Vapor-liquid equilibrium minimum boiling azeotropes

Minimum boiling point azeotrope with no data given Vapor-liquid equilibrium data are given in the original reference Azeotropic concentration is given in volume per cent. Unless so indicated, all concentrations are weight per cent Pressure in mm. of mercury absolute Approximate Greater than Less than... 

A minimum boiling azeotrope is indicated by the peak in the total pressure between X, = 0.5 and X, = 0.7. Azeotropes, discussed in the following section, are equilibrium mixtures that at a certain temperature and pressure can have the same composition in the liquid and vapor. For this mixture, the azeotrope lies somewhere between X, = 0.5 and 0.7. Below the azeotrope (at X, = 0.5) Y, > X,. Above the azeotrope (at X, = 0.7) y, < X,. 

Figure 8-7 Minimum boiling azeotrope (top), and maximum boiling azeotrope (bottom). Data from Vapor-Liquid Equilibrium Data Collection, J. Gmeliling, U. Onken, and W. Arlt, DECHEMA. 

Up to this point we have looked at systems with fairly ideal vapor-liquid equilibrium behavior. The last separation system examined is a highly nonideal ternary system of methyl acetate (MeAc), methanol (MeOH), and water. Methyl acetate and methanol form a homogeneous minimum-boiling azeotrope at 1.1 atm with a composition of... 

The vapor-liquid equilibrium (VLB) and liquid-liquid extraction (LLE) correlations in Aspen Plus are not always as accurate as possible. This can cause significant errors, particularly near pinch points in distillation columns. If data is available, Aspen Plus will find values of the parameters for any of the VLB or LLE correlations by doing a regression against the data you input. This is illustrated to obtain an improved fit for the non-random two-liquid (NRTL) VLB correlation for the binary system water and isopropanol (IPA). VLB data for water and isopropanol is listed in Table B-1. This system has a minimum boiling azeotrope at 80.46°C. The Aspen Plus fit to the data with NRTL is not terrible, but can be improved. 

If we add another CH2 group and move to the ethanol-water system, there is more repulsion because the CH3-CH2 end of the ethanol molecule is quite different from the OH end of the water molecule. The system exhibits more nonideality and a minimum-boiling azeotrope occurs. This azeotrope is homogeneous (only one liquid phase in equilibrium with a vapor phase). If we add two more CH2 groups and move to the n-butanol-water system, the... 

Isopropyl alcohol and water form a minimum boiling point azeotrope at 88 wt% isopropyl alcohol and 12 wt% water. Vapor-liquid equilibrium (VLE) data are available from several sources and can be used to back-calculate binary interaction parameters or liquid-phase activity coefficients. The process presented in Figure B.3 and Table B.6 was simulated using the UNIQUAC VLE thermodynamics package and the latent heat enthalpy option in the CHEMCAD simulator. This package correctly predicts the formation of the azeotrope at 88 wt% alcohol. 

In this section, we consider the case when three phases are in equilibrium a vapor phase and two liquid phases, a and p. A generic diagram of a system with m components in vapor-liquid-liquid (VLLE) equilibrium is shown in Figure 8.15. How does such behavior come about Let s return to the binary mixture of a and b. Consider the case where we have both an azeotrope in VLE and liquid-liquid equilibrium (ELE). This scenario corresponds to a minimum-boiling azeotrope where the like interactions are stronger than the unlike interactions. Figure 8.16a shows the phase diagram for the case... 

An important system in distillation is an azeotropic mixture. An azeotrope is a liquid mixture which when vaporized, produces the same composition as the liquid. The VLE plots illustrated in Figure 11 show two different azeotropic systems one with a minimum boiling point and one with a maximum boiling point. In both plots, the equilibrium curves cross the diagonal lines. 

Many liquid mixtures exhibit azeotropes at intermedrate concentrations such that the liquid and its equilibrium vapor have the same composition. No separation of (his concentration is possible by partial vaporization. A binary mixture may have a minimum bailing azeotrope, where the boiling temperature of the azeotrope is less than that of the pare components, or a maximum boiling azeotrope, where (he boiling temperature is higher (han that of the pare components. About 90% of die known azeotropes are of the minimum variety. 

For the mixture isopropyl ether/isopropyl alcohol, positive deviations from Raoult s law occur. They are so strong that the total pressure reaches a maximum for a certain concentration. The vapor pressure maximum corresponds to a boiling temperature minimum as it is depicted in the middle row. Boiling curve and dewpoint curve contact each other in the so-called azeotropic points. Here the mole fractions of vapor y and liquid have the same value which also follows from the equilibrium diagram below. In the azeotropic point A the equilibrium curve intersects the diagonal Pa = To the left of point H the mole fraction of compo-... 

The Uquids in the immiscible region boil at a constant temperature of about 200°F. As long as two liquid phases coexist at equilibrium, the boiUng point and the equiUbrium vapor composition are constant. This is a heterogeneous azeotrope The mixture has a minimum boiUng point and the vapor is at equilibrium with two liquid phases. The appearance of a second Uquid phase is a phenomenon that is used to effect separation in certain processes, as described in Chapter 10, by splitting the phases and processing each liquid phase separately. 

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