Apparatus for
FIash- Dist iIlat ion
of Butadiene
A. P. HOBBS A N D M. R. RECTOR, The D o w Chemical Company, Midland, M i c h . sample to be flash-distilled is introduced into the cooled, evacuated ampoule. A tra is connected to C, evacuated, and closed off a t A . Cup H is &led with a dry ice bath and an excess of dry ice is maintained in the cup throughout the distillation. The trap is opened into the ampoule, the bath is removed from around it, and the trap is placed therein. Caution should be used to keep out all air or noncondensable gases a t dry ice bath temperature. Material that does not condense will prevent the distillation of the butadiene, since the distillation is carried out in a closed system. The dry ice bath in the cup maintains a reflux of butadiene separatingthe dimer and high-boiling materialfromthe butadiene and CS'S. If the cork is not in the tube, a heavier reflux is caused, requiring a longer time for distillation; with the cork in place about an hour is required. When the ampoule has come to room temperature, the trap is closed a t B and the sample is ready
A n apparatus for the flash-distillation of butadiene i s described and a diagram shown. Its efficiency has been determined with the aid of the Dorell weathering-test apparatus. Substantially complete removal of butadiene dimer i s accomplished without appreciable loss of Cij hydrocarbons.
IN
T H E analysis of butadiene, the determination of Cb hydrocarbons by a Dorell (Dow-Cottrell) weathering tester ( 2 ) gives high percentages if butadiene dimer is present. Preliminary to the determination it is usually necessary to carry out a flashdistillation of the sample t o remove dimer (vinyl cyclohexene) and high-boiling material. Previous methods of doing this have been defective in failing to give a complete removal of dimer without loss of the C i s which should remain in the volatile fractions. To remedy this difficulty, the apparatus described below has been developed. APPARATUS
The apparatus (Figure 1) consists of the following parts: F is an ampoule forming the kettle of the apparatus. A neck, G (15 cm. long), connects the kettle with cup D, having an inner cup, H . From H a closed tube, T , extends through the neck and just into the kettle. A cork, E , is inserted in the closed tube t o keep materials placed in the cup from entering the tube. C is a side arm through which the apparatus is filled and emptied. The apparatus is made of Pyrex t o lessen the danger of breakage by sudden changes of temperature. OPERATION
The ampoule is evacuated through C, closed off, and the apparatus cooled in a dry ice bath (dry ice in a mixture of chloroform and carbon tetrachloride, 50-50 by weight, 1 ) . The
hI
!
J
I
I
A_--__
j~ I
1
-A 1
n i
I '
I I
P
c lQ0
Figure 1.
Ampoule and Trap
80
90
Figure 2.
140
70
60
SO
Readings of Dorell Tube
4 0
VI.
30
20
IO
Degrees Centigrade of Variation
ANALYTICAL EDITION
February, 1946
Table Residual Volume
M1.
I.
Temperature Readings Temperature O
c.
Temperature Difference O
c.
... ...
10.0 9.0
-4.5 -4.7
-4 7
n o
7.0 6.0 5.0 4.0 3.0 2.5 2.0 1.5 1.0 0.8 0.6 0.4 0.2 0.1 Pump stops Dry point
-4.7 -4.7 -4.7 -4.7 -4.7 -4.7 -4.6 -4.6 -4.6 -4.6 -4.6 -4.6 -4.5 -4.5 -4.4 -4.3
0.0 0.0 0.0 0.0
x n
0.0 0.0 0.1 0.1 0.1 0.1 0.1 0.1 0.2 0.2 0.3 0.4
for C6 determination or any other determination requiring a flash-distilled sample. DISCUSSION
I n order to test the efficiency of the apparatus, butadiene samples have been submitted to flash-distillation and then analyzed in the Dorell weathering-test apparatus. For the determination of CShydrocarbons, 40 ml. of distilled sample are placed in the boiler of the Dorell and 30 ml. are allowed to “weather away” before the heat is turned on and temperature readings are taken. These readings are taken a t 10.0, 9.0, 8.0, 7.0, 6.0, 5.0, 4.0, 3.0, 2.5, 2.0, 1.5, 1.0, 0.8, 0.6, 0.4, 0.2, and 0.1 ml., and when the pump stops and the boiler becomes dry. -4typical record is given in Table I. The differences starting at 8.0 ml. between the initial and succeeding temperatures observed are plotted. This curve is compared with curves obtained by plotting the temperature differences of butadiene using known amounts of isopentane run in the same way. Temperature readings a t 10.0 and 9.0 ml. are disregarded because the thermometer is still in the liquid phase only and will not give a true boiling point.
141
Figure 2 (upper) shows the curves produced by center-cut butadiene with varying amounts of butadiene dimer added. Curve F is made by plotting temperature differences of centercut butadiene. It gives almost a straight line, as would be expected. There are significant differences between the curves obtained with varying amounts of dimer. Figure 2 (center) shows butadiene with different amounts of isopentane. In Figure 2 (lower) are plotted curves obtained with the following mixtures:
A . Butadiene with 0.25% dimer and 0.25570 isopentane, not
flash-distilled. B. Butadiene with 0.25% dimer, not flash-distilled. C. Butadiene with 0.?5”/, isopentane, not flash-distilled. D. Curve after flash-distillation of A. E. Curve after flash-distillation of B . F . Curve after flash-distillation of C. G. Curve of center-cut butadiene.
Curve D shons the almost complete removal of dimer and the retention of C i s with the butadiene. Curve E is representative of the removal of dimer with no C5’s present. The amount of dimer left after flash-distillation with this apparatus espressed as C i s would be approximately O.OSCI, which is very small. Curve F shows the effect of the flash-distillation on CE’S. Although the flash-distillation apparatus described WRS designed specifically for removing dimer and other high-boiling materials from butadiene containing Cb’s, it is believed to offer possibilities for other separations. Reflux ratios might be changed by the use of different cooling media or by allowing tube T to be filled with coolant. LITERATURE CITED (1) American Institute of Physics, “Temperature”, p. 205, New York, Reinhold Publishing Corp., 1941. ( 2 ) Podbielniak, Inc., 8312 South Chicago Ave., Chicago 17, Ill.,
Circ. 28, “Dorell Weathering Test Apparatus”.
PREBEWTED before the Division of Analytical and hIicro Chemistry at the SOCIETY, September, 1945. Meeting-in-Print of the AMERICAN CHEMICAL
Simple Hydrostatic Gravitometer For Rapid Determination of the Specific Gravity of Liquids WILLIAM SEAMAN A N D J. J. HUGONET Calco Chemical Division, American Cyanamid Company, Bound Brook, A n apparatus is described for the rapid, precise determination of the specific gravity of selected liquids. Its use is based upon the principle that the change in height of two columns of liquids exposed to the same change in vacuum (or pressure) is inversely proportional to the specific gravity. W h e n one liquid i s of known specific gravity, the specific gravity of the other may b e calculated. The apparatus is simple, easily constructed, and inexpensive, and is particularly suitable for determining the specific gravity of a large number of similar samples in control testing. The standard deviation of a single value from the value obtained b y pycnometer is +I.4 x 10-4 specific gravity unit. The speed with which the determination may b e made makes it practical to improve this agreement b y calculating the average of a number of determinations on a single sample.
I
T IS a well-known principle of hydrostatics that the heights to which two columns of liquids of different specific gravities will rise when exposed to the same vacuum are inversely proportional to their specific gravities. This principle has been applied to the measurement of specific gravities. Ciochina (1) described an apparatus for this purpose which consisted of two U-tubes placed side by side, with a millimeter scale between two of the a r m s - o n e from each U-tube-and with
N. J.
those arms joined. By means of a system of stopcocks water is placed in one U-tube and the sample in the other. The levels are read on the millimeter scale, pressure or vacuum is applied through the joined arms, and the levels are read again. From the change in levels and the known specific gravity of the standard liquid (water), the specific gravity of the liquid to be measured may be calculated by a simple inverse proportion. Accuracy t o within a few units in the fourth decimal place was reported, but the authors were not able to confirm this. Some of the difficulty may have been caused by the stopcocks which are part of this apparatus. Another disadvantage of this apparatus is that it is necessary (according to Ciorhina) to use a vernier in order to get the precision reported. Another apparatus based on the same hydrostatic principle has been proposed by Davidson and co-workers (2, 3 ) . The liquid under examination is placed in a Z-tube, so that its height is fixed, and the standard liquid is placed in an L-tube manometer. By proper graduation of a scale fixed to the L-tube, the specific gravity of the liquid in the Z-tube may be read. A precision of from 0.1 to 0.2% is claimed (in other words the specific gravities are readable only to the third decimal place). This apparatus is constructed for use with small volumes of liquid. Frivold ( 5 ) described an apparatus, which was claimed to be precise to * 10-7, but i t is too complicated for rapid routine use. This paper describes an apparatus which is based on the same hydrostatic principle as those just mentioned, but has certain ad-
