The two-phase region detaches from the C 1–C 4 side of the diagram at the critical pressure of the C 1–C 4 pair (approximately 1,800 psia). If the pressure is increased above 1,000 psia, the liquid composition line shifts to higher methane concentrations methane is more soluble in both C 4 and C 10 at the higher pressure (see Fig.
3 shows, at 1,000 psia the two-phase region is a band that stretches from the C 1–C 10 side of the diagram to the tie line on the C 1–C 4 side. 4 – Pressure-composition phase diagram for methane/butane and methane/decane binary systems at 160☏.Īs Fig. Depending on the pressure, temperature, and components, a plait point may or may not be present.įig. Thus, the plait-point mixture has a critical temperature and pressure equal to the conditions for which the diagram is plotted. The liquid and vapor portions of the binodal curve meet at the plait point, a critical point at which the liquid and vapor phases are identical. 3 is another lever rule similar to that described for binary diagrams. If the mole fractions of Component i in the liquid, vapor, and overall mixture are x i, y i, and z i, the fraction of the total moles in the mixture in the liquid phase is given byĮq. Only the amounts of liquid and vapor change as the overall composition changes from the liquid side of the binodal curve to the vapor side. Any mixture with an overall composition along a tie line gives the same liquid and vapor compositions. Tie lines connect compositions of liquid and vapor phases in equilibrium. Mixtures with overall compositions that lie inside the binodal curve will split into liquid and vapor. 2 shows the typical features of a ternary phase diagram for a system that forms a liquid and a vapor at fixed temperature and pressure.
For vapor/liquid equilibrium diagrams, mole fractions are most commonly used.įig. Compositions represented on a ternary diagram can be expressed in volume, mass, or mole fractions. 1d, lie on a straight line connecting the two points on the ternary diagram. Finally, mixtures of any two compositions, such as A and B in Fig. In addition, mixtures lying on any line connecting a corner with the opposite side contain a constant ratio of the components at the ends of the side ( Fig. For mixtures along any line parallel to a side of the diagram, the fraction of the component of the corner opposite to that side is constant ( Fig. Several other useful properties of triangular diagrams are a consequence of this fact. Thus, the composition of a point in the interior of the triangle can be calculated as Such diagrams are based on the property of equilateral triangles that the sum of the perpendicular distances from any point to each side of the diagram is a constant equal to the length of any of the sides. Phase behavior of mixtures containing three components is represented conveniently on a triangular diagram such as those shown in Fig.
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