NOTES ON ANALYTICAL PROCEDURES N e w H e a d for Laboratory Fractionating Columns J. D. BARTLESON, A. L. C O N R A D ,
AND
P. S. F A Y
Chemical Research Division, Standard Oil Co. (Ohio), Cleveland 6, Ohio
I
K DISTILLATIOK systems, take-off heads which are capable of maintaining a constant reflux ratio regardless of variations
Advantages found during operation are: (1) simplicity of operation due to automatic take-off with variable setting for reflux ratio; (2) ruggedness of construction; (3) protection of the steel ball from corrosion and of the distillate from contamination; (4) usefulness for high-temperature distillation because of a small surface area and vapor volume; ( 5 ) usefulness for lowtemperature distillation because of a positive closure and a variable coolant; (6) high-capacity take-off valve permitting rapid distillation of large volumes; and (7)adaptability to vacuum distillations. The construction of the apparatus requires glass-blowing skill. However, i t can be made readily by a professional glass blower or obtained a t a reasonable cost from the Euclid Glass Engineering Laboratory, 6 East 242nd St., Euclid, Ohio. This type of distillation head may be made to fit any size of fractionating column by the proper choice of joint sizes.
in distillation rate and other factors have been described by Bruun (1) using a two-way valve, by Carter and Johnson (2) using a magnetically operated funnel, and by Snyder and Steuber (3) using a U-shaped take-off tube and pressurized receiver which is intermittently vented to the still pressure. Kone of these devices is satisfactory for the routine laboratory distillation of petroleum products in which appreciable amounts of condensed butane hydrocarbons are to be measured. These low-boiling components tend to vaporize in the take-off line and re-enter the column. The take-off device described here overcomes this difficulty and has the further advantages of high throughput and low holdup. The feature of this take-off, which is designed for a totally condensing head, is a steel ball bearing encased in glass. This assembly is seated by a joint ground into the throat of a glass funnel leading t o the receiver. For alternate use with the head, a doubletype condenser utilizing dry ice cooling in addition t o the conventional type is described. This condenser gives efficient and complete condensation of C, fractions. It avoids the troublesome change from dry ice t o liquid coolant, which is encountered in the operation of the usual dry ice head, and eliminates the need for expensive cooling systems.
ACKNOWLEDGMENT
The authors are ;ndebted to C. J. Schugt of the Euclid Glass Engineering Laboratory and to E. C. Hughes and M. hl. Fink of the Standard Oil Company of Ohio Research Laboratory for suggestions in design and for the drawings. LITERATURE CITED
CONSTRUCTION AND OPERATION
(1) Bruun, J. H., IND. ENQ.CHEM., 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) Snyder, J. D., and Steuber, W., IXD. ENQ.CHEM.,ANAL. ED., 16, 454 (1944).
Figure 1 (left) shows the side view of the head, with the takeoff mechanism enlarged a t center. The steel ball, A , encased in glass is shown in position for total reflux, and illustrates the small vapor volume-free space and liquid holdup. The glass funnel. B. forms a tinht seal for total ieflux, the gondensate from the drip tip, C, flowing over the valve and returning to the c o l u m n . During takeoff a cycle timer connected t o an electromagnet, D (heavy duty-220volt alternating current coil 900- resistance), operates to pull the steel ball up to the position of the dotted line and all condensate flows into the receiver. At the end of the take-off period, the valve reseats by gravity and condensate again returns to the column. I t has been found desirable, for best operation, to have an indentation blown into the head as shown a t E to allow closer approach of the magnet core to the valve. Figure 1 (right) shows an alternate type of condenser F permitting the use of coolant in center core and in outer jacket. Replaceable attachment G on center core facilitates addition of dry ice to the condenser, necessary for condensation of volntile distillates.
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Figure I. Diagram of Head 724
RECEIVER
