Energy & Fuels 2009, 23, 1093–1100
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Flame-Made Durable Doped-CaO Nanosorbents for CO2 Capture Hong Lu,† Ataullah Khan,† Sotiris E. Pratsinis,‡ and Panagiotis G. Smirniotis*,† Chemical and Materials Engineering Department, UniVersity of Cincinnati, Ohio 45221-0012, and Particle Technology Laboratory, Department of Mechanical and Process Engineering, ETH Zurich, CH-8092 Zu¨rich, Switzerland ReceiVed September 18, 2008. ReVised Manuscript ReceiVed NoVember 10, 2008
The present study deals with the design and development of novel calcium-oxide-based refractory sorbents synthesized by flame spray pyrolysis (FSP) for carbon dioxide capture. The FSP-derived sorbents inherently exhibit very large CO2 uptake capacity in the present investigation. Sorbents derived from conventional wet chemistry, possessing identical composition, were synthesized and evaluated. A wide range of refractory dopants (Si, Ti, Cr, Co, Zr, and Ce) were employed, aiming at developing sorbents with good mechanical strength. Among all of the doped CaO sorbents, Zr-doped CaO was found to exhibit the best CO2-capture performance under identical conditions of operation. To study the effect of Zr in depth and find out the optimal concentration of Zr needed in the CaO matrix, a series of Zr-incorporated CaO sorbents were synthesized by varying the relative composition of Zr in the CaO base matrix. The present studies suggest that Zr/Ca in the 3:10 atomic ratio results in the formation of the most robust nanosorbent for multicyclic operation. This sorbent retained, unchanged, its ability to capture CO2 during extended cycles. It also demonstrated excellent stability under operating in the presence of water vapor (10 vol %). The present paper represents two novel developments in the field of CO2 capture, first, the superiority of FSP process and, second, the role of ZrO2 dopant in improving the durability and robustness of the CaO-based sorbent.
1. Introduction Carbon dioxide emission into the atmosphere is widely believed to be an important contributor to global warming. To contain the greenhouse effect, the most viable solution is to find out cost-effective ways to capture and sequestrate CO2 before it is released into the atmosphere. Currently, the most common commercial technology to capture CO2 is amine-based absorption, but its application is limited to small scale (102 ton/ day) and low temperature (40-150 °C).1 Alternatively, these drawbacks can be overcome by using metal-oxide-based inorganic sorbents to capture CO2 selectively from flue gas streams. Suitable sorbents should exhibit fast carbonation and regeneration within the temperature range of 200-800 °C. To date, CaObased sorbents have been the most promising candidates for CO2 capture2-12 and are cost-effective.13,14 Capture of CO2 by * To whom correspondence should be addressed. Telephone: +1-513556-1474. Fax: +1-513-556-3473. E-mail:
[email protected]. † University of Cincinnati. ‡ ETH Zurich. (1) Bailey, D. W.; Feron, P. H. M. Oil Gas Sci. Technol. 2005, 60 (3), 461–474. (2) Abanades, J. C. Chem. Eng. J. 2002, 90 (3), 303–306. (3) Gupta, H.; Fan, L.-S. Ind. Eng. Chem. Res. 2002, 41 (16), 4035– 4042. (4) Ida, J.-I.; Lin, Y. S. EnViron. Sci. Technol. 2003, 37 (9), 1999– 2004. (5) Reddy, E. P.; Smirniotis, P. G. J. Phys. Chem. B 2004, 108 (23), 7794–7800. (6) Alvarez, D.; Abanades, J. C. Energy Fuels 2005, 19 (1), 270–278. (7) Manovic, V.; Anthony, E. J. EnViron. Sci. Technol. 2007, 41 (4), 1420–1425. (8) Martavaltzi, C. S.; Lemonidou, A. A. Microporous Mesoporous Mater. 2008, 110 (1), 119–127. (9) Li, Y. J.; Zhao, C. S.; Qu, C. R.; Duan, L. B.; Li, Q. Z.; Liang, C. Chem. Eng. Technol. 2008, 31 (2), 237–244. (10) Lu, H.; Reddy, E. P.; Smirniotis, P. G. Ind. Eng. Chem. Res. 2006, 45 (11), 3944–3949.
CaO sorbents is based on the reversible reactions between CaO and CO2, leading to the formation of CaCO3 as follows: CaO + CO2 T CaCO3
(1)
The capture efficiency for CaO-based sorbents is only limited by the equilibrium between CaO, CO2, and CaCO3, which allows for CO2 capture efficiency approximately 85%14 at high temperatures. Currently, a significant amount of research is being carried out to improve the performance of CaO-based sorbents by increasing porosity and stability. In the past, Gupta and Fan3 synthesized high-surface-area CaO sorbents from precipitated calcium carbonate (PCC). Recently, Smirniotis and his coworkers15 obtained high-performance CaO-based sorbents derived from different organometallic precursors. Some researchers16 promoted CaO sorbents by using additives, such as NaCl or Na2CO3, while others5 have improved the sorbent capacity by doping with alkali metals. Intermediate hydration treatment between consecutive carbonation and regeneration cycles17 was also employed by some researchers to improve CO2 capture capacity and enhance durability of CaO sorbents. However, the disadvantage associated with conventional CaO-based sorbents is that their real time performance decays with each passing (11) Florin, N. H.; Harris, A. T. Energy Fuels 2008, 22 (4), 2734–2742. (12) Florin, N. H.; Harris, A. T. Chem. Eng. Sci. 2008, 63 (2), 287– 316. (13) Abanades, J. C.; Grasa, G.; Alonso, M.; Rodriguez, N.; Anthony, E. J.; Romeo, L. M. EnViron. Sci. Technol. 2007, 41 (15), 5523–5527. (14) MacKenzie, A.; Granatstein, D. L.; Anthony, E. J.; Abanades, J. C. Energy Fuels 2007, 21 (2), 920–926. (15) Lu, H.; Khan, A.; Smirniotis, P. G. Ind. Eng. Chem. Res. 2008, 47 (16), 6216–6220. (16) Salvador, C.; Lu, D.; Anthony, E. J.; Abanades, J. C. Chem. Eng. J. 2003, 96 (1-3), 187–195. (17) Kuramoto, K.; Fujimoto, S.; Morita, A.; Shibano, S.; Suzuki, Y.; Hatano, H.; Lin, S. Y.; Harada, M.; Takarada, T. Ind. Eng. Chem. Res. 2003, 42 (5), 975–981.
10.1021/ef8007882 CCC: $40.75 2009 American Chemical Society Published on Web 12/29/2008
1094 Energy & Fuels, Vol. 23, 2009
cycle. On the basis of an empirical equation2 derived from the previous investigations, CaO carbonation conversion quickly decays quite rapidly to
