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Activated Carbon for Capturing Hg in Flue Gas under O2/CO2 Combustion Conditions. Part B: Modeling Study and Adsorption Mechanism Hui Wang, Shen Wang, Yufeng Duan, Ya-ning Li, and Zhanfeng Ying Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.7b03381 • Publication Date (Web): 17 Jan 2018 Downloaded from http://pubs.acs.org on January 17, 2018

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Activated Carbon for Capturing Hg in Flue Gas under O2/CO2 Combustion Conditions. Part B: Modeling Study and Adsorption Mechanism Hui Wang*, a, b , Shen Wangc, Yufeng Duan*, b, Ya-ning Lib, Zhanfeng Ying a a

School of Energy and Power Engineering, Nanjing University of Science and

Technology, Nanjing, 210094, China. b

Key Laboratory of Energy Thermal Conversion and Control of Ministry of Education,

Southeast University, Nanjing, 210096, China. c

School of Chemical and Material Engineering, Nanjing Polytechnic Institute, Nanjing

210048, China. KEYWORDS. Mercury Adsorption; O2/CO2; Prediction; Kinetic Model

ABSTRACT: Based on the kinetic study with three kinetic models, this paper predicted mercury adsorption by activated carbon (AC) under O2/CO2 combustion atmosphere. Results showed that Bangham’s model, pseudo-second-order kinetic model, and Elovich model could describe the mercury sorption process by AC under both O2/N2 atmosphere and O2/CO2 atmosphere. The kinetic constant k1 was the highest at oxygen concentration

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of 8% under O2/N2 atmosphere but 4% under O2/CO2 atmosphere. The equilibrium adsorbed amount qe was larger under O2/N2 atmosphere than that under O2/CO2 atmosphere at the same oxygen concentration, and it exhibited great effects on the initial mercury adsorption rate α. Elovich model verified that the chemical adsorption of active sites was the rate of the control step in the mercury removal on the AC surface. All these results were very significant for mercury removal under oxy-fuel combustion atmosphere.

1. INTRODUCTION The combustion of the fossil fuels becomes the largest anthropogenic source of greenhouse gases and aggravates the increasing concerns of the greenhouse effects1, 2. It was reported that temperature of the earth’s surface could exceed the historical value in 20473. If the greenhouse gas emission continued to grow at the present rate, which would exhibit harmful effects on human health and environment4. Since CO2 is one of the main greenhouse gases, it is essential to develop new technologies for CO2 capture5. There are mainly three kinds of technologies6, namely pre-combustion technology, in-combustion (oxy-fuel combustion and chemical looping combustion) technology, and the post-combustion technology. The schematic diagram of the carbon capture and storage technologies7 is shown in Figure 1. The Canmet and Babcock& Wilcox company, Tsinghua University, Huazhong University of Science and Technology, Zhejiang University, Southeast University and other research institutes have conducted various researches on the oxy-fuel combustion S2


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technology8-11. Due to economic advantages, oxy-fuel combustion is recognized as one of the most promising technologies12. It was well known that mercury could pose a great threat to the human health and environment. Besides, Treharne RW13 indicated that gaseous mercury in the flue gas could destroy the CO2 storage unit in oxy-fuel combustion system, which might cause security problems. Based on the two aspects mentioned above, it was essential for studying the sorbent for mercury removal under oxy-fuel combustion atmosphere. Numerous researchers14-21 have concentrated on the sorbent on mercury removal under air combustion atmosphere. Qu et al.22 studied the mechanism of a novel regenerable sorbent for mercury capture. Gunugunuri K. Reddy et al.23 explored the mechanism of mercury removed by Mn-Ce-Ti sorbents by the X-ray photoelectron spectroscopy (XPS). Lu et al.24 displayed the mercury capture efficiency in the Mulberry twig chairs. Liu et al.25 reviewed the mercury control by the advanced oxidation process. For the mercury control under the oxy-fuel combustion atmosphere, there have been some reports26-29. C.Gómez-Giménez30 investigated mercury adsorption by an Au/C regenerable sorbent under oxy-fuel combustion atmosphere, and results showed that the mercury adsorption rate was over 90% by Au (0.1 wt%)/C. Zhao et al.31 studied the mercury control by the sorbent AC-I( AC modified by I2 vapor) under oxy-fuel combustion atmosphere. However, few scholars considered effects of oxygen concentration on mercury adsorption by AC under O2/CO2 combustion atmosphere, which should be further investigated. Besides, the kinetic study on the mercury adsorption by AC under air combustion atmosphere was reported32-34. A.Fuente-Cuesta et al.35 predicted the mercury adsorption S3


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process with Yoon-Nelson kinetic model. Hude et al.36 used the pseudo-first-order adsorption kinetic model to display the mercury sorption mechanism. However, prediction of mercury adsorption by AC under oxy-fuel combustion atmosphere was little. Thus, prediction of mercury adsorption process under O2/CO2 combustion atmosphere was necessary. The recent work (Part A)37 presented the mercury adsorption by AC under O2/CO2 combustion atmosphere in a fixed-bed reactor. In the recent experimental work (Part A), the total gas flow rate was 2000 ml/min, with the mercury vapor carrier gas, the Hg concentration and the AC sorbent of 200 ml/min, 40±1 µg/m3, and 200mg, respectively. The ultimate and structural analysis of the activated carbon was listed in Table S1. Besides, the experimental results of the recent work (Part A) were shown in Figure S1. Based on the kinetic study with three kinetic models, this paper predicted effects of oxygen concentration on the mercury adsorption by AC under O2/CO2 combustion atmosphere. All results under O2/CO2 combustion atmosphere were also compared to those under O2/N2 combustion atmosphere. 2. COMPUTATIONAL DATA AND PROCEDURE 2.1 Evaluation of Sorbents 2.1.1 Breakthrough Rate η. The breakthrough rate (η) was calculated by the following equation:

η=

0 Cout × 100% Cin0

Eq.1

Where, S4


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η was the breakthrough rate; Cin0 was the inlet mercury concentration of the reactor, µg/m3; Cout0 was the outlet mercury concentration of the reactor, µg/m3. 2.1.2 The Sorption Capacity. The sorption capacity of the sorbent at ‘t’ min (qt) was calculated by the following equation38 ti ct + cti +∆t t t  q t = ∫ [(c 0 − c ) V/ m]d τ = (V/ m) ∫ ( c 0 − c ) d τ ≈ (V/ m)∑  c0 − i 0 0 2 τ =0 

 ∆t 

Eq.2

Where, qt was the sorption capacity of sorbent at ‘t’ min, µg Hg/g sorbents; V was the volume flow rate of the simulated flue gas, m3/min; m was the mass of sorbent, g; ∆t was the time interval between two sampling points, min; t was the sorption time, min; cti was the mercury concentration at the i sampling point, µg/m3; cti +∆t was the mercury concentration at i+1 sampling point, µg/m3.

2.2 Adsorption Kinetic Models and Parameters. The sorbed Hg amount and the sorbed Hg rate were two key factors for estimating the mercury sorbent properties. Kinetic models could display the adsorption process. This paper adopted Bangham’s model, pseudo-second-order kinetic model, and Elovich model to explore the mercury adsorption mechanism. The Bangham’s Model was used to explore the pore diffusion39 with the following equation:

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dq q = Eq.3 dt mt Integrated by the boundary condition t = 0, q = 0; t = t, q = q , the above equation Eq.3 was transformed to

q = k1t

1

m

Eq.4

Where, q was the equilibrium absorbed amount, µg/g; t was the absorbed time, min; m was the physical parameter of Bangham kinetic equation; k1 was the kinetic constant of Bangham kinetic equation. The Pseudo-Second-Order Kinetic Model, derived from the Lagergren equation40, was used to study the chemical adsorption process with the following equation:

dq = k2 (qe − q) 2 Eq.5 dt Integrated by the boundary condition t = 0, q = 0; t = t, q = q , the above equation Eq.5 was transformed to

q = qe ×

qe ⋅ k2 ⋅ t 1 + qe ⋅ k2 ⋅ t

Eq.6

Where, qe was the equilibrium absorbed amount, µg/g; q was the equilibrium absorbed amount at ‘t’ time, µg/g; t was the absorbed time, min; k2 was the kinetic constant of pseudo-second-order kinetic equation, g/(µg·min). The Initial Mercury Absorption Rate α was derived from the pseudo-secondorder kinetic equation, with the expression as follows41:

α=

dqt = k2 qe2 dt

Eq.7

The Elovich Model, derived from the Temkin equation42, was used to study the chemical adsorption process with the following equation:

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dq = α e− β q Eq.8 dt Integrated by the boundary condition t = 0, q = 0; t = t, q = q , the above equation Eq.8 was transformed to q=

1

β

ln(t + t0 ) −

1

β

(t0 )

Eq.9

Where,

t0 = 1/ (α ⋅ β ) ; α was the initial mercury absorption rate, µg·(g·min1/2)-1; β was the kinetic constant of the Elovich model, g/µg; t was the absorbed time, min; qt was the equilibrium absorbed amount at ‘t’ time, µg/g.

3. RESULTS AND DISCUSSION In this paper, three kinetic models were used to explore the mercury adsorption mechanism by AC. The correlation coefficient (Rccb2, Rccp2, Rcce2) represented the difference between the experimental data and the calculated result of the Bangham’s model, the Pseudo-second order model and the Elovich model, respectively. A high value of R2 meant a good prediction of the kinetic model to the experimental data. If Rccb2 was the largest, it could be indicated that the major adsorption process was pore diffusion by the AC, which could be described by the Bangham’s mode; if Rccp2 was the largest, the major adsorption process followed the Langmuir isotherm equation used in the physisorption and chemisorption process, which could be described by the Pseudosecond order; if Rcce2 was the largest, the Temkin reaction used in the chemisorption process could predict the major sorption process, and the Elovich model could be applied

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to depict this process.

3.1 Kinetic Analysis of Mercury Uptake on AC by Bangham’s Model. Figure 3 and Figure 4 showed the fitting results of the equilibrium absorbed amount under O2/N2 and O2/CO2 atmosphere by Bangham’s model. The parameters involved were listed in Table 1. Figure 3 indicated a good agreement between the calculated results by the Bangham’s model and the experimental data. The correlation coefficient Rccb2 was higher than 0.998, which showed that Bangham’s model could describe the mercury sorption process by AC under O2/N2 atmosphere. The kinetic constant of Bangham kinetic equation k1 represented the adsorption rate, reflecting the sorbent performance directly. As shown in Table 1, k1 rose from 0.29902 to 0.35204 with the increased oxygen concentration, with a fluctuating value of 0.35881 at oxygen concentration of 8%, which indicated that oxygen concentration could affect the adsorption rate. k1 reached the highest value (0.35881) under O2/N2 atmosphere, which was consistent with results about the kinetic analysis of the mercury adsorption on the rice huck ash by Q Feng43. The kinetic analysis results by the Bangham’s model under O2/CO2 atmosphere were displayed in Figure 4, which displayed a good agreement between the calculated results by the Bangham’s model and the experimental data. The correlation coefficient Rccb2 was higher than 0.9992, which showed that the Bangham’s model could describe the mercury sorption process by the AC under O2/CO2 atmosphere. Besides, compared to O2/N2 atmosphere, the calculated results under O2/CO2 atmosphere were closer to the experimental data. As shown in Table 1, k1 decreased from 0.46210 to 0.34542 with the increased oxygen concentration with a fluctuating value of 0.30146 at the oxygen S8


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concentration of 8%, which indicated that the oxygen concentration could affect the adsorption rate, and k1 reached the lowest value (0.30146) at the oxygen concentration of 4% under O2/CO2 atmosphere.

3.2 Kinetic Analysis of Mercury Uptake on AC by Pseudo-Second-Order Kinetic Model. Figure 5 and Figure 6 showed the fitting results of the equilibrium absorbed amount under O2/N2 and O2/CO2 atmosphere by the pseudo-second-order kinetic model. The parameters involved were listed in Table 1. Figure 5 indicated that there was a good agreement between the calculated results by the pseudo-second-order kinetic model and the experimental data. The correlation coefficient Rccp2 was higher than 0.9996, which revealed that the pseudo-second-order kinetic model could describe the mercury sorption process44 under O2/N2 atmosphere. As shown in Table 1, the kinetic constant of pseudo-second-order kinetic equation k2 increased at first and then decreased with the increased oxygen concentration with a fluctuation at the oxygen concentration of 8%, which indicated that the oxygen concentration could affect the adsorption rate34. k2 reached the highest value at the oxygen concentration of 8% (2.14E-05 g/(µg·min)), and the lowest value at the oxygen concentration of 10% (1.33E-05 g/(µg·min)) under O2/N2 atmosphere. The equilibrium adsorbed amount qe increased from 108.166 to 140.551 with the increase of the oxygen concentration. For the oxygen concentration of 4% and 8%, qe was almost the same (109.395 µg/g at 4% O2, 108.166 µg/g at 8% O2). The highest value of qe was 140.551 µg/g at the oxygen concentration of 10%, whereas the lowest value was 108.166 µg/g at the oxygen concentration of 8%.

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From Figure 6, it could be found that there was a good agreement between the calculated curves by pseudo-second-order and experimental curves, and the correlation coefficient Rccp2 was higher than 0.9996. Thus, the pseudo-second-order kinetic model was suitable for both O2/N2 and O2/CO2 atmosphere. As shown in Table 1, k2 decreased at first and then increased with the increased oxygen concentration, with a fluctuation at the oxygen concentration of 8%. k2 reached the highest value at the oxygen concentration of 10% (2.45E-05 g/(µg·min)), and the lowest value at the oxygen concentration of 8% (1.06E-05 g/(µg·min)) under O2/CO2 atmosphere. The equilibrium adsorbed amount qe increased at first and then decreased with the increased oxygen concentration. The highest value of qe was 511.100 µg/g at the oxygen concentration of 8%, whereas the lowest value was 122.068 µg/g at the oxygen concentration of 4%, which was consistent with results by Q Zhou45. It also found that qe and k2 was larger under O2/N2 atmosphere than that under O2/CO2 atmosphere at the same O2 concentration (except at the oxygen concentration of 8%).

3.3 Kinetic Analysis of Mercury Uptake on AC by Elovich Model. 3.3.1 Effect of Oxygen Concentration on Initial Mercury Absorption Rate. The initial mercury adsorption rate α was one of the important parameters to evaluate the sorbent properties46. Because the time of the injected sorbent in the duct was less than 2s, α limited the highest mercury removal efficiency. Figure 7 showed the effects of the oxygen concentration on the initial mercury adsorption rate under both O2/N2 and O2/CO2 atmosphere. Under O2/N2 atmosphere, α increased with the increased oxygen concentration, whereas under O2/CO2 atmosphere, α S10


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decreased at first and then increased with the increased oxygen concentration, which indicated that the atmosphere exhibited great effects on the initial mercury adsorption rate α. From Figure 5-Figure 7, it could be found that the equilibrium adsorbed amount qe could also affect the initial mercury adsorption rate α.

3.1.2 Kinetic Analysis of Mercury Uptake on AC by Elovich Model. The fitting results by the Elovich model were displayed in Figure 8 and Figure 9, and the parameters α, β, and Rcce2 were listed in Table 1. Figure 8 illustrated a good agreement between the calculated results by the Elovich model and the experimental data. The correlation coefficient Rcce2 was higher than 0.9996, which revealed that the Elovich model could describe the mercury adsorption process47 by the AC under O2/N2 atmosphere and the chemical adsorption of active sites was the rate of the control step in the mercury removal on the AC surface under O2/N2 atmosphere. There was little difference in β with the variation of the oxygen concentration, which presented little relationship between the adsorbed activation energy on the AC surface and the oxygen concentration under O2/N2 atmosphere. A similar results was found by L Zhong48. As shown in Figure 9, it could be found that there was a good agreement between the calculated results by the Elovich model and the experimental data, and the correlation coefficient Rcce2 was higher than 0.9997. Similar to O2/N2 atmosphere, the chemical adsorption of active sites was the rate of the control step in the mercury removal on the AC surface under O2/CO2 atmosphere. As the oxygen concentration increased, β decreased from 0.01760 g/µg to 0.00401 g/µg. The highest value of β was 0.01760 g/µg at the oxygen concentration of 4%, whereas the lowest value was 0.00401 g/µg at the S11


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oxygen concentration of 8%, which indicated that the oxygen concentration could affect the adsorbed activation energy on the AC surface under O2/CO2 atmosphere49. In summary, according to Table 1, Rccp2 was the largest correlation coefficient compared with Rccb2 and Rcce2 under O2/N2 conditions, which indicated that the adsorption process followed the Langmuir isotherm equation and the homogeneity of the sorbent surface. Besides, Rccp2, Rcce2 were the largest correlation coefficients compared with Rccb2 under O2/CO2 conditions, which indicated that the Temkin and Langmuir isotherm equation could describe the adsorption process and the sorbent surface was heterogeneous.

4. CONCLUSION Effects of the oxygen concentration on the mercury adsorption under O2/N2 and O2/CO2 atmosphere were studied in this paper. Some conclusions could be drawn as follows: Under O2/N2 atmosphere, the adsorption process followed the Langmuir isotherm equation and the sorbent surface was homogeneous, whereas under O2/CO2 atmosphere, the Temkin and Langmuir isotherm equation could describe the sorbent and the sorbent surface was heterogeneous. The Bangham’s model, the pseudo-second-order kinetic model, and the Elovich model were employed to describe the dynamic mercury adsorption. It was found that there existed a good agreement between the calculated results by all kinetic models and the experimental data.

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The Bangham’s model showed a better performance under O2/CO2 atmosphere compared to O2/N2 atmosphere. k1 reached the highest value at the oxygen concentration of 8% under O2/N2 atmosphere, but 4% under O2/CO2 atmosphere. The pseudo-second-order kinetic model could perfectly describe the mercury adsorption process under O2/N2 atmosphere and O2/CO2 atmosphere. The equilibrium adsorbed amount qe was larger under O2/N2 atmosphere than that under O2/CO2 atmosphere at the same O2 concentration. The different atmosphere could affect the rule of α, and the equilibrium adsorbed amount qe could also affect the initial mercury adsorption rate α. The Elovich model verified that the chemical adsorption of active sites was the rate of the control step in the mercury removal on the AC surface.

AUTHOR INFORMATION Corresponding Author *E-mail for Hui Wang: [email protected]. Tel/Fax: +86-025-84314965. *E-mail for Yufeng Duan: [email protected]. Tel/Fax: +86-025-83795652.

NOTES The authors declare no competing financial interest.

ACKNOWLEDGMENT This work was supported by the National Natural Science Foundation of China (No 51706104); the Natural Science Foundation of Jiangsu Province (BK20170849); the National Key R&D Program of China (2016YFC0201105).

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M.; Ruiz, B., Activated carbons from biocollagenic wastes of the leather industry for mercury capture in oxy-combustion. Fuel 2015, 142, 227-234. (27).

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titania catalyst in CO2-enriched conditions. Chem Eng J 2015, 263, 356-363. (28).

Wang, F.; Shen, B.; Yang, J.; Singh, S., Review of Mercury Formation and

Capture from CO2-Enriched Oxy-Fuel Combustion Flue Gas. Energ Fuel 2017, 31, (2), 1053-1064. (29).

Yang, J.; Ma, S.; Zhao, Y.; Zhang, J.; Liu, Z.; Zhang, S.; Zhang, Y.; Liu, Y.;

Feng, Y.; Xu, K., Mercury emission and speciation in fly ash from a 35 MWth large pilot boiler of oxyfuel combustion with different flue gas recycle. Fuel 2017, 195, 174-181. (30).

Gómez-Giménez, C.; Izquierdo, M.; de las Obras-Loscertales, M.; de Diego, L.;

García-Labiano, F.; Adánez, J., Mercury capture by a structured Au/C regenerable sorbent under oxycoal combustion representative and real conditions. Fuel 2017. (31).

Zhao, B.; Liu, X.; Si, J.; Wang, C.; LI, D.; Wu, W.; Xu, M., Impact of SO2 and

H2O on Mercury Removal by Activated Carbon in Simulated Flue Gas of Oxy·coal Combustion. Proceedings of the CSEE 2013, 33, (17), 24-29.

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zinc using activated carbon derived from bagasse—an agricultural waste. Water Res

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Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 32

FIGURE CAPTIONS Figure 1. Schematic diagram of carbon capture and storage technologies Figure 2. Schematic diagram of a fixed-bed reactor system Figure 3. Kinetic analysis of mercury uptake on AC by Bangham’s model (Different oxygen concentration under O2/N2 atmosphere)

Figure 4. Kinetic analysis of mercury uptake on AC by Bangham’s model (Different oxygen concentration under O2/CO2 atmosphere)

Figure 5. Kinetic analysis of mercury uptake on AC by pseudo-second order kinetic model (Different oxygen concentration under O2/N2 atmosphere)

Figure 6. Kinetic analysis of mercury uptake on AC by pseudo-second order kinetic model (Different oxygen concentration under O2/CO2 atmosphere)

Figure 7. Effect of oxygen concentration on initial mercury absorption rate Figure 8. Kinetic analysis of mercury uptake on AC by Elovich model (Different oxygen concentration under O2/N2 atmosphere)

Figure 9. Kinetic analysis of mercury uptake on AC by Elovich model (Different oxygen concentration under O2/CO2 atmosphere)

TABLE CAPTIONS Table 1 Kinetic parameters obtained from three kinetic models

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Page 23 of 32 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Figure 1. Schematic diagram of carbon capture and storage technologies

S23


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

T

Page 24 of 32

Heater Heater Control

Gas Mixer Hg Sorbent

Hg Gas Analyzer

Valve MFC

Activated Carbon

Hg Analyzer

Water Btah

Figure 2. Schematic diagram of a fixed-bed reactor system

S24


Page 25 of 32

35

Mercury Uptake (µg/g)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

N2+ 4% O2

30

N2+ 8% O2 N2+10% O2

25

Calculated

20 15 10 5 0 0

20

40

60

80

100

120

140

Time (min) Figure 3. Kinetic analysis of mercury uptake on AC by Bangham’s model (Different oxygen concentration under O2/N2 atmosphere)

S25


Energy & Fuels

35


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 26 of 32

CO2+ 4% O2

30

CO2+ 8% O2 CO2+10% O2

25

Calculated

20 15 10 5 0 0

20

40

60

80

100

120

140

Time (min) Figure 4. Kinetic analysis of mercury uptake on AC by Bangham’s model (Different oxygen concentration under O2/CO2 atmosphere)

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Page 27 of 32

30 N2+ 4% O2


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

N2+ 8% O2

25

N2+10% O2 Calculated

20 15 10 5 0 0

20

40

60

80

100

120

140

Time (min) Figure 5. Kinetic analysis of mercury uptake on AC by pseudo-second order kinetic model (Different oxygen concentration under O2/N2 atmosphere)

S27


Energy & Fuels

35 CO2+ 4% O2


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 28 of 32

30

CO2+ 8% O2 CO2+10% O2

25

Calculated

20 15 10 5 0 0

20

40

60

80

100

120

140

Time (min) Figure 6. Kinetic analysis of mercury uptake on AC by pseudo-second order kinetic model (Different oxygen concentration under O2/CO2 atmosphere)

S28


Page 29 of 32

0.32 0.30

α µg/(g⋅min)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

0.28

O2/N2 O2/CO2

0.26 0.24 0.22 0.20 4%

8%

10%

Oxygen Concentration Figure 7. Effect of oxygen concentration on initial mercury absorption rate

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Energy & Fuels

35


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 30 of 32

N2+ 4% O2

30

N2+ 8% O2 N2+10% O2

25

Calculated

20 15 10 5 0 0

20

40

60

80

100

120

140

Time (min) Figure 8. Kinetic analysis of mercury uptake on AC by Elovich model (Different oxygen concentration under O2/N2 atmosphere)

S30


Page 31 of 32

35


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

CO2+ 4% O2

30

CO2+ 8% O2 CO2+10% O2

25

Calculated

20 15 10 5 0 0

20

40

60

80

100

120

140

Time (min) Figure 9. Kinetic analysis of mercury uptake on AC by Elovich model (Different oxygen concentration under O2/CO2 atmosphere)

S31


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47

Page 32 of 32

Table 1 Kinetic parameters obtained from three kinetic models Bangham’s model Atmosphere

O2/N2

O2/CO2

Pseudo-second order model qe

k2

µg/g

g/(µg·min)

0.99922

109.395

1.81E-05

1.14005

0.99883

108.166

0.35204

1.11112

0.99875

4%

0.46210

1.15679

8%

0.30146

10%

0.34542

O2

Elovich model α

β

µg/(g·min1/2)

g•µg-1

0.9998

0.2168

0.01935

0.99980

2.14E-05

0.99967

0.2500

0.01973

0.99966

140.551

1.33E-05

0.99968

0.2629

0.01502

0.99965

0.99927

122.068

2.08E-05

0.99976

0.3095

0.01760

0.99978

1.03015

0.99951

511.100

1.06E-06

0.99969

0.2774

0.00401

0.99969

1.05548

0.99988

346.655

2.45E-06

0.99990

0.2940

0.00603

0.99990

k1

m

Rccb2

4%

0.29902

1.12177

8%

0.35881

10%

32 ACS Paragon Plus Environment

Rccp2

Rcce2

CO2

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