Ind. Eng. Chem. Res. 2005, 44, 9273-9278
9273
Facilitated Transport of CO2 through Immobilized Liquid Membrane Mohamed H. Al Marzouqi,*,† Mohamed A. Abdulkarim,† Sayed A. Marzouk,‡ Muftah H. El-Naas,† and Hasan M. Hasanain† Department of Chemical & Petroleum Engineering, and Department of Chemistry, United Arab Emirates University, Al-Ain, United Arab Emirates
Selective removal of acid gases from a contaminated gas stream was studied using four amines (diethylenetriamine (DETA), diaminoethane (DAE), diethylamine (DEYA), and bis(2-ethylhexyl)amine (BEHA)) as immobilized liquids in a facilitated transport membrane. The effect of amine concentration, CO2 partial pressure, and operating temperature on the permeance of CO2 and CH4 was investigated for each aqueous amine solution. The observed CO2 permeance decreased with increasing CO2 feed pressure, whereas the permeance of CH4 remained constant for all tested amines. The permeance of CO2 and the selectivity were in the order DETA > DAE > BEHA ≈ DEYA. This order is related to the number of nitrogen atoms per amine molecule, which can be correlated to loading capacity and consequently to amine reactivity with CO2. The permeance of CO2 in 2 M DETA increased with increasing temperature. The permeance of CO2 using DETA was about 4 times that obtained using diethanolamine (DEA) and monoethanolamine (MEA), which are the most commonly used solvents in industrial applications. 1. Introduction Aqueous amine solutions are the most commonly used reactive solvents in the industry for gas treatment. Reaction rates, absorption capacities, regeneration costs, and availability of the alkanolamines as well as the process requirements are the major factors of concern in the selection of a particular amine in such industrial applications. Aqueous primary, secondary, and tertiary amine solutions, mainly monoethanolamine (MEA), diethanolamine (DEA), and N-methyldiethanolamine (MDEA), are often used for the removal of acid gases (CO2 and H2S) from industrial and natural gas streams. The use of alkanolamines in industrial separation processes is often accomplished by chemical absorption, where an amine solution reacts with and absorbs the acid gas selectively. Generally, CO2 and aqueous solutions of amine at equilibrium go through several reactions to form the carbamate anion, protonated cation, bicarbonate ion, and carbonate ion.1 Since these reactions play a major role in the selective separation of acid gases, the reaction rate of CO2 with alkanolamines was studied extensively. The amine that has the ability of producing higher concentrations of carbamate anions has a higher reaction rate with CO2, and due to this reason, the reaction of the secondary amines with CO2 is faster than that of primary amines. However, the formation of carbamate anions leads to relatively low loading capacity (0.5 mol of CO2/mol of amine) based on the overall reaction stoichiometry. The mechanism and kinetics of the reaction between CO2 and tertiary amines in aqueous solutions is also studied.2 In this case, the bicarbonate and protonated tertiary alkanolamines are formed due to the hydration of CO2 in the presence of water. The heat of formation * Corresponding author. Tel.: (+9713) 713 3597. Fax: (+9713) 762 4262. E-mail:
[email protected]. † Department of Chemical & Petroleum Engineering. ‡ Department of Chemistry.
of bicarbonate ions is much lower than that of carbamate formation; hence, the regeneration cost for tertiary amines is lower than that for primary and secondary amines. In addition, the loading capacity is 1 mol of CO2/ mol of amine during the formation of the bicarbonate ion.3 Therefore, tertiary amines have the advantage in terms of loading capacity and regeneration cost. On the other hand, it has been reported4 that sterically hindered amines have a low tendency to form carbamates and therefore do not react with CO2 to the same extent as conventional primary or secondary amines. Sterically hindered amines also offer high CO2 loading capacity along with appreciable rate of absorption.4 Sterically hindered amines cannot form stable carbamates which lead to much higher carbonation ratios (moles of CO2 to moles of amine). In an attempt to improve the efficiency of acid gas removal from a contaminated gas stream and to reduce the associated cost, aqueous blends of primary or secondary amines with tertiary amines are gaining more interest for bulk CO2 removal. These blends combine the higher reaction rates between CO2 and primary/ secondary amines and the easier regeneration and higher absorption capacities associated with the use of tertiary amines.4 The investigated mixtures include N-methyldiethanolamine/diethanolamine,5,6 monoethanolamine/N-methyldiethanolamine,5,7,8 2-amino-2-methyl1-propanol/monoethanolamine,5,8,9 monoethanolamine/ triethanolamine,10 monoethanolamine/piperazine,11 piperazine/methyldiethanolamine,12-14 2-amino-2-methyl-1propanol/piperazine,15 N-methyldiethanolamine/2-amino2-methyl-1-propanol,5,16 and 2-amino-2-methyl-1-propanol/diethanolamine.5 For more efficient removal of acid gas from a contaminated gas stream, several alternative stripping media have been proposed. These include immobilized amine groups on solid support particles,17 nonaqueous amine systems,18 aqueous solutions of amino acid salts,19 calcium nitrate,20 and aqueous potassium car-
10.1021/ie050526y CCC: $30.25 © 2005 American Chemical Society Published on Web 10/21/2005
9274
Ind. Eng. Chem. Res., Vol. 44, No. 24, 2005
Figure 1. Schematic diagram of the experimental apparatus.
bonate solution.21 For CO2 separation from CO2/N2 mixtures, some authors proposed the use of glycerol carbonate,22 sodium carbonate-glycerol,23,24 and dendrimer25 in an immobilized liquid membrane configuration and immobilized solutions of Na2CO3-glycerol in porous and hydrophilic poly(vinylidene fluoride) (PVDF) substrate.25 The prime objective of this paper is to experimentally investigate the facilitated transport of CO2 using four different amine solutions, which were selected with different numbers of nitrogen atoms (i.e., from one to three) per amine molecule. The ultimate goal is to select an amine that will give the highest CO2 removal efficiency and selectively.
Figure 2. Effect of CO2 feed pressure on the permeance of CO2 (A) and CH4 (B) for different amines. Pfeed,total ) 160 kPa and Pstrip ) 135 kPa. Amine concentration ) 2 M.
2. Experimental Setup A laboratory-scale unit was specially constructed to study CO2-CH4 separation through an immobilized liquid used as a facilitated transport membrane. A schematic diagram of the unit is shown in Figure 1. Poly(vinylidine difluoride) (PVDF) porous membrane (Millipore) was used as an inert support for the amine solution. Durapore hydrophilic PVDF disks (0.1 µm pore size, 0.1 mm thick, and 47 mm diameter) were soaked in a known amine solution for a predetermined period (about 24 h) to ensure complete filling of the micropores with the amine solution. The immobilized liquid membrane was then placed in a stainless steel holder, which was designed to allow both feed and sweep gas streams to pass on opposite sides of the immobilized liquid membrane. The PVDF disk is supported with a circular stainless steel mesh. Different proportions of CH4 and CO2 mixtures were prepared from pure gases using high accuracy mass flow controllers (Brooks Instrument, Model 5850 E series). A known gas mixture was then fed to the membrane unit. Helium was used as a sweep gas to carry the permeated CH4 and CO2 gases to the online gas chromatograph for analysis. Each experiment was conducted in triplicate. 3. Results and Discussion 3.1. Effect of CO2 Partial Pressure and Amine Concentration. The effect of amine concentration on permeability and selectivity of CO2/CH4 at different CO2 partial pressures was investigated for the four amines (DETA, DAE, DEYA, and BEHA), and the results are presented in Figures 2 and 3. For the sake of simplicity, the selectivity of CO2/CH4 will be referred to throughout this paper as selectivity. Figure 2 clearly shows that CO2
Figure 3. Effect of CO2 feed pressure on CO2/CH4 selectivity for different amines. Pfeed,total ) 160 kPa and Pstrip ) 135 kPa. Amine concentration ) 2 M.
permeance decreases with increasing CO2 feed pressure (Figure 2A), whereas the permeance of CH4 is mainly constant for all the tested amines (Figure 2B). These trends result in a decreased selectivity with increasing CO2 feed pressure (Figure 3). This indicates that the transport mechanism of CO2 through the immobilized liquid membrane is due to both diffusion and reaction, whereas the transport mechanism of CH4 is due to diffusion alone. The transport mechanisms are discussed in more detail in section 3.2. In addition, the CH4 permeance using DETA and DAE are lower than those of BEHA and DEYA, indicating lower diffusion rates and, consequently, lower diffusion coefficients of CH4 in both DETA and DAE as compared with the other two amines. Contrary to CH4, CO2 exhibited favorable permeance in DETA and DAE solutions which led to higher observed selectivity using DETA and DAE as compared with the other two amines. This effect is more pronounced at low CO2 partial pressures. The permeance of CO2 and the selectivity using DETA are approxi-
Ind. Eng. Chem. Res., Vol. 44, No. 24, 2005 9275
Figure 6. CO2 transport through immobilized liquid membrane.
Figure 4. Effect of CO2 feed pressure on the permeance of CO2 (A) and CH4 (B) for different DETA concentrations. Pfeed,total ) 160 kPa and Pstrip ) 135 kPa.
was obtained with the 2 M amine concentration (Figure 5). A higher concentration of amine in the solution is expected to result in a higher facilitation effect (higher reaction rate), resulting in higher CO2 permeance and higher selectivity. This effect is observed up to 2 M amine solution. 3.2 Transport Mechanism(s) through Immobilized Liquid Membrane. The transport of CO2 through immobilized liquid membrane is shown in Figure 6. In this process, a chemical carrier (amine molecule) binds reversibly and selectively with the permeate species (CO2) at the feed side of the liquid membrane, transports the permeate through the film, and then releases it at the strip side. In this process, chemical reaction and diffusion occur simultaneously, which accelerates the transport of the permeate species through the liquid membrane film. The continuity equation for each species during the simultaneous mass transfer and chemical reaction in a reactive absorption system can be expressed as
∂Ci ) -3Ni ( Ri,overall ∂t
(3.1)
where Ci, Ni, and Ri,overall are the concentration, flux, and reaction rate of species i, respectively, and t is time. For one-dimensional steady-state operation and assuming Fick’s law, eq 3.1 can be simplified to
Di Figure 5. Effect of CO2 feed pressure on CO2/CH4 selectivity for different DETA concentrations. Pfeed,total ) 160 kPa and Pstrip ) 135 kPa.
mately 4 and 18 times higher than those of BEHA or DEYA at low partial pressure of CO2 (5% CO2-95% CH4 mixture). There are two related effects on the permeance of CO2: the permeate flux and CO2 partial pressure. Permeate flux increases with increasing CO2 partial pressure; however, the relative increase in the flux is much smaller than the increase in CO2 partial pressure, resulting in lower permeance of CO2 (Figure 2A) and consequently lower selectivity (Figure 3). Therefore, DETA was used for further studies since it showed the highest CO2 permeance and highest selectivity among the four amines. The effect of DETA concentration on CO2 permeance was investigated in the range of 0.05-4.0 M. The results are shown in Figures 4 and 5. The CO2 permeance increased with increasing DETA concentration up to 2 M. No significant increase in the permeance is observed with higher DETA concentration. The highest CO2 permeance was obtained with 2 M and decreased with decreasing amine concentration (Figure 4A), whereas CH4 permeance remained almost independent of DETA concentration (Figure 4B). Hence, the highest selectivity
d2Ci dx2
( Ri,overall ) 0
(3.2)
The two required boundary conditions for the permeate species (CO2 and CH4) are
Ci,permeate )
Pi,feed H
at x ) 0
Ci,permeate )
Pi,strip H
at x ) L
where Pi is the partial pressure of the permeate species in the gas phase and H [atm m3 kmol-1] is the solubility or Henry’s law constant. The gas-phase resistance in both sides of membrane is assumed to be negligible for this analysis. Therefore, the transport of permeate species generally consists of diffusion (through the membrane) and reaction (with aqueous amine), as represented by eq 3.2, and the solution interface (gas-liquid), as represented by the boundary conditions. Using eq 3.2, the flux of nonreactive species (Roverall ) 0) through the liquid membrane (with the same boundary conditions) can be derived as
Ni,nonreactive )
Di Pi,feed - Pi,strip H L
(3.3)
9276
Ind. Eng. Chem. Res., Vol. 44, No. 24, 2005 Table 1. Henry’s Law Constant, H (kPa m3 kmol-1), of CO2 in Amine Solutions at 303 K DEA
exptl values (this work) lit. values
Figure 7. Effect of CH4 flux on pressure gradient using DETA. Pfeed,total ) 160 kPa and Pstrip ) 135 kPa. Amine concentration ) 2 M.
where L is the thickness of the liquid membrane. Equation 3.3 represents the transport of the permeate species due to diffusion alone. However, the flux of the reactive species would be higher since it is the combination of both diffusion and reaction. As an example, if carbamate formation represents the effect of reaction, then the total flux for the reactive species may be presented as
Ni,reactive )
Di Pi,feed - Pi,strip + H L Dcarbamate
Ccarbamate,feed - Ccarbamate,strip (3.4) L
Therefore, the total flux is the combination of diffusion (first term) and reaction (second term). The solubility effect is embedded in both eqs 3.3 and 3.4 through the boundary conditions. In the system studied, a plot of flux vs pressure gradient for CH4 is linear (Figure 7), which indicates that the transport of CH4 through the liquid membrane is by diffusion alone. This behavior is expected since CH4 is considered to be nonreactive (eq 3.3). On the other hand, a plot of CO2 flux vs pressure gradient (Figure 8) is not linear and shows much higher flux, which indicates a different transport mechanism. Due to the reaction of CO2 with aqueous amine, carbamate is formed generating a concentration gradient across the membrane. Higher reaction rate leads to a higher carbamate concentration gradient and, consequently, higher flux (eq 3.4). Therefore, since the CO2 flux in DETA is much higher than that in DEA, it is expected that the effect of the second term (reaction term) in eq 3.4 is much higher for DETA than for DEA. To verify the transport mechanisms for CO2 in aqueous amine, the CO2 solubility (Henry’s law constant) and
30% w/w
10% w/w
30% w/w
3515 352026 367727 367128
4648 471626 520727 398928
5126 N/A N/A N/A
5880 N/A N/A N/A
Table 2. Apparent Reaction Rate, kapp (s-1), of CO2 with Amine Solutions at 298 K DEA exptl values (this work) lit. values
Figure 8. Effect of CO2 flux on pressure gradient. Pfeed,total ) 160 kPa and Pstrip ) 135 kPa. Amine concentration ) 2 M.
DETA
10% w/w
DETA
1M
4M
1M
4M
537 51329 52030
7025
2195 N/A N/A
51926 N/A N/A
apparent CO2 reaction rate in DEA and DETA were measured and are presented in Tables 1 and 2, respectively. The Henry’s law constant and apparent reaction rate of CO2 in DEA are in good agreement with the literature values. The Henry’s law constant of CO2 in DETA is about 1.3 and 1.5 times higher than that in DEA for 30% w/w and 10% w/w, respectively, whereas the apparent reaction rate of CO2 with DETA is about 4 times (for 1 M) higher than that in DEA. The values of the diffusion coefficient of CO2 in different known amine solutions are reported31 to be similar. Therefore, it is expected that the difference in CO2 diffusion coefficients in DETA and DEA will be small. It is obvious, therefore, that the higher flux of CO2 in DETA is mainly due to a higher apparent reaction rate, since the differences in diffusion coefficients and solubilities are relatively small. 3.3. Loading Capacity of DETA. Based on the experimental results presented in section 3.1, the CO2 permeance and selectivity obtained with the four tested amines were in the order DETA > DAE > BEHA ≈ DEYA. This trend could be reasonably correlated to the number of nitrogen atoms per amine molecule. DETA, DAE, DEYA, and BEHA are amines with three, two, one, and one nitrogen atoms per molecule, respectively. From the structure properties of the four amines, it is evident that DETA has two primary amino groups and a secondary amino group and DAE has two primary amino groups, whereas BEHA and DEYA are both secondary amines, each with one amino group. It has been reported3 that the loading capacity for primary and secondary amines is 0.5 mol of CO2/mol of amine. However, the loading capacity of CO2 in an aqueous bis(3-dimethylaminopropyl)amine (TMBPA), a polyamine, solution is reported32 to be 3 mol of CO2/ mol of TMBPA. In addition, the loading capacity of N-(2aminoethyl)-1,3-propanediamine (AEPDNH2), a polyamine, which has two primary amino groups and a secondary amino group, and 2-(2-aminoethylamino)ethanol (AEE), a diamine, were determined experimentally to be 2.45 and 1.35, respectively.33 It was also concluded that AEPDNH2, a polyamine, has the highest loading capacity, followed by AEE, a diamine, and then monoamine. Therefore, the higher CO2 permeance of DETA and DAE might be due to higher number of amino groups which might result in higher loading capacities as compared with the other two amines. Higher loading capacity means higher access to CO2, which in turn leads to higher reactivity.
Ind. Eng. Chem. Res., Vol. 44, No. 24, 2005 9277
Figure 11. Effect of CO2 feed pressure on the permeance of CO2 in DETA, DEA, and MEA at 318 K. Pfeed,total ) 160 kPa and Pstrip ) 135 kPa. Amine concentration ) 2 M.
using diethanolamine (DEA) and monoethanolamine (MEA), two of the most commonly used solvents in the natural gas industry. The results, presented in Figure 11, indicate that the CO2 permeance using DETA is almost 4 times that of DEA and MEA for low partial pressure of CO2. This difference decreases as the partial pressure of CO2 increases. 4. Conclusions Figure 9. Effect of CO2 feed pressure on the permeance of CO2 (A) and CH4 (B) for different DETA temperatures. Pfeed,total ) 160 kPa and Pstrip ) 135 kPa. Amine concentration ) 2 M.
Figure 10. Effect of CO2 feed pressure on CO2/CH4 selectivity for different DETA temperatures. Pfeed,total ) 160 kPa and Pstrip ) 135 kPa. Amine concentration ) 2 M.
3.4. Effect of Temperature. Figures 9 and 10 show the effect of temperature on permeance of both CO2 and CH4 and selectivity using DETA in a facilitated transport membrane. Increasing temperature increases the permeation rate of both CO2 and CH4. The permeation rate of CO2 is enhanced with increasing temperature by increasing diffusion (diffusion coefficient) and reaction rate (rate constant). The increase in both CO2 diffusion coefficient in amine solutions and the rate constant with temperature is exponential as reported by several investigators. Thus, the CO2 permeance is expected to increase with increasing temperature. Similar behavior is observed using DETA solution, as seen in Figure 9A. The CH4 permeance increases with increasing temperature as a result of increasing the diffusion coefficient of CH4 in amine solution (Figure 9B). The effect of this increase is more pronounced for CH4 compared to CO2, which in turn reduces the selectivity with increasing temperature (Figure 10). 3.5. Comparison of DETA with Common Amines. The CO2 permeation rate through DETA, as an immobilized liquid membrane, is compared with those
Four different amines, DETA (polyamine), DAE (diamine), BEHA (secondary monoamine), and DEYA (secondary monoamine), were used as immobilized liquid membranes to study the selective removal of carbon dioxide from a gas mixture. The obtained permeance and selectivity of CO2 with the different amines were in the order DETA > DAE > BEHA ≈ DEYA. This is related to the number of nitrogen atoms per each amine molecule, which is closely related to the loading capacity. Higher loading capacity can be correlated to higher access to CO2 for reaction. The CO2 transport rate through immobilized liquid membrane using DETA was superior to those using DEA and MEA, which are the most commonly used solvents in the natural gas industry. Acknowledgment The authors would like to express their sincere appreciation to The Research Council, United Arab Emirates University, for the financial support of this project under Contract No. 02/12-7-01. Literature Cited (1) Ohno, K.; Inoue, Y.; Yoshida, H.; Matsuura, E. Reaction of Aqueous 2-(N-Methylamino)ethanol Solutions with Carbon Dioxide. Chemical Species and Their Conformations Studied by Vibrational Spectroscopy and ab Initio Theories. J. Phys. Chem. A 1999, 103 (21), 4283. (2) Kierzkowska-Pawlak, H.; Zarzycki, R. Solubility of Carbon Dioxide and Nitrous Oxide in Water + Methyldiethanolamine and Ethanol + Methyldiethanolamine Solutions. J. Chem. Eng. Data 2002, 47, 1506. (3) Rinker, E. B.; Ashour, S. S.; Sandall, O. C. Absorption of Carbon Dioxide into Aqueous Blends of Diethanolamine and Methyldiethanolamine. Ind. Eng. Chem. Res. 2002, 39 (11), 4346. (4) Ali, S.; Merchant, S.; Fahim, M. Reaction Kinetics of Some Secondary Alkanolamines with Carbon Dioxide in Aqueous Solutions by Stopped Flow Technique. Sep. Purif. Technol. 2002, 27, 121. (5) Bensetiti, Z.; Iliuta, I.; Larachi, F.; Grandjean, B. P. A. Solubility of Nitrous Oxide in Amine Solutions. Ind. Eng. Chem. Res. 1999, 38 (1), 328.
9278
Ind. Eng. Chem. Res., Vol. 44, No. 24, 2005
(6) Zhang, X.; Zhang, C. F.; Liu, Y. Kinetics of Absorption of CO2 into Aqueous Solution of MDEA Blended with DEA. Ind. Eng. Chem. Res. 2002, 41 (5), 1135. (7) Hagewiesche, D. P.; Ashour, S. S.; Alghawas, H. A.; Sandall, O. C. Absorption of Carbon Dioxide into Aqueous Blends of Monoethanolamine and N-Methyldiethanolamine. Chem. Eng. Sci. 1995, 50 (7), 1071. (8) Mandal, B. P.; Guha, M.; Biswas, A. K.; Bandyopadhyay, S. S. Removal of Carbon Dioxide by Absorption in Mixed Amines: Modeling of Absorption in Aqueous MDEA/MEA and AMP/MEA Solutions. Chem. Eng. Sci. 2001, 56 (21-22), 6217. (9) Xiao, J.; Li, C. W.; Li, M. H. Kinetics of Absorption of Carbon Dioxide into Aqueous Solutions of 2-Amino-2-Methyl-1-Propanol + Monoethanolamine. Chem. Eng. Sci. 2000, 55 (1), 161. (10) Horng, S. Y.; Li, M. H. Kinetics of Absorption of Carbon Dioxide into Aqueous Solutions of Monoethanolamine + Triethanolamine. Ind. Eng. Chem. Res. 2002, 41 (2), 257. (11) Dang, H. Y.; Rochelle, G. T. CO2 Absorption Rate and Solubility in Monoethanolamine/Piperazine/Water. Sep. Sci. Technol. 2003, 38 (2), 337. (12) Bishnoi, S.; Rochelle, G. T. Absorption of Carbon Dioxide in AqueousPiperazine/Methyldiethanolamine. AIChE J. 2002, 48 (12), 2788. (13) Bishnoi, S.; Rochelle, G. T. Thermodynamics of Piperazine/ Methyldiethanolamine/Water/Carbon Dioxide. Ind. Eng. Chem. Res. 2002, 41 (3), 604. (14) Zhang, X.; Wang, J.; Zhang, C. F.; Yang, Y. H.; Xu, J. J. Absorption Rate into a MDEA Aqueous Solution Blended with Piperazine under a High CO2 Partial Pressure. Ind. Eng. Chem. Res. 2003, 42 (1), 118. (15) Seo, D. J.; Hong, W. H. Effect of Piperazine on the Kinetics of Carbon Dioxide with Aqueous Solutions of 2-Amino-2-methyl1-propanol. Ind. Eng. Chem. Res. 2003, 39 (6), 2062. (16) Davis, R. A.; Pogainis, B. J. Solubility of Nitrous Oxide in Aqueous Blends of N-Methyldiethanolamine and 2-Amino-2methyl-1-propanol. J. Chem. Eng. Data 1995, 40 (6), 1249. (17) Schubert, S.; Grunewald, M.; Agar, D. W. Enhancement of Carbon Dioxide Absorption into Aqueous Methyldiethanolamine Using Immobilized Activators. Chem. Eng. Sci. 2001, 56, 6211. (18) Ali, S. H.; Merchant, S. Q.; Fahim, M. A. Kinetic Study of Reactive Absorption of Some Primary Amines with Carbon Dioxide in Ethanol Solution. Sep. Purif. Technol. 2000, 18, 163. (19) 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 (1), 203. (20) Vucak, M.; Peric, J.; Zmikic, A.; Pons, M. N. A Study of Carbon Dioxide Absorption into Aqueous Monoethanolamine Solution Containing Calcium Nitrate in the Gas-Liquid Reactive Precipitation of Calcium Carbonate. Chem. Eng. J. 2002, 87, 171.
(21) Lee, Y. T.; Noble, R. D.; Yeom, B. Y.; Park, Y. I.; Lee, K. H. Analysis of CO2 Removal by Hollow Fiber Membrane Contactors. J. Membr. Sci. 2001, 194 (1), 57. (22) Kovvali, A. S.; Sirkar, K. K. Carbon Dioxide Separation with Novel Solvents as Liquid Membranes. Ind. Eng. Chem. Res. 2002, 41 (9), 2287. (23) Chen, H.; Kovvali, A. S.; Sirkar, K. K. Selective CO2 Separation from CO2-N2 Mixtures by Immobilized Glycine-NaGlycerol Membranes. Ind. Eng. Chem. Res. 2000, 39 (7), 2447. (24) 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 (1), 75. (25) Kovvali, A. S.; Sirkar, K. K. Dendrimer Liquid Membranes: CO2 Separation from Gas Mixtures. Ind. Eng. Chem. Res. 2001, 40 (11), 2502. (26) Abu-Arabi, M. K.; Al-Jarrah, A. M.; El-Eideh, M.; Tamimi, A. Physical Solubility and Diffusivity of CO2 in Aqueous Diethanolamine Solutions. J. Chem. Eng. Data 2001, 46, 516. (27) Haimour, N. M. solubility of N2O in Aqueous Solutions of Diethanolamine at Different Temperatures. J. Chem. Eng. Data 1990, 35, 177. (28) Little, R. J.; Versteeg, G. F.; van Swaaij, W. P. M. Solubility and diffusivity Data for the Absorption of COS, CO2, and N2O in Amine Solutions. J. Chem. Eng. Data 1992, 37, 49. (29) Blauwhoff, P. M. M.; Versteeg, G. F.; Van Swaaij, W. P. M. A Study on the reaction between CO2 and Alkanolamines in aqueous solutions. Chem. Eng. Sci. 1984, 39 (2), 207. (30) Xu, S.; Wang, Y.-W.; Otto, F. D.; Mather, A. E. Kinetics of the reaction of carbon dioxide with 2-amino-2-methyl-1-propanol solutions. Chem. Eng. Sci. 1996, 51 (6), 841. (31) Ko, J.-J.; Tsai, T.-C.; Lin, C.-Y.; Wang, H.-m.; Li, M.-h. Diffusivity of Nitrous Oxide in Aqueous Alkanolamine Solutions. J. Chem. Eng. Data 2001, 46, 160. (32) Dallos, A.; Altsach, T.; Kotsis, L. Enthalpies of Absorption and Solubility of Carbon Dioxide in Aqueous Polyamine Solutions. J. Therm. Anal. Calorim. 2001, 65, 419. (33) Bonenfant, D.; Mimeault, M.; Hausler, R. Determination of the Structural Features of Distinct Amines Important for the Absorption of CO2 and Regeneration in Aqueous Solution. Ind. Eng. Chem. Res. 2003, 42, 3179.
Received for review May 4, 2005 Revised manuscript received September 11, 2005 Accepted September 19, 2005 IE050526Y
