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2007_6_Nr6_EEMJ

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Environmental Engineering and Management Journal November/December 2007, Vol.6, No.6, 555-561 http://omicron.ch.tuiasi.ro/EEMJ/ “Gh. Asachi” Technical University of Iasi, Romania ______________________________________________________________________________________________ KINETICS OF CARBON DIOXIDE ABSORPTION INTO AQUEOUS SOLUTIONS OF 1, 5, 8, 12- TETRAAZADODECANE (APEDA) Ilie Siminiceanu 1∗ , Ramona-Elena Tataru-Farmus 1 , Chakib Bouallou 2 1 Technical University “Gh. Asachi” of Iaşi, Faculty of Chemical Engineering, 71 Bd. Mangeron, RO- 700050 Iaşi, Romania 2 Ecole Nationale Supérieure des Mines de Paris, Centre d’Energétique (CENERG), 60 Bd. Saint Michel, 75006 Paris, France Abstract 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. The rate constant derived from the experimental data (k ov , s -1 ) was correlated through the Arrhenius plot ( ln k ov = A- B/T), and the optimal values of the constants A and B were obtained by the linear regression. The absorption of CO 2 from flue gas into APEDA solution is a promising process for practical application at least from the kinetic point of view. 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. Key words: acid gas absorption, Lewis cell absorber, enhancement factor, rate constant 1. Introduction The removal of carbon dioxide from gas streams by selective absorption into aqueous solutions is an important industrial process in both natural gas sweetening and ammonia synthesis gas production. Aqueous hot potassium carbonate promoted by diethanolamine (DEA) is the chemical solvent used in the ammonia plants of Romania. Today, there are seven such ammonia plants in Romania (each of 1000 t NH 3 / day) where the absorption is operated at 30- 40 bar, 343 K, solution with 25- 30 % K 2 CO 3 and 1-2 % DEA, in packed columns. The carbon dioxide, recovered by the reverse reaction (1) in the stripping column, is then consumed in the reaction (2) with ammonia, to produce urea- the best nitrogen fertilizer (Siminiceanu, 2004). CO 2 + K 2 CO 3 + H 2 O = 2 KHCO 3 (1) CO 2 + 2 NH 3 = CO (NH 2 ) 2 + H 2 O (2) The question is: could be this process applied with the same high performances as in ammonia production to the capture of carbon dioxide from combustion flue gas of the fossil fuel power plants? Unfortunately, the answer is no. This is because the flow rates, composition, temperature and pressure of flue gas are different. The CO 2 partial pressure in the flue gas is much lower then in ammonia synthesis gas. It is of maximum 15 kPa. Therefore, more reactive absorbents are needed, like monoethanolamine (MEA) aqueous solution. The absorption of CO 2 into MEA solution is also a well established process (Kohl and Nielsen, 1997). It has been already applied in the only three industrial plants in the world for CO 2 capture from fossil fuel power plant flue gas (Abu- Zahra et al., 2007a; 2007b). They have the commercial names Econamine FG, Econamine FG Plus, and ABB Lumnus, respectively. The simplified flow diagram of such a process is presented in Fig.1.After the removal of NO x and SO x ∗ Author to whom all correspondence should be addressed: isiminic@ch.tuiasi.ro

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