Vapor-Liquid Equilibria for Binary sn-water Systems RIKI KOBAYASHIl AND DONALD L. KATZ University of Michigan, Ann Arbor, M i c h .
on the vapor-liquid phase relations of hydrocarbon-
W O R water K systems was initiated by Scheffer in 1913 on the hexme-water ( 3 1 ) and the pentane-water ( 5 2 ) systems. His studies were primarily confined to the phase relations of the systems in the region bounded by the vapor pressure curve for the pure hydrocarbon and the conditions under nhich three phases coexist -a vapor phase, a lighter liquid phase rich in hydrocarbon, and a heavier liquid phase rich in water. Scheffer found that as the temperature of the hydrocarbon-water mixtures under the coexistence of three phases was increased, a temperature was reached a t which the intensive properties of the vapor phase and the lighter. liquid phase became continuously identical. The conditions under which this critical phenomenon occurs have been referred to as the three-phase critical conditions and the composition of the identical phases as the three-phase critical composition ( 1 9 ) . The solubility of methane in water has been reported a t 25' C. by Michels, Gerver, and Bijl ( 2 1 ) up to a pressure of 6800 pounds per square inch and a t the same temperature by Frolich et al. ( 1 2 ) up to a pressure of 2060 pounds per square inch. The studies of the saturated water content of hydrocarbon gases were undertaken in connection with the dehydration of natural gases to prevent the formation of natural gas hydrates. Lauhlere and Briscoe ( 1 6 ) and Deaton and Frost ( 9 ) determined the saturated concentration of water in natural gases up to 100" F. and 600 pounds per square inch. These data on natural gases were supplemented by those of Russell, Thompson, Vance, and Huntington (26) for pressures up to 2000 pounds per square inch. Sage, Lacey, and coworkers have determined the dew point composition of the methane-water (a$) and the ethane-water ( 2 4 )systems from 100" to 460" F. up to 10,000 pounds per square inch. Reamer e l al. (25) have also determined the concentration of water in the n-butane-water system in the vapor and the lighter liquid phases in the three-phase region. Similar data on the concentration of water in the vapor and the lighter liquid phases for the propane-water system have been reported by Poettman and Dean ( 2 3 ) . Data on the water content of a natural gas saturated with water and the solubility of the same natural gas in water and in brine solutions up to 250' F. and 5000 pounds per square inch have been presented by Dodson and Standing (10). McKetta and Kat2 (19, 2'0) made an extensive study of the methane-n-butane-water system in the two -phase and threephase regions, and developed general plots for the estimation of the solubility of water in hydrocarbon gases and liquids (20). Culberson, Horn, and McKetta ( 6 ) reported data on the solubility of ethane in water up t o 1200 pounds per square inch and methane in water a t 77" F. up to 10,000 pounds per square inch. Culberson and McKetta (7, 8) have recently extended their data on the solubility of methane in water and ethane in water over the temperature range from 100' t o 340' F. up to 10,000 pounds per square inch. I n this investigation vapor-liquid equilibria data were obtained in the two-phase and three-phase, regions for the propane-water system a t temperatures from 54' to 300' F. and pressures from 100 to 2800 pounds per square inch. The system has been studied with relative thoroughness, especially in the region surrounding 205.7' F. and 637 pounds per square inch, the three-phase critical Present address, Department of Chemical Engineering, The Rice Instit u t e , Houston, Tex. 1
440
conditions. This paper also present.8 a correlation for the water content of hydrocarbon-rich phases and a procedure for extending and smoothing the data on solubility of volatile hydrocarbons in water. EXPERIMENTAL DETERMINATION OF PROPANE-WATER SYSTEM
This vapor-liquid equilibria study was conducted using a batch operation. Propane and water were placed in a pressure cell in the desired amounts and the contents of the cell were brought to phase equilibrium by mechanical agitation. A thermostatically controlled air bath surrounding the cell maintained it a t thermal equilibrium. The resulting phases were sampled under equilibrium conditions by injecting mercury into the cell as the individual samples were being removed from it.
0-150 OR
0-1000 PSI
0-3000 PSI GAU6E
TO T R A I N TO BURETTE F R O M MERCURY S O U R C E
Figure 1. Flow Sheet of VaporLiquia Equilibria Apparatus The flow sheet of the vapor-liquid equilibria apparatus is shown in Figure 1. The electrically powered stirrer, which is mounted entirely within the cell, has been deleted from the drawing to show the relative locations of the sampling ports within the cell. The high pressure equilibrium cell has a glass window which permits the observation of liquid levels. The cell was constructed by Chaddock ( 4 ) and the auxiliary apparatus was built by McKetta ( 1 9 ) . Some revisions of the apparatus were made by the authors in order to adapt the equipment to the study of the propane-water system.
A portable pressurizing unit constructed for general use was utilized to compress mercury and gas during the charging and sampling operations. Ports located a t four different and appro-
INDUSTRIAL AND ENGINEERING CHEMISTRY
February 1953
priate positions in the cell were uced for charging, sampling, and discharging the contents of the cell. In Figure 1, V , L,,and F . 1 designate the vapor, lighter liquid phase, and the heavier liquid phase sampling ports, respectively. The difierent sampling ports provide a means for sampling each phase through a different port located in its own phase to avoid contamination of the sample lines by a second phase. The vapor phase sampling line, V-T4-16, was wrapped with a n electrical rasistance heater in order to superheat the vapor sample leaving the cell. It is especially important that the con? densation of the vapor phase be prevented when sampling in the three-phase region, as complete condensation of that phase could occur with a very slight cooling below the equilibrium temperature. The resulting change in phase would cause the loss of water from the sample in the sample lines. Heating the vapor s a m p h g line also hastened the purging of any excess water remaining in the lines from previous runs.
i'
B
I A
0
c
D R D
Figure 2.
D
D
C
E G H
NEEDLE VALVE,VAPCR NEEDLE VALVE, LIQUID ASOARITE TOWER D E H m R l T E TOWERS WATER-PROOFED CONNECTIONS TRAP SETTLING BULB V VACUUM
MERCURY BUBBLER MERCURY MANOMETER M CALIBRATED BOTTLE N THERMOMETER 0 G L A S S CASE P WIRE GUARD U DRYING TUBES PUMP J
K
_ _
Analytical Train for Analysis of HydrocarbonRich Phases
The equilibrium cell was evacuated and flushed several times with propane gas a t the beginning of each series of isothermal runs and whenever the cell was contaminated with other gases. The individual constituents, propane and water, were charged into the cell in quantities that would satisfy the desired conditions of pressure, number of phases, and quantity of each phase. Before the beginning of the stirring operation the liquid sampling lines were filled with clean, dry mercury to displace any other liquids in them and to block off the lines during the agitation period. The agitator was operated intermittently for a t least 2 hours under constant conditions of pressure and temperature before any samples were taken. Using a stirring period of 2 hours, it was found that the final phase concentrations of the dilute components were reproduced, regardless of whether a given equilibrium pressure was approached from a pressure greater or less than the final equilibrium pressure. A quiescent period of 15 minutes was allowed after agitation periods before the samples were displaced from the cell. The samples were transferred directly from the cell to the analytical apparatus through steel tubing of small diameter. The vapor phase was sampled through V-T4-l6, the lighter liquid phase through Lz-11-12, and the water-rich liquid phase through Li-15-14-13.
The same analytical procedure was used to analyze the vapor phase and the lighter liquid phase, as both are propane-rich. Figure 2 shows the train used to analyze these two phases.
44 1
mosphere, it was necessary to prove the effectiveness of Dehydrite as a drying agent a t reduced pressures. No loss in weight of previously used drying tubes could be detected after the pressure within the drying tubes had been maintained a t less than 0.1 mm. of mercury absolute pressure for 12 hours. Figure 3 shows the apparatus utilized in the analysis of the water-rich liquid phase.
Prior to the agitation period of each run the water-rich liquid phase sample line was evacuated from valve 13 (Figure I), to stopcock S (Figure 3 ) . The entire line was then filled with mercury through valve 13 (Figure 1 ) . The water-rich phase sample was passed through the cooler at the equilibrium pressure and flashed to the barometric pressure at needle valve S (Figure 3). The mercury leveling bulb was adjusted continually to maintain the gas pressure in the buret at precisely the barometric value. The water jacket surrounding the gas buret was maintained at a constant temperature near room temperature. When the,desired amount of sample had been displaced from the cell, valve 13 (Figure 3) was closed and the sample in the lead lines allowed to cool to room temperature. Valve S (Figure 3 ) was then opened slowly to allow the liquid in the lead lines to expand to atmospheric pressure. Finally mercury was introduced through valve 13 (Figure 1 ) to displace all the liquid and gas in the lead lines into the buret. In this way, any of the gas leaving the solution which remained trapped in the lead lines was ultimately caught in the gas-water buret. To see if the flash vaporization a t valve S occurred under equilibrium conditions, mercury was dropped for several minutes through the buret to agitate the flash liquid. No change in the volume of the flash gas or liquid could be detected.
t- I'I
The volume of the flash liquid and flash gas, the equilibrium cell temperature and pressure, the temperature of the buret water jacket, and the 1 barometric pressure were MERCURY recorded. The propane SOURCE d i s s o l v e d i n t h e flash Figure 3. Apparatus for liquid was computed using Analysis of Water-Rich Liauid Phase the solubility data of propane in water a t atR. Concentric-tube cooler mospheric pressure (17), S. Needle valve U . 70-mm. borosilicate glass the volume of the flash tubing U . Gas-water buret liquid, and its density. V. Cooling water The vapor pressure data W. Metric scale IX. Air inlet of pure water were used to Y . Mercurv leveling bulb correct for the water present in the equilibrium flash vapor. The compressibility factor of propane gas was applied to correct for the nonideal volunietric behavior of the flash gas. A material balance of the propane and water made on the over-all sample yielded the final composition of the sample. I
EXPERIMENTAL MEASUREMENTS
The vapor and liquid phases were expanded from the equilibrium pressure to the pressure of the analytical train a t valves 16 and 12, respectively. The expanded sample was passed through two U-tubes in series and the dehydrated propane gas was measured in a calibrated glass bottle. Dehydrite (magnesium perchlorate) was used as the dehydrating agent. The gain in weight of the U-tubes, the pressure rise of the gas in the bottle and the temperature of the gas collected in the bottle were recorded. The compressibility factors of propane gas a t atmospheric and lower pressures were applied in the calculation of the phase composition from the observed data. Because the dehydration of the propane was conducted a t pressures ranging from less than 0.1 mm. of mercury to 1 at-
The equilibrium temperature of the cell was measured by means of two calibrated copper-constantan thermocouples inserted into the walls of the equilibrium cell. The thermocouples were calibrated to an accuracy of 0.1' F. in a water bath and in an oil bath with high precision thermometers which are periodically calibrated by the National Bureau of Standards. The temperature of the cell did not vary over 0.3' F. during the equilibrating and sampling operations €or temperatures up to 200" F. and not over 0.5" F. for the higher temperatures. The equilibrium pressures were measured by means of steel tube Bourdon gages calibrated at frequent intervals by a dead weight tester. Three different gages of different ranges were used. The accuracies of the pressure readings were estimated to be within = k l % of the readings taken with the 0 to 150 pounds per
'
INDUSTRIAL AND ENGINEERING CHEMISTRY
442
00040
,
Vol. 45, No.
1
I
1
1
PROPANE-WATER
,012
i
1 SYSTEM
i
i
140
160
,010 00036 W
4 z
008
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$00032
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IL
z
z
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Figure 4.
TABLEI.
100
120
140
160
180
200
EXPERIMEXTAL DATA IN THREE-PHASEREGION
63.0 64.1 83.1 87.0 102.5 111.6 111.8 127.7 128.2 144.1 144.1 170.0 179.0 179.2 187.6 188.6 190.3 192.8 193.0 201.6 201.7
Pressure Lb./Sq. Inch' Abs.
Composition of Vapor Phase, Mole Fraction Water
Concentration of Water in Vapor Phase 113.8 0.002322 114.6 0.002370 151.8 0.003582 159.7 0.003708 195.0 0.004855 220 0.00552 220 0.00549 270 0.00696 271 0.00696 328 0.00854 328 0.00863 0.01097 437 0.01175 488 487 0.01177 529 0.01263 535 0.01278 540 0.01282 0,01282 561 0.01270 562 0,01212 613 0.01208 612
Concentration of Wal>ei-in E'ror lane -Rich Li.quid Phase Propane-Rich Liquid Phase 107.1 0.0001368 58.4 142.5 78.5 0.0003340 142.5 0.0003403 78.7 195.0 0.000614 101.9 195.6 0.000626 101.9 272 0.001368 128.5 271 0.001378 128.8 0.001995 330 144.6 0.003555 438 170.0 443 0.003682 171.0 0.00542 535 188.6 551 0.00605 191.4 0.00544 549 191.6 0.00659 572 195.6 0,00764 611 201.7 0.00769 612 202.15 0.01001 633 205.4 0.00995 638 206.1a
~
Concentration of Propane in Water-Rich Liquid Phase Water-Rich Liquid Phase 82.2 42.3b 101 53.9 142 78.1 143 79.1 191 100.2 191 100.6 284 132.9 300 137.7 366 154.2 391 160.3 446 172.2 482 179.7 538 189.6 543 191.1 608 201.7 632 205.4 a Critical region. 6 Quadruple point by extrapolation.
60
80
100
120
TEMPERATURE,
2;
Concentration of Water in Propane-Rich Phases in Three-phase Region
Temp., O F.
'
80
Figure 5.
'E
I80
200
2
Concentration of Propane in Water-Rich Phase in Three-phase Region
square inch gage, *0.667% of the readings taken with the 0 t o 1000 pounds per square inch gage, and &0.5y0 of the readings taken with the 0 to 3000 pounds per square inch gage. During equilibrating and sampling, the pressures were maintained with variations from the equilibrium pressures not exceeding the abovementioned uncertainties of the gage readings.
TABLE 11. EXPERIMENTAL DATAI N TWO-PHASE REGION (Concentration of water in propane-rich phases) Propane-Rich CompositionPhase of Temp., Pressure O F. Lb./Sq.Inoh' Abs. Mole Fraction Wate; 102 100 0.00954 141 100 0.00492 0.00696 533 100 818 100 0.000587 1015 100 0.000540 0.000673 2018 100 2023 100 0.000591 0 000643 2798 100 2798 100 0.000623 I
150 150 150 150 150 150 150
146 217 289 856 1564 2484 2803
0.02649 0.01702 0.01200 0.002328 0.002224 0.002060 0.002046
190 190 190 190 190 190
190 309 465 1342 2003 2803
0.04967 0.02910 0.01722 0.00502 0.00475 0.00463
205.7 205.7 205.7 205.7 205.7 205.7 205.7 205.7 205.7
207 445 603 637 696 755 1217 2023 2803
0.0637 0.02639 0.01568 0.00998 0.00813 0.00779 0.00726 0.00674 0.00640
230 230 230 230 230 230 230 230
252 446 630 718 823 1530 2023 2704
0.08094 0.04325 0.02659 0.02028 0.01366 0.0133 0.00959 0.00919
260 260 260 260 260 260 260 260
439 675 812 1411 2023 2023 2755
0.07856 0.04660 0.03599 0.02499 0.01843 0.01646 0.01490 0.01649
300 300 300 300 300 300
622 928 1217 1441 2023 2803
996 ~ .
.
0.10146 0.06360 0.04496 0.03875 0.03105 0.02684
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INDUSTRIAL AND ENGINEERING CHEMISTRY
February 1953
443
2.303 R T
Figure 6.
Concentration of Water in Propane-Rich Phases in Two-Phase Region
PRESSURE, PSlA
Figure 7.
Concentration of Propane in Water-Rich Liquid Phase in Two-Phase Region
MATERIALS USED
EXPERIMENTAL RESULTS
The propane used in this investigation was supplied through the courtesy of the Phillips Petroleum Go., Bartlesville, Okla. The propane was reported to contain not less than 99 mole % propane. The principal impurities were approximately 0.2% of other hydrocarbons, mainly ethane and isobutane. Before the propane was charged into the cell, it was passed through a high pressure filter charged with activated carbon, Ascarite, and sodium hydroxide. The distilled water, obtained from the departmental source, was tested for chlorides, boiled several minutes prior to use, and injected into the cell while still above 160' F.
The experimental vapor-liquid equilibria data for the propanewater system are presented in the three-phase region from 54' F. to the three-phase critical of 205.7' F. and 637 pounds per square inch absolut,e in Table I and Figures 4 and 5. The experimental data in the two-phase region from 100 to 2800 pounds per square inch are presented at isotherms of loo", 150°, 190', 205.7', 230°, 260°, and 300' F. for the propane-rich phases in Table I1 and Figure 6, and at isotherms of 54", loo', 133", 190', 205.7", 230', 260°, and 300' F. for the water-rich phase in Table I11 and Figures 7 and 8. The graphically smoothed data in the three-phase region for all three phases are presented in Table IV.
INDUSTRIAL A N D E N G I N E E R I N G C H E M I S T R Y
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TABLE 111.
EXPERIMEXTAL
Vol. 45, No. 2
DATAI N TWO-PHASE REGION
(Concentration of propane in water-rich liquid phase) Pressure, I,h./Sq. Inch A h .
Composition of WaterRich Liquid Phase, Alole Fraction Propane
54.0 54.0 54.0 54.0
617 617 1222 1988
0.0002963 0.0003029 0.0002906 0.0002948
100 100 100 100 100 100 100 133.0 133.0 133.0 133.0
72 117 428 622 1531 2012 2687
0.0000863 0.0001552 0.0002046 0.0002178 0.0602151 0.0002239 0.0002304
188 1199 1810 2787
0.0001499 0.0002249 0.0002267 0.0002364
181 307
O.OOO1146 0.0001763
190 190 190 190
131 224 359 990 1523 2012 2787
205.7 205.7 205.7 205.7 205.7 205.7
230 400 478 910 1810 2787
230 230 230 230 230 230
222 504 810 1128 1810 2787
2 60 260 260 260 260 260
170 332 511 751 1232 1810 2787
0 . WOO796 0.0001330 0.0001960 0,0002580 0.0002703 0.0002745 O.M)02880 0.0001261 0,0002162 0.0002449 0.0002842 0.0003008 0.0003134 0,0001301 0.0002633 0.0003243 0.0003414 0,0003542 0.0003765 0.0001001 0.0001964 0.0002892 0.0003665 0 0004197 0.0004393 0.0004766
300 300 300 300 300 300 300
265 471 ’ 694 987 1565 1810 2787
0.0001666 0.0003031 0.0004130 0.0004876 0.0005801 0.0006078 0 0006861
Temp.,
170 170 100 190
F
’
190
260
N
PRESSURE, PSlA
Figure 8. Concentration of Propane in Water-Rich Liquid Phase in Tw-o-Phase Region at Low Pressures
Tal~lesV and VI list the graphically smoothed equilibrium concentrat,ion of water in the propane-rich phases and the propane respect,ively. ~~D~~~~~ ~~ ~ ~R~~~~~~ ~ FOX~Lk121, ~ in the ~~ A-ater-rich ~ ~ phase ~in the - two-phase ~ pregion, ) ~ T ~11’. ~s ~ , Ix ~ THREE PHASES Figures 9 and 10 present the smoothed data of Tables T‘ and VI along isobars, with Figure 10 showing the niinimum isohaik Composition, Xole Fraction Pressure. Water in Propane in solubility for all pressures above 300 pounds per square inch. Temp., I,b./Sq. Water in propane-rich water-rich F. Inch. Ahs. vapor phase liquid phase liquid phase THESO1,UBILITY O F \%-ATER I S H Y I ) R O C b R B O N - r t I C H I’I-I.4SES. 42.3 82.2 0,00140 0 . 000105 0 000366 I n the three-phase region, the so1ubilit~-of water in the propane60.0 108.5 0.00218 0.000187 0.000264 rich liquid phase and in the vapor phase describes a continuous 80.0 146.0 0.00335 0.000344 0.000219 100.0 191.5 0.00466 0.00061; 0.000203 envelope (Figure 4), which closes a t t.he three-phase critical con120 246 0.00625 0.00109 0.000199 ditions. A t the three-phase critical conditions the intensive 140 311 0.00813 0.00184 0.000202 160 389 0.01002 0,00291 0.000212 properties of these two phases become continuously identical. 170 432 0.01097 0.00358 0 000223 180 483 0.01191 0.00446 0.000236 The critical composition occurs a t the highest. temperature 538 0.01280 0.00558 0.000250 190 a t which t,he three phases coesist. At the critical composition, 195 468 0.01278 0.00632 0.000256 200 602 0.01237 0.00723 0.000264 t.he rates of cha.nge of the concentration of the vapor phase 205.7“ 637 0,00998 0.00998 0.000272 and t.he lighter liquid phase ‘I 3-phase critical. with respect to temperature are minus and plus infinity, reTABLE I-. GRIPHICSLLY SMOOTHED DATA IK TM-O-PHASE REGION spectively. Pressure, Temperature, F. Figure 6 indicates that the Lb./Sq. 100 130 160 190 205.7 220 250 280 310 Mole Fraction Water in Propane-Rich Phases solubility of water in the proInch Abs. 0.1330 0 4920 0.7727 0,02360 0 0505 0.0962 0.2999 pane-rich phases is related to 0.00979 0.04678 0.1489 0 02382 0.0647 0 2449 0.3837 0.000605 0.01104 the volumetric behavior of the 0.2547 0 01500 0 1618 0.03034 0.0984 0.04246 0.0562 0.000605 0,00139 0,1892 0 1205 0.03034 0.04083 0.0726 0.000604 0.001380 0 002911 0.02123 same phases. As the concen0.1489 0.02218 0.03041 0 , 0 5 5 2 0 0931 0.000604 0.001374 0 002877 0.01503 0.1222 trations of water in these 0.000604 0.001365 0 002838 0.005507’ 0.01563 0.02264 0.04935 0 0764 0.1146 0.00998 0.01941 0.04065 0 0711 0.000603 0.001361 0 002829 0.00547 phases are low, the volu0.1030 0.00815 0.01486 0.03622 0 0637 0.000603 0.001358 0 002819 0.00542 0.0887 0.00782 0.01124 0,02898 0 0540 0.000602 0,001355 0 002799 0 00635 metric behavior of these phases 0 00767 0.01001 0.02323 0 04581 0.0778 0.000601 0.001352 0 002773 0.00527 0.00752 0.00964 0.01897 0 03917 0,0687 0,000600 0,001349 0 002760 0,00521 mag be expected to be similar 0.0518 0 01563 0 02992 0.001340 0,00.509 0,00705 0 002729 0.00933 0.000698 to that of pure propane ( 1 2 ) . 0.000597 0,001327 0 002698 0.004978 0.00703 0,00895 0.01455 0 02642 0.04405 0.000596 0.001321 0 002655 0.004809 0.00665 0.00845 0,01370 0 02280 0 3642 From thermodynamic consid0.000594 0.001315 0 002600 0,004571 0 00619 0.00787 0.01265 0 02009 0.03112 (%rations,both the volumetric O
~
INDUSTRIAL AND ENGINEERING CHEMISTRY
February 1953
TEMPERATURE, DEG.
Figure 9.
445
F
Concentration of Water i n Propane-Rich Phases in Two-Phase Region
0 Figure 10.
Concentration of Propane in Water-Rich Liquid Phase in Two-Phase Region Along Isobars
behavior of the propane-rich phases along isotherms below 205.7” F. and the concentration isotherms of the solubility of water in the same phases below 205.7’ F. are discontinuous. Raoult’s law (18) predicts that an isotherm of a “log concentration us. log pressure plot’’ is a straight line of slope minus 1 passing through the point representing the vapor pressure of pure water a t that temperature. The dotted lines of this slope of Figure 6 indicate portions of these ideal isotherms which have been used wherever appropriate to aid in drawing the “best
curve” through the experimental points and in extrapolating the data. The data indicate both positive and negative deviations from Raoult’s law. SOLUBILITY OF PROPANE IN WATER. Figures 7 and 8 represent the original data on the solubility of propane in water along isotherms from 54” t o 300’ F. The concentration of propane in the water-rich phase in the three-phase region is shown as a concaved curve with a minimum a t about 250 pounds per square inch, which terminates at 205.7’ F. and 637 pounds per square
TABLE VI. GRAPHICALLY SMOOTHED DATAI N Pressure, Lb./Sq. Inch. Abs. 100 200 300 400 500 600 637 700 800 900 1000 1500 2000 2500 3000
Vol. 45, No. 2
INDUSTRIAL AND ENGINEERING CHEMISTRY
446
60
100
130
0.0002873 O.OOO2670 0.0002679 0.0002687 0.0002696 0.0002703 0.0002706 0.0002711 0.0002717 0,0002722 0.0002728 0,0002748 0.0002760 0.0002768 0.0002775
0.0001273 0.0002045 0.0002060 0.0002076 0.0002091 0.0002106 0.0002112 0.0002122 0.0002137 0.0002152 0.0002166 0.0002221 0.0002264 0.0002287 0.0002302
0.0000876 0.0001603 0.0002003 0.0002043 0.0002075 0.0002090 0.0002108 0.0002124 0.0002145 0.0002164 0.0002182 0.0002228 0.0002276 0.0002307 0.0002355
TWO-PHASE
Temperature, O F. 160 190 205.7 Mole Fraction Propane in Water-Rich 0.0000609 0.0000698 0.0000582 0.0001303 0.0001172 0.0001197 0.0001700 0.0001782 0.0001696 0.0002132 0.0002138 0.0002107 0.0002400 0.0002210 0.0002468 0.0002530 0.0002680 0.0002261 0.0002550 0.0002271 0.0002723 0.0002295 0.0002578 0.0002767 0.0002319 0.0002602 0.0002815 0.0002623 0.0002341 0.0002846 0.0002358 0.0002642 0,0002865 0.0002415 0.0002715 0.0002957 0.0002462 0.0002783 0,0003043 0.0002507 0.0002835 0.0003116 0.0002542 0.0002877 0.0003160
inch absolute. T o preserve the clarity of Figure 7, some of the isotherms for the temperatures greater than 170” E’. have been omitted a t low pressures but are shown in Figure 8. As in the case of the solubility of water in the propane-rich phases, the solubility of propane in the water-rich phase is seen to be directly related to the volumetric behavior of the propane-
REQIOY
220 Phase 0.0000562 0.0001180 0.0001708 0.0002173 0.0002550 0.0002798 0.0002878 0.0002952 0.0003053 0.0003115 0.0003155 0.0003257 0.0003357 0.0003445 0.0003526
250
280
310
0.000513 0.0001170 0.0001768 0.0002307 0.0002767 0.0003107 0.0003222 0.0003375 0.0003562 0,0003695 0.0003787 0.0003995 0.0004144 0.0004293 0,0004442
0.0000415 0.0001160 0.0001857 0.0002480 0.0003000 0.0003453 0.0003602 0.0003828 0.0004087 0.0004287 0.0004444 0.0004927 0.0005246 0.0005502 0.0005753
0.0000220 0.0001147 0.0001923 0.0002677 0.0003277 0.0003803 0.0004007 0.0004290 0.0004627 0.0005133 0.0004886 0.0006160 0.0006858 0.0007332 0.0007703
rich phases or t o pure propane. Thus, if the compressibility o f the propane-rich phase is high, as in the behavior of a gas, the effect of pressure on the solubility of propane is high. On the other hand, a low compressibility of the propane-rich pha5e,e.g., that of a liquid,-is marked by a small effect of pressure on the solubility.
(Vapor-Liquid Equilibria f o r Binary Hyd rocarbon-Water Systems) CORRELATION OF DATA
P
ROCEDURES for correlating data are useful when they permit the prediction of the behavior of systems for which data are not available or when they may be used to extrapolate experimental data. The water contents of hydrocarbon-rich phases are correlated, whether the phase be gaseous, liquid, or in the fluid region. The hydrocarbon-rich portion of the hydrocarbon-water system may consist of a liquid phase and a gas phase, or of a single phase. The proposed correlation uses temperature and the molal volume of the hydrocarbons in the phase as variables and in this manner avoids reference to the number of phases in the system and to pressure. Several correlations have been made of the saturated water content a t high pressures of gases such as nitrogen, hydrogen, methane, ethane, and complex hydrocarbon mixtures ( I , 20, 22, 24). These methods, however, do not treat the vapor phase and the hydrocarbon-rich liquid phase as continuous phases. The simplest relation expressing the saturated water content in the vapor phase, which is generally valid a t low pressures for the nonpolar gases, is that Y = P”/P (1) where y = mole fraction of water in the vapor a t the temperature of the system p o = vapor pressure of water at the temperature of the system P = total pressure of the system Equation 1 results from the use of Dalton’s law of partial pressure and Raoult’s law, and the liquid phase is substantially pure water. Under conditions of temperature and pressure where the vapors no longer behave ideally, Equation 1 leads to serious error. Saddington and Krase ( 2 7 ) have found that a t high pressures the saturated water content of nitrogen greatly exceeds the value predicted from the application of Poynting’s relationship (18),and this has been found to be true for aqueous hydrocarbon systems ( 2 2 ) . That the relationship cannot explain the increased volatility of water with increased pressure
a t a given temperature indicates that the nonpolar gases actually have a solvent effect upon the water inolecules a t high pressures. It is evident that the same attractive and intramolecular forces come into play a t high pressures in the “solubility of a liquid in a gas” as in the solubility of a gas in a liquid. These forces are the same as those which create critical phenomena, The experimental data of the propane-water system suggr.t a correlation based upon the volumetric behavior of the hytli ocarbon-rich phases and temperature as parameters. Figuro 1 1 presents an empirical correlation in which the concentration of vater in the hydrocarbon is plotted as a function of the anhydrous molal volume of the hydrocarbon for several isotherms along lines of constant molecular weight. The correlation has been primarily developed from binary hydrocarbon-water systems, although available data on complex mixtures have been used. The molal volume is expressed here in milliliters of anhydrous hydrocarbon per gram mole of anhydrous hydrocarbon. I t is permissible to use the anhydrous molal volume rather than the actual molal volume as a correlating variable because of the low concentrations of water present in the hydrocarbon-rich phase, except a t low pressures where the solubility relationships follow Equation 1. The effect of molecular weight on the isotherms is almost nonexistent a t high molal volumes (low pressures), but becomes appreciable as the molal volumes approach those of light hydrocarbon liquids. On Figure 11, the saturated concentrations of water in methane ( 2 2 ) and in ethane ( 2 4 ) were obtained from the xork of Olds, Sage, and Lacey. The solubility of water in propane was obtained from experimental data of the authors and the threephase data of n-butane-water system from Reamer, Olds, Sage, and Lacey (25). The methane-n-butane-water data were obtained from the work of McKetta and Kat2 ( 1 9 ) . The threephase points of the last-mentioned work have been distinguished from the two-phase points on Figure 11. The data on the water content of a natural gas measured by Dodson and Standing (10)have been utilized. Additional experimental points on the
