Designs for Laboratory Fractionating Columns J. H. SIJIOKS The Pennsylvania S t a t e College, S t a t e College, Pa.
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nating the need of grease. A groove, ground on the surface of the plug in the direction of its length and to a depth of about 1 mm., enables the liquid to flow from the condenser to receiver. Adjustment is made by turning the plug from above. A dropping tip on the lower end of the condenser directs the liquid into a
HE perfection and use of small glass rings for packing laboratory fractionating columns as first described b y Wilson, Parker, and Laughlin (3) have greatly improved t h e efficiency and flexibility of laboratory fractionations. I n order t o make more complete use of this improved efficiency as well as t o make i t more adaptable for a variety of uses, t h e following designs for glass columns were devised, and were found satisfactory for t h e special purposes for which they were made. Their use requires no special equipment nor apparatus not found in any moderately well-equipped laboratory, and their construction from the usual stock sizes of Pyrex glass tubing is relatively easy.
L FIGURE3. COLUMNFOR MODERATELY Low TEMPERATURES
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M
FIGURE 2. VAPORPARTITION TAKE-OFF
FIGURE1. LIQUIDPARTITION TAKE-OFF
For laboratory use total condensation columns are usually more easily operated and require less attention than partial condensation columns. In t h e usual construction of t h e former, however, a stopcock for the liquid take-off is a disadvantage, as i t is difficult t o adjust accurately, is Prone t o leak, and adds stopcock grease t o the product. I n the first four designs described, t h e use of stopcocks for total reflux columns parThe diagrams shown in tKs has been ticuIarIY Figures 3, 4, and 5, are not drawn t o scale. The chief deviation is t h a t t h e vertical direction is foreshortened. In addition, Some of t h e smaller parts are enlarged i n order better t o show the details of construction.
small cup, which is connected to the plug seat by a piece of capillary tubing. For vacuum distillations and for distillations requiring the exclusion of atmospheric air, a small rubber tubing (not shown in the diagram) placed below the plug handle and over its jacket closes that opening, and the top of the condenser is appropriately closed.
Vapor Partition Take-off In Figure 2 is shown a design of the head of a column with a device for partitioning the hot va or between two condensers, one for r e f l u and the other for ta{e-off. This design has been found very satisfactory in regard to rigidity of construction, ease of use, and the fineness of adjustment possible. The valve stem is made of a piece of tubing that makes a sliding fit without grinding in its jacket. A ground joint is made with its jacket a t the top. The lower end is trimmed off as shown in the side view. The thermometer is hung inside the vaIve stem. The take-off trap is made of capillary tubing, and the eccentric dropping tip of the condenser enables the liquid to be directed into a small cup just above the capillary. This cup enters the outside tube slightly, so that it does not receive the liquid condensing on the outer wall. As the partition valve is sealed only with a film of the liquid being distilled, it does not make a complete gas-tight.joint. Eon-ever, if 100 per cent reflux is desired, the take-off condenser can be rotated so that its eccentric dropping tip is not above the receiving cup.
Liquid Partition Take-off In Figure 1 is shown a design for the head of a column in which the liquid is partitioned for take-off by means of a ground plug. The liquid condensate itself forms the lubricant, elimi29
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A diagram of a glass pressure column is shown in Figure 4. As neither stopcocks nor ground-glass joints can be used under pressure, especially when in contact with nonpolar substances being distilled, a method of take-off not depending on their use is employed. The liquid dropping from the end of the reflux condenser is caught in a small cup, which has a hole in its side for the escape of the reflux liquid. A capillary t'ube connected to the bottom of this cup makes a small trap and then extends through the wall of the column, where it is connected to a larger tube extending upward. Take-off is accomplished and controlled by reboiling the liquid in this larger tube, using a small electric heater made of a winding of Nichrome wire. The reevaporated material is then condensed in a second condenser. Air pressure is applied a t the top of the column and controlled by an air-filled and sealed glass bulb floating in mercury. This has a ground-in seat at the top, and regulation is obtained by adjusting the height of the mercury leveling bulb. The escaping air exhausts to the atmosphere. A similar device below the takeoff condenser enables the condensate to be removed to atmospheric or lower pressure without reducing the pressure on the column. In the design shown, which was used for liquids boiling below room temperature, the condensate evaporates on reaching the low-pressure side of this second regulating valve and is caught in traps. For other purposes and especially for distilling materials that melt close to their normal boiling points, variations of this design would be used, depending upon the properties of the particular substance to be distilled. Heat is supplied from a winding of resistance wire around a small extension a t the base of the pot. Temperatures are determined by thermocouples, one on the side of the pot and the other in a thermocouple well a t the top of the column. A nonsilvered vacuum jacket provides heat insulation for the column proper. A closed-tube air-filled manometer is used to determine the pressure. Pressures as high as five atmospheres can be used with safety, provided the tubing is not of extremely large size and the seals are well made.
FIGURE 4. PRESSURE COLUMN The two condenser wells and also the take-off tube are connected with bridges of tubing to equalize the pressure. This design is suitable for vacuum distillations.
Low-Temperature Column A number of designs for low-temperature columns h a r e previously been described. For example, Rose (2) showed one design and gave a partial bibliography of others. In a recent paper Booth and Bozarth (1) described in det'ail the construction and operation of R low-t'emperature column. The one shown in Figure 5 is included here because it has some novel
Column for Moderately Low Temperatures Distillations carried out between about -5" C. and room temperature offer some difficulties. For this work columns using laboratory water cooling are not suitable and low-temperature columns using liquid air for the condensing medium a r e expensive t o make, difficult to operate, and usually work poorly in this temperature range. Figure 3 is a diagram of a simple column made to operate in this range. A vapor partition valve similar to the one described above is used. The condenser is a large double-walled vessel in which can be placed ice, ice and salt, or other cooling materials. A nonsilvered vacuum jacket is used t'o heat-insulate the column proper. A jacket of this construction is only slightly more difficult to make than an ordinary all-glass condenser. The small section of the base of the column shown on the left is the detail of the support for the packing. The small circle with three extending arms is made of thin rod, and it can be easily sealed into the column tube by resting it on a rod of graphite. When the column is in operation a wide-mouthed laboratory vacuum flask containing the same cooling materials used in the condenser surrounds the receiver. Multiple receivers can of course be used.
Pressure Column Distillations a t pressures above one atmosphere are desirable for a number of purposes, such as: (1) distillations of mixtures for which rectification a t one atmosphere causes little or no separation b u t for which a better separation can be obtained at higher pressure, because of the change of t h e phase diagram with pressure; ( 2 ) distillation with laboratory water cooling of mixtures normally boiling below room. temperatures; and (3) distillation of substances which solidify not far from the normal boiling point.
FIGURE 5 . LOW-TEMPERATURE COLUMN
JAXUARY 1.5, 1938
ANALYTICAL EDITION
features, because it is inexpensive and not too difficult of construction, but chiefly because it has proved very reliable and requires very little attention in operation. The auxiliary parts of the system, such as receiving bulbs and storage vessels, are also shown in the diagram. The completed system is all-glass and vacuum-tight. I t operates as a closedsystem partial-condensat ion column. The condenser is double-walled. Within the inner tube copper shot and sheet furnish a heat capacity. In this is embedded a copper tube for the admittance of liquid air, nhich is supplied from a 5-liter container by means of an air pressure siphon. The air is allowed to flow continuously during a distillation, but a by-pass before the liquid air container permits it to escape to the atmosphere. When the pressure in the column rises to a value for which the system has been adjusted, an electrical contact is made in the pressure regulator manometer, and an electrical circuit is closed. This brings the hammer of a relay onto the end of the air escape tube, and liquid air is then forced into the condenser. This lowers the pressure in the column, the electrical contact is broken, and the flow of liquid air stops. By this means distillations can be carried out a t any desired pressure from atmospheric down, and the pressure fluctuations during operation are insignificant in regard to the operation of the device for fractional distillations. The column proper is heat-insulated by a vacuum jacket, which is silvered except, for a vertical strip left clear to permit observations of the column. The condenser head is insulated by two concentric glass tubes with an air space between and either silvered or containing a polished metal foil. Tempera-
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tures are determined by means of thermocouples, one located in'a well a t the t'op of the column and the other on the side of t,he pot. Heat is supplied by a vinding of resistance Lvire around a small extension on the base of the pot. In operation a cooled widemouthed laboratory vacuum flask surrounds the pot. In addition to the regulating manometer an evacuated closed-tube manometer is provided for pressure mesurements. . Take-off is adjusted by means of stopcocks. The receiving vessels are arranged in parallel on a manifold. One of these has a thermocouple well in it, and its stopcock is located as shown in the diagram to prevent the accumulation of grease in the bulb. Freezing points and vapor pressures are determined on samples in this vessel, which is surrounded with a heavy-Tvalled copper tube. -4 vacuum flask is placed around the copper tube, and time-temperature XT-arming curves are taken of the sample. Pressures are determined a t the same time. A gas density balance (not shown in the diagram) enables the molecular weight to be simultaneously determined. The storage vessels are 12-liter flasks provided with condensing bulbs. The material is condensed in the bulb, the stopcock is closed, and the material is allowed to evaporate into the flask.
Literature Cited (1) Booth and Bozarth, IND. EXG.C m l f . , 29, 470 (1937). 12) Rose, Ibid.,Anal. Ed., 8, 478 (1936). ( 3 ) Wilson, Parker, and Laughlin, S. -4772. Chem. Soc., 5 5 , 2795 (1933). RECEIVED September 6 , 1937.
Devices for Extraction by Immiscible Liquids H. J. WOLLNER
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AND
JOHN R. MATCHETT, U. S. Treasury Department, Washington, D. C.
N CHEMICAL technology it is frequently necessary t o
scrub a solution containing one or more solutes, b y means of a n immiscible solvent. T h e efficiency of transferring a dissolved substance from one of two immiscible solvents t o the other is a function of the area of contact developed between the two liquids. T h e development of very large areas of contact usually requires high dispersion of one of the solvents in the other, frequently resulting in stable emulsions. This condition is further aggravated by the desire for maintaining the quantities of extracting liquid as low as possible-usually a fraction of t h e volume of t h e original solution. Where small amounts of the more viscous, solute-bearing phase are intentionally dispersed in large proportions of t h e less viscous (scrubbing) phase, clean partial separation generally follows when agitation is stopped. However, since it is usually desirable t o maintain t h e extracting phase in smaller volume t h a n t h e extracted phases, t h e above condition cannot readily be met in a n intermittent process. T h e device described below affords rapid and convenient means for maintaining the necessary preponderance of less viscous material, and of making a n y required number of extractions in a single operation. T h e device consists of a n emulsification chamber and a settling chamber, connected b y two ducts which permit the continuous cycling of t h e emulsion. Of these two ducts, the first continuously bleeds t h e emulsified solutions into t h e settling chamber, where partial separation takes place. T h a t portion which has not clarified is continuously recycled through the second duct back t o the emulsification chamber. T h e clarified extracted solution (previously dispersed phase) is bled off the separating chamber a t the same rate a t which the unextracted original solution enters the emulsification chamber from a previous reservoir.
Inasmuch as the separation is largely a function of the relative densities of the two liquids and the relative densities of the two phases may vary, it was necessary t o design two modifications of t h e device-one for extracting solvents of lower density than the dispersed phase, and the other vice versa.
Solute-Bearing Liquids of Greater Density than Extracting Liquid The emulsification chamber, A , is provided with an efficient stirrer, driven by a high-speed motor, and so designed as to lift the solution from the bottom rather than force it down from above. Suitable baffles are provided to ensure thorough mixing of the liquids. The separation chamber, B , consists simply of a
nG C
FIGURE1
