FLUID MULTIPHASE BEHAVIOR IN TERNARY MIXTURES, OF CO2, H2O AND 1-BUTANOL

A unique feature in the CO2-H2O-1-butanol system is the formation of f our fluid phases in thermodynamic equilibrium. Investigations into thi s phenomenon now permit a complete description of phase behavior betwe en 296 K and 315 K at pressures ranging from 5.8 MPa to 11.0 MPa, The experimental programme covers the determination of equilibrium composi tions in fluid three-and four-phase equilibria as well as measurements of critical lines and critical endpoints. Experiments were selected i n order to prove Gibbs' theorems on the formation of four-phase equili bria in ternary systems. Calculations using the Redlich-Kwong-Soave eq uation of state in combination with mixing rules proposed by Huron and Vidal complete the description of phase behavior in regions hardly or not accessible by experiment. The model, at least qualitatively, is c apable of predicting the full extent and variety of the phase behavior for CO2-H2O-1-butanol mixtures from binary two-phase equilibrium data alone. Considerable improvement towards a quantitative description, h owever, can be achieved when p,T-data along the four-phase line of the system is incorporated in the evaluation of the interaction parameter s of the empirical mixing rules. (C) 1997 Elsevier Science B.V.