Ind. Eng. Chem. Res. 2008, 47, 9925–9930
9925
PROCESS DESIGN AND CONTROL Simplified Estimation of Regeneration Energy of 30 wt % Sodium Glycinate Solution for Carbon Dioxide Absorption Ho-Jun Song,† Seungmoon Lee,‡ Kwinam Park,§ Joonho Lee,† Dal Chand Spah,† Jin-Won Park,*,† and Thomas P. Filburn‡ Department of Chemical Engineering, Yonsei UniVersity, 134 Shinchon-dong, Seodaemun-gu, Seoul 120-749, Republic of Korea, Clean Energy Institute, Department of Mechanical Engineering, UniVersity of Hartford, 200 Bloomfield AVenue, West Hartford, Connecticut, 06117, and Gyeonggi Daejin Technopark, San 11-1 Sundan-dong, Pocheon City, Gyeonggi-do 487-711, Republic of Korea
A simple method for estimating the regeneration energy of CO2 absorption was devised. The regeneration energy of a 30 wt % sodium glycinate (SG) solution was calculated by the summation of the enthalpy of reaction, the sensible heat and the heat of vaporization. Each form of heat energy was determined experimentally. Solubilities of carbon dioxide in the SG solution was determined by gas chromatography (GC) analysis for the gas phase with the help of a virial equation for the liquid phase in the temperature range of 40-120 °C. Heat capacity of the solution was measured by a differential scanning calorimeter (DSC) and was used to calculate sensible heat. The heat of vaporization was evaluated by applying the Clausius-Clapeyron equation to 20 data points of vapor pressure. All of the experiments were carried out with either a 30 wt % aqueous solution of SG or the same concentration of monoethanolamine (MEA). Regeneration energy of the SG solution was found to be higher than that of the MEA solution by about 1000 kJ/kg of CO2. From the CO2 solubility data it was observed that SG had a higher capacity to absorb carbon dioxide than MEA even at the regeneration temperature (120 °C). In addition, the 30 wt % basis SG demonstrated a reduction in cyclic capacity at this regeneration temperature. So, our main effort is to establish a reasonable method for estimating CO2 absorbent regeneration energy along with the regeneration energy of 30 wt % aqueous solutions of SG. 1. Introduction Alkanolamines have been extensively used for last seven decades for the removal of acidic gases (CO2, H2S, etc.) from natural, refinery, and synthesis gas streams.1 Recently, with the effectuation of the Kyoto protocol, there have been global efforts to improve alkanolamine based absorbents for CO2 capture in large quantities from large point sources such as fossil fueled power plants and various chemical industries. The important alkanolamine absorbents in industrial processes are monoethanolamine (MEA), 2-amino-2-methyl-1-propanol (AMP), diethanolamine (DEA), and N-methyldiethanolamine (MDEA). But these amines generally undergo oxidative degradation in ordinary flue gas resulting in the formation of undesirable byproducts2 or difficult to reverse reactions. On the other hand, amino acid salts have some advantages over alkanolamines, such as low volatility due to their ionic structure, high surface tension, greater absorption capacity than MEA, and high oxygen stability.2-6 Van Holst et al.,6 Majchrowicz et al.,7 and Hamborg et al.8 presented various amino acid salt absorbents; they obtained measurements of physical properties, identified precipitates, and performed a kinetic study. Kumar et al.4,9-11 have proposed a potassium salt of taurine and glycine as alternatives to the alkanolamines, and they studied the thermodynamic character* To whom correspondence should be addressed. Tel.: +82-2-3641807. Fax: +82-2-312-6401. E-mail:
[email protected]. † Yonsei University. ‡ University of Hartford. § Gyeonggi Daejin Technopark.
istics and reaction kinetics of the potassium salt. The sodium salt of glycine (SG) which was chosen in this work and was also used as a liquid membrane by Chen et al.12,13 to remove the carbon dioxide from the atmosphere in closed loop life support systems such as spacecraft or space suits. In addition, Lee et al.3,14-16 and Song et al.17 have extensively investigated the sodium salt of glycine as a wet absorbent for the removal of CO2 in flue gas from power plants. For the selection of an energy-efficient CO2 absorbent, some criteria such as rate of reaction, absorption capacity, heat of reaction, solution regeneration energy, durability, thermal stability, and corrosion are essential to consider. Among them, the solution regeneration energy is an important factor which decides the economics of the absorption process. As much as 50-80% of the total process energy is consumed during solution regeneration. Regeneration energy is defined as the summation of (1) reaction enthalpy between amine and CO2, (2) sensible heat for heating the CO2-loaded amine solution to the temperature of the reboiler and, (3) latent heat of vaporization to generate the stripping vapor.18 Regeneration energy of each amine solution can be measured experimentally or computed by summation of each component of regeneration energy which is measured separately. Sakwattanapong et al.19 devised a bench-scale stripping system and experimentally measured the reboiler heat duties of both single (MEA, DEA, MDEA) and blended alkanolamines (MEA-MDEA, DEA-MDEA, MEA-AMP) with the parameters of alkanolamine concentration and rich and lean CO2 loading. Rochelle et al.20 proposed eq 1 (below) to estimate the total energy required to regenerate the amine solution. In addition, each component
10.1021/ie8007117 CCC: $40.75 2008 American Chemical Society Published on Web 11/14/2008
9926 Ind. Eng. Chem. Res., Vol. 47, No. 24, 2008
(reaction enthalpy, sensible heat, and latent heat of vaporization) can be expanded as a function of physical properties and CO2 desorption condition. Ma’mun et al.21 estimated regeneration energy of aqueous 30 wt % MEA and 2-((2-aminoethyl)amino)ethanol using eq 1 at the identical condition. Yeh et al.22 evaluated the regeneration energy of aqueous ammonia by summation of the reaction enthalpies of ammonium bicarbonate and ammonium carbonate which were reaction products of ammonia and CO2. QT ) Qdes + Qsens + Qstrip ) -∆HS +
FCP∆T + (Rrich - Rlean)Camine
PHsat2O(Ttop,des)xH2O,freebasis / PCO (Ttop,desRrich) 2
∆HHvap (1) 2O
As one component of amine solution regeneration energy, the heat of reaction (-∆Hs) expressed in Qdes in eq 1 is the heat which is released by the chemical reaction of CO2 and amine. In the reverse direction, this amount of heat must be supplied to break up the CO2-amine complex. The heat of reaction can be measured experimentally by calorimetric method or calculated indirectly using CO2 solubilities into aqueous amine solution. Mathonat et al.23,24 devised a mixing unit coupled with calorimeter so that reaction enthalpies between CO2 and MDEA, CO2, and MEA were measured as functions of CO2 loading, operating temperature, and total pressure. Jou et al.,25 Xu et al.,26 and Ma’mun et al.27 estimated reaction enthalpies applying the Gibbs-Helmholtz equation to CO2 solubilities into each aqueous amine solution. Reaction enthalpies of 30 wt % MEA and MDEA solution were estimated at each CO2 loading and found in good agreement with the experimentally measured results of Mathonat et al.23,24 Sensible heat in relation to heat capacity is the energy to heat the CO2 rich amine from the bottom temperature of the absorber to the temperature of the reboiler. Chiu et al.28,29 measured heat capacities of some important alkanolamines and aqueous alkanolamine solutions at 30-80 °C by differential scanning calorimetry (DSC). Weiland et al.30 measured heat capacities of MEA, DEA, MDEA, and MDEA blends not only for lean CO2-amine solution but also for CO2-loaded amine solution using Dewar flask coupled with devised calorimeter. Heat capacities of CO2-loaded amine solution were decreased by a maximum of 10% with respect to those of the CO2-lean amine solution. And, Maham et al.31 reported the heat capacities of various alkanolamines through a group contribution method. Latent heat of vaporization is the heat to produce water vapors for CO2 stripping at the stripper and can be calculated applying the Clausius-Clapeyron equation to vapor pressure data. To separate 1 kg of carbon dioxide from flue gas, 0.03 kg of steam must be generated.32 Xu et al.33 measured the vapor pressure of aqueous MDEA solution using an ebulliometer. As a result, the measured vapor pressure of MDEA was in good agreement with the estimated vapor pressure by Raoult’s law because MDEA is a relatively low volatility sorbent. In the CO2 solubility experiment at low temperature, vapor pressure can be ignored because of low volatility of amine and at high temperature it can be estimated by Raoult’s law. It is also wellknown that the higher the water content in the amine solution, the higher should be the heat of vaporization. In these studies, CO2 solubility, heat capacities, and vapor pressure of 30 wt % SG solution were measured and applied to appropriate thermodynamic equations to estimate reaction enthalpies, sensible heat, and heat of vaporization. Each term was calculated for the energy required to remove 1 kg of CO2
Figure 1. Experimental setup for the measurement of the solubilities of carbon dioxide.
and added up according to the definition of amine solution regeneration energy. For the validation of this methodology, each term was calculated for 30 wt % MEA solution and then it was compared with the results of Go¨ttlicher32 which were derived by similar methodology. Experimental Section 2.1. Materials. SG, MEA, and MDEA (for the measurement of heat capacity) used in the present investigations were obtained from Sigma-Aldrich Chemical Co. with a mass purity of >99%. The aqueous solutions were prepared from doubly distilled water. All solutions were prepared by mass with a balance precision of (1 × 10-4 g. 2.2. Vapor Pressure. For the measurements of the vapor pressure and isobaric vapor-liquid equilibrium, a Dr. Sieg & Ro¨ck type recirculating glass still was used. For the both above said measurements, approximately 250 mL of aqueous sodium glycinate solution was introduced into the still and the pressure of the still was controlled by using a Baratron pressure regulating system with an accuracy of (0.1 kPa. The inside pressure of the equilibrium cell was also measured by using a Wallace & Tiernan precision mercury manometer during the entire process. When the desired equilibrium pressure was reached, the liquid phase was heated to boil vigorously, and the liquid as well as vapor phases were circulated in the still for about 2 h. Then, the equilibrium temperature was measured with a Pt-100 temperature probe with accuracy of (0.01 °C. 2.3. Solubility of CO2. The apparatus used for the measurement of CO2 solubility is given in Figure 1. The equilibrium solubility was measured with an equilibrium cell. The apparatus consisted of an equilibrium cell (503 mL) made of 316 stainless steel, a CO2 storage cylinder (3960 mL), a mechanical agitator, a precision pressure gauge, a pressure transducer-digital indicator, digital thermometer, and data acquisition system. The digital pressure gauge and thermometer were obtained from Hybrid Recorder (Yokogawa Co., Japan). The air bath was controlled by a forced convection oven (OF-22, JEIO Tech Inc., Korea) within (0.05 °C of the operating temperature. The amount of aqueous solution of amine (SG and MEA) taken into the equilibrium cell was prepared by mass with a balance precision of (1 × 10-4 g. The degassed amine solution kept at the same temperature of the experiment was injected into the equilibrium cell. The CO2 gas was fed from the cylinder to the cell by pressure difference, and two check valves were put in to prevent the reverse flow of N2 from the cell to the cylinder. Gas-liquid equilibrium
Ind. Eng. Chem. Res., Vol. 47, No. 24, 2008 9927
was obtained by mechanical agitation. It required 6 h to attain equilibrium at each point. The partial pressure of CO2 was approximately 0.1 to 400 kPa at T ) 40-120 °C. The composition of gases was determined by a gas chromatograph (Hewlett-Packard, 5890 Series II). The gas chromatograph included a thermal conductivity detector (TCD) and a column packed with Porapak Q. The analysis conditions of the gas chromatograph were a detector temperature of 140 °C, a column temperature of 30 °C, and carrier gas total flow rate of 75 mL/min. The concentration of CO2 in liquid phase was determined by a virial equation which is defined as PL1VL1 PAVA PLoVLo ) +n ZLoRTLo ZL1RTL1 ZARTA
(2)
where, subscript L and A stand for CO2 loading cylinder and absorption cell, respectively; 0 and 1 represent the state before and after the feed of CO2 into absorption cell; and VA is the volume of gas phase inside the absorption cell. The compressibility factor (Z) in the experiments was obtained from the following relationship:
( ) ( )
Z)
BPc Pr BP PV )1+ )1+ RT RT RTc Tr
(3)
Z)
BPc Pr PV BP )1+ )1+ RT RT RTc Tr
(4)
B0 ) 0.139 -
0.172 Tr1.6
(5)
B1 ) 0.139 -
0.172 Tr1.6
(6)
The symbols used in all of the above equations carry their standard meaning. The critical properties of CO2 were obtained from the literature.34 2.4. Heat Capacity. The heat capacities of aqueous solution of SG were measured by a DSC-Q100 and a thermal analysis controller from TA Instruments by using eq 7. The heat capacities of the absorbents in the experiments and their calculation were described by Chiu et al.28 The measurements were made at T ) 30-80 °C using nitrogen as a purge gas with a flow rate of 50 mL/min. The mass of absorbents used were approximately 20 mg. First, synthetic sapphire (Al2O3) was employed to obtain the calibration coefficient (E in eq 7) of the DSC-Q100 and exact heat capacities of sapphire were obtained from the literature.35 Heating rate (Hr) was kept at 5 °C/min. The differences of heat flows (∆H) between the empty pan and each sample at different temperatures were recorded in real time. Each data point reported was taken as an average of six readings. CP )
[ ]
60E ∆H Hr m
(7)
3. Results 3.1. Assumptions. Essential conditions for calculating each component were the concentration of amine solutions, which kept at 30 wt % for both the SG and MEA. Rich CO2 loading meant the material saturated by CO2 at the bottom of the absorber assumed to be 0.4. The temperature difference between the top and bottom of the stripper was maintained at about 50 °C, and the estimated vapor needed for stripping CO2 was 0.03 kg for 1 kg of CO2.
Figure 2. Solubility of CO2 in a 30 wt % MEA solution.
Figure 3. Comparison of the solubility of CO2 in 30 wt % SG solution with that of 30 wt % MEA solution.
3.2. Enthalpy of Reaction. CO2 solubilities in 30 wt % aqueous solution of MEA at 40, 80, and 120 °C with the data of Jou et al.36 and Shen et al.37 are shown in Figure 2. In the whole range of pressures, the results are in relatively good agreement. At high temperatures, vapor pressures of the liquid could not be ignored. Therefore, it was subtracted from the total pressure of the equilibrium cell. Figure 3 shows a comparison between the solubility of CO2 in aqueous solutions of SG and MEA. The solubilities of CO2 into aqueous solution of SG were higher than those of MEA at every operating temperature (40-120 °C). Although more CO2 was absorbed by SG than MEA at desorption temperature (120 °C), however, the high CO2 solubility at this temperature resulted in a decrease of effective CO2 loading (rich CO2 loading-lean CO2 loading). Effective CO2 loading in SG and MEA for various flue gases are presented in Table 1. In all cases, the effective loading of SG is lower than MEA.
9928 Ind. Eng. Chem. Res., Vol. 47, No. 24, 2008 Table 1. Effective CO2 Loading of 30 wt % Aqueous Solutions of MEA and SG MEA CO2 source
Rrich
Rlean
SG effective loading
natural gas power plant 0.489 0.132 (PCO2 ) 3.5 kPa) coal-fired power plant 0.525 0.241 (PCO2 ) 12 kPa) iron and steel industry 0.549 0.299 (PCO2 ) 25 kPa)
Rrich
Rlean
effective loading
0.357
0.538 0.243
0.295
0.284
0.584 0.333
0.251
0.250
0.613 0.382
0.231
Table 2. Reaction Enthalpy of CO2 into 30 wt % Amine Solution at rrich ) 0.4 MEA
SG
Shakma18
Kohl1
this work
this work
72
84
79
69
reaction enthalpy (kJ/mol of CO2)
Figure 5. Heat capacity of 30 wt % SG and MEA aqueous solutions. Table 3. Parameters of Heat Capacity of 30 wt % Aqueous Amine Solutions amine
a
103b
SG MEA
3.17024 2.48649
0.9067 4.1630
Figure 4. Heat capacity of pure MDEA.
Approximate values of -∆Hs, enthalpy of reaction of CO2 into amine solutions, can be calculated by following the Gibbs-Helmholtz equation:
[
]
∂ ln PCO2 ∆Hs ) (8) R ∂(1 ⁄ T) R where PCO2 is the partial equilibrium pressure of CO2, T is the absolute temperature of the system, R is the CO2 loading, and R is the gas constant. The enthalpy of reaction of CO2 in 30 wt % MEA solution with the data of Shakma18 and Kohl1 and 30 wt % SG solutions at (R ) 0.4) are given in Table 2. The reference results are in fair agreement with the present work. The value of -∆Hs for SG solution is lower than that of MEA solution by about 10 kJ for removing 1 mol of CO2 which means less heat is required to break off the CO2-SG solution complex formed during the absorption process. 3.3. Sensible Heat. The heat capacities (Cp) of nonvolatile pure MDEA with the data of Lee,38 Chen et al.,39 Missenard,40 and Chueh et al.41 are shown in Figure 4. The measured Cp values of pure MDEA for temperatures from 30 to 80 °C are in good agreement with the Cp values of the literature40,41 but are slightly higher than those of Lee38 (0.7%) and Chen et al.39 (0.9%). The heat capacities of 30 wt % SG and MEA solutions are shown in Figure 5. The literature of Cp values of 30 wt % MEA solution was little, hence Cp values of 30 wt % MEA -
Figure 6. Vapor pressure of 30 wt % SG and MEA aqueous solutions.
solution were calculated with the data of Chiu9 from the following Redlich-Kister equation: CEp ) Cp - (x1Cp,1 - x2Cp,2)
(9)
E
where Cp is the excess molar heat capacity for a binary mixture and xi and Cp,i are the mole fraction and molar heat capacity, respectively, of each pure component. Both the measured and estimated Cp values were expressed as a function of temperature as follows Cp (kJ/kg·K) ) a + bT (K)
(10)
The a and b parameters of Cp for SG and MEA solution are presented in Table 3. The temperature dependence of the Cp values of aqueous SG solution is less than that of aqueous MEA solution as shown in Figure 5. The sensible heat required to raise the rich amine solution temperature to the stripper temperature can be obtained by multiplying the mass of solution needed for removing 1 kg of CO2 by the integral of the heat capacity. Calculated sensible heats for SG and MEA were 3220 and 2325 kJ/kg of CO2, respectively. Despite the lower heat capacity of SG compared to the MEA solution, the SG mass
Ind. Eng. Chem. Res., Vol. 47, No. 24, 2008 9929 Table 4. Total Energy Requirements (kJ/kg of CO2)
solution concentration sensible heat latent heat of vaporization reaction enthalpy total energy expended on regeneration
MEA32
MEA (this work)
SG (this work)
30 wt % 2191 676 1636 4503
30 wt % 2325 629 1795 4749
30 wt % 3220 955 1568 5743
absorbent is defined as the summation of reaction enthalpy, sensible heat, and heat of vaporization. For the measurement of each contribution, CO2 solubility, heat capacities and vapor pressures were measured experimentally and were applied to well-known thermodynamic equations. Amine solution regeneration energy of 30 wt % SG solution was 5743 kJ/kg of CO2, so it was about 1000 kJ higher than that of 30 wt % MEA solution which means more energy is needed for desorbing same amount of CO2. This fact can also be reaffirmed from the CO2 solubility into SG solution at regeneration temperature (120 °C) (Figure 3) and effective CO2 loading (Table 1). By this proposed method, amine solution regeneration energy which is an important factor for the selection of CO2 absorbents was estimated quickly without any rigorous experiments. But, this method has some limitations such as (1) reaction kinetics were not reflected, (2) amine solution regeneration energy was also not a function of lean amine loading, and (3) the same desorption conditions were assumed for SG and MEA. Nevertheless, the most important advantage of this method is the estimation of amine solution regeneration energy by making use of physical properties of any novel CO2 absorbent. Thus, one can easily compute the amine solution regeneration energy in a fast manner using the measured physical properties and if the appropriate assumptions of regeneration are made, then this method can be a fast and reasonable mode of selecting efficient CO2 absorbents. Acknowledgment
Figure 7. Total energy requirements (kJ/kg of CO2).
required to absorb an unit amount of CO2 for the same weight concentration basis (MWMEA ) 61.09, MWSG ) 97.05) is larger. Consequently, the sensible heat of SG was found 38% higher than that of MEA. 3.4. Heat of Vaporization. Latent heat of vaporization of aqueous amine solution was determined by applying the following Clausius-Clapeyron equation to the vapor pressure data. d ln Psat (11) d(1 ⁄ T) Vapor pressure of 30 wt % SG and MEA36 solution are presented in Figure 6. Since SG is a solid powder, vapor pressure depression was observed in comparison with MEA solution. To separate 1 kg of carbon dioxide from flue gas, 0.03 kg of steam must be generated.32 Accordingly, the heat of vaporization of 30 wt % SG and MEA solution are 955 and 629 kJ/kg of CO2, respectively. 3.5. Regeneration Energy Requirements. The total energy required to regenerate the CO2-saturated amine solutions are reported in Table 4 and depicted in Figure 7. Also, the energy required for MEA solution was compared with the data of Go¨ttlicher32 and presented in Table 4. Individually all three components of regeneration energy and total calculated regeneration energy of 30 wt % MEA solution are in good agreement with that of Go¨ttlicher. It was observed from these investigations that the energy required for regeneration of CO2-loaded SG solution is 1000 kJ higher than the energy required for MEA solution regeneration. Qv ) ∆Hlv ) -
Conclusion In the present investigations, the energy required for regeneration of CO2-saturated 30 wt % SG and MEA solution were estimated under same conditions. Regeneration energy of CO2
The authors are grateful to the Korea Electric Power Research Institute, Daejeon, for funding this research work. Nomenclature Qdes ) heat of desorption, kJ/mol of CO2 Qsens ) sensible heat, kJ/ mol of CO2 Qstrip ) latent heat of vaporization () Qν ) ∆Hlv), kJ/ mol of CO2 -∆Hs ) heat of reaction, kJ/ mol of CO2 F ) density of aqueous solution, kg/m3 Cp ) heat capacity, kJ/(kg °C) ∆T ) temperature difference, °C Rrich ) rich CO2 loading, mol of CO2/mol of amine Rlean ) lean CO2 loading, mol of CO2/mol of amine Camine ) concentration of aqueous amine solution, kmol/m3 Psat ) vapor pressure, kPa PCO2 ) equilibrium partial pressure of CO2, kPa Ttop,des ) top temperature of stripper, °C xH2O,freebasis ) mole fraction of water in aqueous amine solution, dimensionless ∆HHvap 2O ) heat of evaporation of water, kJ/mol of H2O P ) internal pressure, kPa V ) internal volume, mL Z ) compressibility factor of gas phase, dimensionless R ) gas constant, m3 Pa/(mol K) T ) internal temperature, °C n ) moles of CO2 dissolved into aqueous amine solution, mol B, B0, B1 ) second virial coefficient, dimensionless ω ) acentric factor, dimensionless E ) calibration coefficient, dimensionless Hr ) heat rate, °C/min ∆H ) heat flow difference between empty pan and sample, mW m ) mass of solution, mg CPE ) excess molar heat capacity, kJ/mol xi ) mole fraction of i component, dimensionless CP,i ) molar heat capacity of i component, kJ/mol a ) parameter for heat capacity, kJ/(kg K) b ) parameter for heat capacity, kJ/kg
9930 Ind. Eng. Chem. Res., Vol. 47, No. 24, 2008 Subscripts L ) CO2 cylinder A ) equilibrium cell 0 ) before the feed of CO2 into equilibrium cell 1 ) after the feed of CO2 into equilibrium cell c ) critical value of CO2 r ) reduced value
Literature Cited (1) Kohl, A. L. Gas Purification, 5th ed.; Gulf Publishing Company: Houston, TX, 1997. (2) Hook, R. J. An Investigation of Some Sterically Hindered Amines as Potential Carbon Dioxide Scrubbing Compounds. Ind. Eng. Chem. Res. 1997, 36, 1779–1790. (3) Lee, S.; Song, H. J.; Maken, S.; Park, J. W. Kinetics of CO2 Absorption in Aqueous Sodium Glycinate Solutions. Ind. Eng. Chem. Res. 2007, 46, 1578–1583. (4) Kumar, P. S.; Hogendoorn, J. A.; Versteeg, G. F. Kinetics of the Reaction of CO2 with Aqueous Potassium Salt of Taurine and Glycine. AIChE J. 2003, 49, 203–213. (5) Penny, D. E.; Ritter, T. J. Kinetics Study of the Reaction between Carbon Dioxide and Primary Amines. J. Chem. Soc., Faraday Trans. 1 1983, 79, 2103–2109. (6) Van Holst, J.; Politiek, P. P.; Niederer, J. P. M.; Versteeg, G. F. CO2 Capture from Flue Gas using Amino Acid Salt Solutions. http:// www.co2-cato.nl/doc.php?lid)317. (accessed March 28, 2008). (7) Majchrowicz, M.; Niedere, J. P. M.; Velders, A. H.; Versteeg, G. F. Precipitation in Amino Acid Salt CO2 Absorption Systems. http://www.co2cato.nl/doc.php?lid)129. (accessed March 28, 2008). (8) Hamborg, E. S.; Niederer, J. P. M.; Versteeg, G. F. Determination of Dissociation Constants of CO2 Absorbents between 293-353 K using Electromotive Force Measurements. http://www.co2-cato.nl/doc.php?lid)121. (accessed March 28, 2008). (9) Kumar, P. S.; Hogendoorn, J. A.; Feron, P. H. M.; Versteeg, G. F. Density, Viscosity, Solubility, and Diffusivity of N2O in Aqueous Amino Acid Salt Solutions. J. Chem. Eng. Data 2001, 46, 1357–1361. (10) Kumar, P. S.; Hogendoorn, J. A.; Feron, P. H. M.; Versteeg, G. F. Equilibrium Solubility of CO2 in Aqueous Potassium Taurate Solutions: Part 1. Crystallization in Carbon Dioxide Loaded Aqueous Salt Solutions of Amino Acids. Ind. Eng. Chem. Res. 2003, 42, 2832–2840. (11) Kumar, P. S.; Hogendoorn, J. A.; Timmer, S. J.; Feron, P. H. M.; Versteeg, G. F. Equilibrium Solubility of CO2 in Aqueous Potassium Taurate Solutions: Part 2. Experimental VLE Data and Model. Ind. Eng. Chem. Res. 2003, 42, 2832–2840. (12) Chen, H.; Kovvali, A. S.; Sirkar, K. K. Selective CO2 Separation from CO2-N2 Mixtures by Immobilized Glycine-Na-Glycerol Membranes. Ind. Eng. Chem. Res. 2000, 39, 2447–2458. (13) Chen, H.; Obuskovic, G.; Majumdar, S.; Sirkar, K. K. Immobilized glycerol-based liquid membranes in hollow fibers for selective CO2 separation from CO2-N2 mixtures. J. Membr. Sci. 2001, 183, 75–88. (14) Lee, S.; Choi, S. I.; Maken, S.; Song, H. J.; Shin, H. C.; Park, J. W.; Jang, K. R.; Kim, J. H. Physical Properties of Aqueous Sodium Glycinate Solution as an Absorbent for Carbon Dioxide Removal. J. Chem. Eng. Data 2005, 50, 1773–1776. (15) Lee, S.; Song, H. J.; Maken, S.; Shin, H. C.; Song, H. C.; Park, J. W. Physical Solubility and Diffusivity of N2O and CO2 in Aqueous Sodium Glycinate Solutions. J. Chem. Eng. Data 2006, 51, 504–509. (16) Lee, S.; Song, H. J.; Maken, S.; Yoo, S. K.; Park, J. W.; Kim, S.; Shim, J. G.; Jang, K. R. Simulation of CO2 Removal with Aqueous Sodium Glycinate Solutions in a Pilot Plant. Korean J. Chem. Eng 2008, 25, 1–6. (17) Song, H. J.; Lee, S.; Maken, S.; Park, J. J.; Park, J. W. Solubilities of Carbon Dioxide in Aqueous Solutions of Sodium Glycinate. Fluid Phase Equilib. 2006, 246, 1–5. (18) Chakma, A. CO2 Capture Processes-Opportunities for Improved Energy Efficiencies. Energy ConVers. Manage. 1997, 38, S51–S56. (19) Sakwattanapong, R.; Aroonwilas, A.; Veawab, A. Behavior of Reboiler Heat Duty for CO2 Capture Plants using Regenerable Single and Blended Alkanolamines. Ind. Eng. Chem. Res. 2005, 44, 4465–4473. (20) Rochelle, G. T.; Goff, G. S.; Cullinane, J. T.; Freguia, S. Research Results for CO2 Capture from Flue Gas by Aqueous Absorption/Stripping. The Laurance Reid Gas Conditioning Conference, Norman, USA, 2002; pp 131-151.
(21) Ma’mun, S.; Juliussen, O.; Hoff, K. A.; Kim, I.; Svendsen, H. F. Absorption of Carbon Dioxide using Aqueous 30 Mass % 2-((2-Aminoethyl)amino)ethanol Solution. https://events.adm.ntnu.no/ei/ viewpdf.esp?id)24&file)d%3A%5CAmlink%5CEVENTWIN%5Cdocs% 5Cpdf % 5Cghgt8Abstract00142.pdf. (22) Yeh, J. T.; Resnik, K. P.; Rygle, K.; Pennline, H. W. Semi-Batch Absorption and Regeneration Studies for CO2 Capture by Aqueous Ammonia. Fuel Process. Technol. 2005, 86, 1533–1546. (23) Mathonat, C.; Majer, V.; Mather, A. E.; Grolier, J. P. E. Enthalpies of Absorption and Solubility of CO2 in Aqueous Solutions of Methyldiethanolamine. Fluid Phase Equilib. 1997, 140, 171–182. (24) Mathonat, C.; Majer, V.; Mather, A. E.; Grolier, J. P. E. Use of Flow Calorimetry for Determining Enthalpies of Absorption and the Solubility of CO2 in Aqueous Monoethanolamine Solutions. Ind. Eng. Chem. Res. 1998, 37, 4136–4141. (25) Jou, F. Y.; Otto, F. D.; Mather, A. E. Vapor-Liquid Equilibrium of Carbon Dioxide in Aqueous Mixtures of Monoethanolamine and Methyldiethanolamine. Ind. Eng. Chem. Res. 1994, 33, 2002–2005. (26) Xu, H. J.; Zhang, C. F.; Zheng, Z. S. Solubility of Hydrogen Sulfide and Carbon Dioxide in a Solution of Methyldiethanolamine Mixed with Ethylene Glycol. Ind. Eng. Chem. Res. 2002, 41, 6175–6180. (27) Ma’mun, S.; Nilsen, R.; Svendsen, H. F. Solubility of Carbon Dioxide in 30 Mass % Monoethanolamine and 50 Mass % Methyldiethanolamine Solutions. J. Chem. Eng. Data 2005, 50, 630–634. (28) Chiu, L. F.; Liu, H. F.; Li, M. H. Heat Capacity of Alkanolamines by Differential Scanning Calorimetry. J. Chem. Eng. Data 1999, 44, 631– 636. (29) Chiu, L. F.; Li, M. H. Heat Capacity of Alkanolamine Aqueous Solutions. J. Chem. Eng. Data 1999, 44, 1396–1401. (30) Weiland, R. H.; Dingman, J. C.; Cronin, D. B. Heat Capacity of Aqueous Monoethanolamine, Diehtnaolamine, N-Methyldiethanolamine, and N-Methyldiethanolamine-Based Blends with Carbon Dioxide. J. Chem. Eng. Data 1997, 42, 1004–1006. (31) Maham, Y.; Hepler, L. G.; Mather, A. E.; Hakin, A. W.; Marriott, R. A. Molar Heat Capacities of Alkanolamines from 299.1 to 397.8 K. J. Chem. Soc., Faraday Trans. 1997, 93, 1747–1750. (32) Go¨ttlicher, G. The Energetics of Carbon Dioxide Capture in Power Plants; US Department of Energy, National Energy Technology Laboratory, 2004. (33) Xu, S.; Qing, S.; Zhen, Z.; Zhang, C. Vapor Pressure Measurements of Aqueous N-Methyldiethanolamine Solutions. Fluid Phase Equilib. 1991, 67, 197–201. (34) Smith, J. M.; Van Ness, H. C.; Abbott, M. M. Introduction to Chemical Engineering Thermodynamics, 6th ed.; McGraw Hill: Boston, 2001. (35) Ditmars, D. A.; Bernstein, G.; Chang, S. S.; Ishihara, S.; West, E. D. Enthalpy and Heat-Capacity Standard Reference Material-Synthetic Sapphire (R-Al2O3) from 10 to 2250 K. J. Res. Nat. Bur. Stand. 1982, 87, 159–163. (36) Jou, F. Y.; Mather, A. E.; Otto, F. D. The Solubility of CO2 in a 30 Mass Percent Monoethanolamine Solution. Can. J. Chem. Eng. 1995, 73, 140–147. (37) Shen, K. P.; Li, M. H. Solubility of Carbon Dioxide in Aqueous Mixtures of Monoethanolamine with Methyldiethanolamine. J. Chem. Eng. Data 1992, 37, 96–100. (38) Lee, L. L. Thermodynamic Models for Natural Gas Sweetening Fluids; Annual report to Gas Sweetening Fluids, University of Oklahoma: Norman, OK, 1994. (39) Chen, Y. J.; Shih, T. W.; Li, M. H. Heat Capacity of Aqueous Mixtures of Monoethanolamine with N-Methyldiethanolamine. J. Chem. Eng. Data 2001, 46, 51–55. (40) Missenard, F. A. Metho de additive pour la determination de lachaleur molaire des liquides. C.R. Acad. Sci. 1965, 260, 5521–5523. (41) Chueh, C. F.; Swanson, A. C. Estimation of liquid heat capacity. Chem. Eng. Prog. 1973, 69, 596–600. (42) Union Carbide Chemical Co. Gas Treating Chemicals; 1957; Vol. 1.
ReceiVed for reView May 1, 2008 ReVised manuscript receiVed September 25, 2008 Accepted September 30, 2008 IE8007117
