Chuen-cheh Shen and Paul Mellus Auburn University Auburn. Alabama 36830
II
A Simple Apparatus for Continuous Distillation
As hatchwise distillation reauires freauent attention and excess feed distillation waste; the distiilate, an apparatus hased on the "chicken-waterer" principle was designed to eliminate hoth problems.' The apparatus is convenient hut still reauires oeriodic removine, refilling, and replacing of the supply bottle, and i t is not easy to invert a bottle with a size over 5 eal. We modified the excess feed distillation apparatus to avoid wasting the distillate. The distillation can he ooerated continuouslv as l o w as i t is required. The only attehtion required is to refill thereservoir which is a 13-gal. bottle or larger in capacity. The apparatus is shown in the figure. The reservoir (D) is stopped with a rubber stopper which has two holes. The holes are filled with two glass tubes, one is long enough to reach the bottom of the reservoir and the other is short, just a few cm below the stopper. The short tubing is bent and attached to a rubber tube. The faucet of the reservoir is turned around 180" so the water will come out upward instead of downward as it would normally. This will eliminate the accumulated air in the faucet, if any. The distilling flask ( A ) ,which is 5 1in capacity, has a side tube ( B )which contains a smaller tuhe. This smaller tuhe is used to release the overloaded water and should not stand over % height of the body of the flask. The side tuhe is connected to the flask by a side arm. The flask and the reservoir are arranged in such position that the top end of the smaller tuhe in the side tuhe is a centimeter ahove the bottom end of the long tubing in the reservoir. This is a key point in this set up. It is easy to fix the position of the reservoir first and then adjust the position of the flask. A leveling tuhe ( C ) is set between the side tuhe of distillating flask and the reservoir. The side arm of the leveling tuhe, which is bent to fit the connection, is attached to the faucet of the reservoir by a short Tygon tuhe. The end of the leveling tuhe is immersed in the side tuhe of the flask almost to the bottom. The top of the leveling tube is attached to a stopcock. The flask and the reservoir are filled with water. To fill the reservoir, either fill from the top by removing the stopper or from the long tube without removing the stopper. After the reservoir is filled up, some water or air is drained from the short tuhe until some air bubbles come out of the long tuhe. Then close the short tuhe with a clamp. The pressure at the bottom end of the long tube equals the atmospheric pressure. Now open the faucet of the reservoir. Apply suction to the glass tube of the stopcock on the leveling tube until the leveling tube is filled with water and close the stopcock. The leveling tuhe, which is used to conduct water from the reservoir to the flask, should contain water ahove the side arm. Otherwise, the water will not he siphoned from the reservoir to the flask. The leveling tuhe also serves as an air trap. Air, which comes from the water as the temperature of the water changes, will accumulate a t top of the tuhe and can he removed by suction. T o test if the system works, draw some water from the flask. The level of water in the flask should stay about a centimeter helow the top end of the smaller tuhe, even if a large amount of water is drawn. As water comes out of the reservoir, air bubbles will come out of the long tube. If no air hubhles appear, make sure
' Burrhus, K. D. and Hart, S. R.,Anal. Chem., 44,432, (1972). 262 / Journal of Chemical Education
To the
dram
F Diagram of continuous distillation apparatus (not to scale).
that the reservoir is air tight, except for the long tuhe which conducts air into the reservoir. If water continuouslv comes out of the reservoir, the top of the smaller tube &I the side tuhe ( B ) is below the bottom end of the long tuhe in the reservoir. Make sure that the former is about acentimeter ahove the latter. After the flask is fixed, a heating mantel (E) is placed underneath the flask. A magnetic stirrer (8') is placed under the heating mantel. A magnetic stirrer bar is placed in the flask before the adaptor, the connector and the condensing tube are attached to the flask (see figure). T o avoid the bumping and the overheating the water should he stirred while it is heating, and the heating mantel is connected to a variable voltage control. T o conserve energy, the flask is covered with glass fiber. The' adaptor and the connector can he wrapped with ashestos strip. T o start the distillation, turn on the heater and magnetic stirrer. Open the faucet and the cooling system. As the water in the flask distills over, the level of water in the flask will decrease. The water in the side tuhe will he siohoned into the flask to keeo the water in the side tube and In the flask a t the same levei. This will lower the water level in the side tuhe and water will be siuhoned from the reservoir into the side tuhe. The level o i the water in the flask and that in the side tuhe will reach the height of the hottom end of the long tuhe in the reservoir. This is due to the same pressure, which is equal to the atmospheric pressure, a t these points. So in this way, the volume of water distilled from the flask is equal to the volume of water siphoned from the reservoir until there is no more water left in the reservoir. The reservoir can be refilled while it is distilling. This is done hy the following procedures. Turn the faucet of the reservoir off. Open the short tuhe or remove the stopper. Water is refilled from the long tuhe or from the top as before. After the reservoir is full, some water is drained from the short tube until some air bubbles come out of the long tuhe. Close the short tuhe and make sure
the reservoir is air tight except for the long tube. Then open the faucet. These procedures will not disturb the distillation. T o stop the distillation, turn the power of the heater, magnetic stirrer, the faucet and the cooling system off. No special attention is required while it is distilling if the cooling system runs normally and the faucet does not accumulate air. Air which is dissolved in water will come off slowly if the temperature of a new batch of water filling into the reservoir is lower than the room temperature. Air usually will accumulate in the leveling tube as the water is siphoned from the reservoir into the flask. I t may he removed from the stopcock by suction. Air may accumulate in the faucet hut in most cases it will move to the leveling tube. If air accumulates in the faucet. as water is not siphoning, i t should be removed. Otherwise, the flask may he damaeed when the flask becomes dm. I t is better to check the f a k e t by pressing the Tygon tube several times a few
hours after the reservoir is refilled with a new batch of water. If the power is off while i t is distilling the siphon will stop automatically. If the power is on again the siphon will start again. In both cases only a small amount of water will he lost. We have operated the apparatus described above to distill cootiouously deionized water from alkaline permanganate for one month without interruption. (Of course the apparatus can be operated as long as you need.) The only attention required was to refill the reservoir, which was done every three days. The resistance of the distillate is 0.5 X lo6 ohm cm compared to 0.8 X lo6 ohm cm obtained from distilling without permanganate. The same principle can be applied to distill water with high purity. Acknowledgment
Mr. Gene Nelson fabricated the distilling flask A-B, designed by R. D. Phillips, and the leveling tube in his glass blowing shop.
Volume 53. Number 4. April 1976 / 263
