Specific Gravity
OF
M.R. DEAN AND T. W.
Butadiene
LEGATSKI
Phillips Petroleum Company, Research Department, Bartlesville, O k l a .
The details of one of the pycnometer units are shown in Figure 1, where A is the pycnometer and B is the expansion chamber. C is a high-pressure stainless steel needle valve of such construction that when fully opened the pressure of the material in the chambers is held by a metal-to-metal seat instead of by valve packing, thus reducing the chance for errors due to leakage. Valve D is a brass body steel needle valve. Both pycnompter units were tested before use with hydrogen gas a t 27-kg. (600 pounds) pressure to assure absolute freedom from leaks. The two units were used simultaneously for check determinations. The thermometer used for the measurement of bath temperatures was graduated in 0.2" F. divisions. I t was checked before use against a Bureau of Standards calibrated mercury-in-glass thermometer. The torsion balance was checked before use for accuracy, sensitivity, stability, and equality of length of balance arms. I t was tested during use for reproducibility of weights by weighing an iron weight of about 9 kg. (20 pounds) a t various times during the day and on successive days. These tests indicated that a weight in the desired range-Le., 7.7 to 8.6 kg. (17 to 19 pounds)could be reproduced to 68 nig. (*0.0015 pound). The set of brass weights used were calibrated to 9 mg. (==0.0002pound). CALIBRATION OF PYcxonmmRs. After being carefully cleaned and dried, both internally and externally, the two pycnometer units were evacuated and the tare weights determined and checked by repeated weighings to the nearest 22 mg. (0.0005 pound). The volumes of the pycnometer chambers were then ascertained for temperatures of 4.44', 15.56', 26.67", 37.78', 48.89" and 60" C. (40°, 60°, SO", loo', 120°, and 140' F.), and with no internal pressure on the chambers, by weighing the waterfilled chambers a t the various temperatures and then making corrections for the changing density of water. Freshly boiled distilled water was used. The effect of internal pressure on pycnometer chamber volumes was ascertained for a temperature condition of 15.56' C. (60' F.) and pressures of 0,14, and 28 kg. per sq. cm. (0, 200, and 400 pounds per square inch) gage, respectively. The final results of the calibrations expressed in terms of volume for various conditions of temperature and internal pressure, were plotted to arrive a t a smooth relationship for use in the subsequent experiments. It is believed that the finally assigned volumes for the varigus con&tions were known to -0.2 cc. for the entire temperature range.
The specific gravities ( t / 6 0 ' F.) of 1,3-butadiene of 99.6 mole per cent purity were determined experimentally for the temperature range of 17.78 a to 60" C. (0 to 140 O F.), b y means of a specially constructed steel pycnometer of approximately 4500-cc. capacity and capable of withstanding the resultant vapor pressures without undergoing a permanent change in volume. The experimentally determined specific gravities were smoothed graphically and the experimental and smoothed values were compared to show the magnitude of the probable error in the smoothed data. The densities reported here were compared with densities found in the literature, and it was concluded that the final interpolated values determined in this work were probably correct to t 0 . 0 0 0 1 5 . The best value for the specific gravity (60°/600 F.) of pure 1,3-butadiene was estimated to b e 0.6274 * 0 . 0 0 0 1 5 .
-
T
HE current interest in 1,3-butadiene as a synthetic rubber raw material has created a need for more accurate and more complete information on the physical properties of this hydrocarbon. Landolt and Bornstein (3) give a table of liquid densities for 1,3butadiene for the temperature range -20" to 20' C. (-4' t o 68" FJ, Prevost ( 4 ) has reported a value a t 6.22" C. (21.2' F.), and Doss (1) lists a value a t 68" F. Because these data cover a range of temperature too small to meet most requirements, it seemed advisable to check previous values and extend the temperature range. This paper reports experimentally determined liquid specific gravities for 1,3-butadiene for the temperature range -17.78' to 20' C. (0" to 140" F.). METHOD
The procedure consisted essentially of comparing the determined weights of known volumes of butadiene under a number of temperature conditions and under pressures approximately equal to the vapor pressures with the weights of identical volumes of water a t 15.56' C. (60' F.) and a t atmospheric pressure. This procrdure has been employed previously by the writers to arrive a t similar data for propane, iso- and n-butane, the various butylenes, and a number of commercial roducts falling in the classification of liquefied petroleum gases &).
MEASUREMENT OF DENSITIES
COMPOSITION OF BUTADIENE USED
The 1,a-butadiene used in the investigation was obtained from the by-product butadiene plant of the Phillips Petroleum Company and was representative of the commercial product of the plant a t the time of sampling. The sample was inhibited against oxidation with 0.02 weight per cent of phenyl-betanaphthylamine. No solvent for the inhibitor was used. The quantity of added inhibitor was calculated to increase the specific gravity by no more than 0.00005 and its presence in the sample could, therefore, be ignored. The composition of the sample was ascertained by two different analytical techniques, both based upon the well-known chemical reaction between maleic anhydride and 1,3-butadiene. Analyses by the two techniques gave a purity of 99.6 mole per cent. The impurities present were believed to consist of 1-butene and the high- and low-boiling 2-butenes. APPARATUS
The apparatus consisted of two steel pycnometers of approximately 4500-cc. capacity fitted with expansion chambers to facilitate measurements a t temperatures below room temperature. A constant-temperature bath, a centrifugal pump for stirring the bath liquid, a torsion balance with calibrated weights, and a calibrated mercury-in-glass thermometer were also provided.
Figure I. M e t a l Pycnometer Unit
7
The p y c n o m e t e r u n i t s w e r e evacuated to an absolute pressure of less than 1 mm. of mercury. S u f f i c i e n t b u t a d i e n e was then charged into the units to fill A completely and B to half its capacity. Valve D was closed and C was left open. The units were then placed in a constant-temperature bath in such a manner that cell A was totally immersed in the bath liquid, but with no part of cell B immersed. Heat was applied externally to B by means of an electrically heated removable jacket to maintain its temperature, 6" to 9" C. (10" to 15" F.) higher than the bath temperature. The temperature of B was measured by a thermocouple on the outside surface of the cell a t a point below the liquid level in the cell. In a preliminary series of observations it was determined that approximately one hour was required to bring the temperature of the pycnometer and its charge of butadiene to the bath temperature. The pycnometers were consequently held in the constant temperature bath for 1.5 hours before being
8
Vol. 16, No. 1
INDUSTRIAL AND ENGINEERING CHEMISTRY
Table
1.
Summary of Experimentally Determined Specific Gravities of 1,3-Butadiene This Work (99.6 Mole Per Cent 1,a-Butadiene) TemperaPycnometer Literature, ture NO. Specific gravity Specific Gravity O F. (2/60° F.)O (t/60° F.)o 0
1 1 2 2
0.66671 0.66671 0.66675 0.66675
0.6659 (0)b
20
1 2
0.65414 0.65410
0.6640 (I)b
1
0.6409 ($)a
2 2
0.64097 0.64097 0.64070 0.64065
1 2
0.62732 0.62725
0.6273 ( 8 )b
1
0.61361 0.61371
....
1
1 1 2 2 2
0.59933 0.59944 0.59944 0.59932 0.59937 0.59947
....
1 2
0.58445 0.58422
1
0.56920 0,56890 0.56850 0,56870
0.6493 (4)
21.2 40
1
60
68 80
0.6213 (f) 2
100
120 140
1
2 2 Q
b
....
Specific gravity a t temperature t with reference to water a t 60' F. Interpolated values.
Pure 1,3-Butadiene (99.6 mole per cent 1,3-butadiene)
Temperature * F.
(t/60° F.)a
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 60 62 64 66 68 70
0.6668 0.6655 0.6643 0.6631 0.6618 0.6606 0.6593 0.6580 0.6667 0.6554 0.6541 0.6529 0.6515 0.6502 0.6489 0.6476 0.6463 0.6449 0.6436 0.6423 0.6409 0.6396 0.6382 0.6369 0,6356 0.6342 0.6328 0.6314 0,6300 0.6286 0.62731, 0.6259 0.6245 0.6232 0.6218 0.6205
RESULTS
The specific gravities of the butadiene were subsequently arrived a t by dividing the determined weights of the butadiene contained in A a t the various temperatures by the weight of the same volume of water when a t 60" F. and atmospheric pressure. The value for the density of water a t 60" F. used in these calculations was taken as 0.999017 gram per cc. All experimental results are presented in Table I together with comparable data from Doss ( I ) , Landolt and BKrnstein ( 8 ) , and Prevost ( 4 ) . An analysis of the method used showed that errors in determined gravities traceable to air buoyancy effects were of small magnitude. The buoyancy correction, calculated to be $0.00003, was not applied since it was too small in comparison with the experimental error to be significant. Within the experimental error it has been concluded that the determined specific gravity values can be accepted as equivalent to those taken in a vacuum. The specific gravities presented in Table I were plotted against temperature, and, from a smooth curve drawn through the points, the specific gravity values for the various intermediate temperatures were determined. These smoothed specific gravity values are presented in Table 11. Of the twenty-two different specific gravity measurements made a t temperatures of 48.89" C. (120" F.) and below, only those made a t 4.44' and 26.67' C. (40'
Specific Gravity
Temperature F. 72 74 76 78 80 82 84 86 88 90 92 94 96 98 100 102 104 106 108 110 112 114 116 118 120 122 124 126 128 130 132 134 136 138 140
Specific Gravity (t/60°
F.)"
0.6191 0.6177 0.6163 0.6149 0.6135 0.6121 0.6106 0,6091 0.6077 0,6063 0.6049 0,6038 0.6021 0.6007 0.5993 0.5978 0.5963 0,5949 0.5934 0.5919 0.5904 0.5889 0.5874 0.5859 0,5844 0,5828 0.5813 0.57Y8 0.5783 0.5767 0.5751 0.5736 0.5720 0.5704 0.5689
a Specific gravity a t temperature t with reference to water a t 60' F. b Probable specific gravity ( 6 O 0 / 6 O o F.) for pure 1,3-butadiene, arrived a t by applying corrections for assumed impurities, was estimated t o be
0.6274
removed for weighing. During that time, the bath temperature was held constant to 0.06" C. (*0.1' F.), Just before removing a pycnometer from the bath, C was closed. I m m e diately upon removal, the outside surface was dried and B was evacuated. D was then closed, C was opened, and the unit was weighed. I n those instances where the bath temperature was below the dew point temperature of the room air, the temperature of the pycnometer was raised to above room temperatures to avoid errors in weighing occasioned by condensation of moisture on the surface. I n such cases B served as a receiver for the liquid butadiene displaced from A .
II. Smoothed Specific Gravity Values for Commercially
Table
*
0.00015.
and 80" F.) in pycnometer unit 2 differed from the smoothed value by more than the predicted probable amount of 0.00018. I t was believed that the 0.4 mole per cent of impurities present in the sample consisted of 1-butene and the high- and low-boiling 2-butenes. By making certain assumptions, it was possible to predict the specific gravity a t 60" F. of pure 1,3-butadiene. Thus, if it were assumed that the three probable impurities were present in substantially equal proportions, the computed value of pure 1,Sbutadiene would be higher than the determined specific gravity of the test material by 0.00007. On adding the buoyancy correction of 0.00003 and subtracting the correction of 0.00005 for the amount of inhibitor present, the final value rounded off to 0.6274 was obtained for the specific gravity (60'/ 60' F.) of pure 1,3-butadiene. This was considered to be the most nearly correct value for pure 1,3-butadiene a t 60" F. ACKNOWLEDGMENT
The writers wish to acknowledge the helpful suggestions made by various members of the Phillips Petroleum Company Research Department in the development of the experimental method and, in particular, the assistance rendered by L. R. Fruit on all experimental measurements. Acknowledgment is also made both to Phillips Petroleum Company and to the B. F. Goodrich Company for the use of certain analytical techniques. LITERATURE CITED
(1) Doss, "Physical Constants of the Principal Hydrocarbons", 4th ed., p. 47, Texas Co., 1943. (2) Landolt, Hans, and Bornstein, Richard, "Physikalisch-Chemische Tabellen", 2nd Supplement, Part 1, p. 207, Berlin, Julius
Springer, 1931.
(3) Natural Gasoline Assoc. America, IND. ENQ.CHEM.,34, 1240-3 (1942). (4) Prevost, C., Compt. Rend., 186, 1209 (1928).
