Solubility of Ethvlene in Water J
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EFFECTOFTEMPERATURE ANDPRESSURE E. J. BRADBURY, DOROTHY MCNULTY, R. L. SAVAGE', AND E. E. NICSWEENEY Battelle Memorial I n s t i t u t e , Columbus,Ohio
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NCREASED use of stringent conditions in chemicalprocessing to promote desired reactions has brought attendant problems. The use of pressure in reactions involving gases or vapors often brings the problem of the solubility of the gas or vapor in a solvent. Considerable work has been done on the solubility of certain of the permanent gases-Le., hydrogen and nitrogenin numerous solvents, but information on the solubility of gases such as ethylene is somewhat limited. Heretofore, published data on the solubility of ethylene under pressure have been confined to narrow ranges of temperature and pressure, and primarily to organic solvents. An attempt was made by Frolich et al. (1) to systematize the study of gases in various liquids under pressures ranging up to 200 atmospheres. Hydrogen, methane, and nitrogen were used in the majority of the solubility determinations using various alcohols, hydrocarbons, and water. TheRe experimenters concluded that if a gas does not form a compound with the solvent, it followR Henry's law over a wide pressure range. The validity of the assumption, however, is largely dependent upon the extent t o which the gas obeys the ideal gas law. Since ethylene normally does not behave as as an ideal gas, it appeared advisable to determine experimentally its solubility characteristics in water. This study includes four temperatures (35", 55", 75", and 100" C.) and pressures up to SO00 pounds per square inch.
PROCEDURE. After closing and re eatedly flushing (evacuating and subsequently filling with ettylene) the autoclave, the controller and Variaa were set to maintain the desired temperature. Ethylene was pressured into the system and the reactor was allowed to rock until repeated pressure readings, using the Crosbz r g e tester a t 15-minute intervals, indicated that equilibrium a been reached. The period of time necessary to attain equilibrium varied as the temperature and pressure were changed. When pressure readings indicated equilibrium conditions, the rocker was stopped and sufficient water was drawn from the bottom valve of the system to eliminate any li uid which might have been held in the hi h pressure tubing and Rad not come t o equilibrium. During &is initial withdrawal and the subsequent sampling, the system pressuqe was held constant (as shownon thepressure balance) by slowly admitting ethylene and manipulating the loading piston of the gage tester to maintain the equilibrium pressure.
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EXPERIMENTAL
APPARATUS.Apparatus similar to that used by Frolich et al. ( 1 ) and by Prutton and Savage (3) was employed in this study.
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The equilibrium pressure chamber shown in Figure 1E was a Miter rocking autoclave. The equilibrium temperature of this system was recorded and controlled by a Micromax controller, shown in Figure lH, coupled with a Variac variable transformer t o provide an even flow of heat. Measurements of the solution temperatures were made with a portable potentiometer ( I ) using a chromel-alumel thermocouple in a well in the pressure chamber. Rough pressure measurements were determined by a Bourdontype gage. The equilibrium pressures were read and maintained during sampling by using a Crosby gage tester, designated in Figure lF, which was connected into the system. This instrument had a maximum capacity of 25,000 pounds per square inch and a rated accuracy of &0.25%. The system was pressurized by using a mercury iston to compress ethylene in a second high pressure autoclave gee Figure 1D) and by using a high pressure needle valve to control the amount of ethylene admitted into the solubility chamber (E). The solubility apparatus was mounted a t an elevation which allowed the buret system shown in Figure 1G. used for measurine the gas and liquid dolumes, t o be conn&ted directly to the contrd valve a t the bottom of the solubilit chamber. Gas and liquid volumes were measured directly in d e calibrated gas buret (100ml. capacity with 0.1-ml. y d u a t i o n s ) maintained at 25" i 0.1" C. by circulating liquid rom a constant temperature bath. The water used in this study was boiled, distilled water drawn hot into the flushed and evacuated reactor. Commercial ethylene obtained from Ohio Chemical Co., listed as 99.570 pure, was used in this work. 1 Present
address, Case Institute of Technology, Cleveland, Ohio.
Figure 1. Apparatus f o r Determining Solubility of Ethylene in Water A. B. C. D. E. F. G. R. I.
Nitrogen cylinder Meroury reservoir Mercury p u m p Ethylene reaervoir Rocking autoclave Crosby gage tester Gas buret Micromax controller Potentiometer
Next, the manifold leading to the measuring buret was completely filled with mercury and then attached to the bottom control valve of the autoclave. A sample was then slowly drawn, keeping the ressure constant, until sufficient Sam le had been obtained to &I the buret. After enough time had ekpsed for the sample t o reach 25" C., the pressure within the buret was adjusted to atmospheric pressure and readings were obtained on the gas and water volumes. A barometer readin was always obtained immediate1 following these volume rea8ngs to be used in the calculation of t%e volumeof the desorbed ethylene, The partial pressure of the desorbed ethylene was calculated and the equilibrium volume of ethylene remaining in the water was calculated by applying the Bunsen absorption coefficient (6) for the observed buret temperature and the calculated ethylene partial pressure. No attempt was made t o determine whether any supersaturation existed, as a prolonged standing time was used to ensure thermal equilibrium of the sample. The weight of the total e t h y l e n d e s o r b e d ethylene plus 211
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DISCUSSION O F RESULTS OF ETHYLENE IN WATER^ TABLE I. SOLUBILITY
The results of this study, which are Temperature, 75' C . Temperature, 55' C. Temperature, 35" C. plotted in Figure 2, show the solubility Solubility b , Total Total Solubilityb, Total Solubilityb, of ethylene in grams per 100 grams of gram per 100 pressure, pressure, gram per 100 pressure, gram per 100 grams water atmospheres grams water atmospheres water for the four isotherms for ures-prams water atmospheres 8.3 0.043 4.75 0.03? 4.55 sures up t o 523 atmospheres. Astudy 0.084 15.7 8.8 0.063 7.9 0.099 0.093c of Figure 2 indicates that the solu28.6 20.4 0.111 14.8 0.178 0.197 55.8 35.0 0.209 28.9 0.302 0.307 bility of ethylene in water decreases 111.0 0.321C 35.6 0.339 55.4 0.455 69.0 0.460 112.0 0.467 121 .o with increasing temperature in the 0.460 122.0 0.475' 69.0 0.527 169.0 0.472 0.542 137.0 0.563 219.0 0.527 174.0 range studied below 25 atmospheres. 228.0 194.0 0.622 344.0 0.566 0.593 However, with increasing pressures an 310.0 220.0 0.660 404.0 0.628 0.607 0.621 23G.0 0.688 443.0 0.667 382.0 inversion is noted, above which the 440.0 0.637 265.0 4OO.O 0.700 0.695 solubility of ethylene shows a tendency 518.0 0.647 272.0 0.713 524.0 0.728 Temperature, over 100' C. to increase with increasing temperature 0.651 293.0 0.654 297.0 Solubilityb, Total in the range of conditions examined. 0.654 297.0 TemEerature, gram per 100 pressure. 0.665 318.0 C. grams water atmospheres A similar tendency for a gas solubility 0.668 349.0 27.7 392.0 104 0.160 0.696 in water to increase with increasing tem75.0 448.0 101 0.410 0.720 0.740 510.0 104 0.536 149.0 perature was found by Saddington and 256.0 106 0.632 102 0.678 362.0 Krase ( 4 ) , who investigated the solu102 0.707 433.0 bility of nitrogen in water from 50" to a Decimal placement in these tabulated results has been made consistent with the accuracy of the 240" C. under pressures of 100, 200, and original determinations. 300 atn1osPheres. This nitrogen-w'ater b Includes weight of ethylene dissolved in water a t the corrected partial pressure of ethylene. Dissolved ethylene determined by use of the Bunsen coefficlents (6). system showed a decreased c Equilibrium from decreasing pressures, beginning a t 2000 pounds per squsre inch gage for 35' C. isotherm. with increasing temperature to 80' C. and slowly increasing solubility above 150" C. Wiebe and Gaddy (6) reported a similar behavior for helium in water. This system was investigated from 0" to 75" C. for pressures u p to 1000 atmospheres. These investigators reported a minimum solubility around 25" C. and 100 atmospheres. It was shown by Frolich et al. ( 1 ) that gas solubilities tend to follow Henry's law over a wide pressure range if the gas obeys the ideal gas law. Inspection of the compressibility factors (2) for ethylene, Table 11, indicates considerable deviation from the ideal gas law a t the lower temperatures. The tabulation indicates, however, that ethylene tends t o approach the behavior of an ideal gas with increasing temperature. Therefore, calculations of the solubility of ethylene in water using Henry's law should be substantiated by experimental data. PRESSURE. ATMOSPHERES
Figure 2.
dissolved ethylene-was calculated using the compressibility factor modification of the ideal gas law. EXPERIMENTAL DATA
The experimentally determined solubility of ethylene in grams per 100 grams of water is presented in Table I. Solubilities are presented for 35", 55", 7 5 O , and 100' C., and for pressures ranging from 1 t o 523 atmospheres.
TABLE11. VARIATION OF COMPRESSIBILITY FACTORS WITH TEMPERATURES AND PRESSURES Temperature, O
c.
35 55 75 100
ACKNOWLEDGMENT
Effect of Temperature and Pressure on Solubility of Ethylene in Water
Pressure a t Which Maximum Deviation Occurs, Lb./Sq. In.
Compressibility Factor
1345 1720 1980 2240
0.39 0.48 0.60 0.66
This work was conducted at Battelle Memorial Institute under the sponsorship of the Standard Oil Co. (Indiana). The authors gratefully acknowledge the interest of W. H. Bahlke of the Standard Oil Co. (Indiana) during the investigation and his encouragement t o publish this work. C. R . Gray contributed greatly to the successful operation and maintenance of the high pressure equipment,. The authors are indebted to J. S. McNulty for his helpful criticism and suggeetions on this paper. LITERATURE CITED
(1) Frolich, P.K., Tauch, E. J., Hogan, J. J., and Peer, A. A . , IND. ENG.CHEM.,23, 548-50 (1931). (2) Hougen, 0. A., and M'atson, K. M . , "Chemical Process Principles Charts," Figure 103, Madison, Wis., The Democrat Printing Co., Copyright 1946,5th printing, 1948. (3) Prutton, C. F., and Savage, R. L., J. A m . Chem. SOC.,67, 1550-4 (1945). and Krase, N. W., Ibid., 56,353-61 (1934). (4) Saddington, A.W., (5) Seidell, A., "Solubility of Organic Compounds," 3rd ed., Vol. 2, pp. 94-5, New York, D.Van Nostrand Co., 1941. ( 6 ) Wiebe, R., and Gaddy, V. L., J. Am. Chem. SOC.,57, 847-51 (1935).
RECEIVED July 5, 1951.
