The Ternary Systems H2O‐CH4‐NaCl and H2O‐CH4‐CaCl2to 800 K and 250 MPa

Abstract Experimental results are reported for the fluid phase equilibria of the ternary system H 2 O‐CH 4 ‐NaCl and to a lesser degree of H 2 O‐CH 4 ‐CaCl 2 . Measurements were extended to 800 K and 250 MPa. A “synthetic” method, described previously, was used, supplemented with an electrolytic indication. The high pressure autoclave with sapphire windows and variable volume together with its auxiliary equipment is described. Pressure‐temperature curves on the three‐dimensional PTx ‐surfaces at constant compositions, x , were obtained (“isopleths”). Data for 21 isopleths with NaCl‐concentrations of 0.6, 1.7 and 8 weight percent relative to water with CH 4 ‐concentrations ranging from 6 to 71 mol percent are presented together with three isopleths for H 2 O‐CH 4 ‐CaCl 2 mixtures. Molar volumes at the phase boundary surfaces are given. In comparison with the binary H 2 O‐CH 4 system, investigated earlier, the addition of only 0.53 mol% NaCl shifts the range of partial immiscibility to higher temperatures by more than 100 K (for example from 610 to 715 K at 100 MPa for 51 mol% CH 4 ). The shift produced by CaCl 2 appears to reflect incomplete ionic dissociation at high temperatures. Encouraging results of computations of critical curves using pseudo‐binary approximations and a new equation of state based on defined interaction models are shown.