H. H. Reamer, R. H. Olds, B. H. Sage, and W. N. Lacey CALIFORNIA INSTITUTE OF TECHNOLOGY, PASADENA. CALIF.
F
EW investigations of the volumet'ric properties of ethane have been made a t pressures and temperatures above the ctritical state values. Beattie and co-workers reported two separate studies of ethane ( 1 , 2). The first covered the region of molal volumes greater than 3.0 cubic feet per pound mole; the second study treated the range of volume from 3.0 to 1.6 cubic feet per pound mole at temperatures ranging from 77" to 527' F. The upper limit of pressure in the experimental observations was about 5000 pounds per square inch. Sage, Webster, ftnd L ~ c e ypublished the results of an experimental study of ethane involving the determination of its volumetric behavior a t temperatures from 70' to 250" F. and at pressures up to 3500 pounds per square inch ('7). The agreement between the results of the two groups of investigators was not entirely satisfactory. Diswepancies of nearly 2% may be noted upon comparing their rewits. This difference is somewhat larger than the estimated experiInent'a'luncertainty reported in either case. In the course of studying the properties of ethane in binary mixtures of industrial importance ( 4 , 5 ) ,it was deemed advisable to reinvestigate the volumetric behavior of this substance over somewhat larger ranges of pressure and temperature than were encompassed in the previous study of pure ethane ( 7 ) . The results reported here extend to pressures of 10,000 pounds per square inch at seven uniformly spaced temperatures ranging from 100" to 460' F. The equipment and methods have been described (6) and were found to yield reliable data in the case of methane ( S ) , a substance whose volumetric behavior has been well established by many investigations. The instruments for measuring pressure, temperature, volume, and sample weight were carefully constructed and calibrated to ensure the determination of these quantities with an uncertainty of less than O.l%, of their absolute values. Impure ethane was obtained from Carbide h Carbon Chemicals Corporation. It was fractionated three times at atmospheric pressure with a reflux ratio of approximately 50 to 1 in a 4-foot, vacuum-jacketed column packed with glass rings. The overhead was condensed in vacuo at liquid air temperatures with continuous removal of an] noncondensable gases which might have accumulated during the condensation process. The purity of the material obtained in this way was verified by the nearly constant vapor pressure observed upon isothermally vaporizing a sample
VOLUMETRIC BEHAVIOR OF ETHANE
Figure 1. Effect of Pressure and Temperature on Conipressibility Factor o f Ethane
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The volumetric behavior of ethane wab investigated at pressures up to 10,000 pounds per square inch in the temperature interval between 100"and 460" F. The results of the experimental work are presented in tabular and graphical form. Comparisons are made with values obtained by others in recent investigations and with extrapolations based on Reattie-Bridgeman equation of state.
INDUSTRIAL AND ENGINEERING CHEMISTRY
October, 1944
FACTORS FOR ETHANE TABLEI. COMPRESSIBILITY Pressure, Lb./Sq. In. Abs. 0 200 400 600 800
1.000 1250
1:500
1,750 2,000 2,250 2,500 2,750 3,000 3,500 4,000 4,500 5,000 6.000 7,000 8,000 9,000 10,000
,-
100" F. 1.0000 0.9057 0.7921 0.6411 0.2935 0.2571 0.2955 0.3387 0.3820 0.4251 0.4676 0.5100 0.5520 0.5937 0.6756 0.7565 0.8362 0.9154 1.0714 1.2219 1.3688 1.5129 1.6530
16O'F. 1.0000 0.9328 0.8594 0.7784 0.6878 0.5881 0.4769 0.4391 0.4500 0.4753 0,5081 0.5426 0.5778 0.6134 0.6846 0.7563 0.8285 0.9004 1.0423 1.1793 1.3134 1.4454 1.5770
Compressibility 220'F. 280'F. 1.0000 1.0000 0.9508 0.9635 0.8999 0.9267 0.8476 0.8900 0.7939 0.8541 0.7394 0.8194 0.6753 0.7792 0,6242 0.7440 0.5939 0.7175 0.5845 0.7010 0.5915 0.6954 0.6083 0.6979 0.6314 0.7073 0.6579 0.7218 0.7158 0.7632 0,7771 0.8114 0.8398 0.8639 0.9030 0.9184 1.0287 1.0298 1.1548 1.1439 1.2799 1.2576 1.4016 1.3698 1.6211 1.4799
Factor-34O'F. 1.0000 0,9728 0.9461 0.9201 0.8950 0.8712 0,8440 0.8200 0.8010 0.7877 0.7807 0.7788 0.7827 0.7908 0.8162 0.8531 0,8955 0.9418 1.0387 1.1404 1.2431 1.3461 1.4488
4OOOF. 1.0000 0.9798 0.9602 0.9414 0.9236 0.9071 0.8884 0.8722 0.8591 0.8494 0.8438 0.8419 0.8441 0.8494 0.8683 0.8957 0.9296 0.9674 1.0518 1.1430 1.2365 1.3309 1.4250
460'F. 1.0000 0.9853 0.9713 0.9580 0.9455 0.9340 0.9210 0.9100 0.9006 0.8937 0.8898 0.8887 0.8903 0.8943 0.9099 0.9334 0.9619 0.9951 1.0658 1.1477 1.2332 1.3188 1.4050
TABLE11. SUPPLEMENTARY DATAIN REGIONOF RAPIDCURVATURN OF COMPRESSIBILITY ISOTHERMS 160' F. looo F.
--
--
Pressure Ib./sq. .;i abs. 700 750 775 800 820 840 860 880 900 920 940 960 980
Compressibility factor Z 0.5297 0.4443 0.3746 0.2935 0.2615 0,2532 0.2496 0.2485 0.2485 0.2493 0.2509 0.2527 0.2548
Pressure, Ib./sq. in.
Compressibility
1100 1200 1300 1400 1500 1600 1700 1800 1900
0.6380 0.4949 0.4638 0.4462 0.4391 0.4408 0.4463 0.4540 0.4638
abs.
faotor Z
957
as functions of pressure and temperature on 20 X 30 inch coordinate paper, and smooth curves were drawn through the points representing the experimental data. These curves served for interpolation of the experimental results to obtain the values a t the pressures recorded in Tables I and 11. The graphical operations described above are believed to have improved the consistency of the results without introducing significant uncertainties in the reported values with the possible exception of those for 460' F. a t the higher pressures. Figure 1 shows the isothermal relation between the compressibility factor and pressure a t the temperatures involved in the study. The experimentally determined points are shown, and only a t 460' F. and a t pressures greater than 5000 pounds per square inch is there any appreciable discrepancy between the experimentally determined points and the smooth curves. The results reported in Table I were obtained from the smooth curves because it was believed that they represented the most probable behavior of ethane. Table I11 presents a comparison of compressibility factors computed from the data of several investigations. The values obtained by the authors are everywhere larger than those obtained by Beattie and co-workers. The authors confirmed this discrepancy by recalibrating the volumetric apparatus and duplicating their initial results with another sample of ethane. The agreement between the present results of the authors and those obtained previously at this laboratory by Sage, Webster, and Lacey is not entirely satisfactory. The more recent data are believed t o be the more reliable because many refinements in the design and operation of apparatus for measurement of pressure, volume, and temperature have been developed since the initial investigation. It is estimated that this work was performed with sufficient care and precision in regard to the calibration of instruments, measurement of primary variables, and graphical smoothing and interpolating of results so that the reported results are representative of actuality with a n uncertainty of 0.2% a t pressures less than 5000 pounds per square inch and with an uncertainty increasing to 0.4% a t 10,000 pounds per square inch. As an illustration of the hazards associated with the use of an equation of state to extrapolate curves outside the region of the experimental data, Figure 2 compares the extrapolated and ob-
from bubble point to dew point a t 80" F. At this temperature the observed bubble-point and dew-point pressures were, respectively, 630.6 and 630.4 pounds per square inch absolute. For the determination of its volumetric behavior in the highpressure region, 47.713 grams of ethane were distilled into the equilibrium cell; a t each of the seven experimentally studied temperatures about eighteen volumetric observations were made a t pressures ranging from 1000 to 10,000 pounds per square inch. The region of lower pressures was studied with a sample consisting of 13.804 grams of ethane a t pressures varying from 300 to 3000 pounds per square inch. Where the two sets of observations yielded duplicate data, the discrepancy WJS less than 0.2%. The experimental data were expressed in terms of molal volumes, compressibility factors, and residual molal volumes. Compressibility factor Z represents the ratio of observed volume to the corresponding perfect gas volume of the substance and is equal to PVIRT. The residual molal volume is defined as the difference between the perfect gas molal volume and the observed molal volume of the substance a t any given pressure and temperature and may be expressed as (RTJP) V. All calculations involving molal quantities are based upon a value of 30.069 for the molecuI I I I I I I I I 0.81 4000 6000 8000 lar weight of pure ethane. 2000 The compressibility factor and the residual PRESSURE LB. PER SQ. IN molal volume have the useful property of reFigure 2. Comparison of Experimentally Observed Volumetric maining finite as the volume of system is indefiBehavior of Ethane with That Computed from Beattie-Bridgeman nitely expanded. These quantities were plotted 0 Equation of State
-
958
INDUSTRIAL AND ENGINEERING CHEMISTRY ~-
TABLE111. pressure,
(:OMPARISOS
F,--
OF
__
COMPRESSIBILITY FACTOR F'ALUES -1600 F
--
--220° Sage, 13eattie TYebster, Author? 1.acey u f al. Authors Lacey 0.7235 0.8251 0 8165 0 81YY 0.8782 0.2571 0.5872 0.5854 0.5881 0.7410 o.3387 0.4348 o.4371 0.4391 0.6248 0.4251 0 4658 0.4737 0.4753 0.5826 n.jion 0 . ~ 2 9 ~ . ... o 5426 0.6017 :Jon0 ... , , . . .. .... ... .... y8()0 F.-.3400 F,~~---. . 400' F . 7 Reat tie 13 ea ttie I3 ea trie et nl. .4uthars rt ml. .Authors et nl. Authors 5011 0.9047 0 9083 n 9284 'O 9330 n 9436 Y50i 0.8712 1000 0 8 1 : ~ 0.8194 o 8644 0 8993 0.0071 0.8134 0.8~00 i5oo o.,4m 0.7440 0 8641 0.8721 2000 0.6992 0.7010 0.787i 0.7835 0.8432 0.8495 0 7788 0.6955 0.6979 0 7766 0.8336 2500 0 8419 0.7903 0.719Y 0.7218 0 7877 0 8470 3000 0.8494 4000 0.8076 0.8114 0.8507 0.8531 0.8931 0.8957 8ono , . , . .., . n . 9 . x ~ 0.9418 0.9642 0.9675 Factor 0.7184 otitained hi- Heattie r f ( z l . a t 100' F. and 500 pounds. ---I000
Sage, Webster, In. A h . Lace, 500 0.7293" 1000 0.2529 1500 0.3303 2000 0.4132 2500 0.4958 Lb./Sq.
Sage, Vv-ehster.,
r___
'1
FOR ETHANE
F.--Beattie et al. 0.8704 0.7351 0.6208 0.5822 0.6055 0.6551 --460°
Authors 0.8739 0.7394 0.6242 0.5845 0.6094 0.6579
F.--.
Reattie et al.
Authors
0.9551 0.9229 0.8900 0.8858 0.8842 0.8931 0.9318 0.9924
0.9645 0.9340 o.9100 0.8937 0.8887 0.8942 0,9333 0.9951
Vol. 35, No. 10
sufficiently linear to permit extrapolationr. of as much as 50% beyond the range of the experimental data. This technique was employed in testing the consistency and smoothness of the data obtained in the investigation. ACKNOWLEDGMENT
Financial support from the American Petroleum 1nst.itute is acknowledged, this work having been a part of the activities of its Research Project 37. Assistance in the laboratory measurements and in the calculations was contributed by H. A. Taylor, E. Turner, and L. M. Reaney. NOMENCLATURE
served volumetric behavior of ethane. The extrapolated values were computed by means of the Heattie-Bridgeman equation of state, the empirical constants of the equation having been determined by Heattie, Hadlock, and Poffenberger ( I ) from their rxperimental measurements of the volumetric properties of ethane a t densities less than that of the critical state. Their calculations indicate that for densities less than the critical value, the equation represents the volumetric behavior of ethane with an average deviation of about 0.270 from the experimentally determined behavior. However, Figure 2 shows that for pressures of the order of 10,000 pounds per square inch the equation deviates from the actual volumetric behavior of ethane by nearly 20qJ. .% more reliable extrapolation of the volumetric data is accomplished graphically by plotting curves of constant volume on pressure us. temperature coordinates. Such curves are usually
R
=
O
T
= V =
V
x
=
Z =
P
+
PAPER44 in the series "Phase Equilibria in Hydrocarbon Syatems". l'revious articles have appeared during 1934-40 (inclusive), 1942, 1943, and in Janunrg, March, and April, 1944.
hes
RIOK. to the war,. the United States imported 300-403 million pounds of tapioca starch annually, mostly from the Ilutch East Indies. At present, relatively small amounts are being imported from Brazil and 'the Dominican Republic. Of the tapioca starch imported, it is estimated that about 50 million pounds are bought by users who are willing to pay a premium price over that of any other currently available starch. Although this amount is not necessarily essential according to the War Production Board's use of the term, it is an indication of the quantity of a substitute starch with tapioca-like properties, that might be expected to find a commercial market. Sufficient information was already a t hand to show that waxy or glutinous corn and glutinous sorghum starches are promising substitutes for tapioca starch. Waxy or glutinous rice, sorghum, millet, and corn have apparently been known for over a century in the Orient, where they have found special food and nonfood uses. Their cultivation has been successful because they are grown in isolation. Because the waxy or glutinous characteristic is recessive, glutinous cereals under conditions favoring cross pollination with nonglqtinous varieties tend to revert to thv nonglutinous type. The fracture
( O
LITERATUHE CITED (1) Beattie, Hadlock, and Poffenberger, J . Chem. Phys., 3, 93 (1935). ( 2 ) Beattie, Su, and Rimard, J . Am. Chem. SOC.,61, 926 (1939). ENG.CHEM.,35, 922 (1943). (3) Olds, Reamer, Sage, and Lacey, IND. (4) Reamer, Olds, Sage, and Lacey, Ibid., 35, 790 (1943). ( 5 ) Ibid., 36, 88 (1944). ( 6 ) Sage and Lacey, Trans. Am. Inst. Mining M e t . Engrs., 136, I I A (1940). (7) Sage, Webster, and Lacey, IND.ENG.CHEM.,29, 658 (1937).
Glutinous Co
Sorghum St
P = pressure, lb./sq. in. abs. universal gas constant, 10.732 (lb./sq. in.) (cu. ft./lb. mole) / R. temperature, R. F. 459.69) molal volume. cu. ft./lb. mole residual molal volume, cu. ft./lb. mole compressibility factor
MAJEL M. MACMASTERS AND G. E. HILBERT Northern Regional Research Laboratory,
U. S. Department of Agriculture, Peoria, Ill.
of glutinous cereal grains appears dull and opaque, while that of most common varieties is horny or vitreous. European investigators in the latter part of the last century first 'recognized t h a t starch in glutinous cereals is unique in that it stains red-brown with iodine rather than blue as does nonglutinous starch. Although the early chemical work on glutinous starch was crude and open t o criticism, the microscopic observations and those 011 swelling properties were accurate and have been repeatedly confirmed. The name "waxy" was applied t o corn in 1909 by Collins ( 7 ) who failed to recognize the fact that he was dealing with a glutinous variety. The term "waxy" is unfortunate and confusing since it refers to the physical appearance of the endosperm rather than to a chemical characteristic of the starch. "Glutinous", is more suitable because it dedefined as "sticky" or scribes the most obvious characteristic of the cooked flour or pasted starch from this type of cereal. Botanists and agronomists, recognizing the applicability of the term, have used the adjective glutinosus as the varietal designation in the Latin name of glutinous cereals ever since the first European discovery of glutinous rice from the Orient.
