Simple Distillation and Condensation

Simple Distillation. Distillation without rectification can be carried out by several methods. The two most generally considered cases are (1) continuous simple distillation and (2) differential distiUor tion. In continuous distillation, a portion of the liquid is vaporized under conditions such that all the vapor produced is in equilibrium with the unvaporized liquid. In differential vaporization, the liquid is vaporized progressively, and each increment of vapor is removed from contact with the liquid as it is formed and, although each increment of vapor can be in equilibrium with the liquid as it is formed, the average composition of all of the vapor produced will not be in equilibrium with the remaining liquid. 

Continuous Simple Distillation. Distillations that approximate this type are usually carried out on a continuous basis such that the liquid feed is added continuously to a well-mixed still in which a definite fraction is vaporized and removed and the excess unvaporized liquid is withdrawn from the still. An alternate arrangement is to preheat the feed and add it to a flash or disengaging section where vapor and liquid are separated and removed without additional heat requirements. In either case, assuming that the vapor and liquid leaving are in equilibrium with each other, the two fractions are related to each other by equilibrium constants and material balances. Thus for each component in a mixture the following material balance can be written  

Thus if the fraction vaporized, the feed composition, and the relation 

Differential Distillation. This type of distillation is usually carried out as a batch operation although continuous units may also-operate in this manner. Considering first a batch distillation, if a mixture of liquid is distilled, the distillate contains a greater portion of the more volatile material than the residue, and as distillation proceeds both the distillate and the residue become poorer in the more volatile components. This change in composition may be estimated quantitatively if the relation of the composition of vapor to that of the liquid is known. Consider W parts of original mixture containing Xo fraction of component A, Allow a differential amount —dW to be vaporized of a composition, y, under such conditions that the vapor is continually removed from the system. 

This equation was developed by Rayleigh (Ref. 2) and is often termed the Rayleigh equation. It can be used with W as weight and X as weight fraction, or with W as mols and x as mol fraction. It is usually applied on the basis that, at any given instant, y is in equilibrium with X, but the derivation does not require this condition. A similar equation applies to each component in a mixture. 

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On the other hand, simple distillation and condensation processes will be used in practically every experiment in transferring gases or effecting rough separations. Thus a plot ( for low temperatures) of vapor pressures as a function of temperature for rare gases and other volatile species commonly encountered will prove very handy to the radiochemist. The reader is referred to the generally available Handbook of Chemistry and Physics for data... 

The advance of distillation in the petroleum industry may be epitomized by saying that we started with simple evaporation and condensation, progressed through rectification, and now are in the age of fractionation—that it was formerly an art and is now a science. 

Note 7). When the reaction has subsided, the oil bath is lowered and the condenser is removed. The flask is fitted for simple distillation, and ethyl bromide is distilled from the reaction mixture over a period of 3-4 hr by continued heating at 115°C (oil bath). The resulting light yellow oil is cooled to room temperature, whereupon it solidifies (Note 8). The crude product is collected by suction filtration and washed with three 100-nL portions of cold petroleum ether (bp 60-68°C) to give 50.1-56.3 g (80-90%) of diethyl phthalimidomethylphosphonate as white crystals, mp 60-63°C, which are used in the next step without further purification. Recrystallization of this material from diethyl ether/petroleum ether (bp 60-68°C) affords pure 3, mp 65-67°C (lit.,3 67 C) (Note 9). 

In this experiment, tritiated water is purified by simple distillation, and the tritium beta particles in the condensate are measured with a liquid scintillation (LS) counter. Such distillation also can collect tritiated water samples from solids. Tritium in other forms must be processed before it can be counted like tritium in water for example, tritiated hydrogen gas and tritiated organic substances can be oxidized to form water. Additional separations may be needed if the liquid or solid sample contains radioactive gases or volatile substances other than tritium that may be collected with the distilled tritiated water. Such radioactive impurities can be identified in the data output from the LS counter of an energy spectrum that differs from that of pure tritium, or of counts in energy regions where tritium counts are not found. 

Move the cursor to simple distillation and hit enter . This moves the cursor to the on the line with Condenser. Hitting enter brings up a menu of options for the operation of the condenser ... 

The reader is reminded that the word distillation can be translated as separation drop by drop (see Chap. 2). It can therefore be used as a collective term for processes in which mixtures of mutually soluble liquids can be separated by evajmration and condensation of the liquid, the condensed part becoming richer in the most volatile component. The word gives no indication of the technique adopted in the sejjarating process. The terms simple distillation and countercurrent distillation , however, define the inode of operation (Fig. 23). In a strictly physical sense distillation need not produce any separation we also speak of distillation when a pure liquid is eva-jiorated, the vapour is condensed and the condensate is removed. 

Apparatus A 125-mL and a 25-mL round-bottom flask, two 5-mL syringes, stillhead, reflux condenser, separatory funnel, microburner, apparatus for magnetic stirring, simple distillation, and ffame/ess heating. 

Apparatus A3- and 5-mL conical vial, 2-mL glass syringe, Claisen adapter, gas trap, ice-water bath, reflux condenser, a screw-cap centrifuge tube, apparatus for magnetic stirring, column chromatography, simple distillation, and flameless heating. 

Consider again the simple process shown in Fig. 4.4d in which FEED is reacted to PRODUCT. If the process usbs a distillation column as separator, there is a tradeofi" between refiux ratio and the number of plates if the feed and products to the distillation column are fixed, as discussed in Chap. 3 (Fig. 3.7). This, of course, assumes that the reboiler and/or condenser are not heat integrated. If the reboiler and/or condenser are heat integrated, the, tradeoff is quite different from that shown in Fig. 3.7, but we shall return to this point later in Chap. 14. The important thing to note for now is that if the reboiler and condenser are using external utilities, then the tradeoff between reflux ratio and the number of plates does not affect other operations in the flowsheet. It is a local tradeoff. 

Let us now consider a few examples for the use of this simple representation. A grand composite curve is shown in Fig. 14.2. The distillation column reboiler and condenser duties are shown separately and are matched against it. Neither of the distillation columns in Fig. 14.2 fits. The column in Fig. 14.2a is clearly across the pinch. The distillation column in Fig. 14.26 does not fit, despite the fact that both reboiler and condenser temperatures are above the pinch. Strictly speaking, it is not appropriately placed, and yet some energy can be saved. By contrast, the distillation shown in Fig. 14.3a fits. The reboiler duty can be supplied by the hot utility. The condenser duty must be integrated with the rest of the process. Another example is shown in Fig. 14.36. This distillation also fits. The reboiler duty must be supplied by integration with the process. Part of the condenser duty must be integrated, but the remainder of the condenser duty can be rejected to the cold utility. 

Most students will be familiar with simple distillation from their practical inorganic chemistry. Other students should determine the boiling-point of acetone (56°), using a water-bath and water-condenser, or of benzene (81 ), using a sand-bath and water-condenser, and finally of either aniline (184 ) or nitrobenzene (210 ), using for both these liquids a sand-bath and air-condenser. 

Setup your glassware for simple distillation with a claisen adapter, three way adapter, pressure-equalized addition funnel, water cooled condenser, vacuum adapter and receiver flask to catch any condensed solvent vapors. 

The pressure used in producing gas wells often ranges from 690— 10,300 kPa (100—1500 psi). The temperature of the inlet gas is reduced by heat-exchange cooling with the gas after the expansion. As a result of the cooling, a liquid phase of natural gas liquids that contains some of the LPG components is formed. The liquid is passed to a set of simple distillation columns in which the most volatile components are removed overhead and the residue is natural gasoline. The gas phase from the condensate flash tank is compressed and recycled to the gas producing formation. 

Distillation is a method of separation that is based on the difference in composition between a Hquid mixture and the vapor formed from it. This composition difference arises from the dissimilar effective vapor pressures, or volatihties, of the components of the Hquid mixture. When such dissimilarity does not exist, as at an a2eotropic point, separation by simple distillation is not possible. Distillation as normally practiced involves condensation of the vaporized material, usually in multiple vaporization/condensation operations, and thus differs from evaporation (qv), which is usually appHed to separation of a Hquid from a soHd but which can be appHed to simple Hquid concentration operations. 

FIG. 13-1 Schematic diagram and nomenclature for a simple distillation column with one feed, a total overhead condenser, and a partial rehoiler. 

In distillation operations, separation results from differences in vapor-and liquid-phase compositions arising from the partial vaporization of a hquid mixture or the partial condensation of a vapor mixture. The vapor phase becomes enriched in the more volatile components while the hquid phase is depleted of those same components. In many situations, however, the change in composition between the vapor and liquid phases in equihbrium becomes small (so-called pinched condition ), and a large number of successive partial vaporizations and partial condensations is required to achieve the desired separation. Alternatively, the vapor and liquid phases may have identical compositions, because of the formation of an azeotrope, and no separation by simple distillation is possible. 

Use of the trapping agent is recommended as the most efficient method for running acyloin condensations for many reasons. Among them are (a) the work-up is very simple filter and distil (b) the bis-(silyloxy)olefin is usually easier to store than the free acyloin and is readily purified by redistillation (c) unwanted base-catalyzed side reactions during reduction are completely avoided and (d) the bis-(silyloxy)olefin can be easily converted directly into the diketone by treatment with 1 mole of bromine in carbon tetrachloride.Other reactions are described in Riihlmann s review and in Organic Reactions ... 

Consider now the consequences of placing simple distillation columns (i.e. one feed, two products, one reboiler and one condenser) in different locations relative to the heat recovery pinch. The separator takes heat Qreb into the reboiler at temperature Treb and rejects heat Qcond at a lower temperature Tcond There are two possible ways in which the column can be heat integrated with the rest of the process. The reboiler and condenser can be integrated either across, or not across, the heat recovery pinch. 

Consider now a few examples of the use of this simple representation. A grand composite curve is shown in Figure 21.2a. The distillation column reboiler and condenser duties are shown separately and are matched against it. The reboiler and condenser duties are on opposite sides of the heat recovery pinch and the column does not fit. In Figure 21.2b, although the reboiler and condenser duties are both above the pinch, the heat duties prevent a fit. Part of the duties can be accommodated, and if heat integrated,... 

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