2007_6_Nr6_EEMJ

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Siminiceanu et al. /Environmental Engineering and Management Journal 6 (2007), 6, 555-561 Table 6. The kinetic parameters derived from the Arrhenius plot a Ea A= 0 ln k molCO 2 /mol ov B=Ea/R, APEDA cal/mol kJ/mol K 0.00-0.05 10 553.89 44.11 26.496 5 311.02 0.05-0.10 10 616.18 44.37 26.877 5 342.72 0.10-0.20 10 782.52 45.06 27.272 5 426.27 0.20-0.30 10.552.85 44.11 25.931 5 310.52 0.30-0.40 9 599.42 40.12 24.238 4 830.90 0.40-0.50 8 890.80 37.16 24.671 4 474.08 4. Conclusions The aqueous monoethanolamine (MEA) is now considered the most convenient among the available absorption technologies for removing carbon dioxide from flue gas streams. Nevertheless, this process has a number of drawbacks, pointed out in the introductory section of this paper, which make it rather expensive. Its application to fossil fuel power plants could increase the cost of electricity production by up to 82.8 % (Abu- Zahra et al., 2007b). This paper presents some results of a study aiming to develop a new solvent in order to improve the efficiency of the CO 2 removal from flue gas. The absorption of CO 2 into an aqueous solution with 1.45 mol/L 1,5,8,12- tetraazadodecane (APEDA) polyamine has been studied at three temperature (298, 313, 333 K) in a Lewis type absorber with a constant gas- liquid interface area of (15.34 ± 0.05) x 10 -4 m 2 . The experimental results have been interpreted using the equations derived from the two film model with the assumption that the absorption occurred in the fast pseudo- first- order kinetic regime. The results confirmed the validity of this assumption for the experimental conditions: the enhancement factor was always greater than 3. According to the results, the rate constat (kov) increased with the temperature, and decreased with the carbonation degree/ loading (a= mol CO 2 /mol amine). For each loading the Arrhenius equation was satisfactory verified. The activation energy (41.9 kJ/mol) indicated that the process proceeded close to the boundary between the kinetic and the mass transfer regime. The optimal values of the constants A and B from the Arrhenius equation (lnk = A- B/T) were derived by linear regression, for each loading. These will be useful for the industrial absorption column modeling and simulation. The rate constant derived from experiments is of the same order of magnitude as that for the absorption into 2- amino- 2- methyl- 1- propanol (AMP) activated with piperazine (PZ) which was found to be the most advanced system among the published data up to now( Sun et al., 2005). At T= 313 K and a< 0.05, for instance, k ov = 17 255 s -1 for APEDA, compared to 20 572 s -1 for 1.5M of AMP with 0.3M of PZ under the same conditions. The preliminary results presented in this paper show that, from the kinetic point of view, the absorption of CO 2 from flue gas into APEDA solution is a promising process for practical application .Other potential advantages of APEDA compared to MEA : higher loadings( smaller solution flow rates), less energy required for regeneration, lower degradability and corrosiveness. It is still to prove the unavoidable existence of some drawbacks, such as, volatility, toxicity and cost. Notation A, area of the gas- liquid interface, m 2 ; a, moles of gas absorbed per mole of amine (loading), mol/mol; C i , molar concentration, kmol/m 3 ; D o i , diffusion coefficient of i in water, m 2 /s; D i , diffusion coefficient of i in solution, m 2 /s; D c , absorption cell internal diameter, m; d st , stirrer diameter, m; E, enhancement factor of absorption by the chemical reaction; H i , Henry constant for the absorption of CO 2 in the APEDA solution, Pa. m 3 / mol; H i o , Henry constant for the absorption of CO 2 in water, Pa. m 3 / mol; Ha, Hatta number; k L 0 , liquid side mass transfer (without chemical reaction) coefficient, m/s; k L= E k L 0 , liquid side mass transfer with chemical reaction coefficient, m/s; k ov , pseudo- first order reaction rate constant, s -1 ; N, rotation rate, s -1 ; n i , number of moles of i; P, total pressure, Pa; P i , partial pressure of the gas i, Pa; P v , vapor pressure of the solution, bar; R, gas constant (8.314 Pa m 3 / mol); Re, Reynolds number; Sc, Schmidt number; Sh, Sherwood number; T, temperature, K; t, time, s; V g , gas phase volume, m 3 ; β, the slope in the equation (3), s -1 ; ρ L, liquid density, kg/ m 3 ; µ L, liquid viscosity, Pa s; µ, viscosity of water, Pa s. References Abu-Zahra M.R.M., Schneiders L.H.J., Niederer J.P.M., Feron P.H.M., Geert F., (2007), CO 2 capture from power plants. Part I. A parametric study of the technical performance based on monoethanolamine, International Journal of Greenhouse Gas Control, 1, 37- 46. Abu-Zahra M.R.M., Niederer J.P.M., Feron P.H.M., Versteeg G.F., (2007), CO 2 capture from power plants. Part II. A parametric study of the economic performance based on monoethanolamine, International Journal of Greenhouse Gas Control, 1,136- 142. Amararrene F., Bouallou Ch., (2004), Kinetics of carbonyl sulfide absorption with aqueous solutions of 560
Kinetics of carbon dioxide absorption into aqueous solutions of 1, 5, 8, 12- tetraazadodecane (APEDA) diethanolamine and methyldiethanolamine, Ind. Eng. Chem. Res., 43, 6136-6141. Bello A., Idem R.O., (2005), Pathways for the formation of products of the oxidative degradation of CO 2 loaded concentrated aqueous MEA solutions during CO 2 absorption from flue gases, Ind. Eng. Chem. Res., 44, 945- 969. Dallos A., Altsach T., Kotsis L., (2001), Enthalpies of absorption and solubility of carbon dioxide in aqueous polyamine solutions, J. Thermal Analaysis and Calorimetry, 65, 419- 423. Hilliard M.D., (2005), Dissertation Proposal, University of Texas at Austin, 1-27. Kohl A.L., Nielsen R., (1997), Gas Purification, 5th ed., Gulf Publ.Corp., Texas, 250-281. http://www.chemicalland21.com/arokorhi/specialtychem/fi nechem/1,5,8,12-TETRAAZADODECANE. Siminiceanu I., (2004), Procese chimice gaz- lichid, Editura Tehnopres, Iasi, 180- 288. Siminiceanu I., Tataru-Farmus R.E., Amann, J.-M., (2006), Kinetics of carbon dioxide bsorption into aqueous solutions of etilenediamine, Buletinul Inst. Polit. Iaasi, Tom 52, 1-2, Chim. Ing. Chim., 45- 50. Strazisar B.R., Anderson R.R., White C.M., (2003), Degradation pathways for MEA in a CO 2 capture facility, Energy Fuels, 17, 1034- 1039. Sun W.-C., Yong C.-B., Li M.-H., (2005), Kinetics of the absorption of carbon dioxide into mixed aqueous solutions of 2- amino- 2- methyl- 1- propanol and piperazine, Chem. Eng. Sci., 60, 503- 516. Tanthapanichakoon W., Veawab A., McGarvey B., (2006), Electrochemical investigation of the effect of heat stable salts on corrosion in CO 2 capture plants using aqueous solution of MEA, Ind. Eng. Chem. Res., 45, 2586- 2593. Tataru- Farmus R.E., Siminiceanu I.,Bouallou Ch., (2007), Carbon dioxide absorption into new formulated amine solutions (I), Chemical Engineering Transactions, 12, 175- 181. Thitakamol B., Veawab A., Aroonwilas A., (2007),Environmental impacts of absorption- based CO 2 capture unit for post- combustion treatment of flue gas from coal fired power plant, International Journal of Greenhouse Gas Control, 1, 318- 342. Versteeg G.V., van Swaaij W.P.M., (1988), Solubility and diffusivity of acid gases (CO 2 , N 2 O) in aqueous alkanolamine solutions, J. Che. Eng. Data, 33, 29- 34. 561
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November/December 2007 Vol.6 No. 6
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