Study on the Activity of New Amine Based Absorbents for CO 2 Absorption from Flue Gases

1. Study on the Activity of New Amine Based Absorbents for CO2 Absorption from Flue Gases Gomes, J. F. P., Costa, J.J., Bordado, J.C. IBB – Institute for Biotechnology and Bioengineering, Centre for Biological and Chemical Engineering, Instituto Superior Técnico, Av. Rovisco Pais, 1049-001 Lisboa, Portugal E-mail: jgomes@deq.isel.ipl.pt Introduction The capture of CO2 from flue gases can be done by chemical absorption with aqueous amine solutions like MEA (monoethanolamine). Although this is a proven process, there are still operational problems to overcome [1], namely those resulting from solvent degradation, precipitation, corrosion and foaming. Also, the absorption capacity of the most current amines must be improved in order to obtain a more profitable operation. It has been shown previously that relationships exist between the amine structure and the activity/capacity for CO2 absorption. The introduction of amine substituents at the α-carbon creates a carbamate instability, which causes the hydrolysis to go faster, thus increasing the amount of bicarbonate, allowing for higher CO2 loadings. In order to obtain a better understanding of the structure-activity relationship, laboratory studies have been made comprising solvent screening experiments investigating the effect of variables such as chain length, increase in number of functional groups, side chain at α-carbon position, alkyl group position in cyclic amine and side effect of cyclic amine with different functional groups. The description of these effects, in a quantitative way, on the initial rate of absorption for CO2, as well as the capacity of various solvents for CO2 absorption is also supported by simulation using ASPEN/HYSYS and it is believed to benefit on the design of more efficient absorption systems for CO2 capture from flue gases. Results and Discussion Using this pilot facility we were able to test different absorbing amine solutions in order to assess the best combination of solvents to be used for CO2 absorption: the CO2 concentration, after the absorption column. The total maximum capacity of CO2 absorption was then measured in terms of mol CO2/mol amine and the obtained results are as follows: Optimised operation parameters Flowsheet of pilot installation For simulation purposes the use of an absorbing aqueous solution of methanolamine (MEA), 30% (wt) was considered. The thermodynamic properties used were the ones contained in the Kent-Eisenberg package. The simulation was performed in order to obtain the main optimal operation characteristics for study the CO2 absorption from the gaseous effluent generated from the power plant. Therefore, considering the base operation parameters, the following optimised operation parameters were obtained: These results clearly show that the reactivity of the amine absorbing solutions are greatly dependent of the amine structure. In fact, this seems to be related with the increase in the number of functional groups: an increase in the number of amine groups from 1, as in ethylamine, to 2 in ethylenediamine, results in a moderate increase of 18% in absorption capacity. A much more significant absorption capacity increase can be noticed when the number of amine groups is increased to 3, as in diethylenetriamine, where the absorption capacity increases by 70%. From 3 to 4 it only increases about 32%. Conclusions The obtained early results are promising in what regards the search for more efficient absorbents for CO2 capture from flue gases. This study is only partial as it considered only the absorption of CO2 in an absorption column thus lacking the regeneration of the absorbing solution in the stripping column, that is to be tested at a later stage. Further tests will include the determination of absorption/stripping cycle characteristics for real gaseous effluents instead of simulated gases. This experimental set-up will provide important information for process optimization such as data on amine solution degradation as well as corrosion characteristics. References Greer, T., Bedelbayev, A., Igreja, J., Gomes, J.F.P., Lie, B., “A simulation study on the abatement of CO2 emissions by de-absorption with monoethanolamine”, Environmental Technology, 31(1), 107-155 (2010) Costa, J.J., “Projecto e simulação de uma instalação para estudo da absorção de CO2 com soluções de aminas”, Tese de Mestrado, ISEL, 2010 Flowsheet of the process used in HYSYS simulation