The LABORATORY BUBBLING COLUMN in the TEACHING of FRACTIONAL DISTILLATION GREGG M. EVANS Yankton College. Yankton, South Dakota
T N SUCH descriptions or diamams of commercial dis-
1 tilling appara&s as are given in organic chemistry texts it 1s generally indicated that the composition
TABLE I
somob
Original mixture Distillate Upper bulb Middle bulb LOW= bulb Flask
R@. Ind.. 25'
1.3376 1.3272 1.3322 1.3410 1.3406 1.3347
% CHIOH* 19
100 92 83 39 8
of the mixture changes progressively from residue to distillate and that liauids of intermediate com~ositions may be drawn offfrom appropriate plates of the column. * I C T . . " ". This is difficult to show convincingly to an elementary class because of lack of time, and insufficientprepara- was then raised to a reflux ratio of about six to one, tion of the students for the theory of fractional distilla- and a few drops of distillate were collected. This and samples from the three tion. It seemed to the writer sample bulbs, the flask, and that the laboratory bubthe original mixture were analyzed by means of an bling column1 offered a possible solution of this Abb6 refractometer. The diiculty. One was acresults are shown in Table cordingly constructed hav1. ing five of the bulbs which The compositions of the correspond to the plates of samples from t h e two a commercial column. To lower hulbs were, for this three of these were sealed article, confirmed by means short side-tubes. These of specific g r a v i t y tests, could be closed by means but this would not be neco f r u b b e r tubing and essary for a lecture demonpinchcocks and used for stration. While t h e ret h e removal of samples fractometer offers the most from.the hulbs. convenient means of analyOne procedure for demonsis, it is possible by startstrating the progressive ing with a sufficientlylarge change in composition was quantity of original mixas follows. A mixture of ture, to collect simultaneone p a r t methanol and ously samples of such size three parts water by volthat they may be analyzed ume was placed in a roundby rough specific gravity bottomed flask attached to methods. Weighing in a the apparatus as shown in 10-ml. graduate cylinder is Figure 1. The reflux consufficiently accurate to be denser at the top was set convincing. sufficiently low for total An instructive variation reflw and boiling was conconsists in removing the tinued for about five mininternal reflw condenser, utes after all the bulbs had the diierence in the comfilled. The reflux condenser position of the resulting distillate showing the effect of fractional condensation. ' AND RAFIRS, Ind. Eng. Chem., 18, 1092 (1926); Another possibility is the Syn. Org. 'Chmzicols, 3, No. 1 demonstration of continu(Oct., 1929); ibid., 4, No. 5 ous fractionation. This is (July. 1931). ~~
best shown by sealing a side-tube onto the bulb of the flask for continuous discharge of the residue. The feed may be siphoned into one of the side-tubes through a simple sight drop device. In one experiment the column was insulated with "balsam wool" and some residues from a class experiment, containing about 17% methanol, were fed continuously into the lower bulb. These furnished continuous residue and distillate containing 3% and 97% methanol, respectively. A tube to permit the insertion of a thermometer may be sealed into each bulb so that the progressive change in boiling point is demon-
strated. In the first experiment described the uncorrected temperatures were 90.8" in the flask and 62.5' a t the top of the column. For details of the construction one of the original articles should be consulted, but it may be said here that the apparatus is not so difficult to construct as it may seem. That shown in the figure was constructed by the writer who is by no means an experienced glass worker. 25 mm. pyrex test-tubes were used for the bulbs, and standard pyrex tubing for the remainder. A commercial blast lamp requiring only water-gas and air was used throughout.
