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Potential Synergy of Chlorine and Potassium, Sodium Elements in Carbonation Enhancement of CaO-Based Sorbents Yongqing Xu, Haoran Ding, Cong Luo, Ying Zheng, Qi Zhang, Xiaoshan Li, Jian Sun, and Liqi Zhang ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/acssuschemeng.8b01941 • Publication Date (Web): 23 Jul 2018 Downloaded from http://pubs.acs.org on July 30, 2018

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ACS Sustainable Chemistry & Engineering

Potential Synergy of Chlorine and Potassium, Sodium Elements in Carbonation Enhancement of CaO-Based Sorbents

Yongqing Xu,† Haoran Ding,† Cong Luo,∗,† Ying Zheng,† Qi Zhang,‡ Xiaoshan Li,† Jian Sun,†,§ and Liqi Zhang† † State Key Laboratory of Coal Combustion, School of Energy and Power Engineering, Huazhong University of Science and Technology, Wuhan 430074, P. R. China ‡ School of Energy and Power Engineering, Huazhong University of Science and Technology, Wuhan 430074, P. R. China § School of Energy and Mechanical Engineering, Nanjing Normal University, Nanjing 210042, P. R. China

Abstract: Calcium looping process is well regarded as one of the most prospective technologies for trapping CO2 from flue gas. However, the carbonation conversion of CaO derived from natural Ca-precursors decayed drastically during the long-term cycles. Doping has been considered as a promising method to improve the cyclic carbonation performance. But alkali salt, which derives from abundant natural sustainable resources such as seawater, saline, bittern deposit and so on, is regarded as low melting material that can hardly enhance the cyclic carbonation performance of ∗

C. L: tel,+86-27-87542417-301; fax,+86-27-87545526; e-mail, [email protected]

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the CaO-based sorbents. In this study, two common alkali salts, sodium- and potassium-, were doped to investigate the potential enhancing effect of alkali salt on CaO-based sorbents. The cyclic carbonation performance of those sorbents was tested in a simultaneous thermal analyzer (STA), and the enhancing mechanisms were illustrated by scanning electron microscope (SEM), X-Ray Powder Diffraction (XRD) and N2 physical absorption method. The results illustrated that KCl, NaCl and K2CO3 boosted the carbonation property of CaO markedly, while KOH, NaOH and Na2CO3 were detrimental to the sorbents. The synergistic effect of K+, Na+ and Cl- can improve the cyclic carbonation performance of CaO. After 50 cycles, the carbonation conversions of CaO modified by KCl or NaCl were about twice that of unmodified CaO. In general, the KCl and NaCl are promising dopants that can markedly enhance the carbonation property of CaO-based sorbents.

Keywords: calcium looping; cyclic carbonation; synergistic effect; potassium and sodium chlorides doping

Introduction The ever-increasing atmospheric CO2 concentration, which is principally caused by human activities, is regarded as a major contributor to global warming 1, and about a third of CO2 emissions are derived from the consuming of fossil fuels for power generation 2, 3. Nevertheless, because of the reason that renewable energy sources such as solar, biomass or wind still can hardly meet the huge energy needs for industrial 2 ACS Paragon Plus Environment

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production, the CO2 capture, usage and storage (CCUS) from fossil fuel-fired power plant should be urgently pursued 4-6. Absorption

7, 8

, adsorption

membranes separation

13, 14

9, 10

, chemical looping combustion (CLC)

and cryogenic distillation

15

11, 12

,

are well considered as

effective methods to isolate CO2 from atmosphere. Among them, Calcium looping (CaL)

16

, a typical absorption technique, has been considered as one of the most

important technologies for CO2 isolating. It is based on the reversible reaction between CaO and CO2 as illustrated in Figure 1. CO2 in flue gas is absorbed by CaO sorbents (transformed into CaCO3 in a carbonator) and then the CaO is regenerated from CaCO3 in a calcinator, where a pure CO2 steam is produced, which can be utilized or geological isolated. Compared to other absorption technologies, this technique consist of a host of inherent thermodynamic merits such as high CO2 capture capacity 17, abundant source 18, which attracted a number of researches.

Figure 1. schematic diagram of calcium looping (CaL) process.

But the major disadvantage of this technique is sintering of CaO occurred during the long-term high temperature reactions 19. Accordingly, the carbonation conversion of CaO sorbents underwent a sharp decrease with the increase of the number of carbonations

20

. Based on abundant experimental data under varied operating

conditions, Grasa and Abanades et al. 21 have formulated a semi-empirical formulas to assess the decay of carbonation conversion of CaO in repeated cycles, as illustrated in 3 ACS Paragon Plus Environment


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Eq. (1)

XN =

1 1 + kN 1− Xr

(1)

+ Xr

Where, X N represents the carbonation achieved after Nth carbonation, k represents the de-activation constant and X r represents the residual carbonation conversion after infinite number of cycles. Sintering is the primary reason for the drop of the carbonation conversion of CaO 22. Because of the fact that the reaction temperature (650~950 oC) is generally higher than the Tammann temperature of CaCO3 (approximately 529 oC), the CaO-based sorbents will sinter a lot over the long-term CaL cycles

23

. During the carbonation

process, the reduction of carbonation conversion rates of CaO is attributed to the generation of a product layer on the wall of pores within it, accordingly preventing ready gas-phase diffusion to intra-CaO for reaction. As Alvarez et al.

24

stated that

there is a critical thickness of product layer of CaCO3, which is accepted as 49 nm (±19% of standard deviation), when the kinetics of carbonation transferred to the slow product-controlled stage from the rapid reaction-controlled stage. Due to the sintering occurred during the high temperature reactions, the pore structure and specific surface area of CaO sorbents are spoiled with the increasing number of carbonation cycles 25. German and Munir et al.

26

put forward a sintering model to correlate the rates of

specific surface area decline in a nitrogen atmosphere, as shown in Eq. (2). (

S0 − S γ ) = K st S0


(2)

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Where γ represents a mechanism-derived parameter and K s is a sintering constant which grows-up exponentially with temperature ( min −1 ), t is the sintering time (min), S0 and S are specific surface areas before and after sintering. Coble et al

27

also proposed a semi-empirical model to predict the porosity

reduction during long-term sintering of CaO crystalline, as show in Eq. (3).

ε 0 − ε = k p ln(

t+a ) t0 + a

(3)

Where k p is a constant on diffusion, ε represents the porosity at time t , ε 0 and

t0 are initial porosity and time when grain shrinkage begins, a is a constant which is associated with the property of materials. A mass of fresh sorbent is still required due to the drop of carbonation conversion of the sorbents, which will add the cost of CaL system. Hence, recycling the waste sources has been proposed 28-33, and a host of technologies have also been developed for enhancing the carbonation conversion of the CaO-based sorbents, including acid-pretreatment 34, steam hydration 35, doping 36 or supporting 37, 38 with other inert oxides, multi-shelled CaO nanoparticles 40-42

39

, templated with pore forming materials

, screening of effective organic calcium precursor

43, 44

, development of advanced

preparation methods 39, 45, 46, optimizing of reaction conditions 47-49 and so on. Among these techniques, doping 36 has been considered as a cost-effective method to improve the carbonation performance. But alkali salt, which commonly derives from abundant natural sustainable resources such as seawater, saline, bittern deposit and so on, is regarded as low melting material that can hardly enhance the cyclic carbonation performance of the CaO-based sorbents. Nevertheless, in our previous work 5 ACS Paragon Plus Environment

50

, we


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have found that sea water hydrated lime-based sorbent achieved a carbonation conversion of 41.7% after 40 cycles, which was 140 % higher than that of unmodified limestone. However, the limestone and sea salt were mixture that failed to fully illustrate the effect of the alkali metal ions on the crystalline texture. In this study, several common alkali metals (sodium- and potassium-) were doped to investigate the enhancing effect of alkali salt and potential synergistic effect of chlorine and potassium, sodium elements in cyclic carbonation enhancement of CaO-based sorbents.

Experimental Section Materials and Sample Preparation All of the materials used in this work were analytical reagent (AR) purchased from Sinopharm Chemical Reagent Co., Ltd., Shanghai, China. The sorbents were prepared by the process which has been reported in our previous work

51

. 10 g of CaCO3

precursor was calcined at 850 oC, after that it was placed in 50 ml of salt solution which contains a given mass of alkali salt, and the mass ratio of alkaline salt to CaCO3 precursor was 2 wt.%. Then the milk-like mixture was stirred intensely for three quarters of an hour at 80 oC and next the mud-like mixture was dried at 100 oC for two days. Finally, the blocky mixture was ground and sieved to particles within the range of 0.2-0.3 mm. For the sake of description, the original CaCO3 precursor (analytical grade reagent) was named “CaCO3, AR” and the obtained doping sorbents were named as “XX/CaO” (“XX” is the doping materials). In addition, a sorbent 6 ACS Paragon Plus Environment

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hydrated by deionized water was prepared as a control group, which was named as “Hydrated CaO”.

Sorbent Testing The cyclic calcination/carbonation performance of these sorbents were tested in a simultaneous thermal analyzer (STA 2500 Regulus, Netzsch), and the testing principle was introduced in Figure S1. A measure crucible, loading of about 8 mg samples, was placed on the end of the measure holder, while another crucible was held on the end of the reference holder. A high sensitive analytical balance system and thermal analysis unit were connected with these two holders. To obtain the fresh CaO sorbents, the samples were heated to 850 oC under N2 (high pure, 99.999%) at 150ml/min before the cyclic CO2 capture testing. The cyclic carbonation and decarbonation testing conditions are shown in Table S1. The carbonation conversion of CaO sorbents is generally calculated as Eq. 4: Xn =

mn − m0 M CaO ⋅ × 100% m0 ⋅ b M CO2

(4)

Where X n represent the carbonation conversion of CaO, which reflects the reversibility of CaO in the sorbents, mn represent the mass of samples after Nth carbonation, m0 is the mass of samples after calcination, M CaO and M CO2 are molar mass of CaO and CO2, b is the content of CaO in fresh sorbent.

Results and Discussion Phase Transformation of Samples 7 ACS Paragon Plus Environment


During the process of sample preparation, the phase composition of the sorbents would change, and the phase composition and crystal structure parameters for samples were examined by polycrystalline X-ray diffraction technique (XRD, X'Pert PRO, PANalytical B.V.) with Cu Kα radiation. The precursor sorbents (CaCO3, AR) hold a complete calcite phase as shown in Figure 2(a). After hydration process, the sorbents transformed to Ca(OH)2 completely, as shown in Figure 2(b). Finally, fresh CaO sorbents have been produced after calcination stage, as shown in Figure 2(c).

Figure 2. XRD patterns of the sorbents during different preparation stages: a, calcium precursor; b, sorbents after hydration process; c, sorbents after calcination process. (1#, CaCO3; 2#, Ca(OH)2; 3#, CaO)

Cyclic Carbonation Performance of the Doped Sorbents The cyclic carbonation performance of the hydrated CaO, KCl doped CaO, NaCl doped CaO and the CaO derived from calcining the analytically pure CaCO3 were tested in the STA for 50 cycles, and the results were shown in Figure 3. The carbonation conversion of “CaCO3, AR” underwent a dramatic attenuation over 50 cycles, from 0.788 during the 1st carbonation to 0.180 during the 50th carbonation. While the hydrated CaO without doping materials showed better carbonation behavior than that of original CaCO3 precursor. The decay rates of carbonation conversion of “Hydrated CaO” was slower than that of “CaCO3, AR” over the initial 20 cycles, although the enhancement was still quite limited from a long-term perspective. 8 ACS Paragon Plus Environment

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However, when the samples doped with KCl and NaCl, they showed much higher carbonation conversion and better cyclic stability. The “KCl/CaO” and “NaCl/CaO” exhibited carbonation conversion of 0.620 and 0.468 respectively during the 1st cycle (slightly lower than that of “Hydrated CaO”), but shared almost the same attracting carbonation performance after 7 cycles. They kept carbonation conversions of about 0.35 after 50 carbonation/decarbonation cycles, which was roughly 96% and 70% higher than that of “CaCO3, AR” and “Hydrated CaO” separately.

Figure 3. Enhancing effects of potassium, sodium chloride on cyclic carbonation of CaO-based sorbents.

What precisely triggered off the enhancing carbonation conversion of the CaO sorbents? A CaCl2 doped CaO was also tested under the same condition to study the impact of Cl anion, as the results shown in Figure 4. Notably, the “CaCl2/CaO” behaved a much poorer carbonation performance over the 50 cycles. It showed a carbonation conversion of 0.373 during the 1st cycle, and the following 6 cycles witnessed a drastic decay of carbonation conversion, bottomed out at 0.049 during the 7th carbonation. After that, the carbonation conversion of it maintained a much lower level (about 0.12) over the following cycles. The result suggested that the Cl anion did harm to the cyclic carbonation for CaO sorbents, and the enhancing mechanism could be attributed to the effect of K cation and Na cation. 9 ACS Paragon Plus Environment


Figure 4. Enhancing effect of calcium chloride on cyclic carbonation of CaO-based sorbents.

To investigate the enhancing mechanism of K cation and Na cation to the cyclic carbonation of CaO-based sorbents, the authors have further tested the enhancing effects of various sodium salt and potassium salt with different anions. As Figure 5 illustrated that KCl and NaCl were two ideal dopants, but NaOH and KOH were detrimental to the carbonation conversion of CaO. The “NaOH/CaO” and “KOH/CaO” were even worse than the original precursor (CaCO3, AR). However, the enhancing effect of Na2CO3 differed extremely from that of K2CO3. The carbonation conversion of “Na2CO3/CaO” underwent a severe decay over 50 cycles, with the worst carbonation behavior; in contrast, the “K2CO3/CaO” kept an interesting carbonation performance during this repeated cycles. When modified by K2CO3, the carbonation conversion of the sorbents had endured a drastic decay over the first 10 cycles, bottomed out at 0.210, which followed by an ever-increasing of carbonation conversion and ended up with 0.319 during the 50th carbonation process. Hence, it can be speculated that Cl anion and K cation or Na cation exhibited a synergistic effect, accordingly showed a perfect enhancement. NaOH and KOH failed to enhance the carbonation conversion of CaO, however, K2CO3 can boost the carbonation conversion of CaO, and the optimal dopants are KCl and NaCl.


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Figure 5. Enhancing effects of potassium, sodium salts on cyclic carbonation of CaO-based sorbents.

Characteristics of the Sorbents after Repeated Reactions The microstructures of different calcined sorbents were analyzed by a field emission scanning electron microscope (FSEM, Nova NanoSEM 450) with 1000 kV of accelerating voltage. After 1st calcination, there is a wide variation in the microstructure and microtopography of these fresh CaO. The calcined fresh “CaCO3, AR” presented shapes of diamonds, with a large number of mesopores, as show in Figure 6(a)(magnified 10,000 times) and Figure 6(d)(magnified 50,000 times). The fresh “KCl/CaO” showed shapes of clumps (about a micron), with plenty of mesopores, as shown in Figure 6(b) and Figure 6(e). However, the fresh “CaCl2/CaO” revealed uniform nanoscale spheres, as shown in Figure 6(c) and Figure 6(f). It indicated that after hydration process, the microstructure and microtopography of these fresh sorbents underwent great change, accordingly altered the carbonation performances. Because of the various microstructures, the carbonation behaviors of these sorbents during the 1st carbonation may be different.

Figure 6. SEM images of different sorbents after 1st calcination: (a) and (d) “CaCO3, AR”; (b) and (e) “KCl/CaO”; (c) and (f) “CaCl2/CaO”.

After 50 cycles, the “CaCO3, AR” underwent a severe fusion of grains, as shown in 11 ACS Paragon Plus Environment


Figure 7(a); besides, the pores inside the grains got bigger and bigger as shown in Figure 7(d). However, when doped with KCl, the sorbent got rich macroporous structure during the long-term cycles, as illustrated in Figure 7(b), and the well-connected macropores might act as good scaffolds that suppress the fusion of grains, as shown in Figure 7(e), accordingly, kept a much higher carbonation conversion of “KCl/CaO”. By contrast, after 50th calcination, the “CaCl2/CaO” represented a porous and fluffy surface topography, as shown in Figure 7(c), but it pulverized seriously as shown in Figure 7(f) at higher magnification. The reaction is so complex at high temperatures that it is reasonable to examine the N2 physical absorption behavior of the calcined sorbents to further study the mechanism of KCl enhancing effect.


BET specific surface areas of these sorbents were tested by nitrogen physical absorption at -196 oC (3H-2000PS, Beishide Instrument Technology Co., Ltd.). Prior to the test, about 1g of sorbent was degassed at 200 oC for 3 hours, and the data of specific surface area were calculated based on Brunauer−Emmett−Teller (BET) model. The results were shown in Table 1. The fresh CaO derived from “CaCO3, AR” possessed the largest BET surface area, with 10.719 cm2/g, which was followed closely by fresh CaO derived from “Hydrated CaO”, with 10.322 cm2/g, while the 12 ACS Paragon Plus Environment

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“KCl/CaO” behaved the minimum surface area with 2.502 m2/g. After 30 cycles, the BET surface area of calcined “CaCO3, AR” decreased to 6.368 cm2/g, which was about 3 quarters larger than that of calcined “Hydrated CaO”; by contrast, the surface areas of calcined “KCl/CaO” and calcined “CaCl2/CaO” were 7.507 cm2/g and 5.131 cm2/g, ranking the second and the third, while the “KOH/CaO” sintered a lot, with only a specific surface area of 3.392 m2/g after the same cycles. The isothermal N2 adsorption/desorption profiles of these sorbents were shown in Figure 8. All the calcined samples have no turning point in the low pressure section (0-0.1, relative pressure), which illustrates weak interactions between adsorbents and adsorbate. With the increasing of relative pressure, the quantity of adsorption increases, which represents the N2 molecular filling process of pores inside the sorbent (except for the “Hydrated CaO” and “CaCO3, AR” after 30 cycles). Fresh CaO derived from “CaCO3, AR” and “Hydrated CaO” shows Ⅲ isotherm sorption behavior and hold notable H1 type hysteresis loops, which accord with the uniform pore model. However, after 30 cycles, the isotherm sorption curves of these two sorbents are so smooth that displays almost no pores. After 30 cycles, “CaCl2/CaO” illustrates H1 type hysteresis loops, while “KCl/CaO” shows H3 type of hysteresis loops, which is attributed to slit poles formed by several piled grains, just as show in SEM figures (Figure 7). In addition, owing to the accumulation of uniform grains and accordingly formed of different microstructure, the fresh CaO derived from “Hydrated CaO” displays larger hysteresis loops than that of “CaCO3, AR”. Because of the effect of K+ and Cl-, the porosities of 13 ACS Paragon Plus Environment


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“KCl/CaO” and “CaCl2/CaO” are much better than that of CaO without doping. Hydrated CaO without salt doping were much more vulnerable to sinter, but when doped with KCl, the “KCl/CaO” sorbents behaved much more stable of microstructure during long-term CO2 capture cycles. Besides, the CaCl2 doping could also retard sintering, Nevertheless, Cl anion failed to enhance the carbonation conversion of doped CaO. Hence, it can be proposed that due to the synergistic effect of K cation and Cl anion, the “KCl/CaO” sorbents can not only became more resistant to sinter, but also kept higher carbonation conversion than “CaCO3, AR” and “Hydrated CaO”, which was accordant with the mechanism of previous literature

52

that K+ has the ability of enhancing the gas-solid reactivity activity of CaO-based sorbents.

Figure 8. N2 isotherm adsorption/desorption curves of the calcined samples after various cycles.

In order to clarify the potential synergistic mechanism between potassium and chloride on enhancing the cyclic carbonation performance, the CO2-temperature programmed adsorption (TPA) and temperature programmed desorption (TPD) profiles were tested in the STA. Figure 9(a) presents the CO2-TPA curves of the different sorbents. After calcined completely, these fresh sorbents were heated with 20%CO2 from 50 oC to 900 oC at a heating rate of 10 oC/min. The results illustrated that the sorbents behaved better 14 ACS Paragon Plus Environment

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carbonation conversion as the temperature increasing from 400 oC to 750 oC. Limited by equilibrium thermodynamics, these sorbents decomposed rapidly when the temperature of the samples was higher than 800 oC. Nevertheless, the “KOH/CaO” behaved much better reactivity between 400 oC and 800 oC, especially it absorbed CO2 quickly from 400 oC to 500 oC, while other sorbents almost cannot react with CO2 at this temperature range. Figure 9(b) presents the TPD profiles of the different sorbents. The calcined fresh sorbents were carbonated at 650 oC for 6 hours with 20% CO2, after that they were cooled to 50 oC, and then these sorbents were heated with pure N2 at a heating rate of 10 oC/min from 50 oC to 900 oC. The results displayed that these sorbents began to decarbonation when the temperature higher than 600 oC, and the “CaCl2/CaO” behaved the fastest decomposition rate as the temperature increase, which was closely followed by “KOH/CaO”, while the “KCl/CaO” shared almost the same slowest decarbonation performance.

Figure 9. CO2-TPA and TPD profiles of the doped sorbents.

The sorbents were further tested to investigate the cyclic carbonation performance under lower carbonate temperatures and the results were shown in Figure 10. The conversion of “CaCO3, AR” spoiled rapidly over 50 cycles, from 0.343 during the 1st cycle to 0.104 during the 50th cycle, while “KOH/CaO” showed a much better carbonation behavior over the initial few cycles, which displayed a conversion of 15 ACS Paragon Plus Environment


0.468 during the 1st cycle, and the following several cycles witnessed a drastic attenuation. The “CaCl2/CaO” unfolded the worst carbonation conversion over the repeated cycles. However, the “KCl/CaO” showed a relatively higher and more stable carbonation property, which held a conversion of 0.149 after 50th cycles.

Figure 10. Cyclic carbonation performance of the sorbents under lower carbonate temperature. (550 oC carbonation, 15min; 850 oC decarbonation, 2min)

Hence, it can be speculated that potassium can enhance the carbonation rate of the doped sorbents in larger range of carbonation temperatures, while KOH failed to maintain the microstructure and the specific surface area of the sorbents as illustrated by the N2 physical adsorption methods. CaCl2 was detrimental to the carbonation conversion of CaO, but chloride did improve the stability of microporous structure and specific surface area. The synergism of potassium and chloride significantly enhanced the cyclic carbonation conversion and stability of the sorbents.

Conclusions This study investigated the enhancing effect of potassium salt, sodium salt on carbonation conversion rate of CaO sorbents. The enhancing effect followed the order KCl> NaCl> K2CO3. “Hydrated CaO” got slightly better carbonation performance than that of CaCO3 precursor, but KOH, NaOH and Na2CO3 were detrimental to its cyclic carbonation. Hence, not all potassium salt and sodium salt can improve the 16 ACS Paragon Plus Environment

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carbonation conversion of doped CaO. Cl anion doping can retard sinter, but spoil the carbonation activity of doped CaO. The synergistic effect of K+, Na+ and Cl- do boost the carbonate performance of CaO, and the carbonation conversions of CaO modified by KCl or NaCl are about twice that of unmodified CaO. In general, the KCl and NaCl are promising dopants that can markedly enhance the carbonation conversion of CaO sorbents.

Supporting Information Schematic diagram of the lab scale calcium looping system and the reaction conditions for carbonation/decarbonation Figure S1. Schematic diagram of the simultaneous thermal analysis (STA) system. Table S1. Reaction conditions for calcium looping.

Acknowledgements This work was supported by the National Natural Science Foundation, P. R. China (No. 51606076) and the Foundation of State Key Laboratory of Coal Combustion (FSKLCCB1705). The authors also acknowledge the “Analysis and Test Center” of Huazhong University of Science & Technology.

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Figure 1. schematic diagram of calcium looping (CaL) process.


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Figure 2. XRD patterns of the sorbents during different preparation stages: a, calcium precursor; b, sorbents after hydration process; c, sorbents after calcination process. (1#, CaCO3; 2#, Ca(OH)2; 3#, CaO)



Figure 3. Enhancing effects of potassium, sodium chloride on cyclic carbonation of CaO-based sorbents.


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Figure 4. Enhancing effect of calcium chloride on cyclic carbonation of CaO-based sorbents.



Figure 5. Enhancing effects of potassium, sodium salts on cyclic carbonation of CaO-based sorbents.


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Figure 8. N2 isotherm adsorption/desorption curves of the calcined samples after various cycles.



Figure 9. CO2-TPA and TPD profiles of the doped sorbents.


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Figure 10. Cyclic carbonation performance of the sorbents under lower carbonate temperature. (550 oC carbonation, 15min; 850 oC decarbonation, 2min)



Table 1. BET specific surface area of calcined samples after various cycles. Sample

BET specific surface area(m2/g)

CaCO3-AR after 0 cycles

10.719

Hydrated-CaO after 0 cycles

10.322

KCl/CaO after 0 cycles

2.502

CaCO3-AR after 30 cycles

6.368

Hydrated-CaO after 30 cycles

3.652

KCl/CaO after 30 cycles

7.507

CaCl2/CaO after 30 cycles

5.131

KOH/CaO after 30 cycles

3.392


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Potential synergy of Cl- and K+, Na+ in carbonation enhancement of CaO-based sorbents for CO2 isolating 673x356mm (120 x 120 DPI)

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Potential Synergy of Chlorine and Potassium and ... - ACS Publications

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