ANALYTICAL EDITION
138
Vol. 3, No. 2
Flow Divider for Fractionation under Diminished Pressure* A. M. Schwartz and M. T. Bush CORNELL UNIVERSITY, ITHACA,N. Y.
Figure 1-Stillhead
and Mercury Valve
The ordinary method of providing a divided flow by means of a stopcock regulator is fairly satisfactory for ordinary pressures. I n vacuum, however, it is open to several objections. The stopcock invariably freezes, especially if the temperature is above 100' C., there is contamination of the distillate by stopcock grease, and the regulation is not par-
D
April 15, 1931
INDUSTRIAL AND ENGINEERING CHEMIXTRY
is 9 cm. long and 3 mm. in diameter. The dimensions of the assembly are shown on the diagram. The surface of the mercury at E may be cleaned readily by pouring in a suitable solvent and then expelling it through D by plugging up A and C and blowing a t B. If the surface of the mercury is oxidized or corroded, a small portion of the mercury itself may be expelled in the same way. Thus it is only occasionally necessary to refill the divider. This device has proved to be satisfactory at pressures as low as 1 mm. The adjustment is sensitive, and the screw turns easily. If the tube A-C is of small bore, say less than 15 mm., the reading of the thermometer may be affected by the proximity of the cold reflux returning from B. We may modify the construction of the stillhead itself so as to return the reflux a t a lower point, as shown in Figure 2. This con-
139
struction gives rigidly accurate temperature readings, but is fragile. A simpler, although not quite as effective method of eliminating thermometer error is to flare out the joint at F into a bulge of 2 to 3 cm. in diameter. The returning stream is then far enough away from the thermometer bulb not to affect the reading, A simpler valve, one which may be used where there is not a large amount of fractionation to be continuously done, can be made from the same stillhead. At E, instead of sealing on the valve, a piece of rubber tubing is slipped over the stem. This is closed tightly at the far end, and is filled with mercury. The level of the mercury in the elbow is controlled by an ordinary pinchcock around the rubber tubing. This device is quite as efficacious as the more complicated one. Its disadvantage is that it is difficult to keep the tube from leaking over long periods of time.
Glass Temperature and Float Regulators' D. F. Othmerz EASTMAN KODAKCOMPANY, ROCHESTER, N. Y.
The development of industrial processes on a labothe cock with the free end unARGE distillation projratory and pilot-plant scale is frequently hindered der the liquid surface of a dish ects are usually deby the lack of controlling apparatus of such simplicity containing both the volatile veloped as a result of and smallness as will fit in with the minute process liquid and mercury. The des t u d i e s m a d e with small equipment employed. Several types of temperature sired amount of volatile liquid units, and in the operation and float controllers representative of those which is drawn in first, then merof such pilot eqJipment i t have been successfully employed are described as being cury is allowed to fill the rest is f r e q u e n t l y desirable to suitable not only for use with ordinary chemical laboof the tube. have apparatus to regulate ratory apparatus, but adaptable to the regulation of The flow controller, Figure the processes similar to the pilot-plant distillation and related operations. 3, is mounted above the conautomatic controllers of indensers and its bottom outdustrial usage. The electrical thermostat circuit described (3) in a previous paper has been let connected to the inlet tube of the Sensitive bulb. The used as a pressure regulator for glass and pilot-plant stills and, connecting tube is filled with mercury and the system by means of its use with a n inclined manometer and a n in- heated to the desired operating temperature, as shown by ternal electric heater, a very constant rate of distillation may an auxiliary thermometer. The level of the flow controller be maintained, A similar manometer circuit with the bulb is adjusted so that the vapor pressure of the liquid in the of a vapor-pressure or liquid-expansion thermometer as the sensitive bulb a t the set temperature forces the mercury sensitive element may be used for controlling temperature, high enough to submerge the inverted V-weir of the central but it has the disadvantage of a simple on-and-off regulator tube. Cooling water flows into the tube at the upper left of the with no intermediate steps automatically controlled. A self-contained temperature controller using a vapor flow controller and, when the mercury is below the level of pressure bulb as the sensitive element and requiring no auxili- the weir, down the annular space, up through the inner ary power is shown in the accompanying figures.* Its use tube, and out through the discharge tube on the left to waste. as applied to control of stillhead temperature by regulation As the mercury rises and throttles the flow through the weir, of the amount of wash liquid returned to a fractionating the water rises in the central tube and overflows the tube column is indicated in Figure 1. The sensitive bulb of Figure on the right side. Both outflow tubes have insealed tips 2 is inserted above the depblegmator condenser of a double to enable visual inspection of the comparative amounts condenser unit (2) and maintains the temperature of the flowing in each, and are vented to prevent siphoning. The vapor stream between the two condensers at a constant pre- right, and higher outlet discharges through a rubber determined value. It is previously charged with a liquid tube to the base of the dephlegmator coils and furnishes of suitable volatility, preferably one with a vapor pressure cooling water for condensing the liquid to be refluxed as of about 90 to 125 cm. of mercury, at the temperature to be wash. As the temperature in the head of the dephlegmator maintained. Only enough of the volatile liquid is required rises, the flow of water through the weir and to waste is to give always a liquid phase. A bubble of air is allowed to throttled and a larger amount overflows the right tube and remain to insure a gas and vapor phase, and the rest of the thus passes through the dephlegmator condenser. This tube is filled with mercury. The bulb is readily charged by additional cooling water produces more condensate, which, Connecting with a straight glass cock, evacuating with a by its washing action in the rectifying column, reduces the water pump, disconnecting the vacuum hose, and opening amount of high boilers in the vapor and therefore the temperature Because of the lag caused by the small time in1 Received November 3, 1930. * Present address, 356 Clay Ave., Rochester, N . Y. terval in the change of the distillation with a change of reflux 8 All the glass apparatus described and pictured herein has been conratio, the amount of cooling water required is never exactly structed of Pyrex glass by the Technical Glass Co., 42 Galusha St., obtained as a steady stream, and the temperature varies which is also prepared to supply additional equipment of Rochester, N. Y., slightly with accompanying changes in flow of cooling water name type.
L
