Phase Equilibria in Hydrocarbon Systems J
Propane-n-Pentane System'
B. H. SAGE AND W. N. LACEY California Institute of Technology, Pasadena, Calif.
determined by means of a calibrated pressure balance and did not involve any uncertainties larger than 0.2 per cent except a t pressures below 100 pounds per square inch, where determinations were made within 0.2 pound per square inch. The elevation of the mercury surface within the working section was established by the use of a vertical-component cathetometer It is believed with no uncertainties greater than 0.003 inch. that the total volume of the hydrocarbon sample was determined within 0.5 per cent except in a few instances involving very small total volumes. The n-pentane and propane were added t o the apparatus gravimetrically, which involved an uncertainty of about 4.4 X pound ( 2 mg.) in the weight of each component added. This large an uncertainty was due in part t o absorption of these hydrocarbons by the packing in the valves and t o adsorption on the walls of the glass tube below the working section. The precision of measurement was adequate for the large samples involving 2.2 X 10-3 pound of material ( 1 gram) but was not sufficient t o establish either the weight or composition of the small samples ( 2 x 10-4 pound) used in the investigation of the behavior in the gaseous region a t low temperatures. For this reason the compositions of these small samples were determined from the bubble-point pressures a t high temperatures, which were evaluated in terms of composition by interpolation of the results from the large samples. The weights of the small samples were determined from their volumetric behavior extrapolated to infinitesimal pressure where they were assumed to follow the laws of ideal solution ( 4 ) . I n every case the composition and weight of the sample fell between the limits of the values determined from the gravimetric method when allowance was made for a n uncertainty of 4.4 X 10-6 pound in the weight of each of the components added. It is
The volumetric and phase behavior of nine mixtures of propane and n-pentane have been investigated experimentally throughout the two-phase region at temperatures above 130' F. From these primary data the specific volume and composition of coexisting phases of the system have been established within this range of conditions.
T
HE behavior of mixtures of propane and n-pentane does not appear t o have been investigated throughout a n y extended range of compositions. T h e behavior of a single mixture of these hydrocarbons was studied i n the twophase a n d condensed liquid region at temperatures between 70" and 220" F. ( 7 ) . The vapor pressure at two temperatures, the critical constants, a n d the volumetric behavior of gaseous propane were determined b y Beattie and co-workers (1, 2 ) , and values of the thermodynamic properties of this hydrocarbon at temperatures between 70" and 250' F. a r e also available (10). T h e volumetric behavior of n-pentane in the liauid, gaseous, and two-phase regions, as well as the critical constanis of this hydrocarbon, were determined b y Rose-Innes and Young (6, 12). The volumetric behavior i n t h e condensed liquid region was confirmed at temperatures below 250" F. (9). These data serve t o establish the volumetric and phase behavior of propane and n-pentane with an accuracy sufficient for most purposes. -
I
Apparatus and Materials The apparatus employed in this investigation is a modified form of that employed in an earlier study of the propane+-butane system ( 5 ) . It consisted of a heavy-walled Pyrex glass tube, having a n inside diameter of 0.12 inch and an outside diameter of 0.4 inch, with an effective length of 14 inches within which the hydrocarbon sample was confined. The volume of this tube was varied by the addition and withdrawal of mercury, while the temperature was maintained constant by means of a vacuum-jacketed ebullition thermostat. The temperature of the apparatus was determined by means of a multilead copper-constantan thermocouple used in conjunction with a White potentiometer. This thermocouple was calibrated in place against a strain-free platinum resistance thermometer which had been standardized by the National Bureau of Standards. It is believed that the temperature of the apparatus was known within 0.3" F. relative t o the international platinum scale. The pressure was 1 This is the thirtieth paper in this series. Previous articles appeared during 1934-39, inclusive, and in January, M a r c h , and .May, 1940.
200
300
400
PRESSURE
500 LB.
PER
SQ.
I
I
600
700
IN.
VOLUME-PRESSURE DIAGRAM FOR A MIXTURE COXTAINFIGURE 1. SPECIFIC 0.444 MOLEFRACTIOX TL-PEXT.4SE IN THE CONDENSED LIQUID AND T W O PHASE REGIOSS
ING
992
JULY, 1940
993
INDUSTRIAL AND E N G I N E E R I N G CHEMISTRY
0.9
0.8
0.7
PRESSURE
LE. PER
SP.
IN.
0.20
FIGURE 2. COMPRESSIBILITYFACTOR-PRESSURE DIAGRAM FOR A MIXTURE CONTAINING 0.752 MOLEFRACTION ?&-PENTAXE
0.40 MOLE
FRACTION
0.60 TI-
0.80 PENTANE
FIGURE 3. EFFECTOF COMPOSITION o s COMPRESSIBILITY FACTOR FOR GASEOCS MIXTURES O F P R O P A S E AND n-PENTANE AT 250" F.
believed t h a t this procedure established the composition with a n absolute uncertainty of not more than 0.005 in the weight fraction of either component. The estimated maximum uncertainty in the specific volume is 2 per cent except in the immediate vicinity of the critical states of the mixtures, where it becomes somewhat larger. The composition of the gas phase of a heterogeneous mixture of propane and n-pentane was determined a t 160' F. for three
pressures. These data were obtained by withdrawing samples of the gas phase and determining the relative amounts of propane and n-pentane present by a low-temperature fractionation analysis (11). These data serve t o establish the relation of the dew-point pressure t o composition at this temperature and offer a n added check upon the composition of the small samdes emdoved for the investigation of the gase6us"region. The propane and n-pentane used in TABLE I. COMPRESSIBILITY FACTORS FOR GASEOUS MIXTURES OF PROPANE AND nthis investigation were obtained from the PENTASE Phillips Petroleum Company whose special Abs. r 160" F. . 190° F. analysis indicated t h a t the propane conPressure, 0.855'' 0 752 0 3489 0.1810 0.1468 0 8555 0.752 0.3489 0 1810 0 1468 tained less than 0.03 mole per cent of Lb./Sq.In. (49.2)a (56.5) (112.5) . . . (190) (75.8)b (86.2) (171.8) (257) (289) impurities. This propane was refluxed Dew point . . . 0.896 0 . 8 6 6 ... 0.810 0.867 0.863 0.823 0.773 0.743 for a short period in a column packed 20 ... 0.966 0.983 ... 0.982 . . . 0.971 0.986 . . . 0.987 40 .. .. .. 0.931 0.954 ... 0.964 0.940 0.963 ... 0.973 with glass rings in order to remove any 60 ... 0.931 ... 0.955 O:i77 0.910 0.945 . . . 0.959 noncondensable gases and was then dis80 ... ... 0 906 ... 0.926 . . . 0.874 0.926 . . . 0.944 tilled into a small steel weighing bomb. ... . . . 0.880 ... 0,906 ... ... 0.906 ... 0.927 100 150 ... ... .,. ... ... ... 0.848 0.884 The n-pentane was reported t o contain 200 ... ... ... . . . 0.855 ... ... ... . . . ... ... ,.. 0.784 0.836 approximately 0.7 mole per cent isopen250 ... ... ... ... ... ... ... ... tane. This hydrocarbon was carefully 220" F. 250' F. fractionated in a column packed with glass 0.8550 0.752 0.3489 0.1810 0 , 1 4 6 8 0 . 8 5 9 0.752 0.3489 0.1810 0.1468 rings, and the intermediate portion of the (lO9.9)a (125.5) (254.8) (402) (438) (l54.2)b (177.9) (369.2) (587) ... sample was removed for use in the apDew point 0.824 0.817 0 . 7 6 4 0.667 0.620 0.775 0.762 0.681 0.494 paratus. The vapor pressure of this hy20 . . . 0.974 0.988 . . . 0.989 . . . 0,976 0.990 . . . 0 '990 drocarbon varied only 0.3 pound per square 40 ... ... ... 0.946 0.969 0.977 0.952 0.974 0.979 60 0:902 ... 0.918 0 . 9 5 4 0.968 ... 0.965 0.915 0.928 0,960 inch from dew point t o bubble point a t a 80 0.869 0.888 0.937 ... ... 0,952 0 , 8 8 7 0.904 0.946 0 957 temperature of 250" F., which indicated a 0.838 0.858 0.921 100 ... ... 0 946 0.939 0 . X58 0.878 0.932 relatively high degree of purity. ... ... ... ... 0.876 150 0.905 0.784 0.806 0.895 0 915 ... . . . 0.826 . . . 0,867 . . . . . . 0.854 200 ... 0 882 .
7
250
300
350 400
500
...
...
... ... ...
...
...
...
...
...
0 . 767
...
... ... ...
--280° F.--310° 0.855O 0.752 0.855O (216.0)b (246.2) (294.3)b Dew point 0.720 0.701 0.644 0,980 20 ... 0.961 40 60 0 : 926 0.941 0:936 80 0.903 0.919 0.916 0.877 0,898 0.895 100 0.811 0.838 0.839 150 0.738 0.769 0.779 200 0.710 250 ... ... 300 ... ... ... 350 ... ... ...
...
400
...
...
...
... ... ...
...
...
0,827 0.782
7
...
0.732
.. . ..
...
...
0.674
. .
F.-340' F,-0.752 0.855" 0.752 (333.5)(390.8)b (436.7) 0.621 0 . 5 5 0,518 ... 0,986 0.984 0.968 0,972 0.950 0 : 946 0.956 0.932 0.927 0.940 0.914 0,909 0.924 0.863 0 . 6 8 4 0.865 0.811 0.816 0 640 0.750 0.763 0.799 0.674 0.703 0.737 0 673 ... ... ... ,.. 0 391
... ... ... ...
...
0.810 0,760
... ...
...
... ... ... ...
...
0.849
0.813 0'7i3
Experimental Results
0.638
a The top row of figures for each temperature represents mole fractions of n-pentane. b Figures in parentheses are dew-point pressures in lb. per sq. in. abs.
I n t h e course of this experimental work t h e volumetric behavior of four mixtures of propane a n d n-pentane were studied i n t h e gaseous region a n d i n a p a r t of t h e two-phase region. These d a t a serve t o establish t h e dewpoint pressure as a function of temperature and composition. Five mixtures were also investigated in t h e condensed liquid region a n d a p a r t of t h e two-phase region adjacent t o bubble point. These
TABLE 11. PRESSURES AND SPECIFIC VOLUMES FOR BUBBLEPOINTLIQUID IN THE PROPANE+-PENTANE SYSTEM Temp. F.
129.6 159.5 189.3 219.2 249.1 278.9 298.9 308.8 338.7
Sp. Vol. Abs. Pressure L b . / a q . in. Cu. f t . / l b . L b . / s q . in. - - - - 0 . 6 5 0 2 ' - - - - - - - .-.4443"105.8 0.02885 156.3 148.2 0.03007 214.7 203.9 0.03160 289.1 267.8 0.03337 373.1 343.2 0.03549 473.9 430.7 0.03841 588.0 495.3 0.04145 650.5 529.2 0.04345 608.8 0.0662
129.6 159.5 189.3 219.2 229.2
W . 1 3 8 7 " 237.3 0.03299 0.03539 322.6 0.03937 443.9 573.8 0.04609 620.0 0.049
Abs. Pressure
___O.1810"-
130 160 190 220 240 250
223 309.5 415.3 546.0 630.4 667
0.0332 0.0362 0.0383 0.0436
W
. 2 211.1 294.0 401.7 521.2
0
Sp. Vol.
Cu.f t . / l b . 0.03098 0.03251 0.03458 0.03722 0.04048 0.04717 0.0655 7 9 0 0.03189 0.03381 0.03668 0.04107
a Mole fraction of pentane.
~
~-
.... ....
TABLE111. PROPERTIES OF PROPANE-WPENTANE SYSTEM IN REGION
THE
Mole fraction of n-pentane
1.00
0.6502
0.4443 0.2079
0.1810
Critical atste Pressured lb./sq. in. Temp., F. Vol., cu. ft./lb.
494 386.0 0.0680
608 339.0 0.070
648 300.9 0.070
671 255.8 0.069
664 250.4 0.069
Point of max. temp. Pressure. Ib./sq. in. Temp. O F Vol., &. ft.)lb.
.. ....
...
590 343.2 0.089
628 305.8 0.099
641 259.4 0.097
650 255.2 0.096
Point of msx. uressure Pressure, lb.;/sq. in. Temp.. F. Vol., cu. ft./lb.
... .. .. ..
609 338.0 0.067
650 299.2 0.067
671 255.6 0.068
665 250.6 0.068
~
VOL. 32, NO. 7
INDUSTRIAL AND ENGINEERING CHEMISTRY
994
latter measurements established the relationship of bubblepoint pressure to the temperature and composition of the system. I n addition, they permitted the estimation of the critical states of the mixtures from visual observation of the condition of the material within the working section, The experimental results for a typical mixture in the liquid region are shown in Figure 1. The absence of appreciable quantities of noncondensable gases is indicated by the absence of change in the curvature of the isotherms in the two-phase region adjacent to bubble point. The agreement of the experimental points is within the precision of measurement indicated. The experimental results obtained for one of the mixtures investigated in the gaseous region is presented in Figure 2. I n this instance the compressibility factor 2 is used to describe the volumetric behavior. I n general, the change in slope of the isotherms a t dew point afforded a satisfactory indication of the phase boundary and was in good agreement with the dew point as determined visually. The compressibility factors and the dew point pressures for the gaseous mixtures investigated experimentally are recorded in Table I. These data were interpolated to even values of pressure. It is believed that the compressibility factors do not involve uncertainties greater than 2 per cent. The specific volume a t bubble point and the bubble-point pressure for the mixtures investigated in this region are recorded in Table 11. It is believed that bubble-point pressures were established within 0.3 per cent, and the specific volumes do not involve uncertainties larger than 1.5 per cent. The pressure, temperature, and specific volume corresponding to the point of maximum temperature for existence of two phases, the point of maximum pressure, and the critical state, are recorded for each of the mixtures investigated in Table 111.
It is difficult to ascertain the uncertainty of measurement involved in establishing these states. I n general, the precision is less than that obtainable in other regions. The compositions and specific volumes of coexisting liquid and gas phases a t some of the temperatures investigated experimentally are recorded at even pressures in Table IV. I n addition, the gas-liquid equilibrium constants ( K = Y/X) for propane and n-pentane are included. These data were obtained from the compositions of the coexisting phases as determined by graphical interpolation of the experimental results. It is believed that this interpolative process was carried out with sufficient precision so that no significant additional uncertainty was introduced by its use. The compressibility factor 2 for the gas phase of the propane-n-pentane system a t 250' F. is shown in Figure 3 as a function of composition for several pressures. The experimental points indicate the agreement obtained between the various compositions measured experimentally. I n general, the behavior is similar to that found for other binary mixtures (8). A specific weight-composition diagram for dewpoint .gas and bubble-point liquid a t several temperatures is depicted-in Figure 4. The locus CRITICAL of the critical states is indicated by a dashed curve. 0 The behavior of a number of the mixtures investigated experimentally is presented in the 622 205.8 pressure-temperature diagram of Figure 5. These 0.0689 data indicate a maximum critical pressure of approximately 670 pounds per square inch, which ... is consistent with values predicted from the estab.. . .. , lished behavior of other binary paraffin hydrocarbon systems. For the most part the dew-point curves shown were interpolated from measurements made a t other compositions which were not included in Figure 5. The vapor pressure
30
C' L L
3:
z
a
9 20 c P
B
u
LL
IO
, 0.20
I
I
0.40 0.60 0.80 MOLE F R A C T I O N N-PENTANE
FIGURE 4. SPECIFIC WEIGHT-COMPOSITION DIAGRAM FOR DEW-POINT GASAND BUBBLE-POINT LIQUID
JULY, 1940 TABLE Iv.
INDUSTRIAL AND ENGINEERING CHEMISTRY PROPERTIES OF COEXISTING PHASES I N PROPANE-n-
PENTANE SYSTEM Abs.
Temp.,
Pressure, Lb./Sq. I n
160
60 80 100 125 150 200 250 300 350
190
80 100 125 150 200 250 300 350 400 450 500
220
100 125 150 200 250 300 350 400 450 500 550 600
F.
250
280
310
340
370
995
150 200 250 300 350 400 450 500 550 600 650
Mole Fraction n-Pentane Liquid Gas
Sp. Vol., Cu. Ft./Lb. Liquid Gas
Equilibrium Constants Pronpane Pentane 0.748 0.591 0.493 0.411 0,354 0.276 0.232 0,208 0.186
0.942 0.876 0.811 0.730 0.650 0.496 0.343 0.201 0.075
0.970 0.888
b.808
0.728 0.643 0.563 0.486 0.412 0.348 0.285 0.224
0.888 0.679 0.549 0.454 0.375 0.313 0.263 0.225 0,200 0.180 0.167
0.03165 0.571 0.03251 0.456 0.03340 0.377 0,03435 0.319 0,03549 0 , 2 7 4 0.03698 0.238 0.03874 0 , 2 0 7 0.04013 0.179 0.0438 0.152 0.04801 0 . 1 2 5 0.0549 0.096
200 250 300 350 400 450 500 550 600 650
4.82 3.89 3.28 2.52 2.06 1.75 1.53 1.38 1.27 1.18 1.11 1.06
0.950 0,804 0.710 0.590 0.520 0.476 0.450 0.438 0.429 0.427 0.444 0.53
3.74 2.87 2.34 2.01 1.75 1,57 1.43 1.32 1.23 1.15 1.08
0.915 0,765 0,680 0,623 0.583 0.556 0.542 0.545 0.574 0.63 0.74
1
100
0.988 0.836 0.725 0.642 0.577 0.524 0 482 0 457
0.03539 0.03604 0.03689 0.03791 0.0391 0.0404 0.0424 0.0462
0 . 3 0 3 3.00 0.260 2 . d 4 0.225 2.20 0.195 1.94 0.168 1.72 0.144 1 . 3 4 0.121 1 . 3 9 0.099 1 . 2 5
350 400 450 500 550 600
0.971 0.917 0.865 0,811 0.757 0.696
0.929 0.823 0.747 0,690 0.654 0,642
0.0391 0.0398 0.0410 0.0424 0.0448 0.0508
0.198 0.172 0.148 0.125 0.100 0.081
2.46 2.14 1.87 1.64 1.42 1.18
450 500
0.97 0.93
0.95 0.88
0.0459 0.0481
0.124 0.101
2.06 1.68
roo
250
300
350
'F.
FIGURE 5. PRESSURE-TEMPERATURE DIAGRAM PANE-WPENTANE SYSTEM
FOR THE PRO-
a00
700
600
1.10
0.996 0.935 0.875 0.816 0.754 0.691 0.628 0.567
1
150
T E M P E R ATU R E
3.23 2.72 2.25 1.96 1.74 1.59 1.45 1.34 1.23
250 300 350 400 450 500 550 600
.
0,992 0,893 0.829 0.788 0.764 0.758 0.767
1 0 yI
500
mY
0.81
400 P Y
300
0.97 0.94
200
100
curves for propane and n-pentane were taken from published data (1, 2 , 10, 12). During the course of this investigation the vapor pressures and critical constants of propane and n-pentane were determined. These data were somewhat incidental to t'he investigation and therefore are not considered of the highest accuracy. They are reported in Table 111. Corresponding values obtained by Beattie ( 2 ) for propane are: critical pressure, 617.4 pounds per square inch; critical temperature, 206.25" F.; and critical specific volume, 0.0722 cubic foot per pound. The present measurements agree with these values within the uncertainty of determination. Some earlier values (10) disagree significantly as to critical pressure and temperature from those quoted above, and we believe that Beattie's values for the critical pressure and temperature are
PRESSURE
L B PER
SQ
IN.
FIGURE 6. EQUILIBRIUM CONSTANTS FOR PROPANE AND nPENTANE IN THE PROPANE-TZ-PENTAKE SYSTEM
to be preferred. The present data concerning the critical constants of n-pentane agree reasonably well with those determined by Rose-Innes and Young (6, 12) which are as follows: critical pressure, 485.3 pounds per square inch; critical temperature, 387.0' F. ; and critical specific volume, 0.0689 cubic foot per pound. It is probable that the be-
996
INDUSTRIAL AND ENGINEERING CHEMISTRY
havior of n-pentane was studied in greater detail by Young and his associates than in the present instance. Figure 6 presents the phase behavior of propane and npentane in this system. The product of the equilibrium constant and the pressure was employed for this representation in order to show the behavior in somewhat greater detail than would be possible otherwise. The results are similar to those obtained by Kay (3) for the ethane-n-pentane system. The phase behavior of propane a t temperatures below its critical temperature is in reasonable agreement with the behavior of the ideal solution. However, above this temperature rather marked divergences are encountered. I n general, n-pentane follows the behavior of ideal solutions reasonably well up to a temperature of about 200' F. except under such conditions that the concentration of pentane in each of the phases is small. At the higher temperatures the divergences from this generalization become large.
Nomenclature b = specific gas constant (per pound) K = gas-liquid equilibrium constant P = pressure, pounds per square inch absolute T = thermodynamic temperature, F. absolute, V = specific volume, cubic feet per pound O
R.
X Y Z
VOL. 32, NO. 7
= mole fraction of a component in liquid phase = mole fraction of a component in gas phase =
compressibility factor, PV/bT
Acknowledgment This work was carried out as a part of the activities of Research Project 37 of the American Petroleum Institute. Lee Carmichael contributed to the experimental program, and G. P. Hinds and Louise &I. Reaney assisted with the numerical calculations.
Literature Cited Beattie, Kay, and Kaminsky, J . Am. Chem. Soc., 59, 1589 (1937). Beattie, Poffenberger, and Hadlock, J. Chem. Phys., 3,96 (1935). Kay, IND.ENQ.CHEM..30, 459 (1938). Lewis, J.Am. Chsm. Soc., 30,668 (1908). Nysewander, Sage, and Lacey, IND.ENQ.CHEJI.,32,118 (1940). Rose-Innes and Young, Phil. Mag., [5]47, 353 (1899). Sage, Backus, and Vermeulen, IND.ENQ.CHEM., 28,489 (1936). Sage and Lacey, Ibid., 32, 118 (1940). Sage, Lacey, and Schaafsma, Ibid., 27, 48 (1935). Sage, Schaafsma, and Lacey, Ibid., 26, 1218 (1934). Taylor, Wald, Sage, and Lacey, Oil Gas J.,38,No.13,46 (1939). Young, J.. Sci. Proc. Roy. Dublin Sac.. 12, 374 (1910).
Bactericidal Properties of Commercial Antiseptics A Further Studv of the Effect of pH' J
INCE the time of Pasteur (1879) it has been known that acidity has an effect on the growth of some bacteria. Subsequent work has definitely shown that bacteria are affected by acidic media and that some compounds are often more highly bactericidal in acidic media (1, 2, 6). Because of these facts a previous study of the effect of pH on the bactericidal properties of some commercial antiseptics was made (1). It was then found desirable to continue these studies on other commercial products. I n this type of study it is desirable to eliminate pH values below 3 because such solutions are bactericidal in themselves as a consequence of their high acidity, and no suitable comparisons can be obtained.
S
Solutions of Definite pH The apparatus used in adjusting these solutions to a definite pH consisted of a membrane-type glass electrode with a saturated calomel electrode as previously described (1). The glass electrode was checked against buffer solutions of known hydrogen-ion content before and after each period of use. The following commercial products were tested as supplied and at pH values of 3.0, 4.0, 5.0, 6.0, 7.0, and 8.0 in solutions 1 This is the fifth of a series of articles by Degering and oo-workers on the effect of p H and substituent groups on the bacteriostatic and bactericidal properties of certain antiseptics [IND.ENQ.CHEM.,30, 646 (1938),31, 742 (1939); J. A m . P h a r m . Assoc., 27,865-70 (1938). 28, 514-19 (1939)l.
W. A. BITTENBENDER, ED. F. DEGERING, P. A. TETRAULT, C. F. FEASLEY, ANDB. H. G W Y " Purdue University, Lafayette, Ind.
In a further study of the effect of pH on the bactericidal properties of commercial antiseptics, tests have been made on adjusted solutions of Amphyl, Chlorazene, gentian violet, Listerine, Lysol, malachite green, mandelic acid, Mercurochrome, Mercurophen, methylene blue, Pepsodent antiseptic, potassium dichromate, potassium permanganate, sodium nitrite, zinc sulfate, Zonite, and Sulphonmerthiolate. Eschericia coli and Staphylococcus aureus were used as test organisms, over a pH range of 3 to 8 and on the unadjusted solutions of the antiseptics. The bactericidal activity of Chlorazene, gentian violet, Listerine, Lysol,
