A Continuous Liquid-Liquid Extractor RICHARD KIESELBACH Bakelite Corporation, Bound Brook, N. J.
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IQUID-liquid extraction can be an extremely tedious and time-consuming operation, particularly when the two liquids tend to emulsify. Most commercial laboratory continuous extractors, though labor-saving, are expensive and very slow in operation. Kossfeld (1) describes an apparatus which is a considerable improvement over previous extractors, but which requires a motor and moving glass parts, always a potential source of trouble in careless or inexperienced hands.
There are tivo possibly undesirable features inherent in the design of the extractor. One is that a long and efficient reflux condenser is necessary to prevent the loss of solvent vapor entrained in the stream of air. However, using a 50-cm. West-type condenser, this loss is negligible in routine work for the 1-hour period of operation. The other disadvantage lies in the fact t h a t the stream of air may oxidize the material being extracted. An inert gas could, of course, be used to obviate this difficulty.
Details of Construction and Operation The specifications for the extractor are fairly flexible. It was designed to contain approximately 1 liter of liquid, but there is no apparent reason why the flask could not be altered to any desirable shape and capacity. In this case, an 800-ml Kjeldahl flask with a 24/40 standard-taper neck was used as the mixing flask, and a side arm approximately 25 cm. long was constructed of 3-cm. tubing. The seals at both ends of this arm were made a t the top, to allow a maximum amount of space for the separation of the liquids. These openings must be at least 1 cm. in diameter to ermit the flow of liquid and vapor in opposite directions. $owever, the opening at the flask end should not be larger than necessary, lest the turbulence of the contents of the mixing flask be carried into the settling chamber. In order to permit the extracted liquid to flow back to the drain, C, the side arm should be sealed on a t a slight upward angle. The inner tube, D, was a length of 8-mm. tubing, whose lower end was drawn down to an opening of about 0.25 mm. It was sealed through the wall of the flask at the top. to prevent the loss of liquid when the air was turned off. FIGURE1. EXTRACTOR The apparatus here described was devised for the routine analysis of cresylic acids, in -which pyridine, oils, and naphthalene are extracted with benzene from an alkali solution of the cresylic acid. The potassium phenolates present ordinarily cause a high degree of emulsification. B y use of this apparatus, a quantitative extraction is completed in 1 hour, as against more than 12 hours for a commercial extractor dispersing the solvent b y means of a fritted-glass bubbler. The apparatus is relatively compact, inexpensive, and simple to build and operate. The extractor is illustrated in Figure 1. Benzene passes from the boiling flask, A, to the reflux condenser, whence it drips into the solution in the mixing flask. Air passing through the inner tube, D, enters the flask in a fine jet at the bottom, agitating the mixture vigorously. The mixture of extract and solution overflows into the settling chamber, B , from which the extract overflows into the boiling flask, and the solution returns via the trap, C, to the mixing flask.
FIGURE2. ORIGINALDESIGN
This design represents a simplification of a n attempt to eliminate the moving parts in Hossfeld’s extractor. The original design is shown in Figure 2. I n this case, the reflux was led through inner tube E to the intake, F , of the aspirator, G. The aspirator, operated b y a jet of air, circulated fresh solvent through the mixture, while the air served also t o agitate the mixture. Surprisingly enough, i t was found that removing E and closing F had no effect on the efficiency of the apparatus. Accordingly, the simpler and more compact device shown in Figure 1 was constructed. I n operation, there was no measurable difference in efficiency between these two designs.
In operation, the flask is filled with the liquid to be extracted to a point just below the bottom of the side arm, B. The volume of the air bubbles and solvent brings the level to the overflow. The stream of air should be regulated t o the minimum required to give thorough mixing, as indicated by the homogeneity of the contents of the flask. Where colored material is being extracted, completion of extraction is easily estimated by the appearance of the extract in the settling chamber.
Literature Cited (1) Hossfeld, R. L.,IXD.ENG.CEEM.,ANAL.ED., 14, 118 (1942).
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