Distillation multistage

In sum, distillation is a countercurrent vapor-liquid operation with the external reflux of a condensed liquid phase at the top and the external recycle or reflux of reboiled or vaporized vapor at the bottom. This reflux or recycle feature produces a sharp separation between the two key components of the feed mixture, and the same applies to membrane operations. The key components are the two components of a mixture between which the separation is to be made. 

The feed mixture or its molar flow rate is generally denoted by the symbol F. The upper or lighter, relatively more volatile product, called the distillate product, is denoted D. The lower or heavier, less volatile product, called the bottoms product, is denoted B. 

At the same time, a small pressure gradient forms up and down the column, with the highest pressure at the bottom. Normally in distillation practice, this pressure drop is minor compared to the working pressure, and the working pressure is assumed to be the same constant value up and down the column. 

If viewed alone, without reflux or recycle, it may be noted that the top or rectifying section of a distillation column corresponds to simple vapor-liquid absorption that is, to the absorption of a key component or components from a gas or vapor using a liquid absorbent or solvent. The bottom section similarly corresponds to simple liquid-vapor stripping that is, to the stripping of the key component or components from a liquid using a gas or vapor phase. 

Characteristically, neither absorption nor stripping produces a sharp separation unless, say, the solvent is highly specific to the selective absorption of the key component s) or the vapor phase is highly specific to the selective removal of the key component(s). If reflux is used at the top of an absorber, for instance, there will be the tendency to produce the more-volatile component as the distillate product but with a poor or sloppy 

Although the exact origins of the art of distillation remain obscure, there is considerable evidence that its invention and early development took place in the first century in Alexandria, Egypt. A millennium later it was used for the first time in Northern Italy to produce alcoholic beverages. As may have been surmised, it was this enticing application that preoccupied the practitioners of the art in subsequent years. The early installations consisted of 

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Distillation. Distillation separates volatile components from a waste stream by taking advantage of differences in vapor pressures or boiling points among volatile fractions and water. There are two general types of distillation, batch or differential distillation and continuous fractional or multistage distillation (see also Distillation). 

Availability of large digital computers has made possible rigorous solutions of equilibrium-stage models for multicomponent, multistage distillation-type columns to an exactness limited only by the accuracy of the phase equilibrium and enthalpy data utilized. Time and cost requirements for obtaining such solutions are very low compared with the cost of manual solutions. Methods are available that can accurately solve almost any type of distillation-type problem quickly and efficiently. The material presented here covers, in some... 

Tassoney, J. P, Fast Analysis for Multistage Distillation, Chem. 

The conditions at which the separations are performed depend on the properties of the materials. Let us suppose we wish to separate n butane from n pentane. Table 4-3 gives the boiling points of these compounds. When possible the pressure in a distillation column is usually kept close to atmospheric. Since all multistage distillation columns require reflux, which is obtained by condensing the exiting vapor stream, if the top of the column were producing nearly pure butane the condensing temperature would be around 31°F( - 1°C). To obtain condensation at this temperature a coolant is needed at a temperature at least 10°F (5°C) cooler. This means that... 

Baratella, P., Carra, S., Giardini, G. and Santi, R. S., 1974, Multistage distillation with chemical reaction. Ing. Chim. Ital. 10, 1-6. 

In contrast to the description of distillation given earlier, which dealt with multistage distillation, flash distillation (Fig. 15) is carried out in a single stage. Liquid flows continuously through a heater, across a valve, and into a flash vessel. By heating the liquid and reducing its pressure across the valve, partial vaporization occurs in the flash... 

Step by Step the McCabe-Thiele Method Introduction to the McCabe-Thiele method for countercurrent multistage distillation, from your About.com Guide, Dr. Bernhard Spang. http //Chemeneineer. about comllibrarvlweeklylaa 11 1599.h. 

The simplest case of multistage distillation is the continuous distillation of binary systems where the feed contains only two components. Here the most widely used method of analysis is that of... 

The organic phase enters a multistage distillation unit, where both products, fatty aldehydes and acids, are isolated. Solvent as well as unchanged fatty alcohol is recycled to the reactor. In this way a very effcient overall oxidation with MM/H202 can be achieved. 

For a multiple-stage cascade, and for a feed the enters in the midregion of the cascade, the representation of a multistage distillation column emerges, as shown in Fig. 5.3-4. In this column, vapor stream Vt is... 

FIGURE 5.3-13 Tridiagonal matrix foratulation or multistage distillation material balances. A similar matrix is required for each component. 

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