Article pubs.acs.org/jced
Density and Solubility of CO2 in Aqueous Solutions of (Potassium Carbonate + Sarcosine) and (Potassium Carbonate + Pipecolic Acid) Hoyong Jo, Min-gu Lee, Beomsoo Kim, Ho-Jun Song, Hyungbae Gil, and Jinwon Park* Department of Chemical & Biomolecular Engineering, Yonsei University, 50 Yonsei-ro, Seodaemun-gu, Seoul 120-749, Republic of Korea ABSTRACT: The density of (30 mass % potassium carbonate + 3 mass % sarcosine) and (30 mass % K2CO3 + 3 mass % pipecolic acid) were measured for temperature ranging from (303 to 353) K. The experimental data are presented with an aqueous solution of 30 mass % K2CO3. The solubility of the aqueous blended solution was measured at (353, 373, and 393) K over CO2 partial pressure ranging from (0.1 to 1500) kPa. The results are shown with the solubility of CO2 in 30 mass % K2CO3. Due to the fact that the amino acid has acidic character, the CO2 solubility of aqueous blended solutions is slightly lower than that of the solution of 30 mass % K2CO3. NH 2RCOOH + H3O+ ↔ NH3+RCOOH + H 2O
1. INTRODUCTION Aqueous potassium carbonate solutions are used as an absorbent for removal of acidic gases such as carbon dioxide (CO2) and hydrogen sulfide (H2S) from crude hydrogen, natural gas, etc. (Benfield process).1 The solubility of potassium carbonate increases at high temperature, which makes the process suitable for the effective removal of CO2. The absorber and stripper are operated around 343 K and higher and around about 403 K, respectively.2 However, the performance of aqueous potassium carbonate is hampered by a low absorption rate of CO2 into the solvent. Due to low absorption rate of CO2 into the aqueous potassium carbonate, there have been various studies on the kinetics and thermodynamics with the addition of amines and inorganic catalysts. Several amines are used as a promoter to enhance the absorption rate, such as diethanolamine (DEA)3 or piperazine.4 Primary and secondary amines have fast absorption rates of CO2, and tertiary amines are known to have high equilibrium capacity. On the other hand, amines suffer from oxidative degradation at high temperature and in oxygen-rich environments. Unlike amines, amino acids are much more stable toward oxygen and do not show any degradation in the oxygenated atmosphere but show similar performance toward CO2 absorption capacities and absorption rates.5 The ionic structure of amino acids makes the vapor pressure of the aqueous solution to be relatively low at high temperature, which prevents the loss of vapors in the stripping section.6 Amino acids exist in the acid states (eq 1), and the unstable zwitterion state, eq 2, in water. Because of its acidic character, the solution of amino acid hardly absorbs CO2.In base solution, amino acids exist in the deprotonated zwitterion state, eq 3. The deprotonated zwitterion of amino acid is completely dissociated and can rapidly and reversibly react with CO2 to form carbamate and bicarbonate, eq 4.7 Therefore, Industrially, alkali salts of amino acids are being used for the rate promotion of the CO2 absorption in carbonate-bicarbonate solution.3 © 2012 American Chemical Society
+
+
−
−
NH3 RCOOH + H 2O ↔ NH3 RCOO + H3O +
−
−
+
NH3 RCOO + H 2O ↔ NH 2RCOO + H3O
(1) (2) (3)
CO2 + 2NH 2RCOO− ↔ COO−NHRCOO− + NH3+COO−
(4)
In this study, the density and solubility of CO2 in promoted potassium carbonate solution by addition of amino acids (sarcosine and pipecolic acid; Figure 1) were measured. The concentration of
Figure 1. Chemical structures of sarcosine and pipecolic acid.
aqueous potassium carbonate and amino acid is 30 mass % and 3 mass %, respectively. The experimental results are required to generate the complete database for the design of the CO2 separation process.
2. EXPERIMENTAL SECTION Potassium carbonate (K2CO3, purity > 99 %), sarcosine (purity > 99 %), and pipecolic acid (purity > 99 %) were obtained from Alfa Aesar. All aqueous solutions were prepared without purification and doubly distilled water. The purity of CO2 and Received: July 23, 2012 Accepted: November 16, 2012 Published: November 29, 2012 3624
dx.doi.org/10.1021/je300782p | J. Chem. Eng. Data 2012, 57, 3624−3627
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Table 1. Experimental Values of the Densities (ρ) of Aqueous 30 mass % K2CO3(PC), 30 mass % K2CO3(PC) + 3 mass % Sarcosine (SAR), and 30 mass % K2CO3(PC) + 3 mass % Pipecolic Acid (PA) Solutions at Pressure p = 0.1 MPa ρ/g·cm
Table 2. Solubility of CO2 (1) in Aqueous 30 mass % K2CO3 (2)a T/K = 373.2 K PCO2
−3a
30 mass % PC T/K 298.2 303.2 313.2 323.2 333.2 343.2 353.2 a
± ± ± ± ± ± ±
0.1 0.1 0.1 0.1 0.1 0.1 0.1
this work
ref 8
1.2888 1.2841 1.2786 1.2734 1.2671 1.2610
1.2866 1.2840 1.2787 1.2735 1.2673 1.2620
30 mass % PC + 3 mass % SAR
30 mass % PC + 3 mass % PA
1.2919 1.2868 1.2814 1.2756 1.2698 1.2650
1.2921 1.2861 1.2801 1.2745 1.2694 1.2634
T/K = 393.2 K
Uncertainty in the density is 0.1 %.
PCO2
x1
αb
kPa
x1
αb
kPa
0.0767 0.1305 0.2071 0.2590 0.3265 0.3707 0.4213 0.4504 0.4758 0.4947 0.5063
0.0830 0.1501 0.2611 0.3496 0.4848 0.5890 0.7280 0.8195 0.9078 0.9791 1.0256
0.4 0.9 4.6 8.0 25.9 49.4 117.6 224.3 480.4 970.1 1465.4
0.0683 0.1672 0.2321 0.2939 0.3353 0.3809 0.4102 0.4372 0.4607 0.4830 0.4935
0.0733 0.2007 0.3022 0.4162 0.5043 0.6152 0.6955 0.7769 0.8542 0.9344 0.9743
1.6 6.1 15.0 31.8 51.3 94.4 149.0 248.0 432.6 860.9 1268.1
a
u(T) = 0.1 K; u(α) = 0.001, u(PCO2) = 0.2 kPa; u(x1) = 0.0002. bCO2 loading in the absorbent (mol of CO2/mol of absorbent).
Figure 2. Density of aqueous blended solution at different temperatures: ●, 30 mass % K2CO3; ◆, (30 mass % K2CO3 + 3 mass % pipecolic acid); ×, (30 mass % K2CO3 + 3 mass % sarcosin).
Figure 3. Comparison of the solubility of CO2 in aqueous 30 mass % K2CO3 solution. Experimental data: ▲, 373 K; ●, 393 K; ×, 363.15 K. Data of Tosh et al.:11 ◇, 383.15 K.
N2 used for measurement of CO2 solubility in this work was 99.999 %, and both were purchased from Gas Valley. Density. The densities of the aqueous solutions were measured in the temperature range of (303 to 353) K using a Gay−Lussac pycnometer (36.940 cm3) at 298 K which was calibrated using degassed water. The temperature was maintained by the thermostatic water bath (RBC-11, Woori Science Instrument Co.) within ± 0.1 K. The balance precision for measuring mass was 1·10−4 g. The density of 30 mass % K2CO3 was compared with that from ref 8. The uncertainty of the density measurements was 0.1 %. CO2 Solubility. The solubility of CO2 in aqueous blended solutions was measured at three different temperatures (353, 373, 393) K from (0.1 to 1500) kPa. The apparatus used in this study was similar to that reported by Song et al.9 The apparatus for the measurement of CO2 solubility consists of a 3960 cm3 gas cylinder and a 503 cm3 equilibrium cell. Both were designed to operate at pressure up to 2000 kPa and were placed in a convection air bath. The pressure in these cells was measured by using a Wallace & Tiernan precision mercury manometer with an accuracy of ± 0.1 kPa, and the temperature was
measured with a Pt-100 temperature probe with an accuracy of ± 0.1 K. Before running the experiment, the apparatus was flashed with N2 gas. The aqueous solution of 250 g was fed into the equilibrium cell, and pure CO2 was also fed into the gas cylinder. As the temperature in the cell was maintained at the designated value, CO2 in the gas cylinder was fed to the equilibrium cell. The pressure and temperature of the equilibrium cell were continuously monitored by computer. When the temperature and pressure in the equilibrium cell were constant, 0.5 cm3 of gas sample was withdrawn from the cell and analyzed by gas chromatography (Acme 6000 GC, Younglin Ins.) to determine the ratio of N2 and CO2. Then, the CO2 mole was determined by the application of experimental P−T data to the following virial equation. Z=1+
⎛ BP ⎞ P BP = 1 + ⎜ c⎟ r PT ⎝ RTc ⎠ Tr
BPc = B0 + ωB1 RTc 3625
(5)
(6)
dx.doi.org/10.1021/je300782p | J. Chem. Eng. Data 2012, 57, 3624−3627
Journal of Chemical & Engineering Data
Article
Table 3. Solubility of CO2 (1) in Aqueous 30 mass % K2CO3 (2) + 3 mass % Sarcosine (3)a T/K = 353.2 K
T/K = 373.2 K PCO2
a
T/K = 393.2 K PCO2
PCO2
x1
αb
kPa
x1
αb
kPa
x1
αb
kPa
0.1001 0.1652 0.2438 0.3076 0.3570 0.3945 0.4154 0.4325 0.4465 0.4586 0.4677
0.0759 0.1372 0.2339 0.3105 0.4274 0.5164 0.6265 0.6896 0.7566 0.7896 0.8574
0.1 2.7 7.2 15.4 39.8 78.7 196.1 357.4 694.5 939.4 1465.4
0.0706 0.1207 0.1895 0.2370 0.2994 0.3405 0.3852 0.4081 0.4307 0.4412 0.4524
0.0431 0.0898 0.1400 0.2282 0.3088 0.3990 0.4868 0.5709 0.6520 0.7193 0.7571
3.3 6.4 12.7 20.9 35.0 60.1 107.2 192.0 360.3 646.1 1196.1
0.0413 0.0824 0.1228 0.1858 0.2359 0.2852 0.3274 0.3634 0.3947 0.4184 0.4309
0.1113 0.1978 0.3224 0.4443 0.5553 0.6514 0.7106 0.7621 0.8068 0.8469 0.8785
0.8 3.2 9.9 25.8 60.7 136.3 241.3 419.3 672.6 1023.0 1423.7
u(T) = 0.1 K; u(α) = 0.001; u(PCO2) = 0.2 kPa; u(x1) = 0.0002. bCO2 loading in the absorbent (mol of CO2/mol of absorbent).
Table 4. Solubility of CO2 (1) in Aqueous 30 mass % K2CO3 (2) + 3 mass % Pipecolic Acid (3)a T/K = 353.2 K
T/K = 373.2 K PCO2
a
T/K = 393.2 K PCO2
PCO2
x1
αb
kPa
x1
αb
kPa
x1
αb
kPa
0.0967 0.1754 0.2422 0.3058 0.3569 0.4013 0.4334 0.4539 0.4667 0.4760 0.4823
0.1070 0.2128 0.3196 0.4406 0.5550 0.6702 0.7649 0.8313 0.8749 0.9084 0.9315
1.1 3.1 7.6 16.1 34.7 75.8 168.3 368.9 606.8 953.9 1433.0
0.0782 0.1451 0.2035 0.2534 0.2980 0.3395 0.3789 0.4135 0.4402 0.4579 0.4744
0.0849 0.1697 0.2555 0.3394 0.4246 0.5139 0.6100 0.7050 0.7862 0.8447 0.9027
2.1 5.5 9.4 15.4 26.9 47.4 89.4 188.7 352.3 642.6 1251.0
0.0355 0.1114 0.1909 0.2319 0.2780 0.3199 0.3613 0.4003 0.4311 0.4546 0.4686
0.0368 0.1254 0.2359 0.3019 0.3850 0.4104 0.5656 0.6674 0.7577 0.8335 0.8818
3.7 8.3 16.2 22.7 35.6 58.0 102.6 196.9 374.8 678.7 1058.8
u(T) = 0.1 K; u(α) = 0.001; u(PCO2) = 0.2 kPa; u(x1) = 0.0002. bCO2 loading in the absorbent (mol of CO2/mol of absorbent).
B0 = 0.083 − B1 = 0.139 −
0.422 Tr1.6
(7)
0.172 Tr1.6
(8)
where Z is the compressibility factor, Tc (304.2 K) is the critical temperature, Pc (72.8 atm) is the critical pressure, Pr is the reduced pressure, Tr is the reduced temperature, ω(0.225) is the acentric factor, and B0 and B1 are a function of the generalized second virial coefficient correlation.10 The apparatus and measurement methods are the same as in our previous work.9 The uncertainty of the CO2 solubility was 2.5 %.
3. RESULTS AND DISCUSSION Density. The densities of the (30 mass % K2CO3 + 3 mass % sarcosine) and (30 mass % K2CO3 + 3 mass % pipecolic acid) were measured at (303, 313, 323, 333, 343, and 353) K and are shown in Table 1 and Figure 2. The density decreases with an increase in temperature. The density of (30 mass % K2CO3 + 3 mass % sarcosine) is higher than that of (30 mass % K2CO3 + 3 mass % pipecolic acid) at the same temperature. CO2 Solubility. The solubility of CO2 in aqueous 30 mass % K2CO3 was measured at (373 and 393) K and is shown in Table 2. The measured solubility is also presented with those of Tosh et al.11 in Figure 3. As seen from Figure 3, the CO2
Figure 4. Solubility of CO2 in aqueous solution. Experimental data of aqueous (30 mass % K2CO3 + 3 mass % sacrosine): ■, 353 K; ●, 373 K; ▲, 393 K. Experimental data of aqueous 30 mass % K2CO3: ○, 373 K; △, 393 K.
solubility of this work is in good agreement with the data in the literature. 3626
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(3) Kohl, A.; Riesenfeld, F. Gas Purification; Gulf Publishing Company: Hpuston, TX, 1997. (4) Cullinane, J. T.; Rochelle, G. T. Kinetics of carbon dioxide absorption into aqueous potassium carbonate and piperazine. Ind. Eng. Chem. Res. 2006, 45, 2531−2545. (5) Hook, R. J. An investigation of some sterically hindered amines as potential carbon dioxide scrubbing compounds. Ind. Eng. Chem. Res. 1997, 36, 1779−1790. (6) Goan, J. C.; Miller, R. R.; Piatt, V. R. Alkazid M as a regenerative carbon dioxide absorbent, NRL Report 5465; Naval Research Laboratory: Washington, DC, 1960. (7) Aronu, U. E.; Hartono, A.; Svendsen, H. F. Kinetics of carbon dioxide absorption into aqueous amine amino acid salt: 3(methylamino)propylamine/sarcosine solution. Chem. Eng. Sci. 2011, 66, 6109−6119. (8) Knuutila, H.; Juliussen, O.; Svendsen, H. F. Density and N2O solubility of sodium and potassium carbonate solutions in the temperature range 25 to 80 °C. Chem. Eng. Sci. 2010, 65, 2177−2182. (9) Song, H. J.; Lee, M. G.; Kim, H. T.; Gaur, A.; Park, J.-W. Density, Viscosity, Heat Capacity, Surface Tension, and Solubility of CO2 in Aqueous Solutions of Potassium Serinate. J. Chem. Eng. Data 2011, 56, 1371−1377. (10) Smith, J. M. Introduction to Chemical Engineering Thermodynamics; McGraw-Hill: New York, 1987. (11) Tosh, J. S.; Field, J. H.; Benson, H. E.; Haynes, W. P. Equilibrium Study of the System Potassium Carbonate, Potassium Bicarbonate, Carbon Dioxide, and Water. U.S. Bureau of Mines Rept. Invest. No. 5484; 1959; 23 pp. (12) Kumelan, J.; Jamps, P. S.; Maurer, G. Solubility of CO2 in aqueous solutions of methionine and in aqueous solutions of (K2CO3 and Methionine). Ind. Eng. Chem. Res. 2010, 49, 3910−3918.
Figure 5. Solubility of CO2 in aqueous solution. Experimental data of aqueous (30 mass % K2CO3 + 3 mass % pipecolic acid): ■, 353 K; ●, 373 K, ▲, 393 K. Experimental data of aqueous K2CO3: ○, 373 K; △, 393 K.
The measured solubility of CO2 in aqueous (30 mass % K2CO3 + 3 mass % sarcosine) and (30 mass % K2CO3 + 3 mass % pipecolic acid) at (353, 373, and 393) K is shown in Tables 3 and 4, respectively. To compare the effect on solubility of CO2 by the addition of rate promoters, the experimental data of 30 mass % K2CO3 + 3 mass % sarcosine and 30 mass % K2CO3 was plotted as shown in Figure 3. The solubility of CO2 in aqueous (30 mass % K2CO3 + 3 mass % pipecolic acid) and 30 mass % K2CO3 are also depicted in Figures 4 and 5. The CO2 solubility of the promoted absorbent is lower than that of 30 mass % K2CO3. Due to the fact that sarcosine and pipecolic acid have acidic character, these reduce the absorption capacity of potassium carbonate for CO2.12
4. CONCLUSIONS In this work, the densities of (30 mass % K2CO3 + 3 mass % sarcosine) and (30 mass % K2CO3 + 3 mass % pipecolic acid) were measured in the range from (303.15 to 353.15) K. The density of (30 mass % K2CO3 + 3 mass % sarcosine) is slightly higher than that of (30 mass % K2CO3 + 3 mass % pipecolic acid). The solubility of CO2 in (30 mass % K2CO3 + 3 mass % sarcosine) and (30 mass % K2CO3 + 3 mass % pipecolic acid) was determined. The results show that the solubility of CO2 decreases with an increase in temperature and addition of amino acid. The experimental thermodynamic data are essential for the development of a CO2 absorption process.
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AUTHOR INFORMATION
Corresponding Author
*Tel.: +82-2-364-1807. Fax: +82-2-312-6401. E-mail: jwpark@ yonsei.ac.kr. Notes
The authors declare no competing financial interest.
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REFERENCES
(1) Bartoo, R. K. Removing acid gas by the Benfield process. Chem. Eng. Prog. 1984, 80 (10), 35−39. (2) Kamps, A.P.-S.; Meyer, E.; Rumpf, B.; Maurer, G. Solubility of CO2 in aqueous solutions of KCl and aqueous solutions of K2CO3. J. Chem. Eng. Data 2007, 52, 817−832. 3627
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