I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
362 T.4BLE
Iv. EVALUATION OF k AND S
FOR
V, = volume o f gas at STP adsorbed at saturation HYDROCARBON V, (liq.) =: volume of liquid adsorbate a t boiling point.
A4.DSoRPTIoN D A T A
In
5
= -k/Rs where z = P/Po, B = V / V m
k
Vol. 46, No. 2
s 1.8
1.6 1.3 1.3 1.6
these conditions, and the value of 8 at saturation is of the order of 10, demanding agreement over a wide range of 8. The above equation in the form In z = - X ’eq where 8 is V / V , as above, and k and s are constants, has been applied to the authors’ data, and k and s have been evaluated for the different adsorbates. The results are listed in Table IV. A close fit to the experimental data was obtained up to 0.975 relative pressure. Hill (2) indicated that values of k S 4 should be of the right order of magnitude; this waq not true in this instance. No significance of the values of k and s obtained is suggested. ACKBOW‘LEDGMENT
The authors wish to acknowledge the valuable experimental assistance given by H. J. Streich and Anthony Rock, of the Floridin Co L. B. Christie, also of this laboratory, prepared the curves. The authors are also grateful to P. H. Emmett of Mellon Institute for his review of the early phases of this study. N0;VENCLATURE
Vm = volume
of gas a t S T P adsorbed at monolayer coverage V, (corr.) = monolayer volume corrected to give coverage equal to nitrogen
Corresponds to pore volume Vmraalar = volume of I mole of liquid a t its boiling point and 760 mm. mercury pressure P = equilibrium gas pressure PO = pressure a t saturation, corresponding t o vapor pressure of adsorbate at temperature employed DL = density of adsorbate a t boiling point X = molecular weight = geometrical pore radius. A 2v ( h . 9 R,, s.A . A = Avogadro’s number 0 = V/V,, number of molecular layers a t any P r = P/Po F = surface concentration k , s, a = constants S.A. = surface area LITERATURE CITED
(1) Egloff, G., “Physical Constants of Hydrocarbons,” Vol. I, New York, Reinhold Publishing Corp., 1939. (2) Frankenburg, W. G.. Komarewaky, V. I., and Rideal, E. K.,
eds., “‘Advances in Catalysis and Related Subjects,” Vol. IV, New York, Academic Press. Inc., 1952. (3) Granquist, W. T., ISD. ENG.CHEM..42, 2572 (1950). (4) Granquist, W. T., and Amero, R. C., J. Am. C h e m Soc., 70, 3265 (1948). (5) Harris, B. L., and Emmett. P. H., J. Phys. R. CoZZoid Chem., 53, 811 (1949). (6) Hodgman, C . D., ed.. “Handbook of Chemistry and Physics.” 31st ed., Cleveland, Ohio, Chemical Rubber Publishing Co.. 1949. (7) Joyner. L. G., and Emmett, P. E.,J. Am. Chern. Soc.. 70,2353 (1948). (8) Kraemer, E. D., ed., “ddvances in Colloid Science,” Vol. I, New York, Interscience Publishers, 1942. ,and Morrison, J. L., Can. J , Reseaich, 27B,205 (1949). (10) Bpangler, C. V.,Bodle, W. W., and Granquist, W. T., Oil Gas J., 48, 170 (April 20, 1950). RWBIVEDfor review August 13, 1953.
ACCEPTED December 10, 1953.
ressibility Factors ne Mixtures i GEORGE BI. \TATSOAT, A . B. STEVENS, R . B. E V A 3 3 111, AND DOS HODGES, JR.] Agricultural and Mechanical College of Texas, College Station, Tex.
ITROGEN is an important and common component of industrial gaseous mixtures. Adequate tabulations of experimental data on the pressure-volume-temperature behavior of pure nitrogen (1, 6. 8, 16) and of pure propane (4,12, 16, 16) are available in the literature. Literature references for fluid mixtures with propane as one of the components are given by Sage (14), but no references are found for nitrogen-propane mixtures. Xtrogen-methane mixtures have been investigated by Keyes and Burks (11), and the Beattie-Bridgeman equation of state has been tested for mixtures from these measurements ( 2 ) . Nitrogen-ethane data have been presented by Reamer et al. (19). Pressure-volume-temperature relations for nitrogen-ethylene mixtures have been reported by Hagenbach and Comings (9). To date, the authors are unaware of any previous experimental measurements on nitrogen-propane mixtures. The present investigation is the first of a series of pressurevolume-temperature studies on nitrogen-hydrocarbon mixtures contemplated in this laboratory. 1
Preeent address, The Texas Co , Bellaiie, Tex.
IIATERI h L S
The 99.9901, C.P. grade propane used was obtained from the Mathieson Co., East Rutherford, K.J. The nitrogen was acquired from the Linde Air Products Co., East Chicago, Ind., and it was, according to the manufacturer’s specification, 99.99% pure. The purity of these gases Tyas checked by means of the mass spectrometer and found to be pure within the experimental uncertainty of the analytical procedure. APP4RATUS AND PROCEDURE
A modified Burnett system ( 7 , 1 7 ) was used in this investigation. Briefly the apparatus consists of an Amagat-type dcadweight pressure gage, expansion bomb and diaphragm, thermostat, injection system, and sampling system. The dead-weight gage is similar to that described by I l e p s (10). The piston-cylinder combination for the gage was built by the Pratt and Whitney Co., WePt Hartford, Conn., and meets the specifications enumerated by Beattie ( 3 ) . The gage constant was determined by calibrations against the vapor pressure of liquid carbon dioxide a t 0’ C. This method is described by Bridgeman (6). The value of the vapor pressure of liquid car-
INDUSTRIAL AND ENGINEERING CHEMISTRY
February 1954
1.20
-
1.10.
I-
a \
0. I1
N
P
EXPERIMENTAL DATA DATA. SAQE (L LACEY (I5'
0 40
0 30
1000
3000
2000
4000
5000
d 60C
PRESSURE, PSlA Figure 1. Compressibility Factors for Propane-Ni trogen Mixtures at 259.08' F.
bon dioxide a t 0" C. was taken to be 505.56 pounds per square inch absolute, a value determined by Bridgeman (6). The results of three independent calibrations agreed within 0.027,. The expansion bomb ( 7 , 17) consists of tn-o interconnected chambers, each of x-hich may be isolated from the other and from the remainder of the system by one middle and two end valves. As described ( 7 , l 7 ) , the Burnett method of determining compressibility factors includes a succession of isothermal expansions of a given quantity of gas from a volume, V (of one chamber), to some greater volume, V+V' (of both chambers). The method does not require a knowledge of the exact volume of either chamber or of both chambers as a whole, but the volume ratio, V/V+V', must be known precisely. This ratio was determined from the results of four independent series of expansions a t each temperature with hydrogen by a graphical method of extrapolation to zero pressure as recommended by Burnett. The uncertainty in the volume ratio is estimated to be within 0.02%. A diaphragm mechanism serves as a flexible interface between the deadweight gage or hydraulic system and the gas system within the expansion bomb, and as an indicator of balance between the hydraulic pressure and the gas pressure. The diaphragm was of the type used by Burnett ( 7 ) and similar to a type described by Sage and coworkers (18). With this arrangement, pressure balance between the hydraulic and gas system can be ascertained within &1 gram on the dead-weight gage pan, corresponding to a pressure uncertainty of f0.01% for pressures higher than 200 pounds per square inch absolute.
363
For the determination of an isotherm the gas mixture was injected into one chamber of the expansion bomb, which was held a t constant temperature. ilfter the pressure was recorded at thermal equilibrium, the gas mixture was allowed to expand into the second chamber and the pressure was again recorded, The second chamber Was evacuated and the procedure R as repeated until the pressure measurements lost significance. Gas samples were collected periodically and analyzed by means of the mass spectrometer. The analyses of the samples could be reproduced within 1.0 mole yo for the 259.08" F. isotherm and within *0.1 mole % for the 300.00° F. isotherm, The reason for the difference in precision in the analyses is that the data for the 259.08" F. isotherm were obtained 1 year previous to those for the 300.00° F. isotherm and two different mass spectrometers were used. To make certain t h a t the mixture remained in the gas phase, samples
FOR PROPAXE-NITROGEN MIXTURES TABLE I. COMPRESSIBILITY FACTORS
99.9% Nitrogen
Pressure, Ib./sq. inch abs.
44.4% Propane Presswe, lb./sq. 2, inch abs. Pu/RT
2 Pv/kT
51.6% Propane
Pressure, lb./sq. inch abs.
Z,
Pu/RT
A t 259.08° F. 3622 2279 1472 962.0 636.1 417.8 277.0 183.5 121.7 80.8
4016 2372 1573 1070 723.0 489.2 329.5 220.7 148.0 98.9
z,
Pv/RT
6010 2737 1770 1253 897.6 634.5 440.9 302.8 205.8 139.2
6110 3502 2237 1486 999.2 674.6 454.7 306.1 205.5 137.8 92.2
3375 2070 1391 95%5 660.7 449.1 303.1 202.9 136.3
At 300.00° F. 71.3% Propane Pressure, Ib./sq. z, inch abs. Pv/RT
31 9% Piopane
Pressure, lb./sq. inch ebs.
1.024 0.910 0.908 0.929 0.944 0.961 0.974 0.981 0.990 0.996
...
0.997
...
78.9% Propane
0.940 0.868 0.877 0.909 0.943 0.964 0.978 0.985 0.988
Pressure, lb./sq. inch abs.
Pu/RT
3792 1792 1252 924.6 664.9 472.9 328.5 222.4 149.6
0,943 0.670 0.704 0,782 0.847 0,906 0.947 0,964 0.976
.
Z,
83.4% Propane
Pressure, lb./sq. inch abs.
z,
Pv/RT
6038 2359 1543 1136 840.3 610.6 433,O 301,2 207.3 140,9
...
. I .
::I 1.301
1.00
0.40
0.30
i O O I
~
I
PROPANE
1
I
1
INDUSTRIAL AND ENGINEERING CHEMISTRY
364 T4BIE
11.
SMOOTHED T - k L l E S O F COAIPRESSIBI1,ITY
graphically for pure nitrogen as \vel1 as values obtained by interpolation from Sage and Lacey's tables (15). Eyperimental values for mixtures of 44.4, 51.6, and 78.9% propane are also given. At 300.00' F. esperimental measurements arc presented for 31.9, 71.3, and 83.4% propane. For convenience, Tahlr I1 is included with smoothed values.
FACTOR^
Pres~.
sure,
":;Ahs. ?. 250 ,500 750 1000 1500 2000 2300 3000 4000 5000 6000
% Propane a t 259.080 F.
% Propane a t 300.00° F.
44.4
51.6
78.9
31.9
71.2
83.4
0,981 0.962 0.946 0.932 0.907 0.900 0.918 0.951 1.022
0.976 0.954 0.930 0.903 0.870 0,864 0.883 0.916
...
...
0.987 0.975 0.967 0,960 0.953 0.955 0.963 0.980 1.034 1 101 1 167
0 . 954 0.911 0.863 0.817 0.752 0.732 0.747 0.788 0,897 1,000
0.936 0.862 0.785 0.719 0.628
0.991
0,926 0,897 0.822 0.760 0,682 0.681 0.748 0.823 0.973
1
.
.
...
...
...
1,114
Vol. 46, No. 2
ACKIVOW LEDGM EhT
The gas samples used in the 259.08" F. isotherm were analyded by F. A. Tatum of the Electrical Engineering Department of the college. Those used in the 300.00° F. isotherm were anal\zed by E, A. Hinkle, Monsanto Chemical Co. This assistance is gratefully acknowledged.
0.615
0.687 0.716 0.838 0.962 1.083
LITER4TURE CITED
fox analysis were taken after the first and last elrpansions. The composition %asconsistent within the error of the analytical procedure. The temperature was contiolled within 0.03" F. and was measured with a platinum resistance thermometer, nhich had been calibrated by the Sational Bureau of Standards, in conjunction iyith a Mueller bridge. The volume was measured indirectly by determination of the volume iatio of the expansion chambers, which had been determined previously. Because of the nature of the calculation of compressibility factors by the Burnett method, requiring two extrapolations to zero pressure, the over-all results are believed to be accurate to 3% for the 259.08' F. isotherm and 2% for the 300.0O0F isotherm. I t is hoped that they are more piecise, but because of the practical impossibility of reproducing gaseous mixture compo.;itions, the results could not be expeiimentally rechecked. For pure nitrogen the experimental results vxre compared with interpolated values from the tabulation by Sage and Lacey (15);the agreement was from within 0.1% for the lower pressures to 1% at the higher pressures. Cross plots indicated that the data are appai ently internally consistent to n ithin i 1 %.
(1) Bartlett, E. P., Cupples. H. I,.. and Tremearne, T. H., . I . A m Chem. Soc., 50, 1275 (1928). (2) Beattie, J. A , Ibid., 51, 19 (1929). (3) Beattie, J. A.. Proc. Am. Acad. A r t s Sei., 69, 389 (1934). (4) Beattie, J. A , Kay, W.C., and Kaminsky, 3 . . ,J, Am. C'hein. Soc., 59, 1589 (19371.
(5) Benedict, Ill., Ibid., 59, 2224 (1937). (6) Bridgeman, 0. C., Ihid., 49, 1174 (1927). (7) Burnett, E. S., Appl. Mechanics, 3 (a), 137 (1936). (8) Deming, W.I?., and Deniing, I,.S.,Pkys. Rea., 45, 109 (1934). (9) Hagenbach, TV, P., and C'omings. E. W., 1x11.Esc. CHEJI.,45. 606 (1953). (10) Keyes, F. G., P m .Am. A c d . A ~ t Sei., s 68, 505 (1933). (11) lieyes, F. G., and Tiuiks, 13. Q., %J. ,4m.Chem. Soc., 50, 1100 (1928). (12) Reamer, H. H., Sage, E. XI.. and Laccy, 15'. S . , 1x11. I h o . CHEZI.,41, 482 (1949). (13) Reamer, H. I%.,Selleck, F. T., Rage, B. FI., and Lacey, I T r , S . . Ibid., 44, 19s (1952). (14) Sage, B. H., Ibid.. 42, 631 (1950). (15) Sage, B. H., and I,ncey, W.E., "3Ionograph on X.P.l. Research Projert 3 7 . 'I'heniiodynaniic Properties of the Lighter I-Iyrlrocarbons and Xitrogrn," 1st ed., Ken, York, American Petroleum Institute, 1950. (IC;) Page, B. H., Schaafsnia, .J. G., and h c e y , 13'. X . , 1x1).F k c + . CHEX, 26, 1218 (1934). (17) Schneider, W. G., Can. J . Reamrcli, 27B,363 (1949). (18) Yelleck, F. T., Carmichael. L.'I?., and Sage, 13. H., lsn. I h o . CHEM..44, 2219 (1952).
EXPERI>lENTAI, DATA
The experimental data are presented in Figures 1 and 2 by plots of the compressibility factor of the mixture against pressure at different compositions. The data are also given in Table I. For the 259.08' F. isotherm experimental values are presented
RECEIVED for review ilpril 28, 1953. ACCEPTED September 2 5 , 1953. Presented in part before t h e Seventh Southrvest Regional Meeting, AicexrC A S CHEXICAL BOCIETU, Ailstin, Tex., December 1951.
ielectric onstants ethylsilicones J
8.B. YOUNG AND CR4RLES E. DICKERJIAN Southern Illinois University, Curbondale, I l l . LTHOUGH the polysiloxanes constitute a relatively ncw family of synthetic compounds, research into the chemical characteristics of thwe polymers has already produced a considerable body of published literature. Liquid dimethylpolysiloxanes have received much of the a b tention directed toward the polysiloxane group. These materials are distinguished by quadrivalent silicon atoms, each of which is linked to two methyl groups and two oxygen atoms. The oxygen-silicon linkages form a chain molecule analogous to the molecule formed by the carbon-carbon linkages of the hydrocarbon oils. This investigation was undertaken as part of a joint research agreement between the Physics Department of Southern Illinois
University and the Sanganio Electric Go., Capacitor Divieion, a t Ordill, Ill. Its aim was to obtain information conccrnirig the physical properties of dimethylsilicone oils which would be of use in determining the advisability of utilizing these silicones as impregnating compounds for oil-impregnated capacitors Oils of three viscosities, 20, 50, and 350 cs., were selected because they offer more promise than oils of other viscosities for use as impregnating compounds. PROCEDURE
The silicone oils used are manufactured by the Dow Corning Corp.. Midland, Mich., and are marketed as now Corning (or
