Fngineering
A Constant Reflux Ratio Distilling Head LLOYD BERG
AND
LEWIS
and rrocess development
L j
K. SMITH
MONTANA STATE COLLEGE, BOZEMAN, MONT,
A
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CONSTANT reflux ratio type of dietilling head has been developed and used in this laboratory and appears to possess certain advantages not available in any other design reported to
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date. Lloyd and Hornbacher ( I ) described several heads consisting of a number of condensing surfaces in parallel, some of which allowed their condensate to be taken off as product while the remainder returned their condensate as reflux. This general type of distilling head was given the name Corad to indicate the ability to produce constant reflux ratio. The distilling head described in this paper is similar to the Corad head design in that it also employs parallel condensing surfaces, but a major difference is that the amount of material condensing on the parallel surfaces is not necessarily proportional to their respective areas. A diagram of this equipment is shown in Figure 1. It consists essentially of a vertical jacketed cylinder inside of which is placed a fmger-type condenser. The vapors from the still condense on the inside surface of the vertical cylinder and on the outside surface of the fmger condenser. The material which condenses on the vertical cylinder is returned directly to the top of the still as reflux. A cup attached’to an outlet is placed under the finger condenser and condensate from that source is removed as product. A valve or stopcock in this line can be closed to enable operation a t total reflux. Figure 1 shows a stopper as a means of closure between the finger and jacket condensers. A glass seal closure or, if the apparatus be made of pipe, pipe fittings may be substituted for the stopper. The rates of flow of coolant (usually, but not necessarily, water) to the vertical cylinder and the finger condenser are controlled separately and independently. I n order to ascertain and maintain a definite reflux ratio it is necessary to be able to determine the rate of flow of coolant to both condensers and in addition the temperature rise of the coolant as i t passes through the condensers. Rotameters have been found particularly well adapted for measuring these flow rates, but their use is recommended only when the amount of usage of the still head warrants the extra expense. The determination of the flow rate and the temperature rise of the coolant in both condensers enables the calculation of the heat transferred per unit time. The amount of heat transferred in each condenser is directly proportional to the amount of vapor condensed and thus the reflux ratio can be calculated. The dimensions or construction details are not critical. A finger condenser outside diameter of from one tenth to one fourth of the cylinder condenser inside diameter has been found satisfactory. Heads ranging in size from 1-inch cylinder diameter to 6 inches and larger have been constructed. Heads of this design have been fabricated from glass, iron pipe, and copper tubing and the performance from these sizes and materials has been satisfactory. Reflux ratios from 1 to 1 to as high as 50 to 1 have been obtained with a single unit. The principal advantages of this apparatus are its simplicity and its low cost. It has been successful under vacuum and in pressure rectifications and it handles heterogeneous condensates as readily as homogeneous. LITERATURE CITED
Figure
(1) Lloyd, L. E., and Hornbaoher, H. G., AnaE. Chem., 19, 120 (1947).
Reflux Ratio Distilling
Head
RECEIVED January 14, 1950.
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