Apparatus for Low-Temperature Investigations: Phase Equilibrium Measurements for Systems Containing Ammonia

In this paper, a low-temperature apparatus was designed to measure vapor-liquid and vapor-liquid-liquid equilibria for binary systems containing ammonia. The standard combined uncertainties of the temperature, pressure, and the mole fraction are less than ±5 mK, ±0.0008 MPa, and ±0.005, respectively. The saturated vapor pressures of the ammonia, n-butane, and 1-butene were measured, and there were quantitative similarities between the experimental data and the data from Refprop 9.1, with differences less than 0.0007 MPa. The reliability of the experimental setup was verified. The experimental data of the (ammonia + n-butane) system and the (ammonia + 1-butene) system were presented. The homogeneous azeotropic behavior was shown at T = (293.150 and 283.150) K and a heterogeneous azeotropic was found at 273.150 K for the (ammonia + 1-butene) system. Besides, a heterogeneous azeotropic was found at T = (273.150 and 263.150) K for the (ammonia + n-butane) system. All the experimental data were correlated with the PR-MHV2-NRTL model. The maximum root mean square deviations in temperature, pressure, liquid mole fraction, and vapor mole fraction for the systems concerned are 0.010 K, 0.0035 MPa, 0.011, and 0.011, respectively. (Graph Presented).