Azeotropic transformation, conditions

In this paragraph we shall investigate the conditions under which a transformation of this kind can occur, restricting ourselves for the moment to a two-phase system in which there are no chemical reactions other than the passage of components from one phase to another. Prom the definition of an azeotropic transformation we must have... 

We shall therefore limit ourselves for the rest of this chapter to a consideration of systems of uniform composition. The relationship between these and the occurrence of azeotropic transformations is so close that we shall call such systems azeotropic states. The study of the conditions relating to the rates of transfer will be deferred until the last volume of this work, when it will be shown that these conditions correspond to the minimum rate of entropy production. 

However, we can find the appropriate values of T and p such that the system initially in the above state will undergo an azeotropic transformation in time. This is possible because, at any time t, we have to satisfy the two conditions (28.5) referring to the rates of transfer ... 

Thus, the necessary and sufficient conditions for a phase change to be an azeotropic transformation are that ... 

This fourth volume of the set concerns the study of chemical equilibria. The conditions of evolution of systems are first discussed through the De Donder affinity method. The modes of movement and stability under the action of disturbances are examined as well as the Gibbs and Duhem phase laws. The azeotropic transformations and the description of indifferent states complete this study. 

The transformed variables describe the system composition with or without reaction and sum to unity as do Xi and yi. The condition for azeotropy becomes X, = Y,. Barbosa and Doherty have shown that phase and distillation diagrams constructed using the transformed composition coordinates have the same properties as phase and distillation region diagrams for nonreactive systems and similarly can be used to assist in design feasibility and operability studies [Chem Eng Sci, 43, 529, 1523, and 2377 (1988a,b,c)]. A residue curve map in transformed coordinates for the reactive system methanol-acetic acid-methyl acetate-water is shown in Fig. 13-76. Note that the nonreactive azeotrope between water and methyl acetate has disappeared, while the methyl acetate-methanol azeotrope remains intact. Only... 

A singular point of reactive membrane separation should be denoted as kinetic arheotrope because it is a process phenomenon rather than a thermodynamic phenomenon. The condition for arheotropy can be elegantly expressed in terms of new transformed variables, which are a generalized formulation of the transformed composition variables first introduced to analyze reactive azeotropes. 

In the synthesis of imines and enamines by this method, the water produced in the reaction must be removed azeotropically to drive the reaction to the right. In aqueous acid, equilibrium conditions favor the ketone rather than the imine. This relationship is the reason why Grignard reaction of a nitrile provides a good route to the synthesis of ketones. The intermediate imine formed is hydrolyzed easily to the corresponding ketone (e.g., the transformation of 3-3 to 3-4 in Example 3.13). 

These necessary and sufficient conditions for reactive azeotropes have been generalized and theoretically established for the case of multicomponent mixtures undergoing multiple equilibrium chemical reactions by Ung and Doherty (19956). The starting point for their analysis is the introduction of transformed compositions. It is widely recognized that mole fractions are not the most convenient measures of composition for equilibrium reactive mixtures, as they might lead to distortions in the equilibrium surfaces (Barbosa and Doherty, 1988a Doherty and Buzad, 1992). In order to visualize in a much more... 

Let us perform an azeotropic displacement (see section 1.9) of that state to bring it to the final state eharacterized by the same variables assigned the prime index. During the course of that transformation, as the system remains closed, it obeys the closure condition [2.45], which enables us to write ... 

Dehydrosulfurizations. The thiophilicity of tin compounds is often utilized in functional group transformations. Thus conversion of aromatic and aliphatic thioamides to the corresponding nitriles can be accomplished by using (80380)2 in boiling benzene under azeotropic conditions (eq 15). ... 

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