1328
IXDUSTRIhL AND ENGINEERING CHEMISTRY
TABLE 11. AXALYSIS OF
ALMEN P I N SURFACE STRUCTURES, SECOND SERIES PERPENDICCLAR TO CYLINDRICSL A X I S
Blend Commercial solvent treated oil (base) tricresyl phosphate chlorinated petroleum wax 1 o chlorodiphenylene oxide 1% chlorodiphenyl
Load Weight8 1 2 2 2 2
Y
-DifferencesBefore -4fter use use
4.5 8.0
4.2 4.8 4.5
% .Re-
Phase Equilibria
maining Fibered
0.5 0.2 1.8 1.9 0
11.1 3.3 42.8 39.6 0
XVII. Ethane-Crystal Oil System'
TABLE 111. COMPARIsON OF LOADS ON ALMENPINS, SURFaCE WEAR,AND FILMSTRENGTH OF LUBRICATING OIL Oil
+ 1%
of:
Mineral oil Mineral oil Dichlorostearic acid Dichloromethyl stearate Chlorodiphenylene oxide Chlorodiphenyl Tricresyl phosphate Tricresyl
Unit Load Lb./sq. in, 2000
1000 2000 2000 2000 2000 2000
Fiber Remaining
% 0
0 37 47 40 0 3.3
VOL. 28. NO. 11
Timken Film Strength Lb.load on arm 8.8 8.8 38.5 28.0 28.0 25.5 23.0
As an example, 0 represents a diffraction line that exhibits equal intensity throughout its entire length and, therefore, indicates a random arrangement of the metal crystals. Where numbers appear, they correspond to a fiber structure and are the linear differences between maxima and minima. Table I1 gives the results of a second series. Here only the patterns for the beam perpendicular to the cylindrical axis were examined, and only one diffraction line instead of two. Table I11 summarizes data for several blends for which Timken film strengths were measured.
Conclusions Table I1 shows the superior wear resistance of certain blends over a straight mineral oil. A well-known highly treated oil used as a lubricant a t only half the load employed for the other samples gave a wear equivalent to a decrease in fibering of 88.9 per cent. Another oil showed a complete destruction of fiber structure a t this load. Addition of 1 per cent dichloromethyl stearate t o the mineral oil, for example, gave excellent protection of the surface as shown by the fact that, after the test, 47 per cent of the original surface fibering remained unchanged a t twice the load, showing only a 53 per cent decrease in fibering under an extreme load condition. Literature Cited (1) Clark, G. L., "Applied X-Ray," 2nd e d , pp. 368-9, 1932.
B. H. SAGE, J. A. DAVIES, J. E. SHERBORNE, AND W.N. LACEY California Institute of Technology, Pasadena, Calif.
Specific volumes and specific heats of several mixtures of ethane and a heavy hydrocarbon oil, known as crystal oil, were experimentally determined. From these data were calculated some of the thermodynamic properties of one of the mixtures which are presented in graphical form. The results of the experimental measurements are tabulated.
A
S PART of a general investigation by Research Project 37 of the American Petroleum Institute, a study of the thermodynamic properties of simple hydrocarbon mixtures is being made. In this paper are reported the results of a study of the ethane-crystal oil system. The six mixtures investigated vary in composition systematically from crystal o i l to mixtures containing over 80 mass per cent ethane. The temperature range studied was from 70" to 220' F., and each mixture was investigated from a pressure of 3000 to well below 500 pounds per square inch absolute. The data here reported consist of the specific volume of the six mixtures as a function of pressure for six temperatures, the specific heat a t a constant volume of 0.035 cubic foot per pound of four of these mixtures for a series of temperatures, a graphical presentation of some of the thermodynamic behavior of a mixture containing 26.32 mass per cent ethane.
Q
Materials The crystal oil used for this work has already been described ( 4 , 6 ) . It was water-white in color and had a viscosity of 284 millipoises a t 100" F., a specific gravity (referred to water a t its maximum density) of 0.8663 a t 100" F., and a vapor pressure of about 10-4 inch of mercury a t room temperature. The ethane used was obtained, in an impure state, from the Carbide and Carbon Chemicals Corporation. This material was fractionated in a glass-ring-packed column (IO), 0.5 inch in diameter and 4 feet long. Suitable reflux was obtained by a regenerative cooling system similar to that used in the Linde cycle for the production of liquid air. One cubic foot of free air per minute compressed t o a pressure of 2000 pounds per square inch and expanded t o about 50 pounds per square inch was sufficient to yield a reflux ratio of about 1 Previous articles in this series appeared during 1934 and 1935, and in earlier issues of 1936.
in
Hydrocarbon Systems 20 to 1, with a production of about 0.05 pound of ethane per hour. The middle fraction from the overhead of the column was condensed a t liquid air temperature a t a pressure less than 0.003 inch of mercury. The ethane thus purified exhibited less than 0.5 pound per square inch change in vapor pressure from dew to bubble point a t 70" F.
0.0375 _I
a
w a
g
0.035(
LL
5
Experimental Results 0.0325
w
f
0
> 0.030C
u'i
0 ri
a
"
0.0275
I I25
IO0
T E MPERATLiRE
150
I75
200
"F *
FIGURE 2 (Above). EFFECTOF TEMPERATURE UPON SPECIFICVOLUME FOR A MIXTURECONTAININQ 49.81 MASS P E R C E N T ETHANE FIQCRE 3 ( B e b W ) . PRESSCRE-TEMPERATURE DI.4GRAM FOR A MIXTURE COXT.4INING
49.81
hfhSS P E R C E X T E T H A N E
1329
The apparatus and experimental methods used have been previously described ( 3 , 6 , 6 , 7 ) . The volumes of the mixtures were determined by adding known weights of oil and gas to a chamber, which was maintained a t a constant temperature and whose effective volume could be varied by the addition or withdrawal of mercury. The corresponding equilibrium pressure for each mixture a t a series of total volumes was then measured a t eight temperatures between 70" and 220" F. Equilibrium was assured by a niechanical agitator within the chamber. The varioumeasurements were made with sufficient precision and adequate c a l i b r a t i o n to ensure an accuracy within the following limits : presqure. 1 pound per square inch; temperature, 0.02 O F. ethane and crystal oil quantities, 0.1 per cent oi the mass used: volumes, 0.1 per cent. Close to bubble point, a few values shoir.ed irregularities larger than would be consistent with the above limits of error. This variation was due t o the nonattainment of equilibrium a t these point.. Over 1600experimental points were taken in order to determine the pressure, volume, temperature relations of the system as a whole. Figure 1 s h o w the experimental results fc1r a mixture of 49.81 mass per cent ethane and 50.19 per cent crystal oil throughout the bubble-point region. From such data on five additional niixtures the properties of bubble point liquid were established. I n Table I are reported the specific volumes of the above-mentioned mixture for a series of pressures a t six temperatures. The effect of temperature upon the behavior of the system is clearly shown in Figure 1. At lower
because of the uncertainty in t h e l o c a t i o n of the phase boundaries in this region. The change in bubble-point pressure with composition for the temperatures investigated is shown in Figure 5 . The values shown for a temperature of 85" F., just below the critical temperature of pure ethane, are higher than the v a p o r p r e s s u r e of pure ethane of this t e m p e r a t u r e (approximately 680 pounds per square inch), for mixtures cont a i n i n g more than 35 mass per cent of ethane. The bubblepoint p r e s s u r e s under these c o n d i t i o n s exceed the corresponding v a p o r p r e s s u r e s of pure ethane by as much as fifty times the experimental error of the m e a s u r e m e n t s . MASS
PERCENT
FIGURE 4. PRESSERE-COMPOSITION DIAGRAM
ETHANE FOR 160' F.
temperatures the ethane is very soluble in the liquid phase, and there is small change in pressure for rather large changes in volume in the two-phase region. The isotherms for this mixture for 70" and 85' F. showed a small increase in compressibility, ( bV / W j T, with increase in pressure a t specific volumes somewhat larger than those shown in Figure 1. The rapid decrease in compressibility close t o bubble point at 85" F. is unusual and may result from the range of properties of the hydrocarbons which make up the crystal oil. Thib mixture (49.81 mass per cent ethane) was the highest in ethane content of those investigated for which bubble point could be clearly distinguished by a break in the pressure-volume relations. To aid in the visualization of the behavior of these mixtureh, several other diagrams were drawn. Figure 2 depicts the change in specific volume with temperature a t a series of pressures for the mixture just discussed. The more complex behavior of this mixture under these conditions is shown by the change in slope of the isobars in the two-phase region near bubble point. These isobars invert curvature and become convex upward a t the larger specific volumes. I n Figure 3 the relation of pressure t o temperature for a series of constant volumes is shown for the same mixture. The increase in curvature of the bubble-point curve indicates approach to the critical temperature of the mixture. It appears that the true behavior of a two-component system is masked by the complex equilibria resulting from the range of properties of the components making up the crystal oil. All of the line5 of constant specific volume for the two-phase region nearly coincide in the lower-left hand part of Figure 3 . This fact corresponds to the large range in specific volume resulting from a small change in pressure in this region, which is clearly indicated by the 70" F. isotherm of Figure 1. In Figure 4 is presented the change in pressure with composition for a series of constant volumes a t 160" F. It was impossible to determine the position of the bubble-point liquid line a t the compositions high in ethane. For this reason the isochores in the upper right-hand portion of the diagram were omitted, although the specific volumes of the system a t these pressure. and compositions were measured. Extrapolation of the isochores of Figure 4 t o a composition corresponding t o that of pure ethane gives values which are in agreement with the data of Beattie and co-workers ( 1 ) . The diagram was not extended to the composition corresponding t o pure ethane
m O.OE J
a W
f
0.05
L
5 0.04 W
f 0
>
0.0:
I! k u
5
0.0;
I IO
20 MASS
I 30 PERCENT
I
40
50
ETHANE
FIGURE 5 (Above). EFFECTOF COMPOSITION UPON BUBBLEPOINTPRESSURE FIQURE 6 (Below). VOLUME-COMPOSITION DIAGRAMFOR 160' F.
INDUSTRIAL AND ENGINEERING CHEMISTRY
NOVEMBER. 1936
Interpretation of this phenomenon is complicated in this case by the fact that crystal oil consists of a number of hydrocarbons, and the behavior of the ethane-crystal oil system is, therefore, more complex than would be expected > k in a truly tn-0-component system. This unusual 2 behavior is limited to mixtures rich in ethane a and to temperatures and pressures not far re0 moved from those corresponding to the critical state of ethane. Indications of the same type 0 of behavior were found in a previous study of 4 0 the propanecrystal oil system (8) but were not W a evident in the case of the n-butane-crystal oil Lo system. A discussion of some cases of maximum bubble-point pressure for two-component systems is given by Kuenen ( 2 ) . Figure 6 is a volume-composition diagram for a temperature of 160' F. Again the position of the bubble-point curve at the higher compositions of ethane is uncertain. It is of interest to note FIQURE how nearly straight the isobars are for the lower pressures, while there is a distinct curvature (not shown) for similar pressures in the condensed liquid region. The change in specific gravity (referred to water at its maximum density at atmospheric pressure) with pressure for bubblepoint liquid is shown in Figure 7. The more rapid decrease in specific gravity at the lower temperatures is due to the increase in solubility ( 3 ) as the vapor pressure of ethane is approached. The flex in the isotherms between 85" and
T.4EtLE
I.
SPECIFIC
.
.
(139ja ( 2 0 4 ) (412) (506) (562) Bubble point 0.01867b 0.01900 0.02065 0.02260 0.02777
.....
. . . . . 0.0510 . . . . . 0.02401 0.01897 0.02063 ..... . . . . . 0.02061 . . . . . 0.02058 1000 o:oiSi6 0.01889 0.02055 1250 ..... ..... MOO o:oisiz 0,01882 0.02046 1750 ..... ..... 2000 o:oiS47 0.01876 0.02037 2250 ..... ..... 2500 o:oiSi3 0.01870 0.02029 2750 ..... ..... 3000 o:oiSig 0.01864 0.02020
100.0
130' F. is in accord with the abnormal behavior depicted for this region in the other diagrams. The specific heats of these mixtures were determined in a constant-volume adiabatic calorimeter (6). The calorimeter measurements yielded values of the specific heat at constant volume for the mixture as a function of temperature. As these measurements were not made at the same specific
o:oiSii
(172)
.....
(264)
(568)
.....
160'o Rnhhle
(207)
(1141:
....
0: 03735
0.03626 0.03579 0.03494 0.03442 e.03400 0.03362 0.03327 0.03297 0.03268 0.03246
190.0
(1608)
Bubble point 0,01914 0.01955 I).02138 0,02347
(330)
(736)
0.02890
0.0213 300 . . . . . 400 ..... 500 o:oiQog 0.01953 600 . . . . . .....
2000 2250
2500 2750 3000
3.19%
Mass P e r C e n t E t h a n e as Follows:5.79% 16.43% 26 32% 49.82%
o:oiioe
0.0878 0.05882 0.04146 0.03051 . . . . . 0.02136 0.01945 0.02130
o:oiSQ:
0.01937 0,02119
.....
.....
.....
.....
o:oiSia 0.01930 0.02108 ..... ..... o:oisSs 0.01923 0.02097 ..... ..... o:oiSSs 0.01916 0.02087
.....
0.1029 0.0744 0.05585 0.03350 0.02346 0.02337 0.02328 0.02319 0.02310 0.02302 0.02294 0.02288 0.02281
220.0
,
. . . . . . . . . . , , ,
0.01984 0.0291 0.01984 0.01982
.....
0.01974
o:oiQis .....
0.01958
o:oigio
.....
0,1943 (476)
(933)
(1310)
81.12%
(2021)
0.02174 0.02394 0.02968 ..... 0.0995 ..... .... 0.06914 0.1167 0.05168 0.0880 0 1754 0 . 0 4 0 0 0 0,06858 0.1383 0.02265 0,04509 0.0912 0.02171 0.03225 0.0632 . . . . . 0.02487 0,04310 0.02157 0.02385 0.03500 . . . . . 0.02374 0.03168 0.02144 0.02364 0,02989 ..... 0.02354 0.02934 0.02132 0.02346 0,02902 . . . . . 0.02337 0.02877 0.02120 0.02329 0.02852 (1140) (1626) (2372)
.....
0.0354 0.1100 0.0249 0.07816 0.01964 0.02012 0,05983 . . . . . . . . . . 0.04780 . . . . . . . . . . 0.03309 0.01956 0.02003 0.02531
.....
..... ..... 0.01944 ..... 0.01939 .....
..... ..... ..... ..... 0.01986 0.02181 ..... ..... 0.01979 0.02167 ..... .....
0.01949 0.01994 0.02195
0.01934 0.01972 0.02154 (560) (1350) (329)
400 . . . . . 0.0295 500 0.01994 0.0228 600 0.02043 800 . . . . . ..... 1000 0.01985 0.02033 1260 . . . . . ..... 1500 0.01978 0.02024 1750 . . . . . ..... 2000 0.01972 0.02016 2250 . . . . . ..... 2500 0.01967 0.02008 2750 . . . . . ..... 3000 0.01961 0.02001 Figures in parentheses refer t o Specific volume, cu, ft./lh. .
,
o:i2a'
0,0686 0.0460 0.04117 0.03914 0.03806 0.03734 0.03672 0,03622 0,03576
(400)
.....
0.1283 ..... 0.0992 0.0790 0: i542 0.05439 0.1061 0.03074 0.04046 0.0778 0.0557 0.02578 0.04348 0.02436 0.03700 0.02423 0.03364 0.02411 0.07145 0.02401 0 03033 0.02391 0 02999 0.02381 0 02964 (1920) (2690)
Bubble point 0,01998 0.02044 0,02240 0.02496 0.03152 300 . . . . . 0.0406 0,1202 . . . . . ....
..... .
0.01940 300 ..... 400 . . . . . 500 0.01935 600 . . . . . 800 . . . . . 1000 0.01928 1250 . . . . . 1500 0.01922 1750 . . . . . 2000 0.01917 2250 . . . . . 2500 0.01912 2750 . . . . . 3000 0.01908 (285)
300 400 500 600 800 1000 1250 1500 1750 2000 2250 2500 2750 3000
..........
0,1557 0.1196 0.0722 0.04306 0.03210 0.02950 0.02870 0.02842 0.02816 0.02794 0,02775 0.02756
(245)
Bubble point 0.01968 0.02014 0.02207 0.02443 0.03056 .....
.....
.....
(988)
1000 1250 1500 1750
--
point
..........
0.0586 0.154 0.02426 0.0935 0,02257 0.02772 0.02251 0.02750 0.02246 0.02731 0.02239 0.02711 0.02233 0.02693 0,02227 0.02678 0.02221 0.02664 0.02215 0.02649 0.02209 0.02635 0.02205 0.02623 0,02199 0.02612 (716)
. ,
500 o:oiSS4 0.01924 0.02758 0,05689 0.1318 ..... 600 . . . . . 0.02102 0.03750 0.0943 800 . . . . . 0.02097 0,02300 0.03372 0:0519 1000 o:oiSis 0.01917 0.02092 0.02293 0.02916 0,0408 1250 ..... . . . . . 0.02285 0.02814 0.03823 1500 o:oiS74 0.01910 0.02082 0.02277 0.02785 0.03704 1750 ..... . . . . . 0.02269 0.02764 0.03630 2000 o:oisig 0.01903 0.02073 0,02263 0.02744 0.03568 2250 ..... . . . . . 0.02256 0.02726 0.03514 2500 o:oiS64 0.01896 0,02063 0.02250 0.02708 0 . 0 3 4 7 2 2750 ..... . . . . . 0,02244 0.02692 0.03436 3000 o:oisio 0.01890 I). 02053 0,02238 0.02676 0.03403
800
ETHAXEA N D CRYSTAL OIL
Abs. Temp. Pressure
Bubble p o i n t 0.01890 0.01928 0.02102 0.02303 0.02828 , . , . 0.0731 300 ..... . . . . . . . . . 400 . . . . . 0,04449 0.0852 0.186 . . .
130.0
OF
F. Lb.lsq. in.
F. Lb./sq. in.
300 400 500 600 800
LBS. PER S Q - I N .
7 . EFFECTOF PRESSURE UPON THE SPECIFIC GRAVITYOF BUBBLE-POINT LIQCID
VOLUMESOF MIXTURES
Abs. c -Mass P e r C e n t E t h a n e as ITollows: T e m p Pressure 3.19% 5.79% 16.43% 26.32% 49.82'3, 81.12% 70.0
PRESSURE
1331
b
.
I
.
.
0.08662 0.06699 0.05441 0.03877 0.03017
.....
.....
0.151 0.1018 0.0656 0,0508 0.0446 0.04186 0.04022 0.03916 0,03838 0.03774
... .....
.....
..... ..... ..... .....
0.125 0.0870 0.0657 0.0542 0.04807 0.04436 0.04233 0.04105 0.04004
.....
0,1090 0.0883 0 : i6si 0.06226 0.1185 ..... 0.04738 0,0888 0.146 . . . . . 0.03620 0.0663 0,1059 0.02234 0.02995 0 , 0 5 2 4 0.0804 . . . . . 0.02646 0.02489 0,04360 0.0652 0.02217 0.03833 0.05613 . . . . . 0,02474 0.03502 0.05047 0.02202 0.02460 0.02446 0.03281 0.04677 ..... 0.03140 0.04431 0.02188 0.02434 0.03091 0.04279 bubble-point preasure, Ib.,/sq. in. a b s .
INDUSTRIAL -4ND ENGINEERING CHEMISTRY
1332
VOL. 28, NO. 11
volume, they were reduced to the basis of a common specific volume by applying a correction obtained from a graphical integration of the following expression from the experimental specific volume in each case to 0.035 cubic foot per pound:
were obtained bv Values of the second differential two successive -graphi"cal differentiations of the change in pressure with temperature at constant volume. The correction was small in all cases except for the mixture containing the greatest amount of ethane, in which cases a correction of approxi0.55 mately 5 per cent was applied. Figure 8 gives the results of specific heat determinations on two mixtures. The decrease in specific heat with rise in tem0.50 perature for the mixture containing the greater amount of ethane is in accord with the behavior of pure substances just above 0.45 their critical temperature and might be 75 IO0 125 I50 175 20 0 expected in this temperature range for a r E MPE RAr URE 'F. mixture containing a large percentage of FIGURE 8. EXPERIMENTAL SPECIFICHEATMEASUREMENTS FOR Two MIXethane. Figure 9 presents the isothermal TUREB AT A SPECIFIC VOLUMEOF 0.035 CUBICFOOTPER POUND change in specific heat with composition for a constant specific volume of 0.035 cubic foot per pound. The points shown were taken from smooth curves drawn through the corrected experimental data such as those presented in Figure 8. It 0.55 is believed that the accuracy of the specific heat data is about 1.5 per cent a t compositions below 30 mass per cent ethane and 0'0.50 about 2 per cent for the other mixture. A tabulation of the specific heats of these mixtures for a constant volume of 0.035 cubic foot per pound is reported in Table
0'
11. Because of the unusual behavior of this system, several diagrams illustrating part of the thermodynamic behavior of one of the mixtures are presented. The graphical methods employed in calculating these functions haJ7-e already been described ( 9 ) .
I 5
I5
10
MASS
FIGURE 9. EFFECTOF
20 PER C E N T
25
30
35
ETHANE
COMPOSITION UPON SPECIFIC HEAT
-20 HEAT C O N T E N T
B.T.U. P E R LB.
FIGURE 10. HEATCONTENT-TEMPERATURE DIAQRAM FOR A MIXTURECONTAINING 26.32 MASS PER CENTETHANE
500
1000 PRESSURE
I
I
1500
2000
2500
LBS. P E R
SQ. IN.
ENERGY-PRESSURE DIAGRAM FOR FIGURE 11. INTERNAL MIXTURECONTAININQ 26.32 MASS PER CENT ETHANE
A
NOVEMBER. 1936
INDUSTRIAL AND ENGINEERING CHEMISTRY
The change in heat content with temperature for a series of constant pressures is presented in Figure 10 for the two-phase region of the mixture containing 26.32 mass per cent ethane. The change in internal energy with pressure is shown in Figure 11. It is of interest to note the much larger effect of pressure in the two-phase region at the lower temperatures.
1333
Acknowledgment The authors express their indebtedness to the American Petroleum Institute for financial support, the work having been done as part of its Research Project 37. The aid of D. C . Webster in the calculations and the preparation of the figures is acknowledged.
Literature Cited TABLE11. SPECIFIC HEATSOF MIXTURESOF ETHANEAND CRYSTAL OIL' MSBB
Per Cent Ethane 70" F. 100' F. 130" F. 160' F. 190' F. 3.19 0.452 0.469 0.520 0.486 0.503 5.79 0.458 0.473 0.488 0.519 0.504 0.517 16.43 0.488 0.495 0.502 0.509 0.527 0.513 26.32 0.530 0.523 0.518 0.55 0.52 40.0 0.60 0.54 0.53 a At a constant volume of 0.035 oubio foot per pound.
220' F. 0.537 0.534 0.524 0.509 0.51
Again bhe temperature-entropy plane affords the most useful plane for the presentation of a more complete picture of the thermodynamic behavior of a mixture. Figure 12 is such a diagram for the mixture shown in Figure 11. Because of the small isothermal change in entropy as compared to the change with temperature, a function of entropy is used for the abscissas in order to show the isothermal changes on a better scale. Lines of constant entropy are included upon the diagram as well as those for constant values of pressure, volume, and heat content. Yalues of entropy for a given state can be obtained from the abscissa of the corresponding point on the figure by adding t o it the quantity 0.0008 ( t - 60), where t is the temperature in ' F.
(1) Beattie, J. A., Hadlock, C., and Peffenberger, N., J. Chem. Phys., 3, 93 (1935). (2) Kuenen, J. P., 2. physilc. Chem., A24, 666 (1897). (3) Lacey, W.N.,Sage, B. H., and Kircher, C. E., IND. ENG.CHEM., 26, 652 (1934). (4) Sage, B. H.,Backus, H. S., and Lacey, W. N., Ibid., 27, 686 (1935). (5) Sage, B. H., and Lacey, W. N., Ibid., 26, 103 (1934). (6) Ibid., 27, 1484 (1935). (7) Ibid., 28,265 (1936). (8) Sage, B. H., Lacey, W. N., and Sohaafsma, J. G., Ibid., 26,874 (1934). (9) Sage, B. H.,Schaafsma, J. G., and Lacey, W. N., Zbid., 26, 1218 (1934). (IO) Young, W. G., and Jasaitis, Z., J. Am. Chem. SOC.,58, 377 (1936). RECEIVED July 9, 1936.
