Fractionators packed columns

The column is swept continuously by a carrier gas such as helium, hydrogen, nitrogen or argon. The sample is injected into the head of the column where it is vaporized and picked up by the carrier gas. In packed columns, the injected volume is on the order of a microliter, whereas in a capillary column a flow divider (split) is installed at the head of the column and only a tiny fraction of the volume injected, about one per cent, is carried into the column. The different components migrate through the length of the column by a continuous succession of equilibria between the stationary and mobile phases. The components are held up by their attraction for the stationary phase and their vaporization temperatures. 

In the case of a packed column, the terms on the right-hand side should each be divided by the voidage, ie, the volume fraction not occupied by the soHd packing (71). In unpacked columns at low values of the sHp velocity approximates the terminal velocity of an isolated drop, but the sHp velocity decreases with holdup and may also be affected by column internals such as agitators, baffle plates, etc. The sHp velocity can generally be represented by (73) ... 

When low boiling ingredients such as ethylene glycol are used, a special provision in the form of a partial condenser is needed to return them to the reactor. Otherwise, not only is the balance of the reactants upset and the raw material cost of the resin increased, but also they become part of the pollutant in the waste water and incur additional water treatment costs. Usually, a vertical reflux condenser or a packed column is used as the partial condenser, which is installed between the reactor and the overhead total condenser, as shown in Figure 3. The temperature in the partial condenser is monitored and maintained to effect a fractionation between water, which is to pass through, and the glycol or other materials, which are to be condensed and returned to the reactor. If the fractionation is poor, and water vapor is also condensed and returned, the reaction is retarded and there is a loss of productivity. As the reaction proceeds toward completion, water evolution slows down, and most of the glycol has combined into the resin stmcture. The temperature in the partial condenser may then be raised to faciUtate the removal of water vapor. 

There are notable cases where plate columns have been converted to packed columns to gain advantage of the low pressure drop exacted from the vapor stream. More recently the packings have been largely of the stmctured type. Illustrative of this is the trend toward the use of stmctured packing in ethylbenzene—styrene fractionators, some of which have diameters of 10 m or higher. 

Note 1). The mixture is heated with a mantle with stirring for 32 hr under a 50-cm fractionating column packed with 5-nm glass beads and topped by a Dean-Stark trap. The reaction mixture is then distilled through the packed column. The fraction which boils at 120 -126°C is collected. The yield is 86.0-87.3 g (77-78%) of 2,2-dimethyl-4-pentenal (1) as a clear, colorless oil, n 1.4216 (Note 2). 

Washed with 10% (vol) aqueous H2SO4 (three times), 10% aqueous KOH (three times), and then with water until neutral. Dried with MgS04 and fractionally distd from CaH2 through a glass helices-packed column under reduced pressure. 

Fractionally distd below ISmm pressure, using packed column and taking precautions to avoid absorption of water. 

Epoxybutane [106-88-7] M 72.1, b 66.4-66.6 , d 0.837, n 1.3841. Dried with CaS04, and fractionally distd through a long (126cm) glass helices-packed column. The first fraction contains a water azeotrope. 

Hept-l-ene [592-76-7] M 98.2, b 93 /771mm, d 0.698, n 1.400. Distd from sodium, then carefully fractionally distd using an 18-in gauze-packed column. Can be purified by azeotropic distn with EtOH. Contained the 2- and 3-isomers as impurities. These can be removed by gas chromatography using a Carbowax column at 70°. 

V-Methylmorpholine [109-02-4] M 101.2, h 116-117 /764mm, d 0.919, n 1.436, pK 7.38. Dried by refluxing with BaO or sodium, then fractionally distd through a helices-packed column. 

Refluxed with sodium wire, then fractionally distd twice through a Fenske (glass helices packing) column. 

Also purified by dissolving in CHCI3, adding solid K2CO3 and Drierite, filtering and fractionally distilling through an Sin helix packed column. The sulfate has m 205°, and the picrate (from hot H2O) has m 155-156°. [Frank and Meikle J Am Chem Soc 72 4184 1950.]... 

Tri-n-hexylborane [1188-92-7] M 265.3. Treated with hex-l-ene and 10% anhydrous Et20 for 6h at gentle reflux under N2, then vacuum distilled through an 18in glass helices-packed column under N2 taking the fraction b 130"/2.1mm to 137"/1.5mm. The distillate still contained some di-n-hexylborane [Mirviss J Am Chem Soc S3 3051 7967]. 

Carefully fractionated through a gauze-packed column. Redistil and collect in weighed glass vials and seal. Keep away from moisture. It undergoes alkyl exchange with alcohols and forms azeotropes, e.g. with MeOH the azeotrope consists of 70% (MeO)3B and 30% MeOH with b 52-54"/atm, d 0.87. [J Chem Soc 2288 7952 Chem Ind (London) 53 7952 J Am Chem Soc 75 213 7955.] Also dried with Na, then distilled. 

Trimethylsilyl trifluoromethane (trifluoromethyl trimethylsilane) [81290-20-2] M 142.2, b 54-55°, 55-55.5°, d 0.962, n 1.332. Purified by distilling from trap to trap in a vacuum of 20mm using a bath at 45° and Dry ice-Me2CO bath for the trap. The liquid in the trap is then washed with ice cold H2O (3x), the top layer is collected, dried (Na2S04), the liquid was decanted and fractionated through a helices packed column at atmospheric pressure. H, C, F, and Si NMR can be used for assessing the purity of fractions. [Tetrahedron Lett 25 2195 1984 J Org Chem 56 984 1991.]... 

Packed columns are gaining ground on trayed columns. Lieberman states that based on his design and operating experience, a properly designed packed tower can have 20-40% more capacity than a trayed tower with an equal number of fractionation stages. 

For packed columns see the rules of thumb in Chapter 3, Fractionators, in the Packed Columns section. 

F = Factor for fractionation allowable velocity or packed column packing factor or pump developed head, ft. 

G = Fractionator vapor rate, Ib/hr or packed column gas rate, Ibs/ft sec or pump flow, gpm GPM = Pump flow, gpm... 

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