Azeotropic or extractive distillation

The usual procedures of fractional, azeotropic, or extractive distillation under inert gases, crystallization, sublimation, and column chromatography, must be carried out very carefully. For liquid, water-insoluble monomers (e.g., styrene, Example 3-1), it is recommended that phenols or amines which may be present as stabilizers, should first be removed by shaking with dilute alkali or acid, respectively the relatively high volatility of many of these kinds of stabilizers often makes it difficult to achieve their complete removal by distillation. Gaseous monomers (e.g., lower olefins, butadiene, ethylene oxide) can be purified and stored over molecular sieves in order to remove, for example, water or CO2. 

A separation process is sought that can satisfy both our present economic and enviromental constraints. It would also provide an alternative to present practice that relies on expensive azeotropic or extractive distillation processes used in the recovery of products from low relative volatility streams. As an example, virtually all industrial butadiene recovery processes now rely on extractive distillation using acetonitrile or other equivalent agent to enhance the relative volatility of the C4 components. The use of supercritical or near critical separation of these streams may satisfy these requirements provided certain pressure, temperature and recompression criteria can be met. Such a process would also reduce the need for a complex train of distillation towers. 

The design of azeotropic or extractive distillation columns, as with con-A ventional columns, demands a knowledge of the vapor-liquid equilibrium properties of the system to be distilled. Such knowledge is obtained experimentally or calculated from other properties of the components of the system. Since the systems in azeotropic or extractive distillation processes have at least three components, direct measurement of the equilibrium properties is laborious and, therefore, expensive, so methods of calculation of these data are desirable. 

The success of the NRTL equation in undergoing this test would suggest that it will be a powerful tool in the design of processes involving azeotropic or extractive distillation. The effect of the addition of a third... 

To separate solutions of both liquids and of solids in a liquid (particularly water), two methods usually are considered first (1) vaporization—i.e., evaporation or distillation—to utilize the different relative volatilities of the components, either normally or accentuated by another liquid in azeotropic or extractive distillation and (2) liquid-liquid extraction to take advantage of the relative preferential solubility of one component in an added liquid. 

Derivation Interaction of methanol and ammonia over a catalyst at high temperature. The mono-, di-, and trimethylamines are all produced and yields are regulated by conditions. They are separated by azeotropic or extractive distillation. 

The terms entrainer and solvent are commonly used interchangeably to refer to the separating agent used to enhance the separation of close boilers or azeotropes by azeotropic or extractive distillation. For consistency, the term entrainer will be used to designate the azeotropic distillation agent and solvent, the extractive distillation agent. 

Formic add displays an unusual behavior, however, significantly complicating the scheme for the separation of the different products formed and for the purification of the acetif acid. Formic acid, which boils at a temperature approaching that of water (bpi.013 - 100.7°Q forms an azeotrope with water, with a boiling point higher than those of the pure components ( ,.ou = 107.2°C, water content, percent weight, 2Z6). Hence its separation requires azeotropic or extractive distillation. 

A second alternative for the separation of hydroformylation products from a rhodium [8] or cobalt [9] catalyst is to perform the catalytic reaction in a polar solvent using complexes of monosulfonated trialkyl- or triarylphosphines (e.g., TPPMS). Addition of both water and an apolar solvent such as cyclohexane gives a biphasic system. After separation of the apolar layer, the added apolar solvent must be stripped from the products. In order to form a homogeneous system with new substrate alkene, the polar catalytic phase must be freed from water, e.g., by azeotropic or extractive distillation. Clearly, these extra co-distillation steps are energy-consuming. 

The Almost Band Algorithm presented in Chap. 5 may be used to describe a single column in which either an azeotropic or extractive distillation is carried out provided that the accumulator contains only one liquid phase and one vapor phase. In many azeotropic distillation columns, the accumulator contains two liquid phases and one vapor phase. In order to describe a column whose accumulator contains three phases, the Almost Band Algorithms presented in Chap. 5 must be modified. To illustrate the modifications of the Almost Band Algorithm which are required in order to describe a column having three phases in the accumulator, the [N(2c + 1) -f 2] formulation of the Almost Band Algorithm for a column with a two-phase partial condenser is selected as the base case. Then the modifications required to describe a three-phase partial condenser are presented. 

Owing to the non-ideality of binary or multicomponent mixtures, the liquid phase composition is often identical with the vapor phase composition. This point is called an azeotrope and the corresponding composition is called the azeotropic composition. An azeotrope can not be circumvented by conventional distillation since no enrichment of the low-boiHrig component can be achieved in the vapor phase. Separating azeotropic mixtures therefore requires special processes, e.g. azeotropic or extractive distillation or pressure swing distillation. Azeotropic information is available in literature (Gmehling et al., 2004). 

The usual procedures of fractional, azeotropic, or extractive distillation under inert gases, crystallization, sublimation, and column chromatography, must be... 

Which solvent can be applied to separate the azeotropic system ethanol-water by azeotropic or extractive distillation. ... 

In most cases, special distillation processes such as azeotropic or extractive distillation are applied to separate azeotropic systems by distillation, where a suitable solvent is added. While in the case of azeotropic distillation a solvent is required which forms a lower boiling azeotropic point, in the case of extractive distillation a high-boiling selective solvent is used which changes the separation factor in a way that it becomes distinctly different from unity. Both processes are shown in Figure 11.16 together with the column configuration. 

Figure 11.17 Flow diagram for the selection of suitable solvents for azeotropic or extractive distillation by direct access to the Dortmund Data Bank or the application of predictive methods.

In any given case there are usually a number of compounds that are effective as azeotropic- or extractive-distillation agents, and the choice depends on a number of factors ... 

For either type of vaporization, the general consideration of solution laws apply and can be used to predict the results of modifying the liquid phase. Thus it would be possible to modify the composition of the vapor removed in molecular distillation just as in azeotropic or extractive distillation. 

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