Negative azeotropy

AZEOTROPIC SYSTEM. A system of two or more components that has a constant boiling point at a particular composition. If the constant boiling point is a minimum, the system is said to exhibit negative azeotropy, if it is a maximum, positive azeotropy. 

Fig. 5. Boiling-point diagram of an azeotropic system exhibiting negative azeotropy...

On the other hand when (28.40) is negative the azeotropic state corresponds to a maximum in T and a minimum in p this state is called negative azeotropy. If the azeotropy is negative, an increase in temperature decreases the mole fraction of the component with the higher heat of evaporation. 

In our discussion of (vapor + liquid) phase equilibria to date, we have limited our description to near-ideal mixtures. As we saw in Chapter 6, positive and negative deviations from ideal solution behavior are common. Extreme deviations result in azeotropy, and sometimes to (liquid -I- liquid) phase equilibrium. A variety of critical loci can occur involving a combination of (vapor + liquid) and (liquid -I- liquid) phase equilibria, but we will limit further discussion in this chapter to an introduction to (liquid + liquid) phase equilibria and reserve more detailed discussion of what we designate as (fluid + fluid) equilibria to advanced texts. 

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