Ind. Eng. Chem. Res. 1990,29, 1535-1546 Dubinin, M. M. The Potential Theory of Adsorption of Gases and Vapours for Adsorbents with Energetically Nonuniform Surfaces. Chem. Rev. 1960,60, 235-241. Flanigan, E. M.; Bennett, J. M.; Grose, R. W.; Cohen, J. P.; Patton, R. L.; Kirchner, R. M.; Smith, J. V. Silicalite, a New Hydrophobic, Crystalline Silica Molecular Sieve. Nature 1978, 272, 512-516. Glessner, A. J.; Myers, A. L. The Sorption of Gas Mixtures in Molecular Sieves. Chem. Eng. Prog. Symp. Ser. 1969,65(96),73-79. Hayhurst, D. T.; Paravar, A. R. Diffusion of C1 to C5 normal Paraffins in Silicalite. Zeolites 1988, 8, 27-29. Jaroniec, M. Physical Adsorption on Heterogeneous Solids. In Fundamentals of Adsorption; Myers, A. L., Belfort, G., Eds.; Engineering Foundation: New York, 1984; pp 239-248. Kiselev, A. V.; Lopatkin, A. A.; Shulga, A. A. Molecular Statistical Calculations of Gas Adsorption by Silicalite. Zeolites 1985, 5, 261-267. Klein, S. M.; Abrahim, W. H. Adsorption of Ethanol and Water Vapors by Silicalite. AIChE Symp. Ser. 1983, 79(230), 53-58. Lechert, H.; Schweitzer, W. Gas Chromatographic Sorption Studies of Hydrocarbons in Pentasils with Different Si/Al Ratio. In Proc. 6th Int. Zeol. Conf.; Olsen, D., Bisio, A., Eds.; Butterworths: England, 1983. LeVan, M.; Vermeulan, T. Binary Langmuir and Freundlich Isotherms for Ideal Adsorbed Solutions. J. Phys. Chem. 1981,85,22. Ma, Y. H. Adsorption and Diffusion of Gases in Shape Selective Zeolite. In Fundamentals of Adsorption; Myers, A. L., Belfort, G., Eds.; Engineering Foundation: New York, 1984; pp 315-324. Mathews, A. P.; Weber, W. J., Jr. Mathematical Modelling of Adsorption in Multicomponent Systems. Am. Chem. SOC.,Symp. Ser. 1980, 135, 27-53. Maxwell, J. B. Data Book of Hydrocarbons; Van Nostrand: New York, 1968. Myers, A. L. Molecular Thermodynamics of Adsorption of Gas and Liquid Mixtures. In Fundamentals of Adsorption: Liapsis, A. S., Ed.; Engineering Foundation: New York, 1987; pp 3-25. Myers, A. L.; Prauznitz, J. M. Thermodynamics of Mixed Gas Adsorption. AIChE J . 1965, 11, 121-126. Perry, J. H.; Chilton, C. H.; Kirkpatrick, S. D. Chemical Engineers Handbook; McGraw-Hill: New York, 1963. Ruthven, D. M. Simple Theoretical Adsorption Isotherm for Zeolites. Nature Phys. Sci. 1971, 232, 70-72. Ruthven, D. M. Principles of Adsorption and Adsorptive Separative Processes; Wiley-Interscience: New York, 1984.
1535
Ruthven, D. M.; Loughlin, K. F.; Derrah, R. I. Sorption and Difjusion of Light Hydrocarbons and other Simple Nonpolar Molecules in Type A Zeolite; Advances in Chemistry 121; American Chemical Society: Washington, DC, 1973a; pp 330-344. Ruthven, D. M.; Loughlin, K. F.; Holborow, K. A. Multicomponent Sorption Equilibria in Molecular Sieve Zeolites. Chem. Eng. Sci. 1973b, 28, 701-709. Ruthven, D. M.; Wong, F. Generalized Stastistical Model for the Prediction of Adsorption Equilibria in Zeolites. Znd. Eng. Chem. Fundam. 1985,24, 27-32. Schay, G. J. Chem. Phys. Hung. 1956,53, 691. Schay, G. J.; Fejes, P.; Szethmary, J. Adsorption of Gas Mixtures. 1. Theory of Physical Adsorption of The Langmuir Type in Multicomponent Systems. Acta Chim. Acad. Sci., Hung. 1957,12, 299-306. Sips, J. R. On the Structure of a Catalyst Surface. J. Chem. Phys. 1948, 16, 490-495. Sips. J. R. On the Structure of a Catalyst Surface 11. J. Chem. Phvs. 1950, 18, 1024-1027. Stach, H.; Thamm, H.; Janchen, J.; Fiedler, K.; Schirmer, W. Experimental and Theoretical Investieations of the AdsorDtion of n-paraffins, n-olefins and Aromatics i n Silicalite. In Proc.'Gth Znt. Zeol. Conf.; Olsen, D., Bisio, A., Eds.; Butterworths: England, 1984; pp 225-231. Suwanayuen, S.; Danner, R. P. Vacancy Solution Theory of Adsorption from Gas Mixtures. AIChE J. 1980, 26(1), 76-83. Valenzuela, D. P.; Myers, A. L.; Talu, 0.;Zwiebel, I. Adsorption of Gas Mixtures: Effect of Energetic Heterogeneity. AZChE J. 1988, 34, 397-402. Wang, J.-G.; Chang, Y.-C.; Ma, Y. H.; Li, H.-Q.; Tong, T. D. Adsorption Equilibrium of Ethylene-Carbon Dioxide Mixtures on Zeolite ZSM-5. In New Developments in Zeolite Science and Technology: Proc. 7th Znt. Zeol. Conf., Tokyo; Murakami, Y., Iijima, A., Ward, J. W., Eds.; Elsevier: Amsterdam, 1986. Wu, P.; Ma, Y. H., The Effect of Cation on Adsorption and diffusion in ZSM-5. In Proc. 6th. Znt. Zeolitic Conf.; Olsen, D., Bisio, A., Eds.; Butterworths: England 1984; pp 253-260. Yon, C. M.; Turnock, P. H. Multicomponent Adsorption in Molecular Sieves. AIChE J . Symp. Ser. 1971, 67(117), 75-83.
Received for review October 11, 1988 Revised manuscript received July 14, 1989 Accepted August 3, 1989
Quaternary, Ternary, Binary, and Pure Component Sorption on Zeolites. 2. Light Alkanes on Linde 5A and 13X Zeolites at Moderate to High Pressures K. F. Loughlin,* M. A. Hasanain, and H. B. Abdul-Rehman King Fahd University of Petroleum & Minerals, Dhahran 31261, Saudi Arabia
Pure component and multicomponent equilibrium adsorption data are reported for the adsorption of the light n-alkanes on Linde 5A and 13X pellets in the temperature range 275-350 K and at pressures up to 1.732 MPa but primarily a t a pressure of 345 kPa. The intrinsic Henry constants and heats of adsorption are extracted from the data using virial isotherm techniques. T h e experimental KOvalues for 13X are in excellent agreement with theoretical quantum mechanical calculations. For zeolite 5A, predictions of theoretical pure component, binary, and ternary profiles employing the Ruthven isotherm using intrinsic Henry constants are satisfactory. For 13X zeolite, profile predictions using the Ruthven isotherm require that the intrinsic Henry constant be increased by on average 212% to adequately fit the data. This increase is attributed to the increase in the heat of sorption with loading for these systems.
As mentioned in the previous paper in this issue (Abdul-Rehman et al., 1990), the objective of this study is to select from the published models a reliable, simple iso-
* To whom correspondence should be addressed. 0888-5885/90/2629-1535$02.50/0
therm explicit in pressure that can be incorporated in the column design of pressure swing adsorption units for the demethanization of a natural gas stream consisting of methane, ethane, propane, and n-butane. The previous paper was concerned with pure component and multi0 1990 American Chemical Society
1536 Ind. Eng. Chem. Res., Vol. 29, No. 7, 1990 Table I. Literature Review of Isotherm Data for the Sorption of the First Four n-Alkanes on 5A (ICaA) or 13X (SNaX) Zeolites" authors methane ethane DroDane n-butane comments 5A (105K0,molecules/cavity/kPa) 5.78 9.3 6.45 experimental isotherms Ruthven and Loughlin (1972) 14.25 7.13 6.0 3.98 theoretical Ruthven et al. (1973a) 10.28 experimental isotherms Ruthven (1976) 45.00 3.9 2.62 experimental isotherms Hamad (1984) 1.56 experimental isotherms Holborow (1974) Hamad (1984) Cochran e t al. (1985) Bezus et al. (1979) Ruthven et al. (1973a,b),qSt Schirmer et al. (19681, -AHo Ruthven (19761, qat Schirmer (1979), -AHo Kiselev and Du (1981), -AHo Stroud et al. (1971), -AHo Fiedler et al. (1979), -AHo Fiedler et al. (1979), -AHo Fiedler et al. (1979), -AHo Hamad (1984), -AHo Bezus et al. (1979), -AHo Rolniak and Kobayashi (1980), -AHo Richards et al. (1976), -qSt Zuech et al. (1983), -AHo Holborow (19741, qo Antonson and Dranoff (19691, -AHo Anderson et al. (1973), -AHo Anderson et al. (1973), -AHo Anderson et al. (19731, -AHo
13X (lO5Ko,molecules/cavity/ kPa) 5.1 0.825 0.228 0.44 0.178 0.164
1.016
5A (qStor -AHo or -AUo, kJ/mol) 27.6 33.9 42.7 24.7 35.2 43.53
19.00 21.34
experimental isotherms experimental isotherms theoretical (ST) isotherms isotherms
24.7-28.9 25.53 25.2 26.4 32.24
16.74 22.4 18.42 26.21 21.09
25.95
18.29 16.42
35.2 35.2
43.54 44.8
36.0 38.27 34.27 35.37 34.74
43.95 44.30 43.68 44.37 41.86
calorimetric theoretical ST isotherms isotherms
25.15 20.9 39.3
isotherms
26.2 45.67 36.71 35.41
50.98 49.18 46.76
13X (qat or -AHo or -AUo, kJ/mol) 23.8 32.8 37.3 23.5 32.0 37.0
Kiselev and Du (19811, -No Kiselev and Du (1979), -AUo Ding et dl. (1988), -mo Harlfinger et al. (1982), -AHo Hamad (1984), -AHo Stach et al. (1979), -AHo Stach et al. (1979), -Wo Stach et al. (19791, -AHo Stach et al. (1979), -AHo Rolniak and Kobayashi (1980), - A H 0 Cochran et al. (1985), -AHo Hyun and Danner (1982), qo Hyun and Danner (1982), qo Hyun and Danner (1982), qo Hyun and Danner (1982), qo Fiedler e t al. (19791, -AHo Schirmer (1979), -AUo Schirmer (1979), -AUo Schirmer (19791, qet Schirmer (1979), qst
17.1 16.0 19.0
Rolniak and Kobayashi (1980) Zuech et al. (1983) Ruthven (1976) Ruthven and Kumar (1980) Anderson e t al. (1973) Holborow (1974) Ruthven et al. (1973a,b) Loughlin and Ruthven (1972)
12.9 12.5-12.9 10.0-13.5
Ruthven and Loughlin (1972)
10
26.37 26.4 24.8 22.86
15.4
32.23 35.58 35.6 34.2
54.8 44.37 38.51 38.5 43.5 37.15
theoretical (ST) calorimetric at 0 = 0.8 (exp) isotherms calorimetric theoretical (ST) isotherms
16.12 27.75
14.7 15.2 17.8 18.3 (a)
26.4 23.5 23.3 26.2 26.0 (b)
29.22 32.22 26.71 25.12 35.6 32.5 32.3 35.0 34.8 (c)
Langmuir isotherm isotherm (ST) VSM ref 38.5 36.6 37.4 41.4 41.8 (d)
theoretical (ST) calorimetric theoretical (ST) calorimetric: (a) 373 K, (b) 323 K, (c) 296 K, (d) 523 K
5A (Maximum Number of Molecules per Cage)
Danner and Choi (1978) Rolniak and Kobayashi (1980) Cochran et al. (1985) Danner and Choi (1978)
5.97-9.95 (a) 5.1 (b) 6.63 Eqt
9.34-10.9 (a)
7.32 6.98-8.34 (b) 4.65-6.68 (c) 7
5
a t 298 K at 308-298 K at 277-190 K (a) 348-296 K, (b) 299 K 5.19 evaluated a t NBP eq 4, paper 1 4.56 a t 308 K 3.41-4.33 (d) (a) 273-185 K, (b) 273-190, (c) 398-190 K, (d) 498-323 K 3
13X (Maximum Number of Molecules per Cage) 9.82-7.71 12.93
a t 298-323 K a t 298 K
4.84 6.00
Volume of 5A cavity = 776 A3; volume of 13X cavity = 822 A3. For 5A, 1 mmol/g = 1.78 molecules/cage (crystals) or 2.22 molecules/cage (pellets). For 13X, 1 mmol/g = 1.68 molecules/cage (crystals) or 2.09 molecules/cage (pellets). ST statistical thermodynamics.
Ind. Eng. Chem. Res., Vol. 29, No. 7, 1990 1537 Table 11. Adsorption Equilibrium Data on Linde 5A Pellets 275 K 300 K 325 K P, kPa q, mmol/g P,kPa q, mmol/g P,kPa q, mmol/g Methane 37.96 73.26 109.96 169.17 214.90 288.30 346.08 402.85 498.48 568.36 870.22 1049.14 1174.86 1252.28 1304.04 1328.98
0.448 0.764 1.028 1.358 1.564 1.819 1.973 2.133 2.270 2.398 2.684 2.812 2.889 2.946 2.972 2.995
34.98 69.24 110.69 202.57 257.62 308.09 384.36 449.73 553.24 692.45 761.12 936.88 1008.71 1150.21 1242.96 1295.86 1582.59 1760.36
0.216 0.398 0.595 0.675 1.103 1.235 1.408 1.534 1.694 1.871 1.947 2.108 2.164 2.263 2.324 2.362 2.552 1.651
53.90 116.55 167.88 232.82 307.08 389.66 476.83 562.42 662.34 827.21 967.99 1059.46 1059.46 1192.36 1271.64 1618.72 1897.56
0.10 0.26 0.55 1.78 6.92 22.84 58.95 178.95 267.31 318.67 345.96 361.52 367.81
0.426 0.788 1.080 1.363 1.591 1.780 1.905 2.040 2.089 2.118 2.132 2.140 2.147
0.55 1.06 1.59 2.43 5.68 13.40 28.48 85.70 209.06 286.70 330.02 353.36
0.298 0.676 0.909 1.120 1.377 1.529 1.643 1.815 1.927 1.969 1.984 1.990
0.40 0.88 1.56 2.86 5.31 11.73 52.68 114.55 235.52 298.96 339.50
0.187 0.373 0.512 0.686 0.813 0.956 1.110 1.231 1.352 1.537 1.654 1.783 1.774 1.884 1.928 2.167 2.309
P, kPa
350 K q, mmol/g
46.31 102.79 169.17 242.86 326.87 388.37 456.04 521.84 568.44 726.28 831.51 927.56 1062.75 1129.71 1237.23 1507.61 1828.75
0.102 0.216 0.342 0.464 0.585 0.666 0.750 0.829 0.873 1.021 1.121 1.191 1.286 1.329 1.397 1.578 1.760
1.45 4.92 15.35 106.22 236.70 313.52 352.38 373.93 382.20
0.330 0.717 1.095 1.467 1.589 1.636 1.653 1.675 1.746
300 K
P, kPa
q, mmol/g
0.04 0.17 0.29 0.48 0.80 1.16 2.48 7.40 35.15 130.03 198.36 272.20 310.68 331.09
0.133 0.277 0.416 0.610 0.809 0.985 1.214 1.445 1.686 1.881 1.949 1.990 2.012 2.028
Propane 0.198 0.411 0.662 0.896 1.097 1.282 1.537 1.670 1.784 1.858 1.848
Table 111. Adsorption Equilibrium Data on Linde 13X Pellets 275 K 300 K
325 K
350 K
Methane 20.20 47.44 76.85 104.80 138.35 172.64 206.84 277.17 345.15 413.68 555.72 669.89 861.08 1034.97 1160.73 1438.86
0.232 0.475 0.729 0.938 1.165 1.367 1.544 1.883 2.106 2.318 2.582 2.724 2.833 3.001 3.074 3.222
25.39 58.93 95.63 138.58 186.78 237.52 290.13 348.87 375.07 431.06 489.39 560.61 677.75 812.68 953.27 1046.62 1166.59 1304.83
0.140 0.319 0.488 0.673 0.860 1.037 1.202 1.367 1.435 1.571 1.693 1.823 2.002 2.189 2.412 2.508 2.626 2.740
0.10 0.18 0.24 0.30 0.52 0.92 1.83 4.32 14.24 36.47 73.33 136.52 196.78 271.58
0.298 0.633 0.854 1.040 1.451 1.748 1.973 2.151 2.304 2.407 2.492 2.568 2.634 2.694
0.22 0.41 0.63 0.86 1.23 1.85 3.83 6.96 11.87 29.10 61.50 107.56 162.37 231.32 293.03
0.195 0.386 0.557 0.756 1.007 1.305 1.659 1.867 1.996 2.159 2.279 2.344 2.405 2.457 2.474
58.00 103.59 146.91 188.27 224.49 262.11 307.37 347.43 446.78 692.23 834.95 984.57 1107.29 1369.29
0.187 0.322 0.446 0.557 0.652 0.744 0.851 0.945 1.137 1.535 1.709 1.854 1.978 2.202
25.79 65.54 104.25 147.55 195.77 254.76 311.60 412.10 551.58 689.89 830.32 971.74 1106.88 1245.88 1342.68
0.061 0.182 0.236 0.318 0.408 0.513 0.610 0.768 0.982 1.155 1.313 1.448 1.579 1.692 1.763
0.191 0.416 0.660 0.880 1.031 1.273 1.546 1.749 1.971 2.102 2.190 2.240
1.05 2.83 4.85 7.07 11.62 20.72 37.11 67.43 124.79 222.01 300.47 342.67
0.164 0.432 0.686 0.900 1.162 1.429 1.635 1.814 1.956 2.065 2.126 2.148
Propane 0.57 1.16 1.86 2.66 3.43
5.12 9.58 17.24 42.40 79.98 137.34 207.53
1538 Ind. Eng. Chem. Res., Vol. 29, No. 7, 1990 PARAYETER
IS
TEMPERATURE IN KELVIfv
W
a
LEGEND I75
30'. 322 35:
'
-01
'
'
50
'
1.5
1.0
2.S
2C
3.0
0 A
D
c ?
C (MMOLESIGM PELLET)
Figure 1. Virial isotherm plot of methane on Linde 5A pellets. P PARAMETER
IS TEMPERATURE
IN
1
KE-Vhl
$1
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l
a W
z.F
LEGEND zr3 o 125
A 0
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a
.
1
.
,
.
-
.
.
.
,
.
.
I
Table IV. Intrinsic Henry's Constant (K), Preexponential Adsorbate Molecular Volume ( p ) , and Heat of Factor (KO), Adsorption (-AH,) for Linde 5A Crystals or Pellets temp, 8, A3/ -M0, kJ/molK molecule K" KO" Sorbate-Methane 189 5.265 190' 57.5 2.47 212' 64.5 0.623 230' 64.5 0.2475 230" 0.2948 250b 0.246 250' 0.122 253' 64.5 0.0825 273' 77 0.0525 3.384 X lo6 21.43 273' 0.0406 275 0.0315 298, 0.0203 29Sk 0.0247 300 0.015 300 78 0.01725, 0.0255 308, 0.0161 30Sk 0.0334 325 0.0090 348 97 0.00675 350 0.0053 230' 273O 273' 275 2938 296 298c 298' 29Sd 300 30Sd 30Sh 31Sd 323 324" 325 3450 347c 348 348' 350 390' 423e
78
106
111
130
Sorbate-Ethane 12.82 1.776 0.855 0.3933 0.22 0.3150 0.3525 0.6983 0.33 0.2475 0.4575 0.300 4.4936 0.153 0.1687 0.1755 0.0688 0.0698 0.0713 0.06375 0.1117 0.0188 0.0240 0.0232
X
lo6
27.87
.
component equilibria of these hydrocarbons on silicalite; this paper is concerned with a similar assessment of these gases on older commercially available zeolites, namely Linde 5A and 13X zeolites. 5A and 13X zeolites are crystalline aluminosilicates having a uniform regular pore size of molecular dimensions capable of sieving molecules based on molecule size. The fundamental building block is tetrahedra of four oxygen ions bonded to silicon or aluminum ions. These tetrahedra are joined together to form the sodalite cage (0cage), composed of square and hexagonal faces, havin an interior diameter of 6.6 A, having a free volume of 150 and with accessibility restricted only to small molecules of less than 2.2 (e.g., H20, NH3). Joining the square faces of the individual sodalite cages produces a cubic lattice, enclosing the (Y cage, of diameter 11.4 A and free volume 776 A3. The size of the pore opening is controlled by the cation used to balance the ionic deficiency in the aluminum oxide tetrahedra. For 5A zeolite, calcium ions are used, to give a free aperture of 4.2 A, permitting passage of molecules
13,
273 2731 275 2938 29Sh 300 323' 325 350 358' 398' 398'"
131
152
Sorbate-Propane 29.703 28.652 11.2975 7.96 7.8756 2.1467 2.408 1.09 X lo* 1.2631 0.5370 0.9225 0.2475 0.263
32.64
"Experimental data Dr. R. I. Derrah, UNB Laboratories, Canada. bTheoretical values of Brauer et al. (1971). CExperimental data of Kondis (1968) for Linde 4A zeolite. dExperimental data of Glessner for Linde 5A zeolite. OExperimental data for Linde 4A zeolite. f Loughlin (1970). 8Carra and Morbidelli (1987). Ruthven and Wong (1985). 'Loughlin and Roberts (1980). 'Zuech et al. (1983). kRolniak (1976). 'Ruthven (1976). '"Hamad (1984). "In molecules/cavity/kPa.
of kinetic diameter 4.9 A such as n-paraffins but excluding isoparaffins. Joining the six-membered hexagonal faces of the sodalite cages forms a more open lattice structure, 13X, with a 13-A-diametercage (822A3 per unit cell) with
Ind. Eng. Chem. Res., Vol. 29, No. 7, 1990 1539 Table V. Intrinsic Henry's Constant ( K ) ,Adsorbate Molecular Volume ( B ) , Preexponential Factor (KO), and Heat of Adsorption (-AHo)for Linde 13X Pellets temp, fi, As/ -mor component K molecule Kd lO5KOd kJ/mol methane 275 80.67 0.02303 0.01146 1.284 16.83 300 83.53 325 86.40 0.00689 350 89.26 0.00229 ethane 323 108.4 0.0543 0,01910 1.289 22.50 373* 115.3 423b 122.3 0.00740 propane 275" 130.6 6.8749 1.7536 32.90 3000 133.2 325" 135.7 0.7051 0.368 350" 138.2 0.3088 348c 138.0 0.4661 423c 145.5 0.0640 0.680 32.21 0.0160 498c 153.1 4.8122 n-butane 348' 181.3 0.3791 0.110 44.42 423c 203.0 0.0461 498c 224.7 OThis work. bKaul (1984). cHamad (1984). pellets/ kPa.
t =b
2.o
2.8
3.6 I/T
5.2
4.4
6.0
~ % 1 0 ~ )
Figure 3. van't Hoff plot for light alkanes on Linde 5A pellets.
mmol/g of
passages of free aperture of 7.4 A, permitting passage of molecules of kinetic diameter 8.1 A. Union Carbide Co. bond both of these zeolites with 20% clay binder to form 1/8- or 1/16-in.pellets for use in packed beds. Equilibrium adsorption of C1-C, hydrocarbons on 5A and 13X zeolites is well documented (Barrer and Sutherland, 1956; Lederman and Williams, 1964; Loughlin and Ruthven, 1972; Ruthven and Loughlin, 1973; Richards et al., 1976; Rolniak and Kobayashi, 1980; Zuech et al., 1983; Rybolt and English, 1988) but has been chiefly limited to atmospheric pressure with the exception of methane high-pressure studies (Lederman and Williams, 1964; Rolniak and Kobayashi, 1980; Zuech et al., 1983). Isotherms are of the Langmuir shape and have been modeled by using the loading ratio correlation (Yon and Turnock, 1971), Ruthven's isotherm (1970), Bakaev's isotherm (19661, virial isotherm of Barrer and Lee (1968), vacancy solution theory of Suwanayuen and Danner (1980), or the Dubinin-Polanyi potential theory (Cook and Basmadjian, 1964; Veyssiere and Cointot, 1975; Doong and Yong, 1988). Saturation loadings are close to theoretical assuming the adsorbed state behaves as a highly compressed liquid and may be calculated using the principles given by Breck (1974). The energies of sorption have been determined both calorimetrically and from isotherms (Bezus et al., 1979; Schirmer et al., 1969; Kiselev and Du, 1979; Stroud et al., 1971; Fiedler et al., 1979; Hamad, 1984; Stach et al., 1979): the calorimetric studies reveal that the differential heats of sorption are invariant for 5A except for the standard decrease at saturation but increase with loading for 13X. Theoretical attempts to calculate the limiting heats of sorption considering the forces involved in physical adsorption indicate that van der Waals forces (dispersion-repulsion) and electrostatic interactions (polarization) are the primary contributors to the heat of adsorption (Ruthven, 1984). Theoretical calculations of the Henry constants assuming that the adsorbed species can be regarded as retaining complete translational, rotational, and internal freedom within the free volume of the discrete 5A cage have been made by Ruthven et al. (1973a,b) and are quite close to the experimental values. The pertinent constants for these sorbentsorbate systems KO,-AHo, and N o available in the literature are presented in Table I. Binary component or multicomponent sorption of hydrocarbons on 5A or 13X zeolite have been reported mostly at atmospheric pressure (Danner and Choi, 1978; Kaul,
LEGEND METHANE
0
ETHANE
A 0 0
PROPANE N-BUTANE
18
22
2.6 I/T
3.0
34
38
K - ' ( x IO')
Figure 4. van't Hoff plot for light alkanes on Linde 13X pellets.
1984; Cochran et al., 1985; Hyun and Danner, 1982; Veyssiere and Cointot, 1975; Ruthven and Kumar, 1980; Ruthven and Wong, 1985; Buelow et al., 1972; Singhal, 1978; Hamad, 1984; Holborow, 1974; Glessner and Myers, 1969; Loughlin et al., 1975; Ruthven et al., 1973a,b;Costa et al., 1984, 1987; Holborow and Loughlin, 1977). Highpressure mixture studies of hydrocarbons have been reported by Yon and Turnock (1971) and of mixtures of methane and nitrogen or carbon dioxide by Lederman and Williams (1964) and Rolniak and Kobayashi (1980). Model isotherms that have been used to explain the data are the loading ratio correlation (Yon and Turnock, 1971), statistical thermodynamics (Ruthven et al., 1973a,b),vacancy solution model (Suwanayuen and Danner, 1980), and the ideal adsorbed solution theory (Glessner and Myers, 1969; O'Brien and Myers, 1988). Theoretical Section The intrinsic Henry constants, preexponential factors heats of adsorption, and molar volumes of adsorbates were derived by using the same procedures as employed in the previous paper in this issue (Abdul-Rehman et al., 1990). The reader should refer to eq 1-4 in that paper. The only difference is that the units of the Henry constants have been altered to molecules/cavity/kPa, using the conversion factors given at the bottom of Table I.
1540 Ind. Eng. Chem. Res., Vol. 29, No. 7 , 1990
"'1
PARAMETER
TEMPERATURE
IS
IN
Table VI. Fit of Multicomponent Ruthven Model for Binary Adsorption of Light Alkanes et 345 or 655 kPa on Linde 5A Pellets. Theoretical Parameters from Table XI adsorbed-phase concn partial pressure, exptl, mmol/g theor, mmol/g kPa pellet pellet
KELVIN
4". LEGEND 275
0 h
300
321 390
TENS
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t
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MUNDRLOS
FUGACITY ( K P A I
a PARAMETER
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0 A 0 -
'
' ' ( I I I I '
0
0
' ' ' 0 1 1 1 1 '
1
1
350
'
' "'-
s " l l , a l '
' " ' 1 ' ' '
1
0
1
Five simple isotherms were fitted to the data, namely, the loading ratio correlation (Yon and Turnock, 1971); Toth isotherm (Jaroniec, 1984), Mathews and Weber isotherm (1980), Jaroniec isotherm (1984), and Ruthven isotherm (1970). The results of these fits can be found in the thesis of Abdul-Rehman (1988). The most satisfactory fit was obtained from Ruthven isotherm,
C=
where C is the concentration in molecules/cavity, K is the Henry constant in molecules/cavity/kPa, p is the molecular volume in A3/molecule, u is the cavity volume in A3, and the isotherm is subjected to the restriction that m 5
methane 133.81 165.54 194.95 217.26 236.76 249.51 258.31 268.84 277.43 282.18 287.60 284.00 291.84 294.61 297.11 301.61 302.15 303.91 305.46 308.55 310.16 311.93 312.46 314.56 318.72 317.02 317.78 318.72
ethane 221.68 250.38 157.71 130.02 111.01 96.12 84.91 75.96 68.75 69.93 64.72 58.25 54.27 50.41 47.01 44.23 44.31 41.72 39.42 37.36 35.54 33.70 32.00 30.66 29.53 28.13 26.96 25.88
methane 98.13 155.60 214.19 240.80 261.72 294.78 291.81 300.58 298.41 307.27 314.83 313.97 316.25 319.68 330.13
propane methane propane methane propane 0.031 2.053 266.67 0.060 1.690 188.72 0.070 1.630 0.061 1.993 0.098 1.933 139.78 0.090 1.560 108.49 0.126 1.885 0.100 1.510 85.43 0.155 1.838 0.160 1.460 70.50 0.170 1.410 0.191 1.793 0.207 1.757 58.17 0.170 1.380 49.46 0.231 1.722 0.190 1.340 0.246 1.692 42.67 0.200 1.310 37.40 0.210 1.290 0.269 1.659 33.28 0.291 1.630 0.210 1.260 0.306 1.604 29.73 0.210 1.240 26.83 0.324 1.577 0.220 1.220 0.342 1.553 24.51 0.240 1.200 0.424 1.437 16.46 0.250 1.190
ethane propane 84.43 258.79 144.42 204.25 180.86 164.16 210.06 136.12 229.40 114.79 245.70 99.38 258.05 87.31 267.81 77.48 169.04 179.14 198.65 145.81 222.34 122.53 239.77 104.83 254.06 91.37 265.28 80.77 274.58 72.16 283.34 65.26
u/@.
methane 0.40 0.130 0.210 0.290 0.360 0.410 0.460 0.520 0.560 0.560 0.580 0.620 0.660 0.690 0.720 0.740 0.740 0.770 0.800 0.830 0.850 0.880 0.910 0.940 0.960 0.980 1.000 1.010
ethane methane 2.210 0.174 0.200 1.920 1.910 0.300 0.367 1.820 0.430 1.750 0.484 1.680 1.610 0.529 1.550 0.576 1.490 0.619 0.623 1.490 0.655 1.440 0.677 1.390 0.713 1.350 0.739 1.310 0.765 1.270 0.792 1.230 0.792 1.230 1.190 0.814 0.834 1.160 0.856 1.130 0.874 1.100 0.894 1.070 0.910 1.040 0.927 1.010 0.947 0.980 0.957 0.960 0.971 0.940 0.985 0.910
ethane propane 0.090 1,990 0.230 1.880 0.320 1.780 0.400 1.680 0.500 1.600 0.550 1.530 0.610 1.460 0.670 1.400 0.270 1.900 0.350 1.810 0.450 1.730 0.520 1.650 0.590 1.580 0.640 1.520 0.700 1.460 0.810 1.410
ethane 0.895 1.914 1.721 1.622 1.535 1.458 1.391 1.327 1.270 1.274 1.230 1.181 1.138 1.098 1.061 1.026 1.026 0.995 0.965 0.936 0.910 0.882 0.857 0.835 0.813 0.792 0.771 0.752
ethane propane 0.100 1.989 1.197 1.884 0.282 1.791 0.364 1.703 0.439 1.624 0.509 1.553 0.573 1.487 0.633 1.426 0.249 1.827 0.332 1.737 0.410 1.655 0.482 1.580 0.550 1.510 0.613 1.446 0.672 1.387 0.728 1.331
The cavity volume is 776 A3 for Linde 5A and 822
A3 for Linde 13X.
The binary form of this isotherm was derived by
Ind. Eng. Chem. Res., Vol. 29, No. 7, 1990 1541 Table VII. Fit of Multicomponent Ruthven Model for Ternary Adsorption of Light Alkanes at 345 or 655 kPa on Linde 5A Pellets. Theoretical Parameters from Table XI adsorbed-phase concn partial pressure, kPa exptl, mmol/g pellet theor, mmol/g pellet methane ethane propane methane ethane propane methane ethane propane 92.71 159.88 203.65 234.77 255.15 269.82 282.45 292.42 301.26 310.61 308.71 163.86 110.00 72.43 152.80 195.69 223.35 244.72
178.15 128.82 97.60 75.84 60.69 49.70 41.43 35.12 30.48 26.60 23.27 157.84 198.15 232.10 169.53 130.16 103.03 84.19
75.46 55.28 42.52 34.13 28.25 23.98 20.78 18.44 16.58 15.04 13.72 34.58 37.97 39.73 29.10 22.54 18.08 15.14
0.022 0.053 0.085 0.117 0.143 0.170 0.194 0.216 0.237 0.249 0.231 0.098 0.071 0.054 0.145 0.127 0.155 0.183
0.540 0.489 0.441 0.400 0.364 0.333 0.305 0.281 0.259 0.239 0.222 0.769 0.866 0.937 0.866 0.800 0.741 0.688
Ruthven et al. (1973a,b), and the ternary form is given by Miller (1987). The quaternary form is a simple extension
c1 = KlP, +
subject to the restrictions
i+j+k+lLP (3) Ruthven and Wong (1985) modified the volume function by setting (4) and determined the R, functions by correlation of the data, a procedure that has also been followed by Costa et al. (1984), but this has not been followed in this work. Experimental Section Apparatus and Procedure. Details of the volumetric apparatus and procedure are presented in the previous paper in this issue by Abdul-Rehman et al. (see part 1). Materials. Linde 5A and 13X zeolites supplied by Dr. J. Sherman of Union Carbide, in the form of 1/16-in.pellets (Lots 931 484080037 and 945 385080041) were the adsorbents used. Research-grade high-purity (>99.99%) gases of methane, ethane, propane, and n-butane were purchased from Kreff Co of the U.K.
1.528 1.505 1.483 1.462 1.444 ‘1.427 1.412 1.398 1.385 1.373 1.362 1.285 1.244 1.203 1.191 1.179 1.168 1.158
0.051 0.105 0.153 0.198 0.237 0.272 0.305 0.336 0.364 0.394 0.410 0.127 0.079 0.050 0.124 0.182 0.232 0.279
0.460 0.421 0.388 0.355 0.327 0.302 0.279 0.258 0.241 0.226 0.211 0.652 0.741 0.815 0.754 0.701 0.654 0.609
1.528 1.487 1.449 1.418 1.389 1.363 1.338 1.316 1.295 1.273 1.258 1.237 1.209 1.175 1.138 1.109 1.082 1.059
Table VIII. Fit of Multicomponent Ruthven Model for Binary Adsorption of Light Alkanes at 345 or 655 kPa on Linde 13X Pellets. Theoretical Parameters from Table XI adsorbed-phase concn partial pressure, exptl, mmol/g theor, mmol/g kPa pellet pellet methane
ethane
methane
93.51 148.44 184.68 209.69 228.14 244.22 255.29 261.85 269.89 204.33 326.39 402.83 454.70 484.93 517.13 531.31 544.49 534.27
254.88 197.33 160.06 133.95 115.08 101.55 90.82 82.06 74.84 452.05 331.78 253.89 202.57 168.35 144.08 124.31 109.47 93.84
0.082 0.092 0.183 0.230 0.251 0.323 0.360 0.398 0.431 0.067 0.144 0.235 0.314 0.357 0.455 0.516 0.573 0.631
methane 115.25 183.10 225.98 255.22 272.27 286.91 295.42 303.36 432.33 495.94 536.07 561.44 580.50 595.53 609.40
propane methane 230.53 161.98 119.45 91.17 71.98 58.72 48.97 42.00 222.32 159.54 120.24 93.07 73.95 59.47 50.98
0.025 0.044 0.080 0.155 0.196 0.239 0.289 0.319 0.041 0.076 0.099 0.119 0.169 0.275 0.321
ethane methane 2.629 2.519 2.418 2.324 2.236 2.156 2.082 2.014 1.950 2.621 2.482 2.352 2.231 2.117 2.010 1.917 1.830 1.750
propane 2.531 2.379 2.387 2.342 2.298 2.264 2.227 2.199 2.380 2.321 2.263 2.212 2.168 2.131 2.093
0.057 0.105 0.147 0.184 0.218 0.249 0.275 0.298 0.321 0.089 0.169 0.243 0.310 0.364 0.421 0.467 0.510 0.542
ethane 2.413 2.314 2.227 2.150 2.081 2.021 1.967 1.918 1.871 2.534 2.414 2.303 2.203 2.118 2.038 1.966 1.901 1.831
methane propane 0.022 0.043 0.063 0.084 0.102 0.121 0.138 0.154 0.086 0.120 0.153 0.185 0.217 0.250 0.278
2.292 2.251 2.207 2.162 2.120 2.079 2.041 2.007 2.255 2.206 2.158 2.109 2.060 2.011 1.973
Results and Discussion For 5A zeolite, pure component equilibrium adsorption data were measured for methane (up to 1.723 MPa), ethane (up to 448 kPa), and propane (up to 345 P a ) , and for 13X zeolite, pure component data were obtained for methane (up to 1.723 MPa) and propane (up to 345 kPa) all at 275,
1542 Ind. Eng. Chem. Res., Vol. 29, No. 7, 1990
Table IX. Fit of Multicomponent Ruthven Model for Ternary Adsorption of Light Alkanes at 345 or 655 kPa on Linde 13X Pellets. Theoretical Parameters from Table XI adsorbed-Dhase concn partial pressure, kPa exptl, mmol/g pellet theor, mmol/g pellet ethane
prop an e
methane
ethane
propane
0.291 0.264 0.238 0.214 0.193 0.174 0.157
2.111 2.077 2.045 2.014 1.986 1.960 1.937
0.030 0.058 0.083 0.106 0.128 0.147 0.165
0.347 0.321 0.296 0.273 0.253 0.235 0.217
1.938 1.909 1.881 1.853 1.828 1.802 1.780
n-butane
methane
ethane
n-butane
1.894 1.873 1.855 1.839 1.825 1.812 1.770
0.028 0.037 0.045 0.052 0.059 0.065 0.039
0.129 0.109 0.093 0.081 0.070 0.062 0.225
1.796 1.798 1.798 1.797 1.794 1.790 1.703
propane
n-butane
methane
propane
n-butane
0.590 0.547 0.512 0.480 0.452 0.429 0.409
1.780 1.751 1.729 1.709 1.691 1.677 1.665
0.016 0.027 0.036 0.046 0.052 0.059 0.066
0.422 0.392 0.370 0.359 0.347 0.340 0.335
1.551 1.561 1.565 1.563 1.562 1.556 1.548
methane
ethane
propane
methane
108.64 177.45 220.21 247.84 267.24 279.55 289.49
116.06 81.72 59.99 45.82 36.24 29.29 24.02
120.52 86.81 65.77 51.90 42.64 35.69 30.67
0.071 0.078 0.102 0.076 0.126 0.138 U.151
methane
ethane
n-butane
methane
ethane
176.48 220.15 251.55 272.50 288.83 298.91 193.78
117.35 84.49 61.57 45.92 34.80 26.95 123.73
51.93 40.09 31.61 25.56 21.24 17.91 27.23
0.022 0.031 0.035 0.050 0.068 0.076 0.045
0.174 0.141 0.116 0.095 0.078 0.063 0.255
methane
propane
n-butane
methane
98.97 162.06 205.97 246.36 264.11 280.82 293.23
148.22 108.58 80.00 62.33 48.67 38.54 31.30
105.13 76.16 55.32 42.25 32.64 25.37 20.20
0.033 0.014 0.026 0.037 0.073 0.047 0.053
-
0
W 4
I
= $
E E
o
F’D V
p:
; *
0
a
a
$ 8 e
* c X
23
40
60
ADSORBED PHASE FRACTION
.eo
0
1.0
20
(METHANE)
Figure 6. Binary adsorption of methane and ethane on Linde 5A pellets: fit of Ruthven’s binary model with intrinsic K .
300,325, and 350 K. The experimental data are reported in Tables I1 and I11 for data base purposes. The SoaveRedlich-Kwong equation of state was used to determine the gas-phase density. Fugacities were used for all calculations involving the pure component data as pressures reached 1.723 MPa but were not found necessary for the multicomponent data a t 345 or 655 kPa. The intrinsic Henry’s constants for 5A and 13X zeolites were extracted with the Barrer and Lee isotherm (typical data for methane on 5A and 13X are shown in Figures 1 and 2, respectively) and are tabulated in Tables IV and V, respectively, together with relevent literature data. The scatter in the data is probably a reflection of the different procedures used by the various authors to extract the intrinsic Henry constants from the data. If different isotherm models are used, the intrinsic constants may be different depending on the forced fit of the model to the data (see, for instance, Danner and Choi’s (1978) four different values of the heat of adsorption for the sorption of propane on 5A zeolite for different models in Table I).
X
40
60
ADSORBED PHASE FRACTION
80
1.0
(METHANE)
Figure 7. Binary adsorption of methane and propane on Linde 5A Igellets: fit of Ruthven’s binary model with intrinsic K.
The Barrer and Lee (1968) virial isotherm contains no 3aturation constant and for this reason appears to be more satisfactory than other isotherms in calculating the intrinsic Henry constants. The Henry constants are plotted in the van’t Hoff plots in Figures 3 and 4, respectively. The data have been regressed to calculate all the KOvalues and the heat of adsorption (-AHo). For 5A zeolite, the reported KOvalues are comparable to those reported in the literature for methane and propane [see Table I) but are much higher for ethane. This is probably due to an interaction effect with the heat of sorption where the reported value for ethane tends toward the high end of the range of values quoted in Table I. The reported -AHo value for methane is close to the average but for propane appears low. For 13X zeolite, the reported KOand -AHo values are in very satisfactory agreement with 1the theoretical calculations of Bezus et al. (1979) (see Table
[I.
Using the intrinsic Henry constants from Tables IV and V, respectively (calculated from appropriate KOand -AHo),
Ind. Eng. Chem. Res., Vol. 29, No. 7, 1990 1543 Table X. Fit of Multicomponent Ruthven Model for Quaternary Adsorption of Light Alkanes at 345 kPa on Linde 13X Pellets. Theoretical Parameters from Table XI adsorbed-phase concn partial pressures, kPa exptl, mmol/g pellet theor, mmol/g pellet methane ethane propane n-butane methane ethane propane n-butane methane ethane propane n-butane 104.07 91.29 84.18 65.74 0.003 0.102 0.427 1.622 0.017 0.099 0.352 1.537 173.75 62.51 61.71 47.18 0.009 0.086 0.402 1.604 0.031 0.080 0.333 1.545 44.04 46.59 34.97 0.021 0.071 219.27 0.379 1.589 0.043 0.066 0.320 1.549 31.82 250.18 36.16 26.58 0.038 0.359 1.575 0.059 0.053 0.056 0.311 1.548 272.16 28.98 21.02 0.049 0.341 1.563 23.62 0.048 0.304 1.546 0.061 0.049 23.71 16.91 0.058 17.77 0.039 287.31 0.326 1.553 0.300 1.541 0.069 0.042 13.73 297.67 19.70 13.98 0.072 0.312 1.543 0.032 0.077 0.037 0.293 1.537 192.51 107.39 24.59 20.38 0.041 0.280 1.512 0.229 0.267 1.460 0.045 0.236 179.82 25.72 0.251 1.484 121.75 23.17 0.028 0.251 1.405 0.345 0.027 0.368 ~~
~
~~
Table XI. Parameters Used To Calculate the Theoretical Data in Tables VI-X and Curves in Figures 6-12 Inclusive at 300 K 5A 13X methane ethane propane n-butane a In
Kin: 0.0208 0.3170 5.2090
Bb 58.6 105.2 133.2
Kill: 0.0114 0.1055 1.7496 58.820
Kop:
0.0135 0.5740 6.7430 119.25
Bb 58.6 105.2 133.2 167.4
molecules/cavity/ kPa. *In A3/molecule.
and using molecular volumes /3 (calculated by using eq 4, part l),theoretical isotherms were calculated for all sorbate-sorbent systems and compared to the data by using eq 1. Satisfactory agreement between the theory and experiment was obtained for ethane and propane on 5A, but for all other systems, discrepancies were observed. For the sorption of methane in both 13X and 5A zeolites, it was found necessary to optimize the P value. An optimum P value between 59 and 62 A3/moleculewas obtained which is significantly less than the theoretical value of 80-89 A3/molecule given by eq 4. For low-pressure measurements, Ruthven has successfully used this equation up to 273 K, but for high-pressure studies, both Rolniak (1976) and Zuech et al. (1983) obtained values between 60 and 62 A3/molecule, in agreement with the results found here. Methane is a hypothetical liquid under the condition of these studies. An analogous system to adsorption is the solubility of methane in liquid solutions a t 25 "C,and for this system, Prausnitz and Shair (1961) used a value of 86.34 A3/molecule for methane, which is consistent with Ruthven's results. Discussions with Valderrama (1988) indicate that the present solubility theories permit either an increase or decrease of the molecular volume above the critical point of a solute. As a consequence of these results, it appears desirable to perform both low- and high-pressure studies of the sorption of light gases in 5A and 13X zeolites, which have homogeneous energetics such as oxygen, nitrogen, methane, and ethane between the boiling point temperature and two or three times the critical temperature, and to determine the form of the molecular volume expression in this region. For 13X zeolite, the fit of methane using the optimized /3 value and optimized Henry constants (approximately 20% greater than the intrinsic) is shown in Figure 5a and the fit is observed to be satisfactory. However, for propane on 13X, the use of intrinsic Henry constants close to these values did not prove successful even though the optimized P value varied insignificantly from the theoretical value (&-3%). Values of the optimized K ranged from 224% to 298% greater than the intrinsic: the fit with these values is shown in Figure 5b and is satisfactory except at the low concentrations where the theoretical curve exceeds
0
X
.20
.40
.60
1.0
.80
ADSORBED PHASE FRACTION
(ETHANE)
Figure 8. Binary adsorption of ethane and propane on Linde 5A pellets: fit of Ruthven's binary model with intrinsic K.
LEGEND EXPT INT K OPT K
0
.20
.40
.60
X ADSORBED PHASE FRACTION
0
----
.80
1.0
(METHANE)
Figure 9. Binary adsorption of methane and ethane on Linde 13X pellets: fit of Ruthven's binary model with optimized and intrinsic
K.
the data. This is expected since the optimized K values are much greater than the intrinsic K values. A possible explanation for this phenomenon is that there is molecular interaction as coverage increases, but use of the Ruthven isotherm with molecular interaction term exp(sBe/vRTJdid not improve the results significantly. The differential heats of sorption do increase with coverage in this system going from 38.5 to 55.5 kJ/mol (Fiedler et al., 1979). So the use of an optimized K value approximately 250% greater than the intrinsic is analogous to using an average heat of sorption about 10% larger than the limiting heat of
1544 Ind. Eng. Chem. Res., Vol. 29, No. 7 , 1990
a > 0
0
ADSORBED PHASE FRACTION
X
(METHANE)
Figure 10. Binary adsorption of methane and ethane on Linde 13X pellets: fit of Ruthven's binary model with optimized and intrinsic K.
-
X
.20
.40
.60
ADSORBED PHASE FRACTION
.80
f.0
(METHANE)
Figure 12. Binary adsorption of methane and propane on Linde 13X pellets: fit of Ruthven's binary model with optimized and intrinsic K.
__-,/-
?
LEGEND
0
0
X
.20
.40
.a
ADSORBED PHASE FRACTION
.eo
f.O
(METMNE)
a 4
LEGEND
Figure 11. Binary adsorption of methane and propane on Linde 13X pellets: fit of Ruthven's binary model with optimized and intrinsic K .
sorption and appears reasonable to account for the molecule-to-molecule interaction. Binary and ternary adsorptions on 5A zeolite and binary, ternary, and quaternary data on 13X zeolite are reported in Tables VI-X inclusively. For the 5A zeolite, theoretical predictions are included in Tables VI and VI1 using the parameters given in Table XI (derived from intrinsic K O and -AHoin Table IV). The agreement between theory and experiment included in Tables VI and VI1 and for binaries in Figures 6-8 is satisfactory, indicating that the multicomponent Ruthven isotherm is a good predictive tool for these systems. A point worth noting is that, although the XY diagrams for the IAS method and Ruthven's statistical equation are the same, the two predictions do not precisely agree. However, the statistical method is explicit in pressure, whereas the IAS model is implicit. The binary, ternary, and quaternary predictions for 13X zeolite using the intrinsic constants in Table XI (derived from Table V) and using the Ruthven isotherm were not in agreement with the data (see the X Y plots presented in Figures 9-12); also the adsorbed-phase concentrations predicted were far too low, and this is what is expected based on the pure component propane analysis given above. The data were correlated using the optimized K values given in Table XI, and the fit is now observed to be satisfactory (see Figures 9-13 and Tables VIII-X). The
METHANE
0
ETHANE
A
PROPANE
0
N-BUTANE
0 30
EXPERIMENTAL CONCENTRATION (MMOLES/GM PELLET 1
Figure 13. Fit of multicomponent Ruthven model to ternary and quaternary adsorption data on Linde 13X and 5A pellets.
optimized constants are an average 212% greater than the intrinsic; this suggests that in calculating pure component or multicomponent data using the Ruthven isotherm the heat of adsorption should be increased by about 10% above the limiting value to reflect the molecule-to-molecule interaction of each species in 13X zeolite at higher pressure. Satisfactory predictions should then result. For thermodynamic consistency, the experimental data and theory must intersect on an isobaric x-y diagram (Valenzuela and Myers, 1989). Although the theory (solid line) doesn't agree exactly with the experimental points in Figures 7-12, it is thermodynamically consistent with the single gas isotherms. Note that the dashed lines are inconsistent with the data based on this criterion (Myers, 1989).
Conclusions The sorption of light alkanes in 5A and 13X is Langmuir-like and the relevant isotherm parameters KO, -AHo, and p are presented to enable predictions of isotherms to be made. The Ruthven isotherm is an adequate model of
Ind. Eng. Chem. Res., Vol. 29, No. 7, 1990 1545 the 5A-light n-alkanes system in its present form. However, for the 13X system, the model isotherm probably needs to be modified to incorporate a changing differential heat of adsorption. Work to this effect is underway in these laboratories.
Acknowledgment The authors thank King Abdul-Aziz City for Science and Technology for funding for this research project through Grant AR-6-147 and Dr. J. Sherman of Union Carbide Corporation for samples of zeolites.
Nomenclature
C = adsorbed-phase concentration, molecules/cavity, or mmol/g of pellet
f = fugacity, kPa K = Henry’s constant, molecules/cavity/ kPa K . = Henry’s constant for componentj , molecules/cavity/kF’a I(, = preexponential factor for van’t Hoff relation m, n, o, or p = maximum number of molecules/cavity P = pressure, kPa Pj= partial pressure for component j , kPa q = adsorbed-phase concentration, mmol/g of pellet R = universal gas constant T = temperature, K X = mole fraction in the adsorbed phase Y = mole fraction in the gas phase Greek Symbols
p = molecular volume, A3/molecule -AHo = heat of adsorption, kJ/mol Y = cage volume of adsorbent, A3/cavity Registry No. Methane, 74-82-8; ethane, 74-84-0; propane, 74-98-6; butane, 106-97-8.
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COMMUNICATIONS Effectiveness Factor in a Three-phase Spinning Basket Reactor: Hydrogenation of Butynediol Two types of spinning basket catalytic reactors were compared by measuring the hydrogenation rates of butynediole with a nickel catalyst. The experiments were performed semibacthwise during variations of rotary speed and catalyst mass. The mass-transfer gas-liquid inhibition was calculated using the measured hydrogen absorption rate, and the liquid-catalyst inhibition transfer was tested by hydrodynamic examinations. The effectiveness factor of the catalyst pellets was determined with the reference reaction rate in a slurry reactor. The results show the annular catalyst basket is more favorable for estimating the effective reaction rate without external mass-transfer inhibitions. Catalytic gas-liquid reaction processes in fixed bed reactors are characterized by the coupling of reaction kinetics, transport processes between the phases and in the 0888-5885/90/2629-1546$02.50/0
catalyst particles, and hydrodynamic effects in the catalyst bed. Reaction rate data for catalyst pellets that are unaltered by external mass-transfer effects or partial 0 1990 American Chemical Society
