Phase Behavior of Binary Carbon Dioxide-Paraffin Systems FRED € POETTMA" I. AND D, L. KATZ University of Michigan, Ann Arbor, Mich.
I
N 1897 Kuenen reported the critics3 behavior of the binary
carbon dioxide-ethane system (18, 8#, 91). This system forms a minimum-boiling azeotrope and has a critical locus which is characteristic of this behavior as Figure 1 shows. The azeotrope persists up to the critical locus giving a oritical azeotrope containing 27 mole % ethane. Since the carbon dioxide-ethane system forms a minimum-boiling azeotrope, one of the purposes of this investigation was to determine the effect on the critical behavior of substituting higher paraffin hydrocarbons for ethane This study provides a basis for further examination of the equilibrium constants for carbon dioxide in oomplex hydrocarbon mixtures. The binary systems studied are carbon dioxide-propane, carbon dioxide-butane, and carbon dioxide-pentane. Other binary carbon dioxide systems upon which critical data have been reported are listed in Table I. The apparatus used to obtain the data was similar to that described by Katz and Kurata (12). It consisted primarily of an equilibrium cell with a glass window and suitable tubing and valve connections. Pressure was supplied by a hand pump, using mercury as the confining liquid, and was measured by a calibrated Bourdon gage. The ceIl was surrounded by an air bath which was agitated by a fan and heated by electric coils. The entire mechanism waa mounted on a trunnion and rocked to ensure equilibrium, the mercury in the cell causing severe agitation of the liquid and vapor phases in the cell.
I6O
The vapor-liquid equilibria and critical loct of the binary carbon dioxidepropane, carbon dioxide butane and carbon dioxidgpentane systems have been determined. T h e complete trendtion from the carbon dioxide-ethane system which forms constant-boiling mixtures to the carbon dioxide pentane system which has normal behavior is shown. The experimental data are pmaented in both graphical and tabulated form.
The temperature was measured by a pair of calibrated copperconstantan thermocouples in series, embedded in the walls of the cell. The volume of the fluid in the cell waa determined by a calibrated scale mounted beside the gless window. The ambon dioxide used came from Pure Carbonic Incorpurated and waa stated to have a purity of 99.5%. Successive samples were completely absorbed' in potassium hydroxide solution. The hydrocarbons were furnished through the courtesy of Phillips Petroleum Company. The propane waa stated to have a purity of 99.8%; butane and pentane were 99.0% pure or better. The vapor pressures of the propane and butane checked those of the literature (4, 6, 10, 11, 82, 86,$7') to 1 5 pounds per square inch, which is within the accuracy of the apparatus. The vapor pressures of pentane were taken from the literature (3,94,26, 31). The gas mixtures were analyzed in an Orsat apparatus. The carbon dioxide was absorbed in a 35-40% solution of potassium hydroxide, and the hydrocarbon was determined by difference. The pentane gas mixtures were firat diluted with a fixed volume of nitrogen before analysis to prevent the pentane from condensing after removal of the carbon dioxide. Most of the duplicate analyses checked within 0.2% and never differed more than
" l i i l l i l l 0.4%.
After the proper technique for taking data had been developed, the temperature of the cell was kept within t0.5' F. of the value reported, Pressure observations were probably within * 6 pounds per square inch of the true value. The procedure for charging the cell wm as follows: The cell was first evacuated, the lines were flushed out with hydrocarbon,
TABLIO I. BINARYCARBON DIOXID MIXTURES ~ System C0rC:Hx COrsir
COrC2He
COrHa COrHCl COrCHtCl COrNs
Cot-NxO
COrCeRsNOr COP02
cot-BO:
Figure 1. Critical Loci of Carbon Dioxide-Paraffin Systems 847
Investigators Kuenen Cailletet Van der W a s t Kuenen Kuenen and Robson Verahafielt Anadell Kuenen Caubet Andrew8 ca.u-be~ Kohaatamm and Reedem
Keesom
Caubet
Citation
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Vol. 37, No.
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Figure 4
Figure3
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1000
900
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T E M P E R A T U R E , OF.
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INDUSTRIAL AND ENGINEERING CHEMISTRY
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mercury. Observations were made as to the amount of single phase or of vapor and liquid phase at each pressure. The cell was agitated vigorously before the volume and pressure readings were made. Special care was taken to select isotherms which Figure3. Pressure-TemperatureDiagram cover retrograde regions as completely as possiblg. for Carbon Dibxide-Propane System Three binary systems were studied: carbon dioxide-propane, Figure4. Preesure-TemperatureMagram carbon dioxide-butane, and carbon dioxide-pentane. Six mixfor Carbon Dioxide-Butane System tures were studied in both the carbon dioxide-propane and carbon dioxide-butane systems; five mixtures were studied in the carbon 4 dioxide-pentane system. Figure 2A is a plot of isotherms as pressure against per cent by and the cell was filled with liquid hydrocarbon which was allowed volumeliquid for a mixture containing 71.02% carbon dioxide and to boil off slowly. The cell was again filled with liquid hydro28.98% butane. This diagram and the usual observations procarbon which was allowed to partially boil off. Carbon dioxide vided the bubble and dew point data in Table I1 (page 851). I n was then added. most cases the determination of the dew and bubble points by thie The cell was maintained a t a constant temperature by a method gave values which are believed to be correct within the thermostatically controlled air bath. The material charged into experimental error. However, for some butane and pentane mixthe cell was compressed to a single phase by means of the mercury tures the dew point may be off aa much as 20 pounds per square and hand pump. The preasure was then gradually reduced in inch as a result of the rapid change of pressure with very small amall increments into the two-phme region by withdrawing changes in temperature or per cent liquid by volume. i 500 Figure 2B is a cross plot of 2A and I shows the phase behavior of this mixture and the method for locating the critical temperature and preasure by plotting lines of constant per cent by volume liquid. Figures 3,4, and 5 show the pressuretemperature diagrams of the three series of binary mixtures. The critical loci for these systems were added to that of the carbon dioxide-ethane system in Figure 1. The change in the temperature composition diagram as pressure is increased and the chhnge in the pressure composition diagram as temperature is increased for the systems reported are plotted in Figures 6, 8,and 9. These plots provide the vapor-liquid equilibrium data for the systems. It is apparent from the critical locus of the carbon dioxide-propane system that the forces tending to form a minimum-boiling aneotrope, as in the carbon dioxide-ethane system, have not yet completely disappeared. This is shown by the sharp downward curvature of the critical locus at the carbon dioxide end of the curve. Thus, the carbon dioxide-propane locus is an intermediate stage between that of the constant-boiling azeotrope type of carbon dioxide-ethane system and the normal systems of carbon dioxide with butane or pentane. The purpose of Kuenen in studying the carbon dioxide-ethane system waa to test the van der Waals theory (30)of binary mixtures. The theory worked very well in predicting the critical temperatures and pressures of carbon dioxide-ethane mixtures (ZO), but when applied to the systems of carbon dioxide with propane, butane, and pentane, the method was obviously inadequate since 0 40 80 120 160 200 240 280 320 360 many of the calculatedcriticalpointsdid TEMPERATURE, OF. not fall within therange of the coordinates of Figures 3,4, and 5. The cauae Fiiure 5. Pressure-Temperature Diagram for Carbon Dioxide-Pentane Systsm
Figure?. Isotherms andPhaseDiagramof Carbon Dioxide-Butane System
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Vol. 31, No. 9
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MOLE Figure 6 .
PERCENT
CARBON
DIOXIDE
Vapbr Equilibrium Data for Carbon Dioxidepropane System
of this appears to be the great spread between the bubble and dew point curvea of the latter mixtures. This spread incremes as the vapor pressure curves of the two pure components become more divergent. It eeems that the farther apart the critical temperatures of the pure components are, the less will be the chance of forming critical azeotropic mixtures. This point is brought out in the binary carbon dioxide mixtures studied here. Components with critical temperatures relatively close together, and those with critical pressures apart, are likely to form areotropes but not necessarily, since the nature of the molecules and their bonds determine whether azeotropes are formed. The carbon dioxide-ethane system of Figure 7 A (1420, 2f), ethanenitrous oxide system of Figure 7B (IQ, 2@, carbon dioxide-
nitrous oxide system of Figure 7C @), ethylene-acetylene system of Figure 7 0 (9, IS), and ethane-acetylene system of Figure 7 E (19, 90) form azeotropes; the carbon dioxide-acetylene system of Figure 7C (15) and ethape-ethylene system of Figure 7F (23) do not form azeotropes. The acetylene-nitrous oxide system, which has not yet been determined, would be expected to form an azeotrope. The effect of the chemical bonds is most noticeable in Figures 7 0 and 7 F for the ethylene-acetylene and ethylene-ethane systems. Although the relative positions of the critical points are the same for the two binary mixtures, the ethylene-acetylene system forms a critical azeotrope, whereas the ethylene-ethane system behaves in a normal manner. This difference is attributed to the nature of the acetylene molecule.
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TABLE 11. SUMMARY OF E~PHIRIMHINTAL DATA Compn., Mole %
Temp., CABBON
78.73 COr21.27 CIHI
36.99 CO164.01 CtHi
30.66 COr49.36 CaHa
15.19 COr84.81 CIHO
O
F.
hensure, Lb./Sq. In. dba. Bubble point D e w point
DIOXIDB-PBOPANE
63.1 72.7 83.7 93.0 100.6 101.6 101.4 (orit.)
661 739 826 927 996
72.4. 116.0 141.8 163.3 162.0 167.6 166.1 (orit.)
462 686 824 904 944
80.1 100.7 122.7 141 . 9 147.8 146.9 (orit.)
676 680 837 972
87.0 127.7 163.0 180.3 192.6 200.1 199.4 (orit.)
304 464 616 712 776
..
..
..
..
484
ti:
726 876 936,1001.6 1002
T E M P ERA T U R E
T E H PER A T UR E
A
182 a48 483 670 _.-
1
665
967
986
730,967 276 360 486 690 982,780 169 288 462 660
TEMPERATURE
TEMPERATURE
I D
C
660
790
783,728
96.01 COr8.99 CiHs
78.3 84.0 87.3
926 994 lo31
912 979 1024
93.93 Cot-6.07 CiHi
64.8 76.1 80.0 86.1 87.3 88.0 88.2 (orit.)
763 866 916 976 1012 1018
740 846 903 963 1003 1010
1022
Cn%
3 u) In
w
L F L Y
0.
I
TEMPERATURE
E 46.61 COr64.49 C4Hio
71.02 COr28.98 CdHie
90.2 131.0 172.8 210.2 226.7 234.8 240.2 233.6 (orit.)
612 716 916 1069 1087
91.3 120.7 161.0 161.2 170.6 173.7 179.6 169.0 (orit.)
726 926 1139 1173
....
......
86.09 c o r i a . g i c ~ H ~92.6 ~ 99.9 110.0 116.4 120.2 126.0 119.6 (orit.)
896 976 1066 1104
60.73 COr39.27 ClHi,
80.1 100.2 130.8 160.6 190.0 200.6 206.3 210.1 216.0 203.0 (orit.)
640 666 860 1026 1136 1143
81.8 120.2 160.6 200.0 236.3 246.0 261.7 266.2 264.0 (orit.)
393
83.4 121.0 160.3
198 269 366 469 666 690 726 719
37.61 COr62.39 CtH10
8%: I 272.2
281.0 288.1 289. S 288.8 (erit.)
.. ..
......
1077
1181
Critical Loci of Binary Syatems
TABLE I1 (Continued) Compn. Mole %
140 278 446 636 1183 682 1183' 663 1178: 764
96.11 COa-4.89 QHir
606
1122
609 676 1124 748 1122: 836 88
133 224
Temp. F. 71.9 86.3 100.8 106.4 107.6 110.0 107.0 (orit.) 80.0 100.0 120.0 126.0 129 r9 184.8 140.3 146.0 160.8 126.6 (orit.)
863 636
L140
969
946 940
709
772 904 1086 1134
....
480 64 1 668 710 1167: 1160 760 786 1148
822 1003 1201 1220
276 378 609 644 1241 686 12134' 662 1283'846 1283' 688
..
...... ..
1228
686
.. .... ..
111 209 362 636 609 668 925,711
42 77 144 240 340 627 690 669 704,688
Pressure. Lb./Eq. In. Abs. Bubble point Dew point
970 1226 1391 1429 1441
636 1132 679 1116' 746 109s: 804 66
546
..
Figure 7' ,
446
683 840 946
..
96 162 298 608 612 1072,689 1046,790
TEMPERATURE
F
1441
666 799 1017 1223 1378 1383 1368 1363
.. ..
46.63 COrS4.47 CrHt
80.2 123.8 160.2 200.0 260.1
1238: 972
26 146 260 400 466 490 1441 640 1440' 697 1431: 716 1374,880 24 65
1362
124 272 470 612 670 646 1330,689 1304,747
360 480
20 36
72 1 984
180 293
686
80
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350
300
2 50
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Figure 8.
50 60 70 P E R C E N T CARBON DIOXIDE
40
80
Vapor Equilibrium Data for Carbon Dioxide-Pentane System
90
100
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30
40
LITERATURE CITED
Churchill, Collamore,and Kats, Oil Gae J . , 39, No. 28,34 (1942). Dana, Jenkins, Burdiok, and Tirnm, Refrig. E w . , 12,387 (1926). Desohner and Brown, IND. ENG.CH~M., 32,836 (1940). Kats and Kurata, Ibid., 32, 817 (1940). Kats and McCurdy, Ibid., 36, 674 (1944). Keesom, Commun. Phys. Lab. Univ. Ldden, No. 88 (1903). Keesom, Physik. Ber., [11]60, 668 (1904). Keesom, Proc. A d . Sci. Amterdam, 6, 532 (1903). Kohnstamm and Reeders, Arch. dertand. Sci., FHA] 2, 63 (1912).
60 70 CARBON DIOXIDE
80
90
100
Vapor Equilibrium Data for Carbon Dioxide-Butane System
Andrews, Trans. Roy. Soc. (London), 178, 45 (1887). Ansdell, Proc. Roy. SOC.(London), 34, 113 (1882). Beall, Refiner Natural Gasoline Mfr., 14, 588 (1935).. Beattie, Kay, and Kaminsky, J.Am. Chem. Sac., 59,1509 (1937). Beattie, Shard, and Gouq-JenSu, Ibid., 61,25 (1939). Cailletet, Compt. rend., 90, 210 (1880). Caubet, 2.phyaik. Chem., 40, 257 (1902). Ibid., 49, 101 (1904).
50
MOLE PERCENT
(18) (19) (20) (21) (22)
Kuenen, J. B., Commun. Phya. Lab. UnC. Leiden, No. 4 (1892). Kuenen, J. B., Ph4. Mag.,44, 174 (1897). Kuenen, J. B.,2.physik. Chem., 24, 667 (1897). Kuenen and Robson, Phil. Mag., 4, 116 (1902). Meyers and Van Duesen, Bur. Standards J . Research, 10, No. 8
(23) (24) (25) (26) (27) (28) (29)
Quinn, D. So. thesis in chem. eng., Mass. Inst. Tech., 1940. Sage and Lacey, IND. ENO.CEBM.,34,730 (1942). Sage, Schaafsma, and Lacey, Ibid., 26, 1218 (1934).
(1933).
Ibid., 27, 48 (1935).
Sage, Webster, and Laoey, Ibid., 29, 118 (1937). Vershdelt, Commun. Phys. Lab. Univ. Ldden, No. 47 (1899). Waals, van der “KQntinentat der gmformigen und flussigen Zustandes”, Ong. 1873, Leipsig, Barth, 1881; E n g l i i translation of Phys. Mem. I Phys. SOC.(London), 1888. (30) Waals, van der, 2.physik. Chem., 5, 133 (1890). (31) Young, Sd.Proc. Roy. Dublin Soc., 12, 374 (1910). ABSTBACW of a theah submitted in partial fulfillment of the requirementa for the degree of dootor of philosophy from the University of Michigan.
