Vapor-liquid equilibrium minimum boiling

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... 

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. 

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. 

Let us first consider binary mixtures which we shall term ordinary by this is meant that the liquid components dissolve in all proportions to form homogeneous solutions which are not necessarily ideal and that no complications of maximum or minimum boiling points occur. We shall consider component A of the binary mixture A-B as the more volatile, i.e., the vapor pressure of pure A at any temperature is higher than the vapor pressure of pure B. The vapor-liquid equilibrium for each pure substance of the mixture is of course its vapor-pressure-temperature relationship, as indicated in Fig. 7.1. For binary mixtures an additional variable, concentration, must likewise be considered. Mole fractions are the most convenient concentration terms to use, and throughout this discus-... 

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. 

Comment 2 Suppose that our feed composition had been a little higher, say xp. No matter how many steps we took, we could never get a liquid composition higher than that at the intersection of the operating and equilibrium curves. In that case, any solution for the specified L/V ratio is impossible. Instead the L/V ratio would have to be decreased, which will rotate the operating line clockwise about the specified point. This will raise the liquid composition at the intersection point and make the separation possible. It turns out there exists maximum L/V, or a minimum vapor rate V which allows a particular bottoms composition xp to be produced from a given feed composition xp and liquid flowrate L. This minimum V/L is called the minimum boil-up ratio. 

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,. 

Many liquid mixtures exhibit azeotropes at intermediate concentrations such that the liquid and its equilibrium vapor have the same composition. No separation of this concentration is possible by partial vtqxir-ization. A binary mixture may have a minimum boiling azieotrope, where the toiliiig temperature of the azeotrope is less than that of the pure components, or a maximum boiling azeotrope, whm the boiling temperature is higher than that of the pure components. About 90% of the known azeotropes are of the minimum variety. 

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... 

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... 

Suppose that, under the pressure P, we may observe a condition of indifferent equilibrium where the liquid mixture and the saturated vapor have the same composition f the boiling-point 0 of the mixture of composition is maximum or minimum among the boiling-points which the liquid mixture may have under constant pressure P. 

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