Adsorption of SO2, NO, and CO2 on Activated Carbons: Equilibrium

Article pubs.acs.org/jced

Adsorption of SO2, NO, and CO2 on Activated Carbons: Equilibrium and Thermodynamics Honghong Yi, Zhixiang Wang, Haiyan Liu, Xiaolong Tang,* Ding Ma, Shunzheng Zhao, Bowen Zhang, Fengyu Gao, and Yanran Zuo College of Civil and Environmental Engineering, University of Science and Technology Beijing, Beijing 100083, China ABSTRACT: To investigate the coadsorption of SO2, NO, and CO2 from the flue gas, adsorption equilibrium tests of SO2, NO, and CO2 on coconut shell activated carbon (SAC) and coal-based activated carbon (CAC) were conducted at the temperatures (323, 343, and 363) K by the static volumetric method. The equilibrium data were well fitted by the Toth model. Henry’s constant was calculated by the Virial model; the results showed that adsorption affinity followed the order SO2 > CO2 > NO > N2 on SAC, and SO2 > NO > CO2 > N2 on CAC. Then thermodynamics data, including Gibbs’ free energy, entropy, and enthalpy, were also calculated to characterize adsorption behaviors. SO2 had the highest degree of freedom, while CO2 formed a most regular configuration. The efficiency of molecule packing in CAC was lower than that in SAC. Finally, competitive adsorption of different flue gas components was predicted by the extended Toth model. The adsorption amount followed the order CO2 > N2 > SO2 > NO for both adsorbents. SAC had better adsorption property than CAC in the multicomponent adsorption.

1. INTRODUCTION Sulfur dioxide (SO2) and nitric oxides (NOX) emission from flue gas are main air pollutants which cause acid rain and ozone depletion. It is detrimental to human health and nature. Besides, the increasing carbon dioxide (CO2) causes global warming, which attracts extensive attention. So far, there are many methods to remove the above gases independently. However, those methods have many disadvantages, such as high energy consumption and expensive equipment costs. Therefore, to remove all the three components simultaneously arouses general interests. The co-adsorption process may be a promising technology in removing multiple pollutants owing to its low investment expense and low energy consumption. There are many adsorbents that are used to adsorb independently sulfur dioxide (SO2), nitric oxide (NO), and carbon dioxide (CO2), such as activated carbon (AC), alumina, and zeolite.1−5 Activated carbon were selected as the adsorbent in this study because of its extensive surface, high porosity, and so on. There have been several researches about SO2, NOX removal, and CO2 adsorption over activated carbons, and some achievements have been gained. Bagreev 6 studied the adsorption of SO2 on ACs synthesized with different resources and surveyed the effects of nitrogen functionality and pore size. Lopez7 evaluated the adsorption of NO on AC in the presence and absence of O2. Sumathi8,9 investigated the simultaneous removal of SO2 and NO via carbon-based adsorbents, and the results demonstrated that activated carbon impregnated with several metal oxides processed higher adsorption amounts. Siriwardane10 performed many experiments on CO2 adsorption and proved that AC exhibited higher CO2 capacity at higher © 2014 American Chemical Society

pressure areas. It is easy to see that studies about the simultaneous adsorption and removal of SO2, NO, and CO2 are few. Adsorption equilibrium data is of great significance for analysis of the adsorption process. Moreover, isotherms of single gases are essential to dynamic experiments.11,12 Besides, selecting a suitable adsorbent is crucial for a high-efficiency adsorption process. Thus, to test coadsorption of SO2, NO, and CO2 over activated carbon, we should analyze the adsorption characteristics of all the components. Thus, the goal of this study is several-fold. First, the adsorption equilibrium isotherms for SO2, NO, and CO2 on activated carbons were acquired by static volumetric method. Second, adsorption affinities of SO2, NO, and CO2 on SAC and CAC were analyzed based on Henry’s constant. Third, adsorption behavior was explained by means of thermodynamic analysis. Finally, the competitive adsorption of SO2, NO, and CO2 was predicted.

2. EXPERIMENTAL SECTION 2.1. Materials. The adsorbents used in this study were coconut shell activated carbon (SAC)(high quality coconut shell as raw material, and the particular catalog number was SS05B) and coal based activated carbon (CAC)(coal as raw material). These were obtained from Sensen Carbon Industry, Fujian, China and College of Materials Science and EngineerReceived: December 27, 2013 Accepted: March 31, 2014 Published: April 9, 2014 1556

dx.doi.org/10.1021/je4011135 | J. Chem. Eng. Data 2014, 59, 1556−1563

Journal of Chemical & Engineering Data

Article

were generally used to measure adsorption isotherms. In this study, we used Toth equations to correlate the experimental data. It can be presented as follows:

ing, Kunming University of Science and Technology, Kunming, China, respectively. The SAC and CAC were sieved and washed with deionized water, then dried at 383 K. Purities for SO2, NO, CO2, and N2 were 99.9 %, 99.5 %, 99.9 %, and 99.99 %, respectively. The BET surface area and pore volume were determined by N2-adsorption on a NOVA2000e Quantachrome instrument. The characteristics of activated carbons are shown in Table 1.

Toth isotherm q =

average pore width

SBET

Vmeso

Vmirco

Smirco

styles

3

cm /g

2

m /g

3

cm /g

3

cm /g

m2/g

nm

Vmirco/Vt

SAC CAC

0.552 0.393

1125 736

0.135 0.152

0.417 0.241

903 519

1.96 2.14

0.756 0.612

(1 + (bp)t )1/ t

(1)

where q is the amount adsorbed in equilibrium with the concentration of adsorbate in the gas phase (mmol·g−1), qm is the maximum adsorption amount (mmol·g−1), p (kPa) is the equilibrium gas pressure of adsorbate. b (kPa−1) is the equilibrium constant of adsorption, and t is regarded as the heterogeneous of the adsorbent. Both b and t are special for adsorbate−adsorbent system. 2.3.2. Henry’s constant and selectivity. Henry’s constant was used to evaluate adsorption affinity which was inextricably linked with the interaction between the molecules of adsorbate and the surface of adsorbent when the pressure was low.14 With the increasing of the Henry’s constant, the adsorption affinity became stronger. Henry’s constant was calculated by a virial isotherm model and could be described as

Table 1. Characteristic of Activated Carbons SAC and CAC Vt

qmbp

2.2. Adsorption Equilibrium. Adsorption equilibrium isotherms of SO2, NO, and CO2 on activated carbons were obtained using a static volumetric instrument. Details of used experimental equipment were described elsewhere.13 The experiments were performed in a temperature area ranges from 323 K to 363 K. 2.3. Theory and Method. 2.3.1. Adsorption Equilibrium Isotherm. Many models, such as Langmuir, Sips, and Toth,

⎛ ⎞ P 1 3 4 exp⎜2A1q + A 2 q2 + A3q3 + ...⎟ = ⎝ ⎠ q KH 2 3

(2)

Where KH is Henry’s constant, and A1, A2, and A3 are the virial coefficients. A plot of ln (P/q) vs the loading q, should

Figure 1. Adsorption isotherms for SO2, NO, and CO2 on SAC at (323, 343 and 363) K: a, SO2; b, NO; c, CO2. 1557



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Figure 2. Adsorption isotherms for SO2, NO, and CO2 on CAC at (323, 343, and 363) K: a, SO2; b, NO; c, CO2.

where Ω and R are the surface potential (kJ·mol−1) and gas universal constant (J·mol−1 K−1), respectively. q and T are the symbols for adsorption amount (mmol·g−1) and absolute temperature (K). 2.3.4. Competitive Adsorptions of Flue Gas Components. Single component isotherms are the basis for the analysis of multicomponent adsorption. Hence, the parameters of a single component can be extended to predict multicomponent adsorption by the extended Toth model.17 It is presented as

approach the axis linearly as q close to 0 with slope 2A1 and intercept −ln(KH). On the basis of Henry’s constant, the selectivity α between components can be described as15

a=

KH1 KH2

(3)

Where KHi is Henry’s constant of component i. 2.3.3. Thermodynamic of Adsorption. The analysis about thermodynamic of adsorption, which can elucidate the behavior of adsorption, usually focuses on the free energy (ΔG), entropy (ΔS), and enthalpy (ΔH).16 These were based on the Toth equation fit. Generally, they can be calculated as

qi =

ΔH =

RT ∫ q d(ln p) Ω 0 =− q q

− ΔS =

(4)

⎡ ∂(Ω / T ) ⎤ ⎣ ∂(1 / T ) ⎦ p q

(7)

3. RESULTS AND DISCUSSION 3.1. Adsorption Equilibrium Isotherms. Equilibrium isotherms of single components SO2, NO, and CO2 on SAC and CAC were obtained at temperatures (323, 343 and 363) K. Figures1 and 2 showed the experimental data. All isotherms could be classified as Type I. All species of SO2, NO, and CO2 showed the highest adsorption amount at 323 K among

(5)

( ∂Ω∂T )p q

n

(1 + ∑ j = 1 (bjpj )ti )1/ ti

where qi and pi are the adsorption amount and partial pressure of component i in flue gas system. qmi, bi, and ti are Toth model parameters of a single component, i, and j represent different single components in flue gas system, and n means gas species in the mixture.

P

ΔG =

qmibipi

(6) 1558



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Table 2. Toth Equation Correlation Parameters for SO2, NO, CO2, and N2 at 323 K and the 95 % Confidence Limits for b and t qm/mmol·g−1 SO2 NO CO2 N2

SAC

CAC

5.03 4.05 1.81 0.63

2.402 1.683 0.994 0.168

b·105 (kPa−1) SAC 4.072 0.546 1.784 0.528

± ± ± ±

0.003 0.001 0.002 0.001

R2

t CAC

5.008 3.213 0.699 0.499

± ± ± ±

SAC

0.004 0.003 0.003 0.003

0.969 0.892 0.990 0.909

± ± ± ±

0.001 0.002 0.002 0.002

CAC

SAC

CAC

± ± ± ±

0.982 0.995 0.990 0.989

0.998 0.999 0.999 0.986

0.953 0.732 0.989 0.962

0.001 0.001 0.001 0.002

Figure 3. Adsorption isotherms for SO2, NO, CO2, N2 on SAC and CAC at 323 K: a, adsorbates on SAC; b, adsorbates on CAC.

Since adsorption data for the static volumetric method for SO2 and NO are few, the adsorption equilibria of SO2 and NO were measured by the static volume method; SO2 can be more easily adsorbed than NO on coal-activated carbon.21 The adsorption equilibrium isotherms of SO2, NO, and CO2 on zeolites were studied, and the adsorption amount followed the trend SO2 > CO2 > NO.22 To investigate the differences of equilibrium, Henry’s constant was calculated and listed in Table 3. The higher the

experimental temperatures. The adsorption amount of the three gas species decreased with an increase in the temperature. As the gas partial pressure increased, the adsorption amount increased. With the temperature going up, the adsorbate acquires more thermal energy to overcome the wall potential, thus, less adsorption will occur at higher temperatures. According to Table 1, the BET surface area and micropore volume for SAC and CAC were 1125 m2/g, 0.417 cm3/g and 736 m2/g, 0.241 cm3/g, respectively. SAC had a higher BET surface area and micropore volume than that of CAC, which caused a higher adsorption amount. The adsorption amount followed the trend SO2 > NO > CO2 for both adsorbents. Toth equation parameters were shown as examples SO2, NO, CO2 showed highest adsorption amount at 323 K. According to Table 2, Toth equation fit well for all the isotherms, supported by R2 values ranging from 0.982 to 0.999. The curves fitted by the Toth equation are shown in Figure 3. The parameter qm represented the maximum of adsorption amount. The maximum of adsorption amount of SO2, NO, and CO2 were (5, 4, 1.8) mmol/g and (2.402, 1.683, 0.994) mmol/g for SAC and CAC. The parameter t of the Toth equation is regarded as heterogeneous. t was further away from the unit, which indicated that the system was more heterogeneous.18 Values of t were close to unit, which indicated that the monolayer adsorption might be predominant, and when the adsorbates’ temperature was higher than their crucial temperature, monolayer adsorption may occur. The adsorption data (0.843, 0.256 mmol·g−1 for SAC and CAC at 50 kPa, respectively) of CO2 at 323 K was not completely in accord with the literature relating to this topic, such as AC beads 1.2 mmol·g−1(0.1 MPa, 333 K)19 and activated carbon (0.1 MPa, 328 K)20. This may be due to different reaction conditions and properties of adsorbents.

Table 3. Henry’s Constant and Selectivity Factora of SO2, NO, and CO2 on SAC and CAC at 323 K ̂5

KH·10 α a

styles

SO2

NO

CO2

N2

SAC CAC SAC CAC

20.35 12.03 56.17 143.27

2.18 5.41 6.26 64.40

3.21 0.69 8.86 8.28

0.36 0.08 1 1

KH, the Henry’s constant (mmolg·g−1·Pa−1); α, the selectivity factor.

value was, the greater was the affinity. Henry’s constant for SAC of different gas species followed the sequence: SO2 > CO2 > NO > N2. 13X and 5A showed the same trend toward SAC. SO2 possessed the highest molecular polarizability and dipole moment, which stimulated the strongest dispersion and electrostatic interaction between SO2 and activated carbon.16 It suggested that SO2 had the strongest equilibrium affinity with both adsorbents than CO2 and NO. CO2 possessed the second highest polarizability and the highest quadrupole moment, which made the affinity stronger than NO on SAC. While, for the case of CAC, Henry’s constant followed the trend: SO2 > NO > CO2 > N2. Stronger affinity was found on NO than CO2 for CAC. Thus, CAC had a relative higher adsorption affinity 1559



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Figure 4. Three functions ΔG, ΔS·T, ΔH for all adsorbates on SAC: a, ΔG; b, ΔS·T; c, ΔH.

kJ·mol−1 on CAC. However, when the pressure was high (100 kPa), (−5.19, −10.38, and −17.30) kJ·mol−1 values were obtained on SAC, while (−8.95, −18.15, and −18.43) kJ·mol−1 values were accommodated on CAC. The values followed the trend CO2 > NO > SO2. It indicated that CO2 formed a most ordered configuration on activated carbons, while SO2 had the highest degree of freedom, which might be due to its molecular activity.16 The efficiency of molecule packing in CAC was less than SAC. CO2 forming a most ordered configuration means that the degree of freedom of restricted CO2 after it adsorbed onto activated carbons is the least. As we know, entropy is a measure of the number of specific ways in which a thermodynamic system may be arranged, often taken to be a measure of disorder. CO2 has the minimum entropy of the three components, so CO2 has the least degree of disorder. On the other hand, the entropy of SO2 is the largest, so it has the highest degree of disorder. As shown in Figures 4 and 5, ΔH almost followed the profiles of ΔS·T. As pressure ranged from 1 kPa to 100 kPa, ΔH of SO2 varied from −2.61 kJ·mol−1 to −10.6 kJ·mol−1 on SAC and ranged from −12.27 kJ·mol−1 to −14.72 kJ·mol−1 on CAC. The value of −ΔH on CAC was higher than SAC. The heat of CO2 adsorption was compared with other reported literatures and listed in Table 4.

toward NO than that of CO2. So it was the same with NaY, which might be due to surface polar properties.22 The selectivity for SAC and CAC is shown in Table 3. The selectivity was given with respect to N2. The selectivity followed the same trend as Henry’s constant. Much higher selectivity values of SO2 and NO than N2 were found on CAC than SAC, yet the values of CO2 were very close. 3.2. Thermodynamics of Adsorption. For the same adsorption system, the adsorption behavior is similar at different temperatures, so the adsorption was taken at 323 K as a case. The data of ΔG, ΔS·T, and ΔH were presented in Figures 4 and 5. According to Figures 4 and 5, the free energy ΔG declined monotonically with pressure increasing on activated carbons for all adsorbates. At the same coverage of 0.1 mmol·g−1, the free energy of SO2, NO, and CO2 on SAC and CAC was (−2.73, −2.75, −2.76) kJ·mol−1 and (−2.75, −2.90, −2.85) kJ·mol−1, respectively. It followed the order NO > CO2 > SO2, and similar results were found on both activated carbons. This indicated that CO2 and NO need a higher pressure (and hence chemical potential) than that of SO2 to load in activated carbons. When the pressure was low (5 kPa), ΔS·T on SAC at 323 K for SO2, NO, and CO2 was (−2.41, −0.26, and −20.51) kJ· mol−1, respectively, compared to (−9.79, −17.84, and −22.99) 1560



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Figure 5. Three functions ΔG, ΔS·T, ΔH for all adsorbates on CAC: a, ΔG; b, ΔS·T; c, ΔH.

adsorption heat can provide a valuable reference for the optimum adsorption process design. 3.3. Multicomponent Adsorption. For convenience in this study, it is assumed that flue gas consisted of 0.2 % SO2, 0.1 % NO, and 12 % CO2, with N2 as balance. The adsorption experiment was conducted at 323 K, the predicted results calculated by the extended Toth model were presented in Figure 6. It was noted that the adsorption amount of each component in the multicomponent adsorption was lower than that of a single component. This result indicated that each component was competing for the limited adsorption sites on activated carbons. SAC exhibited a better adsorption amount for almost all components than CAC. As the total pressure increased, the adsorption amount of every component enhanced. At the pressure of 100 kPa in the multicomponent adsorption system, the adsorption amounts of SO2, NO, CO2, and N2 on SAC were (0.023, 0.0011, 0.22, and 0.17) mmol·g−1, respectively, while only (0.015, 0.0025, 0.054, and 0.046) mmol·g−1 were found on CAC. The adsorption amount followed the order CO2 > N2 > SO2 > NO for both activated carbons. The adsorption amount of CO2 was the highest, which would be due to high partial pressure and relatively strong affinity, while adsorption amounts of SO2 and NO on both SAC and CAC were small because of their trace components. Despite the

Table 4. Comparison of Adsorption Equilibrium of CO2 on Activated Carbons activated carbons

q/(mmol·g−1)

P/Mpa

T/K

ΔH/(kJ·mol−1)

lit.

AC beads activated carbon Maxsorb III coconut charcoal G32-H

1.2 0.68 1.05 2.14 5.318

0.1 0.1 4 0.1 2.07

333 328 323 288 298

−23.17

19 20 23 24 25

−20.37 −28

The adsorption data of CO2 agreed with some data in earlier researches,23−25 and the isosteric heat of adsorption was identical ((21.41, 21.89) kJ·mol−1 for SAC and CAC at 100 kPa, respectively) to that of activated carbons, such as G32-H (−28 kJ·mol−1), Maxsorb III (−20.37 kJ·mol−1), and AC beads (−23.17 kJ·mol−1) in previous literature reports. From the comparison, we found that the ΔH was similar under different pressures and temperatures and belong to the scope of physical adsorption heat. Therefore, the CO2 on activated carbon might be physical adsorption. However, the data about isosteric heat of adsorption of SO2 and NO on activated carbon is rare, it is quite difficult to carry out a comparison. After all, lower isosteric heat of adsorption is helpful for the enhancement of the adsorption amount in an adiabatic operation. Therefore, the 1561



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Figure 6. Competitive adsorptions of multicomponent in flue gas: a, SAC; b, CAC. Catalytic Adsorption of NO and SO2 on Activated Carbons at Low Temperatures. J. Phys. Chem. C 2007, 111, 1417−1423. (2) Liu, Q. Y.; Liu, Z. Y.; Wu, W. Z. Effect of V2O5 additive on simultaneous SO2 and NO removal from flue gas over a monolithic cordierite-based CuO/Al2O3 catalyst. Catal. Today 2009, 147S, S285− S289. (3) Lee, J. S.; Kim, J. H.; Kim, J. T. Adsorption Equilibria of CO2 on Zeolite 13X and Zeolite X/Activated Carbon Composite. J. Chem. Eng. Data 2002, 47, 1237−1242. (4) Ziołek, M. I.; Nowak, I. S.; Daturi, M. Effect of Sulfur Dioxide on Nitric Oxide Adsorption and Decomposition on Cu-Containing Micro- and Mesoporous Molecular Sieves. Top. Catal. 2000, 11, 343−350. (5) Juray, D. W.; Guy, B. M. Investigation of Simultaneous Adsorption of SO2 and NOX on Na-γ-Alumina with Transient Techniques. Catal. Today 2000, 62, 319−328. (6) Bagreev, A.; Bashkova, S.; Bandosz, T. J. Adsorption of SO2 on Activated Carbons: The Effect of Nitrogen Functionality and Pore Sizes. Langmuir 2002, 18, 1257−1264. (7) Lopez, D.; Buitrago, R.; Escribano, S. A.; Reinoso, R. F.; Mondragon, F. Low Temperature Catalytic Adsorption of NO on Activated Carbon Materials. Langmuir 2007, 23, 12131−12137. (8) Sumathi, S.; Bhatia, S.; Lee, K. T.; Mohamed, A. R. Selection of Best Impregnated Palm Shell Activated Carbon (PSAC) for Simultaneous Removal of SO2 and NOX. J. Hazard. Mater. 2010, 176, 1093−1096. (9) Sumathi, S.; Bhatia, S.; Lee, K. T.; Mohamed, A. R. Adsorption Isotherm Models and Properties of SO2 and NO Removal by Palm Shell Activated Carbon Supported with Cerium (Ce/PSAC). Chem. Eng. J. 2010, 162, 194−200. (10) Siriwardane, R. V.; Shen, M. S.; Fisher, E. P.; Poston, J. A. Adsorption of CO2 on Molecular Sieves and Activated Carbon. Energy Fuel 2001, 15, 279−284. (11) Lee, J. S.; Kim, J. H.; Kim, J. T. Adsorption Equilibria of CO2 on Zeolite 13X and Zeolite X/Activated Carbon Composite. J. Chem. Eng. Data 2002, 47, 1237−1242. (12) Choung, J. H.; Lee, Y. W.; Choi, D. K. Adsorption Equilibria of Toluene on Polymeric Adsorbents. J. Chem. Eng. Data 2001, 46, 954− 958. (13) Yu, Q. F.; Tang, X. L.; Yi, H. H. Equilibrium and Heat of Adsorption of Phosphine on CaCl2-Modified Molecular Sieve. AsiaPac. J. Chem. Eng. 2009, 4, 612−617. (14) Talu, O. Needs, Status, Techniques and Problems with Binary Gas Adsorption Experiments. Adv. Colloid Interface Sci. 1998, 76−77, 227−269.

selectivity of CAC being higher, SAC revealed higher adsorption amounts in single and multicomponent adsorption. This might be due to the differences of pore structure between CAC and SAC. The SAC had higher total surface areas, pore volumes, and microporous surface areas. Thus, higher adsorption efficiency took place on SAC than CAC.

4. CONCLUSIONS In this work, the adsorption equilibrium of SO2, NO, and CO2 were measured at 323 K, 343 K, and 363 K on activated carbons. The adsorption amounts of SO2, NO, and CO2 on SAC and CAC at 50 KPa, 323 K were (3.286, 0.916, and 0.843) mmol·g−1 and (1.666, 0.811, and 0.256) mmol·g−1, respectively. The adsorption amount followed the trend SO2 > NO > CO2 on both adsorbents. SAC revealed higher adsorption amounts than CAC due to its higher surface area and micropore volume. Henry’s constant of SO2 was the highest; the different affinity could be attributed to adsorbate molecular multiple moment and polarizability. SO2 had the highest degree of freedom due to its high molecular activity. CO2 formed a most regular configuration on activated carbons. The efficiency of molecule packing in CAC was lower than that in SAC. The optimum adsorption process design relied on the heat of adsorption and the efficiency of molecule packing. In the multicomponent adsorption, SAC had better adsorption efficiency than CAC.

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AUTHOR INFORMATION

Corresponding Author

*Tel.: +86 010 62332747. Fax: +86 010 62332747. E-mail: [email protected]. Funding

The work was supported by Program for New Century Excellent Talents in University (Grant NCET-12-0776) and the National Natural Science Foundation of China (Grant 21077047). Notes

The authors declare no competing financial interest.

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REFERENCES

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(15) Yang, R. T. Adsorbents: Fundamentals and Applications; John Wiley & Sons: NJ, 2003. (16) Deng, H.; Yi, H. H.; Tang, X. L.; Yu, Q. F.; Ning, P.; Yang, L. P. Adsorption Equilibrium for Sulfur Dioxide, Nitric Oxide, Carbon Dioxide, Nitrogen on 13X and 5A Zeolites. Chem. Eng. J. 2012, 188, 77−85. (17) Toth, J. Adsorption: Theory, Modelling and Analysis; Marcel Dekker: New York, 2002. (18) Chiang, Y. C.; Wu, P. Y. Adsorption Equilibrium of Sulfur Hexafluoride on Multi-Walled Carbon Nanotubes. J. Hazard. Mater. 2010, 178, 729−738. (19) Shen, C. Z.; Carlos, A. G.; Li, P.; Yu, J. G.; Alirio, E. R. Adsorption Equilibria and Kinetics of CO2 and N2 on Activated Carbon Beads. Chem. Eng. J. 2010, 160, 398−407. (20) Bezerra, D. P.; Oliveira, R. S.; Vieira, R. S. Adsorption of CO2 on Nitrogen-Enriched Activated Carbon and Zeolite 13X. Adsorption 2011, 17, 235−246. (21) Kang, D. J.; Tang, X. L.; Peng, J. H.; Yi, H. H.; Ning, P.; Ye, Z. Q.; Li, K. Adsorption Characteristics of Nitric Oxide and Sulfur Dioxide on Coal Activated Carbon. Adv. Mater. Res. 2012, 383−390, 3056−3062. (22) Yi, H. H.; Deng, H.; Tang, X. L.; Yu, Q. F.; Zhou, X.; Liu, H. Y. Adsorption Equilibrium and Kinetics for SO2, NO, CO2 on Zeolites FAU and LTA. J. Hazard. Mater. 2012, 203−204, 111−117. (23) Bidyut, B. S.; Skander, J.; Shigeru, K.; Ibrahim, I. E. Carbon Dioxide Adsorption Isotherms on Activated Carbons. J. Chem. Eng. Data 2011, 56, 1974−1981. (24) Sarkar, S. C.; Bose, A. Role of Activated Carbon Pellets in Carbon Dioxide Removal. Energy. Convers. Manage. 1997, 38, 105− 110. (25) Siriwardane, R. V.; Shen, M. S.; Fisher, E. P.; Poston, J. A. Adsorption of CO2 on molecular sieves and activated carbon. Energy Fuel 2001, 15, 279−284.

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Adsorption of SO2, NO, and CO2 on Activated Carbons: Equilibrium

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