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Excess enthalpies for (propane + methanol) at the temperatures (298.15, 323.15, 348.15, and 373.15) K and pressures (5, 10, and 15) MPa, and at 363.15K and (5 and 15) MPa
O-41 1
j. Chem. Thermodynamics 1991, 23, 551 559
Excess enthalpies for (propane + methanol) at the temperatures (298.15, 323.15, 348.15, and 373.15) K and pressures (5, 10, and 15) MPa, and at 363.15 K and (5 and 15) M Pa J. T. SIPOWSKA, J. B. OTT," B. J. NEELY, and R. M. IZATT
Department of Chemistry, Brigham Young University, Provo, UT 84602, U.S.A. (Received 23 October 1990) Excess molar enthalpies HE for (propane + methanol) have been determined at the temperatures (298.15, 323.15, 348.15, and 373,15) K and at the pressures (5, 10, and 15) MPa. Measurements were also made at 363.15 K and (5 and 15)MPa. (Propane + methanol) is a type-II mixture (Scott and van Konynenburg's classification) with a (liquid + liquid) phase separation at lower temperatures. The measurements reported in this paper were performed at temperatures and pressures at which both com!~onentswere liquids and where phase separation does not occur.
1. Introduction Recent papers (1 3) from our laboratory have reported measurements of excess enthalpies for (ethane + methanol), (1) (ethane + ethanol), (2) and (propane + propan-l-ol). (3) As a continuation of those studies we have determined excess enthalpies for (propane + methanol). The critical p(T) curve for (propane + methanol) has been investigated by Brunner, (4) and the (liquid + liquid) equilibria by Kuenen. (5) Using these results together with the (vapor + liquid) equilibria for pure propane, (6) and methanol, (6) we have constructed the phase diagram for (propane + methanol) shown in figure 1 as a p(T) projection. It is apparent from figure 1 that, according to Scott and van K o n y n e n b u r g ' s classification, (v) (propane + methanol) is a type-II mixture with a continuous critical line between the critical points of the pure components and a (liquid + liquid) immiscibility at lower temperatures. The critical constants Pc and Tc are 4.24 M P a and 369.98 K for propane, (6) and 7.95 M P a and 513.00 K for methanol. (6) We have measured HE at the temperatures (298.15, 323.15, 348.15, and 373.15) K and the pressures (5, 10, and 15) M P a and at 363.15 K and (5 and 15) M P a . These (T, p) conditions are shown in figure 1. aAuthor to whom correspondence should be sent. 0021 9614/91/060551+09 $02.00/0
© 1991 Academic Press Limited
552
J.T. SIPOWSKA E T AL. 16
i
+
+
+
+
+
+
+
+
+
+
12
+
8
[
0
280
."
I
320
f " ' "
360
I
r
400
440
480
520
T/K
F I G U R E 1. (Fluid + fluid) equilibria for {xC3H 8 + ( 1 - x ) C H 3 O H } : [:], critical point for C3H8; /k, critical point for CH3OH; @, U C E P ; + , (p, T) conditions for the HEm results reported in this paper; - - , (vapor + liquid) critical locus; .... , (vapor + liquid) equilibrium lines for C3H8 and CH3OH; - - - , (liquid + liquid) critical line.
The measurements were made above the (gas + liquid) equilibrium line for propane and between the (liquid + liquid) and critical p(T) lines so that both propane and methanol were liquids at all experimental temperatures except at 373.15 K where the propane was a supercritical fluid. 2. Experimental Methanol (B&J Chrom Pure, 99.9 mass per cent) and propane (Phillips, 99.5 mass per cent) were used without further purification. The methanol was stored over Davison 0.3 nm molecular sieves to remove water. The densities at 293.15 K used to calculate the mole fractions were (0.5110, 0.5215, and 0.5305)g-cm 3 for propane at (5, 10, and 15)MPa, respectively,,and (0.7961, 0.8009, and 0.8060)g.cm 3 for methanol (6) at the same pressures. The propane densities were calculated from the modified Benedict-Webb-Rubin equation with the coefficients given by Younglove et al. (8) The densities of methanol were calculated using an isothermal compressibility of 1.215GPa 1(6) and the density at atmospheric pressure of 0.8913 g. cm-336) The isothermal flow calorimeter used for the measurements has been described. (9) Pressures were measured with a Sensotec Model 450 D transducer calibrated against
HEmF O R ( P R O P A N E + M E T H A N O L )
553
TABLE 1. Experimental excess molar enthalpies HEmfor {xC3H 8 + (1 - x ) C H 3 O H } ; 8H~ is the deviation of the experimental results from equation (1)
X
HE J" m o l - 1
8HEm J ' tool- 1
x
0.0238 0.0489 0.0755 0.1037 0.1336 0.1654 0.1994 0.2357
46,4 87,7 128,9 165.3 202.7 233.7 263.5 287.2
1.2 --0.4 0.3 -- 1.3 0.9 --0.2 0.3 --2.2
0.2746 0.3163 0.3612 0.4096 0.4621 0.5191 0.5812 0.6492
0.0242 0.0586 0.0957 0.1358 0.1793 0.2145 0.2520 0.2921 0.3351
48.2 108.6 164.0 217.6 263.0 290.5 316.8 338.3 354.4
--0.3 --0.8 -- 1.5 1.5 2.1 0.0 0.3 -0.9 4.1
0.3656 0.4143 0.4489 0.4854 0.5239 0.5646 0.6077 0.6535 0.6775
0.0245 0.0504 0.0777 0.1066 0.1373 0.1699 0.2166 0.2543 0.2947 0.3379
48.9 97.1 144.0 186.1 227.7 263.3 304.6 332.8 355.0 376.8
-- 1.2 --l.0 0.5 0.0 1.9 1.0 --0.7 --0.4 -2.0 0.1
0.3685 0.4173 0.4520 0.4885 0.5270 0.5677 0.6107 0.6564 0.6802 0.7302
0.0239 0.0492 0.0759 0.1042 0.1343 0.1774 0.2123 0.2495 0.2894 0.3322
47.5 96.l 151.0 185.3 222.4 282.9 320.7 354.8 388.6 422.7
-- 1.7 --0.7 0.8 - 1.5 -- 6.7 0.5 0.5 - 1.2 1.6 0.2
0.3784 0.4111 0.4457 0.4821 0.5206 0.5614 0.6046 0.6506 0.6994 0.7356
0.0242 0.0498 0.0768 0.1054 0.1358 0.1793
54.1 105.0 155.5 205.3 246.2 313.5
0.1 --0.7 0.1 2.0 --3.8 3.9
0.2145 0.2520 0.2921 0.3351 0.3656 0.4143
HEm J ' tool- 1
8H~ J- mol-- a
x
HE J. tool- x
8H E, J. mol x
0.7236 0.8063 0.8662 0.8978 0.9306 0.9647 0.9734
367.9 341.7 312.3 292.1 258.0 211.8 192.5
1.3 -0.5 -0.1 1.6 --2.4 0.3 0.7
0.7277 0.7540 0.8093 0.8384 0.8996 0.9319 0.9653 0.9739
385.6 380.9 356.6 339.1 291.4 267.8 217.8 197.2
--0.1 3.3 2.1 0.3 --4.5 2.6 0.4 -0.5
0.7563 0.8112 0.8401 0.8699 0.9007 0.9326 0.9657 0.9742
380.8 355.0 341.2 325.9 291.2 263.3 211.5 197.4
0.4 --2.0 0.4 5.5 --3.5 1.8 -2.2 0.9
0.7790 0.8073 0.8366 0.8670 0.8984 0.9310 0.9512 0.9649
582.1 573.5 564.2 546.8 519.6 474.7 425.2 384.9
1.5 --0.8 0.9 1.1 1.4 1.6 -3.8 0.4
0.4489 0.4854 0.5239 0.5646 0.6077 0.6535
535.0 554.5 568.8 584.8 592.8 601.6
-1.1 1.4 0.2 2.3 -1.7 - 1.0
T = 298.15 K, p = 5 MPa 316.8 329.9 346.8 362.1 372.0 377.6 379.6 376.2
4.5 -2.0 - 1.5 0.8 0.8 0.0 -0.4 --1.0
T = 298.15 K, p = 10 MPa 370.2 383.8 394.1 398.3 401.2 404.8 403.7 398.5 395.3
0.6 0.2 2.9 1.0 --0.5 0.8 --0.2 - 1.8 - 1.6
T = 298.15 K, p = 15 MPa 386.7 399.9 407.6 410.8 413.4 416.5 409.0 404.1 400.1 389.2
-0.8 --0.4 1.2 0.2 0.6 3.6 --1.4 --0.9 -0.8 0.4
T = 323.15 K, p = 5 MPa 453.2 473.2 495.4 512.2 527.4 547.4 559.2 568.6 582.4 582.2
-0.2 0.0 3.0 1.3 -- 1.3 2.1 -1.1 --4.3 1.0 - 1.5
T = 323.15 K, p = 10 MPa 352.4 388.9 434.6 466.8 485.9 517.7
-0.1 --4.2 3.5 0.6 -2.0 --0.2
E T AL.
J. T . S I P O W S K A
554
T A B L E 1--continued
HEm
HEm ~.mo1-1
J.mol
J. mol
0.6873 0.7277 0.7702 0.8093
604.5 604.0 597.2 587.3
-0.9 -0.3 0.1 3.0
0.8384 0.8684 0.8996 0.9319
0.0245 0.0504 0.0777 0.1066 0.1373 0.1699 0.2166 0.2543 0.2947 0.3379
62.0 118.9 165.8 222.2 266.2 313.0 371.4 410.6 448.5 483.4
2.4 2.8 -3.6 2.1 -1.9 -0.7 0.8 0.1 0.4 0.2
0.3685 0.4173 0.4520 0.4885 0.5270 0.5677 0.6107 0.6564 0.6899 0.7302
0.0239 0.0492 0.0759 0.1042 0.1343 0.1774 0.2123 0.2495 0.2894 0.3322
56.1 106.9 162.9 217.1 273.1 342.0 390.8 444.6 497.0 550.3
0.5 3.4 --1.2 -0.2 3.1 2.2 -1.5 -0.3 --1.1 --1.8
0.3784 0.4111 0.4457 0.4821 0.5206 0.5614 0.6046 0.6506 0.6994 0.7356
0.0242 0.0498 0.0768 0.1054 0.1358 0.1793 0.2145 0.2520 0.2921 0.3351
67.2 132.9 196.3 265.4 326.2 404.1 467.9 534.2 592.1 644.0
0.0 -0.5 --2.0 3.2 0.9 -3.7 --1.2 4.6 2.7 --4.9
0.3656 0.4143 0.4489 0.4854 0.5239 0.5646 0.6077 0.6535 0.6873 0.7277
0.0245 0.0504 0.0777 0.1066 0.1373 0.1699 0.2166 0.2543 0.2947 0.3379
68.6 137.2 209.5 280.5 347.6 414.3 501.9 563.9 625.7 687.6
0.1 -1.2 1.0 2.1 0.0 -1.0 --0.9 -2.0 --1.4 1.1
0.3685 0.4173 0.4520 0.4885 0.5270 0.5677 0.6107 0.6564 0.6899 0.7302
HEm
8U~ 1
570.2 549.9 521.4 477.2
J' mol-
J.mol 1 -0.1 -1.3 -1.8 1.7
8H~ a
J" t o o l - i
0.9451 0.9653
444.4 368.5
0.0 -0.3
0.7724 0.8112 0.8401 0.8699 0.9007 0.9326 0.9657 0.9742
600.8 586.7 568.2 541.8 508.4 456.7 357.0 302.0
2.3 2.2 -0.2 -3.3 -2.0 1.7 5.6 -5.1
0.7790 0.8073 0.8366 0.8670 0.8984 0.9178 0.9310 0.9512 0.9649
936.6 943.6 933.7 915.7 873.4 820.1 781.8 677.9 573.4
-0.2 3.5 -1.5 -0.9 0.6 -5.8 1.8 1.5 2.8
0.7702 0.8093 0.8384 0.8684 0.8996 0.9319 0.9451 0.9653 0.9739
974.6 963.5 947.5 912.0 858.0 747.2 692.0 541.9 453.7
-1.9 -2.1 0.9 - 1.2 2.9 -3.8 5.8 -0.9 -2.9
0.7563 0.7833 0.8112 0.8401 0.8699 0.9007 0.9326 0.9523 0.9657
977.2 971.1 952.6 931.2 897.3 842.1 751.9 651.3 544.6
1.5 3.2 -1.6 -1.3 --1.7 -2.8 3.3 2.8 -2.9
T=323.15K, p=15MPa 504.0 536.6 555.3 570.6 581.0 591.7 604.9 609.8 608.5 606.7
-1.1 1.5 2.0 1.2 -2.4 -3.4 1.2 1.0 -1.2 -0.2
T = 348.15 K, p = 5 M P a 610.6 644.8 679.4 721.7 759.1 795.4 833.8 869.7 899.7 924.2
T = 348.15K,
3.3 0.4 -2.8 1.5 0.7 -1.2 -0.1 0.0 -2.5 2.7 p =
685.4 747.6 789.2 823.7 853.4 891.5 926.7 948.4 965.5 977.0
10MPa -2.8 1.0 4.3 1.4 --4.9 -0.9 3.3 -1.5 1.0 1.8
T=348.15K, p=15MPa 729.5 784.4 816.6 852.9 888.5 921.7 945.9 965.7 972.8 982.8
4.3 2.3 -2.5 -2.0 -0.3 1.6 -1.0 -1.5 -3.1 4.0
555
H E FOR (PROPANE + M E T H A N O L ) TABLE 1--continued
J.mo1-1
J.mo1-1
J- m o l - 1
J. m o l - 1
J. mol - 1
J. mol 1
T = 363.15K, p = 5 M P a 0.0240 0.0581 0.0948 0.1346 0.1778 0.2127 0.2500 0.2900 0.3328 0.3790
55.6 129.2 206.2 275.8 351.5 413.0 469.7 524.4 588.5 658.7
--0.3 --0.8 2.4 --2.1 --1.2 3.4 1.9 --3.6 --1.8 2.5
0.4118 0.4463 0.4828 0.5213 0.5621 0.6053 0.6418 0.6752 0.7000 0.7265
0.0162 0.0594 0.0970 0.1376 0.1702 0.2170 0.2548 0.2952 0.3384 0.3691
56.2 198.8 297.7 405.4 489.8 596.6 676.0 754.7 838.2 884.8
2.7 0.9 --0.5 --2.0 1.3 0.3 --0.5 -1.5 2.8 --3.3
0.4179 0.4525 0.4891 0.5276 0.5682 0.6113 0.6569 0.6807 0.7306 0.7567
0.0492 0.0759 0.1042 0.1343 0,1774 0,2123 0.2495 0,2894 0.3322
92.7 142.2 181.7 237.5 298.2 340.6 392.4 443.4 494.5
-0.2 2.2 -5.2 3.6 1.7 -3.4 0.2 0.8 -1.7
0.3784 0.4111 0.4457 0.4821 0.5206 0.5614 0.6046 0.6506 0.7356
0.0242 0.0498 0.0768 0.1054 0.1358 0.1793 0.2145 0.2520 0.2921 0.3351
88.7 173.l 257.2 348.6 438.6 548.4 641.6 733.5 837.5 933.1
1.5 1.0 --3.2 1.7 4.3 -4.0 --1.6 -2.3 6.7 4.9
0.3656 0.4143 0.4489 0.4854 0.5239 0.5646 0.6077 0.6535 0.6873 0.7277
0.0245 0.0504 0.0777 0.1066 0.1373
92.0 189.0 280.1 379.9 470.6
--1.5 1.3 --2.0 2.7 --2.6
0.1699 0.2166 0.2543 0.2947 0,3379
700.4 746.1 804.5 858.6 913.7 961.3 1018.5 1052.4 1084.3 1121.4
-1.9 --4.3 3.5 4.5 3.9 -6.6 3.0 -5.0 --2.6 5.2
0.7794 0.8077 0.8370 0.8673 0.8987 0.9312 0.9446 0.9650
1163.4 1180.0 1185.7 1176.5 1137.1 1021.7 938.9 766.9
0.7 -0.6 -1.1 1.1 5.5 -1.8 -7.2 4.7
0.7837 0.8116 0.8404 0.8701 0.9009 0.9328 0.9525 0.9658
1245.3 1221.3 1191.5 1139.7 1064.2 928.3 791.7 651.1
5.4 -1.2 -1.6 -5.2 -l.0 3.3 6.6 -6.5
0.7356 0.7790 0.8073 0.8366 0.8670 0.8984 0.9113 0.9310 0.9512
1130.2 1236.3 1293.7 1353.0 1394.2 1391.6 1375.9 1294.8 1132.3
-5.0 4.7 -0.5 0.2 -1.3 -3.8 3.7 0.6 -0.5
0.7702 0.8093 0.8384 0.8684 0.8996 0.9319 0.9518 0.9653
1532.8 1516.3 1497.7 1428.3 1309,8 1123,0 930.6 746.4
- 3.7 --5.6 7.8 0.0 --7.4 4.4 4.0 -- 3.8
0.3685 0.4173 0.4520 0.4885 0.5270
1067.2 1155.7 1225.8 1283.8 1346.4
5.0 --4.7 1.1 --3.4 --0.6
T = 363.15K, p = 15MPa 967.2 1023.2 1066.6 1112.3 1159.7 1196.1 1226.4 1238.6 1252.6 1249.5
0.8 5.6 --1.0 -2.9 0.5 -1.7 --1.9 -0.8 2.3 1.1
T = 373.15K, p = 5 M P a 5~5.7 600.7 636.5 694,4 756,0 809,8 884.1 960.2 1063.3
1.0 3.5 -6.9 0.4 6.0 -2.6 1.1 -4.1 4.4
T = 373.15 K, p = 10 MPa -
-
991.6 1086.7 1164.1 1237.9 1291.7 1357.8 1419.7 1475.6 1497.5 1534.4
3.0 -- 8.7 1.0 7.6 --4.4 - 1.8 0.8 4.1 --4.8 6.9
T = 373.15 K, p = 15 MPa 572.7 691.9 805.0 899.3 993.2
2.7 --8.0 6.9 2.2 --2.9
556
J. T. S I P O W S K A E T AL. TABLE 1--continued
~m
t4~m
~U~
~m
~/-/~
x
J. m o l - 1
J. mol 1
x
J. m o l - 1
J. m o l - 1
0.7563 0.7833 0.8112 0.8401 0.8699
1517.3 1506.1 1473.3 1422.5 1358.3
0.5 2.5 - 3.4 -8.2 1.5
0.9007 0.9326 0.9523 0.9657
1245.7 1041.9 872.9 699.3
6.6 -4.0 6.0 --4.7
~/~m
x
J" m o l - 1
0.5677 0.6107 0.6564 0.6899 0.7302
1405.2 1450.8 1489.5 1514.2 1522.4
J" m o l i 2.6 --0.9 -- 1.8 3.6 2.2
a dead-weight gauge. Bath temperatures were set and monitored with a Hart Model 1006 platinum resistance thermometer calibrated against a Rosemount Thermometer (ITS-90). We estimated our pressures and temperatures to be accurate to +0.1 MPa and _+0.02 K, respectively. 3. Results and discussion Experimental values of HEm{xCaH8 + (1 -x)CH3OH } are given in table 1. They were fitted to the equation: H~/(J" mo1-1) = x(1 - x ) ~ aj(1-2x)i/{1 - k ( 1 - 2 x ) } .
(1)
j-0
The coefficients at, the skewing factor k, and the standard deviations s are given in table 2. Figure 2 compares the effect of pressure on HE at five temperatures. The pressure coefficient (~H~/~p)r is small at 298.15 K but increases with increasing temperature. At all except the lowest temperature, (OHEm/Op)xchanges sign at x ,~ 0.9. At the highest temperature where the propane is a supercritical fluid, the shape of HEm(X)is TABLE 2. Coefficients for representing HE for {xC3H8 + ( 1 - x ) C H 3 O H } with equation (1); s is the
standard deviation p/MPa
T/K
a0
a1
a2
aa
5.0 5.0 5.0 5.0 5.0 10.0 10.0 10.0 10.0 15.0 15.0 15.0 15.0 15.0
298.15 323.15 348.15 363.15 373.15 298.15 323.15 348.15 373.15 298.15 323.15 348.15 363.15 373.15
1504 2078 2953 3299 2879 1597 2237 3345 5024 1646 2296 3462 4327 5223
1274 1091 668.2 244.3 -537.2 1323 1237 1149 709.8 1492 1441 1306 1273 1372
681.6 541.4 451.3 670.7 1407 667.5 708.3 420.2 355.3 763.2 532.6 500.7 317.0 275.4
465.9 519.1 225.4 295.3 -458.2 637.6 344.6 379.7 70.97 440.4 293.4 802.6 597.8 309.8
a4
a5
26.86 279.2 72.53 1321 73.34 -597.7 197.8 645.1 -79.08 184.1 112.0 316.2 129.1
-1042 - 126.5 -171.3
276.4 -797.2 -542.9
a6
k
-0.98 -0.97 -0.90 -0.91 ,~ - 0 . 8 2 -0.98 756.2 0.92 -0.91 -0.83 --0.99 -0.96 -0.90 -0.88 -0.87
s 1.46 2.58 2.11 3.50 3.18 1.79 1.87 2.82 4.60 1.77 2.30 2.16 2.99 3.93
H~ FOR ( P R O P A N E + M E T H A N O L ) 1600
i
t
I
i
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1200
557
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ii j . , 1 ~ i/// ii /// IIIIIIIIIII i//,s ~ iI II /// I IiI I// 111
\
III
800
ii
,;/
/ ////
f--
.....
I/////"-/
\
400
V
0 0
0.2
0.4
0.6
0.8
X
F I G U R E 2. Temperature and pressure dependence of the excess molar enthalpies for {xC3H8 + (1-x)CH3OH}: - - , 5 MPa; - , 15 MPa. 1, 2, 3, 4, and 5 refer to (298.15, 323.15, 348.15, 363.15, and 373.15)K, respectively. t
very different at the two pressures. The HEm(X)curve at 5 M P a is less symmetrical than at 15 MPa, with the maximum shifted toward high x. The shape of the H~(x) curve at 373.15 K and low x can be explained as being due to a negative contribution to HEm, most important at low x, which results from the condensation of the supercritical propane into the liquid methanol. We have earlier observed similar effects for (ethane + ethanol)/2) The shape of HEm(X)at 15 M P a is more typical of what is observed for (an alkane + an alkanol) at temperatures considerably below the critical temperature. Apparently the condensation effect which we have used to explain the unusual shape of HEm(X)at 373.15 K and 5 M P a is not so important at 15 MPa. This is not surprising since the supercritical propane should be much more "liquid-like" at this higher pressure. In an earlier paper (3) we reported H~(x) for (propane + propan-l-ol) and it is interesting to compare those results with those for (propane + methanol) to see the effect of the size of the alkanol on HE. Figure 3 shows HEm(X)for (propane + methanol) and (propane + propan-l-ol) at 298.15 K and at 5 MPa and 15 MPa, together with HEm(X)predicted from UNIFAC-2. For both mixtures the shapes of the H~(x) curves predicted from UNIFAC-2 are qualitatively in agreement with experimental results. Quantitatively the calculated values agree better with the experimental results at 15 MPa. In earlier papers, Cz'3) we have seen that UNIFAC-2
450
.
.
.
.
lll14b@"X X X l
/*x
/....-
A
#.
=
~
/_--
~.
, /." /
150
/
• • • -
i/-." 0
0.2
0.4
x
0.6
0.8
F I G U R E 3. Comparison of excess molar enthalpies at 298.15 K and at 5 M P a and 15 MPa: A , {xCaH8 + (1 -x)C3HTOH } at 5 MPa; O, {xCaH8 + (1 - x ) C 3 H v O H } at 15 MPa; , UNIFAC-2 prediction for {xC3H8 + (1 --x)C3HTOH}; ×, {xC3H8 + (1 - x ) C H 3 O H } at 5 M P a ; . , {xC3H8 + (1 --x)CH3OH } at 15 MPa; - - - , UNIFAC-2 prediction for {xC3H 8 4- (1-x)CH3OH}.
ii
/ /
7 -6 7
10
/
"\
/
\
!
/
k)
5
00 J"f-'Z~'/~//0.2
,
,
0.4
0.6
,
0.8
1
X
F I G U R E 4. Excess molar heat capacities at 15 M P a for {xC3H 8 + (1 -x)CH3OH}: -- -- - ,303.15 K; • 323.15 K: . . . . . . .348.15 K.
H~ FOR (PROPANE+ METHANOL)
559
predictions (which are pressure independent) agree better with the high-pressure results. Figure 4 shows C~,m at 15 M P a and at (303.15, 323.15, and 348.15) K as calculated from the temperature dependence of HE: (~HEn/~T)p = Cp, E m.
(2)
E
Cp, m values at intervals of 0.05x across the entire composition range were calculated from s m o o t h e d H E values obtained from e q u a t i o n ( l ) . The HEm values at each composition were fitted to a quadratic equation as a function of temperature and E then differentiated. With increasing temperature, Cp, m increases and the m a x i m u m e m features for other (alkanol + alkane) mixtures have shifts to lower x. Similar Cp, been reported and explained in several papers31° ! 6) Acknowledgement is made to the D o n o r s of The Petroleum Research Fund, administered by the American Chemical Society, for the support of this research. REFERENCES 1. Sipowska, J. T.; Graham, R. C.; Neely, B. J.; Ott, J. B.; Izatt, R. M. J. Chem. Thermodynamics 1989, 21, 1085. 2. Ott, J. 13.;Sipowska, J. T.; Owen, R. L.; izatt, R. M. J. Chem. Thermodynamics 1990, 22, 683. 3. Sipowska, J. T.; Ott, 3. B.; Woolley, A. T.; Izan, R. M. J. Chem. Thermodynamics 1990, 22, 1159. 4. Brunner, E. J. Chem. Thermodynamics 1985, 17, 871. 5. Kuenen, J. P. Phil. Mag. 1903, (6), 6, 637. 6. Selected Values o f Properties of Chemical Compounds. Thermodynamic Research Center Project: Texas A&M University, College Station, Texas. 1970. 7. Scott, R. L.; van Konynenburg, P. H. Discuss. Faraday Soc. 1970, 49, 87. 8. Younglove, B. A.; Ely, J. F. J. Phys. Chem. Ref. Data 1987, 16, 577. 9. Ott, J. B.; Stouffer, C. E.; Cornett, G. V.; Woodfield, B. F.; Wirthlin, R.C.; Christensen, J.J.; Deiters, U. K. J. Chem. Thermodynamics 1986, 18, 1. 10. Costas, M.; Patterson, D. J. Chem. Soc. Faraday Trans. 1 1985, 81, 1214. 1I. Benson, G. C.; D'Arcy, P. J.; Kumaran, M. K. J. Chem. Thermodynamics 1985, 17, 501. 12. Benson, G. C.; D'Arcy, P. J. J. Chem. Thermodynamics 1986, 18, 403. 13. Andreoli-Ball, L.; Patterson, D.; Costas, M.; Caceres-Alonso, M. J. Chem. Soc. Faraday Trans. 1 1988, 84, 3391. 14. Kalinowska, B.; Jedlinska, J.; Stecki, J.; W6ycicki, W. J. Chem. Thermodynamics 1981, 13, 357. 15. Kalinowska, B.; W6ycicki, W. J. Chem. Thermodynamics 1984, 16, 609. 16. Costas, M.; Patterson, D. Thermochim. Acta 1987, 120, 161.
j. Chem. Thermodynamics 1991, 23, 551 559
Excess enthalpies for (propane + methanol) at the temperatures (298.15, 323.15, 348.15, and 373.15) K and pressures (5, 10, and 15) MPa, and at 363.15 K and (5 and 15) M Pa J. T. SIPOWSKA, J. B. OTT," B. J. NEELY, and R. M. IZATT
Department of Chemistry, Brigham Young University, Provo, UT 84602, U.S.A. (Received 23 October 1990) Excess molar enthalpies HE for (propane + methanol) have been determined at the temperatures (298.15, 323.15, 348.15, and 373,15) K and at the pressures (5, 10, and 15) MPa. Measurements were also made at 363.15 K and (5 and 15)MPa. (Propane + methanol) is a type-II mixture (Scott and van Konynenburg's classification) with a (liquid + liquid) phase separation at lower temperatures. The measurements reported in this paper were performed at temperatures and pressures at which both com!~onentswere liquids and where phase separation does not occur.
1. Introduction Recent papers (1 3) from our laboratory have reported measurements of excess enthalpies for (ethane + methanol), (1) (ethane + ethanol), (2) and (propane + propan-l-ol). (3) As a continuation of those studies we have determined excess enthalpies for (propane + methanol). The critical p(T) curve for (propane + methanol) has been investigated by Brunner, (4) and the (liquid + liquid) equilibria by Kuenen. (5) Using these results together with the (vapor + liquid) equilibria for pure propane, (6) and methanol, (6) we have constructed the phase diagram for (propane + methanol) shown in figure 1 as a p(T) projection. It is apparent from figure 1 that, according to Scott and van K o n y n e n b u r g ' s classification, (v) (propane + methanol) is a type-II mixture with a continuous critical line between the critical points of the pure components and a (liquid + liquid) immiscibility at lower temperatures. The critical constants Pc and Tc are 4.24 M P a and 369.98 K for propane, (6) and 7.95 M P a and 513.00 K for methanol. (6) We have measured HE at the temperatures (298.15, 323.15, 348.15, and 373.15) K and the pressures (5, 10, and 15) M P a and at 363.15 K and (5 and 15) M P a . These (T, p) conditions are shown in figure 1. aAuthor to whom correspondence should be sent. 0021 9614/91/060551+09 $02.00/0
© 1991 Academic Press Limited
552
J.T. SIPOWSKA E T AL. 16
i
+
+
+
+
+
+
+
+
+
+
12
+
8
[
0
280
."
I
320
f " ' "
360
I
r
400
440
480
520
T/K
F I G U R E 1. (Fluid + fluid) equilibria for {xC3H 8 + ( 1 - x ) C H 3 O H } : [:], critical point for C3H8; /k, critical point for CH3OH; @, U C E P ; + , (p, T) conditions for the HEm results reported in this paper; - - , (vapor + liquid) critical locus; .... , (vapor + liquid) equilibrium lines for C3H8 and CH3OH; - - - , (liquid + liquid) critical line.
The measurements were made above the (gas + liquid) equilibrium line for propane and between the (liquid + liquid) and critical p(T) lines so that both propane and methanol were liquids at all experimental temperatures except at 373.15 K where the propane was a supercritical fluid. 2. Experimental Methanol (B&J Chrom Pure, 99.9 mass per cent) and propane (Phillips, 99.5 mass per cent) were used without further purification. The methanol was stored over Davison 0.3 nm molecular sieves to remove water. The densities at 293.15 K used to calculate the mole fractions were (0.5110, 0.5215, and 0.5305)g-cm 3 for propane at (5, 10, and 15)MPa, respectively,,and (0.7961, 0.8009, and 0.8060)g.cm 3 for methanol (6) at the same pressures. The propane densities were calculated from the modified Benedict-Webb-Rubin equation with the coefficients given by Younglove et al. (8) The densities of methanol were calculated using an isothermal compressibility of 1.215GPa 1(6) and the density at atmospheric pressure of 0.8913 g. cm-336) The isothermal flow calorimeter used for the measurements has been described. (9) Pressures were measured with a Sensotec Model 450 D transducer calibrated against
HEmF O R ( P R O P A N E + M E T H A N O L )
553
TABLE 1. Experimental excess molar enthalpies HEmfor {xC3H 8 + (1 - x ) C H 3 O H } ; 8H~ is the deviation of the experimental results from equation (1)
X
HE J" m o l - 1
8HEm J ' tool- 1
x
0.0238 0.0489 0.0755 0.1037 0.1336 0.1654 0.1994 0.2357
46,4 87,7 128,9 165.3 202.7 233.7 263.5 287.2
1.2 --0.4 0.3 -- 1.3 0.9 --0.2 0.3 --2.2
0.2746 0.3163 0.3612 0.4096 0.4621 0.5191 0.5812 0.6492
0.0242 0.0586 0.0957 0.1358 0.1793 0.2145 0.2520 0.2921 0.3351
48.2 108.6 164.0 217.6 263.0 290.5 316.8 338.3 354.4
--0.3 --0.8 -- 1.5 1.5 2.1 0.0 0.3 -0.9 4.1
0.3656 0.4143 0.4489 0.4854 0.5239 0.5646 0.6077 0.6535 0.6775
0.0245 0.0504 0.0777 0.1066 0.1373 0.1699 0.2166 0.2543 0.2947 0.3379
48.9 97.1 144.0 186.1 227.7 263.3 304.6 332.8 355.0 376.8
-- 1.2 --l.0 0.5 0.0 1.9 1.0 --0.7 --0.4 -2.0 0.1
0.3685 0.4173 0.4520 0.4885 0.5270 0.5677 0.6107 0.6564 0.6802 0.7302
0.0239 0.0492 0.0759 0.1042 0.1343 0.1774 0.2123 0.2495 0.2894 0.3322
47.5 96.l 151.0 185.3 222.4 282.9 320.7 354.8 388.6 422.7
-- 1.7 --0.7 0.8 - 1.5 -- 6.7 0.5 0.5 - 1.2 1.6 0.2
0.3784 0.4111 0.4457 0.4821 0.5206 0.5614 0.6046 0.6506 0.6994 0.7356
0.0242 0.0498 0.0768 0.1054 0.1358 0.1793
54.1 105.0 155.5 205.3 246.2 313.5
0.1 --0.7 0.1 2.0 --3.8 3.9
0.2145 0.2520 0.2921 0.3351 0.3656 0.4143
HEm J ' tool- 1
8H~ J- mol-- a
x
HE J. tool- x
8H E, J. mol x
0.7236 0.8063 0.8662 0.8978 0.9306 0.9647 0.9734
367.9 341.7 312.3 292.1 258.0 211.8 192.5
1.3 -0.5 -0.1 1.6 --2.4 0.3 0.7
0.7277 0.7540 0.8093 0.8384 0.8996 0.9319 0.9653 0.9739
385.6 380.9 356.6 339.1 291.4 267.8 217.8 197.2
--0.1 3.3 2.1 0.3 --4.5 2.6 0.4 -0.5
0.7563 0.8112 0.8401 0.8699 0.9007 0.9326 0.9657 0.9742
380.8 355.0 341.2 325.9 291.2 263.3 211.5 197.4
0.4 --2.0 0.4 5.5 --3.5 1.8 -2.2 0.9
0.7790 0.8073 0.8366 0.8670 0.8984 0.9310 0.9512 0.9649
582.1 573.5 564.2 546.8 519.6 474.7 425.2 384.9
1.5 --0.8 0.9 1.1 1.4 1.6 -3.8 0.4
0.4489 0.4854 0.5239 0.5646 0.6077 0.6535
535.0 554.5 568.8 584.8 592.8 601.6
-1.1 1.4 0.2 2.3 -1.7 - 1.0
T = 298.15 K, p = 5 MPa 316.8 329.9 346.8 362.1 372.0 377.6 379.6 376.2
4.5 -2.0 - 1.5 0.8 0.8 0.0 -0.4 --1.0
T = 298.15 K, p = 10 MPa 370.2 383.8 394.1 398.3 401.2 404.8 403.7 398.5 395.3
0.6 0.2 2.9 1.0 --0.5 0.8 --0.2 - 1.8 - 1.6
T = 298.15 K, p = 15 MPa 386.7 399.9 407.6 410.8 413.4 416.5 409.0 404.1 400.1 389.2
-0.8 --0.4 1.2 0.2 0.6 3.6 --1.4 --0.9 -0.8 0.4
T = 323.15 K, p = 5 MPa 453.2 473.2 495.4 512.2 527.4 547.4 559.2 568.6 582.4 582.2
-0.2 0.0 3.0 1.3 -- 1.3 2.1 -1.1 --4.3 1.0 - 1.5
T = 323.15 K, p = 10 MPa 352.4 388.9 434.6 466.8 485.9 517.7
-0.1 --4.2 3.5 0.6 -2.0 --0.2
E T AL.
J. T . S I P O W S K A
554
T A B L E 1--continued
HEm
HEm ~.mo1-1
J.mol
J. mol
0.6873 0.7277 0.7702 0.8093
604.5 604.0 597.2 587.3
-0.9 -0.3 0.1 3.0
0.8384 0.8684 0.8996 0.9319
0.0245 0.0504 0.0777 0.1066 0.1373 0.1699 0.2166 0.2543 0.2947 0.3379
62.0 118.9 165.8 222.2 266.2 313.0 371.4 410.6 448.5 483.4
2.4 2.8 -3.6 2.1 -1.9 -0.7 0.8 0.1 0.4 0.2
0.3685 0.4173 0.4520 0.4885 0.5270 0.5677 0.6107 0.6564 0.6899 0.7302
0.0239 0.0492 0.0759 0.1042 0.1343 0.1774 0.2123 0.2495 0.2894 0.3322
56.1 106.9 162.9 217.1 273.1 342.0 390.8 444.6 497.0 550.3
0.5 3.4 --1.2 -0.2 3.1 2.2 -1.5 -0.3 --1.1 --1.8
0.3784 0.4111 0.4457 0.4821 0.5206 0.5614 0.6046 0.6506 0.6994 0.7356
0.0242 0.0498 0.0768 0.1054 0.1358 0.1793 0.2145 0.2520 0.2921 0.3351
67.2 132.9 196.3 265.4 326.2 404.1 467.9 534.2 592.1 644.0
0.0 -0.5 --2.0 3.2 0.9 -3.7 --1.2 4.6 2.7 --4.9
0.3656 0.4143 0.4489 0.4854 0.5239 0.5646 0.6077 0.6535 0.6873 0.7277
0.0245 0.0504 0.0777 0.1066 0.1373 0.1699 0.2166 0.2543 0.2947 0.3379
68.6 137.2 209.5 280.5 347.6 414.3 501.9 563.9 625.7 687.6
0.1 -1.2 1.0 2.1 0.0 -1.0 --0.9 -2.0 --1.4 1.1
0.3685 0.4173 0.4520 0.4885 0.5270 0.5677 0.6107 0.6564 0.6899 0.7302
HEm
8U~ 1
570.2 549.9 521.4 477.2
J' mol-
J.mol 1 -0.1 -1.3 -1.8 1.7
8H~ a
J" t o o l - i
0.9451 0.9653
444.4 368.5
0.0 -0.3
0.7724 0.8112 0.8401 0.8699 0.9007 0.9326 0.9657 0.9742
600.8 586.7 568.2 541.8 508.4 456.7 357.0 302.0
2.3 2.2 -0.2 -3.3 -2.0 1.7 5.6 -5.1
0.7790 0.8073 0.8366 0.8670 0.8984 0.9178 0.9310 0.9512 0.9649
936.6 943.6 933.7 915.7 873.4 820.1 781.8 677.9 573.4
-0.2 3.5 -1.5 -0.9 0.6 -5.8 1.8 1.5 2.8
0.7702 0.8093 0.8384 0.8684 0.8996 0.9319 0.9451 0.9653 0.9739
974.6 963.5 947.5 912.0 858.0 747.2 692.0 541.9 453.7
-1.9 -2.1 0.9 - 1.2 2.9 -3.8 5.8 -0.9 -2.9
0.7563 0.7833 0.8112 0.8401 0.8699 0.9007 0.9326 0.9523 0.9657
977.2 971.1 952.6 931.2 897.3 842.1 751.9 651.3 544.6
1.5 3.2 -1.6 -1.3 --1.7 -2.8 3.3 2.8 -2.9
T=323.15K, p=15MPa 504.0 536.6 555.3 570.6 581.0 591.7 604.9 609.8 608.5 606.7
-1.1 1.5 2.0 1.2 -2.4 -3.4 1.2 1.0 -1.2 -0.2
T = 348.15 K, p = 5 M P a 610.6 644.8 679.4 721.7 759.1 795.4 833.8 869.7 899.7 924.2
T = 348.15K,
3.3 0.4 -2.8 1.5 0.7 -1.2 -0.1 0.0 -2.5 2.7 p =
685.4 747.6 789.2 823.7 853.4 891.5 926.7 948.4 965.5 977.0
10MPa -2.8 1.0 4.3 1.4 --4.9 -0.9 3.3 -1.5 1.0 1.8
T=348.15K, p=15MPa 729.5 784.4 816.6 852.9 888.5 921.7 945.9 965.7 972.8 982.8
4.3 2.3 -2.5 -2.0 -0.3 1.6 -1.0 -1.5 -3.1 4.0
555
H E FOR (PROPANE + M E T H A N O L ) TABLE 1--continued
J.mo1-1
J.mo1-1
J- m o l - 1
J. m o l - 1
J. mol - 1
J. mol 1
T = 363.15K, p = 5 M P a 0.0240 0.0581 0.0948 0.1346 0.1778 0.2127 0.2500 0.2900 0.3328 0.3790
55.6 129.2 206.2 275.8 351.5 413.0 469.7 524.4 588.5 658.7
--0.3 --0.8 2.4 --2.1 --1.2 3.4 1.9 --3.6 --1.8 2.5
0.4118 0.4463 0.4828 0.5213 0.5621 0.6053 0.6418 0.6752 0.7000 0.7265
0.0162 0.0594 0.0970 0.1376 0.1702 0.2170 0.2548 0.2952 0.3384 0.3691
56.2 198.8 297.7 405.4 489.8 596.6 676.0 754.7 838.2 884.8
2.7 0.9 --0.5 --2.0 1.3 0.3 --0.5 -1.5 2.8 --3.3
0.4179 0.4525 0.4891 0.5276 0.5682 0.6113 0.6569 0.6807 0.7306 0.7567
0.0492 0.0759 0.1042 0.1343 0,1774 0,2123 0.2495 0,2894 0.3322
92.7 142.2 181.7 237.5 298.2 340.6 392.4 443.4 494.5
-0.2 2.2 -5.2 3.6 1.7 -3.4 0.2 0.8 -1.7
0.3784 0.4111 0.4457 0.4821 0.5206 0.5614 0.6046 0.6506 0.7356
0.0242 0.0498 0.0768 0.1054 0.1358 0.1793 0.2145 0.2520 0.2921 0.3351
88.7 173.l 257.2 348.6 438.6 548.4 641.6 733.5 837.5 933.1
1.5 1.0 --3.2 1.7 4.3 -4.0 --1.6 -2.3 6.7 4.9
0.3656 0.4143 0.4489 0.4854 0.5239 0.5646 0.6077 0.6535 0.6873 0.7277
0.0245 0.0504 0.0777 0.1066 0.1373
92.0 189.0 280.1 379.9 470.6
--1.5 1.3 --2.0 2.7 --2.6
0.1699 0.2166 0.2543 0.2947 0,3379
700.4 746.1 804.5 858.6 913.7 961.3 1018.5 1052.4 1084.3 1121.4
-1.9 --4.3 3.5 4.5 3.9 -6.6 3.0 -5.0 --2.6 5.2
0.7794 0.8077 0.8370 0.8673 0.8987 0.9312 0.9446 0.9650
1163.4 1180.0 1185.7 1176.5 1137.1 1021.7 938.9 766.9
0.7 -0.6 -1.1 1.1 5.5 -1.8 -7.2 4.7
0.7837 0.8116 0.8404 0.8701 0.9009 0.9328 0.9525 0.9658
1245.3 1221.3 1191.5 1139.7 1064.2 928.3 791.7 651.1
5.4 -1.2 -1.6 -5.2 -l.0 3.3 6.6 -6.5
0.7356 0.7790 0.8073 0.8366 0.8670 0.8984 0.9113 0.9310 0.9512
1130.2 1236.3 1293.7 1353.0 1394.2 1391.6 1375.9 1294.8 1132.3
-5.0 4.7 -0.5 0.2 -1.3 -3.8 3.7 0.6 -0.5
0.7702 0.8093 0.8384 0.8684 0.8996 0.9319 0.9518 0.9653
1532.8 1516.3 1497.7 1428.3 1309,8 1123,0 930.6 746.4
- 3.7 --5.6 7.8 0.0 --7.4 4.4 4.0 -- 3.8
0.3685 0.4173 0.4520 0.4885 0.5270
1067.2 1155.7 1225.8 1283.8 1346.4
5.0 --4.7 1.1 --3.4 --0.6
T = 363.15K, p = 15MPa 967.2 1023.2 1066.6 1112.3 1159.7 1196.1 1226.4 1238.6 1252.6 1249.5
0.8 5.6 --1.0 -2.9 0.5 -1.7 --1.9 -0.8 2.3 1.1
T = 373.15K, p = 5 M P a 5~5.7 600.7 636.5 694,4 756,0 809,8 884.1 960.2 1063.3
1.0 3.5 -6.9 0.4 6.0 -2.6 1.1 -4.1 4.4
T = 373.15 K, p = 10 MPa -
-
991.6 1086.7 1164.1 1237.9 1291.7 1357.8 1419.7 1475.6 1497.5 1534.4
3.0 -- 8.7 1.0 7.6 --4.4 - 1.8 0.8 4.1 --4.8 6.9
T = 373.15 K, p = 15 MPa 572.7 691.9 805.0 899.3 993.2
2.7 --8.0 6.9 2.2 --2.9
556
J. T. S I P O W S K A E T AL. TABLE 1--continued
~m
t4~m
~U~
~m
~/-/~
x
J. m o l - 1
J. mol 1
x
J. m o l - 1
J. m o l - 1
0.7563 0.7833 0.8112 0.8401 0.8699
1517.3 1506.1 1473.3 1422.5 1358.3
0.5 2.5 - 3.4 -8.2 1.5
0.9007 0.9326 0.9523 0.9657
1245.7 1041.9 872.9 699.3
6.6 -4.0 6.0 --4.7
~/~m
x
J" m o l - 1
0.5677 0.6107 0.6564 0.6899 0.7302
1405.2 1450.8 1489.5 1514.2 1522.4
J" m o l i 2.6 --0.9 -- 1.8 3.6 2.2
a dead-weight gauge. Bath temperatures were set and monitored with a Hart Model 1006 platinum resistance thermometer calibrated against a Rosemount Thermometer (ITS-90). We estimated our pressures and temperatures to be accurate to +0.1 MPa and _+0.02 K, respectively. 3. Results and discussion Experimental values of HEm{xCaH8 + (1 -x)CH3OH } are given in table 1. They were fitted to the equation: H~/(J" mo1-1) = x(1 - x ) ~ aj(1-2x)i/{1 - k ( 1 - 2 x ) } .
(1)
j-0
The coefficients at, the skewing factor k, and the standard deviations s are given in table 2. Figure 2 compares the effect of pressure on HE at five temperatures. The pressure coefficient (~H~/~p)r is small at 298.15 K but increases with increasing temperature. At all except the lowest temperature, (OHEm/Op)xchanges sign at x ,~ 0.9. At the highest temperature where the propane is a supercritical fluid, the shape of HEm(X)is TABLE 2. Coefficients for representing HE for {xC3H8 + ( 1 - x ) C H 3 O H } with equation (1); s is the
standard deviation p/MPa
T/K
a0
a1
a2
aa
5.0 5.0 5.0 5.0 5.0 10.0 10.0 10.0 10.0 15.0 15.0 15.0 15.0 15.0
298.15 323.15 348.15 363.15 373.15 298.15 323.15 348.15 373.15 298.15 323.15 348.15 363.15 373.15
1504 2078 2953 3299 2879 1597 2237 3345 5024 1646 2296 3462 4327 5223
1274 1091 668.2 244.3 -537.2 1323 1237 1149 709.8 1492 1441 1306 1273 1372
681.6 541.4 451.3 670.7 1407 667.5 708.3 420.2 355.3 763.2 532.6 500.7 317.0 275.4
465.9 519.1 225.4 295.3 -458.2 637.6 344.6 379.7 70.97 440.4 293.4 802.6 597.8 309.8
a4
a5
26.86 279.2 72.53 1321 73.34 -597.7 197.8 645.1 -79.08 184.1 112.0 316.2 129.1
-1042 - 126.5 -171.3
276.4 -797.2 -542.9
a6
k
-0.98 -0.97 -0.90 -0.91 ,~ - 0 . 8 2 -0.98 756.2 0.92 -0.91 -0.83 --0.99 -0.96 -0.90 -0.88 -0.87
s 1.46 2.58 2.11 3.50 3.18 1.79 1.87 2.82 4.60 1.77 2.30 2.16 2.99 3.93
H~ FOR ( P R O P A N E + M E T H A N O L ) 1600
i
t
I
i
/"
1200
557
Xx5
ii j . , 1 ~ i/// ii /// IIIIIIIIIII i//,s ~ iI II /// I IiI I// 111
\
III
800
ii
,;/
/ ////
f--
.....
I/////"-/
\
400
V
0 0
0.2
0.4
0.6
0.8
X
F I G U R E 2. Temperature and pressure dependence of the excess molar enthalpies for {xC3H8 + (1-x)CH3OH}: - - , 5 MPa; - , 15 MPa. 1, 2, 3, 4, and 5 refer to (298.15, 323.15, 348.15, 363.15, and 373.15)K, respectively. t
very different at the two pressures. The HEm(X)curve at 5 M P a is less symmetrical than at 15 MPa, with the maximum shifted toward high x. The shape of the H~(x) curve at 373.15 K and low x can be explained as being due to a negative contribution to HEm, most important at low x, which results from the condensation of the supercritical propane into the liquid methanol. We have earlier observed similar effects for (ethane + ethanol)/2) The shape of HEm(X)at 15 M P a is more typical of what is observed for (an alkane + an alkanol) at temperatures considerably below the critical temperature. Apparently the condensation effect which we have used to explain the unusual shape of HEm(X)at 373.15 K and 5 M P a is not so important at 15 MPa. This is not surprising since the supercritical propane should be much more "liquid-like" at this higher pressure. In an earlier paper (3) we reported H~(x) for (propane + propan-l-ol) and it is interesting to compare those results with those for (propane + methanol) to see the effect of the size of the alkanol on HE. Figure 3 shows HEm(X)for (propane + methanol) and (propane + propan-l-ol) at 298.15 K and at 5 MPa and 15 MPa, together with HEm(X)predicted from UNIFAC-2. For both mixtures the shapes of the H~(x) curves predicted from UNIFAC-2 are qualitatively in agreement with experimental results. Quantitatively the calculated values agree better with the experimental results at 15 MPa. In earlier papers, Cz'3) we have seen that UNIFAC-2
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F I G U R E 3. Comparison of excess molar enthalpies at 298.15 K and at 5 M P a and 15 MPa: A , {xCaH8 + (1 -x)C3HTOH } at 5 MPa; O, {xCaH8 + (1 - x ) C 3 H v O H } at 15 MPa; , UNIFAC-2 prediction for {xC3H8 + (1 --x)C3HTOH}; ×, {xC3H8 + (1 - x ) C H 3 O H } at 5 M P a ; . , {xC3H8 + (1 --x)CH3OH } at 15 MPa; - - - , UNIFAC-2 prediction for {xC3H 8 4- (1-x)CH3OH}.
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F I G U R E 4. Excess molar heat capacities at 15 M P a for {xC3H 8 + (1 -x)CH3OH}: -- -- - ,303.15 K; • 323.15 K: . . . . . . .348.15 K.
H~ FOR (PROPANE+ METHANOL)
559
predictions (which are pressure independent) agree better with the high-pressure results. Figure 4 shows C~,m at 15 M P a and at (303.15, 323.15, and 348.15) K as calculated from the temperature dependence of HE: (~HEn/~T)p = Cp, E m.
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Cp, m values at intervals of 0.05x across the entire composition range were calculated from s m o o t h e d H E values obtained from e q u a t i o n ( l ) . The HEm values at each composition were fitted to a quadratic equation as a function of temperature and E then differentiated. With increasing temperature, Cp, m increases and the m a x i m u m e m features for other (alkanol + alkane) mixtures have shifts to lower x. Similar Cp, been reported and explained in several papers31° ! 6) Acknowledgement is made to the D o n o r s of The Petroleum Research Fund, administered by the American Chemical Society, for the support of this research. REFERENCES 1. Sipowska, J. T.; Graham, R. C.; Neely, B. J.; Ott, J. B.; Izatt, R. M. J. Chem. Thermodynamics 1989, 21, 1085. 2. Ott, J. 13.;Sipowska, J. T.; Owen, R. L.; izatt, R. M. J. Chem. Thermodynamics 1990, 22, 683. 3. Sipowska, J. T.; Ott, 3. B.; Woolley, A. T.; Izan, R. M. J. Chem. Thermodynamics 1990, 22, 1159. 4. Brunner, E. J. Chem. Thermodynamics 1985, 17, 871. 5. Kuenen, J. P. Phil. Mag. 1903, (6), 6, 637. 6. Selected Values o f Properties of Chemical Compounds. Thermodynamic Research Center Project: Texas A&M University, College Station, Texas. 1970. 7. Scott, R. L.; van Konynenburg, P. H. Discuss. Faraday Soc. 1970, 49, 87. 8. Younglove, B. A.; Ely, J. F. J. Phys. Chem. Ref. Data 1987, 16, 577. 9. Ott, J. B.; Stouffer, C. E.; Cornett, G. V.; Woodfield, B. F.; Wirthlin, R.C.; Christensen, J.J.; Deiters, U. K. J. Chem. Thermodynamics 1986, 18, 1. 10. Costas, M.; Patterson, D. J. Chem. Soc. Faraday Trans. 1 1985, 81, 1214. 1I. Benson, G. C.; D'Arcy, P. J.; Kumaran, M. K. J. Chem. Thermodynamics 1985, 17, 501. 12. Benson, G. C.; D'Arcy, P. J. J. Chem. Thermodynamics 1986, 18, 403. 13. Andreoli-Ball, L.; Patterson, D.; Costas, M.; Caceres-Alonso, M. J. Chem. Soc. Faraday Trans. 1 1988, 84, 3391. 14. Kalinowska, B.; Jedlinska, J.; Stecki, J.; W6ycicki, W. J. Chem. Thermodynamics 1981, 13, 357. 15. Kalinowska, B.; W6ycicki, W. J. Chem. Thermodynamics 1984, 16, 609. 16. Costas, M.; Patterson, D. Thermochim. Acta 1987, 120, 161.