Removal of NOx and SO2 from the Coal-Fired Flue Gas Using a

Jun 9, 2019 - The flue gas used for the experiment was coal-fired flue gas from the ...... T. X. Simultaneous desulfurization and denitrification from...
1 downloads 0 Views 1MB Size
Download PDF
Article Cite This: Energy Fuels 2019, 33, 6707−6716

pubs.acs.org/EF

Removal of NOx and SO2 from the Coal-Fired Flue Gas Using a Rotating Packed Bed Pilot Reactor with Peroxymonosulfate Activated by Fe(II) and Heating Xiaojiao Chen and Xiaomin Hu* School of Resources & Civil Engineering, Northeastern University, Shenyang 110819, P. R. China

Downloaded via NOTTINGHAM TRENT UNIV on August 13, 2019 at 07:27:22 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.

S Supporting Information *

ABSTRACT: An advanced oxidation process involving combined activation of peroxymonosulfate (PMS) by Fe(II) ions and heating for NOx and SO2 removal from coal-fired flue gas was conducted for the first time in a rotating packed bed (RPB) pilot reactor. The major influencing factors, radical species, reaction mechanisms and products, the mass transfer process, and the kinetics of simultaneous removal of NOx and SO2 were investigated. The results indicated that the NO removal efficiency reached above 70%, while SO2 and NO2 were almost completely removed. As the temperature increased, the NO removal • 1 • efficiency increased. Moreover, the intensity of SO•− 4 , OH, and O2 radicals generated by the activated PMS and NO radical converted by the radical−radical reaction enhanced with the increasing temperature, assessed by the electron spin resonance spectroscopy test. The increased liquid flow led to a higher NO removal efficiency, and the increased gas flow played the opposite role. The increased rotational speed first resulted in an increase in the NO removal efficiency and then its decrease. Furthermore, the mass transfer coefficient obtained in this RPB was significantly higher than that in the conventional bubbling reactor. Finally, the NO removal process in the PMS/Fe(II)/RPB system was proved to be a pseudo-first-order reaction and was considered to be a fast reaction as the reaction process completed in the liquid film based on the investigation of the Hatta number, strengthening factors, and the liquid-phase reaction utilization efficiency. The pilot experiment is conducted to further study the main parameters affecting the chemical reaction on a certain scale device and to solve the problems that the laboratory cannot solve or discover, and it is the necessary link for the transformation of scientific and technological achievements.

1. INTRODUCTION Emission of NOx (mainly NO ∼90%, NO2 ∼10%) and SO2 during fossil fuel and solid waste combustion causes serious damage to the environment (haze, acid rain, and eutrophication) and human health (cardiovascular and respiratory diseases).1−4 Generally, SO2 has been effectively controlled using the wet flue gas desulfurization process; however, there is no effective measure to control the NOx emission due to its inferior solubility.5 Currently, selective catalytic reduction and selective noncatalytic reduction denitrification technologies have achieved large-scale commercial applications in the field of coal-fired power plants. However, due to the huge economic burden, large area, chemical treatment hazards, and other shortcomings, they cannot be widely used, especially for small and medium industrial furnaces and boilers.6−8 Therefore, the contamination of NOx in the air environment has become a great concern in recent years, and considerable research efforts have been carried out to explore more effective and innovative technologies for simultaneous removal of SO2 and NOx. Fortunately, the researchers have found that a liquid oxidant can significantly increase the solubility of NO in the liquid, thereby improving the removal efficiency of the gaseous pollutant.9−13 Currently, the liquid oxidants commonly employed are peroxymonosulfate (PMS), KMnO4, persulfate (PS), H2O2, NaClO, NaClO2, etc.14−21 Among these oxidation absorbents, PMS seems to be more attractive. PMS is a cost-effective and environmentally friendly oxidant based on some excellent properties such as strong oxidative nonselective behavior, © 2019 American Chemical Society

relative stability at room temperature, and lower energy input.22−26 In general, heat, UV exposure, or transition metal • 1 ions can effectively activate PMS to form SO•− 4 , OH, and O2 27,28 28−31 radicals. Some results have shown that the three kinds of radicals display a strong oxidation−reduction potential, which will enhance the oxidation performance, thereby ultimately elevating the contaminant decontamination efficiency. Liu et al.32 developed the absorption−oxidation process of NO using PMS induced by ultrasound and Mn2+/ Fe2+ in a traditional bubble reactor and investigated the NO absorption rate and the process parameters. Recently, we reported the removal of NO using aqueous PMS with synergistic activation of Fe2+ ions and high temperature in a bubble reactor.33 Meanwhile, various research groups have used various reactor configurations to study the reaction of NO with a strong liquid oxidant at different experimental conditions. Some studies12,26 indicated that the absorption rate was strongly affected by the gas−liquid mass transfer resistance of the oxidation system in these traditional reactors such as a stirred cell and a bubble column. As mentioned above, the performance of PMS activated by heating and Fe(II) ions investigated by our group is generally restricted by the mass transfer rate, especially for the inferior solubility NO treatment. To overcome this obstacle, we designed a rotating packed bed (RPB) with a PMS/Fe(II) oxidation system to Received: March 21, 2019 Revised: June 7, 2019 Published: June 9, 2019 6707

DOI: 10.1021/acs.energyfuels.9b00881 Energy Fuels 2019, 33, 6707−6716

Article

Energy & Fuels

flow rate was 0.112−0.255 m3/s, and the concentrations and flows were regulated by the flow velocity meter. The key part of the reactor was a vertical rotating packed bed with a height of 1.0 m and an inner diameter of 0.9 m, which packed the filler. The filler used in this study was a stainless steel wire mesh having a diameter of 0.2 mm and was wound around in the rotor of the RPB. Also, the pilot reactor had the rotating speed varying from 500 to 1000 rpm, and the rotating speed was measured using a direct current motor speed measuring instrument. The rotor was installed throughout the reactor and connected to the motor. The PMS/Fe(II) (the molar ratio of 1:1; Sinopharm Reagent Co., Ltd.; analytical reagent) solution was introduced from the solution storage tank through a pump at a flow rate of 0.98−2.06 L/s and injected into the inside of the packed bed from the liquid distributor. Then, the liquid stream radioactively moved in the packed bed and smashed into rich ultrafine droplets by the strong shear forces due to centrifugal force. Finally, the liquid stream exited from the lateral export and flowed back to the solution storage tank. Simultaneously, the coal-fired flue gas flowed into the RPB pilot reactor as well. The gas stream flowed inward from the outside of the packed bed by the pressure driving force, reacted with the PMS/Fe(II) oxidation liquid, and then discharged through the gas outlet. The temperature of the oxidation liquid used for experiments was in the 22−80 °C range, and the temperature setting was maintained by the heater until the temperature reached the desired level and stabilized. The exit gas from the reactor was passed through a solid dryer prior to analysis to remove moisture. The data was recorded when the flue gas after the reaction flowed through the outlet flue gas analyzer. The exhaust gas could be further processed by the exhaust gas absorber. A pH probe was used for pH measurement, and the pH was regulated by NaOH and HCl (Sinopharm Reagent Co., Ltd.; analytical reagent). 2.3. Analytical Method. The flue gas analyzers (ZR-3710D) are used to measure the inlet and outlet concentrations of the gas. Ion chromatography (IC, CIC-300) is used to measure NO−3 , SO−2 , SO2− 3 , and SO2− 4 in the PMS/Fe(II)/RPB system. The pH meter (SINpH120) is used to measure the initial and final pH values. The SO•− 4 , • OH, 1O2, and •NO radicals are trapped with 5,5-dimethyl-1pyrrolidine N-oxide (DMPO), 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO), and imidazole nitroxide (IN) and are detected by electron spin resonance spectroscopy (Bruker ESP-A300). The measurements were carried out at a center field of 3570 GS, microwave frequency of 9.93 GHz, sweep width of 100 GS, and modulation frequency of 100 GHz.

improve the mass transfer efficiency and thus to improve the NO removal efficiency because the rotating packed bed is an efficient mass transfer device. When the fluid flows through the filler, it smashes into rich ultrafine droplets by strong shear forces, which increases the interface area of the reaction, thus greatly improving the mass transfer process and micromixing in the gas−liquid phase.34,35 Simultaneously, it has stable operation, small equipment, low energy consumption, and low investment, showing its unique advantages in the exhaust gas absorption treatment.36−38 Excessively high rotational speed may damage the liquid seal, which will cause the flue gas to pass through the reactor without reacting or with reacting in a reduced contact time. This will cause the NO removal efficiency to decrease and to have high energy consumption, so a relatively low-speed rotating packed bed pilot reactor is designed and used by our team. To the best of our knowledge, this article should be considered an innovative and effective study integrating a rotating packed bed pilot reactor, strong oxidants, catalysis, and high temperature to systematically investigate the NO absorption removal process in the coal-fired flue gas. The objectives of the study are to (1) calculate the mass transfer coefficient for NO removal in the PMS/Fe(II)/RPB system; (2) evaluate the mass transfer performance of the RPB with a traditional bubble reactor; (3) investigate the NO removal efficiency in the PMS/Fe(II)/RPB system at different reaction conditions; and (4) study the absorption kinetics of NO removal, in terms of the reaction order Hatta number, strengthening factors, and liquid-phase reaction utilization efficiency.

2. MATERIALS AND METHODS 2.1. Experimental Apparatus. The experimental apparatus mainly includes the following parts: (1) the coal-fired flue gas; (2) relief valve unit; (3) flow velocity meter; (4) rotating packed bed pilot reactor; (5) rotor; (6) motor; (7) solution storage tank; (8) pump; (9) heater; (10) solid dryer; (11) flue gas analyzer of outlet; (12) flue gas analyzer of inlet; and (13) tail gas absorber, which are described in Figure 1.

3. RESULTS AND DISCUSSION The main reaction pathways of NO removal are listed as follows (eqs 1−13).1,9,10,24,26,39 − Fe2 + + HSO−5 → Fe3 + + SO•− 4 + OH

(1)

− − + NO + SO•− 4 + H 2O → HSO4 + NO2 + H

(2)

NO + •OH → NO−2 + H+ 2NO + Figure 1. Schematic design of the rotating packed bed pilot reactor used for removing NO from coal-fired flue gas.

HSO−5

+ H 2O →

HSO−4

(3)

+

2NO−2

+ 2H

1

O2 + 2NO → 2NO2

2.2. Experimental Methods. The experimental setup for NO removal is schematically shown in Figure 1. The apparatus was mainly composed of a flue gas supply system, a gas−liquid reaction system, a measurement system, and an exhaust gas treatment system. The flue gas used for the experiment was coal-fired flue gas from the small boiler. The main gas composition was NO, NO2, SO2, O2, CO, and CO2, and the concentrations measured by the flue gas analyzer were 330−350 mg/m3 NO, 40−50 mg/m3 NO2, 2000−2200 mg/m3 SO2, and O2 with a volume fraction of 8−10%. The flue gas

(4) (5)

SO2 + H 2O ↔ HSO−3 + H+

(6)

HSO−3 ↔ SO32 − + H+

(7)

− SO32 − + •OH → SO•− 3 + OH

(8)

− 2− SO32 − + 2SO•− 4 + H 2O → 2HSO4 + SO4

(9)

SO32 − + HSO−5 → 2SO24 − + H+ 6708

+

(10) DOI: 10.1021/acs.energyfuels.9b00881 Energy Fuels 2019, 33, 6707−6716

Article

Energy & Fuels Table 1. Mass Transfer Coefficients of NO in Gas and Liquid Phases at the Different Parameters parameters T (K)

QG (m3/s)

295 303 313 323 333 343 0.112 0.152 0.178 0.206 0.234 0.255

kNO,L × 103(m/s)

kNO,G × 103(mol/(m2 Pa s))

aNO(m−1)

4.314 4.899 5.701 6.571 7.502 8.612 6.907 7.988 8.611 9.200 9.81 10.219

7.211 8.239 9.705 11.370 13.25 15.36 12.142 14.177 15.361 16.543 17.648 18.435

3400.45 3329.17 3247.10 3171.96 3102.32 3039.27 2625.36 2891.34 3039.27 3182.87 3313.67 3404.89

3NO2 + H 2O → 2H+ + 2NO−3 + NO

(11)

NO2 + •OH → H+ + NO−3

(12)

− − NO2 + SO•− 4 + H 2O → NO3 + 2HSO4

(13)

specific interfacial areas of CO2 and NO (m−1), respectively. DCO2−N2 and DNO−N2 can be obtained by the equation of Champman−Enskog (eq 19)40,41 DA,B = 0.00266

Furthermore, the Fe(III) ions converted from Fe(II) in the reaction system activated HSO−5 to regenerate Fe(II) ions. The catalyst regeneration allowed the progress of catalysis, and the reaction could be cycled until the PMS was completely consumed, affording a sufficient reaction time (eqs 14 and 15).24 − Fe3 + + HSO−5 → Fe 2 + + SO•− 4 + OH

(14)

+ Fe3 + + HSO−5 → Fe 2 + + SO•− 5 + OH

(15)

(19)

where MA and MB stand for the molecular weights (g/mol), 2 MAB = 1 1 . T is the temperature (K); P is the pressure MA

+

MB

σ +σ

(atm); σAB stands for the characteristic length, σAB = A 2 B (σCO2 = 3.941, σNO = 3.492, and σN2 = 3.798);44 and ΩD stands for the collision integral, which can be calculated by eqs S1−S3 in the Supporting Information (SI). DCO2−H2O and DNO−H2O can be estimated as follows (eq 20)40,41

3.1. Mass Transfer Coefficient of Gas in Solution. To quantitatively characterize the mass transfer process of NO removal in the PMS/Fe(II)/RPB system, the gas−liquid mass transfer coefficient is evaluated as the basis of the kinetics for investigation. The NO gas absorption and oxidation by the PMS liquid undergo a moderately fast pseudo-first-order reaction process (the hypothesis will be proved in the following). Therefore, the classical Danckwerts absorption method can be employed to derive the mass transfer coefficients in the gas phase and liquid phase through the conversion the CO2 system to the NO system as follows (eqs 16−18)40,41 ÅÄÅi ÑÉm ÅÅj D NO,N2 zyÑÑÑ j z Å Ñ kNO,G = k CO2,GÅÅÅjjj zzÑÑ ÅÅj DCO2,N2 zzÑÑÑ (16) ÅÇk {ÑÖ ÅÄÅ ÑÉn ÅÅ D NO,H2O ÑÑÑ Å ÑÑ kNO,L = k CO2,LÅÅ ÅÅ DCO ,H O ÑÑÑ ÅÇ 2 2 Ñ Ö aCO2 = aNO

T1.5 0.5 2 PMAB σABΩ D

Dgas,H2O = 7.4 × 10−12

T (x H2OM H2O)0.5 0.6 νH2OV gas

(20)

here, VNO and VCO2 stand for the molar volumes of NO and CO2, which are 23.6 and 34 cm3/mol, respectively; x stands for the association factor (xH2O = 2.6; other nonassociation factors, x = 1); vH2O stands for the kinetic Newtonian viscosities of water (Pa s); and MH2O stands for the molecular weight of H2O. In a conventional reactor, as the bubble reactor and spraying reactor were frequently used in the field of advanced oxidation, the liquid-phase mass transfer coefficient played a key role in the removal of gaseous pollutants. According to some reports,45,46 the liquid-phase mass transfer coefficient of the NO removal reaction was approximately 10−5−10−4 m/s; Liu et al. obtained the value around 1.69 × 10−4 m/s in a bubbler reactor.26 In this research, the liquid-phase mass transfer coefficient of the denitrification process with the RPB pilot reactor was measured to be 8.612 ×10−3 m/s (Table 1). Based on this result, we could conclude that compared to that of the conventional bubbler reactor the mass transfer coefficient of the liquid phase in the RPB was increased by about 1 order of magnitude, which indicated that the RPB showed a very obvious strengthening effect on the absorption process. Some studies47,48 have shown that the mass transfer process was the key parameter for controlling the NO removal process in the oxidation system and the NO removal efficiency can be increased with the increase of the mass transfer coefficient. Therefore, according to the previous comparison results, the

(17) (18)

where kNO,G and kNO,L are the gas-phase and liquid-phase mass transfer coefficients of NO (m/s), respectively; kCO2,G and kCO2,L are the gas-phase and liquid-phase mass transfer coefficients of CO2 (m/s), respectively; DNO,N2 and DNO,H2O are the diffusion coefficients in N2 and water of NO (m2/s), respectively; and DCO2,N2 and DCO2,H2O are the diffusion coefficients in N2 and water of SO2 (m2/s), respectively. In general, m = 0.5−1.0, but according to Sada et al., m = 2/3, so we take the value of 2/3 in this paper.42,43 aCO2 and aNO are the 6709

DOI: 10.1021/acs.energyfuels.9b00881 Energy Fuels 2019, 33, 6707−6716

Article

Energy & Fuels

temperature. Meanwhile, the NO absorption reaction was an exothermic reaction and the increase of temperature caused the chemical equilibrium to move toward the reverse reaction. These were not conducive to the NO removal.40 It could be seen from the experimental results that the effect on the thermodynamics was more obvious after the temperature was raised to 80 °C; thus, the NO removal efficiency did not increase further but tended to be constant, as shown in Figure 2. 3.2.2. Intensity of Free Radicals Changes with Temperature. From the obtained data, it was seen that an increase in temperature had a significant positive influence on NO removal. Moreover, an increase in temperature could activate • 1 PMS solution to dissolve more SO•− 4 , OH, and O2 radicals 7,24,28 (eqs 21 and 22).

RPB of this research could improve the performance of the mass transfer process. Thus, we used the PMS/Fe(II)/RPB oxidation system to further optimize the process of removing NO from the coal-fired exhaust gas, thereby improving the NO removal efficiency. 3.2. Influence of Temperature. 3.2.1. Effect of Temperature on Removal Efficiency. Figure 2 reveals the effect of

• HSO−5 + heat → SO•− 4 + OH

(21)

HSO−5 + SO52 − → HSO−4 + SO24 − + 1O2

(22)

Through the detection of electron spin resonance spectroscopy (ESR), three kinds of characteristic peaks were captured at 22 and 70 °C. At 22 °C, the constants of hyperfine splitting were measured to be aN = 14.8 Gs and aH = 14.7 Gs, maintaining good consistency with the data such as aN = 15.0 Gs and aH = 14.7 Gs from other literature works.49 These parameters were the representative of •OH that reacted with DMPO to form the DMPO−OH. The hyperfine splitting constants were aN = 13.8 Gs, aH = 9.9 Gs, aH = 1.47 Gs, and aH = 0.75 Gs, which were consistent with the previous literature parameters aN = 13.9 Gs, aH = 10.2 Gs, aH = 1.45 Gs, and aH = 0.76 Gs.50 These parameters were the representative of SO•− 4 that reacted with DMPO to form the DMPO−SO4. Meanwhile, a typical triple ESR spectrum of 1O2 was also monitored and the constants of hyperfine splitting aN = 16.5 Gs and g = 2.01 Gs were consistent with the previous literature parameters.28 The • intensity of SO•− 4 and OH radicals increased twice, and the 1 intensity of the O2 radical increased by about 5 times with an increase in temperature, from the ESR spectra in Figure 3. According to previous studies,51 NO was a labile free radical • ( NO), which made it have a strong chemical activity and react • •− with free radicals such as SO•− 4 , OH, and O2 . Then, it reacted with the molecular oxygen dissolved in solution to instantaneously form the •NO2 radical via a radical−radical

Figure 2. Effect of temperature on NOx and SO2 removal from the coal-fired flue gas using the PMS/Fe(II)/RPB system. Conditions: pH = 3.0; CPMS = 10 mmol/L; QG = 0.17−0.18 m3/s; QL = 1.9−2.0 L/s; and relative centrifugal force (RCF) = 322g.

PMS liquid temperature on the NO removal efficiency. With the increase of temperature from 22 to 80 °C, the NO removal efficiency had a remarkable increase from 23.2 to 78.6%; the peak was found to occur at the temperature around 70 °C and then a tendency to stabilize appeared at 70−80 °C. Compared with NO, NO2, and SO2 were almost completely removed at all reaction temperatures because of their very high solubility and relatively high reactive activity in solution. In addition, high temperature could increase the activity of Fe(II) ions to promote the progress of the catalytic reaction, accelerating the generation of free radicals and thus increasing the NO removal efficiency. However, the removal efficiency of NO tended to be constant as the temperature increased from 70 to 80 °C. Through additional experiments in the laboratory, we found that when the temperature was higher than 65 °C the PMS aqueous solution was susceptible to degradation and decomposed into oxygen and potassium sulfate. This occasion hindered the production of free radicals, resulting in a constant value of the target pollutant removal efficiency. Based on the kinetics, when the temperature was increased from 22 to 80 °C, the liquid-phase mass transfer coefficient increased (as shown in Table 1). One possibility could be that the diffusion coefficient that played a key role in increasing the liquid-phase mass transfer coefficient was directly proportional to the temperature and inversely proportional to the viscosity. Herein, an increase in the temperature of the ionic liquid would promote the diffusion coefficient, DNO,L, of NO in the solution based on eq 20, accompanied by an increase of kNO,L. Moreover, the temperature elevation was beneficial to the diffusion process of NO in the PMS/Fe(II) system, which might promote the reduction of the resistance of the gas− liquid mass transfer process. In the end, the liquid-phase mass transfer coefficient, kNO,L, increased with the increase of temperature and played a positive role in NO removal. Therefore, the NO removal efficiency kept increasing. Based on the thermodynamics, the NO solubility in the PMS/Fe(II) absorption liquid decreased with the increasing

• 1 Figure 3. ESR spectra of SO•− 4 , OH , and O2 free radicals trapping by DMPO and TEMPO are shown in the PMS/Fe(II)/RPB system at the room temperature 22 °C and at 70 °C, respectively (the solid quadrilateral represents DMPO−SO4−, the hollow quadrangle represents DMPO−OH, and the circle represents TEMPO−1O2).

6710

DOI: 10.1021/acs.energyfuels.9b00881 Energy Fuels 2019, 33, 6707−6716

Article

Energy & Fuels

here, k is the reaction rate constant, s−1; T is the absolute temperature, K; A is the pre-exponential factor, for the firstorder reaction, s−1, and the second-order reaction, mL/(mol s); E is the activation energy, kJ/mol; and R is the gas constant, 8.314 J/(mol K). Based on eq 26 and the pseudo-first-order rate constant (in Table 2, the calculation formula refers to eq S4 in the SI), the activation energy for NO oxidation removal was calculated to be around 252.4 kJ/mol (R = 0.972) (Figure 5).

reaction, accompanied by generation of nitrate (NO−3 ) and nitrite (NO−2 ) ions via the reaction of •NO2 and H2O (eqs 23−25).51 2• NO + O2 → 2• NO2

(23)

2• NO2 ⇆ N2O4

(24)

H 2O

N2O4 ⎯⎯⎯→ NO−2 + NO−3 + 2H+

(25)

Table 2. Diffusion Coefficient, Reaction Rate Constant, Hatta Number, and Enhancement Factor at a Temperature of 343 K DNO,L (m2/s) −9

5.95 × 10

K (s−1) 5.81 × 10

4

M

E

4.67

2.182

Figure 4. ESR spectra of •NO radical trapping by IN shown in the PMS/Fe(II)/RPB system (a) at 22 °C and (b) at 70 °C.

As shown in Figure 4, it was desirable that the peaks of the • NO radicals were detected by the ESR test in the PMS/ Fe(II)/RPB system at the room temperature 22 °C and at 70 °C with imidazole nitroxide (IN) selected as the spin probe to capture •NO radicals. The iconic nine peaks of the •NO radical were clearly detected based on NO in the liquid in an unsaturated state, and the hyperfine splitting constants were aN = 0.42 mT and g = 0.94 mT at 22 °C and aN = 0.4 mT and g = 0.9 mT at 70 °C, which agreed with the previous literature parameters of aN = 0.44 mT and g = 0.98 mT.51 The typical nine peaks of •NO in the ESR spectrum and two sets of data provided a powerful evidence for the formation of an imidazole−•NO compound. This indicated that there was • NO radical production during the reaction process at different temperatures. Meanwhile, the signal intensity of •NO radicals at 70 °C was twice that of •NO at 22 °C, which strongly demonstrated that the increase of the temperature promoted • 1 not only the mass production of SO•− 4 , OH, and O2 radicals but also the gas−liquid mass transfer, thereby increasing the content of •NO radicals in solution. Thus, increased temperature was more conducive to the reaction between • NO and free radicals, which fundamentally strengthened the removal reaction of NO. This was one of the reasons why the NO removal efficiency increased with temperature as well. 3.2.3. Active Energy in NO Removal Reaction. To better understand the effects of temperature on the NO removal reaction, the apparent activation energy was introduced. The apparent activation energy for the NO removal reaction by PMS was calculated based on the rate constants at different temperatures. The Arrhenius equation was a good explanation of the correlation between the temperature and reaction rate as follows ln k = ln A −

E RT

Figure 5. Activation energy for the NO removal reaction based on the experimental data fitted.

3.3. Influence of Rotational Speed. Since the centrifugal force is not only a function of the rotational speed but also a function of the centrifugal radius, it is not scientific enough to express centrifugal force only by the rotational speed. In recent years, it has been reasonable to use relative centrifugal force (RCF). The gravitational acceleration equation for rotating equipment is converted to eq 2752 g = ω 2r RCF = 0.00001118 × r × N 2

(27)

where RCF represents the relative centrifugal force, g (g = 9.8 m/s2); N represents the rotational speed, rpm; r represents the centrifugal radius, i.e., the distance from the bottom end of the centrifuge tube to the axis, cm. The control experiment was run at a speed of 500−1000 rpm to ensure a supergravity level of 125.8−503.1g. As shown in Figure 6, the highest removal efficiency was 78.6% under 322g with a gas flow rate of 0.17−0.18 m3/s. When the rotation speed exceeded 322g, the NO removal rate started to decline, indicating that the positive effect of the rotational speed on the NO removal efficiency began to decrease as well. This observation was close to that investigated by Pei et al.53 A direct support was available for the conclusions that the high rotating speeds would accelerate the formation of smaller droplets and thinner films, which result in an increase of the gas−liquid mass transfer rate and a continuously increasing state of the NO removal efficiency. Afterward, due to the excessive rotating speed, the liquid seal might be broken such that the flue gas flew through the RPB without reaction or with

(26) 6711

DOI: 10.1021/acs.energyfuels.9b00881 Energy Fuels 2019, 33, 6707−6716

Article

Energy & Fuels

thereby facilitating the increase of kNO,L.52,53 With the enhancement of chemical reactions, the mass transfer step might gradually start to play a momentous role as well. Therefore, as the liquid flow further increased, the growth of the NO removal efficiency gradually flattened.54 3.5. Influence of Gas Flow. As could be seen from Figure 8, NO removal showed a significantly downward trend with

Figure 6. Effect of supergravity level on NOx and SO2 removal from the coal-fired flue gas using the PMS/Fe(II)/RPB system. Conditions: pH = 3.0; CPMS = 10 mmol/L; QG = 0.17−0.18 m3/s; QL = 1.9−2.0 L/s; and temperature = 70 °C.

reaction in a reduced contact time, which caused the decrease of the NO removal efficiency.53 In addition, NO2 and SO2 achieved a removal rate of above 95% and complete removal, respectively. On the other hand, from the perspective of the mass transfer process, the varying NO removal efficiency was analyzed under various rotation velocities. With the increase of rotation speed, the liquid phase smashed on the surface of the filler into lots of finer droplets and the liquid droplet surface was updated faster, which increased the gas−liquid contact area to promote the mass transfer process. The above reasons might increase the NO removal efficiency. 3.4. Influence of Liquid Flow. As shown in Figure 7, obviously, the NO removal efficiency had a steady rise with the

Figure 8. Effect of gas flow on NOx and SO2 removal from the coalfired flue gas using the PMS/Fe(II)/RPB system. Conditions: pH = 3.0; CPMS = 10 mmol/L; temperature = 70 °C; QL = 1.9−2.0 L/s; and RCF = 322g.

the increase of gas flow from 0.112 to 0.255 m3/s. This could be explained by the fact that an increase in the gas flow rate was equivalent to a decrease in the liquid oxidant, oxidizing power of the liquid, and gas−liquid contact time. With the increase of gas flow, the liquid-phase mass transfer coefficient, kNO,L, increased slightly due to the surface of liquid droplets and films being constantly updated (Table 1). However, this was not sufficient to counteract the effect of the increased gas flow on NO removal. NO removal in the PMS solution was a process of liquid-phase mass transfer control, and kNO,L played a dominant role in the entire mass transfer process. Therefore, increasing the gas flow had a very little effect on kNO,L, which is not enough to influence the general trend of NO removal.52 Moreover, there was no significant reduction in the removal efficiency of NO2, and SO2 could still be completely removed. 3.6. Kinetics of NO Removal in the PMS/Fe(II)/RPB System. 3.6.1. Reaction Order. To further strengthen the NO removal process, the effect of PMS concentration on NO removal was investigated and the kinetics of absorption reaction was studied. These investigation results would provide more systematic and comprehensive technical parameters for amplification of industrial experiments. The overall reaction between PMS and NO can be described by eq 28

Figure 7. Effect of liquid flow on NOx and SO2 removal from the coal-fired flue gas using the PMS/Fe(II)/RPB system. Conditions: pH = 3.0; CPMS = 10 mmol/L; QG = 0.17−0.18 m3/s; RCF = 322g; and temperature = 70 °C.

increase of PMS liquid flow. The process of NO2 removal achieved a higher efficiency and SO2 was completely removed. As the liquid flow rate increased, the gas−liquid flow ratio became smaller, causing an increase in the oxidizing liquid distributed per unit volume of gas, which was equivalent to adding the oxidizing power of the liquid, thereby promoting the NO removal.52,53 Meanwhile, when the liquid flow rate increased, the sturdiness of the liquid film enhanced, resulting in a decrease in the mass transfer resistance of the liquid phase and promoting the NO absorption process. Furthermore, the increasing liquid flow would result in the thinning of the boundary layer, which reduced the mass transfer resistance on the liquid side and promoted the gas−liquid mass transfer,

HSO−5 + NO + H 2O → SO24 − + NO−3 + 3H+

(28)

Based on eq 28, the NO removal chemical reaction rate equation can be expressed as follows m n rNO = KC NO,i C PMS

(29)

where CNO,i is the interface concentration of NO, mol/L, and m and n are the partial reaction orders for NO and PMS, respectively. H2O is a solvent; its concentration is generally considered to be a constant, so it is not within the scope of investigation in this study.26,55 A mass transfer rate equation is established on the basis of the double membrane theory 6712

DOI: 10.1021/acs.energyfuels.9b00881 Energy Fuels 2019, 33, 6707−6716

Article

Energy & Fuels

Figure 9. (a) Logarithmic fit of NNO,L and CNO,i and (b) logarithmic fit of

NNO = kNO,L(C NO,i − C NO,L)

NNO,L CNO,i

under the NO import concentrations of 350 and 500 mg/m3, respectively. The value of N could be determined according to m ≈ 1,

(30)

where NNO is the mass transfer rate of NO, mol/(m2 s), and CNO,L is the concentration of NO in the liquid phase, mol/L. According to the mass transfer rate equation (eq 30) and Henry’s law, the expression of CNO,i can be derived as follows C NO,i

ij N yz = HNO,LjjjjPNO,G − NO zzzz kNO,G { k

through converting eq 34 to 35 and fitting ln ln

NNO kNO,G

−2

− 10−5 ≪ PNO,G,

NNO kNO,G

can be omitted and

deleted approximatively. Thus, eq 31 can be simplified to eq 3226,55 C NO,i = HNO,LPNO,G

(32)

To determine the values of m and n, the absorption rate of NO in the PMS solution can be described as follows on account of the double membrane theory and reaction rate equation (eq 33)26,55 m+1 n ji 2km , nD NO,L C NO,iC PMS zyz zz = jjjj zz j m+1 k {

(33)

=

C NO,i

n 1 ln(km , nD NO,L ) + ln(C PMS) 2 2

and ln CPMS.

(35)

D NO,L K 2 kNO,L

(36)

The value of M is calculated and summarized in Table 2. M can be used as a criterion for determinng the rate of a chemical reaction. When M ≪ 1, it means that the liquid membrane reaction capacity is much smaller than the transfer ability. At this time, the chemical reaction takes place in the liquid body, which is considered to be a slow reaction. When M ≫ 1, the reaction rate is much higher than the mass transfer rate and the reaction proceeds in the liquid film. In this case, the NO removal process occurs in the liquid film, indicating that the NO removal reaction is fast. According to eq 36, M has been calculated and is summarized in Table 2; it can be judged that the NO removal reaction is a fast reaction. 3.6.2.2. Enhancement Factor. For an irreversible pseudofirst-order reaction, in line with the double-film theory, the enhancement factor, E, for the chemical absorption reaction can be estimated as follows (eq 37)41,55

By taking the logarithm on both sides of eq 34, the relationship between ln NNO,L and ln CNO,i can be obtained. ln NNO,L =

C NO,i

M=

1/2

NNO,L

NNO,L

NNO,L

As shown in Figure 9b, ln NNO,L/CNO,i and ln CPMS are fitted to a straight line with good correlation coefficients of 0.976 and 0.982, respectively. Two fitted line slopes were nNO/350/2 = 0.92 and nNO/350 = 1.84 with nNO/500/2 = 1.07 and nNO/500 = 2.14. Therefore, according to the reaction order of the PMS, it could be considered that the NO absorption reaction in the PMS/Fe(II)/RPB system was a pseudo-1.84-order reaction under the NO import concentration of 350 mg/m3 and a pseudo-2.14-order reaction under the NO import concentration of 500 mg/m3. 3.6.2. Liquid-Phase Reaction Utilization Efficiency. 3.6.2.1. Hatta Number. The Hatta number, M, represents the ratio of the reaction rate to the mass transfer rate in the liquid phase and is an important parameter for mass transfer kinetics. M can be derived as follows (eq 36)41,55

(31)

where HNO,L is the solubility coefficient of NO in the liquid phase that can be calculated by Henry’s law, mol/(L Pa), and PNO,G is the gas partial pressure of NO in the gas-phase body, Pa. Based on the order analysis method, as

( ) ≈ 10

and CPMS under NO import concentrations of 350 and 500 mg/m3.

n 1 ijj 2km , nD NO,L C PMS yzz m+1 zz + lnjj ln(C NO,i) z 2 jk 2 m+1 {

(34)

Based on the data of NO and PMS concentration versus the NO removal efficiency and eqs 33 and 34, ln NNO,L and ln CNO,i were fitted to a straight line with good correlation coefficients of 0.99 and 0.975, respectively (Figure 9a). Two fitted line slopes were (mNO/350 + 1)/2 = 0.94 and (mNO/500 + 1)/2 = 1.10 with mNO/350 = 0.88 ≈ 1.0 and mNO/500 = 1.2 ≈ 1.0. Therefore, the NO removal process in the PMS/Fe(II)/RPB system could be regarded as a pseudo-first-order reaction 6713

DOI: 10.1021/acs.energyfuels.9b00881 Energy Fuels 2019, 33, 6707−6716

Article

Energy & Fuels E=

M [ M (α − 1) + th M ] M (α − 1)th M + 1

efficiency reached 70% or higher, while SO2 and NO2 were almost completely removed and were hardly affected by other parameter changes. Both the increase of temperature and liquid flow led to elevated conversions of NO in the PMS/ Fe(II)/RPB system. The increased rotational speed resulted in an increase in the NO removal efficiency. When the supergravity level reached 322g, the removal efficiency become maximum. As the supergravity level continued to increase, the removal rate decreased slightly. Nevertheless, the increase in gas flow resulted in a decrease in the NO removal efficiency. Furthermore, the mass transfer coefficient obtained by the classical Danckwerts absorption method was significantly higher than that obtained by the conventional bubbling reaction, indicating that the NO removal reaction had a better mass transfer process in the PMS/Fe(II)/RPB system. Finally, the NO removal process in the PMS/Fe(II)/RPB oxidation system studied was accompanied by a pseudo-first-order reaction and was considered to be a fast reaction as the reaction process completed in the liquid film based on the investigation of the Hatta number, strengthening factors, and the liquid-phase reaction utilization efficiency. In summary, this research conducted a pilot study on the reaction mechanism, gas−liquid mass transfer, and kinetics of the NO removal process via PMS absorption in a rotating supergravity environment. On this basis, the main reaction parameters were optimized to provide the theoretical basis and support for industrial applications. For many years, the pilot test has not received enough attention in China and the “pilot test gap” phenomenon is more serious. Therefore, our research is more practical and creative.

(37)

where α is the ratio of liquid to liquid film thickness. When M ≫ 1, th√M tends to 1, and E = √M can be obtained by simplifying eq 37.55 Also, the values of E were calculated and are summarized in Table 2. Based on the effect of the absorption enhancement factor, the proportion of the liquid-phase mass transfer resistance was lowered, thereby accelerating the absorption rate. 3.6.3. Liquid-Phase Reaction Utilization Efficiency. By a further study on gas−liquid reaction kinetics on the basis of liquid-phase utilization efficiency, the liquid-phase utilization efficiency can be measured as follows (eq 38).55 η=

M (α − 1) + th M α M [(α − 1) M th M + 1]

(38)

where α is the ratio of liquid to liquid film thickness and M, the dimensionless number (Hatta number), indicates the ratio of the reaction rate to the mass transfer rate in the liquid phase. According to the above study, the NO removal reaction with PMS solution had a fast reaction and M was much larger than 1, i.e., th√M tended to 1. Thus, eq 38 could be simplified to eq 39 η=

1 α M

(39)

Since α stands for the ratio of liquid to liquid film thickness and is much greater than 1 (in general, α was between 100 and 104),55 the M value is larger than 1. Hence, η has a very small value, close to 0, which further indicates that the NO removal reaction using the innovative PMS/Fe(II)/RPB system can be regarded as a fast reaction as the reaction process is completed in the liquid film and that the average reaction concentration of the liquid phase approaches 0.

■

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.energyfuels.9b00881.

4. DISCUSSION ON THE APPLICATION OF THIS TECHNOLOGY The results above showed that NOx and SO2 could be efficiently removed using the PMS/Fe(II)/RPB advanced oxidation method in the pilot stage. The advantages of small area, low investment, and simple process made the removal system more promising for small and medium industrial furnaces and boilers. Moreover, from the previous works and the above measurement results,31−33 it can be seen that NOx and SO2 are oxidized into KNO3 and K2SO4, respectively, in the reaction system via absorption−oxidation. KNO3 was widely used in agricultural markets and was a binary compound fertilizer. K2SO4 was also used to prepare other potassium salts, fertilizers, and the like. The KNO3 and K2SO4 aqueous solutions can be further converted to recoverable solids by crystallization and evaporation. Obviously, this new process will not cause secondary pollution. Therefore, simultaneous removal of NOx and SO2 using this PMS/ Fe(II)/RPB removal system will be feasible in future applications.

■

Calculation methods and equations of physical and mass transfer parameters (PDF)

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Xiaomin Hu: 0000-0003-3522-0209 Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS This project was supported by the Natural Science Foundation of China (51678118).

■

REFERENCES

(1) Liu, Y. X.; Wang, Q.; Pan, J. F. Novel process of simultaneous removal of nitric oxide and sulfur dioxide using a vacuum ultraviolet (VUV)-Activated O2/H2O/H2O2 system in a wet VUV-Spraying reactor. Environ. Sci. Technol. 2016, 50, 12966−12975. (2) Pillai, K. C.; Chung, S. J.; Raju, T.; Moon, I. S. Experimental aspects of combined NOx and SO2 removal from flue-gas mixture in an integrated wet scrubber-electrochemical cell system. Chemosphere 2009, 76, 657−664.

5. CONCLUSIONS In this study, use of the advanced oxidation processes in the PMS/Fe(II)/RPB system for multipollutant (NO, NO2, and SO2) reduction in the coal-fired flue gas obtained a good removal effect. The results indicated that the NO removal 6714

DOI: 10.1021/acs.energyfuels.9b00881 Energy Fuels 2019, 33, 6707−6716

Article

Energy & Fuels

tion in aqueous and sediment systems. Appl. Catal., B 2009, 85, 171− 179. (25) Rastogi, A.; Al-Abed, S. R.; Dionysiou, D. D. Effect of inorganic, synthetic and naturally occurring chelating agents on Fe(II) mediated advanced oxidation of chlorophenols. Water Res. 2009, 43, 684−694. (26) Liu, Y. X.; Wang, Y. Simultaneous removal of NO and SO2 using aqueous peroxymonosulfate with coactivation of Cu2+/Fe3+ and high temperature. AIChE J. 2017, 63, 1287−1302. (27) Chen, X.; Wang, W.; Xiao, H.; Hong, C.; Zhu, F.; Yao, Y.; Xue, Z. Accelerated TiO2 photocatalytic degradation of Acid Orange 7 under visible light mediated by peroxymonosulfate. Chem. Eng. J. 2012, 193−194, 290−295. (28) Liang, P.; Zhang, C.; Duan, X. G.; Sun, H. Q.; Liu, S. M.; Moses, O.; Wang, S. An insight into metal organic framework derived N-doped graphene for the oxidative degradation of persistent contaminants: formation mechanism and generation of singlet oxygen from peroxymonosulfate. Environ. Sci.: Nano 2017, 4, 315−324. (29) Qi, F.; Chu, W.; Xu, B. B. Modeling the heterogeneous peroxymonosulfate /Co-MCM41 process for the degradation of caffeine and the study of influence of cobalt sources. Chem. Eng. J. 2014, 235, 10−18. (30) Liu, Y. X.; Zhang, J.; Sheng, C. D.; et al. Simultaneous removal of NO and SO2 from coal-fired flue gas by UV/H2O2 advanced oxidation process. Chem. Eng. J. 2010, 162, 1006−1011. (31) Liu, Y.; Xu, W.; Zhao, L.; Wang, Y.; Zhang, J. Absorption of NO and Simultaneous Absorption of SO2/NO Using a Vacuum Ultraviolet Light/Ultrasound/KHSO5 System. Energy Fuels 2017, 31, 12364−12375. (32) Liu, Y.; Xu, W.; Pan, J.; Wang, Q. Oxidative removal of NO from flue gas using ultrasound, Mn2+/Fe2+ and heat coactivation of Oxone in an ultrasonic bubble reactor. Chem. Eng. J. 2017, 236, 1166−1176. (33) Chen, X. J.; Hu, X. M.; Gao, Y. Removal of NO in simulated flue with aqueous solution of peroxymonosulfate activated by high temperature and Fe(II). Chem. Eng. J. 2019, 359, 419−427. (34) Munjal, S.; Dudukovic, M. P.; Ramachandran, P. Mass transfer in rotating packedbeds: I. Development of gas-liquid and liquid-solid mass-transfer coefficients. Chem. Eng. Sci. 1989, 44, 2245−2256. (35) Bašić, A.; Dudukovic, M. P. Liquid holdup in rotating packed bed: examination of the film flow assumption. AIChE J. 1995, 41, 301−316. (36) Ramshaw, C. The opportunities for exploiting centrifugal fields. Heat Recovery Syst. CHP 1993, 13, 493−513. (37) Zhao, H.; Shao, L.; Chen, J. F. High-gravity process intensification technology and application. Chem. Eng. J. 2010, 156, 588−593. (38) Chen, Y. S. Correlations of mass transfer coefficients in a rotating packed bed. Ind. Eng. Chem. Res. 2011, 50, 1778−1785. (39) Antoniou, M. G.; de la Cruz, A. A.; Dionysiou, D. D. Degradation of microcystin-LR using sulfate radicals generated through photolysis, thermolysis and e-transfer mechanisms. Appl. Catal., B 2010, 96, 290−298. (40) Roberts, D.; Danckwerts, P. V. Kinetics of CO2 absorption in alkaline solutions I. Transient absorption rates and catalysis by arsenite. Chem. Eng. Sci. 1962, 17, 961−993. (41) Danckwerts, P. V. Gas-Liquid Reactions; McGraw-Hill: New York, 1970. (42) Sada, E.; Kumazawa, H.; Takada, Y. Chemical reactions accompanying absorption of NO into aqueous mixed solutions of FeII(EDTA) and Na2SO3. Ind. Eng. Chem. Fundam. 1984, 23, 60−64. (43) Sada, E.; Kumazawa, H.; Hlkosaka, H. A kinetic study of absorption of NO into aqueous solutions of Na2SO3 with added FeII(EDTA) chelate. Ind. Eng. Chem. Fundam. 1986, 25, 386−390. (44) Li, Y. H.; Fen, P. S.; Wand, Y. R. Lennard-Jones (12-6) potential energy parameters are provided by gas viscosity. Chin. J. Chem. Eng. 2003, 31, 54. (45) Liu, Y. X.; Wang, Y.; Xu, W.; et al. Simultaneous absorptionoxidation of nitric oxide and sulfur dioxide using ammonium

(3) Man, C. K.; Gibbins, J. R.; Witkamp, J. G.; Zhang, J. Coal characterization for NOx prediction in air-staged combustion of pulverised coals. Fuel 2005, 84, 2190−2195. (4) Guo, Q. B.; Sun, T. H.; Wang, Y. L.; He, Y.; Jia, J. Spray absorption and electrochemical reduction of nitrogen oxides from flue gas. Environ. Sci. Technol. 2013, 47, 9514−9522. (5) Zhao, Y.; Han, Y. H.; Ma, T. Z.; Guo, T. X. Simultaneous desulfurization and denitrification from flue gas by ferrate (VI). Environ. Sci. Technol. 2011, 45, 4060−4065. (6) Hosoi, J.; Hiromitsu, N.; Riechelmann, D.; Fujii, A.; Sato, J. Simple Low NOX combustor technology. IHI Eng. Rev. 2008, 41, 46− 50. (7) Adewuyi, Y. G.; Khan, A. M. Nitric oxide removal by combined persulfate and ferrous-EDTA reaction systems. Chem. Eng. J. 2015, 281, 575−587. (8) Liu, Y. X.; Wang, Y.; Wang, Q.; Pan, J. F.; Zhang, J. Simultaneous removal of NO and SO2 using vacuum ultraviolet light (VUV)/heat/peroxymonosulfate (PMS). Chemosphere 2018, 190, 431−441. (9) Adewuyi, Y. G.; Owusu, S. O. Aqueous absorption and oxidation of nitric oxide with oxone for the treatment of tail gases: process feasibility, stoichiometry, reaction pathways, and absorption rate. Ind. Eng. Chem. Res. 2003, 42, 4084−4100. (10) Adewuyi, Y. G.; Sakyi, N. Y. Simultaneous absorption and oxidation of nitric oxide and sulfur dioxide by aqueous solutions of sodium persulfate activated by temperature. Ind. Eng. Chem. Res. 2013, 52, 11702−11711. (11) Adewuyi, Y. G.; Sakyi, N. Y. Removal of nitric oxide by aqueous sodium persulfate simultaneously activated by temperature and Fe2+ in a lab-scale bubble reactor. Ind. Eng. Chem. Res. 2013, 52, 14687− 14697. (12) Khan, N. E.; Adewuyi, Y. G. Absorption and oxidation of nitric oxide (NO) by aqueous solutions of sodium persulfate in a bubble column reactor. Ind. Eng. Chem. Res. 2010, 49, 8749−8760. (13) Sweeney, A. J.; Liu, Y. A. Use of simulation to optimize NOX abatement by absorption and selective catalytic reduction. Ind. Eng. Chem. Res. 2001, 40, 2618−2627. (14) Chu, H.; Chien, T. W.; Li, S. Y. Simultaneous absorption of SO2 and NO from flue gas with KMnO4/NaOH solutions. Sci. Total Environ. 2001, 275, 127−135. (15) Thomas, D.; Brohez, S.; Vanderschuren, J. Absorption of dilute NOX into nitric acid solutions containing hydrogen peroxide. Process Saf. Environ. Prot. 1996, 74, 52−58. (16) Chien, T. W.; Chu, H. Removal of SO2 and NO from flue gas by wet scrubbing using an aqueous NaClO2 solution. J. Hazard Mater. 2000, 80, 43−57. (17) Adewuyi, Y. G.; He, X.; Shaw, H.; Lolertpihop, W. Simultaneous absorption and oxidation of NO and SO2 by aqueous solutions of sodium chlorite. Chem. Eng. Commun. 1999, 174, 21−51. (18) Wang, Y.; Liu, Y. X.; Liu, Y. Elimination of nitric oxide using new Fenton process based on synergistic catalysis: Optimization and mechanism. Chem. Eng. J. 2019, 372, 92−98. (19) Mondal, M. K.; Chelluboyana, V. R. New experimental results of combined SO2 and NO removal from simulated gas stream by NaClO as low-cost absorbent. Chem. Eng. J. 2013, 217, 48−53. (20) Yang, S. L.; Han, Z. T.; Pan, X. X.; et al. Nitrogen oxide removal using seawater electrolysis in an undivided cell for oceangoing vessels. RSC Adv. 2016, 6, 114623−114631. (21) Yang, S. L.; Pan, X. X.; Han, Z. T.; et al. Removal of NOx and SO2 from simulated ship emissions using wet scrubbing based on seawater electrolysis technology. Chem. Eng. J. 2018, 331, 8−15. (22) Anipsitakis, G. P.; Dionysiou, D. D. Transition metal/UV-based advanced oxidation technologies for water decontamination. Appl. Catal., B 2004, 54, 155−163. (23) Huang, K. C.; Zhao, Z. Q.; Hoag, G. E.; Dahmani, A.; Block, P. A. Degradation of volatileorganic compounds with thermally activated persulfate oxidation. Chemosphere 2005, 61, 551−560. (24) Rastogi, A.; Al-Abed, S. R.; Dionysiou, D. D. Sulfate radicalbased ferrous-peroxymonosulfate oxidative system for PCBs degrada6715

DOI: 10.1021/acs.energyfuels.9b00881 Energy Fuels 2019, 33, 6707−6716

Article

Energy & Fuels persulfate synergistically activated by UV-light and heat. Chem. Eng. Res. Des. 2018, 130, 321−333. (46) Liu, Y.; Wang, Y.; Xu, W.; Yin, Y. S.; Zhang, J. Oxidation Removal of Nitric Oxide from Flue Gas Using an Ultraviolet Light and Heat Coactivated Oxone System. Energy Fuels 2018, 32, 1999− 2008. (47) Adewuyi, Y. G.; Sakyi, N. Y.; Khan, M. A. Simultaneous Removal of NO and SO2 from Flue Gas by Combined heat and Fe2+ Activated Aqueous Persulfate Solutions. Chemosphere 2018, 193, 1216−1225. (48) Liu, Y. X.; Wang, Y. Gaseous elemental mercury removal using VUV and heat coactivation of Oxone/H2O/O2 in a VUV-spraying reactor. Fuel 2019, 243, 352−361. (49) Liu, Y. X.; Wang, Z. L.; et al. Removal of gaseous hydrogen sulfide using Fenton reagent in a spraying reactor. Fuel 2019, 239, 70−75. (50) Liu, G. S.; You, S. J.; Tan, Y.; Ren, N. In Situ Photochemical Activation of Sulfate for Enhanced Degradation of Organic Pollutants in Water. Environ. Sci. Technol. 2017, 51, 2339−2346. (51) Akaike, T.; Yoshida, M.; Miyamoto, Y.; Sato, K.; et al. Antagonistic action of imidazolineoxyl A-Oxides against endotheliumderived relaxing factor/NO through a radical reaction. Biochemistry 1993, 32, 827−832. (52) Zhang, L. L.; Wang, J. X.; Qian, S.; Zhang, X. F.; Chen, J.-F. Removal of nitric oxide in rotating packed bed by ferrous chelate solution. Chem. Eng. J. 2012, 181−182, 624−629. (53) Pei, S. L.; Pan, S. Y.; Li, Y. M.; Chiang, P. C. Environmental Benefit Assessment for the Carbonation Process of Petroleum Coke Fly Ash in a Rotating Packed Bed. Environ. Sci. Technol. 2017, 51, 10674−10681. (54) Liu, Y. X.; Wang, Q. Removal of elemental mercury from flue gas by thermally activated amtemperature monium persulfate in a bubble column reactor. Environ. Sci. Technol. 2014, 48, 12181−12189. (55) Zhang, C. F. Gas-Liquid Reaction and Reactor; Chemical Industry Press: Beijing, 1985.

■

NOTE ADDED AFTER ASAP PUBLICATION This article published June 25, 2019 with errors in the Intensity of Free Radicals Changes with Temperature section. The corrected article published June 28, 2019.

6716

DOI: 10.1021/acs.energyfuels.9b00881 Energy Fuels 2019, 33, 6707−6716