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Solubilities of carbon dioxide and hydrogen sulfide in propylene carbonate, N-methylpyrrolidone and sulfolane
Fluid Phase Equilibria, 44 (1988) 105-115 Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands
105
SOLUBILITIES OF CARBON DIOXIDE AND HYDROGEN SULFIDE IN PROPYLENE CARBONATE, N-METHYLPYRROLIDONE AND SULFOLANE F L O R E N T I N O MURRIETA-GUEVARA, ASCENCION R O M E R O - M A R T I N E Z and A R T U R O TREJO *
Instituto Mexicano del Petr6leo, Subdireccifn de Investigaci6n B6,sica de Procesos, Eje l_zizaro C6rdenas 152, 07730 M~xico, D.F. (Mexico) (Received December 30, 1987; accepted in final form May 9, 1988)
ABSTRACT Murrieta-Guevara, F., Romero-Martinez, A. and Trejo, A., 1988. Solubilities of carbon dioxide and hydrogen sulfide in propylene carbonate, N-methylpyrrolidone and sulfolane. Fluid Phase Equilibria, 44: 105-115. Gas solubilities of carbon dioxide and hydrogen sulfide have been measured in propylene carbonate, N-methylpyrrolidone and sulfolane at several temperatures ranging from 298 to 373 K and in the pressure range 51-2330 kPa. Values of the Henry's law constant and of heat of solution were derived from the solubility data. The experimental results have been correlated with the Soave-Redlich-Kwong equation of state using a binary interaction parameter.
INTRODUCTION
The investigation of solubilities of gaseous solutes in liquids is of fundamental importance for design of gas absorption processes to purify industrial and natural gases which frequently contain large quantities of carbon dioxide and hydrogen sulfide. The present trend to reduce energy consumption and associated operating expenses together with fulfillment of pollution controls has led to the search for more efficient and economical methods for removing acidic components. Absorption with physical solvents present the advantage of low energy requirements in the regeneration step. Furthermore, they are often preferred for treating gas streams at high pressure with high concentrations of the acid gases (i.e. CO 2 and H2S). * Author to whom correspondence should be addressed. 0378-3812/88/$03.50
© 1988 Elsevier Science Publishers B.V.
106
There are in the literature a large amount of cx~~mental data for gas solubilities of common systems used in the development of models to investigate liquid and solution structure. However, data for many systems of industry interest are not plentiful, particula~~y’at high pressi_lre. This work reports expeiimental results fdr the sbIubifity of carbon dioxide and hydrogen sulfide in the physical solvents: propylene carbonate (PC); N-methylpyrrolidone (NMP) and tetramethylene sulfone or sulfolane (TMSO,), The me~urements were carried out in the temperature range 298-373 K and in partial the pressure range 51-2330 kPa. From the experimental pressure-composition data, values of the Henry’s law constant and of the heat of solution were derived. Further,,we have correlated the s~lubility data with the Soave modification to the Redlich-Kwong equation of state. EXPERiMENTAL
Materials
The pure samples of PC, NMP and TMSO, afe the same as those used in previous work on liquid densities as a function of temperature (MurrietaGuevara and Trejo, 1984a) and their purity was always better than 99.5 mol%. The CO, was obtained from Infra S.A. with a reported purity of 99.7 mol%, whereas the I&S was from Matheson with a reported purity of 99.5 mol%.
The apparatus and operating procedure used in the present work are based on the static method with evaluation of the amount of solute dissolved and are ~senti~ly the same as those used pre~ously in this laborato~ for other solubility studies (Murrieta-Guevara and. Trejo, 1984b; Gonz#ez et al., 1987). The only modifications carried out consisted in using stainless-steel tubing instead of PTFE tubing and substituting a 190 cm3 stainless-steel cell for the equilibrium glass cell (Murrieta-Guevara, 1987). The solubility or mole fraction of the solute in the liquid phase was derived through material balances and equations of equilibrium as discussed in detail in previous work (Gonz&z et al., 1987). Thus the accuracy of the results given here is within 2% at a given partial pressure of the gaseous solute for all the systems studied. The reported partial pressures for the solutes were obtained as the difference between the equilibrium total pressure and the solvent partial pressure. The temperature of the equilibrium cell was controlled within It 0.02 K up to 343 K and within &-0.5 K at 373 K. The equilibrium total pressure was measured with an accuracy ‘of f 3.5 kPa.
107 RESULTS
The solubility of CO 2 and H 2 S individually in PC has been studied by several authors in different ranges of temperature and partial pressures. Hence, we have compared our experimental results, given in Table 1, with data reported in the literature. Figure 1 shows a comparison between our results for CO 2 and those by Isaacs et al. (1977) at 313.15 and 373.15 K and it may be seen that there exists very good agreement. Isaacs et al. carried out
TABLE 1 Experimental partial pressure-composition results for C O 2 and H2S in propylene carbonate T(K)
p (kPa)
Carbon dioxide 298.15 56.3 147.5 298.9 645.2 1134.2 1632.3 2104.1 313.15
373.15
X solute
T(K)
0.0064 0.0178 0.0359 0.0770 0.1341 0.1878 0.2343
Hydrogen sulfide 298.15 81.7 255.2 418.6 652.4 844.0 1017.6 1164.7 1292.4
54.7 139.9 177.2 290.4 405.9 572.6 690.3 1027.2 1035.2 1384.5 1633.0 2162.0
0.0056 0.0137 0.0168 0.0281 0.0371 0.0541 0.0631 0.0933 0.0955 0.1253 0.1462 0.1869
219.4 429.1 647.1 727.9 871.0 1232.6 1339.6 1429.5 1809.1 2228.7
0.0075 0.0146 0.0236 0.0277 0.0333 0.0464 0.0531 0.0561 0.0721 0.0876
p (kPa)
X solute 0.0367 0.1147 0.1866 0.2846 0.3668 0.4418 0.5032 0.5573
323.15
96.5 234.8 407.6 684.3 967.1 1174.8 1446.1
0.0274 0.0665 0,1148 0.1862 0.2580 0.3102 0.3781
373.15
233.1 459.6 817.8 1091.5 1310.4 1595.6
0.0305 0.0609 0.1052 0.1402 0.1672 0.2041
108
200C 373.15K o
•
1500 298.15K
1000
500
o~o
(~20 Xfi0 2
Fig. 1. Solubility of CO 2 in propylene carbonate as a function of temperature. Data of this work, e ; data of Isaacs et al. (1977), o. Full lines calculated with the Soave equation.
a comparison of their results with literature data establishing also good agreement. Figure 1 also contains our experimental results at 298.15 K for which a comparison with literature data was not possible since Rivas and Prausnitz (1979) studied this system but they only reported the corresponding Henry's law constant, the technique used by Lenoir et al. (1971) gives only Henry's constants and Mantor et al. (1982) reports values of Henry's constants at 298.15 K although their solubility measurements were carried out at 299.85 K. Our H2S results at 373.15 K were compared with data by Isaacs et al. (1977) and good agreement was established. Isaacs et al. compared their results with those by other workers establishing also good agreement. Although Rivas and Prausnitz (1979) also studied the solubility of H2S in PC at 298.15, 323.15 and 373.15 K, a direct comparison with our results is not possible since, as in the case of CO 2, they only report values of Henry's law constant. Table 2 lists the experimental partial pressure-composition results for CO 2 and H2S in N M P at 298.15, 323.15 and 373.15 K. Figure 2 illustrates our results for CO 2.
109 TABLE 2 Experimental partial pressure-composition results for CO2 and H2S in N-methylpyrrolidone T(K)
p (kPa)
Carbon dioxide 298.15 184.8 395.7 641.5 859.5 1145.4 1407.8 323.15
373.15
X solute 0.0289 0.0611 0.0948 0.1272 0.1675 0.2048
204.1 419.0 639.3 862.4 1084.1 1421.0
0.0206 0.0412 0.0615 0.0841 0.1071 0.1439
251.3 522.8 883.0 1183.3 1438.5
0.0105 0.0240 0.0410 0.0562 0.0700
T(K)
p (kPa)
Hydrogen sulfide 298.15 211.3 332.3 448.9 568.4 690.4 804.5 917.4 1016.7 1104.4 1186.6
X solute 0.2648 0.3557 0.4250 0.4853 0.5380 0.5814 0.6207 0.6539 0.6812 0.7057
323.15
183.6 324.3 530.5 783.7 1057.4 1253.6 1384.8
0.1499 0.2316 0.3267 0.4192 0.4992 0.5491 0.5798
373.15
175.2 368.1 586.9 840.1 1081.8 1351.1 1558.6
0.0568 0.1112 0.1673 0.2255 0.2778 0.3287 0.3662
Table 3 presents our experimental partial pressure-composition results for CO 2 and H2S in TMSO 2 at 303.15, 323.15 and 373.15 K. Figure 3 shows the results for H2S. Our experimental partial pressure-composition data were fitted to the K r i c h e v s k y - K a s a r n o v s k y equation (Prausnitz et al., 1986) in order to derive values of the Henry's constant for each one of the systems studied. These values are given in Table 4 together with data from the literature. It m a y be observed that the agreement is reasonably good amongst the different authors regardless of the pressure range studied in each case. It should be noted that Lenoir et al. (1971) used the chromatographic technique to obtain Henry's constants whereas all the other workers included in the comparison in Table 4 used the static cell method for their solubility studies.
110
.15K
o
0.65
'
0.'2o ~EO 2
Fig. 2. Solubility of CO 2 in N-methylpyrrolidone as a function of temperature. Data of this work, @; full lines calculated with the Soave equation. TABLE 3 Experimental partial pressure-composition results for CO 2 and H2S in sulfolane T(K)
p (kPa)
Carbon dioxide 303.15 279.5 651.0 1107.2 1529.2 1853.1 2179.3 323.15
373.15
X solute 0.0321 0.0704 0.1157 0.1550 0.1833 0.2106
81.2 278.5 748.2 1133.6 1521.4 1849.9 2221.7
0.0056 0.0220 0.0572 0.0842 0.1082 0.1278 0.1491
331.6 643.9 1116.1 1852.8 2263.4
0.0148 0.0265 0.0449 0.0714 0.0831
T(K)
p (kPa)
Hydrogen sulfide 303.15 55.2 147.3 280.1 526.0 836.2 1103.1 1253.6 1379.1
X solute 0.0314 0.0821 0.1477 0.2588 0.3820 0.4767 0.5263 0.5669
323.15
76.0 170.8 344.7 605.6 958.0 1142.7 1375.7
0.0267 0.0590 0.1166 0.1999 0.3015 0.3504 0.4093
373.15
241.4 441.0 781.0 1091.3 1312.5 1654.6
0.0383 0.0676 0.1155 0.1600 0.1890 0.2344
111
K
•
•
g %
303.15K
500
0.10 ,
0.20 ,
O. 0
O.'4 0
050 ,
XH2S Fig. 3. Solubility of H2S in sulfolane as a function of temperature. Data of this work, e; full lines calculated with the Soave equation.
By fitting the experimental data of each of the systems studied here to the Krichevsky-Ilinskaya equation (Prausnitz et al., 1986) no significant differences were observed between the values of the Henry's constant derived with this equation and those obtained as explained above. Similar results have been obtained by Mantor et al. (1982). As in previous work (Trejo and Patterson, 1984) we have used the temperature coefficient of Henry's constant to derive approximate values of the heat of solution AH s according to A H s = - R T ( O ( l n H1,2)/O(ln T))p
(1)
Table 5 contains values of AH s for the six binary systems at a mean temperature since AH s is independent of temperature over the range studied in this work. CORRELATION OF RESULTS
We have correlated the experimental solubility data with the Soave modification (Soave, 1972) to the Redlich-Kwong equation of state through the use of a binary interaction coefficient kij with a view of carry out phase equilibria predictions of multicomponent systems of interest in the sweetening of gas streams. The evaluation of the optimum value of kij at each temperature for the six binary systems studied was performed by minimization of the pressure deviation.
112 TABLE 4 Comparison of Henry's law constants System
T(K)
This work
Literature
Data " reference a
8.41, 8.22, 6.86 11.8, 10.49, 11.42 22.39, 26.9, 26.07, 22.52
(1), (2), (3) (4), (2), (5) (1), (4), (5), (2)
Hm(MPa)
CO2/PC
298.15 313.15 373.15
8.21 10.23 28.88
H2S/PC
298.15 323.15 373.15
2.22 3.49 7.60
2.56, 2.12 3.91, 3.42 7.50
(1), (3) (1), (3) (1)
CO2/NMP
298.15
6.38
(1), (6), (3), (7), (8), (9)
323.15 373.15
10.13 23.91
6.69, 6.5, 5.99, 6.63, 5.71, 6.47 10.03 18.24
H2S/NMP
298.15 323.15 373.15
0.74 1.17 3.03
0.76, 0.56 1.35 3.21
(1), (3) (1) (1)
CO 2/TMSO 2
303.15 323.15 373.15
8.61 13.17 22.39
9.22 13.27 25.03
(1) (1) (1)
H2S/TMSO 2
303.15 323.15 373.15
1.75 2.83 6.28
2.07 3.07 6.28
(1) (1) (1)
(1) (1)
a Data references: (1) Rivas and Prausnitz (1979); (2) Mantor et al. (1982); (3) Lenoir et al. (1971); (4) Isaacs et al. (1977); (5) Zubchenko et al. (1971); (6) Wu et al. (1985); (7) Shakhova et al. (1966); (8) Shenderei and Ivanovski (1966); (9) Landolt and Boemstein (1960). I n this w o r k w e u s e d f o r t h e s o l v e n t s t h e g a s - l i q u i d c r i t i c a l v a l u e s reported by Murrieta-Guevara and Trejo (1984a), and for the gases the v a l u e s f r o m t h e d a t a b a n k g i v e n b y R e i d et al. (1977). T h e s e a r e g i v e n in Table 6 together with values for the acentric factor.
TABLE 5 Heats of solution AH s for CO 2 and H2S in pure solvents System
T(K)
- A H s (kJ mol- 1)
CO 2 / P C H2S/PC CO 2 / N M P HES/NMP CO 2/TMSO 2 H2S/TMSO 2
335.7 335.7 335.7 335.7 335.7 335.7
15.9 15.2 16.4 17.7 12.4 17.0
113 TABLE 6 Gas-liquid critical constants and acentric factor for pure components Component
p¢(MPa) a
T¢(K) a
Carbon dioxide Hydrogen sulfide N-Methylpirrolidone Propylene carbonate Sulfolane
7.38 c 8.94 c 4.78 5.41 5.03
304.2 c 373.2 c 724.1 775.4 849.5
0.225 0.100 0.356 0.434 0.378
c c b b b
a Values reported by Murrieta-Guevara and Trejo (1984). b Values calculated with the Lee-Kesler method according to Reid et al. (1977). ¢ Reference (2), property data bank. TABLE 7 Values of the binary interaction coefficient kii of the Soave equation of state System
T(K)
kij
op
CO 2 / P C
298.15 313.15 373.15
- 0.00619 - 0.01212 0.00746
2.3 3.0 6.4
H2S/PC
298.15 323.15 373.15
0.00462 - 0.00183 - 0.00625
1.9 1.8 0.8
CO 2 / N M P
298.15 323.15 373.15
0.00152 0.00003 0.03083
1.6 2.5 5.4
H2S/NMP
298.15 323.15 373.15
- 0.10218 - 0.12085 - 0.12855
9.6 8.8 3.3
CO2/TMSO2
303.15 323.15 373.15
0.00704 0.01188 0.00629
4.0 4.7 5.2
H2S/TMSO2
303.15 323.15 373.15
- 0.02032 - 0.02073 - 0.02443
7.8 2.4 1.7
O u r k ; j r e s u l t s a r e p r e s e n t e d i n T a b l e 7 w h e r e v a l u e s o f Op a r e a l s o i n c l u d e d . T h e l a t t e r a r e a l l s m a l l e r t h a n 10% g i v i n g a n o v e r a l l ~p = 4.1. Figures 1-3 include the calculated solubility data with the Soave equation together with the corresponding experimental values. DISCUSSION The experimental results show that the solubility of either CO 2 or H2S increases as the pressure increases at any of the temperatures considered
114 independently of the solvent. Conversely, the solubility of either gas decreases as the temperature increases i n the whole range of pressure studied independently of the solvent considered. The three solvents studied present higher selectivity for H2S at all temperatures and pressures considered. Overall N M P presents larger absorption capacity for both HES and CO 2 than PC or TMSO 2. For HES both PC and TMSO 2 present approximately the same absorption capacity although CO 2 presents higher solubility in PC than in TMSO 2. These results are rather important since they indicate that N M P could be used as a solvent, pure or mixed, in the removal of acid gases in industrial processes. In fact, previous results (Murrieta-Guevara and Trejo, 1984b) for the solubility of both CO 2 and HES at low pressures in mixtures of N M P with monoethanolamine and diethanolamine confirm the above statement. The effect of temperature on gas solubilities or Henry's constant depends on the nature of the components. For the systems studied here the temperature coefficient is always positive, hence the enthalpy of solution is exothermic and its magnitude greater than for hydrocarbon-hydrocarbon systems. The experimental solubility data and derived quantities may prove useful, together with additional thermodynamic data, for the design of gas sweetening units. The binary interaction coefficients, k i j , determined for the Soave equation of state from the experimental solubility data show a weak temperature effect for each one of the systems as well as a relation to the chemical structure of the solvent for a given solute. These kij values will be used in the prediction of vapor-liquid equilibria of multicomponent systems containing the solvent, acid gases and light hydrocarbons. The results will be the subject of a future report.
LIST OF SYMBOLS H~,j AH s kij p Pc R T T~ xi
Henry's law constant for solute i in solvent j heat of solution binary interaction coefficient pressure gas-liquid critical pressure universal gas constant temperature gas-liquid critical pressure mole fraction of component i in liquid phase
115
Greek symbols a
£O
root-mean-square deviation acentric factor
REFERENCES Gonzhlez, R., Murrieta-Guevara, F., Parra, O. and Trejo, A., 1987. Solubility of propane and butane in mixtures of n-alkanes. Fluid Phase Equilibria, 34: 69-81. Isaacs, E.E., Otto, F.D. and Mather, A.E., 1977. Solubility of H2S and CO 2 in propylene carbonate solvent. Can. J. Chem. Eng., 55: 751-752. Landolt and Boernstein, 1960. Zahlenwerte und Funktionen aus Physik Chemie, Astronomie, Geophysik Technik, II, Band 2. Teil. Springer-Verlag, Berlin. Lenoir, J.-Y., Renault, P. and Renon, H., 1971. Gas chromatographic determination of Henry's constants of 12 gases in 19 solvents. J. Chem. Eng. Data, 16: 340-342. Mantor, P.D., Abib, O., Song, K.Y. and Kobayashi, R., 1982. Solubility of carbon dioxide in propylene carbonate at elevated pressures and higher than ambient temperatures. J. Chem. Eng. Data, 27: 243-245. Murrieta-Guevara, F., 1987. M.Eng. Thesis. National University of Mexico, Mexico. Murrieta-Guevara, F. and Trejo, A., 1984a. Liquid density as a function of temperature of five organic solvents. J. Chem. Eng. Data, 29: 204-206. Murrieta-Guevara, F. and Trejo, A., 1984b. Solubility of carbon dioxide, hydrogen sulfide, and methane in pure and mixed solvents. J. Chem. Eng. Data, 29: 456-460. Prausnitz, J.M., Lichtenthaler, R.N. and Gomes de Azevedo, E., 1986. Molecular Thermodynamics of Fluid-Phase Equilibria. Prentice-Hall, Englewood Cliffs, Chap. 7. Reid, R.C., Prausnitz, J.M. and Sherwood Th. K., 1977. The Properties of Gases and Liquids, 3rd. edn. McGraw-Hill, New York. Rivas, O.R. and Prausnitz, J.M., 1979. Sweetening of sour natural gases by mixed-solvent absorption: solubilities of ethane, carbon dioxide, and hydrogen sulfide in mixtures of physical and chemical solvents. AIChE J., 25: 975-984. Shakhova, S.F., Bondareva, T.I. and Sergejeva, I.E., 1966. Chem. Ind. (USSR), 42: 36. Shenderei, E.R. and Ivanovski, F.P., 1966. Chem. Ind. (USSR), 39: 91. Soave, G., 1972. Equilibrium constants from a modified R - K equation of state. Chem. Eng. Sci., 27: 1197-1203. Trejo, A. and Patterson, D., 1984. Prediction of activity coefficients and Henry's constants at infinite dilution for mixtures of n-alkanes. Fluid Phase Equilibria, 17: 265-279. Wu, Z., Zeck, S. and Knapp, H., 1985. Ber. Bunsenges. Phys. Chem., 89: 1009. Zubchenko, Yu. P., Shakhova, S.F., Wei, T., Titelman, L.I. and Kaplan, L.K., 1971. Zhur. Priklad. Khim., 44: 2044.
105
SOLUBILITIES OF CARBON DIOXIDE AND HYDROGEN SULFIDE IN PROPYLENE CARBONATE, N-METHYLPYRROLIDONE AND SULFOLANE F L O R E N T I N O MURRIETA-GUEVARA, ASCENCION R O M E R O - M A R T I N E Z and A R T U R O TREJO *
Instituto Mexicano del Petr6leo, Subdireccifn de Investigaci6n B6,sica de Procesos, Eje l_zizaro C6rdenas 152, 07730 M~xico, D.F. (Mexico) (Received December 30, 1987; accepted in final form May 9, 1988)
ABSTRACT Murrieta-Guevara, F., Romero-Martinez, A. and Trejo, A., 1988. Solubilities of carbon dioxide and hydrogen sulfide in propylene carbonate, N-methylpyrrolidone and sulfolane. Fluid Phase Equilibria, 44: 105-115. Gas solubilities of carbon dioxide and hydrogen sulfide have been measured in propylene carbonate, N-methylpyrrolidone and sulfolane at several temperatures ranging from 298 to 373 K and in the pressure range 51-2330 kPa. Values of the Henry's law constant and of heat of solution were derived from the solubility data. The experimental results have been correlated with the Soave-Redlich-Kwong equation of state using a binary interaction parameter.
INTRODUCTION
The investigation of solubilities of gaseous solutes in liquids is of fundamental importance for design of gas absorption processes to purify industrial and natural gases which frequently contain large quantities of carbon dioxide and hydrogen sulfide. The present trend to reduce energy consumption and associated operating expenses together with fulfillment of pollution controls has led to the search for more efficient and economical methods for removing acidic components. Absorption with physical solvents present the advantage of low energy requirements in the regeneration step. Furthermore, they are often preferred for treating gas streams at high pressure with high concentrations of the acid gases (i.e. CO 2 and H2S). * Author to whom correspondence should be addressed. 0378-3812/88/$03.50
© 1988 Elsevier Science Publishers B.V.
106
There are in the literature a large amount of cx~~mental data for gas solubilities of common systems used in the development of models to investigate liquid and solution structure. However, data for many systems of industry interest are not plentiful, particula~~y’at high pressi_lre. This work reports expeiimental results fdr the sbIubifity of carbon dioxide and hydrogen sulfide in the physical solvents: propylene carbonate (PC); N-methylpyrrolidone (NMP) and tetramethylene sulfone or sulfolane (TMSO,), The me~urements were carried out in the temperature range 298-373 K and in partial the pressure range 51-2330 kPa. From the experimental pressure-composition data, values of the Henry’s law constant and of the heat of solution were derived. Further,,we have correlated the s~lubility data with the Soave modification to the Redlich-Kwong equation of state. EXPERiMENTAL
Materials
The pure samples of PC, NMP and TMSO, afe the same as those used in previous work on liquid densities as a function of temperature (MurrietaGuevara and Trejo, 1984a) and their purity was always better than 99.5 mol%. The CO, was obtained from Infra S.A. with a reported purity of 99.7 mol%, whereas the I&S was from Matheson with a reported purity of 99.5 mol%.
The apparatus and operating procedure used in the present work are based on the static method with evaluation of the amount of solute dissolved and are ~senti~ly the same as those used pre~ously in this laborato~ for other solubility studies (Murrieta-Guevara and. Trejo, 1984b; Gonz#ez et al., 1987). The only modifications carried out consisted in using stainless-steel tubing instead of PTFE tubing and substituting a 190 cm3 stainless-steel cell for the equilibrium glass cell (Murrieta-Guevara, 1987). The solubility or mole fraction of the solute in the liquid phase was derived through material balances and equations of equilibrium as discussed in detail in previous work (Gonz&z et al., 1987). Thus the accuracy of the results given here is within 2% at a given partial pressure of the gaseous solute for all the systems studied. The reported partial pressures for the solutes were obtained as the difference between the equilibrium total pressure and the solvent partial pressure. The temperature of the equilibrium cell was controlled within It 0.02 K up to 343 K and within &-0.5 K at 373 K. The equilibrium total pressure was measured with an accuracy ‘of f 3.5 kPa.
107 RESULTS
The solubility of CO 2 and H 2 S individually in PC has been studied by several authors in different ranges of temperature and partial pressures. Hence, we have compared our experimental results, given in Table 1, with data reported in the literature. Figure 1 shows a comparison between our results for CO 2 and those by Isaacs et al. (1977) at 313.15 and 373.15 K and it may be seen that there exists very good agreement. Isaacs et al. carried out
TABLE 1 Experimental partial pressure-composition results for C O 2 and H2S in propylene carbonate T(K)
p (kPa)
Carbon dioxide 298.15 56.3 147.5 298.9 645.2 1134.2 1632.3 2104.1 313.15
373.15
X solute
T(K)
0.0064 0.0178 0.0359 0.0770 0.1341 0.1878 0.2343
Hydrogen sulfide 298.15 81.7 255.2 418.6 652.4 844.0 1017.6 1164.7 1292.4
54.7 139.9 177.2 290.4 405.9 572.6 690.3 1027.2 1035.2 1384.5 1633.0 2162.0
0.0056 0.0137 0.0168 0.0281 0.0371 0.0541 0.0631 0.0933 0.0955 0.1253 0.1462 0.1869
219.4 429.1 647.1 727.9 871.0 1232.6 1339.6 1429.5 1809.1 2228.7
0.0075 0.0146 0.0236 0.0277 0.0333 0.0464 0.0531 0.0561 0.0721 0.0876
p (kPa)
X solute 0.0367 0.1147 0.1866 0.2846 0.3668 0.4418 0.5032 0.5573
323.15
96.5 234.8 407.6 684.3 967.1 1174.8 1446.1
0.0274 0.0665 0,1148 0.1862 0.2580 0.3102 0.3781
373.15
233.1 459.6 817.8 1091.5 1310.4 1595.6
0.0305 0.0609 0.1052 0.1402 0.1672 0.2041
108
200C 373.15K o
•
1500 298.15K
1000
500
o~o
(~20 Xfi0 2
Fig. 1. Solubility of CO 2 in propylene carbonate as a function of temperature. Data of this work, e ; data of Isaacs et al. (1977), o. Full lines calculated with the Soave equation.
a comparison of their results with literature data establishing also good agreement. Figure 1 also contains our experimental results at 298.15 K for which a comparison with literature data was not possible since Rivas and Prausnitz (1979) studied this system but they only reported the corresponding Henry's law constant, the technique used by Lenoir et al. (1971) gives only Henry's constants and Mantor et al. (1982) reports values of Henry's constants at 298.15 K although their solubility measurements were carried out at 299.85 K. Our H2S results at 373.15 K were compared with data by Isaacs et al. (1977) and good agreement was established. Isaacs et al. compared their results with those by other workers establishing also good agreement. Although Rivas and Prausnitz (1979) also studied the solubility of H2S in PC at 298.15, 323.15 and 373.15 K, a direct comparison with our results is not possible since, as in the case of CO 2, they only report values of Henry's law constant. Table 2 lists the experimental partial pressure-composition results for CO 2 and H2S in N M P at 298.15, 323.15 and 373.15 K. Figure 2 illustrates our results for CO 2.
109 TABLE 2 Experimental partial pressure-composition results for CO2 and H2S in N-methylpyrrolidone T(K)
p (kPa)
Carbon dioxide 298.15 184.8 395.7 641.5 859.5 1145.4 1407.8 323.15
373.15
X solute 0.0289 0.0611 0.0948 0.1272 0.1675 0.2048
204.1 419.0 639.3 862.4 1084.1 1421.0
0.0206 0.0412 0.0615 0.0841 0.1071 0.1439
251.3 522.8 883.0 1183.3 1438.5
0.0105 0.0240 0.0410 0.0562 0.0700
T(K)
p (kPa)
Hydrogen sulfide 298.15 211.3 332.3 448.9 568.4 690.4 804.5 917.4 1016.7 1104.4 1186.6
X solute 0.2648 0.3557 0.4250 0.4853 0.5380 0.5814 0.6207 0.6539 0.6812 0.7057
323.15
183.6 324.3 530.5 783.7 1057.4 1253.6 1384.8
0.1499 0.2316 0.3267 0.4192 0.4992 0.5491 0.5798
373.15
175.2 368.1 586.9 840.1 1081.8 1351.1 1558.6
0.0568 0.1112 0.1673 0.2255 0.2778 0.3287 0.3662
Table 3 presents our experimental partial pressure-composition results for CO 2 and H2S in TMSO 2 at 303.15, 323.15 and 373.15 K. Figure 3 shows the results for H2S. Our experimental partial pressure-composition data were fitted to the K r i c h e v s k y - K a s a r n o v s k y equation (Prausnitz et al., 1986) in order to derive values of the Henry's constant for each one of the systems studied. These values are given in Table 4 together with data from the literature. It m a y be observed that the agreement is reasonably good amongst the different authors regardless of the pressure range studied in each case. It should be noted that Lenoir et al. (1971) used the chromatographic technique to obtain Henry's constants whereas all the other workers included in the comparison in Table 4 used the static cell method for their solubility studies.
110
.15K
o
0.65
'
0.'2o ~EO 2
Fig. 2. Solubility of CO 2 in N-methylpyrrolidone as a function of temperature. Data of this work, @; full lines calculated with the Soave equation. TABLE 3 Experimental partial pressure-composition results for CO 2 and H2S in sulfolane T(K)
p (kPa)
Carbon dioxide 303.15 279.5 651.0 1107.2 1529.2 1853.1 2179.3 323.15
373.15
X solute 0.0321 0.0704 0.1157 0.1550 0.1833 0.2106
81.2 278.5 748.2 1133.6 1521.4 1849.9 2221.7
0.0056 0.0220 0.0572 0.0842 0.1082 0.1278 0.1491
331.6 643.9 1116.1 1852.8 2263.4
0.0148 0.0265 0.0449 0.0714 0.0831
T(K)
p (kPa)
Hydrogen sulfide 303.15 55.2 147.3 280.1 526.0 836.2 1103.1 1253.6 1379.1
X solute 0.0314 0.0821 0.1477 0.2588 0.3820 0.4767 0.5263 0.5669
323.15
76.0 170.8 344.7 605.6 958.0 1142.7 1375.7
0.0267 0.0590 0.1166 0.1999 0.3015 0.3504 0.4093
373.15
241.4 441.0 781.0 1091.3 1312.5 1654.6
0.0383 0.0676 0.1155 0.1600 0.1890 0.2344
111
K
•
•
g %
303.15K
500
0.10 ,
0.20 ,
O. 0
O.'4 0
050 ,
XH2S Fig. 3. Solubility of H2S in sulfolane as a function of temperature. Data of this work, e; full lines calculated with the Soave equation.
By fitting the experimental data of each of the systems studied here to the Krichevsky-Ilinskaya equation (Prausnitz et al., 1986) no significant differences were observed between the values of the Henry's constant derived with this equation and those obtained as explained above. Similar results have been obtained by Mantor et al. (1982). As in previous work (Trejo and Patterson, 1984) we have used the temperature coefficient of Henry's constant to derive approximate values of the heat of solution AH s according to A H s = - R T ( O ( l n H1,2)/O(ln T))p
(1)
Table 5 contains values of AH s for the six binary systems at a mean temperature since AH s is independent of temperature over the range studied in this work. CORRELATION OF RESULTS
We have correlated the experimental solubility data with the Soave modification (Soave, 1972) to the Redlich-Kwong equation of state through the use of a binary interaction coefficient kij with a view of carry out phase equilibria predictions of multicomponent systems of interest in the sweetening of gas streams. The evaluation of the optimum value of kij at each temperature for the six binary systems studied was performed by minimization of the pressure deviation.
112 TABLE 4 Comparison of Henry's law constants System
T(K)
This work
Literature
Data " reference a
8.41, 8.22, 6.86 11.8, 10.49, 11.42 22.39, 26.9, 26.07, 22.52
(1), (2), (3) (4), (2), (5) (1), (4), (5), (2)
Hm(MPa)
CO2/PC
298.15 313.15 373.15
8.21 10.23 28.88
H2S/PC
298.15 323.15 373.15
2.22 3.49 7.60
2.56, 2.12 3.91, 3.42 7.50
(1), (3) (1), (3) (1)
CO2/NMP
298.15
6.38
(1), (6), (3), (7), (8), (9)
323.15 373.15
10.13 23.91
6.69, 6.5, 5.99, 6.63, 5.71, 6.47 10.03 18.24
H2S/NMP
298.15 323.15 373.15
0.74 1.17 3.03
0.76, 0.56 1.35 3.21
(1), (3) (1) (1)
CO 2/TMSO 2
303.15 323.15 373.15
8.61 13.17 22.39
9.22 13.27 25.03
(1) (1) (1)
H2S/TMSO 2
303.15 323.15 373.15
1.75 2.83 6.28
2.07 3.07 6.28
(1) (1) (1)
(1) (1)
a Data references: (1) Rivas and Prausnitz (1979); (2) Mantor et al. (1982); (3) Lenoir et al. (1971); (4) Isaacs et al. (1977); (5) Zubchenko et al. (1971); (6) Wu et al. (1985); (7) Shakhova et al. (1966); (8) Shenderei and Ivanovski (1966); (9) Landolt and Boemstein (1960). I n this w o r k w e u s e d f o r t h e s o l v e n t s t h e g a s - l i q u i d c r i t i c a l v a l u e s reported by Murrieta-Guevara and Trejo (1984a), and for the gases the v a l u e s f r o m t h e d a t a b a n k g i v e n b y R e i d et al. (1977). T h e s e a r e g i v e n in Table 6 together with values for the acentric factor.
TABLE 5 Heats of solution AH s for CO 2 and H2S in pure solvents System
T(K)
- A H s (kJ mol- 1)
CO 2 / P C H2S/PC CO 2 / N M P HES/NMP CO 2/TMSO 2 H2S/TMSO 2
335.7 335.7 335.7 335.7 335.7 335.7
15.9 15.2 16.4 17.7 12.4 17.0
113 TABLE 6 Gas-liquid critical constants and acentric factor for pure components Component
p¢(MPa) a
T¢(K) a
Carbon dioxide Hydrogen sulfide N-Methylpirrolidone Propylene carbonate Sulfolane
7.38 c 8.94 c 4.78 5.41 5.03
304.2 c 373.2 c 724.1 775.4 849.5
0.225 0.100 0.356 0.434 0.378
c c b b b
a Values reported by Murrieta-Guevara and Trejo (1984). b Values calculated with the Lee-Kesler method according to Reid et al. (1977). ¢ Reference (2), property data bank. TABLE 7 Values of the binary interaction coefficient kii of the Soave equation of state System
T(K)
kij
op
CO 2 / P C
298.15 313.15 373.15
- 0.00619 - 0.01212 0.00746
2.3 3.0 6.4
H2S/PC
298.15 323.15 373.15
0.00462 - 0.00183 - 0.00625
1.9 1.8 0.8
CO 2 / N M P
298.15 323.15 373.15
0.00152 0.00003 0.03083
1.6 2.5 5.4
H2S/NMP
298.15 323.15 373.15
- 0.10218 - 0.12085 - 0.12855
9.6 8.8 3.3
CO2/TMSO2
303.15 323.15 373.15
0.00704 0.01188 0.00629
4.0 4.7 5.2
H2S/TMSO2
303.15 323.15 373.15
- 0.02032 - 0.02073 - 0.02443
7.8 2.4 1.7
O u r k ; j r e s u l t s a r e p r e s e n t e d i n T a b l e 7 w h e r e v a l u e s o f Op a r e a l s o i n c l u d e d . T h e l a t t e r a r e a l l s m a l l e r t h a n 10% g i v i n g a n o v e r a l l ~p = 4.1. Figures 1-3 include the calculated solubility data with the Soave equation together with the corresponding experimental values. DISCUSSION The experimental results show that the solubility of either CO 2 or H2S increases as the pressure increases at any of the temperatures considered
114 independently of the solvent. Conversely, the solubility of either gas decreases as the temperature increases i n the whole range of pressure studied independently of the solvent considered. The three solvents studied present higher selectivity for H2S at all temperatures and pressures considered. Overall N M P presents larger absorption capacity for both HES and CO 2 than PC or TMSO 2. For HES both PC and TMSO 2 present approximately the same absorption capacity although CO 2 presents higher solubility in PC than in TMSO 2. These results are rather important since they indicate that N M P could be used as a solvent, pure or mixed, in the removal of acid gases in industrial processes. In fact, previous results (Murrieta-Guevara and Trejo, 1984b) for the solubility of both CO 2 and HES at low pressures in mixtures of N M P with monoethanolamine and diethanolamine confirm the above statement. The effect of temperature on gas solubilities or Henry's constant depends on the nature of the components. For the systems studied here the temperature coefficient is always positive, hence the enthalpy of solution is exothermic and its magnitude greater than for hydrocarbon-hydrocarbon systems. The experimental solubility data and derived quantities may prove useful, together with additional thermodynamic data, for the design of gas sweetening units. The binary interaction coefficients, k i j , determined for the Soave equation of state from the experimental solubility data show a weak temperature effect for each one of the systems as well as a relation to the chemical structure of the solvent for a given solute. These kij values will be used in the prediction of vapor-liquid equilibria of multicomponent systems containing the solvent, acid gases and light hydrocarbons. The results will be the subject of a future report.
LIST OF SYMBOLS H~,j AH s kij p Pc R T T~ xi
Henry's law constant for solute i in solvent j heat of solution binary interaction coefficient pressure gas-liquid critical pressure universal gas constant temperature gas-liquid critical pressure mole fraction of component i in liquid phase
115
Greek symbols a
£O
root-mean-square deviation acentric factor
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