Continuous Extraction of Aqueous Solutions by Acetone-Petroleum Ether M. WAYhIAN
AND
G. F. WRIGHT, Chemical Laboratory, University of Toronto, Toronto, Canada
I
N COKNECTION with the isolation of the yeast growth-
Description of Extractor
promoting factor Bios I I B (a), i t became necessary t o extract the factor from its aqueous solution by means of acetone. Although acetone is completely miscible with water, such a n extraction can be effected by saturating the aqueous solution with certain inorganic salts ( I ) . The acetone layer, however, contains considerable water. This is disadvantageous when the extraction is continuous, owing to the fact that the water accumulates in the boiler. The authors have found that this difficulty can be prevented if, instead of acetone, a 1 to 3 petroleum ether-acetone mixed solvent is used, the aqueous solution being saturated with sodium chloride. Obviously, any solvent having approximately the same boiling point as acetone can, if it be waterinsoluble, effect the vapor distillation of the water carried over with the acetone; the authors have used petroleum ether because of its low cost. Since the use of mixed solvents requires certain precautions, they have elaborated a description of their extractor in the hope that i t may prove useful in separations unrelated to the present problem.
Twelve liters of the aqueous solution to be extracted are saturated by shaking with an excess of sodium chloride. To this solution are added 6.3 liters of acetone and, thoroughly shaking after each addition, 2.1 liters of commercial naphtha (b. p. 60' C. to 90' C.), This is decanted from undissolved salt into the 20-liter bottle, G, and the trap, K,and mixed solvent is added until the 5-liter round-bottomed flask, A , contains about 3 liters. The apparatus is assembled as shown in the diagram, the column, B, being lagged. If the liquor to be extracted contains so much solid that a head of distillate in the stirrer is alternately retained and released, it is advisable to extend the length of H at least 20 cm. (8 inches) above the side arm leading to K. Duprene tubing was used for connections r, r', and 7". The upper connection, r", should be of sufficient length to impart flexibility to E . Since loss of solvent tends to change the composition of the acetone-petroleum ether extractant the vapor surge condenser is installed a t L. A glass tube, M , is loosely hung so that it projects into the center of this condenser and is flexibly attached to E by means of rubber tubing. The u8e of this equalizing device is advisable because the duprene connection at 'T is likely not to have the identical lumen of the tubes to which it is attached. This would cause obstruction due to either constriction or air lock; the equalizing device therefore prevents loss of solvent at this point owing to vapor and liquid surge. Because of this device, the downcoming distillate empties smoothly about 10 cm. (4 inches) below the surface of the liauid in the hollow stirrer. F. This stirrer, bent so as- to circulate the extractant thoroughly, operates more efficiently if a coarsely woven cloth sack, N , is tied over its lower end. It is supported in a brass journal to which is attached the pulley, P, and, in this case, could not rotate faster than 6 r. p. m. While this optimum rate, at which emulsion formation would not occur, was being ascertained, the otherwise unnecessary trap, K , mas included in the extractor. Boiler A is heated by a steam bath which may be constructed by cutting a hole in a can 15 cm. (6 inches) high by 30 cm. (12 inches) in diameter just smaller than the equator of the 5-liter round-bottomed flask. When the latter is set in position the whole bath assembly may be rendered steamtight by means of molding clay. This clay must be replaced every time the boiler is changed, but it is cheap and el'fective.
B
Operating Characteristics
It is evident that the amount and nature of the solute in the aqueous solution will alter the component distribution throughout the extractor. When water alone was used in G, i t was found after the apparatus \vas operated to a n equilibrium state, that the aqueous layer contained 15 per cent of acetone by volume and was saturated with about 180 grams of salt per liter of solution. The solvent above this aqueous layer contained 54 per cent by volume of acetone, 6 per cent of water, and 40 per cent of petroleum ether. The boiler, on the other hand, contained 26 per cent by volume of petroleum ether, the remaining 74 per cent being considered as acetone. The exact weight of salt per liter of solution inav varv with the conditions of the experiment. The essential point is that the aqueous layer be saturated. Literature Cited (1) International Critical Tables, Vol. IV, p. 411, New York, McGraw-Hill Book Co., 1928. (2) Miller, W. L., Trans. Roy. SOC.Can., 111, 31, 159 (1937).
91
