March 1952
INDUSTRIAL AND ENGINEERING CHEMISTRY
tion, respectively), the 9 correction factors suggested are always less than 10% of the corresponding y minus 2. A tabulation of the calculated activity coefficients, smoothed equilibrium pressures, and the calculated and adjusted g values for 190”F. is presented in Table VI1 for illustrative purposes.
tween the experimental and the calculated equilibrium temperatures is 0.2’ F., the average net difference being slightly less than 0.2 F. The average absolute and the average net deviations between the experimental and calculated y minus x quantities are 12 and -275, respectively. O
ACKNOWLEDGMENT
COMPARISON WITH EXPERIMENTAL DATA
Smoothed p-x-y values for the eight isotherms are presented in Table VIII. The smoothed p-x-y curves for temperatures of 100 O F. and below can be considered to obey the Gibbs-Duhem relationship. A graphical demonstration of the good agreement b e tween all of the experimental data and the smoothed curves obtained from this correlation is given in Figure 4. Comparisons of the experimental and smoothed y minus x values and residualpressure values are presented in Figures 5 and 6, respectively. I n evaluating the correlation, the calculated equilibrium pressure (or temperature) for each experimental liquid composition and the calculated y minus x value were compared with the corresponding experimental quantities. The average absolute deviation.and the average net deviation (which considers the “deltas” algebraically) between the experimental and the calculated equilibrium pressures for all the isothermal data are 0.15 and -0.03%, respectively. The average absolute deviation between the experimental and the calculated y minus x quantities is 15.4%, whereas the average net deviation is only -0.02%. Since the isobaric data at 322.5pounds per square inch absolute were not used directly in the development of this correlation, the good agreement between those data and the smoothed curves is an independent check of the reliability of the correlation. The average absolute difference be-
609
The authors wish to acknowledge their indebtedness to the Phillips Petroleum Go. for permission to publish this paper, t o H. H. Reamer, B. H. Sage, M. R. Dean, and Mrs. 0. R. Lang for the use of their experimental data prior t o publication in the development of this correlation, to K. H. Hachmuth for the use of his fugacity-pressure ratios for propane and propylene, and to F. N. Ruehlen for his substantial assistance in the calculation of the smoothed p-x-y curves. LITERATURE CITED (1) Am. SOC.Testing Materials, Research Division IV, Section B, A.S.T.M. D-2, “Proposed Method of Test for Unsaturated’ (2)
Hydrocarbons in Gas Mixtures (Silver-Mercuric Nitrate Absorption Method).” Carlson, H. C., and Colburn, A. P., IND.ENQ.CHEM.,34. 581;
(1942). (3) Dean, M. R., and Lang, 0. R., private communication. (4) Farrington, P. S., and Sage, B. H., Im. ENG.CHEM.,41, 1734 (1949). ( 5 ) Haohmuth, I(.H., private communication.
(6) Reamer, H. H., and Sage, B. H., IND.ENG.CHEM.,43, 1628 (1951). (7) Reamer, H. H., Sage, B. H., and Lacey, W. N., Ibid., 41, 482 (1949). RECEIVED for review April 2, 1951.
ACCEPTEDOotober 31, 1951.
Phase Equilibria in Hydrocarbon N
J
Systems n-BUTANE-WATER SYSTEM IN THE TWO-PHASE REGION H. H. REAMER, B. H. SAGE, AND W. N. LACEY California Institute of Technology, Pasadena 4, Calif.
ANY studies of hydrocarbon-water systems have been made. Water is an important component of the fluids encountered in petroleum production. At temperatures somewhat above the freezing point of water, such systems form hydrates (19, 88-84). At higher temperatures data concerning mixtures of methane, ethane, natural gas, and water (9, 14, 16) are available. These studies indicate a pronounced increase in the concentration of water in the gas phase above that predicted by the Poynting equation (16). The n-butane-water system has been investigated in the three-phase region at temperatures above 100”F., and a critical state was found between the less dense phases at 305.6” F. and 637.5 pounds per square inch (17). However, few data concerning the composition of the coexisting phases at higher pressures for the two-phase region appear to be available (18). The present work involved the measurement of the composition of the coexisting phases at pressures up to 10,000 pounds per square inch in the temperature interval between 100 and 460 O F. The results of the measurement of the volumetric behavior of a single mixture of water and n-butane are included.
THERMODYNAMIC CONSIDERATIONS
In part of the two-phase region investigated the n-butanewater system consists of one denser phase rich in water and containing but a small amount of n-butane and a less dense phase which is primarily n-butane with only a small proportion of water. This latter phase may vary continuously from gas t o liquid. For the purposes of this discussion the more dense waterrich phase will be called the aqueous liquid phase and the less dense n-butane-rich liquid phase will be identified as the hydrocarbon liquid phase. As a basis of correlation it is possible t o utilize the relations applicable to a dilute solution (11) for the water in the hydrocarbon phase and for the hydrocarbon in the aqueous liquid phase. The relations of an ideal solution (10) may be applied t o water in the aqueous phase and to n-butane with a somewhat larger uncertainty in the hydrocarbon phase. Under these circumstances there are obtained (14) the following quantities for the equilibrium distribution of water between the gas and aqueous liquid phases and the hydrocarbon liquid and aqueous liquid phases, respectively:
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
610
phase for a given temperature a t t le three-phase pressure ( 1 7 ) . Below the three-phase pressure no measurements were made of the quantity of n-butane in the aqueous phase for temperatures below 280" F. The relationships of dilute and ideal solutions (IO, 11) were employed at these lower temperatures and pressures to establish the details of the influence of pressure upon the mole fraction of n-butane in the aqueous liquid phase. KO experimental data were available for the mole fraction of water in the gaseous phase a t temperatures below 280' F. and for pressuies lover than that of the corresponding three-phase states. The relationships of dilute solutions ( I f ) were used again in this region to determine the influence of pressure upon the mole fraction of water in the gaseous phase. Poynting (15) and others ( 1 4 ) have indicated a similar method of estimating the influence of pressure upon the mole fraction of water in the gas phase if effects of the change in composition of the aqueous liquid phase are neglected.
u) w
d
Vol. 44, No. 3
0.4
Bx
$ 0.3 I
-z
3
3 0.2 2
0
L d 0.1 LL!
6 2
PRESSURE
POUNDS PEP
EXPERIMENTAL METHODS
SQJARE I N C Y
Figure 1. Composition-Pressure Diagram for Hydrocarbon-Rich Phases
PXl =
Za -XH
fll
Similar expressions may be written for n-butane. y4 641 = f:B__
(3)
Z4
The constant of proportionality, p, may be regarded as a measure of the deviation of the system from idealized behavior. This constant for n-butane shown in Equations 3 and 4 applies to the equilibrium between the gas and aqueous liquid phases, and the hydrocarbon liquid and aqueous liquid phases, respectively. Equation 3 applies a t a pressure below that for the exisknee of three phases a t a stated temperature and Equation 4 a t pressures above it. The fugacity of liquid water in the pure state may be evaluated from available volumetric data ( 1 , 4, 7 , 8, 21) by application of the following equation: log& = log P i n - 2.3026 I RT
The equipment was the same as that used in earlier studies of hydrocarbon-water systems (14, 17). The details of the equipment and the general procedures in its use have been described (20). The uncertainties in the measurement of pressure n w e riot more than 0.1% and temperatures were known within 0.03" F. relative to the international platinum scale. Equilibrium between the phases was obtained by mechanical agitation of the samples confined within a stainless steel chamber over mercury. The specific procedures utilized in this investigation were substantially those employed in the study of the n-butane-water system in the three-phase region (17). In order to facilitate withdrawal of samples of the aqueous liquid phase, a second port v a s provided in the wall of the equilibrium chamber t o permit sampling of this phase without removal of the hydrocarbon phase. The mole fraction of water in the hydrocarbon liquid phase was determined in the same fashion as for the three-phase region ( 1 7 ) . I n the case of the aqueous liquid phase the quantity of n-butane was established by extended refluxing of the sample in a microfractionating column, withdrawing the n-butane from the column overhead through anhydrous calcium sulfate, and collecting it in a weighing bomb (go). It is believed that the mole fractions of water in the gas phase were established within 1 yoof the amount present, whereas the mole fraction of n-butane
x
where
The fugacity of n-butane in the pure state vias obtained from available volumetric measurements (13). It was necessary to make a short extrapolation to obtain this fugacity in the gas
I
I
200
40@
600 PRESSURE
1
800
1000
POUNDS PER
I
1200 1400 SQUARE I N C H
I
1600
1
1800
1
Figure 2. Composition-Pressure Diagram for Hydrocarbon Phases for Three Binary Systems Containing Water
March 1952
INDUSTRIAL AND ENGINEERING CHEMISTRY
611
T o permit a direct comparison with the behavior of the methane-water (14) and ethanewater ( 1 6 ) systems the quantity P Y H / P ~or P X H / P is ~ presented in Figure 2 as a function of pressure. Data for these two hydrocarbonwater systems are included for 100" and 460' F. The relatively complex behavior of the n-butanewater system a t 340' F. as compared to that found for the other two hydrocarbon-water systems is probably the result of proximity t o the three-phase region. The experimental points have been shown, and although the precision is not so great as would be desired, the results leave little doubt as t o the behavior of the system, except for the gas phase a t temperatures below 280' F. The assumption of dilute solution behavior (11) is believed to yield a smaller uncertainty than results from the present experimental techniques in the two-phase region a t temperatures below 280" F. The curves of Figures 1 and 2 have been dashed to indicate where they are not based on experimental measurements. The comM O L E FRACTION WATER positions of the coexisting hydrocarbon liquid and aqueous liquid phases of the n-butane-water Figure 3. Temperature-Composition Diagram for Hydrocarbon Phases system are presented in Table I. Figure 3 indicates the influence of temperature upon the compositions of the gas and hydrocarbon liquid phases in equilibrium with the aqueous liquid. Satisfactory agreement with the vapor pressure of water (7) was obtained. The data indicate a marked increase in the quantity of water in either the 150 gaseous or hydrocarbon liquid phase with an increase in temperav) ture throughout the entire range of pressures. 0 Some difficulties were experienced in deterrrining the quantity x 125 of n-butane in the aqueous liquid phase, The data are not of great accuracy, but nevertheless appear t o be of interest because W of the scarcity of such information. I n Figure 4 is presented the f 100 influence of pressure upon the mole fraction of n-butane in the t3 aqueous liquid phase a t temperatures between 100 and 460' F., with the experimental points indicated. An increase in pressure z 75 a t a given temperature results in an increase in the mole fraction 0 of %butane. Because a t pressures below the three-phase region tu no experimental data were obtained for temperatures below 6 280' F., i t was assumed that in this region under isothermal E 50
?
O
W
-I
0
'
25
50 100 500 1000 5000 10000 PRESSURE POUNDS PER SQUARE INCH
Figure 4.
Composition-Pressure Diagram for Aqueous Liquid Phase
in the aqueous phase was determined with an uncertainty of not more than 575 of that present. RESULTS
Figure 1 shows the effect of pressure upon the composition of the gaseous and hydrocarbon liquid phases in the n-butane-water system. I n this and all subsequent figures the hydrocarbon phases are in equilibrium with the aqueous liquid phase. Experimental points at lower temperatures for the hydrocarbon liquid phase could not be shown effectively on the diagram. A logarithmic pressure scale was employed, so that the data at low pressure could be depicted with reasonable precision. No experimental measurements are shown in this figure for the gas phase a t temperatures below 280' F.
MOLE F R A C T I O N
n-BUTANE
X
IO5
Figure 5. Influence of Temperature uEon Composition of Aqueous Liquid Phase
INDUSTRIAL AND ENGINEERING CHEMISTRY
612
TABLE
Pressure Lb./Sq. Idoh Absolute
I.
COMPOSITIONS OF COEXISTING P H A S E S I N
Phase Composition, Mole Fraction X 10s HydrocarbonQ Aqueousb
Distribution Ratio X 10-3, n-Butane
100' F. ( 5 2 . 4 5 ) C Gad, Liquidd
O.949Ze
16.7 0.5
46.5 22.8 0.5 0.5
200 300 400 500
0.5 0.5
0,024 0.048 0.062 0.062 0.062
40.13 20.33 16.12 16.10 16.08
0.062 0.063 0.063 0.063 0,064 0.064
16.00 15.92 15.84 15.76 15.68 15.53
0.065 0.066
0.5
0.071 0 073 0 075 0.076 0.078
15.38 15.03 14.70 14.08 13.66 13.36 13.15 12,79
0.5
0 080
12.49
0.5
0.5 0 . i)
0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5
.10,000
160' Gasd
Liquidd
4 7416
15.86 16.12
0.000
1000
20 40 60 80 100
600 800
0 : 082
33.8 2.1 1000
0 068
F.(125.4)C 0' b i i
11.11 11.47
0 000
0.029 0.044 0,058 0 071
61.64 31 04 21.23 16.35 13.44
20 20 20 20 20 20
0 088 0 088 0 088 0 089 0 089 0 089
11.41 11.36 11,31 11.27 11.23 11.16
1 000 1:500 2 OOG 3:OOO 4,000
20
0 090
2 0
0 091
20 20
0 092 0 094 0 09G
11.09 10.95 10.83 10,62 10.40
5,000
20 20
0 0 0 0
101 103
10.23 10.08 9.88 9.69
i4o
6.76 7 08
20 40 60 80 100
235 115 75.7 55.7 43.8
200 300 400 500 600
800
6,000 8,000 10,000
'20
2 0
20 220'
Gad Liquidd
17.1868 20 40 60 80 100 200 300 400 500 600
800
1,000 1,250 1,500 1,750 2 000 21500 3,000 4 000 5:OOO 6,000 7,000 8,000 9,000 10,000
54 I
8 2
1000
0 012
098 OR9
F. ( 2 5 9 . 3 ) C 0'
0.000
...
0,002 0.017 0.030 0 044 0.057
68.11 34.71 23.59 18.04 14.72
75.6 8.2 8.0 7.8 7.6 7.4
0.113 0.140 0.140 0.141 0.142 0.143
8.18 7.08 7.06 7.03
7.3
6.96 6.94 6.91 6.88
6.1 5.8
0.143 0.143 0.144 0.144 0.145 0.146 0.148
5.2 4.8 4.5 4.3 4.2 4.0 3.9
0.150 0.153 0.155 0.158 0.161 0.163 0.165
6.63 6.52 6.41 6.30 6.18 6.11 6.04
858 427 2x2 209 166
7.1 6 9
6.7 6.6
Gad
Liquidd 49.2036 20 40 60 80 100 200 300 400 500 600 800
6.81 6.74
Phase Composition, Mole Fraction X 10s Hydrocarbona Aqueousb 280' F.(590.9)c 70.8 0 : 220 26.8 0.000 1000
... ...
4,000 5,000 6,000
7,000 8,000 9,000 10,000
0:008 0,021 0.038 0.096 0.148 0,191 0.220 0.220 0.221 0.222 0.224 0.226 0.228 0.230 0.235 0.240 0.250 0.258 0.265 0.271 0.277 0.281 0,285
17.5 16.3 15.4 13.9 13.0 12.1 11.3 10.6 10.0 9.5 340' F.
118 Ole 200 300 400 500 600
800 1,000 1,230 1,500 1,750 2,000 2,600 3,000 4,000 5,000 6,000
7,000 8,000 9,000 10,000
0 000 0.074 0.151 0.219 0.279 0.322 0.368 0.386 0.400 0.409 0,417 0.423 0.434 0,443 0.463 0.476 0.487
1000
594 391 275 198 142 81.6 61.8 54.5 49.7 46.1 43.3 39.7 36.9 33.3 30.9 28.7 26.6 24.8 23.3 22.1
0.499
0,509 0.518 0.528 400°
247.31' 300
400 500 600 800 1,000 1,250 1,500 1,750 2,000
2,500 3,000 4,000 5,000
F
1000 831
Distribution Ratio X 10-8, %-Butane
4.22 4.42
...
820 614 491 239 148 99.1 26.8 26.2 24.4 22.6 20.9 19.6
18.4
6.99
Composition of hydrocarbon phase expressed as mole fraction water. Composition of aqueous liquid phase expressed as mole fractjon n-butane. 0 Figures in parentheses are three-phase pressures expressed in pounds per square inch absolute. d Three-phase state. e Vapor pressure of water. a b
WBUTANE-WATER SYSTEM
Pressure Lb./S Ikch Abs3ute
7.01
6.8;
Vol. 44, No. 3
0 e
635 512 423 303 225 168 140 123 110 94.8 85.0 73.6 66.5 61.0 57.9 54.7 51.9 49.7
000
0.065
0.175 0.270 0.355 0.488 0.569 0.637 0.677 0.709 0.736 0.777 0.810 0.855 0.891 0.920 0.946 0.966 0.985 1.002
23:78 18.10 14.70 7.94 5.75 4.73 4.44 4.43 4.41 4.40 4.37 4.33 4.31 4.27 4.18 4.11 3.94 3.83 3.73 3.65 3,57 3.52 3.48
... 5.52 4.04 3.31 2.88 2.66 2.50 2.43 2.36 2.32 2.29 2.26 2.21 2.17 2.09 2.04 1.99 1.95 1.92 1 89 1.85
... 2.58 2.09 1.81 1.62 1 ,43 1.36 1.31 1.27 1.24 1.21 1.16 1,14
1.08 1.05 1.02 0.996 0.979 0.962 0.948
460' F 466.ge 500 600 800 1,000 1,250 1,500 1,750 2,000 2 500 3:OOO 4,000 5,000 6,000
7,000 8,000 9,000 10,000
1000 944 811 623 493 382 311 268 238 202 179 150 135 126 120 115 111 108
0.000
...
0.078 0.288 0.600 0.792 0.973 1.089 1,150 1.195 1,265 1.325 1,420 1.498
0.718 0.656 0.644 0.640 0.635 0.633 0.637 0.638 0.631 0.620 0.599 0.577
1,556
0.562
1,603 1.643 1.679 1.711
0.549 0.539 0.530 0.521
INDUSTRIAL AND ENGINEERING CHEMISTRY
March 1952
t MOLE
crease in the fugacity of n-butane with pressure than that for water. The influence of temperature upon the mole fraction of n-butane in the aqueous liquid phase is presented in Figure 5. The threephase data have been indicated in this case by a short dashed line, for ease of identification. Throughout the greater p a r t of t h e diagram an increase in temperature under isobaric conditions results in an increase in the mole fraction of n-butane in the aqueous phase, However, at the lower pressures and temperatures this effect appears t o be reversed. The data of Figure 5 correspond to those presented in Figure 4,and i t is emphasized t h a t the behavior of the system at low temperatures and pressures was not established with certainty. This condition has been indicated by the use of dashed curves. A pressure-composition diagram for the n-butane-water system a t 280" F. is shown in Figure 6. The composition scale has been divided into three parts. The portion near pure water has been expanded so t h a t the full range of this part of the figure corresponds t o 0.00050 mole fraction n-butane. The central section corresponds t o that portion of the system from substantially zero to 0.90 mole fraction n-butane, whereas the right-hand part reflects the behavior from 0.90 t o 1.0 mole fraction hydrocarbon. The pressure scale is uniform for all three parts of the diagram. For this system the three-phase pressure ( 1 7 ) at any temperature is greater than the vapor pressure of either of the components. The influence of pressure upon the mole fraction of n-butane in the aqueous liquid phase and upon the mole fraction of water in the hydrocarbon phase above the three-phase pressure is evident from Figure 6. Since no direct experimental data concerning the two-phase region below the three-phase pressure are available, t h e compositions of the liquid and gas phases at 280" F. for this part of the system have been indicated by dashed lines. The distribution ratio for n-butane is presented in Figure 7 as a function of pressure. Except for states below 800 pounds per square inch, there is only a relatively small change in the ratio with pressure. In order to show the behavior at low pressures to somewhat better advantage, the product of the distribution ratio and the pressure is presented as a function of the latter quantity in Figure 8. The data for pressures below the three-phase region at temperatures below 280' F. have been shown as dashed lines, since the details of the behavior were established from the laws of dilute and ideal solutions (IO, 11) as has heen indicated above. The dotted curve re-
I
0.5
0.9 n-aUTAVE
'RACTION
613
Figure 6. Pressure-Composition Diagram for n-ButaneWater System at 280' F.
conditions the mole fraction of n-butane was proportional to its fugacity in the coexisting gas phase. This latter quantity was estimated on the basis of an ideal solution (10) for the gas phase. Such a procedure is open t o uncertainty. However, because of the difficulties in measuring a small quantity of n-butane in the aqueous liquid phase at low pressures and temperatures, i t is believed t h a t the assumption is desirable until more detailed experimental data are available. The much larger influence of pressure upon the mole fraction of n-butane in the aqueous liquid phase than upon the mole fraction of water in the gaseous and hydrocarbon liquid phases probably results from the more rapid in-
16.0
14.0
5 12.0 W
f
10.0
;i: 0 8.0
t
9
6.0 4.0
2.0
1
I 1000
I
2000
I
i
I
i
I
I
4000 5000 6ooo 7000 8000 PRESSURE POUNDS PER SQUARE INCH
xx)O
1
9000
Figure 7 . Distribution Ratio, Y,/& or X,/Z,, for n-Butane a t High Pressures
Figure 8.
P K Product for n-Butane at Low Pressures
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
614
TABLE11. Pressure Lb./Sq. d o h Absolute Dew point Bubble point 100 200 300 400 500
?r'lOLAL VOLUME O F
MIXTURE
O F n-BUTANE
AND I!'ATER
100' F.
160' F.
Composition 0.5949 mole fraction water 220' F. 250' F. 280° F. 290' F.
(52.5)&
(125.4)
(289.3)
(360.0)
(490.9)
(542.4)
(600.5)
5.924 1.084
3.881 1.208
3.256 1.283
:
....
0 84326
0,9059
8.546 1.007
0,8372 0.8350 0.8329
E:%:?
u.il~i)a
0.8936
Vol. 44, No, 3
340" F.
400' F.
2.559 1.435
.. .. .. ..
....
1:205 1.142 1,100 1.073 1.050 1.030 1.012 0.9970
5.096 2.471 1.439 1.267 1.191 1.144 1.112 1.088 1.067
300' F.
460'
Y.
.... ....
....
.. . . . ^^^
I\
600 0.8312 0.8908 0.9802 1,047 1.155 1.231 800 0.8274 0.8846 0,9672 1,024 1.103 1.146 1000 0.8243 0.8792 0.9556 1.006 1.073 1.104 1250 0.8209 0.8737 0.9426 0.9874 1.047 1.071 1500 0.8175 0.8685 0.9319 0.9730 1.026 1.048 1750 0.8151 0.8634 0.9234 0.9614 1.009 1.028 2000 0.8120 0,8583 0.9148 0.9511 0.9946 1.011 2250 0.8100 0.8535 0.9073 0.9415 0.9813 0.9963 2500 0.8079 0.8497 0.9004 0.9323 0.9689 0.9826 a Figures in parentheses represent bubble point pressures in pounds per square inch absolute. Volumes are expressed in cubic feet per pound mole.
....
. . I .
....
5.175 3.303 2.086 1.603 1.420 1.316 1,252 1,206
6.354 3.969 2.773 2.125 1.782 1.585 1.468
*
-BUTANE-WATER
1.0
10.0
0.8
8.0
0.6
6.0
0.4
4.0
0.2
2 .o
a
PRESSURE
e
P
The detailed values obtained experimentally in this investigation are available (18). As a matter of interest, the deviation of the mixture of hydrocarbon liquid and aqueous liquid phases from the behavior of an ideal solution is shown in Figure 10. At the lower temperatures the differences from additivity of volumes are within the uncertainty of the molal volumes of the components (1, 3-8, 13, 91) and the experimental measurements for this mixture. As a result of the small differences from additivity of volume it is possible to establish the volumetric behavior of the individual phases from only limited experimental data a t the lower temperatures. The values of the molal volumes recorded for the coexisting phases of Table I have been based upon the volumetric measurements for this single mixture and the volumes of the components. It is doubtful whether these data involve uncertainties greater than 2%. The work of RiIcKetta and Katz (12) for the methane-nbutane-water system does not afford a satisfactory comparison
POUNDS PER SQUARE INCH
0.08
Figure 9. Comparative Behavior of Water in Four Binary Systems at 220' F.
resents the lower limit of pressures a t which the aqueous liquid phase exists. The behavior of water in the hydrocarbon phases has been compared with that in an ideal solution (14, 16) by use of the ratio p/P, which has been portrayed in Figure 9 for a temperature of 220 O F. The marked discontinuity in the value of this ratio a t the three-phase state is pointed out by the lower curve. The comparative behavior of water in the methane-water ( I d ) , ethanewater (f6), and nitrogen-water ( 2 ) systems has been indicated. The n-butane-water system yields a somewhat higher value of the quantity PIP than was obtained for the other systems presented in Figure 9. This is not surprising, as in the case of the n-butane-water system the hydrocarbon phase is liquid in character a t this temperature whereas in the other systems it is gaseous. The influence of pressure upon the molal volume of a mixture composed of 0.5949 mole fraction water and 0.4051 n-butane was established at pressures up to 10,000 pounds per square inch in the temperature interval between 100 O and 460' F. The qualitative behavior of this mixture near the three-phase region has been presented graphically (f7). I n Table I1 are recorded the molal volumes a t a limited number of pressures and temperatures.
0.06
>
2
0.04
I > u
0.02
0.00
- 0.02 I
I 100
t 200
I 300
I
I
400
TEMPERATURE O F
Figure 10. Deviation from Additive Volumes of n-ButaneWater Mixture Containing 0.5949 Mole Fraction Water in Two-Phase Region
March 1952
’
INDUSTRIAL AND ENGINEERING CHEMISTRY
with the present measurements, except possibly as to the mole fraction of n-butane associated with the aqueous liquid phase, and this showed reasonable agreement at the lower temperatures. Apparently at the higher temperatures the presence of methane in the aqueous liquid phase influenced the distribution of the n-butane between the aqueous liquid and hydrocarbon liquid phases. Because of the absence of a basis for a direct comparison, no attempt has been made to evaluate the agreement between the measurements of McKetta and Katz and the present data. Again it is emphasized t h a t the information presented here leaves much t o be desired in the way of completeness and is of limited accuracy, but nevertheless it adds to the available knowledge of the influence of water upon the phase behavior of hydrocarbon systems. ACKNOWLEDGMENT
This paper is a contribution from the American Petroleum Institute Research Project 37. R. H. Olds gave material assistance in connection with the preparation of the data for publication. Betty Kendall and Virginia Berry helped with the calculations. NOMENCLATURE
constant of pro ortionality fugacity, poun& per square inch f pressure, pounds per square inch absolute P P” vapor pressure, pounds per square inch absolute R universal gas constant T thermodynamic temperature, R. molal volume, cu. feet per pound“mo1e V residual molal volume, cu. feet per pound mole V X = mole fraction in a hydrocarbon liquid phase Y = mole fraction in a gas phase 2 = mole fraction in an aqueous liquid phase = = = = = = = =
p
N
Subscripts g = gas phase
i
= = =
1
H 4
ideal solution liquid phase water n-butane
615
LITERATURE CITED (1) Amagat, M. E. H., Ann. chim. phys., 29, 505-74 (1893). (2) Bartlett, E. P., J. Am. Chem. Soc., 49, 65-78 (1927). (3) Beattie, J. A., Simard, G. L., and Su, G.-J., Ibid., 61, 24-6 (1939). (4) Bridgman, P. W., Proc. Am. Acad. Arts Sci., 48, 310-62 (191213). (5) Dodson, C. R . , and Standing, M. B., “API Drilling and Production Practice,” pp. 173-9, New York, American Petroleum Institute, 1944. (6) Kay, W. B., IND. ENG.CHEM.,32, 358-60 (1940). (7) Keenan, J. H., and Keyes, F. G., “Thermodynamic Properties of Steam,” New York, John Wiley & Sons, 1936. (8) Keyes, F. G., Smith, L. B., and Gerry, H. T., Mech. Eng., 56, 87-92 (1934). (9) Laulhere. B. M.. and Briscoe. C. F.. Gas. 15, No. 9. 2 1 4 (1939). (10) Lewis, G. N., J . Am. Chem. Soc., 30, 668-83 (1908). (11) Lewis, G . N., and.Randal1, M., “Thermodynamics and the Free
Energy of Chemical Substances,” New York, McGraw-Hill Book Co., 1923. (12) McKetta, J. J., Jr., and Katz, D. L., IND.ENG. CHEM.,40, 853-63 (1948). (13) Olds, R. H., Reamer, H. H., Sage, B. H., and Lacey, W. N., Ibid., 36, 282-4 (1944). (14) Olds, R. H., Sage, B. H., and Lacey, W. N., Ibid., 34, 1223-7 (1942). (15) Poynting, J. H., PhiE. Mag., (5) 12, 32 (1881). (16) Reamer, H. H., Olds, R. H., Sage, B. H., and Lacey, W. N , IND. ENQ.CHEM.,35, 79&3 (1943). (17) Ibid., 36, 381-3 (1944). (18) Reamer, H. H., Sage, B. H., and Lacey, W. N., American Documentation Institute, Washington, D. C., Document 3328 (1950). (19) Roberts, 0. L., Brownscombe, E. R., and Howe, L. S., Oil Gas J., 39. NO. 30. 37-40 11940). (20) Sage; B. H., ’and Lacey, W. N., Trans. Am. Inst. Mining Met. Engrs., 136, 136-57 (1940). (21) Smith, L. B., and Keyes, F. G., Proc. Am. Acad. Arts. Sci., 69, 285-312 (1934). (22) Villard, P., Compt. rend., 106, 1602-3 (1888). (23) Ibid., 107, 395-7 (1888). (24) Wilcox, W. I., Carson. D. B.. and Katz. D. L., IND. ENG.CHEM., 33, 862-5 (1941). RECEIVED for review July 23, 1951. ACCEPTEDOctober 31, 1951. For material supplementary to this article order Dooument 3328 from American Documentation Institute, 1719 N St., N.W., Washington 6, D. C., remitting $1.00 for microfilm (images 1 inch high on standard 35-mm. motion picture film) or $2.70 for photocopies (6 X 8 inches) readable without
Superscript = pure substance
optical aid.
O
Vapor Pressure of Phosphoric Acids EARL H. BROWN AND CARLTON D. WHITTI Tennessee Valley Authority, Wilson Dum, Ala.
D
ATA in the literature on vapor pressures in the system P401o-HzO pertain chiefly to solutions of orthophosphoric acid (72.4% P&) in water. Elmore, Mason, and Christensen ( 9 ) determined the vapor pressures over phosphoric acid in concentrations from 1.2 t o 63.7% P4OlOa t 25” C. by the isotonic method described by Robinson and Sinclair (7). A static method was used by Kablukov and Zagvozdkin (6) for determining the vapor pressures a t 25 40 O, 60 O, and 80 O C . of orthophosphoric acid solutions that contained 4.1 to 63.1% P401a,and by Zagvozdkin, Rabinovich, and Barilko (10) for determining the vapor pressures at 150 O, 200 ’, 250 O, and 300’ C. of acids that contained 63.4 t o 88.7’% P4O10. Britake and Pestov ( 2 ) determined the boiling points of acids that contained 9.1 to 71.0% O,
PaO10.
The present paper describes the determination of the pressure 1
Present address, The Chemstrand Corp., Decatur. A l a .
and composition of the vapor over phosphoric acid containing from 61.6 to 92.7%P4O10. The vapor densities of four of the acids also were determined. The data should be useful in the design and operation of phosphoric acid plants and of plants in which the acids are used as catalysts. The results also have utility in thermodynamic calculations involving the acids. YAPOR PRESSURE MEASUREMENTS
The acids were re ared by heating mixtures of reagent grade phos horic oxide &4&) and 85% orthophosphoric acid in a gold vessef. The P4010contents of the acids were determined through double precipitation as magnesium ammonium phosphate with subsequent ignition to and weighing as magnesium pyrophosphate. The vapor pressure for each acid was measured by determining the boiling point at several reduced pressures in an apparatus, shown in Figure 1, similar t o that described by Mack and France (6). The acids that contained more than 797$ P4010 were heated
