Environ. Sci. Technol. 2010, 44, 841–847
Calcium Precursors for the Production of CaO Sorbents for Multicycle CO2 Capture WENQIANG LIU,† NATHANAEL WL LOW,† B O F E N G , * ,† G U O X I O N G W A N G , ‡ A N D JOÃO C. DINIZ DA COSTA‡ School of Mechanical and Mining Engineering and School of Chemical Engineering, The University of Queensland, St Lucia, Qld 4072, Australia
Received August 9, 2009. Revised manuscript received December 6, 2009. Accepted December 6, 2009.
A screening of potential calcium precursors for the production of CaO sorbents for CO2 capture at high temperature was conducted in this work. The precursors studied include microsized calcium carbonate (CC-CaO), calcium hydroxide (CH-CaO), nanosized ( CCCaO > CaO160 nm-CaO > CF-CaO > CH-CaO > CG-CaO > CC70 nm-CaO. The conversion after 30-min carbonation was ranked as follows: CG-CaO > CA-CaO ≈ CCi-CaO > CL-CaO > CaO160 nm-CaO > CC-CaO > CF-CaO > CH-CaO > CC70 nm-CaO. The difference between the sorbents may be due to variance of the nucleation rates of CaCO3. It is interesting to note that CG-CaO has a shorter induction period compared to the other sorbents and it had the highest conversion of ∼88.6% after 30-min carbonation. The sudden change in conversion-time curve of CC-CaO has been attributed to the closure of small pores during carbonation (49). The observed difference in conversion could be due to the difference in the specific surface area and pore volume observed in different samples (listed in Table S1 of the Supporting Information). As expected, CG-CaO had the highest surface area of 16.96 m2/g, while CC70 nm-CaO had the smallest surface areas of 6.84 m2/g and smallest pore volumes of 28.97 × 10-3 cm3/g. Capture Capacity of CaO Sorbents during Multicycle Carbonation/Regeneration. Figure 1B shows the carbonation
FIGURE 1. Conversion of various CaO sorbents prepared from 9 precursors during the carbonation reaction (carbonation temperature 650 °C, time 30 min, in 15% CO2). A: first carbonation. B: second carbonation. The sorbents were calcined in 900 °C for 10 min in N2 before the second carbonation. curves of the CaO sorbents in the second cycle. The ranking of conversion was changed to be CG-CaO > CA-CaO > CCiCaO > CL-CaO > CaO160 nm-CaO > CC-CaO > CH-CaO > CF-CaO > CC70 nm-CaO for 1-min carbonation and CGCaO > CCi-CaO > CA-CaO > CaO160 nm-CaO > CL-CaO > CH-CaO > CC-CaO > CF-CaO > CC70 nm-CaO for 30-min carbonation. It is clear that the cyclic performance of the sorbents is different. Figure 2A shows 30-min conversions of the CaO sorbents over 9 cycles prepared from different precursors. All CaOs exhibited a decay of conversion with the number of carbonation/regeneration cycle except CG-CaO which exhibits an increase in conversion for the first four cycles, which was referred to as a self-reactivation phenomenon (47). Here CCCaO is used as a reference for comparison because it is the convenient source of CaO, whose property is similar to lime used in the power generation systems. It can be seen that the CaO sorbents obtained from the other sources except CFCaO showed a larger 30-min conversion than that of the reference at the ninth cycle. It is also interesting to note that CG-CaO, which maintained a high 30-min conversion of 83.8% at the ninth cycle, exhibited a significantly better cyclic performance than any other sorbents. CaO sorbents decomposed from the other three OMPs (calcium citrate tetrahydrate, calcium acetate hydrate and calcium L-lactate hydrate) also showed initially high conversion but followed by decay afterward. The 30-min conversions of these OMPs at the ninth carbonation cycle were reduced by ∼32%, ∼40%, and ∼53%, respectively. Both CaO160 nm-CaO and CC70 nm-CaO showed good resistance to capacity decay, and their conversions were reduced by ∼21% and ∼31% from the first
FIGURE 2. Variation of the carbonation conversion of various CaO sorbents with the number of carbonation/regeneration cycles (carbonation temperature 650 °C, carbonation time 30 min, in 15% CO2; regeneration temperature 900 °C, regeneration time 10 min, in 100% N2): A: 30-min carbonation, B: 1-min carbonation. to the ninth cycle, respectively. This suggests that the nanosized sorbents may have a special property to resist sintering and hence capacity decay. It is worth noting that although crystals and/or grains in other sorbents may also be nano-sized (e.g., ∼100 nm for CC-CaO crystals as shown in Figure 3C), they appear to be more vulnerable to sintering compared to nanosized particles. This may be because the spaces between these crystals and/or grains are smaller than those between nanosized particles. CaO160 nm-CaO has the second highest conversion of 58.1% at the ninth cycle. However, CC70 nm-CaO exhibited a low capability of CO2 capture even at the first cycle. The lower initial capture capacity of original CC70 nm-CaO was perhaps due to its 37.5% smaller BJH pore volumes compared to original CaO160 nm-CaO (Figure S2 and Table S1 of the Supporting Information). The 1-min conversions of the sorbents are also compared (in Figure 2B), and it was found that CG-CaO was still the best sorbent that maintained a high 1-min conversion of 65.9% at the ninth cycle. It was also interesting to find that the 1-min conversion of CG-CaO apparently increased with the increase in cycle number over the first 3 cycles and then slightly decreased. The decay in the reactivity of CC-CaO during multiple carbonation/regeneration cycles has been reported by many researchers (7-16), which was believed to be attributable to the decrease of reaction surface and pore volume as a result of sintering (7, 15). For example, the specific surface area and pore volume of CC-CaO after 9 cycles of carbonation/ regeneration was reduced by 49.5% and 52.9%, respectively, VOL. 44, NO. 2, 2010 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
9
843
FIGURE 3. Scanning electron microscope (SEM) images of CaO sorbents. A,C: fresh CC-CaO; B,D: CC-CaO after 9 carbonation/ regeneration cycles; E,G: fresh CG-CaO; and F,H: CG-CaO after 9 carbonation/regeneration cycles. Images A, B, E, F and C, D, G, H have the same scale bars, respectively. It might be worth noting that the carbon sticker is visible in images E, F, G, H. as shown in Table S1 of the Supporting Information. The sizes of fresh CC-CaO crystal (i.e., before the first cycle) were ∼100 nm, with many small pores between them (Figure 3C). The aggregation of crystals was clearly observed after 9 cycles of reaction/regeneration, and the size of the crystals was increased to be ∼200 nm with only small cracks between them (Figure 3D). Meanwhile, the volume of the pores of 900 °C), the sintering of CaO became more important, whereas with the presence of CO2, the as-produced carbonate, which has a lower melting temperature as previously discussed, at the surface of the CaO enhanced sintering during calcination (50). Decomposition Kinetics of Carbonated CG-CaO and CCCaO. The kinetics of thermal decomposition of carbonated CG-CaO after first carbonation reaction were also investigated in this work, in comparison to carbonated CC-CaO. The carbonated CG-CaO demonstrates a faster rate of decomposition reaction and therefore lower decomposition completion temperature of ∼780 °C, compared to 880 °C required for carbonated CC-CaO (Figure 4A), an aspect that would lead to lower cost of regeneration in realistic applications. All experimental data were found to be able to be fitted with a fourth order polynomial function (Figure 4B). The differential method with a pseudofirst-order kinetic equation was used to obtain the activation energy of the decomposition reaction and a value of 326 KJ/mol was found for carbonated CG-CaO and 216 KJ/mol for carbonated CC-CaO. The latter is close to the reported value of 216.7 KJ/mol for conventional calcium carbonate, which was obtained using the same method with the data collected under similar experimental conditions (46). The former is interestingly close to the value reported for ALOOH coated calcium carbonate (48). It is believed that the difference in activation energy between carbonated CG-CaO and carbonated CC-CaO is due to the less diffusional effects during decomposition of the carbonated CG-CaO because CG-CaO has an apparently more porous structure (Figure 2). Prediction of Conversion Decay of CG-CaO and CCCaO. Among available semiempirical equations, the one developed by Abanades and Alvarez (49) (XN ) fmN(1 - fw) + fw) best fit the data of conversion decay of CG-CaO. The
FIGURE 4. Decomposition of carbonated CG-CaO, in comparison to carbonated CC-CaO in the first cycle. A: weight loss of sorbent with increasing temperature; B: polynomial fitting of data for the decomposition of CaCO3 to CaO, C: Arrhenius plots of decomposition.
FIGURE 5. Decay of carbonation conversion with increasing number of cycle. Test conditions: carbonation temperature 650 °C in 15% CO2; calcination temperature 900 °C in N2 for CC-CaO and CGCaO, and calcination temperature 920 °C in 15% CO2 for CG-CaO(2). parameters of fm(0.97) and fw(0.23) were obtained based on the 48-cycle conversion data, and therefore it is expected VOL. 44, NO. 2, 2010 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
9
845
that CG-CaO has a residual carbonation conversion of 0.23 (Figure 5). For comparison, the residual carbonation conversion of CC-CaO was also calculated. It was found that the conversion decay of CC-CaO obeys the equation (XN ) 1/[1/ (1 - Xr) + kN] + Xr) developed by Grasa and Abanades (12). The deactivation constant (k ) 0.42) and the residual conversion (Xr ) 0.098) were obtained based on the 24-cycle conversion data. Therefore, CG-CaO is expected to have a much higher residual carbonation conversion after prolonged cycles, compared with CC-CaO. Interestingly, the predicted residue conversion (0.227) for the more severe calcination conditions of 920 °C in 15% CO2 was very close to the predicted value (0.23) for pure N2 in 900 °C.
Acknowledgments Financial support of the Australia Research Council (Discovery Project DP0770048) is gratefully acknowledged.
Supporting Information Available Four figures showing 1 min conversion of various CaO sorbents prepared from 9 precursors during the carbonation reaction; BJH Pore size distribution for the 9 original sorbents and CC-CaO and CG-CaO after 9 cycles; decomposition of OMPs to form CaO; and effect of experimental conditions on the CO2 capture capacity of CG-CaO. Two tables showing specific BET surface areas of various sorbents used; and decomposition temperatures at different steps and final mass loss for OMPs. This material is available free of charge via the Internet at http://pubs.acs.org.
Literature Cited (1) Herzog, H. What future for carbon capture and sequestration. Environ. Sci. Technol. 2001, 35 (7), 148A–153A. (2) Sun, P.; Grace, J. R.; Lim, C. J.; Anthony, E. J. Sequential capture of CO2 and SO2 in a pressurized TGA simulating FBC conditions. Environ. Sci. Technol. 2007, 41 (8), 2943–2949. (3) Gao, L.; Paterson, N.; Fennell, P.; Dugwell, D.; Kandiyoti, R. The zero emission carbon concept (ZECA): extents of reaction with different coals in steam/hydrogen, tar formation and residual char reactivity. Energy Fuels 2008, 22 (4), 2504–2511. (4) Lackner, K. S. A guide to CO2 sequestration. Science 2003, 300 (5626), 1677–1678. (5) Kuramoto, K.; Ohtomo, K.; Suzuki, K.; Fujimoto, S.; Shibano, S.; Matsuoka, K.; Suzuki, Y.; Hatano, H.; Yamada, O.; Shi-Ying, L.; Harada, M.; Morishita, K.; Takarada, T. Localized interaction between coal-included minerals and Ca-based CO2 sorbents during the high-pressure steam coal gasification (HyPr-RING) process. Ind. Eng. Chem. Res. 2004, 43 (25), 7989–7995. (6) Lin, S.; Harada, M.; Suzuki, Y.; Hatano, H. Hydrogen production from coal by separating carbon dioxide during gasification. Fuel 2002, 81 (16), 2079–2085. (7) Abanades, J. C. The maximum capture efficiency of CO2 using a carbonation/calcination cycle of CaO/CaCO3. Chem. Eng. J. 2002, 90 (3), 303–306. (8) Baker, R. The reversibility of the reaction CaCO3 to CaO plus CO2. J. Appl. Chem. Biotechnol. 1973, 23 (10), 733–742. (9) Chrissafis, K. Multicyclic study on the carbonation of CaO using different limestones. J. Therm. Anal. Calorim. 2007, 89 (2), 525– 529. (10) Feng, B.; An, H.; Tan, E. Screening of CO2 adsorbing materials for zero emission power generation systems. Energy Fuels 2007, 21 (2), 426–434. (11) Fennell, P. S.; Pacciani, R.; Dennis, J. S.; Davidson, J. F.; Hayhurst, A. N. The effects of repeated cycles of calcination and carbonation on a variety of different limestones, as measured in a hot fluidized bed of sand. Energy Fuels 2007, 21 (4), 2072–2081. (12) Grasa, G. S.; Abanades, J. C. CO2 capture capacity of CaO in long series of carbonation/calcination cycles. Ind. Eng. Chem. Res. 2006, 45 (26), 8846–8851. (13) Grasa, G. S.; Abanades, J. C.; Alonso, M.; Gonza´lez, B. Reactivity of highly cycled particles of CaO in a carbonation/calcination loop. Chem. Eng. J. 2008, 137 (3), 561–567. 846
9
ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 44, NO. 2, 2010
(14) Kato, Y.; Yamada, M.; Kanie, T.; Yoshizawa, Y. Calcium oxide/ carbon dioxide reactivity in a packed bed reactor of a chemical heat pump for high-temperature gas reactors. Nucl. Eng. Des. 2001, 210 (1-3), 1–8. (15) Sun, P.; Grace, J. R.; Lim, C. J.; Anthony, E. J. The effect of CaO sintering on cyclic CO2 capture in energy systems. AIChE J. 2007, 53 (9), 2432–2442. (16) Wang, J.; Anthony, E. J. On the decay behavior of the CO2 absorption capacity of CaO-based sorbents. Ind. Eng. Chem. Res. 2005, 44 (3), 627–629. (17) Lu, H.; Reddy, E. P.; Smirniotis, P. G. Calcium oxide based sorbents for capture of carbon dioxide at high temperatures. Ind. Eng. Chem. Res. 2006, 45 (11), 3944–3949. (18) Aihara, M.; Nagai, T.; Matsushita, J.; Negishi, Y.; Ohya, H. Development of porous solid reactant for thermal-energy storage and temperature upgrade using carbonation/decarbonation reaction. Appl. Energ. 2001, 69 (3), 225–238. (19) Baker, R. The reactivity of calcium oxide towards carbon dioxide and its use for energy storage. J. Appl. Chem. Biotechnol. 1974, 24 (4-5), 221–227. (20) Florin, N. H.; Harris, A. T. Reactivity of CaO derived from nanosized CaCO3 particles through multiple CO2 capture-and-release cycles. Chem. Eng. Sci. 2009, 64 (2), 187–191. (21) Lu, H.; Khan, A.; Smirniotis, P. G. Relationship between structural properties and CO2 capture performance of CaO-Based sorbents obtained from different organometallic precursors. Ind. Eng. Chem. Res. 2008, 47 (16), 6216–6220. (22) Dobner, S.; Sterns, L.; Graff, R. A.; Squires, A. M. Cyclic calcination and recarbonation of calcined dolomite. Ind. Eng. Chem. Proc. Des. Dev. 1977, 16 (4), 479–486. (23) Florin, N. H.; Harris, A. T. Preparation and characterization of a tailored carbon dioxide sorbent for enhanced hydrogen synthesis in biomass gasifiers. Ind. Eng. Chem. Res. 2008, 47 (7), 2191–2202. (24) Li, Z. S.; Cai, N. S.; Huang, Y. Y. Effect of preparation temperature on cyclic CO2 capture and multiple carbonation-calcination cycles for a new Ca-based CO2 sorbent. Ind. Eng. Chem. Res. 2006, 45 (6), 1911–1917. (25) Li, Z. S.; Cai, N. S.; Huang, Y. Y.; Han, H. J. Synthesis, experimental studies, and analysis of a new calcium-based carbon dioxide absorbent. Energy Fuels 2005, 19 (4), 1447–1452. (26) Silaban, A.; Narcida, M.; Harrison, D. P. Characteristics of the reversible reaction between CO2(g) and calcined dolomite. Chem. Eng. Commun. 1996, 146 (1), 149–162. (27) Harrison, D. P. Sorption-enhanced hydrogen production: A review. Ind. Eng. Chem. Res. 2008, 47 (17), 6486–6501. (28) Li, Y.; Zhao, C.; Chen, H.; Duan, L.; Chen, X. CO2 capture behavior of shell during calcination/carbonation cycles. Chem. Eng. Technol. 2009, 32 (8), 1176–1182. (29) Florin, N. H.; Harris, A. T. Screening CaO-based sorbents for CO2 capture in biomass gasifiers. Energy Fuels 2008, 22 (4), 2734–2742. (30) Gupta, H.; Fan, L. S. Carbonation-calcination cycle using high reactivity calcium oxide for carbon dioxide separation from flue gas. Ind. Eng. Chem. Res. 2002, 41 (16), 4035–4042. (31) Hughes, R. W.; Lu, D.; Anthony, E. J.; Wu, Y. Improved longterm conversion of limestone-derived sorbents for in situ capture of CO2 in a fluidized bed combustor. Ind. Eng. Chem. Res. 2004, 43 (18), 5529–5539. (32) Manovic, V.; Anthony, E. J. Steam reactivation of spent CaObased sorbent for multiple CO2 capture cycles. Environ. Sci. Technol. 2007, 41 (4), 1420–1425. (33) Manovic, V.; Lu, D.; Anthony, E. J. Steam hydration of sorbents from a dual fluidized bed CO2 looping cycle reactor. Fuel 2008, 87 (15-16), 3344–3352. (34) Li, Y.; Zhao, C.; Qu, C.; Duan, L.; Li, Q.; Liang, C. CO2 capture using CaO modified with ethanol/water solution during cyclic calcination/carbonation. Chem. Eng. Technol. 2008, 31 (2), 237– 244. (35) Li, Y.; Zhao, C.; Chen, H.; Liang, C.; Duan, L.; Zhou, W. Modified CaO-based sorbent looping cycle for CO2 mitigation. Fuel 2009, 88 (4), 697–704. (36) Li, Y.; Zhao, C.; Chen, Duan, L.; Liang, C.; Li, Q.; Zhou, W.; Chen, H. Cyclic calcination/carbonation looping of dolomite modified with acetic acid for CO2 capture. Fuel Process. Technol. 2008, 89 (12), 1461–1469. (37) Li, Y.; Zhao, C.; Chen, H.; Liu, Y. Enhancement of Ca-based sorbent multicyclic behavior in Ca looping process for CO2 separation. Chem. Eng. Technol. 2009, 32 (4), 548–555. (38) Feng, B.; Liu, W.; Li, X.; An, H. Overcoming the problem of loss-in-capacity of calcium oxide in CO2 Capture. Energy Fuels 2006, 20 (6), 2417–2420.
(39) Martavaltzi, C. S.; Lemonidou, A. A. Development of new CaO based sorbent materials for CO2 removal at high temperature. Micropor. Mesopor. Mater. 2008, 110 (1), 119–127. (40) Martavaltzi, C. S.; Lemonidou, A. A. Parametric study of the CaO-Ca12Al14O33 synthesis with respect to high CO2 sorption capacity and stability on multicycle operation. Ind. Eng. Chem. Res. 2008, 47 (23), 9537–9543. (41) Pacciani, R.; Mu ¨ ler, C. R.; Davidson, J. F.; Dennis, J. S.; Hayhurst, A. N. Synthetic Ca-based solid sorbents suitable for capturing CO2 in a fluidized bed. Can. J. Chem. Eng. 2008, 86 (3), 356–366. (42) Wu, S. F.; Li, Q. H.; Kim, J. N.; Yi, K. B. Properties of a nano CaO/ Al2O3 CO2 sorbent. Ind. Eng. Chem. Res. 2008, 47 (1), 180–184. (43) Li, Y.; Zhao, C.; Ren, Q.; Chen, H.; Chen, X. Effect of rice husk ash on CO2 capture behavior of calcium-based sorbent during calcium looping cycle. Fuel Process. Technol. 2009, 90 (6), 825– 834. (44) Li, Y.; Zhao, C.; Chen, H.; Duan, L.; Chen, X. Cyclic CO2 capture behavior of KMnO4-doped CaO-based sorbent. Fuel 2009, in press.
(45) Bathia, S. K.; Perlmutter, D. D. Effect of the product layer on the kinetics of the CO2-lime reaction. AlChE J. 1983, 29 (1), 79–86. (46) Loannou, Z.; Zoumpoulakis, L.; Halikia, I.; Teloniati, T. Overall kinetic study of non-isothermal decomposition of calcium carbonate. Trans. Inst. Min. Metall. C 2009, 118 (2), 98–104. (47) Manovic, V.; Anthony, E. J.; Grasa, G.; Abanades, J. C. CO2 looping cycle Performance of a high-purity limestone after thermal activation/doping. Energy Fuels 2008, 22 (5), 3258–3264. (48) Jin, D.; Yu, X.; Yue, L.; Wang, L. Decomposition kinetics study of AlOOH coated calcium carbonate. Mater. Chem. Phys. 2009, 115 (1), 418–412. (49) Abanades, J. C.; Alvarez, D. Conversion limits in the reaction of CO2 with lime. Energy Fuels. 2008, 17 (2), 308–315. (50) Glasson, D. Reactivity of lime and related oxides. VII crystal size variations in calcium oxide produced from limestone. J. Appl. Chem. 1961, 11 (6), 201–206.
ES902426N
VOL. 44, NO. 2, 2010 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
9
847
