Computation and analysis of surfaces and lines of three-phase equilibrium in ternary systems: Application illustrated for a CO2(1)+H2O(2)+2-propanol(3)-like system

In this work the rich phenomenology of the ternary three-phase equilibrium is studied for a CO2(1)+H2O(2)+2-propanol(3)-like system which presents a highly complex behavior. This is done through computations carried out over wide ranges of conditions using a model of the equation of state type. The developed computation and analysis strategies are applicable to any ternary system as described by any equation of state model, chosen for representing real systems having a high degree of complexity in their phase behavior. A systematic identification of phase equilibrium objects (or points) from which ternary three-phase lines (T-3PLs) originate is performed. Such points are used to start the computation of a variety of T-3PLs. Several computed T-3PLs are used to visualize a number of ternary three-phase surfaces (T-3PSs). Besides, the boundaries of the T-3PSs are established. A strategy to start the calculation of a T-3PL is proposed for each type of originating point. In addition, with the aim of avoiding convergence problems, a numerical continuation method is used to calculate complete T-3PLs. The visualization of 3D projections of T-3PSs in the temperature-pressure-fugacity space is proposed. This way of looking at the T-3PSs is of much help in the understanding on how they behave and interrelate. The results suggest, among other interesting conclusions, the possibility of continuous transitions from T-3PSs of a given type to T-3PSs of a different type.