Formation of a Ca 12 Al 14 O 33 Nanolayer and Its Effect on the Attrition Behavior of CO 2 -Adsorbent Microspheres Composed of CaO Nanoparticles

Ind. Eng. Chem. Res. 2010, 49, 12269 12275 12269 Formation of a Ca 12 Al 14 O 33 Nanolayer and Its Effect on the Attrition Behavior of CO 2 -Adsorbent Microspheres Composed of CaO Nanoparticles Su F. Wu* and Ming Z. Jiang Department of Chemical and Biological Engineering, Zhejiang UniVersity, Hangzhou 310027, China The attrition behavior of microspheres composed of CaO nanoparticles that were used as high-temperature CO 2 -reactive adsorbents was investigated. The nano-cao/al 2 O 3 microsphere adsorbents were prepared by a spray technique from a slurry containing a precursor of CaCO 3 nanoparticles and an aluminum oxide gel. A mechanism of formation of the layer of nano-ca 12 Al 14 O 33 was proposed and optimized, with calcination temperatures ranging from 900 to 1000 C and Ca/Al molar ratios between 2.3 and 3.5. The attrition behavior of the adsorbent was investigated in detail using the air jet method to measure fine loss, as well as with scanning electron microscopy and a particle size analyzer to examine the changes in surface morphology and particle size distribution. The attrition studies showed that complete formation of a Ca 12 Al 14 O 33 nanoscale framework under calcination temperatures ranging from 900 to 1000 C and Ca/Al molar ratios between 2.3 and 3.5 resulted in improved resistance to attrition and increased durability of the reactive sorption capacity of the adsorbent. 1. Introduction CaO-based CO 2 adsorbents with high reactive sorption capacities have been widely studied in the capture of CO 2 from flue gas 1-4 and the reactive sorption-enhanced reforming (ReSER) process. 5-7 A continuous operation of CaO carbonations and CaCO 3 calcinations needs a cycling system, and a cycling fluidized bed reactor system with high efficiency is desirable. However, under the fluidized bed operation conditions, the severe mechanical degradation caused by the motion and collisions of the sorbent particles must be considered. Recently, a number of studies concerning the attrition of limestone-based CO 2 adsorbents in a fluidized bed have been reported. 8-10 The study concluded that natural sorbents such as limestone and dolomite have severe attrition problems. Johnsen et al. 11 compared the attrition resistance of two natural CaO-based sorbents (limestone and dolomite). Their studies concluded that dolomite was an inferior attrition-resistant adsorbent compared to limestone because of its loose structure and low. To improve the attrition resistance of the adsorbent, a synthetic method was introduced to prepare CaO-based CO 2 adsorbent. Binders, such as SiO 2,Al 2 O 3, and SiO 2 - and Al 2 O 3 - containing natural materials (e.g., kaolin and diatomite), were introduced. SiO 2 is commonly used as a binder in Fischer- Tropsch catalysts to improve their strength. 12,13 However, few studies have been conducted on CaO-based CO 2 adsorbents because the mobile phase leads to the adhesion of sorbent particles at high temperatures (greater than 800 C). Alternatively, a number of studies have shown that the CaO/Al 2 O 3 adsorbent has better attrition resistance properties as a CO 2 adsorbent than nonaluminum CaO-based particles. 14,15 Pacciani et al. 16 studied the synthetic CaO/Al 2 O 3 binary sorbent system and its performance in a fluidized bed. The CaO/Al 2 O 3 sorbent system was found to provide relatively high strength due to the formation of mayenite (Ca 12 Al 14 O 33 ). The CaO/Al 2 O 3 adsorbent system is known to have the ability to form a variety of compounds under different conditions with distinct properties. 17 * To whom correspondence should be addressed. E-mail: wsf@ zju.edu.cn. Tel.: +86-571-87953138. Fax: +86-571-87953735. The effect of the composition on the attrition resistance of adsorbents is not clear; similarly, attrition mechanisms are not well understood. A number of studies have shown that particle attrition in a fluidized bed is caused by two mechanisms: abrasion and fragmentation. 18 Results indicate that particle properties such as, framework intensity, and pore channel structure 12,13,19,20 strongly affect the attrition resistance of synthetic CaO-based sorbents. However, no study has been undertaken to understand the abrasion and fragmentation mechanisms. We examined a nano-cao-based adsorbent that has preferable CO 2 sorption properties compared to the micro-cao/al 2 O 3 system. 21 In this study we experimentally examined the formation mechanism of nano calcium aluminate and its effects on the microstructure and attrition behavior of the resulting CO 2 - adsorbent microspheres composed of CaO nanoparticles. In this study we aimed to understand the attrition of the sorbent by analyzing both its abrasion and fragmentation characteristics. 2. Experimental Section Nano calcium carbonate powder (Zhejiang Linghua Co. Ltd.) was mixed in different molar ratios with deionized water and aluminum oxide gel (Zhejiang Yuda Co. Ltd.) in a beaker to form a slurry. The slurry was spray-dried at 150 C to create sorbent microspheres with an average particle size of 60-80 µm. The sorbent was calcined to decompose the CaCO 3 nanoparticles into CaO nanoparticles. The preparation conditions of each sorbent, the Ca/Al molar ratios, and the calcination temperatures are shown in Table 1. The s were kept in the dryer at 45 C until use. The names listed in Table 1 are based on the preparation conditions. For example, in CA-5-8, CA represents the fact that the adsorbent contains calcium and aluminum, 5 represents that the mass concentration of CaCO 3 in the is 50%, and 8 represents the calcination temperature of 800 C. This naming system is used with the other s. The design of the attrition test device was established on the basis of ASTM D5757-95 22 and ref 12. Our setup size was the same as described in ASTM D5757-95. Additionally, in our experiments, 20 g of was used, the feed flow was 5 L/min, and the attrition 10.1021/ie901561e 2010 American Chemical Society Published on Web 10/26/2010

12270 Ind. Eng. Chem. Res., Vol. 49, No. 23, 2010 Table 1. List of Preparative Conditions for the Adsorbents Ca/Al molar ratio calcination temp, C Ca/Al molar ratio calcination temp, C CA-5-8 a 1.5 800 CA-7-9 3.5 900 CA-5-9 1.5 900 CA-8-9 6.0 900 CA-6-8 2.3 850 CA-8-10 6.0 1000 CA-6-9 2.3 900 CA-9-9 13.6 900 CA-6-10 2.3 1000 CA-9-10 13.6 1000 a For example, CA-5-8, in which 5 suggests that the mass concentration of CaCO 3 in the is 50% and 8 represents the calcination temperature of 800 C, was designed with a Ca/Al molar ratio of 1.5. This format is used with the other s. Figure 2. XRD patterns of the different s as a function of the Ca/Al molar ratios (12CA represents Ca 12 Al 14 O 33, and 3CA represents Ca 3 Al 2 O 6 ). Figure 1. Scheme of the formation mechanism of the sorbent structure. test time was 1 h. The air was maintained at moisture levels of 60 ( 5% to avoid electrostatic effects. The fine powder produced the attrition test was collected and weighed, and the fine loss was defined and calculated using the following equation: fine lost ) mass of fines collected at the downstream filter/20 g 100 (1) In addition, we measured the recovery ratio: recovery ratio ) (mass of sorbent particles collected attrition + mass of fines collected at the downstream filter)/20 g 100 (2) The volume mean particle size (VMPS) before and attrition testing was determined with a Mastersizer 2000 particle size analyzer (Malvern Instruments) and was used to calculate the decrease in VMPS: decrease in VMPS ) (APS before attrition - APS attrition)/aps before attrition 100 (3) where APS is the average particle size. Thermogravimetric analysis (TGA) (Pyris1, Perkin-Elmer) was used to measure the reactive sorption capacity. The crystalline phases of the components of the adsorbent were determined with X-ray diffraction (XRD) (D/MAX-RA, Rigaku, Japan). The morphology of the adsorbent was investigated using scanning electron microscopy (SEM) (S-4800, Hitachi, Japan). The Ca and Al contents were measured by energy-dispersive X-rayanalysis(EDX)(EX350,HORIBA,Japan).TheBrunauer-Emmer-Teller (BET) surface area and Barrett-Joyner-Halenda (BJH) desorption average pore diameter analyses were conducted by nitrogen physisorption in liquid N 2 using a Micromeritics ASAP 2020 apparatus. 3. Results and Discussion 3.1. Formation of the Nano-Ca 12 Al 14 O 33 Layer. The proposed process of formation of the CaO/Al 2 O 3 nanoparticle sorbents is shown in Figure 1. The microsphere sorbent was prepared with the method described in the Experimental Section. Initially, the CaCO 3 is surrounded by Al 2 O 3. After 1 h of calcination at 700 C, the CaCO 3 nanoparticles had fully decomposed into CaO nanospheres. This process led to shrinking of single nanoscale CaCO 3 granules. Due to the stability of Al 2 O 3 under high-temperature conditions, a random spacing channel formed between Al 2 O 3 and CaO was generated by the release of CO 2 during decomposition of CaCO 3. After 1 h of calcination at higher temperatures, the tangential surface of CaO nanoparticles began to react with the surrounding Al 2 O 3 to form a nanoscale calcium aluminate layer. 3.2. Factors Affecting the Formation of a Nanoscale Ca 12 Al 14 O 33 Layer. Ca 12 Al 14 O 33 can be generated at a temperature of 900 C by the reaction of small particles of CaCO 3 and amorphous Al 2 O 3. 23 Figure 2 illustrates that, in the case of the CaO/Al 2 O 3 nanoparticles used in this research, the sorbent composition remained as CaO and amorphous Al 2 O 3, and no calcium aluminate formed when the calcination temperature was 800 C. However, when the temperature was increased to over 900 C, calcium aluminate in one of two forms, Ca 12 Al 14 O 33 or Ca 3 Al 2 O 6, was formed. The calcium aluminate was formed according to the following reactions: 12CaO + 7Al 2 O 3 f Ca 12 Al 14 O 33 (4) 3CaO + Al 2 O 3 f Ca 3 Al 2 O 6 (5) Figure 2 shows that the type of calcium aluminate formed depends on the Ca/Al molar ratio, with Ca 3 Al 2 O 6 forming at a Ca/Al molar ratio of 13.6 and Ca 12 Al 14 O 33 forming at a Ca/Al molar ratio of less than 13.6. When the temperature is above 900 C, no Al 2 O 3 crystal is detected, and the type of calcium aluminate that forms does not vary with the Ca/Al molar ratio. The peak heights in Figure 2 represent the amount of calcium aluminate in each adsorbent and show that the calcium aluminate content increases with an increase in calcination temperature and Ca/Al molar ratio. This behavior is caused by the generation of more calcium aluminate by the solid reaction at higher temperatures and larger Ca/Al molar ratios. The surface morphologies of the fresh adsorbent and calcined adsorbent at different temperatures are shown in Figure 3. Figure 3a indicates that, the spray-drying process, each CaCO 3 nanoparticle is coated with Al 2 O 3, and the nanospheres have a particle size of approximately 100 nm. The coated nanograins are symmetrically assembled. After calcination at 900 C (Figure 3b), the Al 2 O 3 has reacted with the CaO nanoparticles to form calcium aluminate. The microspheres of CaCO 3 nanoparticles coated with an Al 2 O 3 layer have reacted and formed a crosslinked framework of calcium aluminate with a larger particle size. The CaO nanograins are embedded in the interior of the

Ind. Eng. Chem. Res., Vol. 49, No. 23, 2010 12271 Table 2. Surface Area and Average Pore Size of Different Adsorbents surface area, m 2 g -1 av pore diam, nm fresh sorbents before calcination 65.41 9.3 CA-6-9 14.13 13.1 CA-6-10 12.41 6.4 from 9.3 to 13.1 nm. A possible reason for this increase in pore size is the decomposition of the CaCO 3 nanoparticles. However, in the case of CA-6-10, the pore size decreased from 9.3 to 6.4 nm, and the surface area decreased from 65.41 to 12.41 m 2 /g. While the pore size changed slightly, the most obvious change was the decrease in surface area. Figure 4 shows that the fresh sorbents without calcination have a large pore volume. After calcination at 900 and 1000 C, the pore volume in both s CA-6-9 and CA-6-10 decreased. All remaining pores are less than 60 nm. A possible reason for this phenomenon is the formation of calcium aluminates, which would cover part of the pore, thereby decreasing the surface area without affecting the pore size greatly. 3.3. Factors Affecting Attrition Resistance. As discussed in section 3.2, the calcination temperature and Ca/Al ratio strongly affect the formation of calcium aluminate and influence the pore size. We expected that they would similarly affect the attrition performance of the sorbent. Attrition is caused by abrasion (characterized by fine loss) and fragmentation (characterized by a decrease in VMPS). The results of the particle attrition evaluations are shown in Tables 3 and 4. The recovery ratios are all greater than 98%, indicating that the test results are credible. First, when a Ca/Al molar ratio was fixed, we found that fine loss is associated with the calcination temperature. Table 3 Figure 3. (a) SEM image of the fresh spray-dried sorbent before calcination. (b) SEM image of CA-6-9 calcination at 900 C. (c) SEM image of CA-6-10 calcination at 1000 C. calcium aluminate framework, and the shape of each CaO nanograin can be distinguished. The porous channels generated by the decomposition of CaCO 3 can also be observed. After calcination at 1000 C (Figure 3c), the framework of calcium aluminate was clearly observed to be highly agglomerated. However, individual coated CaO particles could not be easily identified. Table 2 shows the surface area and pore size of the adsorbents obtained under different calcination temperatures. After calcination at 900 and 1000 C, we obtained s CA-6-9 and CA- 6-10, respectively. The surface area of the adsorbent CA-6-9 decreased from 65.41 to 14.13 m 2 /g. The pore size increased Figure 4. Pore size distributions of different sorbent s: fresh sorbents (without calcination), CA-6-9, and CA-6-10. Table 3. Attrition Test Results with Various Calcination Temperatures fine lost, wt % recovery ratio, % VMPS, µm decrease in VMPS attrition, % before CA-6-8 3.90 98.5 62.08 14.93 0.94 0.71 CA-6-9 2.09 99.1 62.08 10.15 0.94 0.97 CA-6-10 1.55 98.7 62.08 20.82 0.94 0.95 CA-9-9 11.93 98.3 79.41 19.29 0.88 0.72 CA-9-10 9.21 99.2 79.41 28.06 0.88 0.75

12272 Ind. Eng. Chem. Res., Vol. 49, No. 23, 2010 Table 4. Attrition Test Results with Various Ca/Al Molar Ratios fine loss, wt % recovery ratio, % VMPS, µm decrease in VMPS attrition, % before CA-5-9 5.90 97.8 59.90 15.24 0.94 0.78 CA-6-9 2.09 99.1 62.08 10.15 0.94 0.97 CA-7-9 2.14 98.2 61.53 10.91 0.95 1.06 CA-8-9 3.85 98.2 65.34 12.11 0.96 0.91 CA-9-9 11.93 98.3 79.41 19.29 0.88 0.72 shows the attrition data of the adsorbent microspheres prepared with different calcination temperatures. When the Ca/Al molar ratio was fixed at 2.3, the fine loss decreased from 3.90% (CA- 6-8) to 1.55% (CA-6-10) as the calcination temperature increased from 800 to 1000 C. However, the VMPS reached a minimum calcination at 900 C (10.15%, CA-6-9), indicating that fragmentation is minimized at this calcination temperature. When the Ca/Al molar ratio was fixed at 13.6, the fine loss decreased from 11.93% (CA-9-9) to 9.21% (CA-9-10) and the VMPS increased from 19.29% (CA-9-9) to 28.06% (CA-9-10) when the calcination temperature increased from 900 to 1000 C, as shown in Table 3. The greatest resistance to fragmentation occurred at a calcination temperature of 900 C. These results can be explained by the formation and aggregation of a calcium aluminate nanolayer, which enhanced attrition resistance. Second, the effect of different Ca/Al molar ratios on particle attrition is shown in Table 4. Table 4 illustrates that fine loss was lowest (2.09%, CA-6-9) when the Ca/Al molar ratio was 2.3 and was similar (2.14%, CA-7-9) when the Ca/Al molar ratio was 3.5. The decrease in VMPS showed the same trend. The particles had the largest decrease in VMPS at Ca/Al ratios of 2.3 (10.15%, CA-6-9) and 3.5 (10.91%, CA-7-9). When the ratio was below 2.3 or greater than 3.5, both the fine loss and VMPS increased sharply. These results indicate that both abrasion and fragmentation are at levels that result in optimal particle properties when the Ca/Al molar ratio is between 2.3 and 3.5. Figure 5 provides further insight into the attrition test results, by showing the changes in particle morphology before and attrition at different Ca/Al molar ratios. Both abrasion and fragmentation appear in the CA-5-9 sorbent. The CA-6-9 contains particles that are more rounded than those in the CA- 5-9 sorbent, and less fragmentation is observed the attrition test. The small surface holes of the CA-6-9 particles indicate that abrasion is the main cause of its fine loss. The CA-8-9 particle showed some fragmentation, and the CA-9-9 particle was agglomerated with little cohesion. After the attrition test, the CA-9-9 particles broke into fines, showing no basic physical strength. The calcium aluminate structure of the particle is the main factor affecting attrition performance. When the Ca/Al molar ratio is between 2.3 and 3.5, Ca 12 Al 14 O 33 forms and is the main component of the framework of the sorbent because the physical strength of Ca 12 Al 14 O 33 is greater than that of the Al 2 O 3 crystal. When the Ca/Al molar ratio is greater than 3.5, Ca 3 Al 2 O 6 forms. Although Ca 3 Al 2 O 6 is stronger than Ca 12 Al 14 O 33, the amount of calcium aluminate is not enough to support the whole particle as a total structural framework. The increasing amount of CaO nanogranules would have little effect in binding the particle, resulting in severe attrition. Finally, particle is another factor affecting attrition resistance that should be discussed independently. As shown in Tables 3 and 4, a minor change in particle was Figure 5. SEM micrographs of the different sorbent particles before and attrition. Figure 6. Fine loss of the adsorbents as a function of the sorbent. observed calcination. Figure 6 illustrates the trend of particle fine loss relative to particle. The s covered are listed in Tables 3 and 4 except CA-6-8. The CA- 6-8 sorbent was not taken into account because it contains mainly Al 2 O 3. Interestingly, fine loss decreases with an increase in. However, when the is above 0.95, the fine loss remains constant. Entrainment has been recognized as a disrupting phenomenon in the fluidized bed attrition test. When it occurs, the microparticles contained in the test flow directly to the

Ind. Eng. Chem. Res., Vol. 49, No. 23, 2010 12273 Figure 7. Comparison of the particle size distribution of the sorbents (CA- 7-9) before and attrition, as well as the fine powder generated by attrition. Figure 9. Reactive sorption capacity of s treated at different calcination temperatures: (a) Ca/Al molar ratio 2.3, (b) Ca/Al molar ratio 13.6. Figure 8. Comparison of the particle size distribution of the sorbents (CA- 9-9) before and attrition, as well as the fines collected attrition. collection tube, resulting in a misunderstanding of the test results. Figures 7 and 8 showed the distribution of s CA- 7-9 and CA-9-9 and fine powder collected in the tube. The particle size of the fine powder is approximately 6-7 µm, and the particle size of the prepared before attrition is greater than 20 µm. From this result, we can conclude that the fine powder is formed by abrasion and not by entrainment. 3.4. Effect on Sorption Capacity. The TGA results showed that adsorbent attrition resistance changes not only with the variation in Ca/Al molar ratio and calcination temperature, but also with the reactive sorption capacity. As seen in Figure 9a, when the Ca/Al molar ratio is 2.3, the reactive sorption capacity of the tenth cyclic run decreases with increasing calcination temperature: CA-6-8, 1.2 mol/kg; CA-6-9, 1.1 mol/kg; CA-6-10, 0.4 mol/kg. In Figure 9b, when the Ca/Al molar ratio is 13.6, the reactive sorption capacity of the tenth cyclic run also decreases with increasing calcination temperature: CA-9-9, 3.0 mol/kg; CA-9-10, 1.8 mol/kg. Although the reactive sorption capacity decreased with an increase in the calcination temperature, adsorbents that were calcined at higher temperatures had greater reactive sorption capacities due to the formation and aggregation of calcium aluminate. Figure 10. Reactive sorption capacity of s with different Ca/Al molar ratios treated at a calcination temperature of 900 C (carbonate temperature 600 C, regeneration temperature 750 C). Figure 10 illustrates 10 runs the increase in reactive sorption capacity from 0.7 to 3.1 mol/kg when the Ca/Al molar ratio was increased as the content of CaO increased. 3.5. Attrition Mechanism Analysis. As discussed previously, calcium aluminate and CaO nanoparticles are the main components of the adsorbent. Figure 11a show SEM-EDX images of CA-6-9 attrition. The SEM-EDX analytic results shown in Figure 11b,c and Table 5 contain a comparison of the quantities of various elements. Analysis of the content of the particle surface (area B) and the fracturing surface attrition (area C) provides direct evidence as to how the microspheres are broken down during attrition. The amount of Al is greater than the amount of Ca on the intact particle surface (area B), as shown in Figure 11b. In contrast, the amount of Al is much less than that of Ca on the fractured surface (area C), as shown in Figure 11c. The proportion of CaO on the fractured

12274 Ind. Eng. Chem. Res., Vol. 49, No. 23, 2010 calcination at higher temperatures leads to severe fragmentation and attrition. When the Ca/Al molar ratio is between 2.3 and 3.5, Ca 12 Al 14 O 33 is the main component of the sorbent framework. CaO nanocrystallites steadily fill the spaces in the Ca 12 Al 14 O 33 particle, preventing breakage of the CaO nanoparticles. Because Ca 12 Al 14 O 33 provides the main support for the adsorbent particle, the resistance to attrition, in terms of both abrasion and fragmentation, is at its greatest at this molar ratio range. The main cause of fine loss is abrasion, which provides better attrition resistance in the available Ca/Al molar ratios. 4. Conclusions A Ca 12 Al 14 O 33 nanolayer formation mechanism has been introduced in which CaCO 3 nanoparticles and Al 2 O 3 form calcium aluminate adsorbents calcination. The framework improves the strength of the entire sorbent particle. The type of calcium aluminate that is formed depends strongly on the Ca/Al molar ratio during preparation and less strongly on the calcination temperature. Ca 12 Al 14 O 33 is formed when the Ca/ Al molar ratio ranges from 2.3 to 3.5 at a calcination temperature of 900 C. Ca 12 Al 14 O 33 played an important role in strengthening the sorption performance by limiting fine loss and improving the reactive sorption capacity. The attrition of the adsorbent primarily occurred in regions composed of CaO. Acknowledgment We are grateful for support from Sinopec of China, the National Science Foundation of China (Grant No. 20876142), and the State 863 High Technology R&D Project of China (Grant No. 2009AA05Z104). Literature Cited Figure 11. (a) SEM-EDX images of CA-6-9 attrition. (b) SEM-EDX image of the particle surface (marked area B in Figure 8a). (c) SEM-EDX image of the inner pore surface of the particle (marked area C in Figure 8a). Table 5. Elemental Content (atom %) by SEM-EDX elements area B area C Ca, K 17.06 25.51 Al, K 11.46 4.19 O, K 57.19 57.47 C, K 14.30 12.84 surface (area C) is higher than on the intact particle surface (area B). These results indicate that attrition occurred because of breakage of CaO, and CaO is the weakest component of the sorbent particle. As Figure 11 shows, the attrition mechanism is strongly linked to the composition and framework structure of the sorbent particle. First, calcination at a high temperature provides the binding strength and determines the crystalline form of the particle, but provides little attrition resistance. On the other hand, (1) 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, 4035. (2) MacKenzie, A.; Granatstein, D. L.; Anthony, E. J.; Abanades, J. C. Economics of CO 2 Capture Using the Calcium Cycle with a Pressurized Fluidized Bed Combustor. Energy Fuels 2007, 21, 920. (3) Shimizu, T.; Hirama, T.; Hosoda, H.; Kitano, K.; Inagaki, M. A Twin Fluid-Bed Reactor for Removal of CO 2 from Combustion Process. Chem. Eng. Res. Des. 1999, 77, 62. (4) Abanades, J. C.; Anthony, E. J.; Jin, H. W. Fluidized Bed Combustion Systems Integrating CO 2 Capture with CaO. EnViron. Sci. Technol. 2005, 39, 2861. (5) Harrison, D. P. Sorption-Enhanced Hydrogen Production: A Review. Ind. Eng. Chem. Res. 2008, 47, 6486. (6) Johnsen, K.; Ryu, H. J.; Grace, J. R.; Lim, J. Sorption-Enhanced Steam Reforming of Methane in a Fluidized Bed Reactor with Dolomite as CO 2 Acceptor. Chem. Eng. Sci. 2006, 61, 1195. (7) Johnsen, K.; Grace, J. R.; Elnashaie, S. S. E. H.; Kolbeinsen, L.; Eriksen, D. Modeling of Sorption-Enhanced Steam Reforming in a Dual Fluidized Bubbling Bed Reactor. Ind. Eng. Chem. Res. 2006, 45, 4133. (8) Jia, L.; Hughes, R.; Lu, D.; Anthony, E. J.; Lau, I. Attrition of Calcining Limestones in Circulating Fluidized-Bed Systems. Ind. Eng. Chem. Res. 2007, 46, 5199. (9) Montagnaro, F.; Salatino, P.; Scala, F.; Chirone, R. An Assessment of Water and Steam Reactivation of a Fluidized Bed Spent Sorbent for Enhanced SO 2 Capture. Powder Technol. 2008, 180, 129. (10) Lu, D. Y.; Hughes, R. W.; Anthony, E. J. Ca-Based Sorbent Looping Combustion for CO 2 Capture in Pilot-Scale Dual Fluidized Beds. Fuel Process. Technol. 2008, 89, 1386. (11) Johnsen, K.; Grace, J. R. High-Temperature Attrition of Sorbents and a Catalyst for Sorption-Enhanced Steam Methane Reforming in a Fluidized Bed Environment. Powder Technol. 2007, 173, 200. (12) Zhao, R.; Sudsakorn, K.; Goodwin, J. G., Jr.; Jothimurugesan, K.; Gangwal, S. K.; Spivey, J. J. Attrition Resistance of Spray-Dried Iron F-T Catalysts: Effect of Activation Conditions. Catal. Today 2002, 71, 319.

Ind. Eng. Chem. Res., Vol. 49, No. 23, 2010 12275 (13) Wei, D. G.; Goodwin, J. G., Jr.; Oukaci, R.; Singleton, A. H. Attrition Resistance of Cobalt F-T Catalysts for Slurry Bubble Column Reactor Use. Appl. Catal., A 2001, 210, 137. (14) 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, 1447. (15) Wu, S. F.; Beum, T. H.; Yang, J. I.; Kim, J. N. Properties of Ca- Base CO 2 Sorbent Using Ca(OH) 2 as Precursor. Ind. Eng. Chem. Res. 2007, 46, 7896. (16) Pacciani, R.; Müller, C. R.; Davidson, J. F.; Dennis, J. S.; Hayhurst, A. N. Synthetic Ca-Based Solid Sorbents Suitable for Capturing CO 2 in a Fluidized Bed. Can. J. Chem. Eng. 2008, 86, 356. (17) Mercury, J. M. R.; De Aza, A. H.; Pena, P. Synthesis of CaAl 2 O 4 from Powders: Particle Size Effect. J. Eur. Ceram. Soc. 2005, 25, 3269. (18) Ghariri, M.; Ning, Z.; Kenter, S. J. Attrition of Granular Solids in a Shear Cell. Chem. Eng. Sci. 2000, 55, 5445. (19) Magrini-Bair, K. A.; Czernik, S.; French, R.; Parent, Y. O.; Chornet, E.; Dayton, D. C.; Feik, C.; Bain, R. Fluidizable Reforming Catalyst Development for Conditioning Biomass-Derived Syngas. Appl. Catal., A 2007, 318, 199. (20) Zhu, W. H.; Yin, Y. F.; Jiang, L. H.; Che, L. M. Study of Micro Pore Size Distribution and Its Effect on the Strength of Silica Fume Cement Paste. J. Build. Mater. 2004, 7, 14. (21) Wu, S. F.; Li, Q. H.; Kim, J. N.; Yi, K. B. Properties of a Nano CaO/Al 2 O 3 CO 2 Sorbent. Ind. Eng. Chem. Res. 2008, 47, 180. (22) ASTM D5757-95: Standard Test Method for Determination of Attrition and Abrasion of Powdered Catalysts by Air Jets; ASTM: West Conshohocken, PA, 1995. (23) Zhao, R.; Goodwin, J. G., Jr.; Oukaci, R. Attrition Assessment for Slurry Bubble Column Reactor Catalysts. Appl. Catal., A 1999, 189, 99. ReceiVed for review October 6, 2009 ReVised manuscript received September 13, 2010 Accepted October 1, 2010 IE901561E