High Pressure Phase Equilibria andPVT‐Data of the Water‐Oxygen System Including Water‐Air to 673 K and 250 MPa

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Abstract
A high pressure autoclave with sapphire windows, auxiliary equipment and means and precautions needed for experiments with high pressure, high temperature oxygen are described. With water‐oxygen mixtures of different mole fractions,x, determinations were made of liquid‐gas phase equilibria conditions along “isopleths” between 500 and 660 K to 250 MPa. Molar volumes of the mixtures were measured at the three‐dimensional (PTx) phase equilibria surface and in the supercritical region at 673 K. The critical curve, an envelope for the isopleths, begins at the critical point of water (647 K), has a temperature minimum (640 K) at about 75 MPa and proceeds to 250 MPa at 663 K. Phase equilibria and critical curve data are given. The H2OO2critical PT curve is very close to the critical curve recently (10) determined for H2ON2. Values for the Henry‐constant from 300 K to 647 K for mixtures dilute in oxygen are presented. The Henry constant at room temperature has only about half the value of the Henry constant for nitrogen in water. At the critical temperature of water (647 K), however, both constants do not differ by more than the uncertainty of the determinations. The excess volume was calculated at 673 K from 30 to 250 MPa. All values are positive. The excess Gibbs energy and activity coefficients are presented. One isopleth for H2O‐air withx(H2O) = 0.80 was measured and molar volume values for this composition at 673 K between 33 and 280 MPa are given.

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