARBON-DIOXIDE PLUS NITROGEN
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We have designed and constructed an isochoric apparatus for fast and accurate pressurevolume - temperature (pVT) and phase equilibrium measurements. The apparatus allows isochoric (p, T at constant V) measurements for noncorrosive fluids over a wide range of pressures (7105 MPa) and temperatures (100450 K). Densities can be derived from densities determined at one isotherm (p, V at constant T) with another apparatus, such as a pycnometer or a Burnett apparatus. Temperatures are accurate to 10 mK and precise to 1 mK on ITS-90. Pressure measurements are accurate to 10 kPa and precise to 2 kPa. This apparatus requires about 20 min for temperature equilibration for measurements 2 K apart and about 50 min for measurements 10 K apart. We have measured 23 phase boundary points for three mole fractions, x1 = 0.3991, 0.4459, and 0.5037, for CO2 (1) + N2 (2) at temperatures from 207 to 268 K and pressures from 10.8 to 21.5 MPa. The estimated accuracy is 40 mK in temperature and 17 kPa in pressure. The isochoric measurements used to obtain these phase boundary points extend from 205 to 300 K and from 8 to 80 MPa. We have determined the saturation density for 20 of the phase boundary points. The saturation densities and the densities along the isochores were derived from density measurements at 300 and 285 K measured with a pycnometer estimated to be accurate to 0.1%. The behavior of the solid + fluid phase boundary is discussed. 1995, American Chemical Society. All rights reserved.
