- Email: [email protected]
Experimental determination of hydrogen sulfide solubility data in aqueous alkanolamine solutions
Fluid Phase Equilibria 218 (2004) 149–155
Experimental determination of hydrogen sulfide solubility data in aqueous alkanolamine solutions Réda Sidi-Boumedine a , Sven Horstmann b , Kai Fischer b,∗ , Elise Provost a , Walter Fürst a , Jürgen Gmehling c a
b
Laboratoire Chimie et Procédé, UCP, ENSTA, 32 Bd Victor, F-75739 Paris Cedex 15, France Laboratory for Thermophysical Properties (LTP GmbH), Institute at the University of Oldenburg, D-26111 Oldenburg, Germany c Department of Industrial Chemistry, University of Oldenburg, D-26111 Oldenburg, Germany Received 19 September 2003; accepted 28 November 2003
Abstract A computer-operated static apparatus for the measurement of gas solubility data by the synthetic method was used for the experimental determination of hydrogen sulfide solubility data in aqueous N-methyldiethanolamine (MDEA), diethanolamine (DEA) solutions and aqueous solution of a mixture of MDEA/DEA. For these systems, measurements at 313 and 373 K and pressures up to about 1.3 MPa were performed. The experimental data from this work are presented in comparison to literature data. For the aqueous MDEA solution at 313 K, the solubility of H2 S was compared to the solubility of CO2 . © 2004 Elsevier B.V. All rights reserved. Keywords: Vapor–liquid equilibria; MDEA; DEA; H2 S; Gas absorption; Experimental method
1. Introduction Aqueous alkanolamine are commonly used for the removal of acid gases, such as CO2 or H2 S, from natural and industrial gases. The optimal and proper design of the units of treatment requires the knowledge of the solubility behavior of the acid gas in the aqueous alkanolamine solutions. Solubility data for carbon dioxide (CO2 ) in aqueous alkanolamine solutions have already been measured in a previous work [1]. As an extension, H2 S solubility data measured with the static synthetic method are presented in this paper. Experimental solubility data for hydrogen sulfide (H2 S) in aqueous N-methyldiethanolamine (MDEA) and 2, 2 -diethanolamine (DEA) have been presented by several investigators [2–21] and are stored in the Dortmund Data Bank (DDB 2003) [22]. Tables 1 and 2 give an overview on the previous results for H2 S solubility in these amines.
∗ Corresponding author. Tel.: +49-441-798-3832; fax: +49-441-798-3603. E-mail address: [email protected] (K. Fischer).
0378-3812/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.fluid.2003.11.020
It has already been discussed that there are large deviations between the data of different authors [23,24]. Thus, more experiments were performed in this work in order to increase the accuracy of the available data base and to enable the model development for the description of such systems. The new data were measured with a computer-operated static apparatus at 313 and 373 K. An overview about the conditions of our experimental investigations is given in Table 3.
2. Experimental 2.1. Materials Water was distilled twice. N-methyldiethanolamine (final purity > 99.7%) and 2, 2 -diethanolamine (final purity > 99.7%) were purchased from Acros. Both amines were dried over molecular sieves. Then, all liquids were degassed as described previously [25]. Hydrogen sulfide was purchased from Praxair (purity of 99.5%) and was used without any further purification. The final purity and water content of the components were checked by gas chromatography and Karl Fischer titration.
150
R. Sidi-Boumedine et al. / Fluid Phase Equilibria 218 (2004) 149–155
Table 1 Literature review of H2 S solubility in aqueous MDEA solutions References
Concentration MDEA (wt.%)
Temperature (K)
Partial pressure of H2 S (kPa)
Bhairi [2] Jou et al. [3] Jou et al. [4] Kuranov et al.[5] Lemoine et al.[6] Li and Shen [7] MacGregor and Mather [8] Maddox et al. [9] P´erez-Salado Kamps et al. [10]
11.8, 20, 23.4 11.8, 23.4, 48.9 35, 50 19.2, 32.1 11.8, 23.6 30 23.4 11.8, 20, 23.4 48.8
298, 298, 298, 313, 298, 313, 313 298, 313,
13.2–1537.3 0.002–5890 0.002–313 165–4250 0.04–1.5 1.5–426.5 0.5–1600 13.2–1537.2 147.9–2783
311, 313, 373 333, 313 333,
323 343, 373, 393 373, 393, 413 353, 373
311, 323, 339, 389 353, 393
Table 2 Literature review of H2 S solubility in aqueous DEA solutions References
Concentration DEA (wt.%)
Temperature (K)
Partial pressure of H2 S (kPa)
Atwood et al. [11] Bottoms [12] Cheng et al. [13] Jagushte and Mahajani [14] Lal et al. [15] Lawson and Garst [16] Lee et al. [17] Lee et al. [18] Lee et al. [19] Leibush and Shneerson [20] Maddox and Elizondo [21]
10, 25, 50 50 20.60 20.60 20.60 25 20.6, 35.4 5.2, 20.6, 35.4, 49.7 5.2, 20.6, 35.4, 49.7 10.1, 20.6 20, 35, 50
300, 298, 298, 313, 313, 311, 298, 298, 298, 288, 300,
0.001–90.9 0–101.3 0.001–10 0.03–0.5 0.007–3.2 0.001–3506.4 0.7–2109.8 0.07–2068.4 0.7–2109.8 0.006–41.6 0.1–75.3
2.2. Apparatus and procedure The gas solubility measurements (isothermal P-x data) were performed with the same computer-operated static apparatus as used in the previous work [1]. In this synthetic method, the system pressure is measured at constant temperature for different overall compositions. The apparatus can be operated at temperatures between 270 and 400 K and pressures up to 5 MPa. In order to determine the global compositions, the quantities of pure substances charged into the stirred equilibrium cell, which is evacuated and placed in a
311, 308, 313 323 373 325, 323, 323, 323, 298, 339,
322, 333 318, 328
339, 348, 348, 348, 323 389
353, 373, 373, 373,
367, 380, 394, 408, 422 393 393, 413 393
thermo-regulated oil bath, have to be known precisely. The purified and degassed solvents are charged into the cell as compressed liquids using piston injectors (model 2200-801, Ruska or model 260D, Isco), which allow the precise recording of volume differences. Then, the gas is added stepwise using a thermo-regulated gas bomb. Knowing the pressure, temperature, and volume of the bomb, the amount of gas inside the bomb can be calculated using correlated PvT data of the gas. Thus, the injected amount of gas can be obtained from the pressure difference in the bomb before and after each injection. The pressures of the cell and of the gas bomb
Table 3 Solubility of hydrogen sulfide in water + alkanolamine mixtures, solvent compositions, temperature, pressure and loading ranges in this work Gas-free compositions
Temperature (K)
Total pressure range (kPa)
Range of loadings (␣)
Number of data points
Mass fraction (%)
Mole fraction
MDEA 46.78
0.1173
313.16 373.01
6.21–1040.0 90.34–865.41
0.085–1.116 0.039–0.707
13 14
DEA 41.78
0.1095
313.17 313.17 373.01
6.06–882.98 6.14–1337.6 89.06–1008.2
0.177–1.064 0.164–1.154 0.021–0.822
10 13 16
MDEA/DEA 37.73/7.64
0.09253/0.02124
313.16 373.01
6.88–1134.7 93.62–931.98
0.041–1.156 0.052–0.743
13 13
R. Sidi-Boumedine et al. / Fluid Phase Equilibria 218 (2004) 149–155
are measured with the help of differential pressure indicators (model 3051C, Rosemount) whereby the reference system is adjusted using an electronic pressure controller (model DPI 510, Druck, range 0–0.5 and 0–5 MPa). The temperatures are monitored with Pt100 resistance thermometers (model F25, Tempcontrol). Except for the injection of the liquid solvents, each step during a measurement run is controlled by a computer, i.e. the determination of the desired pressures and temperatures, and the operation of the valves which are driven using pressurized air. So, the injection steps of the gas, the refilling of the gas bomb from the gas storage and the detection of the system pressures, and temperatures in the cell during the equilibration are performed automatically. The estimated experimental uncertainties of this apparatus are as follows: σ(T) = 0.03 K and σ(P) = 0.1 kPa + 0.0001 P. Since in the described approach only temperature, pressure, total loadings, and total volumes are measured. The compositions of the coexisting phases have to be determined by evaluation of the raw data. This evaluation procedure is quite complex and described in detail elsewhere [26]. From the known solvent feed, the liquid phase volume is determined using precise information about the density of the liquid solution inside the equilibrium chamber. Therefore, the liquid densities of the alkanolamine + water solutions were measured as function of temperature using a vibrating tube densimeter (model DMA 4500, Anton Paar). From the known total volume of the cell, the remaining gas phase volume can be calculated precisely. At given equilibrium conditions (temperature, gas phase volume and gas pressure) the amounts of gas in the gas phase, and thus, also in the liquid phase are obtained. In this approach, several effects have an influence on the resulting liquid phase compositions. These effects are the small amounts of solvents in the gas phase, the compressibility of the solvent under the gas pressure, the partial molar volume of the dissolved gas, and the sol-
151
Table 4 H2 S (1) solubility data in a solution of water (2) (53.22 wt.%) and MDEA (3) (46.78 wt.%) obtained with the computer-operated apparatus T = 313.16 K
T = 373.01 K
x1
P (kPa)
␣
x1
P (kPa)
␣
0.0000 0.0099 0.0184 0.0294 0.0445 0.0584 0.0704 0.0823 0.0926 0.1009 0.1072 0.1121 0.1158
6.21 8.44 11.21 16.30 27.88 45.45 72.63 127.82 238.04 428.52 654.14 864.64 1040.0
0.000 0.085 0.159 0.258 0.397 0.529 0.646 0.765 0.870 0.957 1.024 1.076 1.116
0.0000 0.0046 0.0113 0.0184 0.0280 0.0381 0.0467 0.0533 0.0584 0.0626 0.0663 0.0700 0.0728 0.0765
90.34 96.11 113.99 141.22 191.41 262.71 342.42 417.73 486.99 554.17 622.25 698.21 763.73 865.41
0.000 0.039 0.097 0.159 0.245 0.337 0.418 0.480 0.529 0.569 0.606 0.642 0.669 0.707
␣ = [mole H2 S/mole amine].
vent activity coefficient. They can be taken into account in an iterative isothermal and isochoric algorithm by solving the mass and volume balances as also described by Fischer and Wilken [26]. The experimental error in composition is estimated to be σ(xi ) = 0.0005. In our previous work [1], it has been shown that the data obtained with this apparatus are reproducible and in agreement with other experimental techniques.
3. Results The experimental results for H2 S solubility in 46.78 wt.% MDEA aqueous solution at 313 and 373 K are presented in Table 4 and plotted in Fig. 1. Data from the literature are
10000
373 K
P H2S / kPa
1000
100
10
313 K 1
0.1 0.0
0.5
α
1.0
1.5
Fig. 1. Partial pressure of hydrogen sulfide in a solution of water (2) 53.22 wt.% and MDEA (3) 46.78 wt.%: (䉱,䊏) our results; data of (×) Jou et al. [3] 48.9 wt.%; (-) Jou et al. [4] 50 wt.%; (䊊,䉫) Kuranov et al. [5] 47.5 wt.%; (+) P´erez-Salado Kamps et al. [10] 48.8 wt.%.
152
R. Sidi-Boumedine et al. / Fluid Phase Equilibria 218 (2004) 149–155 10000
1000
P H2S / kPa
373 K 100
10
313 K
1
0.1 0.0
0.5
1.0
1.5
α Fig. 2. Partial pressure of hydrogen sulfide in a solution of water (2) 58.22 wt.% and DEA (3) 41.78 wt.%: (䉱,) our results at 313 K; (䊏) our results at 373 K.
also included in this diagram. The data of this work show high internal consistency and good agreement with most of the literature data. The experimental pressures of Kuranov et al. [5] and Jou et al. [3] for loadings ␣ (mole of H2 S per mole amine) higher than 0.8 are lower than the new data. However, the data of Pérez-Salado Kamps [10] at the same loadings are in agreement with our data. This illustrates the problem of inconsistency of some data sets reported in the literature. The experimental solubility data of H2 S in 41.78 wt.% DEA aqueous solution at 313 and 373 K are plotted in Fig. 2 and tabulated in Table 5. At 313 K, two independent measurement runs were performed in order to check for reproducibility of the experimental method. These runs were
performed completely independent from each other, and for each one the solvent mixture was prepared separately. As for the aqueous MDEA solution, the temperature effect on the solubility curves in aqueous DEA can be seen in Fig. 2, i.e. the H2 S solubility decreases with increasing temperature. The equilibrium solubility data of H2 S in a mixture 37.73 wt.% MDEA/7.64 wt.% DEA aqueous solution were also measured at 313 and 373 K. The data are presented in Fig. 3 and listed in Table 6. Again, the influence of temperature on the shape of the curves and the H2 S solubility can be observed. Fig. 4 represents the solubility of the H2 S in all amine solutions studied in this work. The three solutions have almost the same mole fraction of water, so that the influence
Table 5 H2 S (1) solubility data in a solution of water (2) (58.22 wt.%) and DEA (3) (41.78 wt.%) obtained with the computer-operated apparatus T = 313.17 K (run 1)
T = 313.17 K (run 2)
T = 373.01 K
x1
P (kPa)
␣
x1
P (kPa)
␣
x1
P (kPa)
␣
0.0000 0.0190 0.0302 0.0372 0.0534 0.0679 0.0799 0.0907 0.0989 0.1043
6.06 8.59 11.18 13.45 23.08 41.69 82.77 220.53 551.52 882.98
0.000 0.177 0.285 0.353 0.516 0.666 0.794 0.911 1.003 1.064
0.0000 0.0177 0.0262 0.0397 0.0539 0.0670 0.0791 0.0897 0.0976 0.1033 0.1073 0.1101 0.1121
6.14 7.97 9.90 14.38 22.81 39.09 76.08 188.44 457.35 766.99 1016.6 1202.8 1337.6
0.000 0.164 0.246 0.377 0.520 0.656 0.785 0.900 0.988 1.052 1.098 1.130 1.154
0.0000 0.0023 0.0080 0.0135 0.0220 0.0299 0.0393 0.0460 0.0517 0.0574 0.0622 0.0658 0.0686 0.0744 0.0789 0.0826
89.06 90.07 95.37 103.91 122.81 147.58 188.88 231.30 276.49 336.70 400.62 457.98 508.66 665.13 829.31 1008.2
0.000 0.021 0.074 0.125 0.205 0.281 0.374 0.441 0.498 0.557 0.606 0.643 0.673 0.735 0.782 0.822
R. Sidi-Boumedine et al. / Fluid Phase Equilibria 218 (2004) 149–155
153
10000
P H2S / kPa
1000
373 K
100
313 K
10
1
0.1 0.0
0.5
α
1.0
1.5
Fig. 3. Partial pressure of hydrogen sulfide in a solution of water (2) 54.63 wt.%, MDEA (3) 37.73 wt.% and DEA (4) 7.64 wt.% (x4 = 0.0212): (䉱,䊏) our results.
of the different amines can be evaluated. The solubility of H2 S in aqueous DEA is higher than in the MDEA/DEA and MDEA solution. When the chemical saturation of the amines at loadings of α > 1 is reached, there is almost no difference between all these three amine solutions since the solubility is only physical. These effects are identical for both temperatures. Finally, the solubility of H2 S measured herein and the solubility of CO2 measured previously [1] in the aqueous solution of MDEA 46.78 wt.% at 313 K are compared in Fig. 5. As can be observed, at a specified MDEA concentration level of the solution, the H2 S solubility is slightly higher than for CO2 especially at high partial pressure. However, the two
solubility curves merge at lower acid gas partial pressure. The amines can be protonated by the acid aqueous H2 S or CO2 , respectively. Tertiary amines cannot form carbamates with CO2 , thus the difference between the H2 S and CO2 solubilities are caused by the differences of the acidity and the physical solubility of the gases. The H2 S solubility curves exhibit a similar shape as it was found for the CO2 solubility data in the previous investigation [1]. The curves show more or less two distinguished break points, one at loadings of α = 0.2–0.3 and the other at loadings of 0.8 to 1.0. Between these loadings the curve of the logarithmic partial pressure of the gas is almost linear dependent on the loading. At lower loadings, significant
10000
373 K
P H2S / kPa
1000
100
10
313 K 1
0.1 0.0
0.5
α
1.0
1.5
Fig. 4. Comparison of all the results obtained for the H2 S solubility: (䉬,䉫) MDEA 46.88 wt.%; (䉱,) DEA 41.78 wt.%; (䊏,䊐) MDEA 37.73 wt.%/DEA 7.64 wt.%.
154
R. Sidi-Boumedine et al. / Fluid Phase Equilibria 218 (2004) 149–155 10000
1000
Pgas / kPa
CO2 100
H2S
10
1
0.1 0.0
0.5
α
1.0
1.5
Fig. 5. Comparison of H2 S and CO2 solubility data in a solution of water (2) 53.22 wt.% and MDEA (3) 46.78 wt.% at 313 K: (䉱) H2 S; (䉫) CO2 .
Table 6 H2 S (1) solubility data in a solution of water (2) (54.63 wt.%), MDEA (3) (37.73 wt.%) and DEA (4) (7.64 wt.%) obtained with the computeroperated apparatus T = 313.16 K
T = 373.01 K
an improved representation of the H2 S/alkanolamine/H2 O systems.
Acknowledgements
x1
P (kPa)
␣
x1
P (kPa)
␣
0.0000 0.0046 0.0148 0.0283 0.0437 0.0579 0.0708 0.0829 0.0935 0.1018 0.1080 0.1127 0.1162
6.88 7.40 9.60 14.78 24.83 41.33 69.45 127.90 260.91 489.87 743.35 960.25 1134.7
0.000 0.041 0.132 0.256 0.402 0.540 0.670 0.794 0.907 0.996 1.065 1.116 1.156
0.0000 0.0059 0.0137 0.0224 0.0336 0.0441 0.0531 0.0599 0.0651 0.0691 0.0729 0.0758 0.0780
93.62 101.18 122.47 157.40 223.43 313.56 419.71 520.99 614.66 697.03 788.12 867.71 931.98
0.000 0.052 0.122 0.201 0.306 0.406 0.493 0.560 0.612 0.652 0.691 0.721 0.743
deviations to the linear extrapolation to zero partial pressures are observed, which is essential for the removal of small traces of H2 S from natural gas. At higher loadings, the change to physical absorption can be observed.
4. Conclusions New solubility data for H2 S in aqueous solutions of the alkanolamines MDEA and DEA were determined using a computer-operated static apparatus. The results of this investigation were compared to the data of other authors and in most cases good agreement was found, although also discrepancies were observed with a few references. In the future, the new data can be used for the model development and
The financial support of this investigation by the German Academic Exchange Service (DAAD) is gratefully acknowledged.
References [1] R. Sidi-Boumedine, S. Horstmann, K. Fischer, E. Provost, W. Fürst, J. Gmehling, Fluid Phase Equilib. 218 (2004) 85–94. [2] A.M. Bhairi, Experimental Equilibrium between acid gas and ethanolamine solutions, PhD Dissertation, Stillwater, OK, 1984. [3] F.Y. Jou, J.J. Carroll, A.E. Mather, F.D. Otto, Can. J. Chem. Eng. 71 (1993) 264–268. [4] F.Y. Jou, A.E. Mather, F.D. Otto, Ind. Eng. Chem. Process Des. Dev. 21 (4) (1982) 539–544. [5] G. Kuranov, B. Rumpf, N.A. Smirnova, G. Maurer, Ind. Eng. Chem. Res. 35 (6) (1996) 1959–1966. [6] B. Lemoine, Y.-G. Li, R. Cadours, C. Bouallou, D. Richon, Fluid Phase Equilib. 172 (2000) 261–277. [7] M.-H. Li, K.-P. Shen, Fluid Phase Equilib. 85 (1993) 129–140. [8] R.J. MacGregor, A.E. Mather, Can. J. Chem Eng. 69 (1991) 1357– 1366. [9] R.N. Maddox, A.H. Bhairi, J.R. Diers, P.A. Thomas, Gas Process Assn. Research Report RR-104, 1987. [10] A. Pérez-Saladao Kamps, G. Maurer, J. Chem. Eng. Data 41 (6) (1996) 1505–1513. [11] K. Atwood, M.R. Arnold, R.C. Kindrick, Ind. Eng. Chem. 49 (9) (1957) 1439–1444. [12] R.R. Bottoms, Ind. Eng. Chem. 23 (5) (1931) 501–504. [13] G.-X. Cheng, W.-L. Tang, F. Shen, Fuel Sci. Technol. Int. 9 (8) (1991) 935–947. [14] M.V. Jagushte, V.V. Mahajani, Ind. J. Chem. Technol. 6 (1999) 125– 133.
R. Sidi-Boumedine et al. / Fluid Phase Equilibria 218 (2004) 149–155 [15] D. Lal, F.D. Otto, A.E. Mather, Can. J. Chem. Eng. 63 (4) (1985) 681–685. [16] J.D. Lawson, A.W. Garst, J. Chem. Eng. Data 21 (1) (1976) 20–30. [17] J.I. Lee, F.D. Otto, A.E. Mather, J. Chem. Eng. Data 18 (1) (1973) 71–73. [18] J.I. Lee, F.D. Otto, A.E. Mather, J. Chem. Eng. Data 18 (4) (1973) 420. [19] J.I. Lee, F.D. Otto, A.E. Mather, Design data for diethanolamine acid gas treating systems, Can. Gas J. Gas Processing, 1973, 26–34. [20] A.G. Leibush, A.L. Shneerson, Zh. Prikl. Khim. 23 (2) (1950) 145– 152.
155
[21] R.N. Maddox, E.M. Elizondo, Gas Process Assn. Research Report RR-124, 1989. [22] Dortmund Data Bank 2003, DDBST Software & Separation Technology GmbH, http://www.ddbst.de. [23] R.H. Weiland, T. Chakravarty, A.E. Mather, Ind. Eng. Chem. Res. 32 (7) (1993) 1419–1430. [24] E. Provost, R. Sidi-Boumedine, W. Fürst, Analyse des faibles taux de charge dans les systèmes gaz acides/alcanolamines/eau, Récents Progrès Génie Procédés 15 (81) (2001) 113–121. [25] K. Fischer, J. Gmehling, J. Chem. Eng. Data 39 (2) (1994) 309–315. [26] K. Fischer, M. Wilken, J. Chem. Thermodyn. 33 (2001) 1285–1308.
Experimental determination of hydrogen sulfide solubility data in aqueous alkanolamine solutions Réda Sidi-Boumedine a , Sven Horstmann b , Kai Fischer b,∗ , Elise Provost a , Walter Fürst a , Jürgen Gmehling c a
b
Laboratoire Chimie et Procédé, UCP, ENSTA, 32 Bd Victor, F-75739 Paris Cedex 15, France Laboratory for Thermophysical Properties (LTP GmbH), Institute at the University of Oldenburg, D-26111 Oldenburg, Germany c Department of Industrial Chemistry, University of Oldenburg, D-26111 Oldenburg, Germany Received 19 September 2003; accepted 28 November 2003
Abstract A computer-operated static apparatus for the measurement of gas solubility data by the synthetic method was used for the experimental determination of hydrogen sulfide solubility data in aqueous N-methyldiethanolamine (MDEA), diethanolamine (DEA) solutions and aqueous solution of a mixture of MDEA/DEA. For these systems, measurements at 313 and 373 K and pressures up to about 1.3 MPa were performed. The experimental data from this work are presented in comparison to literature data. For the aqueous MDEA solution at 313 K, the solubility of H2 S was compared to the solubility of CO2 . © 2004 Elsevier B.V. All rights reserved. Keywords: Vapor–liquid equilibria; MDEA; DEA; H2 S; Gas absorption; Experimental method
1. Introduction Aqueous alkanolamine are commonly used for the removal of acid gases, such as CO2 or H2 S, from natural and industrial gases. The optimal and proper design of the units of treatment requires the knowledge of the solubility behavior of the acid gas in the aqueous alkanolamine solutions. Solubility data for carbon dioxide (CO2 ) in aqueous alkanolamine solutions have already been measured in a previous work [1]. As an extension, H2 S solubility data measured with the static synthetic method are presented in this paper. Experimental solubility data for hydrogen sulfide (H2 S) in aqueous N-methyldiethanolamine (MDEA) and 2, 2 -diethanolamine (DEA) have been presented by several investigators [2–21] and are stored in the Dortmund Data Bank (DDB 2003) [22]. Tables 1 and 2 give an overview on the previous results for H2 S solubility in these amines.
∗ Corresponding author. Tel.: +49-441-798-3832; fax: +49-441-798-3603. E-mail address: [email protected] (K. Fischer).
0378-3812/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.fluid.2003.11.020
It has already been discussed that there are large deviations between the data of different authors [23,24]. Thus, more experiments were performed in this work in order to increase the accuracy of the available data base and to enable the model development for the description of such systems. The new data were measured with a computer-operated static apparatus at 313 and 373 K. An overview about the conditions of our experimental investigations is given in Table 3.
2. Experimental 2.1. Materials Water was distilled twice. N-methyldiethanolamine (final purity > 99.7%) and 2, 2 -diethanolamine (final purity > 99.7%) were purchased from Acros. Both amines were dried over molecular sieves. Then, all liquids were degassed as described previously [25]. Hydrogen sulfide was purchased from Praxair (purity of 99.5%) and was used without any further purification. The final purity and water content of the components were checked by gas chromatography and Karl Fischer titration.
150
R. Sidi-Boumedine et al. / Fluid Phase Equilibria 218 (2004) 149–155
Table 1 Literature review of H2 S solubility in aqueous MDEA solutions References
Concentration MDEA (wt.%)
Temperature (K)
Partial pressure of H2 S (kPa)
Bhairi [2] Jou et al. [3] Jou et al. [4] Kuranov et al.[5] Lemoine et al.[6] Li and Shen [7] MacGregor and Mather [8] Maddox et al. [9] P´erez-Salado Kamps et al. [10]
11.8, 20, 23.4 11.8, 23.4, 48.9 35, 50 19.2, 32.1 11.8, 23.6 30 23.4 11.8, 20, 23.4 48.8
298, 298, 298, 313, 298, 313, 313 298, 313,
13.2–1537.3 0.002–5890 0.002–313 165–4250 0.04–1.5 1.5–426.5 0.5–1600 13.2–1537.2 147.9–2783
311, 313, 373 333, 313 333,
323 343, 373, 393 373, 393, 413 353, 373
311, 323, 339, 389 353, 393
Table 2 Literature review of H2 S solubility in aqueous DEA solutions References
Concentration DEA (wt.%)
Temperature (K)
Partial pressure of H2 S (kPa)
Atwood et al. [11] Bottoms [12] Cheng et al. [13] Jagushte and Mahajani [14] Lal et al. [15] Lawson and Garst [16] Lee et al. [17] Lee et al. [18] Lee et al. [19] Leibush and Shneerson [20] Maddox and Elizondo [21]
10, 25, 50 50 20.60 20.60 20.60 25 20.6, 35.4 5.2, 20.6, 35.4, 49.7 5.2, 20.6, 35.4, 49.7 10.1, 20.6 20, 35, 50
300, 298, 298, 313, 313, 311, 298, 298, 298, 288, 300,
0.001–90.9 0–101.3 0.001–10 0.03–0.5 0.007–3.2 0.001–3506.4 0.7–2109.8 0.07–2068.4 0.7–2109.8 0.006–41.6 0.1–75.3
2.2. Apparatus and procedure The gas solubility measurements (isothermal P-x data) were performed with the same computer-operated static apparatus as used in the previous work [1]. In this synthetic method, the system pressure is measured at constant temperature for different overall compositions. The apparatus can be operated at temperatures between 270 and 400 K and pressures up to 5 MPa. In order to determine the global compositions, the quantities of pure substances charged into the stirred equilibrium cell, which is evacuated and placed in a
311, 308, 313 323 373 325, 323, 323, 323, 298, 339,
322, 333 318, 328
339, 348, 348, 348, 323 389
353, 373, 373, 373,
367, 380, 394, 408, 422 393 393, 413 393
thermo-regulated oil bath, have to be known precisely. The purified and degassed solvents are charged into the cell as compressed liquids using piston injectors (model 2200-801, Ruska or model 260D, Isco), which allow the precise recording of volume differences. Then, the gas is added stepwise using a thermo-regulated gas bomb. Knowing the pressure, temperature, and volume of the bomb, the amount of gas inside the bomb can be calculated using correlated PvT data of the gas. Thus, the injected amount of gas can be obtained from the pressure difference in the bomb before and after each injection. The pressures of the cell and of the gas bomb
Table 3 Solubility of hydrogen sulfide in water + alkanolamine mixtures, solvent compositions, temperature, pressure and loading ranges in this work Gas-free compositions
Temperature (K)
Total pressure range (kPa)
Range of loadings (␣)
Number of data points
Mass fraction (%)
Mole fraction
MDEA 46.78
0.1173
313.16 373.01
6.21–1040.0 90.34–865.41
0.085–1.116 0.039–0.707
13 14
DEA 41.78
0.1095
313.17 313.17 373.01
6.06–882.98 6.14–1337.6 89.06–1008.2
0.177–1.064 0.164–1.154 0.021–0.822
10 13 16
MDEA/DEA 37.73/7.64
0.09253/0.02124
313.16 373.01
6.88–1134.7 93.62–931.98
0.041–1.156 0.052–0.743
13 13
R. Sidi-Boumedine et al. / Fluid Phase Equilibria 218 (2004) 149–155
are measured with the help of differential pressure indicators (model 3051C, Rosemount) whereby the reference system is adjusted using an electronic pressure controller (model DPI 510, Druck, range 0–0.5 and 0–5 MPa). The temperatures are monitored with Pt100 resistance thermometers (model F25, Tempcontrol). Except for the injection of the liquid solvents, each step during a measurement run is controlled by a computer, i.e. the determination of the desired pressures and temperatures, and the operation of the valves which are driven using pressurized air. So, the injection steps of the gas, the refilling of the gas bomb from the gas storage and the detection of the system pressures, and temperatures in the cell during the equilibration are performed automatically. The estimated experimental uncertainties of this apparatus are as follows: σ(T) = 0.03 K and σ(P) = 0.1 kPa + 0.0001 P. Since in the described approach only temperature, pressure, total loadings, and total volumes are measured. The compositions of the coexisting phases have to be determined by evaluation of the raw data. This evaluation procedure is quite complex and described in detail elsewhere [26]. From the known solvent feed, the liquid phase volume is determined using precise information about the density of the liquid solution inside the equilibrium chamber. Therefore, the liquid densities of the alkanolamine + water solutions were measured as function of temperature using a vibrating tube densimeter (model DMA 4500, Anton Paar). From the known total volume of the cell, the remaining gas phase volume can be calculated precisely. At given equilibrium conditions (temperature, gas phase volume and gas pressure) the amounts of gas in the gas phase, and thus, also in the liquid phase are obtained. In this approach, several effects have an influence on the resulting liquid phase compositions. These effects are the small amounts of solvents in the gas phase, the compressibility of the solvent under the gas pressure, the partial molar volume of the dissolved gas, and the sol-
151
Table 4 H2 S (1) solubility data in a solution of water (2) (53.22 wt.%) and MDEA (3) (46.78 wt.%) obtained with the computer-operated apparatus T = 313.16 K
T = 373.01 K
x1
P (kPa)
␣
x1
P (kPa)
␣
0.0000 0.0099 0.0184 0.0294 0.0445 0.0584 0.0704 0.0823 0.0926 0.1009 0.1072 0.1121 0.1158
6.21 8.44 11.21 16.30 27.88 45.45 72.63 127.82 238.04 428.52 654.14 864.64 1040.0
0.000 0.085 0.159 0.258 0.397 0.529 0.646 0.765 0.870 0.957 1.024 1.076 1.116
0.0000 0.0046 0.0113 0.0184 0.0280 0.0381 0.0467 0.0533 0.0584 0.0626 0.0663 0.0700 0.0728 0.0765
90.34 96.11 113.99 141.22 191.41 262.71 342.42 417.73 486.99 554.17 622.25 698.21 763.73 865.41
0.000 0.039 0.097 0.159 0.245 0.337 0.418 0.480 0.529 0.569 0.606 0.642 0.669 0.707
␣ = [mole H2 S/mole amine].
vent activity coefficient. They can be taken into account in an iterative isothermal and isochoric algorithm by solving the mass and volume balances as also described by Fischer and Wilken [26]. The experimental error in composition is estimated to be σ(xi ) = 0.0005. In our previous work [1], it has been shown that the data obtained with this apparatus are reproducible and in agreement with other experimental techniques.
3. Results The experimental results for H2 S solubility in 46.78 wt.% MDEA aqueous solution at 313 and 373 K are presented in Table 4 and plotted in Fig. 1. Data from the literature are
10000
373 K
P H2S / kPa
1000
100
10
313 K 1
0.1 0.0
0.5
α
1.0
1.5
Fig. 1. Partial pressure of hydrogen sulfide in a solution of water (2) 53.22 wt.% and MDEA (3) 46.78 wt.%: (䉱,䊏) our results; data of (×) Jou et al. [3] 48.9 wt.%; (-) Jou et al. [4] 50 wt.%; (䊊,䉫) Kuranov et al. [5] 47.5 wt.%; (+) P´erez-Salado Kamps et al. [10] 48.8 wt.%.
152
R. Sidi-Boumedine et al. / Fluid Phase Equilibria 218 (2004) 149–155 10000
1000
P H2S / kPa
373 K 100
10
313 K
1
0.1 0.0
0.5
1.0
1.5
α Fig. 2. Partial pressure of hydrogen sulfide in a solution of water (2) 58.22 wt.% and DEA (3) 41.78 wt.%: (䉱,) our results at 313 K; (䊏) our results at 373 K.
also included in this diagram. The data of this work show high internal consistency and good agreement with most of the literature data. The experimental pressures of Kuranov et al. [5] and Jou et al. [3] for loadings ␣ (mole of H2 S per mole amine) higher than 0.8 are lower than the new data. However, the data of Pérez-Salado Kamps [10] at the same loadings are in agreement with our data. This illustrates the problem of inconsistency of some data sets reported in the literature. The experimental solubility data of H2 S in 41.78 wt.% DEA aqueous solution at 313 and 373 K are plotted in Fig. 2 and tabulated in Table 5. At 313 K, two independent measurement runs were performed in order to check for reproducibility of the experimental method. These runs were
performed completely independent from each other, and for each one the solvent mixture was prepared separately. As for the aqueous MDEA solution, the temperature effect on the solubility curves in aqueous DEA can be seen in Fig. 2, i.e. the H2 S solubility decreases with increasing temperature. The equilibrium solubility data of H2 S in a mixture 37.73 wt.% MDEA/7.64 wt.% DEA aqueous solution were also measured at 313 and 373 K. The data are presented in Fig. 3 and listed in Table 6. Again, the influence of temperature on the shape of the curves and the H2 S solubility can be observed. Fig. 4 represents the solubility of the H2 S in all amine solutions studied in this work. The three solutions have almost the same mole fraction of water, so that the influence
Table 5 H2 S (1) solubility data in a solution of water (2) (58.22 wt.%) and DEA (3) (41.78 wt.%) obtained with the computer-operated apparatus T = 313.17 K (run 1)
T = 313.17 K (run 2)
T = 373.01 K
x1
P (kPa)
␣
x1
P (kPa)
␣
x1
P (kPa)
␣
0.0000 0.0190 0.0302 0.0372 0.0534 0.0679 0.0799 0.0907 0.0989 0.1043
6.06 8.59 11.18 13.45 23.08 41.69 82.77 220.53 551.52 882.98
0.000 0.177 0.285 0.353 0.516 0.666 0.794 0.911 1.003 1.064
0.0000 0.0177 0.0262 0.0397 0.0539 0.0670 0.0791 0.0897 0.0976 0.1033 0.1073 0.1101 0.1121
6.14 7.97 9.90 14.38 22.81 39.09 76.08 188.44 457.35 766.99 1016.6 1202.8 1337.6
0.000 0.164 0.246 0.377 0.520 0.656 0.785 0.900 0.988 1.052 1.098 1.130 1.154
0.0000 0.0023 0.0080 0.0135 0.0220 0.0299 0.0393 0.0460 0.0517 0.0574 0.0622 0.0658 0.0686 0.0744 0.0789 0.0826
89.06 90.07 95.37 103.91 122.81 147.58 188.88 231.30 276.49 336.70 400.62 457.98 508.66 665.13 829.31 1008.2
0.000 0.021 0.074 0.125 0.205 0.281 0.374 0.441 0.498 0.557 0.606 0.643 0.673 0.735 0.782 0.822
R. Sidi-Boumedine et al. / Fluid Phase Equilibria 218 (2004) 149–155
153
10000
P H2S / kPa
1000
373 K
100
313 K
10
1
0.1 0.0
0.5
α
1.0
1.5
Fig. 3. Partial pressure of hydrogen sulfide in a solution of water (2) 54.63 wt.%, MDEA (3) 37.73 wt.% and DEA (4) 7.64 wt.% (x4 = 0.0212): (䉱,䊏) our results.
of the different amines can be evaluated. The solubility of H2 S in aqueous DEA is higher than in the MDEA/DEA and MDEA solution. When the chemical saturation of the amines at loadings of α > 1 is reached, there is almost no difference between all these three amine solutions since the solubility is only physical. These effects are identical for both temperatures. Finally, the solubility of H2 S measured herein and the solubility of CO2 measured previously [1] in the aqueous solution of MDEA 46.78 wt.% at 313 K are compared in Fig. 5. As can be observed, at a specified MDEA concentration level of the solution, the H2 S solubility is slightly higher than for CO2 especially at high partial pressure. However, the two
solubility curves merge at lower acid gas partial pressure. The amines can be protonated by the acid aqueous H2 S or CO2 , respectively. Tertiary amines cannot form carbamates with CO2 , thus the difference between the H2 S and CO2 solubilities are caused by the differences of the acidity and the physical solubility of the gases. The H2 S solubility curves exhibit a similar shape as it was found for the CO2 solubility data in the previous investigation [1]. The curves show more or less two distinguished break points, one at loadings of α = 0.2–0.3 and the other at loadings of 0.8 to 1.0. Between these loadings the curve of the logarithmic partial pressure of the gas is almost linear dependent on the loading. At lower loadings, significant
10000
373 K
P H2S / kPa
1000
100
10
313 K 1
0.1 0.0
0.5
α
1.0
1.5
Fig. 4. Comparison of all the results obtained for the H2 S solubility: (䉬,䉫) MDEA 46.88 wt.%; (䉱,) DEA 41.78 wt.%; (䊏,䊐) MDEA 37.73 wt.%/DEA 7.64 wt.%.
154
R. Sidi-Boumedine et al. / Fluid Phase Equilibria 218 (2004) 149–155 10000
1000
Pgas / kPa
CO2 100
H2S
10
1
0.1 0.0
0.5
α
1.0
1.5
Fig. 5. Comparison of H2 S and CO2 solubility data in a solution of water (2) 53.22 wt.% and MDEA (3) 46.78 wt.% at 313 K: (䉱) H2 S; (䉫) CO2 .
Table 6 H2 S (1) solubility data in a solution of water (2) (54.63 wt.%), MDEA (3) (37.73 wt.%) and DEA (4) (7.64 wt.%) obtained with the computeroperated apparatus T = 313.16 K
T = 373.01 K
an improved representation of the H2 S/alkanolamine/H2 O systems.
Acknowledgements
x1
P (kPa)
␣
x1
P (kPa)
␣
0.0000 0.0046 0.0148 0.0283 0.0437 0.0579 0.0708 0.0829 0.0935 0.1018 0.1080 0.1127 0.1162
6.88 7.40 9.60 14.78 24.83 41.33 69.45 127.90 260.91 489.87 743.35 960.25 1134.7
0.000 0.041 0.132 0.256 0.402 0.540 0.670 0.794 0.907 0.996 1.065 1.116 1.156
0.0000 0.0059 0.0137 0.0224 0.0336 0.0441 0.0531 0.0599 0.0651 0.0691 0.0729 0.0758 0.0780
93.62 101.18 122.47 157.40 223.43 313.56 419.71 520.99 614.66 697.03 788.12 867.71 931.98
0.000 0.052 0.122 0.201 0.306 0.406 0.493 0.560 0.612 0.652 0.691 0.721 0.743
deviations to the linear extrapolation to zero partial pressures are observed, which is essential for the removal of small traces of H2 S from natural gas. At higher loadings, the change to physical absorption can be observed.
4. Conclusions New solubility data for H2 S in aqueous solutions of the alkanolamines MDEA and DEA were determined using a computer-operated static apparatus. The results of this investigation were compared to the data of other authors and in most cases good agreement was found, although also discrepancies were observed with a few references. In the future, the new data can be used for the model development and
The financial support of this investigation by the German Academic Exchange Service (DAAD) is gratefully acknowledged.
References [1] R. Sidi-Boumedine, S. Horstmann, K. Fischer, E. Provost, W. Fürst, J. Gmehling, Fluid Phase Equilib. 218 (2004) 85–94. [2] A.M. Bhairi, Experimental Equilibrium between acid gas and ethanolamine solutions, PhD Dissertation, Stillwater, OK, 1984. [3] F.Y. Jou, J.J. Carroll, A.E. Mather, F.D. Otto, Can. J. Chem. Eng. 71 (1993) 264–268. [4] F.Y. Jou, A.E. Mather, F.D. Otto, Ind. Eng. Chem. Process Des. Dev. 21 (4) (1982) 539–544. [5] G. Kuranov, B. Rumpf, N.A. Smirnova, G. Maurer, Ind. Eng. Chem. Res. 35 (6) (1996) 1959–1966. [6] B. Lemoine, Y.-G. Li, R. Cadours, C. Bouallou, D. Richon, Fluid Phase Equilib. 172 (2000) 261–277. [7] M.-H. Li, K.-P. Shen, Fluid Phase Equilib. 85 (1993) 129–140. [8] R.J. MacGregor, A.E. Mather, Can. J. Chem Eng. 69 (1991) 1357– 1366. [9] R.N. Maddox, A.H. Bhairi, J.R. Diers, P.A. Thomas, Gas Process Assn. Research Report RR-104, 1987. [10] A. Pérez-Saladao Kamps, G. Maurer, J. Chem. Eng. Data 41 (6) (1996) 1505–1513. [11] K. Atwood, M.R. Arnold, R.C. Kindrick, Ind. Eng. Chem. 49 (9) (1957) 1439–1444. [12] R.R. Bottoms, Ind. Eng. Chem. 23 (5) (1931) 501–504. [13] G.-X. Cheng, W.-L. Tang, F. Shen, Fuel Sci. Technol. Int. 9 (8) (1991) 935–947. [14] M.V. Jagushte, V.V. Mahajani, Ind. J. Chem. Technol. 6 (1999) 125– 133.
R. Sidi-Boumedine et al. / Fluid Phase Equilibria 218 (2004) 149–155 [15] D. Lal, F.D. Otto, A.E. Mather, Can. J. Chem. Eng. 63 (4) (1985) 681–685. [16] J.D. Lawson, A.W. Garst, J. Chem. Eng. Data 21 (1) (1976) 20–30. [17] J.I. Lee, F.D. Otto, A.E. Mather, J. Chem. Eng. Data 18 (1) (1973) 71–73. [18] J.I. Lee, F.D. Otto, A.E. Mather, J. Chem. Eng. Data 18 (4) (1973) 420. [19] J.I. Lee, F.D. Otto, A.E. Mather, Design data for diethanolamine acid gas treating systems, Can. Gas J. Gas Processing, 1973, 26–34. [20] A.G. Leibush, A.L. Shneerson, Zh. Prikl. Khim. 23 (2) (1950) 145– 152.
155
[21] R.N. Maddox, E.M. Elizondo, Gas Process Assn. Research Report RR-124, 1989. [22] Dortmund Data Bank 2003, DDBST Software & Separation Technology GmbH, http://www.ddbst.de. [23] R.H. Weiland, T. Chakravarty, A.E. Mather, Ind. Eng. Chem. Res. 32 (7) (1993) 1419–1430. [24] E. Provost, R. Sidi-Boumedine, W. Fürst, Analyse des faibles taux de charge dans les systèmes gaz acides/alcanolamines/eau, Récents Progrès Génie Procédés 15 (81) (2001) 113–121. [25] K. Fischer, J. Gmehling, J. Chem. Eng. Data 39 (2) (1994) 309–315. [26] K. Fischer, M. Wilken, J. Chem. Thermodyn. 33 (2001) 1285–1308.