Simple apparatus for fractionation

Otherwise expressed, the number of theoretical plates required for a given separation increases when the reflux ratio is decreased, i.e., when the amount of condensed vapour returned to the colunm is decreased and the amount distilled off becomes greater. 

Beyond certain limits increase of the reflux ratio does not appreciably increase the separating power or efficiency of the column. As a rough guide, if the column has an efficiency of n plates at total reflux, the reflux ratio should be between 2 t/3 and 3n/2. 

The efficient fractionating columns in general use may be divided into two main groups — 

The merits of the above contact rings for laboratory fractionating columns appear to have been overlooked. 

However, where small quantities of liquids are involved, a column filled with glass helices will probably give the best results and the cost will not be unduly high. Rings in stainless steel and other metals can be purchased in sizes from to i.  

A number of excellent packings for distilling columns are available commercially. The simplest, cheapest, and yet highly efiFective packing consists of hollow glass rings of and height and diameter i  

A porcelain Lessing rings, or with porcelain rings. The mixture to be fractionated is placed in a bolt - head flask of convenient size (it should be one third to one half full), a few fragments of porous porcelain added, the column fixed in position, and a water condenserattached to t he side arm. The distillate is collected in small flasks or in test-tubes. The bulb of the thermometer should be just below the level of the side arm. 

---

B) Fractional Distillation of an Ethanol-Water Mixture. Place the 50 mL of distillate from the simple distillation experiment in a 100-mL round-bottomed flask, add one or two boiling chips, and assemble the apparatus for fractional distillation. Follow the procedure (above) for the fractional distillation of a cyclohexane-toluene mixture. Repeat the ignition test. Is any difference noted ... 

Another simple form of apparatus, for fractionating low-boiling liquids, which is especially valuable when small quantities only are available, can be constructed from a Claissen flask and a test-tube in the way illustrated in Tig. 10. The cold water enters through the long tube in the test-tube and passes upward. By... 

By changing the density of the supercritical fluid, different fractions may be selectively extracted from the complex mixture or sample matrix. On decompression, the extracted solutes are precipitated and may be collected for injection into a GC or SFC for analysis. Figure 8.4 shows a simple apparatus for on-line SFE/SFC solutes extracted from the sample matrix are deposited from the end of a restrictor into the internal loop of the microinjection valve of the capillary SFC. The valve loop contents are subsequently switched into the SFC column by means of liquid or supercritical carbon dioxide. 

The chief disadvantage of the simple vacuum distillation set up shown in Fig. 11,19, 1 is that, if more than one fraction is to be collected, the whole process must be stopped in order to change the receiver B. It is of value, however, for the distillation of solids of low melting point the distillate can easily be removed from the receiver by melting and pouring out. For routine work, involving the collection of several fractious under reduced pressure, the most convenient receiver is the so-called Perkin triangle the complete apparatus for vacuum distillation is depicted in F g. 11,20, 1. The Claisen fla.sk A is fitted to a. short water... 

Apparatus for the study of TL is usually simple in its design and principles (see, e.g., (10)). The sample, prepared either as grains or a slice a fraction of a mm thick, is placed on an electrically heated plate in an inert gas and, as the temperature is raised, the light output is recorded using a photomultiplier. 

The apparatus for a fractional distillation is more complex in that a column and a distilling head are placed between the pot and the condenser. The purpose of the column is to provide a large surface so that many simple distillations can take place at the same time, and the distilling head allows one to remove only a small portion of the material that reaches the top of the column, sending the rest back down the column to be redistilled, a process known as refluxing. 

A simple method for removing peroxides from high-quality ether samples without need for distillation apparatus or appreciable loss of ether consists of percolating the solvent through a column of Dowex-1 ion exchange resin. A column of alumina was used to remove peroxides and traces of water from ethyl ether, butyl ether, dioxane, and petroleum fractions and for removing peroxides from tetrahydrofuran, decahydronapthalene(decalm), 1,2,3,4-tetrahydro-naphalene (tetralin), cumene and isopropyl ether. 

In a simple chemical apparatus, isotopic fractionation occurs by two mechanisms. The first is isotopic disequilibrium, in which the mass difference between the isotopes causes a significant difference between the equilibrium constants or rates of reactions in which the two isotopic species are involved. The magnitude of the isotopic fractionation is greater for traced elements in which there is a large fractional difference between the mass number of the tracer and that of the traced element this effect is considered neghgible for isotopes of aft elements with atomic numbers >10 (Duncan and Cook 1968). 

Apparatus A 25-mL and two 10-mL round-bottom flasks, drying tube, ice-water bath, apparatus for simple and fractional distillation, magnetic stirring, and flameless heating. 

If only one component of a mixture is volatile, there is no difficulty in obtaining it in a pure state by distillation, and in many cases the constituents of a mixture of two or more volatile liquids may be separated—though frequently at much cost of time and material—by means of the simple apparatus described in this chapter. For the fractional distillation of such complex mixtures as petroleum or fusel oil, the improved still-heads described in Chapters X to XII must be employed. 

Liquid oxygen analyses are customarily made for process control, product purity and to avoid hazards. Usually analytical information required for process control is not extensive. Use of modified Or sat apparatus for manual determination of the oxygen contents of various liquid samples is routine in most plants. Relatively simple thermal conductivity analyzer-controllers govern the flow of liquid air fractions under distillation where differential pressure control is not applicable. Pressure drop and inspection of liquid in a small glass flask are usually sufficient for mechanical filter cycle regulation but a continuous carbon dioxide analysis may be helpful as a check on the overall function. A method which is sufficiently precise for this use is discussed later. 

---