High Pressure Phase Equilibria andPVT‐Data. of the Water‐Nitrogen System to 673 K and 250 MPa

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Abstract
A high pressure autoclave equipped with sapphire windows is described. With water‐nitrogen mixtures of thirteen different concentrations (x) determinations were made of liquid‐gas phase equilibria conditions along “isopleths” between 523 and 673 K and 20 to 270 MPa. Molar volumes of the mixtures were measured at the three‐dimensional (PTx) phase equilibria surface and in the supercritical homogeneous region at 673 K. The critical curve, an envelope of the isopleths, begins at the critical point of water (647 K), has a temperature minimum (639 K) at about 75 MPa and proceeds to 250 MPa at 659 K. Phase equilibria and critical curve data are given. Values for the Henry‐constant to 647 K for mixtures dilute in nitrogen and for the nitrogen solubility from 300 to 600 K and from 10 to 200 MPa are presented. Excess volume,VE, values have been calculated for 673 K from 30 to 250 MPa. AllVEvalues are positive. The maximum is 57 cm3mol−1at 70 mol per cent of H2O at 30 MPa and about 2 cm3mol−1at 40 mol per cent H2O and 250 MPa. Excess Gibbs energy‐values and activity coefficients are presented.