Columns for
Liquid-Liquid Extraction Comparison of the Efficiencies of Packed and Spinner Types
Data presented show that, for liquid-liquid extraction, columns with a diameter of 21 mm. and packed with small Berl saddles are about three fourths as efficient as spinner type columns. Slender smallcapacity columns are very efficient when equipped with spinners. Spinner type columns do not operate efficiently if there is too great a difference in density in the two liquid phases or if they are easily emulsified.
W.0.NEY, JR., AND H.L. LOCHTE University of Texas, Austin, Texas
r. p. m. unless otherwise stated. Column A was also used for runs with no packing and for those using '/h-inch (6.4mm.) Berl saddles as packing. Some preliminary runs were made with the flow of liquids controlled by a piston type proportioning pump, but for very slow rates of flow this did not prove so successful as a scheme that had meanwhile been developed in this laboratory. Attempts to regulate and keep constant the ratio of flow between two different liquids by use of clamp, capillary, or wick regulation of liquid flow proved disappointing since no adjustments could be kept constant for any length of time. When, however, the liquid flow is controlled by regulating the flow of air replacing the liquid in a closed container, adjustments can be kept constant much more readily. In the plan used, the flow of air was controlled by matched capillaries from a broken thermometer supplemented by screw clamps in the common air line and in one of the branch air lines leading t o the liquid reservoirs. To eliminate trouble due to change in
H E spinner type of countercurrent extraction column was introduced by Jantzen (6) and by Tiedcke (11) for the separation of coal tar bases. Cornish, Archibald, Murphy, and Evans (3) used a different type of spinner column for the extraction of vitamins. At the University of Texas the Jantzen column, slightly modified, has been used with success for the separation of both acidic and basic constituents of petroleum (2, 6, 7, 8, 9). There has been no attempt to determine directly the relative efficiencies of the spinner type and packed columns. Sherwood, Evans, snd Longcor (10)compared spray with packed columns and summarized the work reported in the literature with regard to performance of extraction equip ment. The present paper gives results obtained in comparing packed and spinner columns operating on water, acetic acid, and methyl-isobutyl ketone, t h e same system studied by Sherwood, Evans, and Longcor. The experiments were conducted with the same columns, empty, packed, and equipped with a suitable spinner.
T
Columns and Spinners Thrce Pyrex glass column3, A , B, and C, were investigated; their important dimensions are as follows: Column A
DC
EEective Internal Diam., Spinner Length, Cni. .\Im. So. 75 21 1 7.5 100 15.5
21
12
7.3
2
3 4
Diam. of Spinner, M m . 14 8 0
5
Separation of phases was obtained at the top of the column with a loose roll of 24-mesh copper gauze placed in the side arm (Figure 1). At the bottom the side arm liad a capacity sufficiently large to permit complete separation in the time involved. The spinners, constructed of Pyrex glass tubing, extended from the throat of the column to the lower side arm. All spinners except those in column A operated smoothly and without excessive chatter. In column d a bearing had to be employed as shown. The 3-mm. iron rod was fastened into the spinner with a small rubber stopper and sealed with string soaked in sodium silicate solution. It rotated in a suitable comer tube in another rubber stomcr fitted into the bottom of %e column. All spinners operatkd a t 900 to 1000
FIGURE 1. DIAGRAM OF COLUMN SETUP 825
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INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 33, No. 6
Approximately normal acetic acid solution was made up in 15-liter batches and saturated with extracting solvent. Analyses of acid concentration were made on 10-ml. samples by titration with 0.1 AT sodium hydroxide, using 10-ml. microburets and phenolphthalein as indicator. The sodium hydroxide was standardized against potassium acid phthalate and checked against standardized hydrochloric acid.
Extraction
FIGURE 2. EXTRACTION OF ACETIC ACID FROM WATER WITH HEXONEUSING COLUMN A PACKED WITH 1 / 4 - 1 BERL ~~~ ( t o p ) , WITH SPINNER 1 (center), AND WITH SPINNER 2 SADDLES (bottom)
head of liquid in the reservoirs, the air supply was taken from the laboratory air line so that the change in pressure due to change in head was negligible compared with the air line pressure. The extraction of acetic acid from water was chosen from the start as the problem to be studied. Chloroform, the first solvent studied, proved unsatisfactory for this type of study because of the large difference in density between the two phases concerned and because of the large distribution coefficient. Benzene, chosen next, has the desired slight difference in density from the aqueous solution but also has a large distribution coefficient so that calculation of equivalent plates is difficult except a t flow ratios that introduce large errors. Methyl isobutyl ketone (Hexone), however, has both the correct density and also a desirable distribution coefficient.
Rates of flow were adjusted t o the desired values, and the column was filled with the liquid that was t o be the continuous phase. The position of the interphase was fixed by adjusting the height of the overflow tube. The motor driving the spinner (when one was used) was started, and samples were analyzed every 10 minutes until consecutive analyses showed that equilibrium had been attained. In the unpacked column, dispersion of the heavy phase was obtained by a small high-speed stirrer near the upper surface of the liquid in the column. This stirrer emulsified the mikture to such an extent that locally the largest droplets were barely visible with the unaided eye. However, these droplets soon coalesced until within 12 inches (31 cm.) of the top many drops had reached a diameter of 1 mm. or more and probably contributed little more to the extraction. Since thorough local emulsification could not be obtained readily a t the bottom of the column, no data on efficiency with the lighter phase continuous are included. Equilibrium data for the system methyl isobutyl ketonewater-acetic acid were obtained from the literature (IO) Efficiencies were calculated to theoretical equivalent plates by the method of Varteressian and Fenske (1.2) for the btepwise calculation of theoretical plates. Efficiencies were As0 calculated in terms of capacity coefficient according to the method used by Elgin and Browning (4). Table I presents results obtained Kith all of the columns and the various spinners and packing. K,a refers t o the capacity coefficient with ketone as solvent. Column A packed with 1/4-inch Berl saddles had an effective volume of 260 ml. Spinner 2 used in column A had a Chrome1 wire leading from the top through a hole near the bottom and back to the top to provide for more efficient stirring. Column B with spinner 3 a t 1075 r. p. m. had an effective volume of 113 nil., while column C with spinner 4 at 1310 r. p. m. had an effective volume of only 60 ml. Results obtained with columns B and C cannot be plotted to yield accurate results in regard t o the number of plates because operating and equilibrium lines become almost parallel and very close together. The capacity coefficient also is probably only approximately correct for these columns. Figure 2 presents results obtained with column A packed with 1/4-inch Berl saddles, with spinner 1, and with spinner 2 . Figure 3 combines results obtained with all columns and packing or spinners, all operating with a ketone flow of 150 ml. per hour and with the ketone as continuous phase. Preliminary results with a column similar t o D,as well as the results of Jantzen with unpacked slender columns, indicated that column D without packing would shoq- approximately the same height per theoretical plate as column A unpacked; no runs with the tall slender column without packing were made.
Conclusions The results obtained indicate that the spinner type columns were in all cases more efficient than the Berl saddle-packed column and the unpacked one. The capacity coefficient is found to increase with increase in rate of flow, in agreement
TABLEI. EXTRACTION OF ACBTIC ACID F ~ O M WATER BY METHYLISOBUTYL KETON~ Run
No. 1 2 3 4 5 6 7 8 9 10
11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 38 37 39 40 41 42 43 14
45 46
47 48 49 50 61 62 53 54 66 6
Ketone Flow, Ml./Hr.
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Flow, Ml./Hr.
Concentration of: R a 5 n a t e Extract (normality) (normality)
No. of Plates
K K ~
Column A, Berl Saddle Packing, Ketone Phase Continuous 2.2 1.36 0.257 148 49 0.185 3.1 1.54 0.403 0.426 118 153 1.72 3.8 0.524 0.666 146 275 4.15 1.80 0.530 0.754 144 396 4.6 4.85 0.457 0.257 493 328 4.5 6.72 0.524 0.596 500 750 2.5 6.64 0.530 0.788 504 1600 1.7 0.324 0.328 0.393 95 57 0.640 2.5 0.455 0.489 98 98 3.4 1.30 0.524 0.644 195 3.8 1.58 0.530 0.744 lo5 98 273 Aqueous Phase Continuous 1.7 0.260 0.42 56 0.262 145 2.4 0.88 0.445 140 0.483 143 0.525 1.87 3.0 312 153 0.692 3.1 0.356 2.63 214 0.200 450 3.33 3.4 0.423 300 0.298 460 4.40 0.512 3.6 630 0.573 463 Column A , Spinner 1, Ketone Phase Continuous 3.6 0.446 1.17 107 0.317 147 1.62 4.0 0.503 156 153 0.449 4.4 0.620 2.18 218 0.674 152 2.24 4.4 0.458 157 0.267 240 0.518 3.56 5.5 275 0.450 268 >5.0 0.631 4.32 487 258 0.670 15.0 0.533 4.80 1030 226 0.786 0.520 8.0 0.322 730 16.04 882 Aqueous Phase Continuous 0.477 3.7 0.388 1.31 147 130 0.438 0.498 3.9 159 154 1.65 0.525 4.2 0.581 1.99 149 222 540 361 0.245 0.479 5.7 6.36 0.326 0.510 8.3 570 462 8.43 Column A , Spinner 2 with Wire, Ketone Phase Continuous 2.0 140 25 0.084 0.151 0.294 143 0.401 3.4 80 0.239 0.971 148 115 0.349 0.463 3.6 1.250 140 0.411 8.8 155 0.486 1.44 4.5s 156 318 0.688 0.535 2.545 58 0.345 0.389 2.4 0.463 89 72 0.367 0.429 2.8 96 0.620 114 0.489 0.495 106 3.4 0.978 147 0.639 0.519 3.5 0.990 92 248 0.736 0.530 98 3.50 1.50’ 410 0.819 0.525 95 2.40 0.4985 293 0.194 0.452 497 5.5 5.44 544 466 0.357 0.511 6.0 7.58 1188 0.561 0.526 877 5.0 15.62 Aqueous Phaee Clontinuous 145 59 0.242 0.294 2.1 0.678 144 90 0.329 0.385 2.5 0.733 152 130 0.404 0.463 3.2 1.18 144 144 0.467 0.478 3.1 1.19 149 196 0.631 0.508 3.7 1.58 Column A, No Packing, Ketone Phase Continuous 150 159 0.594 0.350 1.2 0.485 153 195 0.618 0.398 1.4 0.680 154 393 0.752 0.492 1.8 1.052 Column B . Spinner 3, Ketone Phase Continuous 230 130 0.513 0.0887 35 27.05 Column C, Spinner 4, Ketone Phase Continuous 104 53.4 0.0437 0.532 Many 52.0 Aqueous Phase Continuous 104 55.4 0.0457 0.529 Many 37.3
Approximate value.
with the results of Appel and Elgin (1) and of Sherwood, Evans, and Longcor (IO). The spinner columns yielded best results when the ketone phase was continuous, and the dispersed phase descended as a spiral of thin bands, often appearing as a stationary closely wound spiral. The same effect can be obtained with the aqueous phase continuous and the ketone phase ascending as a spiral. Spinner 2 with a wire from top to bottom and back up again proved less efficient partly because it tended to produce emulsions that did not separate completely in the settling sections and partly because the flat spirals described pre-
viously were never obtained under these conditions. Tiedcke (11) also found that the excessive turbulence produced reduced the efficiency. Results obtained with co’lumn A show that Berl-saddlepacked large columns are about 75 per cent as efficient as the same column with a spinner. This result with large columns is not unexpected since the spinner column owes its efficiency to operation with very thin films of dispersed phase, and this cannot be obtained easily with a large glass column. Therefore, especially in case solvent is to be evaporated off and recycled for batch operation, the Berl saddle-filled column would be preferred for columns over about 15 mm. in diameter.
RATE OF FLOW OF ACID
CC. HR.
FIGURE 3. COMPARISON OF PLATE EFFICIENCIBS OF THE VARIOUS COLUMNS For small-scale laboratory extractions in which long, slender, small-capacity columns may be employed, the situation is different, however, since such columns were found to be much more efficient than packed or unpacked columns of the same height. The data also show that the spinner type columns have no material advantage over the packed columns if the difference in density of the two phases is large, as when chloroform is used as solvent instead of methyl isobutyl ketone. It proved impossible to obtain flat thin spirals with this solvent, and no data are presented here,
Literature Cited (1) Appel, F. J., and Elgin, J. C., IND. ENG.CHEM.,29,451 (1937). (2) Axe, N.A., and Bailey, J. R., J.Am. Chem. SOC.,61,2609 (1939) (3) Cornish, R. E.,Archibald, R. C.. Murphy, E. A., and Evans, H. M., IND.ENQ.CHEM.,26,397(1934). (4) Elgin, J. C., and Browning, F. M., Trans. Am. Znst. Chem. Enurs., 31,639 (1936). (5) Glenn, R. A., and Bailey, J. R., J. Am. Chem. SOC.,61, 2612 (1939). (6) Jantzen, “Das fraktionierte Destillieren und das fraktionierte Verteilen”, Berlin, Verlag Chemie, 1932. (7) Sohenok, L. M., and Bailey, J. R., J. Am. Chem.SOC.,61 2613 (1939). (8) Schutze, H.G., Quebedeaux, W. A., and Loohte, H. L., IND. ENQ.CHEM.,Anal. Ed., 10,675 (1938). (9) Sohutze, H. G.,Shive, B., and Lochte, H. L., Ibid., 12, 262 (1940). (IO) Sherwood, T. K., Evans, J. E., and Longcor, J. V. A., IND. ENQ. CHEM.,31, 1146 (1939). (11) Tiedcke, K., thesis, Hamburg, 1928. (12) Varteressian, K.A., and Fenske, M. R., IND.EKQ.CHEM. 28, 1353 (1936). ABSTRACTED from the master’s thesis of W. 0. Ney, Jr., Department of Chemistry and Chemical Engineering, University of Texas, 1940.
