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Continuous Liquid-Liquid Extractor IRWIN A. PEARL The Institute of Paper Chemistry, Appleton, Wis.
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standard-taper joint was used for the connection to the boiling flask, C. Tubing of at least 10-mm. outside diameter should be used for the glass part of the trap, D; otherwise, the passage of very slowly breaking emulsions is impeded. The trap itself was made of a short length of fairly thick-walled neoprene tubin . The inner tube, E, was made by sealing a piece of 8-mm. outsite diameter glass tubin to a stock gas inlet adapter. The length of the tube depende8 upon the size of the flask containing the material to be extracted. If a number of gas inlet adapters are not available, a 10/30 standard joint may be sealed to the stock adapter and a number of 8-mm. tubes with standard 10/30 joints of lengths to fit various flasks or bottles may be used.
ECENTLY Kieselbach (1) introduced a new principle into the field of liquid-liquid extractors for use with mixtures which tend to emulsify. His extractor, using air agitation and a settling chamber for the separation of any emulsion formed, made possible the rapid extraction of solutions formerly taking as long as several weeks. However, Kieselbach’s extractor has a number of disadvantages, chief among which are the facts that a separate extractor is necessary for each desired volume of solution t o be extracted and that very stable emulsions do not separate in the narrow settling chamber. The apparatus herein described was an attempt to increase the utility of Kieselbach’s extractor for use with strongly emulsifying sulfite waste liquor reaction mixtures varying in volume from 250 cc. to several gallons. The extractor unit is actually an adapter to be used with standard-taper glass bottles or flasks. It is made from readily available stock glassware and requires a minimum of glass blowing.
The completion of the extraction is usually determined by the change in color taking place in the settling chamber. However, in the case of extractions of colorless substances, samples of the solvent layer in the settling basin may be taken periodically by lowering the solvent solution interface (by withdrawing a little solution through the gas inlet tube, E ) and the appropriate use of several screw clamps on the rubber trap. (Ricbard Kieselbach, after reviewing the paper, suggested that the settling chamber might be provided with a tubulature, close to the point which used to be the neck of the Erlenmeyer flask, which would permit sampling without interruption of the operation of the extractor. This should prove a valuable modification of the present apparatus when dealing with colorless solutions.) A glass T in the rubber trap may be used if a number of such solutions are to be encountered. When the extraction is complete, the solvent in the settling basin may be drawn off in the manner described above. These advantages make the rubber trap preferable to the all-glass U-trap. I n addition, the glass blowing is greatly simplified. An Erlenmeyer flask was used for the settling chamber because many fairly stable emulsions did not break in the small-diameter settling basin of the earlier apparatus. The shape of the Erlenmeyer flask is admirably suited for this purpose because the slopes of its base and sides (when in the position shown in Figure 1) facilitate rapid separation of the two liquid phases. Furthermore, this design is relatively compact. For maximum applicability, the seals a t both ends of the Erlenmeyer flask should be a t the same level. The size of the flask depends upon the nature of the solutions encountered. For fast-breaking emulsions a 250-cc. flask may be used, thereby holding up less solvent in the settling chamber. If a large mixing chamber is used with a correspondingly increased air stream, a larger settling chamber should be used. The specifications of the entire apparatus are flexible. When extracting materials subject to oxidation by air a stream of inert gas should be used for agitation. Furthermore, when extracting gas-saturated solutions (such as bicarbonate or bisulfite solutions), carbon dioxide or sulfur dioxide, respectively, may be used advantageously as the agitating gas. I n extractions of large volumes of solutions with corresponding increases in time, the loss of solvent due to extrainment in the exit gases may become appreciable, and more solvent may have to be added to the boiling flask. I n this case advantage may be taken of a two-necked boiling flask. A long efficient reflux condenser should always be used. An active carbon trap is useful for recovering larger amounts of solvents. A large apparatus, using semiball joints, for use with 22-, 50-, and 72liter flasks was fabricated according to specifications by the Scientific Glass Apparatus Co., Bloomfield, N. J.
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Figure 1
C T h e operation of the complete extractor assembly drawn to scale in Figure 1 is identical to Kieselbach’s. The extractor unit was used successfully for extracting solutions contained in vessels ranging from 250-cc. flasks to 12-liter bottles. The mixing chamber, A , was made by sealing together two standard-taper glass joints. The upper joint in this case was 24/40, although any size compatible with other equipment is satisfactory. The lower joint was 29/42; because of the possibility of constriction, a smaller standard-taper joint should not be used. Both standard joints were connected to 2&mm. outside diameter A 500-cc. Erlenmeyer flask served as the settling chamand was connected to the mixing chamber by a short piece (30 mm.) of 25-mm. outside diameter tubing. A 24/40
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LITERATURE CITED
(1) Kieselbach,
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R.,IND.ENG.CHEN.,ANAL.ED.,15,223 (1943).
