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A static equilibrium apparatus for (vapour + liquid) equilibrium measurements at high temperatures and pressures Results for (methane + n-pentane)
M-2048 .I. Chem. Thermo&namics 1987, 19.467-477
A static equilibrium apparatus for (vapour + liquid) equilibrium measurements at high temperatures and pressures Results
for
(methane
W.-E. REIFF,
P. PETERS-GERTH,
+ n-pentane) and K. LUCAS
Universitiit Duisburg, Fachbereich 7, Thermodynamik Lotharstrasse I, 4100 Duisburg 1, F.R.G. (Received 6 June 1986; in jnal
form 15 September 1986)
A static equilibrium cell is described which permits (vapour + liquid) equilibrium measurements in the range of 273 to 473 K and pressures up to 30 MPa. Both phases are analysed in a gc. Measurements are reported on (methane + n-pentane) between 311 and 411 K and up to 16 MPa.
1. Introduction (Vapour + liquid) equilibrium measurements, particularly at high temperatures and pressures, require much care, if reliable results are to be obtained. This is especially true when equilibria with supercritical fluids are encountered. In this paper we describe an apparatus based on the static method for temperatures between 273 to 473 K and pressures up to 30 MPa in combination with a g.c. system constructed to give reliable compositions of both phases. We report measurements on (methane + n-pentane) between 311 K to 411 K and up to 16 MPa, such that methane is supercritical at all measured isotherms. The new results are compared with the results of earlier authors.
2. Apparatus and materials Figure 1 is a block diagram of the apparatus. cl) The whole can be divided into various sub-systems. The pressure required for a particular point was generated by pressing gas into the autoclave. The gas was taken from commercially available gas cylinders. If the pressure in the gas cylinder was above the desired experimental pressure, the gas was pressed directly into the autoclave. Otherwise, a single-step membrane compressor (Aminco, type 46-13411) brought the gas to the required pressure. A 002 I -9614/87/050467
+ I I $02.00/O
cm 1987 Academic
Press Inc. (London)
Limited
468
W.-E.
REIFF.
P. PETERS-GERTH.
AND
K. LUCAS
VLE
FOR
(METHANE
+ n-PENTANE)
469
hand-operated volumetric pump (Aminco, type 466193 15) allowed fine adjustment of pressure. The liquid was filled into the autoclave from the bottom. Figure 1 shows the system. It was pumped from the storage vessel into the autoclave by a metering pump (Dosapro Milton-Roy, type 57.A3.Bl.Cl.Dl). Before the apparatus was loaded with the desired components, it had to be evacuated. The vacuum was produced by a vacuum pump (Leybold-Heraeus, type Trivac D4A). It was monitored by a thermal-conductivity vacuum meter (Leybold-Heraeus, Thermovac TM 22082) which allowed measurements to be made down to 0.1 Pa. The nominal volume of the autoclave was 2000 cm3. This unusually large volume was selected so as to allow taking several relatively large samples without appreciably disturbing the phase equilibrium, even at low pressures. It was made of (chromium + nickel + molybdenum) steel and is shown schematically in figure 2. As shown in the figure, the lid of the autoclave contained four L-shaped inlets accessible from its side: Bl to B4. Bl to B2 served to load gas and liquid, B3 accommodated the pressure tubing transmitting pressure to the Heise precision gauge and the strain-gauge pressure transducer and additionally connected the vacuum-pump system with the autoclave. B4 served to take samples from the gas phase. Further, the lid of the autoclave contained four straight inlets, Al to A4. serving to accommodate pressure-resistant tubes for thermometers of various lengths. The bottom port served for taking liquid samples, as well as for loading or discharging the liquid. Equilibrium was attained by using a rotating stirrer coupled to an externally mounted rotating permanent magnet.
FIGURE
2. The autoclave.
470
W.-E.
REIFF.
P. PETERS-GERTH,
G.c. sample piping--l
AND
K. LUCAS
Triple-loop >ampling valve SUPP’Y valves /
Loop inlet to the sampling chamber
E -I-
/ Triple-loop_/ assembly :I
FIGURE
3. The sampling
chamber.
Particular care was taken to achieve a uniformity in temperature of better than 0.05 K over the whole autoclave. The autoclave was jacketed by a double-walled brass vessel through which the liquid of the thermostat was forced. The side of the lid was thermostatted by a wound copper tubing, while for its top a double-walled brass plate was used. To achieve an optimum of control, two circulations of the thermostatting liquid were provided, one for the autoclave and one for its lid. The temperature level of the autoclave as a whole was initially disturbed by fluctuations of the laboratory temperature. This effect was eliminated by a particular control system described in detail elsewhere.“’ The pressure in the autoclave was measured by two devices working independently. A Heise precision gauge with a range from 0 to 40 MPa and an accuracy of 0.1 per cent of the full scale was used mainly to control the pressure during pressure generation. The actual pressure measurements were made by use of a strain-gauge pressure transducer (Burster, type TJE) with a digital bridge (Burster, type 982IT/43). Two pressure transducers were available, one in a range of up to 7 MPa, the other up to 50 MPa. Non-linearity, hysteresis, and repeatability of both transducers were rated at 0.1 per cent of the full-scale values. An officially acknowledged pressure-calibrating device (Huber Instrumente, type PRD 3012) was employed to confirm zero-point setting and linearity in appropriate intervals allowing a reliable interpretation of pressure readings within 0.03 per cent of the full-scale value.
VLE
FOR
(METHANE
471
+ n-PENTANE)
b--
-m-
Washer
.!
Cup spring
-/-
Click-stop positioning
‘-...
Spring-loaded lock hall
1
Cylindrical
Gasket
pin -L
1 i6
9
-,E
,,-
ring
Main
body
- Main
gasket
!P
Coupling
Exchangeable triple-loop
FIGURE
4. The sampling
valve
Temperatures were measured by platinum resistance thermometers (Leeds & Northrup, type 8926) at three positions in the autoclave, at the bottom, in the centre, and below the lid. A fourth thermometer in the centre was connected with the thermostat. Using a particular precision temperature bridge (Leeds & Northrup, type 8078) permitted a resolution of 0.025 K, which could be extended to 0.001 K by connecting with a voltmeter. The whole system for temperature measurement was calibrated by use of a high-precision quartz thermometer, which in turn was calibrated at the triple-point temperature of water. The accuracy of temperature measurement was estimated to be kO.01 K. The compositions of both phases were determined by a g.c. (Intersmat, type IGC 16) with a computer-controlled integrator (Perkin-Elmer, type Sigma 10). The
472
W.-E. REIFF, P. PETERS-GERTH.
FIGURE 5. Calibration curves for (xCH,+(l experimental results for t-c. d.
AND K. LUCAS
-x)C,H,,).
x1 Experimental results for T.-i. d.: +.
various steps leading to the final information were sampling, preparation of the samples for the g.c., and the evaluation in the g.c. Samples from the gas phase were taken from the top and samples from the liquid phase from the bottom of the autoclave by use of high-pressure capillaries with an i.d. of 0.15 mm. Samples were transferred into a low-pressure sampling chamber of 700 cm3, where they were homogenized by an electromagnetic stirrer. The sampling chamber was heated to ensure the gaseous state of the sample. Its main objective was to permit relatively large and, therefore, representative samples to be drawn. The sampling chamber, operating at a maximum pressure of 0.05 MPa, is shown in figure 3. Four inlets in its lid served to let in samples from gas and liquid and as connections to the vacuum system and the pressure measurement. A particular feature of the sampling chamber was a tripleTABLE
1. Summary of (vapour + liquid) equilibria for (methane + n-pentane)
Authors
Year
Ref.
T/K
PIMPa
Frohhch et al. Sage et al.
1931 1936
2 3
298 311 to 378
0.1 to 10.1 5.9 to 16
Sage and Lacey
1938
4
311 to 378
1.4 to 13.8
Boomer et al.
1938
5
298 to 358
3.6 to 19
Taylor et al.
1939
6
311 to 378
0.1 to 16.7
Sage et a(. Sage and Lacey
1942 1950
I 8
310to444 311 to 444
0.1 to 16.9 0.1 to 16.9
Berry and Sage Prodany and Williams Chen et al.
1970 1971 1974
9 10 11
280 to 460 17.2 371 6.9 to 13.8 113 to 273 0.1 to 15
Remarks Results in graphical form only. Vapour pressures and volumes for three compositions. Equilibrium constants for methane. Low purity of CH, (94.4 moles per cent). Few experimental results for the liquid phase. Smoothed isothermal results. Graphical interpolation of references 6 and 4. No new measurements. CP,x. Y) Dew point.
VLE TABLE
2. Unsmoothed
FOR
results
(METHANE for {xCH,+(I
473
+ n-PENTANE) -x)C,H,,}(I)
= {yCH,+(l
-y)C,H,,)g
TW
pJMPa
310.89
0.693 1.393 2.763 4.130 5.514 6.950 8.620
0.0300 0.0637 0.1305 0.1906 0.2488 0.3077 0.3773
0.8349 0.9095 0.9433 0.9534 0.9567 0.9564 0.9539
27.83 14.28 7.23 5.00 3.84 3.11 2.53
0.17 0.10 0.07 0.06 0.06 0.06 0.07
10.350 10.560 12.030 12.100 13.770 15.460 16.100
0.4469 0.4512 0.5113 0.5176 0.5826 0.6674 0.7124
0.9497 0.9469 0.9394 0.9372 0.9235 0.8925 0.8661
2.13 2.10 1.84 1.81 1.59 1.34 1.22
0.09 0.10 0.12 0.13 0.18 0.32 0.47
344.45
0.950 1.815 2.772 4.100 5.640 6.970
0.0297 0.0672 0.1093 0.1633 0.2227 0.2740
0.6614 0.8056 0.858 1 0.8807 0.9004 0.9055
22.27 11.99 7.85 5.39 4.04 3.30
0.35 0.21 0.16 0.14 0.13 0.13
8.670 10.310 12.050 12.975 13.785 15.460
0.3382 0.3999 0.4703 0.5083 0.5459 0.6470
0.9081 0.9024 0.8910 0.8777 0.8672 0.8111
2.69 2.26 1.89 1.73 1.59 1.25
0.14 0.16 0.21 0.25 0.29 0.54
360.07
1.048 2.038 3.050 4.075 6.060 8.000
0.0258 0.0687 0.1117 0.1535 0.2303 0.3033
0.5413 0.7375 0.8056 0.8373 0.8640 0.8693
21.02 10.74 7.21 5.45 3.75 2.87
0.47 0.28 0.22 0.19 0.18 0.19
10.100 11.010 12.100 14.010 14.750
0.3813 0.4195 0.4626 0.5517 0.6083
0.8647 0.8590 0.8472 0.8108 0.7768
2.21 2.05 1.83 1.47 1.28
0.22 0.24 0.28 0.42 0.57
377.60
1.020 2.050 2.790 4.170 6.060 6.870
0.0152 0.0580 0.0894 0.1462 0.2168 0.2479
0.3122 0.6136 0.6941 0.7656 0.8017 0.8093
20.54 10.58 7.76 5.24 3.70 3.26
0.70 0.41 0.34 0.27 0.25 0.25
8.570 10.320 12.240 13.820 14.110
0.3123 0.3828 0.4656 0.5634 0.6016
0.8119 0.8066 0.1797 0.7164 0.6798
2.60 2.11 1.67 1.27 1.13
0.27 0.31 0.41 0.65 0.80
410.97
1.829 2.787 4.162 5.520
0.0224 0.0635 0.1196 0.1734
0.2342 0.4350 0.5567 0.6159
10.46 6.85 4.65 3.55
0.78 0.60 0.50 0.46
6.884 8.750 10.250 10.520
0.2269 0.3095 0.3941 0.4131
0.6429 0.6468 0.6196 0.6105
2.83 2.09 1.57 I .48
0.46 0.51 0.63 0.66
Y
Y
fWH,)
W,H,,)
piMPa
:
Y
MN,)
K(C,H,
loop sampling valve, a detailed view of which is shown in figure 4. This valve contained three loops. At a particular moment, the first loop was open to the sampling chamber and thus contained the sample, the second was open to the carrier-gas stream of the g.c., for which we used helium, and the third was open to the vacuum system. The loop valve was next turned into the second position, where the first loop containing the sample was opened to the carrier gas and thus carried the sample to the g.c., the second loop was evacuated, and the third took in the sample. Changing the position of the loop-valve three times opened the first loop again to the sampling chamber and the process repeated itself. This sampling chamber was also used as a mixing chamber, in which well defined gaseous mixtures were prepared to calibrate the g.c. The compositions of the gas mixtures used to calibrate the g.c. were determined from their partial pressures according to Dalton’s law. For the required low-pressure measurements a Baratron pressure transducer (MKS, type 310 BH-10000) was used with an accuracy of f 1 x 10m4 MPa. Alternatively, the g.c. was calibrated with the pure components alone by using the sampling chamber. For the mixtures considered below, i.e. (methane + n-pentane). a flame-ionization detector and a thermal-conductivity detector were used. The
1)
474
W.-E.
REIFF,
P. PETERS-GERTH.
AND
K. LUCAS
1. j
(Figure
.Y, \
6, continued
on following
page)
calibrating curves for both detectors are shown in figure 5. For the f.-i. d. the sensitivity was 10-l’ A. mV-‘; the current in the bridge for the t.-c. d. was set at 200 mA, the temperatures in the oven and in the detector were 308 and 343 K, respectively. Separation of the components was achieved by using a 1.5 m x 3.2 mm column packed with 10 mass per cent of SE30 on 80 to 100 mesh Chromosorb PAW 99.999 moles per cent He was used as the carrier gas with a flow rate of 0.5 cm’. s-r. Methane (Messer Griesheim) had a claimed purity of 99.995 moles per cent. n-Pentane (Merck) had a claimed purity of 99 moles per cent. Methane was checked in the g.c. with satisfactory results. n-Pentane was carefully degassed and then checked in the g.c. as well as by measuring its density and refractive index. Slight impurities were detected in the g.c. and were taken care of by corresponding calibration. No further purification was attempted. The density at 293 K agreed with the literature with 0.02 per cent, the refractive index being within 0.1 per cent. 3. Results on (methane
+ n-pentane)
The apparatus described above was used to determine (vapour + liquid) equilibria for (methane + n-pentane) in a range of temperatures from 311 to 411 K extending
VLE FOR (METHANE
h-
2 4-/ 00
+P
+ n-PENTANE)
475
P +
-1 I 0.4I 0.2
I 0.6
I
0.X
f I 0
sxb42 0 (a), at 310.89 K; (b), at FIGURE 6. (Vapour + liquid) equilibria for (xCH,+(l-x)C,H,,}: 344.45 K; (c), at 360.07 K; (d), at 377.60 K: and (e), at 410.97 K. 0. This work; x. Sage et al.:” A. Taylor er ~1.;‘~’ +, interpolated from Berry and Sage;“” 0. Prodany and Williams.““’
to pressures up to 16 MPa. Table 1 contains a summary of earlier results, including some comments. Table 2 gives a summary of the results obtained in this work including K-factors for both components, where Ki = yi/xi. Figure 6 shows (p, x, y) diagrams for the various experimental temperatures, including the results of this
476
W.-E.
REIFF,
P. PETERS-GERTH.
AND
K. LUCAS
Methane
0.
0.c
I
I
I
1
10
20
pIMPa {xCH,+(l -x)C,H,,}. FIGURE 7. K-values for A, T = 360.07 K; 0, T = 377.60 K; 0, T = 410.97 K.
x/xy
h loE: ‘c.
x
0,
T = 310.89
K:
A,
T = 344.45
K;
@\
/
/ 5sx \0
I 250
’ 200
I 300
I 350
I 400
I 450
T/K FIGURE 8. Critical curve et d.;“’ V, pure components.
for
{xCH,+(l-x)C,H,*}.
0,
This
work;
x1 Chen
et a~.;~lL~ 0,
Sage
VLE FOR (METHANE
+ n-PENTANE)
477
work as well as the results of other investigators. Figure 7 shows the K-factors. The critical locus, as extrapolated from the results, is shown in figure 8 and compared with the results of other authors. The results of this work are generally in good agreement with those of Sage and Lacey and of Sage, Reamer, Olds, and Lacey, respectively. On the bubble line, the agreement in mole fraction is fO.001; on the dew line the new measurements give slightly higher X, on the average f0.015. An error analysis including the errors of the temperature measurement, the pressure measurement, and the composition measurement yields absolute errors in x between to.1 x lop3 and f8.3 x low3 in the liquid phase and between fO.O1 x 10m3 and +8.2x 10m3 in the gas phase. The estimated average error in both phases is kO.003. REFERENCES I.
7. 3. 4. 5. 6. 7. 8.
9. IO. I I.
Reiff. W.-E. E.xperimental determination of vapour-liquid equilibria qf binary systems with supercritical componenrs. Ph.D. Thesis, Universitlt Duisburg. 1985. Frohhch. P. K.; Tauch, E. J.; Hogan, J. J.; Peer, A. A. Ind. Eng. Chem. 1931, 23, 548. Sage, B. H.: Webster, D. C.; Lacey, W. N. Ind. Eng. Chem. 1936. 28. 1045. Sage, B. H.; Lacey, W. N. Ind. Eng. Chem. 1938, 30, 1296. Boomer, E. H.; Johnson, C. A.; Piercey, A. G. A. Can. J. Res. B. 1938, 16, 319. Taylor, H. J.; Wald, G. W.; Sage, B. H.; Lacey, W. N. Oil and Gas J. 1939, 33, 46. Sage, B. H.; Reamer, H. H.; Olds, R. H.; Lacey, W. N. Ind. Eng. Chem. 1942, 34, 1108. Sage, B. H.; Lacey, W. N. Thermodynamic properties of the lighter paraffin h.ydrocarbons and nitrogen. Monograph on API research project 37. API. 1950. Berry, V. M.; Sage, B. H. NSRDS-NBS 1970, 32. Prodany, N. W.; Williams, B. J. Chem. Eng. Data 1971, 16, 1. Chen, R. J. J.; Chappelear. P. S.; Kobayashi. R. J. Chem. Eng. Data 1974, 19. 58.
A static equilibrium apparatus for (vapour + liquid) equilibrium measurements at high temperatures and pressures Results
for
(methane
W.-E. REIFF,
P. PETERS-GERTH,
+ n-pentane) and K. LUCAS
Universitiit Duisburg, Fachbereich 7, Thermodynamik Lotharstrasse I, 4100 Duisburg 1, F.R.G. (Received 6 June 1986; in jnal
form 15 September 1986)
A static equilibrium cell is described which permits (vapour + liquid) equilibrium measurements in the range of 273 to 473 K and pressures up to 30 MPa. Both phases are analysed in a gc. Measurements are reported on (methane + n-pentane) between 311 and 411 K and up to 16 MPa.
1. Introduction (Vapour + liquid) equilibrium measurements, particularly at high temperatures and pressures, require much care, if reliable results are to be obtained. This is especially true when equilibria with supercritical fluids are encountered. In this paper we describe an apparatus based on the static method for temperatures between 273 to 473 K and pressures up to 30 MPa in combination with a g.c. system constructed to give reliable compositions of both phases. We report measurements on (methane + n-pentane) between 311 K to 411 K and up to 16 MPa, such that methane is supercritical at all measured isotherms. The new results are compared with the results of earlier authors.
2. Apparatus and materials Figure 1 is a block diagram of the apparatus. cl) The whole can be divided into various sub-systems. The pressure required for a particular point was generated by pressing gas into the autoclave. The gas was taken from commercially available gas cylinders. If the pressure in the gas cylinder was above the desired experimental pressure, the gas was pressed directly into the autoclave. Otherwise, a single-step membrane compressor (Aminco, type 46-13411) brought the gas to the required pressure. A 002 I -9614/87/050467
+ I I $02.00/O
cm 1987 Academic
Press Inc. (London)
Limited
468
W.-E.
REIFF.
P. PETERS-GERTH.
AND
K. LUCAS
VLE
FOR
(METHANE
+ n-PENTANE)
469
hand-operated volumetric pump (Aminco, type 466193 15) allowed fine adjustment of pressure. The liquid was filled into the autoclave from the bottom. Figure 1 shows the system. It was pumped from the storage vessel into the autoclave by a metering pump (Dosapro Milton-Roy, type 57.A3.Bl.Cl.Dl). Before the apparatus was loaded with the desired components, it had to be evacuated. The vacuum was produced by a vacuum pump (Leybold-Heraeus, type Trivac D4A). It was monitored by a thermal-conductivity vacuum meter (Leybold-Heraeus, Thermovac TM 22082) which allowed measurements to be made down to 0.1 Pa. The nominal volume of the autoclave was 2000 cm3. This unusually large volume was selected so as to allow taking several relatively large samples without appreciably disturbing the phase equilibrium, even at low pressures. It was made of (chromium + nickel + molybdenum) steel and is shown schematically in figure 2. As shown in the figure, the lid of the autoclave contained four L-shaped inlets accessible from its side: Bl to B4. Bl to B2 served to load gas and liquid, B3 accommodated the pressure tubing transmitting pressure to the Heise precision gauge and the strain-gauge pressure transducer and additionally connected the vacuum-pump system with the autoclave. B4 served to take samples from the gas phase. Further, the lid of the autoclave contained four straight inlets, Al to A4. serving to accommodate pressure-resistant tubes for thermometers of various lengths. The bottom port served for taking liquid samples, as well as for loading or discharging the liquid. Equilibrium was attained by using a rotating stirrer coupled to an externally mounted rotating permanent magnet.
FIGURE
2. The autoclave.
470
W.-E.
REIFF.
P. PETERS-GERTH,
G.c. sample piping--l
AND
K. LUCAS
Triple-loop >ampling valve SUPP’Y valves /
Loop inlet to the sampling chamber
E -I-
/ Triple-loop_/ assembly :I
FIGURE
3. The sampling
chamber.
Particular care was taken to achieve a uniformity in temperature of better than 0.05 K over the whole autoclave. The autoclave was jacketed by a double-walled brass vessel through which the liquid of the thermostat was forced. The side of the lid was thermostatted by a wound copper tubing, while for its top a double-walled brass plate was used. To achieve an optimum of control, two circulations of the thermostatting liquid were provided, one for the autoclave and one for its lid. The temperature level of the autoclave as a whole was initially disturbed by fluctuations of the laboratory temperature. This effect was eliminated by a particular control system described in detail elsewhere.“’ The pressure in the autoclave was measured by two devices working independently. A Heise precision gauge with a range from 0 to 40 MPa and an accuracy of 0.1 per cent of the full scale was used mainly to control the pressure during pressure generation. The actual pressure measurements were made by use of a strain-gauge pressure transducer (Burster, type TJE) with a digital bridge (Burster, type 982IT/43). Two pressure transducers were available, one in a range of up to 7 MPa, the other up to 50 MPa. Non-linearity, hysteresis, and repeatability of both transducers were rated at 0.1 per cent of the full-scale values. An officially acknowledged pressure-calibrating device (Huber Instrumente, type PRD 3012) was employed to confirm zero-point setting and linearity in appropriate intervals allowing a reliable interpretation of pressure readings within 0.03 per cent of the full-scale value.
VLE
FOR
(METHANE
471
+ n-PENTANE)
b--
-m-
Washer
.!
Cup spring
-/-
Click-stop positioning
‘-...
Spring-loaded lock hall
1
Cylindrical
Gasket
pin -L
1 i6
9
-,E
,,-
ring
Main
body
- Main
gasket
!P
Coupling
Exchangeable triple-loop
FIGURE
4. The sampling
valve
Temperatures were measured by platinum resistance thermometers (Leeds & Northrup, type 8926) at three positions in the autoclave, at the bottom, in the centre, and below the lid. A fourth thermometer in the centre was connected with the thermostat. Using a particular precision temperature bridge (Leeds & Northrup, type 8078) permitted a resolution of 0.025 K, which could be extended to 0.001 K by connecting with a voltmeter. The whole system for temperature measurement was calibrated by use of a high-precision quartz thermometer, which in turn was calibrated at the triple-point temperature of water. The accuracy of temperature measurement was estimated to be kO.01 K. The compositions of both phases were determined by a g.c. (Intersmat, type IGC 16) with a computer-controlled integrator (Perkin-Elmer, type Sigma 10). The
472
W.-E. REIFF, P. PETERS-GERTH.
FIGURE 5. Calibration curves for (xCH,+(l experimental results for t-c. d.
AND K. LUCAS
-x)C,H,,).
x1 Experimental results for T.-i. d.: +.
various steps leading to the final information were sampling, preparation of the samples for the g.c., and the evaluation in the g.c. Samples from the gas phase were taken from the top and samples from the liquid phase from the bottom of the autoclave by use of high-pressure capillaries with an i.d. of 0.15 mm. Samples were transferred into a low-pressure sampling chamber of 700 cm3, where they were homogenized by an electromagnetic stirrer. The sampling chamber was heated to ensure the gaseous state of the sample. Its main objective was to permit relatively large and, therefore, representative samples to be drawn. The sampling chamber, operating at a maximum pressure of 0.05 MPa, is shown in figure 3. Four inlets in its lid served to let in samples from gas and liquid and as connections to the vacuum system and the pressure measurement. A particular feature of the sampling chamber was a tripleTABLE
1. Summary of (vapour + liquid) equilibria for (methane + n-pentane)
Authors
Year
Ref.
T/K
PIMPa
Frohhch et al. Sage et al.
1931 1936
2 3
298 311 to 378
0.1 to 10.1 5.9 to 16
Sage and Lacey
1938
4
311 to 378
1.4 to 13.8
Boomer et al.
1938
5
298 to 358
3.6 to 19
Taylor et al.
1939
6
311 to 378
0.1 to 16.7
Sage et a(. Sage and Lacey
1942 1950
I 8
310to444 311 to 444
0.1 to 16.9 0.1 to 16.9
Berry and Sage Prodany and Williams Chen et al.
1970 1971 1974
9 10 11
280 to 460 17.2 371 6.9 to 13.8 113 to 273 0.1 to 15
Remarks Results in graphical form only. Vapour pressures and volumes for three compositions. Equilibrium constants for methane. Low purity of CH, (94.4 moles per cent). Few experimental results for the liquid phase. Smoothed isothermal results. Graphical interpolation of references 6 and 4. No new measurements. CP,x. Y) Dew point.
VLE TABLE
2. Unsmoothed
FOR
results
(METHANE for {xCH,+(I
473
+ n-PENTANE) -x)C,H,,}(I)
= {yCH,+(l
-y)C,H,,)g
TW
pJMPa
310.89
0.693 1.393 2.763 4.130 5.514 6.950 8.620
0.0300 0.0637 0.1305 0.1906 0.2488 0.3077 0.3773
0.8349 0.9095 0.9433 0.9534 0.9567 0.9564 0.9539
27.83 14.28 7.23 5.00 3.84 3.11 2.53
0.17 0.10 0.07 0.06 0.06 0.06 0.07
10.350 10.560 12.030 12.100 13.770 15.460 16.100
0.4469 0.4512 0.5113 0.5176 0.5826 0.6674 0.7124
0.9497 0.9469 0.9394 0.9372 0.9235 0.8925 0.8661
2.13 2.10 1.84 1.81 1.59 1.34 1.22
0.09 0.10 0.12 0.13 0.18 0.32 0.47
344.45
0.950 1.815 2.772 4.100 5.640 6.970
0.0297 0.0672 0.1093 0.1633 0.2227 0.2740
0.6614 0.8056 0.858 1 0.8807 0.9004 0.9055
22.27 11.99 7.85 5.39 4.04 3.30
0.35 0.21 0.16 0.14 0.13 0.13
8.670 10.310 12.050 12.975 13.785 15.460
0.3382 0.3999 0.4703 0.5083 0.5459 0.6470
0.9081 0.9024 0.8910 0.8777 0.8672 0.8111
2.69 2.26 1.89 1.73 1.59 1.25
0.14 0.16 0.21 0.25 0.29 0.54
360.07
1.048 2.038 3.050 4.075 6.060 8.000
0.0258 0.0687 0.1117 0.1535 0.2303 0.3033
0.5413 0.7375 0.8056 0.8373 0.8640 0.8693
21.02 10.74 7.21 5.45 3.75 2.87
0.47 0.28 0.22 0.19 0.18 0.19
10.100 11.010 12.100 14.010 14.750
0.3813 0.4195 0.4626 0.5517 0.6083
0.8647 0.8590 0.8472 0.8108 0.7768
2.21 2.05 1.83 1.47 1.28
0.22 0.24 0.28 0.42 0.57
377.60
1.020 2.050 2.790 4.170 6.060 6.870
0.0152 0.0580 0.0894 0.1462 0.2168 0.2479
0.3122 0.6136 0.6941 0.7656 0.8017 0.8093
20.54 10.58 7.76 5.24 3.70 3.26
0.70 0.41 0.34 0.27 0.25 0.25
8.570 10.320 12.240 13.820 14.110
0.3123 0.3828 0.4656 0.5634 0.6016
0.8119 0.8066 0.1797 0.7164 0.6798
2.60 2.11 1.67 1.27 1.13
0.27 0.31 0.41 0.65 0.80
410.97
1.829 2.787 4.162 5.520
0.0224 0.0635 0.1196 0.1734
0.2342 0.4350 0.5567 0.6159
10.46 6.85 4.65 3.55
0.78 0.60 0.50 0.46
6.884 8.750 10.250 10.520
0.2269 0.3095 0.3941 0.4131
0.6429 0.6468 0.6196 0.6105
2.83 2.09 1.57 I .48
0.46 0.51 0.63 0.66
Y
Y
fWH,)
W,H,,)
piMPa
:
Y
MN,)
K(C,H,
loop sampling valve, a detailed view of which is shown in figure 4. This valve contained three loops. At a particular moment, the first loop was open to the sampling chamber and thus contained the sample, the second was open to the carrier-gas stream of the g.c., for which we used helium, and the third was open to the vacuum system. The loop valve was next turned into the second position, where the first loop containing the sample was opened to the carrier gas and thus carried the sample to the g.c., the second loop was evacuated, and the third took in the sample. Changing the position of the loop-valve three times opened the first loop again to the sampling chamber and the process repeated itself. This sampling chamber was also used as a mixing chamber, in which well defined gaseous mixtures were prepared to calibrate the g.c. The compositions of the gas mixtures used to calibrate the g.c. were determined from their partial pressures according to Dalton’s law. For the required low-pressure measurements a Baratron pressure transducer (MKS, type 310 BH-10000) was used with an accuracy of f 1 x 10m4 MPa. Alternatively, the g.c. was calibrated with the pure components alone by using the sampling chamber. For the mixtures considered below, i.e. (methane + n-pentane). a flame-ionization detector and a thermal-conductivity detector were used. The
1)
474
W.-E.
REIFF,
P. PETERS-GERTH.
AND
K. LUCAS
1. j
(Figure
.Y, \
6, continued
on following
page)
calibrating curves for both detectors are shown in figure 5. For the f.-i. d. the sensitivity was 10-l’ A. mV-‘; the current in the bridge for the t.-c. d. was set at 200 mA, the temperatures in the oven and in the detector were 308 and 343 K, respectively. Separation of the components was achieved by using a 1.5 m x 3.2 mm column packed with 10 mass per cent of SE30 on 80 to 100 mesh Chromosorb PAW 99.999 moles per cent He was used as the carrier gas with a flow rate of 0.5 cm’. s-r. Methane (Messer Griesheim) had a claimed purity of 99.995 moles per cent. n-Pentane (Merck) had a claimed purity of 99 moles per cent. Methane was checked in the g.c. with satisfactory results. n-Pentane was carefully degassed and then checked in the g.c. as well as by measuring its density and refractive index. Slight impurities were detected in the g.c. and were taken care of by corresponding calibration. No further purification was attempted. The density at 293 K agreed with the literature with 0.02 per cent, the refractive index being within 0.1 per cent. 3. Results on (methane
+ n-pentane)
The apparatus described above was used to determine (vapour + liquid) equilibria for (methane + n-pentane) in a range of temperatures from 311 to 411 K extending
VLE FOR (METHANE
h-
2 4-/ 00
+P
+ n-PENTANE)
475
P +
-1 I 0.4I 0.2
I 0.6
I
0.X
f I 0
sxb42 0 (a), at 310.89 K; (b), at FIGURE 6. (Vapour + liquid) equilibria for (xCH,+(l-x)C,H,,}: 344.45 K; (c), at 360.07 K; (d), at 377.60 K: and (e), at 410.97 K. 0. This work; x. Sage et al.:” A. Taylor er ~1.;‘~’ +, interpolated from Berry and Sage;“” 0. Prodany and Williams.““’
to pressures up to 16 MPa. Table 1 contains a summary of earlier results, including some comments. Table 2 gives a summary of the results obtained in this work including K-factors for both components, where Ki = yi/xi. Figure 6 shows (p, x, y) diagrams for the various experimental temperatures, including the results of this
476
W.-E.
REIFF,
P. PETERS-GERTH.
AND
K. LUCAS
Methane
0.
0.c
I
I
I
1
10
20
pIMPa {xCH,+(l -x)C,H,,}. FIGURE 7. K-values for A, T = 360.07 K; 0, T = 377.60 K; 0, T = 410.97 K.
x/xy
h loE: ‘c.
x
0,
T = 310.89
K:
A,
T = 344.45
K;
@\
/
/ 5sx \0
I 250
’ 200
I 300
I 350
I 400
I 450
T/K FIGURE 8. Critical curve et d.;“’ V, pure components.
for
{xCH,+(l-x)C,H,*}.
0,
This
work;
x1 Chen
et a~.;~lL~ 0,
Sage
VLE FOR (METHANE
+ n-PENTANE)
477
work as well as the results of other investigators. Figure 7 shows the K-factors. The critical locus, as extrapolated from the results, is shown in figure 8 and compared with the results of other authors. The results of this work are generally in good agreement with those of Sage and Lacey and of Sage, Reamer, Olds, and Lacey, respectively. On the bubble line, the agreement in mole fraction is fO.001; on the dew line the new measurements give slightly higher X, on the average f0.015. An error analysis including the errors of the temperature measurement, the pressure measurement, and the composition measurement yields absolute errors in x between to.1 x lop3 and f8.3 x low3 in the liquid phase and between fO.O1 x 10m3 and +8.2x 10m3 in the gas phase. The estimated average error in both phases is kO.003. REFERENCES I.
7. 3. 4. 5. 6. 7. 8.
9. IO. I I.
Reiff. W.-E. E.xperimental determination of vapour-liquid equilibria qf binary systems with supercritical componenrs. Ph.D. Thesis, Universitlt Duisburg. 1985. Frohhch. P. K.; Tauch, E. J.; Hogan, J. J.; Peer, A. A. Ind. Eng. Chem. 1931, 23, 548. Sage, B. H.: Webster, D. C.; Lacey, W. N. Ind. Eng. Chem. 1936. 28. 1045. Sage, B. H.; Lacey, W. N. Ind. Eng. Chem. 1938, 30, 1296. Boomer, E. H.; Johnson, C. A.; Piercey, A. G. A. Can. J. Res. B. 1938, 16, 319. Taylor, H. J.; Wald, G. W.; Sage, B. H.; Lacey, W. N. Oil and Gas J. 1939, 33, 46. Sage, B. H.; Reamer, H. H.; Olds, R. H.; Lacey, W. N. Ind. Eng. Chem. 1942, 34, 1108. Sage, B. H.; Lacey, W. N. Thermodynamic properties of the lighter paraffin h.ydrocarbons and nitrogen. Monograph on API research project 37. API. 1950. Berry, V. M.; Sage, B. H. NSRDS-NBS 1970, 32. Prodany, N. W.; Williams, B. J. Chem. Eng. Data 1971, 16, 1. Chen, R. J. J.; Chappelear. P. S.; Kobayashi. R. J. Chem. Eng. Data 1974, 19. 58.