INDUSTRIAL AND ENGINEERING CHEMISTRY
454
The benzene solution is evaporated”oh a steam bath, the residue is placed for 20 minutes in a drying oven a t about 90” to 100” C., and the dish is weighed: Weight of residue X 100 = Weight of sample
5 Freon-insoluble solids
The ability to reprodbce resu!ts is shown in Table I. The standard error of the mean of two duplicates of the first 26 samples
Vol. 16, No. 7
ment. While this procedure was worked out for determining the solubility- of _wrethrum extracts in Freon. it can be used for solubility _ determinations of other substances ‘in solvents which are gases under normal pressures. LITERATURE CITED
(1) Goodhue, L. D.,IND.ENO.CHEM.,34,1456(1942).
Simple Cpnstant Reflux Take-Off for Distillation Systems J O H N C. SNYDER
AND
WALTER STEUBER, Catrlytic Development Corporation, Marcus Hook, Pa.
IN
LABORATORY fractional distillation it is often necessary to control the reflux ratio so that it is kept constant, regardless of variations in the distillation rate or empirical factors. This has been accomplished by Carter and Johnson (9) with a magnetically moved funnel, by Bruun ( 2 ) with a two-way valve and capillaries, and by Podbielniak (3) with an automatic valve seated in the take-off tube. All these devices require a degree of skill too great for fabrication by an amateur glass blower, and various mechanical difficulties have been experienced in their operation, due to sticking of moving parts or plugging of capillaries. An easily constructed take-off device of the intermittent type which operates smoothly is described in this paper.
T
1‘
STILL CONSTRUCTION AND O P E R A T l O N
The takeoff is designed for use with any type of total condensing head in which the entire condensate stream passes a point on its return to the column (see Figure 1). The rec,eiver is maintained under a sli h t pressure sufficient to prevent the flow of liquid from the s t i i head through the U-shaped tube into the r e ceiver. A small steady stream of inert gas passing through the nonvolatile oil in the bubbler supplies this pressure. Periodically, the receiver is vented to the operating pressure of the still through an electrically o erated valve controlled by a cycle timer. During this period t\e entire condensate flows by gravity to the receiver, by the merhanism shown in Figure 2. While the receiver is under pressure,,the liquid in the takeoff When the pressure is ca illary is maintained at levels A , A r e L e d , the liquid flows to levels B, B’, which are just at the overflow point. Consequently, all reflux during the “on” period enters the take-off at A and an equal amount of liquid overflows a t B’ into the receiver. At the end of the “on” interval (generally from 2 to 5 seconds), the valve closes and restoration of the receiver to pressure quickly interrupts the take-off stream. For
.
TO ADPlTlONAL STILLS
! j
TO ATMOSPHERE OR VACUUM PUMP
I
I
/
i
RECEIVER
Figure 2.
Detail of Take-Off Line
convenience in emptying the receiver, the take-off line is generally rovided with a stopcock to revent the flow during this per,iod. kowever, if it is desired to [eep the roduct from coming into contact with stopcock grease, and if low-boiling components which will vaporize in the take-off line at the outset of the dmtillation are absent, this stopcock and the one on the receiver may be omitted. The dimensions of the takeoff line de end maiply upon the throu hput of the still, but are not critica?. The diameter must be suhcient to accommodate the entire dist!late during the t a k e off period. A convenient length for Ah, which indicates the pressure head that is maintained by the bubbler, is from 0.5 to 3 cm. The following advantages have been noted:
r
I
i
PRESSURE coma
I
Simplicity of construction, operation, and adjustment. The take-off maintains a constant reflux ratio, irrespective of distillation rate, which is redetermined by simple adjustment of the intervals of an on-ancfoff timer. Low cost. No delicate moving parts in the still head. Very low holdup. Distillations may be conducted out of contact with anything save glass and an inert gas. The method is adaptable, LO distillation at other than atmospheric pressure. Several stills may be operated with the same control system.
I
!
LITERATURE CITED
i
Figure 1. Flow Diagram
(1) Bruun, J. H.,IND. ENO.CHWM., ANAL.ED.,7, 359 (1935). (2) Carter, A. S., and Johnson, F.W. (to E. I. du Pont de Nemours & Co.), U. S. Patent 2,251,185 (July 29, 1941). (3) Podbieiniak, W. J., Podbielniak Centrifugal Super-contactor Co.,Circular 22 (Nov , 1942).
