Enhancement of Mercury Removal Efficiency by Activated Carbon

Nov 11, 2017 - To enhance the performance of activated carbon (AC) for elemental mercury removal, a kind of AC was modified by nonthermal plasma (NTP)...
0 downloads 8 Views 3MB Size
Download PDF
Article pubs.acs.org/EF

Enhancement of Mercury Removal Efficiency by Activated Carbon Treated with Nonthermal Plasma in Different Atmospheres Peng Hu,† Yufeng Duan,*,† Weike Ding,‡ Jun Zhang,§ Liyi Bai,† Na Li,† and Hongqi Wei† †

Key Laboratory of Energy Thermal Conversion and Control of Ministry of Education, School of Energy and Environment, Southeast University, Nanjing, Jiangsu 210096, People’s Republic of China ‡ Jiangsu Post & Telecommunications Planning and Designing Institute Company, Limited, Nanjing, Jiangsu 210006, People’s Republic of China § School of Chemistry and Material Science, Huaibei Normal University, Huaibei, Anhui 235000, People’s Republic of China ABSTRACT: To enhance the performance of activated carbon (AC) for elemental mercury removal, a kind of AC was modified by nonthermal plasma (NTP) and the effects of the modification of the atmosphere (N2, O2, air, and HCl) were investigated by adsorption and desorption experiments. The physical and chemical properties of original and modified ACs were characterized by Brunauer−Emmett−Teller, scanning electron microscopy with energy-dispersive spectroscopy, and X-ray photoelectron spectroscopy (XPS). The results showed that better mercury removal performance of ACs was obtained after modifying by NTP in air, O2, and HCl. The mercury removal efficiency of AC−air, AC−O2, and AC−HCl was obviously enhanced compared to the raw AC and AC−N2 attributed to the large increase of oxygen-containing functional groups [CO and C(O)−O−C] occurring on the AC surface. AC treated in HCl could form C−Cl groups, which were beneficial to improve its oxidizing ability. In addition, stronger etching and cracking on the AC surface during NTP modification in an O2 or a HCl atmosphere were found to decrease its specific surface area and micropore volume, resulting in an adverse effect on mercury removal. It was found that the desorption peaks at 290 and 340 °C of the adsorbed AC samples corresponded to carbonyl groups (CO) and ester groups [C(O)−O−C], respectively, which were verified by combining the results of XPS and temperature-programmed desorption experiments.

1. INTRODUCTION

As one of the multi-pollutant removal technologies, nonthermal plasma (NTP)17 has been demonstrated to have a remarkable potential and predictive prospect in effectively converting elemental mercury to oxidized mercury. It could improve surface properties of adsorbents via creating energetic particles, free radicals, and a series of chemical reactions on the surface.18−20 NTP technology features no chemical reagent, no disrupting physical structures of sorbent and with the advantages of high treatment efficiency, no secondary pollution, low operational cost, and dry process.21 For the past few years, scientific work on the combination of NTP technology with AC for improving the removal efficiency of elemental mercury has been comprehensively investigated. Previous studies showed that mercury removal performance of AC was determined by the physical properties, such as specific surface area and structure parameters, and the amount of active sites,22 upon which the chemical adsorption properties mainly depend.23 The oxygen-containing functional groups24,25 on the surface of AC, such as carbonyl and ester groups, could improve the mercury removal performance by means of supplying active sites for mercury oxidization and adsorption.26,27 Chemisorption plays a dominant role in the process of mercury adsorption in the preference to physical adsorption.28 In addition, the adsorption of mercury by ester groups is more steady and prior to carbonyl groups in chemisorption.28 Furthermore, C−Cl

Coal-fired power plants are the largest anthropogenic source of mercury emission.1,2 Hazardous mercury and its compounds could make great negative impacts on human health, environment, water, and soil on account of its stronger volatility, bioaccumulation, and global mobility.3−5 Elemental mercury (Hg0), as the main existing mercury form in flue gases, which has been attracting enough attention,6−8 is very hard to be removed by conventional air pollution control devices (APCDs) in power plants because of its poor solubility, difficulty to be captured, and strong volatility.9 Activated carbon (AC) has been widely used in the aspects of pollutant capturing as a result of its superior physical and chemical properties.10,11 Although activated carbon injection (ACI) technology 12 has been identified as the most commercialized and most promising technology for mercury removal, its widespread application is limited by its high costs.13 Therefore, to search for available and efficient AC modification methods or technologies has been the common objective for both researchers and coal-fired power plants. Studies indicated that halogens (chlorine,14 bromine,15 iodine,16 etc.) can considerably improve mercury adsorption in terms of physics and chemistry. Many researches have proven that AC impregnated with halogens could gain preferable performance for mercury removal. However, the AC injection with halogen impregnation could cause potential equipment corrosion and mercury re-emission from the sorbent. © 2017 American Chemical Society

Received: July 9, 2017 Revised: November 9, 2017 Published: November 11, 2017 13852

DOI: 10.1021/acs.energyfuels.7b01973 Energy Fuels 2017, 31, 13852−13858

Article

Energy & Fuels

ACs were detected by energy-disperse spectroscopy (EDS, GENESIS 60S). The XPS (ESCALAB250Xi, Thermo Fisher Scientific, Waltham, MA, U.S.A.) technology was used to characterize the surface binding of ACs. 2.4. Mercury Adsorption and Desorption Experiments. The performance of AC for mercury adsorption was conducted in a fixedbed reactor shown in Figure 2. The reactor mainly consists of a

groups could also provide the active sites to improve the removal efficiency of mercury further.29 Some studies30,31 have shown that AC treated by NTP could increase the amount of oxygen-containing functional groups. Zhang et al.29 reported that AC treated with NTP in Cl2 could load Cl on the AC surface in the form of C−Cl groups. AC modified by NTP technology possesses beneficial effects on mercury adsorption, but the influences of modifying conditions and the mechanism of mercury adsorption need further studies in detail. In this work, AC was treated by dielectric barrier discharge nonthermal plasma (DBD-NTP) in different modifying conditions, then the mercury adsorption and desorption tests were conducted in a bench-scale fixed bed and temperatureprogrammed desorption (TPD) furnace, separately. With the assistance of characterization methods, such as Brunauer− Emmett−Teller (BET), scanning electron microscopy with energy-dispersive spectroscopy (SEM−EDS), and X-ray photoelectron spectroscopy (XPS), the mechanism of mercury adsorption was further studied via discussion of its physical− chemical properties of AC.

2. EXPERIMENTAL SECTION 2.1. Sample Pretreatment. The selected commercial AC was washed with deionized water, filtrated to remove ultrafine particles and other impurities, and dried at 105 °C in an oven for 12 h to remove the moisture. After that, the sample was ground and sieved to obtain particles in the range of 0.125−0.180 mm diameter as the raw AC sorbent sample in this experiment. 2.2. Modification of AC. The modification of AC was in a DBDNTP reactor shown in Figure 1. There are three sections in the

Figure 2. Schematic of the elemental mercury adsorption fixed-bed reactor.

mercury vapor generator, mass flow control system of simulated flue gas, temperature control system, adsorption reactor, and mercury analyzer. Quartz tube (15 mm internal diameter) with a porous quartz plate in it is placed in a vertical tubular-type furnace with a temperature controller. The furnace shares two parts in heating: the upper is the preheating section of reactant gases, and the lower is the adsorption reaction section. In this study, 200 mg of AC was distributed on the porous plate as evenly as possible. Mercury vapor was generated by a mercury permeation tube, which was immersed in a temperature-controlled water bath to produce the initial mercury concentration of 35 μg/m3. The total flow rate of the tested gas was 2 L/min, and the flow rate of N2 carrying mercury vapor was 200 mL/min. All gas flow rates were accurately controlled by mass flow controllers, and the mercury adsorption temperature was 120 °C. Mercury desorption experiments were conducted in a TPD furnace shown in Figure 3, in which the adsorbed ACs were loaded in a quartz boat and positioned in the center of the furnace with a heating rate of 10 °C/min. The carrier gas used in this study was pure N2, and the flow rate was controlled at 2 L/min. The concentration of elemental mercury in this study was monitored and recorded by an online mercury analyzer (VM 3000) continuously.

Figure 1. Schematic diagram of DBD-NTP treatment reactor. reactor: DBD reactor, high-voltage power supply, and flow control system for the modification of gases. The alternating current with a voltage of 220 V was used in this reactor. The sorbent surface properties can be changed by adjusting modifying gases and discharging power. A total of 1.0 g of AC sample was evenly distributed in a quartz reactor, and then the modifying gas entered into the reactor. Turn on the power of the NTP reactor, adjust the input power to a set value for 5 min, and then turn off the power after the required time, thus completing the modification of the AC sample. Collect the modified sorbent and preserve it, avoiding sunshine and sealing. The sample AC was treated by NTP, under the conditions of 30 W input power and 10 min modification period, in air, O2, N2, and HCl, separately. The modified AC was marked as AC−air, AC−O2, AC−N2, and AC−HCl, and the original activated carbon was named AC. 2.3. Sample Characterization. The BET specific surface area and pore size of ACs were tested by ASAP-2020M full-automatic surface area and pore analyzer (Micromeritics Instrument Corporation, Norcross, GA, U.S.A.). The morphology of the surface of the samples was analyzed using scanning electron microscopy (SEM, Sirion 200, FEI Company, Netherlands), and the surface elemental analyses of

Figure 3. Schematic of TPD. 13853

DOI: 10.1021/acs.energyfuels.7b01973 Energy Fuels 2017, 31, 13852−13858

Article

Energy & Fuels

3. RESULTS AND DISCUSSION 3.1. Sample Characterization. In the process of removing mercury, the micropore could provide the adsorption sites for active ingredients as well as the mesopore for supplying the transmission channels for mercury adsorption. Therefore, the micropore of sorbents plays an important role in mercury removal.32,33 The BET specific surface area and structure parameters of ACs are listed in Table 1.

The surface configuration of original and modified ACs was investigated with SEM and shown in Figure 4. In combination

Table 1. Specific Surface Area and Structure Parameters of ACs sample

SBET (m2/g)

Vmicro (cm3/g)

Vtotal (cm3/g)

Vmicro/Vtotal (%)

dpore (nm)

AC AC−N2 AC−O2 AC−air AC−HCl AC−2 min AC−5 min AC−15 min AC−10 W AC−20 W AC−40 W

389.82 364.72 328.01 399.56 344.53 391.94 392.46 380.43 381.17 389.40 361.54

0.134 0.049 0.089 0.126 0.095 0.116 0.118 0.116 0.124 0.123 0.111

0.373 0.383 0.218 0.316 0.263 0.363 0.357 0.316 0.395 0.359 0.275

35.8 12.9 40.6 39.9 36.1 31.8 33.3 34.5 33.1 34.3 40.3

3.799 4.231 3.029 3.095 3.237 3.707 3.639 3.091 3.716 3.699 3.038

Figure 4. SEM image of AC and modified ACs.

of the results of SEM with BET, it could be known that the raw AC has a rough surface, large particle size, and flourishing hole structure. High-energy electron and free radicals,35,36 generated by the discharge of NTP in different gases, hit against the surface of AC, and the etching and breaking lead to the disintegration of large-grained AC. Therefore, the reduction of the particle size of AC was observed. Also, in comparison to SEM pictures, it was found that larger impact on the surface occurred when modifying in air, O2, or HCl, separately. The scales on the raw AC surface were broken and disintegrated observably. The surface structure of AC−O2 and AC−HCl changed significantly, and the pore on the surface relatively decreased. The breaking of AC−N2 was relatively weaker compared to other samples. The surface element analyses of raw AC and modified ACs are listed in Table 2. It can be observed that no obvious change

The results indicated that the specific surface area (SBET), micropore volume (Vmicro), total pore volume (Vtotal), and average pore size (dpore) of AC−O2 and AC−HCl were markedly decreased in comparison to that of initial AC, attributing to the strong reaction between AC and O2 or HCl, which could give rise to some changes on the surface structure of AC. AC−N2 had a relatively small surface area, and the specific value of Vmicro/Vtotal was merely 12.9%; the micropore volume is very small in comparison to other samples. In combination with the results of BET and SEM, it can be seen that modification in N2 could bring great influence to the surface structure of AC compared to other modification atmospheres, as a result of destroying the meso- and macropores greatly. However, it was found that the ultrafine powder was generated during the modification that could block the micropores.34 Meanwhile, the etching and breaking31 produced by the NTP treatment may create many new mesoand macropores. Hence, the micropore volume of AC−N2 was decreasing, while the total pore volume and average pore size were increasing. When AC was modified in O2, air, or HCl, the reactions became very strong. The stronger etching and breaking could destroy the structure of the AC surface, making part of the meso- and macropores destroyed and some new micropores created, accompanying with few micropores blocked by the ultrafine powder. Consequently, the amount of micropores of AC−O2, AC−air, and AC−HCl increased in contrast to that of AC−N2. The specific surface area and micropore volume of AC−air found slight variation compared to those of the original AC but a great increase compared to those of the other modified ACs. It might be the reason that plentiful N2 in air would prevent the destruction of the AC structure to a certain extent when modified with NTP in air. Therefore, AC−air could gain a larger specific surface area as well as the amount of micropore volume simultaneously in comparison to AC−O2 and AC−HCl. In conclusion, NTP treatment in different gases could affect the surface characteristics of the initial AC.

Table 2. Surface Element Analyses of ACs (%) sorbent

C

O

Al

Si

S

Cl

Ca

AC AC−N2 AC−O2 AC−air AC−HCl

81.90 81.24 62.78 78.80 57.54

14.93 13.41 15.20 15.15 25.83

0.96 0.47 0.61 0.47 1.11

2.19 2.05 2.67 0.90 1.51

0 0 0.35 0.39 0.41

0 0 0 0 0.11

0.36 2.23 10.72 2.69 8.98

of C was found after modifying with N2. In comparison to original AC, the content of carbon decreased by 3.1 and 19.12% but the oxygen content increased by 0.22 and 0.29% after air and oxygen NTP treatment, respectively, which is in line with the study results by Zhang et al.30 It was illustrated that nonthermal treatment in air or O2 could increase the oxygen content on the surface of ACs but the carbon content decreased obviously after being treated in O2. This is because NTP with O2 could generate a mass of high-energy particles35 in highspeed motion to hit against the AC surface. Long-playing impact could produce etching31 on the AC surface, which could bring about the decrease of carbon on the AC surface. In addition, the appearance of 0.11% chlorine on AC−HCl indicated that a strong reaction occurred between HCl and AC during the process of NTP treatment. The relative content of carbon decreased from 81.90 to 57.54%, but the relative content of oxygen increased from 14.93 to 25.83% after modifying in HCl. Besides, a higher content of Ca and S 13854

DOI: 10.1021/acs.energyfuels.7b01973 Energy Fuels 2017, 31, 13852−13858

Article

Energy & Fuels

Figure 5. XPS spectra of C1s for ACs and Cl2p for AC−HCl.

Table 3. Functional Groups of ACs from XPS C1s relative intensity (%) functional group

electron binding energy (eV)

AC

AC−N2

AC−air

AC−O2

AC−HCl

C−C C−O CO C(O)−O−C

284.8 285.4 286.5 288.7

66.72 22.70 7.30 3.29

62.27 24.39 9.23 4.10

61.18 24.84 9.95 4.03

60.145 25.90 9.62 4.33

59.03 26.23 11.18 3.56

[C−O, CO, and C(O)−O−C] on the surface of sorbents. These results are in conformity with the prior studies.29−31 Furthermore, in comparison to other samples, the relative intensity of C−O and CO reached higher for treatment in HCl, and the highest relative intensity of C(O)−O−C appeared for treatment in O2. It could be concluded that oxygen-containing functional groups on the surface of AC, such as carbonyl and ester groups, increased after being treated by NTP in different atmospheres. The amount of oxygencontaining functional groups on the surface of sorbents, such

detected after NTP treatment indicated the fact that it was the NTP treatment that stimulated the existence of a calcium compound and sulfate in AC to be given out from the inside AC sample. Figure 5 shows the optimum fitting curves of the C1s spectrum of each sample by XPS analyses. Meanwhile, the electron binding energy (eV) and relative intensity of each functional group are given in Table 3. It was found that NTP treatment reduced the relative intensity of C−C but enhanced the relative intensity of oxygen-containing functional groups 13855

DOI: 10.1021/acs.energyfuels.7b01973 Energy Fuels 2017, 31, 13852−13858

Article

Energy & Fuels as carbonyl and ester groups, could greatly promote the performance of mercury removal by providing the active sites for Hg0.37,38 Also, the XPS spectra of Cl2p for AC−HCl indicated that Cl detected in surface element analyses party existed in the form of C−Cl groups. 3.2. Mercury Adsorption of ACs with NTP Treatment in Air. 3.2.1. Effect of the Treatment Time. To investigate the effects of the treatment time on the mercury removal performance of AC, AC was modified in air and 30 W NTP treatment input power with different treatment times. The mercury removal efficiency of ACs was tested in the fixed-bed reactor, and the efficiency curves are shown in Figure 6.

Figure 7. Effect of the input power on the mercury removal efficiency of ACs.

modified AC has the highest mercury removal performance as the input power was 30 W. It can be seen from Table 1 that the average pore size was decreased while the specific surface area and micropore volume were increased continuously accompanying with the increase of input power. This change was beneficial to mercury removal. However, there was a marked decline on the specific surface area and micropore volume of AC when the input power reached 40 W. NTP could break the chemical bonds of C−C and C−O on surface of AC and form new chemical bonds by combining with an oxy compound40 when input power changes. A higher input power could produce a higher energy electron and free radical on the AC surface, thereby promoting the chemical adsorption performance of AC on mercury.41 Nevertheless, the results indicated that the etching effect on the surface of AC will rise gradually along with the increase of input power. The amount of higher energy electrons increased sharply, and the impact was too fast when the input power was too high, which led to the crack of the AC granule and the blockage of the pore channel as a result of the generation of ultrafine powders. Therefore, it restrained the removal of mercury. 3.3. Mercury Adsorption of ACs with NTP Treatment in Different Atmospheres. To further probe into the influences of NTP treatment in different modification atmospheres on the mercury removal performance of AC, samples were treated in air, N2, O2, and HCl under conditions of optimum input power 30 W and 10 min modification time, separately. The efficiency curves are illustrated in Figure 8. It could be found that the mercury removal efficiency of AC−air

Figure 6. Effect of the treatment time on the mercury removal efficiency of ACs.

It indicated that the mercury removal efficiency gradually increased with the extension of treatment time until 10 min. The highest efficiency occurred when the time was 10 min, and the average efficiency was nearly twice as high as the original AC. However, when the treatment time kept continuing to raise to 15 min, the efficiency declined sharply. This is in accordance with the results of Zhang et al.31 In addition, it has been obtained from Table 1 that the specific surface area, micropore volume, and total pore volume were increased and the average pore size was decreased gradually along with the increase of modification time. It was also illustrated that the amount of micropore was increased and reached a maximum at 10 min. The specific surface area and structure parameters dropped sharply when the modification time kept increasing. It may be deduced that a great deal of ultrafine powder could be generated in the surface of AC that blocked the pore passing channel. It is known from the analyses in section 3.1 that increasing the amount of micropore could promote the adsorption of mercury. This is consistent with the result of adsorption tests shown in Figure 6. Consequently, the treatment time has great influence on the efficiency of the adsorption capacity of AC, and a reasonable time of modification could enhance mercury adsorption efficiency by improving physicochemical properties of the surface of AC. 3.2.2. Effect of the Input Power. The NTP input power is also one of main factors that plays a significant impact on the modifying effect of AC. Therefore, it was tested that the AC was treated in air and 10 min treatment time with different input powers. The efficiency curves are shown in Figure 7. The results revealed that the mercury removal efficiency of AC treated by NTP in different input powers increased in most cases. However, the efficiency fell faster within the beginning 30 min period and then tended to be stabilized. The variation trend was similar to the study results of Niu et al.39 The

Figure 8. Effect of the modification atmosphere on the mercury removal efficiency of ACs. 13856

DOI: 10.1021/acs.energyfuels.7b01973 Energy Fuels 2017, 31, 13852−13858

Article

Energy & Fuels

Figure 9. TPD of samples.

3.4. TPD for Adsorbents. A series of desorption experiments were conducted on a TPD furnace after the samples tested in the fixed-bed reactor for mercury removal, and the corresponding TPD curves are shown in Figure 9. It can be seen that two strong desorption peaks occurred at the temperature of around 290 and 340 °C. Zhang et al.30 reported that different desorption peaks corresponded to different functional groups. Some other researchers48 discovered that a higher desorption temperature was associated with the higher adsorption energy of ester groups. It showed from Table 3 that the amount of carbonyl groups (CO) in AC− O2 was less than that in AC−HCl, while ester groups [C(O)− O−C] were more than that in AC−HCl. The relative intensity of oxygen-containing functional groups in AC−O2 and AC− HCl well agreed with the TPD results. Therefore, it could be deduced that the desorption peak at 290 and 340 °C should correspond to carbonyl and ester groups, respectively. In addition, in comparison to original AC, AC−N2 has similar desorption peak values but AC−air, AC−O2, and AC−HCl all have higher adsorption peak values at both temperatures of 290 and 340 °C. This reflected the comprehensive effects of chemical functional groups and physical structures on mercury adsorption.38

was improved significantly compared to that of AC. However, AC−N2 showed slightly higher efficiency in the beginning 20 min and slightly lower efficiency in the successive time in comparison to AC. It indicated that O2 played a leading role in the modification of AC and removal for mercury. Zhang et al.30 reported that sorbents experienced high mercury removal efficiency in the beginning several minutes but a rapid decrease in the subsequent time, which was consistent with the results shown in Figure 8. Oxygen-containing functional groups have already proven to enhance the performance on mercury removal of sorbents.24,25 The characterization results showed that samples modified by NTP in air or O2 could increase the amount of carbonyl groups (CO) and ester groups [C(O)−O−C] on the surface of AC obviously, which could enhance the mercury removal efficiency of AC−air and AC−O2. However, the efficiency of AC−O2 decreased rapidly, and the reason may be the loss of carbon under the high-energy action of the NTP, leading to a significant decrease of the specific surface area, the blocking of the surface pore, and the decrease of the micropore volume. In comparison to AC−O2, AC−air possessed a better performance on mercury removal. The cause might be that oxygen in the air was sufficient enough to modify the sample, and the other gas compositions, such as N2, can buffer and protect the surface texture from great changes when treated with NTP. According to Tables 1 and 3, the specific surface area and pore volume of AC−air experienced very little change compared to ACs and the quantity of oxygen-containing functional group increased dramatically. It could be concluded that air is a suitable gas for the NTP modification of AC. Using halide42−44 or metal halide45,46 to modify sorbents, which could enhance the performance of mercury removal effectively, is a common method to remove elemental mercury from coal-fired flue gases. Therefore, it was tested that the AC was modified in a HCl atmosphere for 10 min and an input power of 30 W by NTP treatment to investigate the effect of halide. It can be seen from Figure 8 that the mercury removal efficiency of AC−HCl was superior to other samples. The XPS characterization results showed that the amount of oxygen functional groups on the surface obviously increased. In addition, according to the above-mentioned results of surface element analyses and XPS, there is 0.11% chlorine loaded on the surface of AC after NTP treatment that existed in the form of C−Cl groups, which could provide active sites to intensify the oxidation and removal of elemental mercury.47,48 The effects of oxygen-containing functional groups and C−Cl groups contributed to the higher efficiency of AC−HCl.

4. CONCLUSION This paper studied the enhancement of AC on mercury removal performance with the modification of NTP technology. To investigate the influence of modification time, input power, and atmospheres on the surface of AC and its mercury removal efficiency, the variation of the physical and chemical properties of samples was analyzed by BET, SEM−EDS, and XPS. The best modification effects were achieved under the conditions of 30 W input power for 10 min. The elemental mercury removal efficiency was improved by approximately 20% in comparison to the original AC. High input power and long modification time resulted in the decrease of the specific surface area and pore volume, which revealed an adverse impact on the performance of AC. The results also indicated that AC treated in N2 could not enhance its mercury removal efficiency. In addition, AC treated in air, O2, and HCl could increase the quantity of oxygen-containing functional groups, such as ester groups [C(O)−O−C] and carbonyl groups (CO), on the surface dramatically. The formation of C−Cl groups during the modification in HCl could enhance the oxidizing capacity of AC by providing active sites and, thus, improve its mercury removal performance. Meanwhile, the stronger etching and cracking on the surface of AC caused by the NTP led to a 13857

DOI: 10.1021/acs.energyfuels.7b01973 Energy Fuels 2017, 31, 13852−13858

Article

Energy & Fuels

(21) Li, S. R.; Huang, Y. F.; Wang, F. F.; Liu, J.; Feng, F. D.; Shen, X. J.; Zheng, Q. Z.; Liu, Z.; Wang, L. H.; Yan, K. P. Plasma Chem. Plasma Process. 2014, 34 (3), 579−603. (22) Zeng, H.; Jin, F.; Guo, J. Fuel 2004, 83 (1), 143−146. (23) Granite, E. J.; Pennline, H. W.; Hargis, R. A. Ind. Eng. Chem. Res. 2000, 39 (4), 1020−1029. (24) Hsi, H. C.; Tsai, C. Y.; Lin, K. J. Energy Fuels 2014, 28, 3300− 3309. (25) Manchester, S.; Wang, X. L.; Kulaots, I.; Gao, Y. M.; Hurt, R. H. Carbon 2008, 46 (3), 518−524. (26) Tan, Z. Q.; Sun, L. S.; Xiang, J.; Zeng, H. C.; Liu, Z. H.; Hu, S.; Qiu, J. R. Carbon 2012, 50 (2), 362−371. (27) Bohli, T.; Ouederni, A. Environ. Sci. Pollut. Res. 2016, 23 (16), 15852−15861. (28) Sun, P.; Zhang, B.; Zeng, X. B.; Luo, G. Q.; Li, X.; Yao, H.; Zheng, C. G. Fuel 2017, 200, 100−106. (29) Zhang, B.; Zeng, X. B.; Xu, P.; Chen, J.; Xu, Y.; Luo, G. Q.; Xu, M. H.; Yao, H. Environ. Sci. Technol. 2016, 50 (21), 11837−11843. (30) Zhang, B.; Xu, P.; Qiu, Y.; Yu, Q.; Ma, J. J.; Wu, H.; Luo, G. Q.; Xu, M. H.; Yao, H. Chem. Eng. J. 2015, 263, 1−8. (31) Zhang, J.; Duan, Y. F.; Zhou, Q.; Zhu, C.; She, M.; Ding, W. K. Chem. Eng. J. 2016, 294, 281−289. (32) Lu, Q. L.; Sorial, G. A. Carbon 2004, 42 (15), 3133−3142. (33) Tennant, M. F.; Mazyck, D. W. Carbon 2007, 45 (4), 858−864. (34) Park, S. J.; Kim, B. J. J. Colloid Interface Sci. 2004, 275 (2), 590− 595. (35) Kim, H. H. Plasma Processes Polym. 2004, 1 (2), 91−110. (36) Liao, X. Y.; Liu, D. H.; Xiang, Q. S.; Ahn, J.; Chen, S. G.; Ye, X. Q.; Ding, T. Food Control 2017, 75, 83−91. (37) Tang, J. C.; Lv, H. H.; Gong, Y. Y.; Huang, Y. Bioresour. Technol. 2015, 196, 355−363. (38) Jew, A. D.; Rupp, E. C.; Geatches, D. L.; Jung, J. E.; Farfan, G.; Bahet, L.; Hower, J. C.; Brown, G. E.; Wilcox, J. Energy Fuels 2015, 29 (9), 6025−6038. (39) Niu, Q.; Luo, J. J.; Sun, S. Q.; Chen, Q.; Lu, J. J. Fuel 2015, 150, 619−624. (40) Boudou, J. P.; Martinez-Alonzo, A.; Tascon, J. M. D. Carbon 2000, 38 (7), 1021−1029. (41) Park, S. J.; Kim, J. S. J. Colloid Interface Sci. 2001, 244 (2), 336− 341. (42) Tan, Z. Q.; Qiu, J. R.; Zeng, H. C.; Liu, H.; Xiang, J. Fuel 2011, 90 (4), 1471−1475. (43) Tao, S. S.; Li, C. T.; Fan, X. P.; Zeng, G. M.; Lu, P.; Zhang, X.; Wen, Q. B.; Zhao, W. W.; Luo, D. Q.; Fan, C. Z. Chem. Eng. J. 2012, 210 (210), 547−556. (44) Mullett, M.; Pendleton, P.; Badalyan, A. Chem. Eng. J. 2012, 211−212 (22), 133−142. (45) Zhang, A. C.; Xing, W. B.; Zhang, D.; Wang, H.; Chen, G. Y.; Xiang, J. Catal. Commun. 2016, 87, 57−61. (46) Yim, Y.-J.; Park, S.-J. Bull. Korean Chem. Soc. 2017, 38 (2), 191− 195. (47) Li, G. L.; Shen, B. X.; Li, F. K.; Tian, L. H.; Singh, S.; Wang, F. M. Fuel Process. Technol. 2015, 133, 43−50. (48) Liu, J.; Cheney, M. A.; Wu, F.; Li, M. J. Hazard. Mater. 2011, 186 (1), 108−113.

negative influence on mercury removal by dropping its specific surface area and pore volume. It could be deduced from the results of XPS and TPD that two strong desorption peaks at 290 and 340 °C for AC−air, AC−O2, and AC−HCl samples corresponded to carbonyl and ester groups, respectively, which played an important role for enhancing mercury removal.

■

AUTHOR INFORMATION

Corresponding Author

*Telephone: +86-025-83795652. Fax: +86-025-83795652. Email: [email protected]. ORCID

Yufeng Duan: 0000-0002-9015-2619 Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS This project was financially supported by the National Key R&D Program of China (2016YFC0201105) and the National Natural Science Foundation of China (51676041).

■

REFERENCES

(1) Wang, J. W.; Zhang, Y. S.; Liu, Z.; Norris, P.; Romero, C. E.; Xu, H.; Pan, W. P. Energy Fuels 2017, 31, 7309−7316. (2) Pirrone, N.; Cinnirella, S.; Feng, X.; Finkelman, R. B.; Friedli, H. R.; Leaner, J.; Mason, R.; Mukherjee, A. B.; Stracher, G. B.; Streets, D. G.; Telmer, K. Atmos. Chem. Phys. 2010, 10, 5951−5964. (3) Xu, W. Q.; Wang, H. R.; Zhu, T. Y.; Kuang, J. Y.; Jing, P. F. J. Environ. Sci. 2013, 25 (2), 393−398. (4) López-Antón, M. A.; Díaz-Somoano, M.; Martínez-Tarazona, M. R. Energy Fuels 2007, 21 (1), 99−103. (5) Bose-O’Reilly, S.; Lettmeier, B.; Matteucci Gothe, R.; Beinhoff, C.; Siebert, U.; Drasch, G. Environ. Res. 2008, 107 (1), 89−97. (6) Li, H. L.; Li, Y.; Wu, C. Y.; Zhang, J. Y. Chem. Eng. J. 2011, 169 (1−3), 186−193. (7) Weng, X. L.; Mei, R. J.; Shi, M. P.; Kong, Q. Y.; Liu, Y.; Wu, Z. B. Energy Fuels 2015, 29 (5), 3359−3365. (8) Wang, Y. J.; Duan, Y. F.; Yang, L. G.; Zhao, C. S.; Shen, X. L.; Zhang, M. Y.; Zhuo, Y. Q.; Chen, C. H. Fuel Process. Technol. 2009, 90 (5), 643−651. (9) Wdowin, M.; Wiatros-Motyka, M. M.; Panek, R.; Stevens, L. A.; Franus, W.; Snape, C. E. Fuel 2014, 128 (28), 451−457. (10) Bonvin, F.; Jost, L.; Randin, L.; Bonvin, E.; Kohn, T. Water Res. 2016, 90 (5), 90−99. (11) Baccar, R.; Bouzid, J.; Feki, M.; Montiel, A. J. Hazard. Mater. 2009, 162 (2−3), 1522−1529. (12) Zhou, Q.; Duan, Y. F.; Zhu, C.; She, M.; Zhang, J.; Yao, T. Energy Fuels 2015, 29 (12), 8118−8125. (13) Sjostrom, S.; Durham, M.; Bustard, C. J.; Martin, C. Fuel 2010, 89 (6), 1320−1322. (14) Hu, C. X.; Zhou, J. S.; Luo, Z. Y.; Cen, K. Energy Fuels 2011, 25, 154−158. (15) Tong, S. T.; Fan, M. X.; Mao, L.; Jia, C. Q. Environ. Sci. Technol. 2011, 45 (17), 7416−7421. (16) Lee, S. J.; Seo, Y. C.; Jurng, J.; Lee, T. G. Atmos. Environ. 2004, 38 (29), 4887−4893. (17) Zhu, T.; Zhou, J. L.; Chen, R.; Wang, F. Lett. Appl. NanoBioSci. 2014, 3 (2), 172−174. (18) Byun, Y.; Ko, K. B.; Cho, M.; Namkung, W.; Shin, D. N.; Lee, J. W.; Koh, D. J.; Kim, K. T. Chemosphere 2008, 72 (4), 652−658. (19) Wu, G. Q.; Zhang, X.; Hui, H.; Yan, J.; Zhang, Q. S.; Wan, J. L.; Dai, Y. Chem. Eng. J. 2012, 185−186 (1), 201−210. (20) Gu, L.; Zhang, X. W.; Lei, L. C.; Zhang, Y. Microporous Mesoporous Mater. 2009, 119 (1−3), 237−244. 13858

DOI: 10.1021/acs.energyfuels.7b01973 Energy Fuels 2017, 31, 13852−13858