A Device to Prevent Bumping and Promote S. PALKIN AND T. C. CHADWICK Bureau of Agricultural Chemistry and Engineering, U. S. Department of Agriculture, Washington, D. C.
N
UMEROUS devices have been advocated to prevent bumping in distillation, but with possibly one exception (1) none has proved completely dependable. Most of them function fairly well a t the start of a distillation, and as long as boiling is not interrupted. However, temporary removal of the source of heat, the addition of more liquid to the distillation flask, or an increase in pressure, in the case of vacuum distillation, often renders the devices ineffective. The need for a convenient and dependable device to ensure smooth ebullition is particularly acute in fractional distillation a t reduced pressure, where bumping may cause flooding and otherwise seriously disturb the operation of the column. The “boiling tube,” glass beads, broken glass, boiling stones (Carborundum), and a gas stream (particularly for vacuum work) probably find most frequent use because of their simplicity. Glass wool, as proposed by Morton ( I ) , is one of the most effective, but a considerable quantity of the wool is required. Because of the large holdup due to the packing, as shown in Table I, it is impossible to recover small pot residues without extensive dilution by wash solvent.
The very close contact of the glass thread with the source of heat renders the thread itself comparable t o a continuous “hot wire,” without introducing hot metal into the distillation liquid, The glass thread windin extends from the bottom of the distillation flask to a point we6 above the surface of the liquid being distilled. Boiling is thus romoted over a large surface throughout the depth of the liquix The device is compact. The thread does not retain any significant amount of the residual liquid, and can easily be cleaned by washing nith solvent. As the heating medium for the boiling promoter is not in direct contact with the liquid being distilled, any suitable means of supplying heat may be used. When the temperature of the liquid being distilled is not above 90’ C., steam may be used very effectively. Oil heated by a rheostat-controlled electric immersion heater made of coiled asbestos-covered wire has been found to serve very well over a wide range of temperatures. In this way a satisfactory temperature differential between the heating medium of the device and the liquid being distilled can be established, and functioning of the device ensured. COVERED WIRE
TABLEI. LIQUIDHOLDUP OF GLASS WOOL Liquid Reta,ined,a No Packing Tur- E t h y l pen- alooPine tine hol Hz0 oil
Drainage Time Min.
cc. cc. cc. cc.
~.
(about 19 hours)
5
.. ..
Co. retained = cc. added
-
00.
,OIL
Liquid Retained a 70 Grams of Glass Wool Tur- Ethyl pen- alooPine tine hol Hs0 oil cc. cc. cc. cc.
..
..
..
..
57
drained.
In these experiments a measured quantity of liquid was poured into a 2-liter round-bottomed flask, shaken to wet the flask and glass wool thoroughly, and then inverted and drained. The flask was shaken six times during each test to break up pockets of liquid in the glass wool, and thus speed up drainage. TABLE11. PRACTICAL TESTSWITH PROPOSED DEVICE Experiment No.
Bath
for Still Pot
Type
Steam Steam Oil Oil Oil Oil
Temp. C. 100 100 121 122 121 194
Vapors ,--Immersion Heaterin Still Temp. of Oil
Pot C. 88 88 88 88 91 153
Bottom
C. 93 89 95 96 108 176
Top ‘ C. 95 89 100 100 121 186
Distillation Pressure
Watts M m . H g 60 7 60 0 60 7 60 16 10 18 20 190
U
FIGURE 1. HEATER TUBE
The device described in this paper has been subjected to rigid experimental tests under varying conditions of use. A few experimental runs are recorded in Table 11.
This device may also be used in a limited way to provide heat for the distillation. It is best used, however, as a b u m p ing preventer and boiling promoter only, the heat for the distillation proper being provided independently by an oil bath, a steam bath, an electric heater, or other suitable means.
Principal Features All parts coming in contact with the liquid to be distilled are of lass. large promoting surface is provided, consisting of glass thread closely wound around a glass “heater tube.’’ This tube is heated by an easil controlled external means, independent of the heat source for d e distillation proper, and activates the glass thread.
1
Construction of Boiling Promoter The heater tube ro er is essentially a, wide test tube, the bottom of which is pusiefup, and has a small glass button sealed to it to permit fastening the glass thread. This construction, as 509
INDUSTRIAL AND ENGINEERING CHEMISTRY
510
VOL. 11, NO. 9
glass joints, as shown in Figure 2. In that case, careful adjustment of the height of the joint on the flask will have to be made, so that the promoter will just clear the bottom of the flask.
FIGURE 2. APPARATUS
shown in Figure 1, permits winding the glass thread virtually to the very bottom of tube a. The thread, after being fastened to the button, is tightly wound upward with the windings (one thread in thickness) fairly close together, covering the promoter t o a height somewhat above that t o which the liquid is expected t o reach, and the end is securely tied by knotting, looping, and reversing the last few turns. The heater tube may be inserted into the boiling flask by way of a stopper, or the flask and tube may be equipped with ground-
I n order to test its effectiveness the device was used not only with a number of liquids, including water, acetone, ether, ethyl alcohol, benzene, methyl chavicol, anethole, ,fenchyl alcohol, turpentine, terpinolene, and pine oil, in simple distillations a t varying pressures, but also as a unit incorporated in a plate column assembly for systematic fractionation. Data on a few typical experiments are recorded in Table 11. As mag be seen from experiments 1and 3, the use V of steam; because of its superior heat-transfer p r o p erties, makes it possible to operate a t a much lower temperature differential between bath and still pot than when oil is used. This device can also function without being heated separately, provided the distillation is not allowed to stop. Thus, without supplying electric current to the promoter, smooth boiling took place throughout experiment 2, and in experiment 4 a t the beginning only. I n the latter case, boiling was interrupted by addition of cold turpentine. Smooth boiling was resumed only after supplying sufficient current to the promoter to raise its internal temperatures to 96’ and 100” C. I n systematic fractional distillation, the device works best when its temperature is carried sufficiently high so that introduction into the system of additional liquid will not inactivate the promoter but interrupt the boiling only long enough for the added material to be heated to the boiling point. Data were obtained in experiment 5 in a normal systematic fractionation of a high-boiling terpene hydrocarbon, during which the device functioned continuonsly.
Literature Cited
I_ 5 0
Laboratorv Flotation Cell
2 5. -4----
J
A Small Pneumatic Cell of All-Glass Construction CLYDE W. LEAF AND ALEXANDER KNOLL Columbia University, New York, N. Y.
the cells of Prausnitz and Taggart, Taylor, and Ince use a large volume of solution and a large sample of mineral. The latter cell, while of excellent design, has a perforated rubber disk and a metal base which make it difficult to clean. The Prausnitz cell is constructed entirely of glass, but both it and the Oberbillig and Fahrenwald cell have flaring tops which cause the froth to collapse during operation, necessitating manual removal of the froth in order to get quantitative results.
t i
1i 1 i i
AGGART, Taylor, and Ince (3), Oberbillig and Fahrenwald and Prausnitz (6) have described laboratory flotation ce& which are designed to. give quantitative results. However,
The cell described here can be made entirely from glass, and has been designed to work in a setup such as that described by Oberbillig and Fahrenwald (1) for controlling the air flow. Compressed air has been found satisfactory as an air source, each run being made at the same pressure reading on the differential manometer. Each run requires only 50 cc. of solution in the cell, and a 5-gram mineral sample (
