August 1948
INDUSTRIAL AND ENGINEERING CHEMISTRY
persions of resinous and polymeric materials. The dry polyvinyl alcohol was milled or mixed into the material to be emulsified and then water was milled in to give an emulsion by the procedure of phase inversion. High quality dispersions of a number of polymeric materials were prepared by this method. In some cases excellent emulsions were prepared by simple stirring without the need of high speed agitation or homogenizing equipment. Good oil-in-water emulsions with droplets all less than 5 microns in size were made by preparing a viscous, aqueous polyvinyl alcohol solution, adding to it all the liquid to be dispersed, and simply stirring by hand with a paddle. Figure 3 is a photomicrograph of an emulsion of a chlorinated paraffin prepared by this means. For this method t o work readily the liquid to be emulsified should be very viscous in character, preferably a t least as viscous as a 10% solution of high viscosity
1453
polyvinyl alcohol. Liquids of low viscosity can sometimes be emulsified satisfactorily by simple hand stirring if the liquid to be emulsified is added to the polyvinyl alcohol solution in small portions with stirring between additions. LITERATURE CITED
(1) Harkins, W. D.,and Beeman, N., J. Am. Chem. Sac., 51, 1674 (1929). (2) King, A.,and Mukherjee, L. N., J. 80c. Chem.I d . (London),58, 245 T (1929). (3) iverrill, R.C.,Jr., IND.ENQ.CHEM.,ANAL.ED.,15,743(1943). (4) White, M. G., and Marsden, J. W., J. Phya. Chem., 24, 619 (1920). RECEIVED July 31, 1946. Contribution No. 203 from the Chemical Department, Experimental Station, E. I. d u Pont de Nemours & Company, Inc., Wilmington, Delaware.
Two Gaseous Mixtures Containing Hydrogen and Nitrogen U
Thermodynamic Properties B. H. SAGE, R. H. OLDS, AND W. N. LACEY California Institute of Technology, Pasadena, tali$. T h e thermodynamic properties of a mixture of hydrogen and nitrogen and of a five-component mixture of hydrogen, nitrogen, carbon dioxide, carbon monoxide, and methane are reported at pressures up to 15,000 and 10,000 pounds per square inch absolute, respectively, at temperatures between 40 ’ and 460 ’ F. The results concerning the binary mixture, which contained 0.76 mole fraction hydrogen, were computed from published volumetric data for the mixture and from spectroscopic information about the isobaric heat capacity of the components at infinite volume. The volumetric behavior of the five-component mixture was determined experimentally, and the thermodynamic properties were computed from these data combined with spectroscopic information concerning the isobaric heat capacity of the components. The calculations were carried out by residual methods and the specific values of the volume, entropy, and enthalpy are recorded as functions of temperature and pressure throughout the intervals cited.
I
N COKNECTION with the industrial fixation of nitrogen it is desirable to know with some accuracy the thermodynamic properties of the multicomponent mixtures involved in these operations. Detailed thermodynamic data do not appear to be available a t present for the mixture of nitrogen and hydrogen of primary importance in the synthesis of ammonia or upon the more complex multicomponent gases utilized in the early stages of the manufacturing process. The experimental work of Wiebe and Gaddy (10) upon the volumetric behavior of mixtures of nitrogen and hydrogen furnishes an adequate background of facts for the calculation of the influence of pressure upon the thermodynamic properties of this system. These data agree well with the earlier measurements of Smith and Taylor (8) and of Holborn (3). The desired thermodynamic properties may be computed from information of this type when taken with the isobaric heat capacities of hydrogen (4) and nitrogen (1)a t infinite volume.
Experimental information is not available for the mixture of hydrogen, nitrogen, carbon dioxide, carbon monoxide, and methane which occurs in certain industrial operations a t the early stages of the compression process. I n order to establish the properties of this five-component mixture, the composition of which is given in Table I, the volumetric behavior was studied a t pressures up to 10,000 pounds per square inch (pressures in this paper are expressed in pounds per square inch absolute) in the temperature interval between 100 O and 460’ F. These data, together with the heat capacities a t infinite volume of hydrogen (4,nitrogen ( I ) , carbon dioxide (6),carbon monoxide ( 4 ) , and methane (9),provide an adequate basis for the computation of the thermodynamic properties of the mixture.
TABLEI. COMPOSITION OF FIVE-COMPONENT MIXTURE Component Hydrogen Nitrogen Carbon dioxide Carbon monoxide Methane
Mole Fraction
0.6141 0.1971 0.1741 0.0108
0.0039
Weight Fraction
. 0.0837
0.3735
0.5182 0.0204
0.0042
MATERIALS
The mixture investigated was prepared by the addition of the individual components to yield the composition reported in Table I. The hydrogen was prepared from that commercially available by passing i t through beds of activated charcoal, Ascarite, and magnesium perchlorate a t pressures in excess of 500 pounds per square inch. The nitrogen was also obtained from commercial sources and was given similar treatment before use. The carbon dioxide was prepared by heating recrystallized sodium bicarbonate. It was purified by repeated sublimation a t F r e s below 2 pounds per square inch (10 cm. of mercury). T e initial and final 5% were eliminated in the course of each sublimation. The carbon monoxide was obtained by the action of concentrated sulfuric acid upon recrystallized oxalic acid and was purified by passage through one bubble tower filled with a solution of pyrogallol in concentrated aqueous potassium hydroxide
INDUSTRIAL AND ENGINEERING CHEMISTRY
1454
Vol. 40, No. 8
ume is varied to known extent by the addition or withdraii-a1 of mercury.
, The teniperaturc of the chamber was cont,rolled by surrounding it with an agitated oil bath, thc t,emperature of which vias automatically maintained within 0.03" F. of t,he desired value. The temperatures covered in t,his investigat'ion were related to the international plat'inum scale with an uncertainty of not more than 0.05O F, by use of' a strain-free platinum resistance thermometer whose resistancc at several t,emperatures was compared with t'he indications of a similar standardized instrument. The pressure was ascertained by a pressure balance ( 6 ) which was calibrated at, appropriat,e time intervals PRESSURE LB/SQ. IN. against the vapor pressure of -carbon Figure 1. Residual Specific Volume for Five-CAmponent Mixture dioxide at the ice point,. It, is believed that the pressure within the cquilibrium chamber Jvas known within and through another corit,aining distilled water. It was dried by O.lY0 throughout the range of pressures involved. The t,ot,al passage through a chamber packed with granular calcium chloride effective volume of the chamber was determined from a calibraand magnesium perchlorate. The relatively small amount of tion involving the graviinet,ric additions or withdrawals of mermethane was obta.ined from a natural source in the San Joaquin cury from the chamber. Uncertainties in the total volume Trew Valley of California and was purified by treatment with granular probably less than 0.257, except, at the smaller tot,al volumes coract,ivated charcoal, potassium hydroxide, Ascarite, and anhydrous responding t o the higher pressures, where uncertainties as great, as calcium sulfate. Experience has shown that such material does O.4yc may have been encountmered. not contain more than 0.0005 mole fraction of material other than ,4mixture of carbon monoxide and methane of the appropriate met'hane. ' composition was prepared in a calibrat.ed glass buret. The dcsired quantity of t.his mixt.ure was introduced int,o the stainless APPARATUS AND METHODS steel chamber of the volumetric equipment, t,he quantity so introduced being determined bv indeuendent volumetric measureThe amaratus used for the studv of the volumetric behavior
TABLE 11. THERMODYNAMIC PROPERTIES O F 9 FIVE-CORIPONEST h k X T U R E Telup. F. Progerty'i 40 Z ~
17 S
H Z V
60
S
H
Z
100
V S
H Z V
160
280
340
400
460
14.70 1.0000 24,680 1.9808 -9.88 1 ..0001 25,67 2,0000 -0.12 1.0002 27.68 2.0366 19.55 1 ,0003
500 1.0017 0.7264 1.4991 -13.89 1 ,0034 0,7570 1.5186 -3.92 1 ,0068 0.8180 1.5563 16,38 1,0101 0.9087 1.6089 47.37 1.0117 0.9983 1,6566 78.39 1.0124 1.0871 1 ,7004 109.42 1.0126 1.1755 1.7409 140.60 1.0124 1,2635 1.7786 171.83 1.0121 1,3513 1.8138 203 15 ~
a
Z
=
H
=
V = S =
__
1000 1.0068 0,3650 1.3986 -17.43 1.009Y 0.3810 1.4185 -7.29 1,0158 0.4127 1.4571 13.82 1.0216 0,4595 1.5113 45.47 1,0248 0,5054 1.5604 77.34 1.0257 0.5507 1.6050 108.98 1.0259 0.5955 1.6462 140.68 ' 1,0255 0.6399 1 ,6843 172.29 1 ,0248 0.6841 1.7198 203.86
Pressure, 1500 1.0152 0,2455 1.3376 -20.39 1,0196 0,2564 1,3579 -10.12 1.0269 0.2781 1.3972 11.07 1,0345 0.3102 1.4527 43.79 1,0383 0.3415 1.5029 76.43 1,0396 0.3721 1.5483 108.63 1,0398 0.4024 1.5902 140.81 1.0393 0.4324 1.6287 172.80 1,0379 0.4619 1.6645 204.62
Pounds per _____ Square Inch Absolute _____ 2000 4000 6000 3000 1.0275 1.1058 1.2119 1.0617 0.0733 0,1863 0.1284 0.1003 1.1205 1.2933 1.2297 1.1843 -22.82 -26.23 -28.05 -28.56 1 ,0322 1.2104 1.0658 1.1086 0.1947 0,1340 0,1046 0.0761 1.3133 1 ,2046 1,1411 1,2499 - 12.45 -15.76 -17.52 -18.01 1,0403 1.1131 1.2076 1.0731 0,2133 0.1130 0,1483 0.0818 1.3536 1,2457 1,1820 1,2908 4.40 9.03 3.95 6.05 1.0486 1,0808 1,1178 1 ,2033 0.2358 0.1257 0.0902 0 . I620 1.2412 1.4101 1.3042 1.3486 42,32 40.12 38.90 38.84 1,1983 1,0530 1 ,0849 1,1201 0.0985 0.1784 0,1382 0.2598 1,4614 1.4016 1 ,3582 1 ,2962 74,51 74.54 75.65 73.96 1.1194 I , 1929 1,0543 1.0887 0,2830 0,1943 0.1068 0.1503 1.5075 1 ,4066 1.3457 1 ,4489 108.10 108.21 109.63 108.36 1,0544 1 ,0852 1.1178 1.1874 0.1622 0.1149 0.3060 0.2100 1.5500 1.4510 1.3914 1.492% 141.56 142.37 144.84 141 .00 1.1144 1.1808 1,0833 1 ,0830 0,1228 0.1738 0.3286 0.2253 1,4334 1.4916 1.5890 1.5323 176.09 179.58 173.36 174.63 1.0513 1,0801 1.1102 1.1736 0.3509 0.2404 0.1853 0.1306 1.4714 1,5288 1.6250 1.5690 213.46 205.41 207,15 209.08
30.82 2.0871 49.40 H 1.0003 Z 33.58 V 2,1336 S 79.54 H Z I ,0004 36.55 V S 2,1764 H 109.93 z 1.0004 V 39.51 2.2162 S l40,56 H 1 .0004 Z 42.48 V S 2,2534 171.42 H 1.0003 Z 45.44 V 2.2884 S H 202.50 compressibility factor. PV/bt. specific volume, cubic feet per pound. entropy l3.t.u. per pound per R. based on d a t u m of 2 0000 a t pressure of 14.696 pounds per square inch a t 60' F. enthalp$, B t.u. per pound based upon datum of zero a t infinite attenuation and temperature of 60' F. S
220
_______.-
-___ 8000
1,3317 0,0604 1,0755 -26.63 1,3253 0.0625 1,0957 - 16.05 1.3143 0.0667 1,1369 5.90 1 ,2993 0.0730 1.1964 40,94 1.2861 0.0792 1,2518 76.97 1.2728 0,0854 1.3022 112.59 1.2616 0,0915 1.3487 148.45 1,2499 0,0975 1.3915 183.89 1,2383 0.1033 1 ,4304 218 50
-
_____
10,000 1.4560 0,0528
1.0407 -23.15 1.4462 0.0546 1.0610 -12.58 1 ,4273 0,0580 1.1022 U.38 1.4008 0.0630 1,1618 44.55 1,3770 0,0679 1.2177 80.80 1,3567 0.0728 1.2686 118.85
1.3377 0,0776 1.3157 153.18 1.3197 0,0824 1.3591 189.17 1,3033 0,0870 1.3985 224.23
INDUSTRIAL AND ENGINEERING CHEMISTRY
August 1948
a
0
N N
0 N
Y,
l-
0
-
0
0
-
N
0
0
The quantities of hydrogen and nitrogen so introduced were ascertained from a knowledge of the volumetric behavior of the hydrogen and nitrogen (IO) at the states in question and the changes in pressure of the isochoric chamber. The uncertainty in the weight of each component added to the five-component system was thought to be less than 0.2% and it is unlikely that the compositions deviated from those recorded in Table I by more than 0,002 mole fraction. After the sample was introduced into the volumetric equip-
51 b
0 0
51
N
1455
0
a
0
hl I
51
I
ment (6), the total volume of the system was determined as a function of pressure for each of seven temperatures systematically chosen between 100" and 460' F. Corresponding measurements of pressure and total volume were made a t each temperature both upon increase and upon decrease in thQtotal volume of the system. The agreement of these data was taken as an indication of the extent to which equilibrium was approached under the conditions of the measurements.
'
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INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 40, No. 3
m
EXPERIMEYTiL KESULTS
gave The measured behavior of the five-coinponent evidence that a slight change in the colllpositlon of the mixture occmred at temperatures above 4.00" F. The discrepancy noted \vas attributed to the loss of approximately 370 of the hydrogen in the sample by diffusion through the n d l s of the stainlesg steel chamber a t the higher trmpci a turcs.
The volumetric data at 400" and at 4.80" F weir iiiodihed >lightlyon the basis of graphical extrapolation of the cvpeiimental I e S d t S obtained at lower tcmpeiatures. The values lecotdcd co~tcspondclosely t o the behavior established from earlier experience with systems of this naturc (3, 8, 10). In any event, the deviation of the extrapolated data from the ok Thii hnvior of the iv>tem n-as in no case more than 2 aPc
INDUSTRIAL AND ENGINEERING CHEMISTRY
August 1948
1457
TABLE 111. THERMODYNAMIC PROPERTIES OF A MIXTUREOF HYDROGEN AND NITROGEN l'elng.,
F. 40
ti0
100
160
220
280
340
_____
(Weight fraction nitrogen 0.8144, mole fraction nitrogen 0.240) Pressure, Pounds per Square Inch Absolute 500 1000 2000 4000 6000 8000 1,0794 1.2886 1.4019 1.0173 1.0365 1.1793 0.3507 1.3213 0,6732 0.1915 0.1395 0.1138 0.7658 1.1134 0.9416 0.5851 0.4773 0.4005 -18.1 -14.7 -17.6 -18.2 -8.5 -0.6 1.0173 1.0365 1.0794 1.1761 1.2810 1.3902 0.7002 0.3646 0.1986 0.1442 0.1174 1 ,3744 0.9752 0.8001 0.6205 0.5135 0,4373 1.1466 3.4 -0.4 -1.1 -0.6 10.0 18.3 1.2674 1.3684 1,0174 1.0364 1.0780 1.1696 0.3922 0.2127 0.1537 0.1244 1.4804 0.7540 0.8653 0.6877 0.5822 0.5070 1.2097 1.0399 39.5 33.4 33.4 34.6 47.0 55.9 1.0750 1.1600 1,2486 1,3396 1.0172 1.0356 0.4330 0.2336 0.1676 0.1349 1.6387 0.8342 0.9547 0.7796 0.6759 0.6020 1.2963 1.1266 87.3 93.7 102.1 111.8 84.4 85.1 1.0714 1.1505 1.2322 1.3150 1.0167 1.0336 0.4733 0.2541 0.1814 0.1452 1.7965 0.9138 1.0354 0.8623 1.3750 1.2060 0.7601 0.6872 147.5 135.5 136.7 139.7 156.7 167.1 1.0677 1.1414 1.2173 1.2933 1.0160 1 .a328 0.5133 0.2744 0.1951 0.1554 1.9538 0.9930 1,1091 0.9376 0.8366 0.7645 1.4471 1.2787 q2.0 200.8 211.0 221.9 186.7 188.3 I .1330 1.0153 1.0312 1.0641 1.2035 1.2737 0.2944 2.1111 1.0719 0.5530 0.2085 0.1656 1.0064 1.5133 1.3456 1.1767 0.9063 0.8349 244.0 253.7 264.6 276.1 239.7 237.7 1.0606 1.1252 1.1909 1.2562 1.0146 1.0296 0,5926 0.3144 0.2218 0.1755 2.2675 1.1505 1.0698 0.9703 0,8995 1.5751 1.4074 1.2391 306.4 288.9 291.0 295.9 317.8 329.8 1.0575 1,1181 1.1793 1.2406 1.0139 1.0280 0,6320 0.3342 0.2350 0.1854 1.2290 . 2.4241 1,1199 1.0298 0.9595 1.465 1.2974 1,6327 347.5 358.7 370.6 383.0 340.0 342.4
.
400
460
a
Z = V = S =
H
=
I _
14.70 10,000 1.0005 1.5166 V 44.22 0,0985 S 1.9673 0.3415 H -16.7 9.1 z 1.0005 1,5001 V 46.00 0.1013 8 2,0000 0.3788 H 0.0 28.2 Z 1.0005 1 ,4698 V 49.53 0.1069 S 2.0622 0.4514 H 33.5 66.1 2 1.0005 1.4305 V 54.83 0.1152 S 2,1479 0.5454 H 83.9 122.5 x 1.0005 1.3973 V 60.15 0.1234 8 2,2257 0.6313 H 134.5 178.3 Z 1.0004 1.3686 V 65.46 0.1316 8 2.2972 0.7091 H 185.2 233.6 z 1.0004 1.3432 V 70.76 0.1396 S 2.3632 0.7800 H 235.9 288.1 z 1 ,0004 1.3210 V 76.07 0.1476 8 2.4244 0.8450 H 286.8 341.9 Z 1,0004 1.3013 V 81.38 0.1556 S 2.4818 0.9054 H 337.8 395.6 compressibility factor, P V / b T . specific volume cubic feet per pound. entropy, B.t.u. her pound R. based on datum of 2 a t pressure of 14.696 pounds per square inch and a temperature of 60° enthalpy, B.t.u. per pound based upon datum of zero a t infinite volume and temperature of 60° F. PropertyfL Z
12,500 1.6601 0,0863 0.2831 22.3 1.6375 0.0885 0.3208 41.5 1.5967 0.0929 0.3919 79.9 1.5447 0.0995 0,4885 136.7 1.5010 0.1061 0.5751 193.1 1,4633 0.1126 0.6535 248.8 1.4308 0.1190 0.7249 303.5 1.4023 0.1254 0.7903 358.0 1.3772 0.1317 0.8510 411.7
15,000 1.8028 0.0781 0.2358 36.6 1.7746 0.0799 0.2737 66.0 1.7235 0.0836 0.3453 94.4 1.6590 0.0890 0.4423 151.8 1.6053 0.0946 0.5294 208.4 1,5593 0.1000 0.6083 264.2 1,5193 0.1053 0.6801 319.3 1.4843 0.1106 0.7459 374.0 1.4531 0.1158 0.8067 427.9
F.
maximuin deviation occurred only a t 460 F. and 10,000 pourids per square inch and for the most part the difference between the recorded information and the observed values was less than 1% at 460' F. and less than 0.5% a t 400" F. The experimental results are summarized in Figure 1, which presents the residual specific volume (7) as a function of pressure for the several temperatures involved. The values of the residual specific:volume were established from the following relation:
k=l
The corresponding values of specific volume and of the compressibility factor are tabulated in a part of Table 11 as a function of state. Equation 1 was also employed in in' arpolating the volumetric data of Wiebe and Gaddy (IO) to even values of pressure, temperature, and a composition corresponding to 0.76 mole fraction hydrogen. The values of the specific volume obtained from this graphical operation are recorded in Table 111. THERMODYNAMIC CALCULATIONS
The heat capacity a t infinite volume of the two mixtures under cwnsideration was established by application of the following equation to the spectroscopic heat capacity data for the oomponents ( 1 , 4, 6, 8).
The isothermal changes in enthalpy and entropy were calculated from the following expressions which make use of residual specific volumes:
PRESSURE LO/SQ. IN.
Figure 4.
Compressibility Factors for Binary and FiveComponent Mixtures
'
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
1458
I
300
I
Vol. 40, No. 8
- TWO-COMPONENT I ,
MIXTURE
I I
2000 TEMPERATURE
'F:
Figure 5. Isobaric Heat Capacity of Mixtures at Infinite Volume
The enthalpy of the mixtuies was asceitaiiied as a function of state by solution of the following equation in which the enthalpy .is takm as zero at a temperature of 60' F and a t infinite volume.
I n order that, all of the entropy values recorded in t,he tables and figures might be positive, the entropy was arbitrarily taken as 2 B.t,.u.per pound per It. at 60" F. and 14.696 pounds per square inch. The corresponding values of entropy at other statcxs were established from the follo\\-ingexpression:
s = 2.0000 + J5.16.;9
/-
,I-
(C? 7 ' ) d T - b I l l
-2 + 14,6( 6
The use of different datum states for entropy and enthalpy introduces no uncertainties or ambiguities in the use of the data ( 2 ) . Values of the enthalpy and entropy as computed from Equations 5 and 6 are recorded in Tables 11 and I11 for the five-component and two-component mixtures, iespectively. Thermodynamic data presented in tabula1 folm are not as useful for certain types of engineering applications as are graphical representations. Figures 2 and 3 are enthalpy-entropy and temprratme-entropy diagrams for the five-component mixture. Diagrams involving these thermodynamic variables were also prepared for the binary mixture but do not appear t o be sufficiently different to justify their presentation here. The consistency of the results was carefully checked by the application of the first and second laws of thermodynamics to several random paths. Such tests indicate that the values of entropy, enthalpy, and specific volume are consistent within 0.5y0 for all states investigated and in many instances the inconsistencies were less than Q.1%.
4000
6000
PRESSURE L @ / S Q
8000
IN.
Figure 6, Isothermal Changes in Enthalpy for Mjxtures
COMPARISON O F BEHAVIOR OF TWO MIXTURES
I n order to facilitate comparison of the volumetric and thermodynamic behavior, Figure 4 presents compressibility factors for both mixtures at, temperatures of 100" and 400" F. There is a substantial difference betiveen the values of compressibility factor for the two mixtures, the binary mixture showing the larger deviations from perfect gas behavior in the lower pressure range. At, the lower temperatures and higher pressures the specific volume of this mixture is approximately 45 % greater than the specific volume of a perfect gas at the Lame state. A comparison of the isobaric heat capacit,y at infinite volume for the two niixturos is shown in Fixure 5 . The isot,hermal changes in enthalpy at 40°, 220°, and 460" F. for t,he two mixtures are shown in Figure 6. The binary mixture shows somewhat the greater isothermal change in enthalpy as well as the greater change with temperature. -1similar comparison of the isothermal change in entropy ivith pressure constitutes Figure 7. The binary mixture again
PRESSURE L B J S Q . IN,
Figure 7.
Irifluemce of Pressure and Temperature upon H r i t r o p j of Alixtures
August 1948
INDUSTRIAL AND ENGINEERING CHEMISTRY
shows the greater change in entropy with pressure and with temperature. Even with the significant deviation from the perfect gas law shown in Figures 1 and 4,the change in entropy is nearly directly ProPortional to the logarithm of the Pressure in both cases, as would be strictly true in the case of a perfect gas.
1459
ACKNOWLEDGMENT
Financial support and cooperation were received from the Hercules Powder Company. The company’s permission to publish the results is appreciated. The assistance of L. Katz and P. S. Farrington in connection with the numerical thermodynamic calculations is acknowledged.
NOMENCLATURE
b
c,
=
specific gas constant
= isobaric heat capacity, B.t.u. per pound
(O
H = enthalpy, B.t.u. per pound n
LITERATURE CITED
R.)
(1) Davis and Johnston, J. Am. Chm. SOC.,56, 1045 (1934). (2) Gibbs, “Collected Works,” Vol. I, New York, Longmans, Green
= weight fraction
P = pressure, pound per square inch absolute
and Co., 1931. (3) Holborn. Ann. Phwsik. 63,674 (1920). (4) Johnston and Davis, J . Am. Chem. SOC.,56,273 (1934). (5) Kassel, Ibid., 56,1841 (1934). (6) Sage and Lacey, Trans. Am. Inst. Mining Met. Engrs., 136, 136 (1940). (7) Sage and :me,, “Volumetric and Phase Behavior of Hydrocarbons, p. 41, Stanford Univ. Press, 1939. (8) Smith and Taylor, J . Am. Chem. SOC.,45,2107 (1923). (9) Vold, Zbid., 57,1192 (1935). (10) Wiebe and Gaddy, Ibid., 60, 2300 (1938).
s =
entropy, B.t.u. per pound ( O R) t = temperature, O F . T = thermodynamic temperature, a R. specific volume, cu. ft. per pound residual specific volume, cu. ft. per pound z = compressibility factor, PV/bT Superscripts * = infinitevolume ’ = referencestate Subscripts N = nitrogen H = hydrogen k = componentk ~
v = v =
RECEIVED Maroh 10, 1947
Liquid-Vapor Equilibrium Relations in Binarv Svstems J
d
Ethylene-n-Heptane System W. B. KAY1 Standard Oil Company (Indiana), Whiting, Ind. T h e P - V - T - X relations at the liquid-vapor phase boundaries for the ethylene-n-heptane system were obtained from measurements of a series of mixtures varying in composition from nearly pure ethylene to nearly pure heptane. T - X diagrams of the coexisting liquid and vapor at constant pressure were constructed, from which data were obtained for calculating the phase-equilibrium constants for ethylene and n-heptane. From a comparison with previously published data on binary paraffin systems it is concluded that the substitution of an olefin for a paraffin in a binary mixture of paraffin compounds has relatively little effect on the P-V-2’-X relations if the olefin has about the same boiling point as the replaced paraffin compound.
T
HIS paper presents the P-V-T-X relations at the liquid-vapor phase boundaries of the ethylene-n-heptane system. The work is a continuation of a research program designed to discover the factors affecting the P-T-X relations in the critical region in mixtures of petroleum hydrocarbons. The three binary systems that have already been investigated in accordance with ( 4 ) , ethane-butane (6),and buthis program-ethane-heptane tane-heptane (6)-have provided quantitative data on the effect of a difference in the physical and thermal properties of the components in mixtures of the n-paraffin series. With the study of the olefin-paraffin system, ethylene-heptane, information is obtained on the effect of a differenoe in the chemical nature of the components. 1 Present address. Department of Chemical Engineering, Ohio State University, Columbus, Ohio.
The apparatus and experimental procedure were the same as those employed in the study of the ethane-heptane system (4). Before the experimental measurements were begun, the calibrations of the pressure gage and thermocouple were carefully checked. The check on the pressure gage was made by determining the vapor pressure of pure water at several temperatures corresponding to pressures u p to 1200 pounds per square inch. The pressure-temperature relations for water given in the International Critical Tables (2) were used t o determine the true pressure from which the correction for the gage was calculated. PURIFICATION OF MATERIALS AND PREPARATION OF MIXTURES
Cqmmercial ethylene of high purity was further purified by fractional distillation in a silvered and vacuum-jacketed column filled with Stedman packing and having an efficiency equivalent to about 100 theoretical plates. Eighty milliliters of liquid ethylene were charged to the still and a middle cut of 35 ml. was collected. The sample was then transferred to the high vacuum degassing apparatus where i t was alternately frozen and melted and the noncondensable gases over the solid were pumped off each time. Finally, the purified sam le was distilled into a steel storage bomb. The high purity of tEe sample was indicated by the fact that the pressure change between the boiling and dew points amounted to only 0.2 pound per square inch a t 32.17” F. where the vapor pressure was found to be 598.2 pounds per square inch. The n-heptane was from the same sample that was used in the work on the ethane-heptane and butane-heptane systems. The pressure change during condensation of the samples used in the preparation of the mixtures amounted to about 1 pound per square inch %hen the vapor pressure was approximately 192 pounds per square inch. Mixtures of ethylene and heptane were prepared by loading the experimental tube with a sample of pure heptane, calculating 6
