Azeotropes transformation

An azeotropic transformation is said to occur when, in a closed system, the mass of one of the phases increases at the expense of the others, without changing the composition of any of these phases. 

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. 

Azeotropic transformations in systems in which chemical reactions may take place in addition to transfers from one phase to another, or which have more than two phases, are not necessarily associated with states of uniform composition but with the more general class of indifferent states. A study of systems of uniform composition is a natural introduction to the more general question of indifferent states. 

Consider an equilibrium azeotropic transformation, that is to say an equilibrium transformation as defined in 1 of chapter XIX but during which, in addition, the composition remains constant. We now proceed to show that a transformation of this kind must take place at constant temperature and pressure. 

We thus obtain equation (28.36) once more except that the entropy and volume are expressed per unit mass. Similarly, we may put (29.77) into a form analogous to (28.35) in terms of a latent heat of azeotropic transformation. ... 

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 ... 

We see, for example, that the theorem (29.122) enables us to determine, whether we can expect to find an indifferent state compatible with the arbitrary masses m. .. m% which constitute the closed system. If this state exists then a further analysis concerned with the rates of transfer enables us to decide whether or not an azeotropic transformation is realisable starting from this state. ... 

A closed system undergoes an azeotropic transformation when, during the course of the transformation, the masses of some of the phases increase at the expense of others, without a change in the composition of the phases. This is expressed, for all phases a and all compositions, by the property ... 

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

An example of azeotropic transformations, besides certain phase changes, includes the transformation ... 

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. 

Chapter 1 describes transformations and chemical equilibria using Bonder s affinity method. Equilibrium couditious are examined in enclosed media, where one or more equilibrium states are present, and in open systems. The chapter closes with a general look at azeotropic transformations. 

We shall now apply the ideas of this chapter to the azeotropes introduced in Chapter 7. For an azeotrope in equilibrium with its vapor, the composition of the liquid and the vapor phases are the same. At a fixed pressure, a liquid mixture is an azeotrope at a particular composition called the azeotropic composition. An azeotropic transformation is one in which there is an exchange of matter between two phases without change in composition. In this regard, an azeotrope is similar to the vaporization of a pure substance. This enables us to obtain the activity coefficients of azeotropes just as for a pure substance. 

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... 

When R2 substituent is flourocontaining alkyl group, the transformation 17 18 becomes hindered and its proceeding requires some special methods. For example, in [48] Biginelli-like cyclocondensations based on three-component treatment of 3-amino-l,2,4-triazole or 5-aminotetrazole with aldehydes and fluorinated 1,3-dicarbonyl compounds were investigated. It was shown that the reaction can directly lead to dihydroazolopyrimidines 20, but in the most cases intermediate tetrahydroderivatives 19 were obtained (Scheme 10). To carry out dehydration reaction, refluxing of tetrahydroderivatives 19 in toluene in the presence of p-TSA with removal of the liberated water by azeotropic distillation was used. The same situation was observed for the linear reaction proceeding via the formation of unsaturated esters 21. 

Octahydroazocine (1) behaves as a typical secondary amine and forms an azeotrope with water, b.p. 96 °C (52M386). It can be transformed into 1-nitroso and 1-amino derivatives in the usual way (74JMC948). The imine (1) can also be cyanoethylated, and adds ethylene oxide (59MI51900) to give the N- hydroxyethyl derivative. Attempts to convert (1) to an enamine by oxidation with silver acetate gave only a low yield of pyridine (52M386). 

Because of their very similar boiling points and azeotrope formation, the components of the C4 fraction cannot be separated by distillation. Instead, other physical and chemical methods must be used. 1,3-Butadiene is recovered by complex formation or by extractive distillation.143-146 Since the reactivity of isobutylene is higher than that of n-butenes, it is separated next by chemical transformations. It is converted with water or methyl alcohol to form, respectively, tert-butyl alcohol and tert-butyl methyl ether, or by oligomerization and polymerization. The remaining n-butenes may be isomerized to yield additional isobutylene. Alternatively, 1-butene in the butadiene-free C4 fraction is isomerized to 2-butenes. The difference between the boiling points of 2-butenes and isobutylene is sufficient to separate them by distillation. n-Butenes and butane may also be separated by extractive distillation.147... 

Applications of the Karl Fischer method are numerous food stuffs (butter, margarine, powdered milk, sugar, cheese, processed meats, etc.), solvents, paper, gas, petroleum, etc. Before the determination can be made, solid components that are not soluble must either be ground into powders, extracted with anhydrous solvents, eliminated as azeotropes or heated to eliminate water. Problems are encountered with very acidic or basic media that denature reactants and transform ketones and aldehydes into acetals that interfere with the titration. Special reagents must be used in these instances. 

The vapor curve KLMNP gives the composition of the vapor as a function of the temperature T, and the liquid curve KKMSP gives the composition of die liquid as a function of die temperature. These two curves have a common point M. The state represented by M is that in which the two states, vapor and liquid, have the same composition xaB on die mole fraction scale. Because of die special properties associated with systems in this state, the Point M is called an azeotropic point and the system is said to form an azeotrope. In an azeotropic system, one phase may be transformed to the other at constant temperature, pressure and composition without affecting the equilibrium state. This property justifies the name azeotropy, which means a system diat boils unchanged. 

The surfaces described by Eqs. (27a) and (27b) in the three-dimensional composition space intersect with each other and yield the PSPS as curves given in Fig. 4.10(a). The PSPS contain several branches, three of which pass through the pure components HOAc, IPOAc and water, and are located outside the composition space but are not depicted. The branch passing through the I PA-vertex locates four nonre-active azeotropes - that is, IPA-IPOAc, IPOAc-Water, IPA-IPOAc-Water, and IPA-Water. This branch also contains the reactive azeotrope. The PSPS is also displayed in the transformed composition space (Fig. 4.10(b)). 

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. 

Another possibility is the representation in a two-dimensional diagram, as in Figure A.4 (right). The component C being chosen as the reference, the relation (A.3) gives the transformed co-ordinates XA = (xA + xc)/(l + xc) and X, = (xB + xc) / (1 + xc). The residue curves run from the reactive azeotrope to the vertex of component I. This situation is denoted by two degrees of freedom systems . 

Intramolecular nitrone-alkene cycloaddition. Reaction of cycloalkanones substituted by a 3-(2-propenyl) or a 3-(3-butenyl) side chain with alkylhydroxylamines with azeotropic removal of water results in a bridged bicycloalkane fused to an isoxazolidine ring. The transformation involves formation of a nitrone that undergoes intramolecular cycloaddition with the unsaturated side chain. 

Reactive azeotropes are not easily visualized in conventional y-x coordinates but become apparent upon a transformation of coordinates which depends on the number of reactions, the order of each reaction (for example, A + B C or A + B C + D), and the presence of nonreacting components. The general vector-matrix form of... 

---