Laboratory Continuous Countercurrent Liquid-Liquid Extractor J. J. KOLFENBACH, E. R. K 0 0 1 , E. 1. FULMER,
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H E inefficiency of the ordinary types of laboratory extraction apparatus makes the recovery of solutes from solutions by extraction with immiscible solvents a very timeconsuming operation. In the conventional type of laboratory extractor the immisciblc solvent is vaporized in the boiling flask, condensed in a single upright condenser placed above the flask containing the eolutioo to be extracted, and allowed to run down a funnel tube fitted a t the bottom with a diffuser plate. The diffuser plate produces a fine dispersion of the immiscible solvent which rises through the solution to be extracted and flows back to the boiling flask through a suitable overflow arm. The inefficiency of this type of extractor is due to a low rate of solvent flow or lack of intimate contact between solvent and solution. The use of a diffuser plate of low porosity in order to obtain intimate liquidsolvent contact necessarily limits the rate of solvent flow; the interference between ascending vapor and descending liquid in the condenser limits the rate a t which the solvent may be vaporized and condensed. T o increase the efficiency of liquid-liquid extraction an improved type of extractor waa designed by Hossfeld ( 1 ) which is equipped with separate arms for vapor outlet and solvent return, thus affording a high rate of solvent flow. The centrifugal dispersion of the solvent and the agitation of the solution in the Hossfeld apparatus result in intimate contact between solvent and solution. The Hosefeld apparatus is a definite advance over the conventional laboratory extractor.
L. A. UNDERKOFLER, Iowa State College, Amer, Iowa under these conditions a t an ether flow rate of 2.0 liters per hour with no noticeable loss of ether. In extractions of fermentation liquors, emulsion formation is sometimes encountered. Although the emulsion-forming constituents can frequently be removed by treatment with bwic lead acetate or similar precipitating agents, this treatment also often removes considerable quantities of the constituent to be recovered. Whenever a tendency toward emulsion formation was noted in the extraction column it was effectively overcome by passing a slow stream of air upward through the column. The circulating pump employed for rirculation of the solution is diagrammed in detail in Figure 2. The spool, B , bearing the rollers, A , rotates within the ring, C, which is welded to the plate, D. The rollers press against the rubber tubing, E, and force the liquid through. The tubing is held against the rollers by the sliding block, F, and the pressure between rollers and tubing is adjusted b screws, H, on the U-Clamps, G. Grooves are cut in the ends oPring C and block F to hold the tubing in place. The tubing used is 9 mm. in diameter. The spool diameter is 7.5 cm. (3 inches) and the rollers are 0.93 X 1.56 cm. (a/a X I / o inches). The roller spool is driven a t 50 r.p.m The extraction rate of the extractor described above was compared with the rates for two other types of extractors. No. 1 was the conventional type of laboratory extractor, procured from a laboratory supply company, ronswtin of a 4-liter bottle fitted with a stirrer, a sintered-glass gravity-feed dispersing plate, and the usual upright Allihn condenser and boiling flask. Extractor 2 was constructed according to the specification of Hossfeld ( I ) .
A new type of laboratory countercurrent extractor has been designed and used extensively in these laboratories for the recovery of 2,a-butylene glycol and acetylmethylcarbinol from fermentation mashes and mash concentrates by extraction with diethyl ether. The unit employed has been found more efficient than any other type of extractors tested, and is diagrammed in Figure 1. The column is 1220 mm. in length and 45 mm. in diameter. The fermentation mash solution to be extracted is plachd in the &liter Erlenmeyer flask shown a t the left of the diagram and a layer of this solution is also placed in the bottom of the extraction column as shown. The column is then filled with solvent and about 1.5 liters of solvent are placed in the 3-liter boilin flask shown a t the right. The vaporized solvent is condensed f y the Allihn condensers, flows down through the tube at the right, enterethe bottom of the extraction column, flows upward through the column, and returns to the boiling flask through the overflow arm. The mash is forced by the circulating pump out of the mash flask into the top of the extraction column through the et, which is merely a piece of glass tubing constricted a t the ower end. The interfaciitl tension and the pressure on the liquid produce dispersion into droplets at the ti . When a jet of the proper size is used, the pressure forces a $ne spray of the liquid into the column of solvent. The droplets of solution then fall through the solvent to the bottom of tho column. The solution is pumped to the mash flask and continuowily recirculated. The rate of ether flow in rhis unit is 2.0 liters per hour and the rate of mash circulation is 4.2 liters per hour. Rubber connections in the unit are coated with water glass to prevent solvent lose, and all ground-glass joints are standard taper 24/40.
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The purpose of the two condensers is to ensure a more complete condensation of the solvent. This is a particularly important consideration when diethyl ether is used as the solvent. The use of an angle condenser before the upright condenser allows a higher rate of solvent flow, since there is then less turbulence at the lower tip of the upright condenser. I n ether extractions where emulsions are not encountered, placing a finger cut from a rubber glove or a rubber finger-stall over the top of the upright condenser prevents much of the ether loss which would otherwise occur The extractor has been operated continuously for 3 days
ASH LAYER
Figure 1
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Countercurrent Extraction Apparatus
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INDUSTRIAL A N D ENGINEERING CHEMISTRY
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time required to remove 50% of the butylene glycol present for extractors 1,2, and 3 were 140,48, and 19 hours, respectively. The extraction unit aa described has been used in these laboratories for a considerable period of time for extracting 2,bbutylene glycol or acetylmethylcarbinol from fermentation mashes, using diethyl ether as the solvent. It could be used equally well for extracting other liquids and with other immiscible solvents. No change in arrangement of the equipment would be necessary for other solvents of less density than the liquid to be extracted, and modifications could easily be made to enable the use of solLID€ VIEW vents of density greater than the liquid to SECTION THROUQH CCNTER be extracted. In the latter case the layer of li uid to be extracted is a t the top and the s i v e n t fills the lower portion of the column. The pump draws the liquid from the top and introduces it into the solvent through a jet extending up from the bottom of the column, the droplets of liquid rising through the heavier 801vent, The solvent from the condenser flows by g r a d through a vertical tube extending from the top of the column dbwn into the solvent layer. The solvent flows from the bottom of the column through a U-tube and a vertical leg of tubing connected horizontally a t the top with the solvent boiling flask. The length of the vertical leg must be adjusted according to the density of the materials employed, so as to maintain the proper solvent level, and the horizontal tube connecting with the boiling flask must be of relatively large diameter to revent siphoning action. The authors have successfully t e s t e l this arrangement, wing chloroform as the solvent to extract an aqueous solution. In setting up the countercurrent liquid-liquid extractor for any particular purpose the dimensions of the extraction column and the sizes of the flash employed could of course be altered. The rate of extraction is naturally associated with the rate of recirculation of the liquids. If a smaller volume of liquid were extracted employing the same rate of circulation, the extraction would be completed more quickly, and vice versa.
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ACKNOWLEDGMENT
This work wassupported by a grant from the Industrial Science Research Institute of the Iowa State College for studies on t,he fermentative utilization of agricult,ural products.
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LITERATURE CITED
(1) Hoeafeld, R., IND.ENG.CHEM.,ANAL.ED., 14, 118 (1942). /O
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Extraction Rates for Three Exbaefsrs
The stirrer was driven a t 700 r.p.m. Extractor 3 was the one described in this paper (Figure 1). The solvent flow rates were nearly the aame for extractors 2 and 3, but for No. 1 the rate was somewhat lw, being limited by the resistance of the diffuser plate. The time-movery data for the three extractors for 4 litera of mash concentrate containing 15% of 2,bbutylene glycol extracted with diethyl ether are plotted in Figure 3. The extractions were not carried to completion, since it is more efficient to reconcentrate the mash after the butylene glycol content has been considerably reduced. It is evident from Figure 3 that the extraction rate for the extractor described in this paper is greater than that of either of the other two extractors. The periods of
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