Calcium oxide derived from different calcium precursors is emerged as one of the most potential candidates to trap CO2 and prevent its emission into the atmosphere [1–3], based on the reversible carbonation/calcination reaction, especially when the pilot scale facilities have been successfully demonstrated (1 MWt and 1.7 MWt) [4,5]. However, there are still problems for this tech- nology and one issue is the decline in sorbent carbonation capacity with the number of cycle which affects the process economics [6]. Sintering of the sorbents is believed to be the major cause of deactivation due to the great expansion and shrinkage of crystal struc- ture of CaO created during the calcination–carbonation process, resulting in structure collapse as evidenced by the change of sor- bent surface texture, i.e., the loss of suitable pore volume after sev- eral cycles [7,8]. Therefore, it is the most important step for large scale application of calcium based sorbents for CO2 capture to solve the problems of rapid decline in CO2 capture capability.
Great effort has been done to maintain high reactivity of sorbents for CO2 capture by different methods [9–17], among which creating synthetic sorbents by adding supporting materials is regarded as one of the most effective ways to prepare high-performance CaO- based sorbents, attributed to the inert material acting as the frame- work and thus effectively reduced sintering of CaO sorbents during the multiple cycles [18]. The CaO–MgO absorbent was prepared by the co-precipitation method achieving excellent cyclic stability but
poor absorption capacity ($8–14 g CO2/100 g absorbent) under the mild calcination condition (carbonation: 90% CO2 at 700 C; calcina- tion: pure He at 700 C) [19]. CaO sorbents with 26 wt% MgO con- tent was made by physical mixing of Ca(CH3COO)2 with small MgO particles followed by high temperature calcination, gave as high as 53 wt% CO2 capacity after 50 cycles (carbonation: 100% CO2 at 758 C for 30 min; calcination: 100% He at 758 C for 30 min) [20]. A sorbent of 91 wt% CaO prepared by the sol–gel tech- nique using calcium acetylacetonate as the calcium precursor, achieved a high CO2 capture capacity of 0.51 gCO2/g sorbent after 30 cycles (carbonation: 40% CO2 at 750 C for 20 min; calcination: pure N2 at 750 C for 20 min) [21]. The CaO–Ca9Al6O18 developed with 90 wt% CaO, displayed a capacity of 0.59 gCO2/g sorbent after 35 cycles (carbonation: 15% CO2/N2 at 650 C for 30 min; calcina- tion: pure N2 at 800 C for 10 min) [22]. The CaO–La2O3 sorbent made by a sol–gel-combustion-synthesis (SGCS) method with a molar ratio of Ca to La of 10:1 displayed CO2 capture capacity of 0.44 gCO2/g sorbent after 20 cycles under the mild calcination of pure N2 at 850 C for 10 min [23]. The CaTiO3-coated nano-CaO- based CO2 sorbent via hydrolysis and calcination, achieved a perfor- mance of 5.3 mol/kg after 10 cycles (carbonation: 20% CO2 at 600 C; calcination: N2 at 750C) [24]. And the sorbent CaO/CaZrO3 (50:50 wt%) using flame spray pyrolysis to dope zirconia on CaO maintained 23% conversion after 100 cycles (carbonation: 100% CO2 at 700 C; calcination: pure He at 900 C) [25].
Unfortunately, almost all of these sorbents were investigated under the mild calcination conditions, without including steam in calcination atmosphere, neither the carbonation atmosphere, whose reference value is largely reduced. Actually, a general con- tent of 5–15% steam is contained in the combustion flue gas orig- inating from both the moisture and hydrogen found in coal or other carbonaceous fuels. Studies from Borgwardt reported that water vapor strongly catalyzed the sintering process of CaO and resulted in surface area reduction in CaO due to crystallite growth, agglomeration and closure of pores as well [26]. The sintering was reported affected more by differences in steam concentration at higher temperature during calcination of Ca(OH)2 (up to 1152 C) [27]. Studies also reported that steam could reactivate the spent CaO and result in an immediate increase in carrying capacity [28], but only a slight improvement in carbonation with steam in the calciner [29]. Donat et al. [30] presented the highest carbona- tion reactivity achieved with steam injected to both carbonator and calciner, better than that only at the same calcination condi- tions. Although there are some studies relating to steam effect on reactivity of natural limestone and spent CaO [26–30], the effect of steam on carbonation of sorbents with high reactivity has rarely been reported. It is quite necessary to better understand how steam affects the reactivity of the synthesized sorbents, since a great effort has been made to synthesize sorbents to reduce the decay in CO2 capture performance during multiple cycles.
In this work, calcium-based sorbents were developed by doping metal oxides through the sol–gel process based on orthogonal design. Metal oxides of high melting point such as MgO and MnO2 were chos
ได้มาจากสารตั้งต้นต่าง ๆ แคลเซียมแคลเซียมออกไซด์จะกลายเป็นหนึ่งในผู้ที่มีศักยภาพมากที่สุดเพื่อดักจับ CO2 และป้องกันการปล่อยสู่ชั้นบรรยากาศ [1-3], อิงปฏิกิริยา carbonation/เผา กลับ โดยเฉพาะอย่างยิ่งเมื่อสิ่งอำนวยความสะดวกระดับนำร่องได้รับเรียบร้อยแล้วแสดงให้เห็น (1 MWt และ 1.7 MWt) [4, 5] อย่างไรก็ตาม ยังมีปัญหานี้อมูลเทคโนโลยี และปัญหาหนึ่งคือ การลดลงของกำลังดูดซับ carbonation ด้วยหมายเลขของวงจรซึ่งมีผลต่อเศรษฐศาสตร์การ [6] เผาของ sorbents เชื่อว่าเป็นสาเหตุสำคัญของการปิดใช้งานเนื่องจากการขยายตัวที่ดี และการหดตัวของคริสตัล struc ture ของ CaO สร้างขึ้นในระหว่างกระบวนการเผา – carbonation ผลยุบโครงสร้างเป็นหลักฐานการเปลี่ยนแปลงของพื้นผิวสองอ เช่น การสูญเสียความกระชับรูขุมขนเหมาะหลัง sev eral รอบ [7.8] จึง มันเป็นขั้นตอนสำคัญที่สุดสำหรับแอพลิเคชันขนาดใหญ่ของ sorbents คะแนนแคลเซียมสำหรับจับ CO2 เพื่อแก้ปัญหาของการลดลงอย่างรวดเร็วในความสามารถในการจับ CO2พยายามทำการรักษาปฏิกิริยาสูงของ sorbents สำหรับจับ CO2 โดยวิธีอื่น [9-17], ซึ่งสร้าง sorbents สังเคราะห์ โดยเพิ่มวัสดุสนับสนุนถือว่าเป็นหนึ่งในวิธีที่มีประสิทธิภาพสูงสุดเพื่อเตรียมความพร้อมประสิทธิภาพสูง CaO - คะแนน sorbents ประกอบกับวัสดุเฉื่อยที่ทำหน้าที่เป็นกรอบการทำงาน และมีประสิทธิภาพลดลงจึง เผาของ CaO sorbents ในระหว่างรอบหลาย [18] สารดูดซับ CaO – MgO จัดทำ โดยวิธีการตกตะกอนร่วมบรรลุความเสถียรทุกรอบดี แต่poor absorption capacity ($8–14 g CO2/100 g absorbent) under the mild calcination condition (carbonation: 90% CO2 at 700 C; calcina- tion: pure He at 700 C) [19]. CaO sorbents with 26 wt% MgO con- tent was made by physical mixing of Ca(CH3COO)2 with small MgO particles followed by high temperature calcination, gave as high as 53 wt% CO2 capacity after 50 cycles (carbonation: 100% CO2 at 758 C for 30 min; calcination: 100% He at 758 C for 30 min) [20]. A sorbent of 91 wt% CaO prepared by the sol–gel tech- nique using calcium acetylacetonate as the calcium precursor, achieved a high CO2 capture capacity of 0.51 gCO2/g sorbent after 30 cycles (carbonation: 40% CO2 at 750 C for 20 min; calcination: pure N2 at 750 C for 20 min) [21]. The CaO–Ca9Al6O18 developed with 90 wt% CaO, displayed a capacity of 0.59 gCO2/g sorbent after 35 cycles (carbonation: 15% CO2/N2 at 650 C for 30 min; calcina- tion: pure N2 at 800 C for 10 min) [22]. The CaO–La2O3 sorbent made by a sol–gel-combustion-synthesis (SGCS) method with a molar ratio of Ca to La of 10:1 displayed CO2 capture capacity of 0.44 gCO2/g sorbent after 20 cycles under the mild calcination of pure N2 at 850 C for 10 min [23]. The CaTiO3-coated nano-CaO- based CO2 sorbent via hydrolysis and calcination, achieved a perfor- mance of 5.3 mol/kg after 10 cycles (carbonation: 20% CO2 at 600 C; calcination: N2 at 750C) [24]. And the sorbent CaO/CaZrO3 (50:50 wt%) using flame spray pyrolysis to dope zirconia on CaO maintained 23% conversion after 100 cycles (carbonation: 100% CO2 at 700 C; calcination: pure He at 900 C) [25].Unfortunately, almost all of these sorbents were investigated under the mild calcination conditions, without including steam in calcination atmosphere, neither the carbonation atmosphere, whose reference value is largely reduced. Actually, a general con- tent of 5–15% steam is contained in the combustion flue gas orig- inating from both the moisture and hydrogen found in coal or other carbonaceous fuels. Studies from Borgwardt reported that water vapor strongly catalyzed the sintering process of CaO and resulted in surface area reduction in CaO due to crystallite growth, agglomeration and closure of pores as well [26]. The sintering was reported affected more by differences in steam concentration at higher temperature during calcination of Ca(OH)2 (up to 1152 C) [27]. Studies also reported that steam could reactivate the spent CaO and result in an immediate increase in carrying capacity [28], but only a slight improvement in carbonation with steam in the calciner [29]. Donat et al. [30] presented the highest carbona- tion reactivity achieved with steam injected to both carbonator and calciner, better than that only at the same calcination condi- tions. Although there are some studies relating to steam effect on reactivity of natural limestone and spent CaO [26–30], the effect of steam on carbonation of sorbents with high reactivity has rarely been reported. It is quite necessary to better understand how steam affects the reactivity of the synthesized sorbents, since a great effort has been made to synthesize sorbents to reduce the decay in CO2 capture performance during multiple cycles.ในงานนี้ sorbents คะแนนแคลเซียมถูกพัฒนา โดยยาสลบโลหะออกไซด์ผ่านออกแบบกระบวนการโซลเจล โลหะออกไซด์ของจุดหลอมเหลวสูงเช่น MgO และ MnO2 ถูก chos
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