1092
IYDGSTRIAL A-VD ENGISEERISG CHE-1fISTRY
Vol. 18, No. 10
A “Bubbler” Laboratory Fractionating Column’.‘ By H. T. Clarke and E. J. Rahrs EASTMAN KODAKCo., ROCHESTER, s.Y .
I
T IS universally recognized that by far the most efficient form of distillation column is that in which the ascending vapor is washed by bubbling through the refluxing liquid. While all industrial distillation columns depend upon this principle, it has never been satisfactorily adapted to laboratory apparatus, which must necessarily be simply c o n s t r u c t e d and preferably contain neither metals nor movable parts. The well-known columns devised by Glinsky and by Young and Thomas both depend upon w i r e - g a u z e obstructions, through which the vapor forces its way into the layers of liquid by which it is washed on its way up. The disadvantage of such an arrangement, apart from the presence of metal and of loose parts, consists in the high resistance which the vapor has to overcome; this is necessary in order to maintain a layer of liquid above each obstruction. I n the Le Bel-Henninger column metal and loose parts are absent, the obstructions consisting of a series of constrictions through which the vapor has to pass a t a high velocity in order to prevent the wash liquid from descending through them, instead of the external reflux tubes provided for that purpose. I n all these types the wash liquid falls through the column and returns entirely to the boiling flask if the distillation is halted or slackened, if only for an instant. I n some types of Le Bel-Henninger columns this disadvantage is met by the insertion of a glass bead, which acts as a valve. This offers a n increased resistance to the vapor and adds the grave danger of jamming in the upper constriction when lifted by too violent a current of vapor. The column here described resembles the Le Bel-Henninger type in principle, with the difference that the wash liquid is retained in traps. which prevent i t from falling and offer only slight resistance to the upward passage of the vapor. The general construction is shown in the figure. 1 Received June 23, 1926. Presented before the Division of Organic Chemistry a t the 72nd Meeting of the American Chemical Society, Philadelphia, P a , September 6 t o 11, 1926 2 Communication No 278 from the Research Laboratory of the Eastman Kodak Company
The traps consist of elbows formed by downwardly inclined vapor-inlet tubes (10 to 12 mm. internal diameter, 7 to 8 cm. long) entering the vertical bubbling chambers (24 to 28 mm. internal diameter, 9 to 11 em. long). The reflux tubes ( 5 to 6 em. internal diameter) enter the bubbling chamber a t a point below that a t which the vapor enters and leave at a point (conveniently on the opposite side) 3 to 6 mm. above the highest l e ~ e of l the vapor inlet. This forces the vapor to pass through a layer of condensed liquid 3 to 6 mm. deep; the excess of liquid passes downwards through the reflux tube to the trap below-. The column may contain any number of these traps. Eight has been found to be a suitable number. The reflux liquid is provided by a water-cooled condenser such as is recommended by the writers for a column of another type.3 I n order that the upper units of the column shall possess the same efficiency as the lower, the loss of heat by radiation must be cut down to a minimum. This is more conveniently done by lagging all the tubes rather than by surrounding the entire apparqtus. Electrician’s tape serves satisfactorily; it is well to apply a coat of varnish t o the finished wrapping. The efficiency of this column can be judged by the following results obtained on distilling a mixture of 2000 cc. each of commercial benzene and toluene: R:nge Volume C. cc. 79 to 82 1480 82 to 85 340 S6 to 90 186 90 to 95 70 95 to 100 hO 100 to 105 135 105 to 109 175 Residue 1465 Remaining in column 7 0
-TIME--Hours 7 2 1
Min. 30 20
35 45 55
It will be observed that the “hold up” of this column is relatively high. For the distillation of large volumes of liquid in the laboratory this is not a grave disadvantage, as the retained liquid can readily be run into the flask by rocking ,the coluinn a few times from side to side. A stillhpad of the same type, but containing only one or two bubbler units and no reflux condenser, is of value in the distillation of solvents containing dissolved material. Thus an alcoholic solution of a dye such as eosin, which on distillation in the ordinary way yields a highly colored distillate, gives an almost colorless distillate when the yapor passes through two traps. 3
THISJ O U R N A L , 16,349 (1923).
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