INDUSTRIAL AND ENGINEERING CHEMISTRY
1150
tilled extracts on a calculated unitage basis ( 1 microgram of carotene = 1.66 I.U. of vitamin A) are as potent for broilers as carotene in broccoli leaf meal and vitamin A feeding oil over a range of 500 to 3000 I.U. per pound, and as potent as vitamin A for egg production a t 3000 I.U. per pound (8). SUMMARY
A number of carotene and vitamin 9 concentrates were mixed with solid carriers. Loss of carotene or vitamin A during storage followed the over-all pattern of a first-order reaction. By plotting the logarithm of the carotene concentration against the storage time, the reaction rate constants and time for 50% loss were calculated. These constants provide a simple mathematical means for comparing a large number of storage experiments. The following factors play an important role in the stability of dry carotene or vitamin A mixtures:
TEMPERATURE. Decreasing storage temperature increased stability. CONCENTRATION. A 100-fold increase in concentration from 3000 to 300,000 I.U. per pound resulted in marked increase in stability. CARRIER. The effects of this factor were often obscured by other variables. Extracted soybean meal afforded highest stability; extracted broccoli leaf meal was excellent for carotene but poor for vitamin A; chick mash was inferior. VITAMINSOURCE. Effects of this factor were often overshadowed by the other environmental conditions. When a stable carrier was used, there were no significant differences between the vitamin A and carotene preparations a t the 3000 I.U. level. At 300,000 I.U., the molecularly distilled carotene from broccoli showed a marked increase in stability over corresponding
Vol. 43, No. 5
vitamin d or undistilled carotene preparations. The distilled carotene consists largely of neo-p-carotene isomers. The carotene thus prepared has been shown by Skoglund et al. (7-8) to have full biological potency for poultry. ACKNOWLEDGMEYT
The authors wish to express appreciation t o James Garvin and Samuel Krulick for analytical assistance in the course of this investigation. LITERATURE CITED
(1) Beadle, B. W., and Zsoheile, F. P.. J . Bid. Chem., 144, 21 (1942). (2) Biokoff, E., and Williams, K. T., IND.ENG. CHEM.,36, 320
(1944).
(3) Legault, R. R., Hendel, C. E., Talburt, W. F., and Rasmussen, L. B., Ibid., 41, 1447 (1949). (4) Mitchell, H. L., Schrenk, W. G., and King, H. H., Ibid., 41, 570 (1949). (5) Morgal, P. W., Byers, L. W., and Milier, E. J., Ibid., 35, 794 (1943). (6) Silker, R. E., private commnnication. (7) Skoglund, W.C., Tomhave, ,4.E., Kish, A. F., Kelley, E. G., and Wall, M. E., Del. ilgr. Expt. Sta., Bull. 268 (1947). (8) Skoglund, W. C., Tomhave, A. E., Mumford, C. W., Kelley, E.G.,and \&'all, M. E., Poultry Sci., 28, 298 (1949). (9) Wall, M. E., IND. ESG.CHEX., 41, 1465 (1949). (10) Wall, M. E., and Kelley, E. G., Anal. Chem., 20, 757 (1948). (11) Wall, M. E., and Kelley, E. G., IND.ENG. CHEM.,38, 215 (1946). (12)Wall, M. E., and Kelley, E. G., ISD.ENQ.CHEM.,ANAL.ED.,15, 18 (1943). (13) Ibid., 18, 198 (1946). (14) Zechmeister, L., Chem. Rev., 34, 267 (1944).
RECEIVED June 28, 1950.
L
4-
3
VAPOR PRESSURE, CRITICAL CONSTANTS, AND SATURATED VAPOR AND LIQUID DENSITIES WEBSTER B. I U Y AND F. fiIORGAN WARZEL T h e Ohio State University, Columbus, Ohio
In connection with
a study of the liquid-vapor equilibrium relations i n binary systems, the vapor pressure and orthobaric liquid and vapor densities of 2,2,4-trimethylpentane (iso-octane) were carefully measured. The vapor pressure measurements cover a temperature range from the normal boiling point to the critical point, whereas the liquid densities start at 50" C. and the vapor densities at 205' C. and extend to the critical point. The vapor pressure i n atmospheres at a temperature t o C. may be calculated with a high degree of accuracy by the equation: l o g p = 4.45144 - 1657.71/(t 4- 273.160), when supplemented with a deviation curve. A table of the vapor pressure and liquid and vapor densities at regular temperature intervals is given. These fundamental data will be of interest and practical value to those working with this industrially important chemical and fuel.
N CONNECTION with the study of the vapor-liquid equilibrium composition relations in binary hydrocarbon systems, the vapor pressure and orthobaric liquid and vapor densities of 2,2,4-trimethylpentane (iso-octane) were carefully measured. The vapor pressure measurements cover a temperature range
from the normal boiling point to the critical point, whereas the liquid densities start a t 50" C. and the vapor densities a t 205" C., and extend t o the critical point. About the time that this work was completed, Beattie and Edwards (2) published the results of a similar investigation of iso-octane, with the exception that the orthobaric vapor densities were not determined experimentally but were estimated. DESCRIPTION OF SAMPLE
The sample of iso-octane was made available through the courtesy of the Phillips Petroleum Co. It was stated to be 99.87 * 0.05 mole % ' iso-octane with a melting point of -107.398" C. Rossini and coworkers ( I ) give -107.365 * 0.013' C. for the freezing point of pure iso-octane. The snniple was used without further purification, except that possible traces of moisture were eliminat,ed by distilling it in the presence of phosphorus pentoxide into the degassing and loading train of the vapor pressure apparatus. APPARATUS AND PROCEDURE
The apparatus employed for the determination of the vapor pressure and density was very much the same as that previously described ( 3 , 4 ) , except for a few changes which were made to increase the sensitivity and accuracy of the measurements.
I N D U S T R I A L A N D E N G I N E E R.I N G C H E M I S T R Y
May 1951
. I I
For the temperature measurements, a latinum resistance thermometer and a Mueller bridge were use$ both of which had been calibrated at the National Bureau of Standards. The thermometer and the section of the experimental tube containing the sample were shielded from radiation by wrapping a iece of aluminum foil around the corresponding section of t f e high temperature vapor jacket. This shield could be shifted up or down a t will when it was desired to observe the phase condition of the sample. The experimental tube was constructed of precision bore borosilicate glass capillary tubing of approximately 2-mm. bore, and its volume per unit length was accurately determined from the weight of mercury required to fill the tube. For the pressure measurements a dead weight gage, which had been calibrated against the vapoi. pressure of pure carbon dioxide a t 0" C., was used. With the gage it was possible to detect changes in pressure of 0.0007 atmosphere (0.01 pound per square inch) over the pressure range investigated. The apparatus used for loading an air-free sample of the liquid into the experimental tube was essentially the same as that previously described (4,except that the vacuum-tight mercury seal was eliminated by sealing the experimental tube directly to the neck of the flask. The tube was then broken off a t the seal when the loading operation was completed. The weight of the sample of iso-octane in the tube was calculated from measurement of the volume and the density of the liquid a t 25' C. The value of the liquid density used in the calculation was 0.68781 gram per cubic centimeter (1). Vapor pressure and volume measurements were made a t the bubble point and a t the dew point when the volume of the tube was sufficiently large so that the dew point could be reached. From a knowledge of the weight of the sample and the volume readings, the saturated liquid vapor densities were calculated. I n order to measure the liquid densities with a high degree of accuracy] a relatively large volume of liquid sample, occupying about 105 mm. of the length of the ex erimental tube, was initially loaded into the tube. The liquig density and bubble point pressure were determined for this sample u p t o 215" C. Then a quantity of the Sam le was withdrawn leavin only 25 mm. of liquid in the tube. $he remainder of t6e liquif density measurements u p to the critical point as well as all of the vapor density measurements were made upon the smaller sample. Upon the completion of the measurements, the bubble and dew points of the sample were redetermined a t 215.00' C. in order to determine if thermal decomposition of the sample had occurred a t temperatures in the region of the critical point. It was found that the vapor pressure had increased by approximately 0.007 atmosphere (0.1 pound per square inch). It would appear, therefore, that there was very little decomposition of the sample. POUNDS PER SQUARE INCH o a5 0.1 1.5 20
-to -a5
I
l
25
l
0.1
0.2
03 G/CC
1151
0.4 .
0.5
0.6
0.7
DENSITY
Figure 2.
Densities of Saturated Liquid and Vapor of Iso-octane
This is in contrast with the work of Beattie and Edwards ( 2 ) ,who reported a very definite decomposition of their iso-octane during the course of their high temperature measurements. The normal boiling point was determined by means of the platinum resistance thermometer by the method of comparative measurements (7), using two ebulliometers and water as the reference liquid. RESULTS
The density a t 27.0" C., the standard boiling point, and the critical temperature, critical pressure, and critical density of isooctane are given in Table I and compared with the more recently published values of these properties. The literature value for the liquid density was obtained by extrapolating the values given by API Research Project 44 (1)a t 20" and 25' C. The critical point was determined by the disappearance-of-the-meniscus method. With the aid of the magnetic stirrer the critical temperature was located within 0.001 ' C. with the variation in pressure in separate determinations on the same sample amounting t o about 0.014 atmosphere (0.2 pound per square inch). The critical density was obtained b y extrapolating the mean density line to the'critical temperature.
- 500 STANDARD BOILING POIKT,AND CRITICAL TABLEI. DENSITY, CONSTANTS OF ISO-OCTANE Found
-400 'F
- 300
Li uid density at 27O C. St!. b.p., O C. Crit. temp., O C. Crit. pressure, atm. Crit. density, g./cc.
p w . - PUPI
Figure 1. Deviations of Observed Vapor Pressure from Standard Vapor Pressure Equation for Iso-octane
Diff.
Expt.-Lit.
0.6862 0.68616 ( 8 ) 0 99.239 99.238 (8) 0.001 270.676 * 0.01 271.15 ;I; 0.10 -0 47 2 ) 25.308 A 0.014 25.50 * 0.10 -0:19 t8) 0.243 0.001 0.237 0.006 (8) f
The vapor pressure was measured a t 16 temperatures ranging from near the standard boiling point t o the critical point. The results have been expressed by*meansof the equation or
-200
Lit.
log p (atm.) = 4.45144
- 1657.71/(t0 C. + 273.160)
log p (lb./sq. inch) = 5.61864
-
2983.88/(t0 F.
+ 459.688)
supplemented with the deviation curve shown in Figure 1. The constants in the equation were evaluated using the experimental values of the temperature and pressure a t the critical point and the standard boiling point. I n the construction of the deviation curve both the bubble
INDUSTRIAL AND ENGINEERING CHEMISTRY
1152
TABLE11. VAPOR PRESSURE, SATURATED LIQUID, AND VAPORDENSITIESOF ISO-OCTANE Density, G./CC. Temp.,
c.
50 60 70 80 90 99.239 120 140 160 180 190 200 205 210 215 220 225 230 235 250 245 250 255 260 263 266 269 270.676
Pressurea. Atm.
. . .. . .. . .. .. .. ..
0 1.736 2.783 4.253 67 .. 24 74 95 8,867 9.635 10.452 11.320 12.238 13.214 14.249 15.342 16.500 17.724 19.022 20.406 21.873 22.793 23.746 24.735 25.308
Liquid Found Lit. 0.6673 0.6676 (6) 0.6586 0.6496 0.6498'(6) 0.6408 0.6316 0.6303'(6) 0.6228 ..... 0.6027 ..,.. 0.5821 ..... 0.5602 ..... 00.5229 .5360 .. .. .. .. .. 0,5088 0 . 5 0 7 (8) 0,5011 ..... 0.4929 0.4847 ..... 0.4760 0.4667 0.466'(8) 0.4570 0.4462 0.4350 ..... 0.4222 ,.... 0.4084 0 . 4 0 7 (8) 0.3920 ..... 0.3720 ..... 0.3575 ..... 0.3400 ..... 0.31300 . 2 4 3
Vapor Found ..
Lit.
.. .. .. .. ..
..... ..... .....
....
.. .. .. ,. .. .....
.... ....
.....
.
I
.
.
0.0380 0.0418 00 .. 00 45 50 85 0.0555 0.0611 0.0676 0.0747 0.0828 0.0929 0.1049 0.1200 0.1321 0.1484 0.1749
..... 0.0479'(2)
.....
Vol. 43, No. 5
are in excellent agreement, while those of Beattie and Edwards are in good agreement only a t the higher temperatures. Using the equation and deviation curve, values of the vapor pressure in atmospheres a t even temperature intervals in degrees centigrade have been calculated and are given in Table 11. The saturated liquid and vapor densities are shown graphically in Figure 2 and listed in Table 11. The values reported in the table are smoothed values read from a large scale plot. Literature values are given for comparison. Smyth and Stoops (6) reported the density of liquid iso-octane up to 100" C. Their data agree well up to and including 80" C., but values a t 90" and 100" C. are at variance with those reported here. Beattie and Edwards ( 2 ) measured liquid densities, but estimated the vapor densities using the theorem of corresponding states and the density of n-heptane as a reference liquid. Their values for the liquid are in fair agreement, but the vapor densities a t the two comparable temperatures, 225" and 250" C., are approximately 14% smaller than those reported here.
0.0793'(0)
.....
..... .....
0 Calculated b means of equation log p &tm.) = 4.45144 - 1657.71/(t0 C . -t 273.160) and deviation ourve, Figure 1.
ACKNOWLEDGMENT
Grateful acknowledgment is made to the General Electric Co. for &anoia1 aid in the form of the Swope Fellowship to one of the authors (F.M.W.) and to t,he Phillips Petroleum Co. for furnishing the sample of iso-octane. LITERATURE CITED
point and dew point data were plotted and the curve was drawn midway between the two points. At the lower temperatures where the dew Doints were not obtained, the curve was located by assuming that the difference between the bubble and dew points was the same as a t higher temperatures. Because the difference was approximately constant and amounted to only 0.017 atmosphere, the error that might be introduced by such an assumption is relatively small. For the sake of comparison, the vapor pressure data reported by Smith ( 5 ) and by Beattie and Edwards ( d ) , expressed as a deviation from the smoothed values resulting from this investigation, are shown in Figure 1. As will be noted, the data of Smith
(1) Am. Petroleum Inst., "Selected Values of Properties of Hydrocarbons," API Research Project 44, National Bureau of Standards, Washington, D. C., Table 3a, June 30, 1945. ( 2 ) Beattie, J. A., and Edwards, D. G., J . Am. Chem. SOC.,70, 3382 (1948). ( 3 ) Kay, W. B.,
1x0. ENG.CHEM.,28, 1014 ( 1 9 3 6 ) . ~w.~B., ,J , Am. Chem. sot., 68, 1336 (1946). ( 5 ) Smith, E. R.. J. Research Natl. Bur. Standards. 24. 229 (1940). (6) Smyth, c. p., and Stoops, IV. N., J. Am. Chem.' S O C . , ' 1883 ~~, (4) K
(1928).
Swietoslawski, W'., "Ebulliometric Measurements," p. 57, New York, Reinhold Publishing Corp., 1945. (8) WilIingham, C. B., Taylor, W. J., Pignooco, J. M., and Rossini, F. D., J. Research N a t l . Bur. Standards, 35, 219 (1945). (7)
RECEIVED December 4, 1950.
artial Pressure of Acrylonitrile over Water J
C. E. FUNK, JR. Stamford Research Laboratories, American Cyanamid Co., Stamford, Conn. I n purifying acrylonitrile by distillation, losses are incurred through condenser vents, etc. Data on the partial pressure of acrylonitrileover water were required to permit the design of scrubbers to minimize these losses. Determinations were made at concentrations in which acrylonitrile is completely soluble in water, at both 25" and 40" C. Assuming Raoult's law to hold for the water, the acrylonitrile follows Henry's law over the range 0 to 3% acrylonitrile. The expressions: at 25' C., p = 14 c and at 40" C., p = 27 c , may be used for design purposes within this range. 0. = partial pressure of acrylonitrile, millimeters of mercury; c = concentration, weight per cent.) The data presented should be of importance, not only to those interested in reducing distillation losses, but also to any large scale user of acrylonitrile in an aqueous sys-
tem. The latter will be able to predict to what extent losses may occur from his solutions, and to take steps to conserve this valuable reagent when necessary.
T
HE currently preferred methods of manufacturing acrylonitrile ( 6 ) ,an important chemical in the synthetic elastomers industry, require that it be separated from a mixture of by-products before being suitable for use or for sale. Separation is normally by distillation. Sound engineering practice dictates that the concomitant losses through condenser vents, etc., be held to a minimum. The solubility of acrylonitrile in water, although low, is still sufficient to make the use of water scrubbers attractive for this purpose. The determination of the partial pressure of acrylonitrile over water was undertaken specifically to permit the design of such
