Separation and Purification Technology 150 (2015) 80–85
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Removal of sulfur dioxide from diesel exhaust gases by using dry desulfurization MnO2 filter Yugo Osaka a,⇑, Tsuyoshi Kito b, Noriyuki Kobayashi b, Shinya Kurahara c, Hongyu Huang d, Haoran Yuan d, Zhaohong He d a
School of Mechanical Engineering, College of Science and Engineering, Kanazawa University, Kakuma, Kanazawa, Ishikawa 920-1192, Japan Department of Chemical and Biological Engineering, Nagoya University, Nagoya, Aichi 464-8603, Japan Department of Mechanical Engineering, Aichi Institute of Technology, Yakusa, Toyota, Aichi 470-0392, Japan d Chinese Academy of Science, Guangzhou Institute of Energy Conversion, No. 2 Nengyuan Rd. Wushan, Tianhe District, Guangzhou 510640, PR China b c
a r t i c l e
i n f o
Article history: Received 5 November 2013 Received in revised form 28 January 2015 Accepted 3 February 2015 Available online 23 February 2015 Keywords: Dry desulfurization Diesel engine exhaust Sulfur dioxide Manganese oxide
a b s t r a c t The sulfur dioxide (SO2) contained in combustion exhaust gases from medium-scale facilities or ocean ships must be removed because of its role as an air pollutant. In this study, dry DeSOx filter of manganese oxide was used to capture SO2 with a simple sulfate reaction. The thermogravimetry (TG), experiments shows that the MnO2 sample having a specific surface area of 250 m2/g absorbed SO2 at about 0.45 g-SO2/g-MnO2 and 0.18 gSO2/gMnO2 at 450 °C and 250 °C, respectively. Desulfurization breakthrough experiment in a packed bed was employed to evaluate the possibility of deep desulfurization. As a result, the inlet SO2 is almost absorbed by the high specific surface area (HSSA) MnO2 bed, over 99.5% absorbed at space velocity of 0.5 104 h1. Higher space velocity condition is targeting a more compact filter. Under the condition of 5.0 104 h1, SO2 over 80% against inlet SO2 can be absorbed at early time. Conclusively, this material has a large enough SO2 absorption rate to capture significant amounts of SO2 gas. Ó 2015 Elsevier B.V. All rights reserved.
1. Introduction Sulfur dioxide (SO2) from combustion exhaust gas is a major source of air pollution, harmfully affecting humans at levels lower than 100 ppm. Moreover, it is reported that SO2 from diesel exhaust deteriorates NOx catalyst [1–3]. The International Marine Organization regulates total NOx emissions, whereas sulfur concentrations are only regulated within fuel [4]. The amount of sulfur found within fuel can vary from hundreds of ppm to thousands of ppm. Chemically, sulfur is in high demand in its uses in fertilizer, sulfuric acid, and a neutralization solution of alkaline. The SO2 removal achieved through fuel upgrades and exhaust gas scrubbing is not significantly impactful. Exhaust removal devices are only used in large-scale facilities owing to size limitations and are therefore not installed in automotive bodies such as marine ships. The SO2 discharge at one voyage becomes 0.8t (8500 kW class ocean ship and 480 h crossing time). In Japan’s current social climate, medium-scale power generation, such as diesel power, is regularly demanded and used. Compact SO2 removal devices are needed for these facilities even though they have high water usage
⇑ Corresponding author. Tel./fax: +81 76 264 6475. E-mail address:
[email protected] (Y. Osaka). http://dx.doi.org/10.1016/j.seppur.2015.02.001 1383-5866/Ó 2015 Elsevier B.V. All rights reserved.
and are therefore costlier. This study focused on dry-DeSOx filtration by sulfate reaction of alkaline metal oxide (MxOy + ySO2 + 0.5xO2 ? Mx(SO4)y). From our fundamental studies, we newly found this oxide has the potential to be more compact and less costly due to lessened water demands and high reaction activity at low temperature. The downsizing and low temperature activation of the DeSOx filter is necessary for mounting on mobile machines such as automotive cars or ships. So, DeSOx filter is developing dry desulfurization filter having good SO2 capture performance for downsizing, simple SO2 capture materials for sulfur reuse. In dry desulfurization technologies, the improvement of low temperature reaction activity is necessary, considering performance enhancement of future engines and decreased NOx emissions. Unfortunately, desulfurization materials with low temperature activation are rare. Kasaoka [5] aimed to improve the reaction activity using a complex compound based on copper oxide. Nishioka [6] investigated the low-temperature reaction activity using a platinum catalyst. The application of activated carbon to the removal of SO2 from flue gas has received attention due to its low temperature SO2 removal and available H2SO4 byproducts [7,8]. Davini [9] have reported that metal additives favor the interaction between SO2 and oxygen physically absorbed and chemically bonded to the surface of
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81
Nomenclature C M m q t w P X
concentration of SO2 per unit time, ppmv/s amount of material, g/mol weight, mg volume flow rate of the simulated exhaust gas, m3/min time, s SO2 throughput capacity, mg-SO2/g-absorber SO2 capture performance per unit mass, gSO2/gmateria reaction ratio, %
activated carbon. Cu [10], V [11], Ni [12] and Mn [13] supported on activated carbon for the removal of SO2 have been studied. However, in these studies, SO2 capture capacity is very small due to low SO2 concentrations (a few hundred ppm). Furthermore, research is rarely conducted under high space velocity conditions, especially over 104 h1. In a previous study by the authors, CaCO3 showed good reaction and capture capacity with SO2 at 650 °C and 104 h1 [14,15]. However, in low temperature conditions, sulfate reaction rates decrease because sulfate reaction of metal carbonate is complicated due to decarbonation. Physical modifications involve upgrading the material itself in terms of its effectiveness, its reactivity after repeated use, recovery of the reacted material, and its environmental affinity. Improvement of the desulfurization property by modifying physical properties of materials, such as particle diameter, specific surface area, and pore diameter distribution, have also been studied [16]. Materials with simple reaction paths and high specific surface areas are excellent at SO2 capture performance in the low temperature region. Thus, manganese oxide is focused on as desulfurization material with a simple sulfate reaction. In this study, manganese oxide with a high specific surface area (HSSA MnO2) is developed. Basic performance of the HSSA MnO2 particle is measured by using a TG (thermogravimetry) device at low temperature. Then, SO2 capture performance of HSSA MnO2 is investigated in specialized conditions such as a low temperature of 250 °C and a high space velocity, which is defined by flow rate over reactor volume, of 0.5–5.0 104 (m3 h1)/m3.
Greek symbols q standard density, mg/m3 g absorption efficiency, % n differential SO2 absorption ratio, % Subscripts in input out output
that this material reacted extensively with the SO2, so that not only the surface layers of the spherical particles, but also the inside of the particles, could not retain their original shape. From this result of pore diameter distribution measurement of HSSA MnO2, a relatively large pore diameter of 80 Å is generated. The molecular diameter of SO2 is 1.4 Å. The particle diameter of HSSA MnO2 is about 100 lm. However, this material consists of the first order condensation particle of 1.0 lm. BET surface area of HSSA MnO2 is 250 m2/g. That of commercial MnO2 is about 20 m2/g. Consequently, large pore diameter has no influence on the diffusion of the inner SO2 particles. 3. Experimental procedures 3.1. TG experiment The effectiveness of the HSSA MnO2 reaction with sulfate was measured by using TG. Fig. 3 shows a schematic drawing of the TG analysis experiment, while Table 1 shows the simulated exhaust-gas composition used in the TG experiment (TGA-50, Shimadzu Co. Ltd., resolution of 10 lg). The SO2 capture performance in terms of the reaction rate per single particle, as well as the sulfate reaction rate, were evaluated. The SO2 capture performance per unit mass P is expressed by the following equation:
P¼ 2. Materials HSSA MnO2 was supplied by Japan Material and Chemical Co., Ltd. This material was produced by acid treatment of raw materials. Commercial MnO2 (Kanto Chemical Co., Inc.) with physical properties of high specific surface area (HSSA) MnO2 was also investigated. In this study, the specific surface area, pore size distribution, and surface structure were analyzed to assess the physical characteristics of the target materials. The specific surface area was measured using the nitrogen adsorption uptake at the boiling point of nitrogen of 77 K using a capacitive measurement method. The specific surface area of materials with large pores only was calculated by the BET (Brunauer, Emmett, and Teller) method. The pore-diameter distribution of materials was calculated using the BJH (Berret–Joyner–Helenda) method by measuring the nitrogen adsorption uptake under normal relative pressure at the melting point of nitrogen (relative pressure of 0.1–1.0). Fig. 1 shows SEM photographs of HSSA MnO2. Fig. 2 shows the pore diameter distribution of HSSA MnO2. The micrograph of the formed-grain material is seen to be composed of small to large smooth spherical particles that are distributed non-uniformly throughout the mass. Some very small agglomerates can however be observed in the spaces between the larger particles. The observed high porous structure from the result of Fig. 2 indicates
MMnO2 mt m0 ½gSO2 =gMnO2 M MnSO4 M MnO2 m0
ð1Þ
P is the SO2 capture performance per unit mass [gSO2/gMnO2], MMnSO4 is the molar mass of MnSO4 [g/mol], MMnO2 is the molar mass of MnO2 [g/mol], m0 is the initial weight [mg], and mt is the weight after ts [mg]. 3.2. SO2 capture performance measurement of HSSA MnO2 under high space velocity conditions The SO2 capture performance of HSSA MnO2 at a low temperature was also investigated for the possibility of SO2 capture under high space velocity conditions. The SO2 absorption rate in both high space velocity and low temperature is investigated. Fig. 4 shows the experimental set-up for the characterization of the desulfurization breakthrough. This experimental equipment consists of an exhaust-gas synthesizer, the packed bed reactor, in which the reaction temperature for the absorption of SO2 is controlled, the sampling liquid, which captures SO2 as SO2 4 , and an ion chromatograph (Metrohm Co. Ltd., 761 compact IC) to determine the amount of leaked SO2 from the SO2 4 concentration. The HSSA MnO2 particle is picked up with glass wool to preventing channeling. The simulated exhaust-gas compositions are shown in Table 2. The concentration of SO2 is adjusted to 300 ppmv to account for
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Fig. 1. SEM photographs of HSSA MnO2.
5.0
captured by 0.3 wt% H2O2. Thus, the desulfurization breakthrough of the HSSA MnO2 was measured to evaluate the influence of space velocity. The fraction of the total amount of SO2 absorbed, g [%], vs. the SO2 throughput capacity, w [mgSO2/gMnO2] and differential SO2 absorption ratio n [%], vs. SO2 reaction ratio X [%], was evaluated. g and m are expressed by the following formulas:
Pore volume [cc/g]
4.0
3.0
gðtÞ ¼ 100 1
2.0
Z 0
t
C outðtÞ C in
dt ½%
ð2Þ
1.0
0.0
Electrical balance Inlet gas 1
10
100
Pore diameter [
1000
]
SO2
CO2
O2
N2
MFC
MFC
MFC
MFC
Fig. 2. Pore diameter distribution of HSSA MnO2.
ocean ships that use banker A as a fuel. The packing density of this HSSA MnO2 particle is 5.0 g/cm3. Fill ratio of this material is fixed by space velocity. The reaction temperature of the packed bed was 250 °C, and the space velocity was 0.5 104 h1 and 5.0 104 h1 to evaluate the influence of space velocity. The SO2 passing into the packed bed reactor was concentrated and
MFC : Mass flow controller Fig. 3. Schematic drawing of TG analysis.
Sample
Outlet gas
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Y. Osaka et al. / Separation and Purification Technology 150 (2015) 80–85 Table 1 Simulated exhaust gas composition of TG experiment.
Table 2 Simulated exhaust gas composition of desulfurization breakthrough characteristic measurement.
SO2
CO2
O2
H2O
N2
100 ppm
6 wt%
10 wt%
6 wt%
Base
wðtÞ ¼
1 mMnO2
nðtÞ ¼ 100
Z
C outðtÞ C in
SO2
CO2
O2
H2O
N2
300 ppm
6 wt%
10 wt%
6 wt%
Base
t
0
ðq C in qSO2 Þdt ½gSO2 =gMnO2
½%
ð3Þ
ð4Þ
X ðtÞ ¼ 100 gðtÞ wðtÞ =M SO2 ½%
ð5Þ
Cin [ppmv] is the inlet concentration of SO2 per unit time (in this experiment, Cin was 300 ppmv), Cout [ppmv] is the concentration of leaked SO2 per unit time from the monolith reactor, q [m3/min] is the volume flow rate of the simulated exhaust gas, and qSO2 [mg/m3] is the standard density of SO2. 4. Results and discussion
Fig. 5. SO2 capture performance comparing HSSA MnO2 with commercial MnO2 and temperature dependence on SO2 capture performance of HSSA MnO2.
100
Toatal amount of SO2 absorption ratio [%]
Fig. 5 shows a comparison of the SO2 capture performance of HSSA MnO2 and commercial MnO2 at 250 °C. Based on the results shown in Fig. 2, the BET surface area of HSSA MnO2 is 250 m2/g, and the commercialized MnO2 is 20 m2/g. Because it carries away other gas such as, CO2 and O2 before carrying away SO2 gas, it may be said that the weight gain are reactions with SO2 gas. Based on the results shown in Fig. 6, it is evident that the activation of SO2 capture is improved for the high surface area under the static condition of single particle reaction. Therefore, HSSA MnO2 has a better SO2 capture capacity than the commercial MnO2. As seen from the results of the SEM photography, the HSSA MnO2 is composed of large-scale grain of the micro order. Increase of surface area and granular separation caused improvement of SO2 capture performance. The maximum SO2 capture capacity of MnO2 is 0.74 gSO2/gMnO2. After SO2 absorption of 1.0 h, HSSA MnO2 capacity decreases to 0.07 gSO2/gMnO2, which is 7 times greater than commercialized MnO2. However, its reaction ratio is about 10%. It is thought that a surface chemical reaction has a limited path because surface area is enough large. For a further improvement of SO2 capture performance, chemical modification of HSSA MnO2 is necessary. Then, Fig. 5 also shows temperature dependence on SO2 capture performance of HSSA MnO2. The SO2 capture performance of HSSA MnO2 is apparent in all of the evaluated temperature regions. However, in the low temperature region, SO2 capture performance decreases. From the result of Fig. 5, in the reaction temperature of
99
98
97
96
95
0
0.3
0.6
0.9
1.2
1.5
SO2 through-put capacity[mgSO2/gMnO2] Fig. 6. SO2 capture performance of HSSA MnO2 at 0.5 104 h1 and 250 °C.
Fig. 4. Schematic measurement.
drawing
of
desulfurization
breakthrough
characteristic
200 °C, the HSSA MnO2 has good SO2 capture performance. In the 450 °C test, its performance is over 0.4 gSO2/gMnO2. Therefore, both the reaction rate and the SO2 capture capacity increase with a rise in reaction temperature. General desulfurization materials, for example calcium and magnesium oxide, hardly have any SO2 capture capacity in the reaction temperature of 200 °C. But, SO2 capture capacity of HSSA MnO2 at 200 °C maintains about 40% of its 400 °C capture capacity. Thus, this material maintains desulfurization performance at a wide temperature range, which is unusual among desulfurization materials. DeSOx filter design guidance at low temperatures will dictate the performance of this filter. The result of SO2 capture performance at space velocity of 0.5 104 h1 is shown in Fig. 6. As seen in the results of Fig. 6, inlet SO2 is over 99.5% absorbed by HSSA MnO2. Consequently, the
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SO2 concentration. In the plug flow experiment, the SO2 concentration in a packed bed decreases gradually due to SO2 absorption by the absorbent. Ishida [17] and Borgward [18] reported that the reaction rate of SO2 with CaO depends linearly on SO2 concentration. Therefore, in the backward of packed bed, leakage of SO2 with decrease of SO2 concentration is emanated. Nonetheless, in this high space velocity condition, it is found that high SO2 capture performance over 80% is achieved. This means this material can tolerate severe conditions and has possibility of deployment in a mobile capacity, such as an oceangoing vessel. In the future, we intend to evaluate SO2 capture performance by using this material wash coated on honeycomb.
Toatal amount of SO2 absorption ratio [%]
100
90
80
5. Conclusions 70 0.0
1.0
2.0
3.0
4.0
SO2 through-put capacity[mgSO2/gMnO2] Fig. 7. SO2 capture performance of HSSA MnO2 at 5.0 104 h1 and 250 °C.
Differential SO2 absorption ratio [%]
100
95
90
85
80 0.0
0.5
1.0
1.5
2.0
Total SO2 reaction ratio [%] Fig. 8. Influence of space velocity against SO2 capture rate of HSSA MnO2.
amount of passing SO2 is 14.4 lgSO2/(gMnO2 min). This SO2 capture performance is explained by the SO2 capture rate of HSSA MnO2, which is 1.2 103 lgSO2/(gMnO2 min), as seen in Fig. 5. Utilization efficiency of this material is at most 2.0%. However, for marine ship use, more testing of SO2 capture performance at high space velocity is needed. A higher utilization efficiency, i.e., a smaller device, is more important than deep desulfurization over 99.5%. Evaluation of SO2 capture performance at a higher space velocity of 5.0 104 h1 is investigated and its result is shown in Fig. 7. From this result, high SO2 capture performance is maintained at first, with performance gradually decreasing over time. Deep desulfurization is sustained for less time here than at the 0.5 104 h1 condition. In this condition, the amount of passing SO2 is 1.4 102 lgSO2/(gMnO2 min). The SO2 capture rate of HSSA MnO2 is 1.2 103 lgSO2/(gMnO2 min), seen in the result of Fig. 5, is adequate. Fig. 8 shows the influence of space velocity against the SO2 capture rate of HSSA MnO2 to investigate the decrease of SO2 capture performance in high space velocity conditions. From this result, the differential SO2 absorption ratio in high space velocity conditions decreases at an early stage. It is thought that the inhibition of inner particle diffusion by volume expansion, forming hydrosulfate, does not occur in this reaction range. In the TG experiment, the chamber is maintained with a constant given
DeSOx filters are used for onboard dry desulfurization to maintain air quality. The dry DeSOx filter which captures sulfur at a low temperature was investigated. To establish this, HSSA MnO2 with a high specific surface area was focused on. SO2 capture performance of single particles and the desulfurization breakthrough characteristics of HSSA MnO2 in a packed bed under high space velocity and low temperature conditions were investigated. The following knowledge was obtained from this study: HSSA MnO2 has good SO2 capture performance. It has over 0.4 gSO2/gMnO2 at 450 °C, and about 0.2 at 250 °C, because of its large specific surface area and pore diameter. SO2 capture rate of the HSSA MnO2 particle is 1.2 103 lgSO2/ (gMnO2 min) at 250 °C in a TG experiment. In the low temperature condition, it is thought that SO2 reaction rate depends on chemical reaction inner the particle. The capture of more than 99.5% SO2 was possible under the high space velocity condition of 0.5 104 h1. It is found that this material has enough SO2 reaction rate at low temperature for deep desulfurization. In this high space velocity condition, it is found that high SO2 capture performance over 80% against inlet SO2 is achieved. This material has a high enough SO2 absorption rate to capture large amounts of SO2 gas. For deep desulfurization at low temperature and high space velocity conditions, reaction rate of material is needed to increase.
References [1] J.S. Choi, W.P. Partridge, J.A. Pihl, C.S. Daw, Sulfur and temperature effects on the spatial distribution of reactions inside a lean NOx trap and resulting changes in global performance, Catal. Today 136 (2008) 173–182. [2] L. Lietti, P. Forzatti, I. Nova, E. Tronconi, NOx storage reduction over Pt/Ba/cAl2O3 catalyst, J. Catal. 204 (2001) 175–191. [3] D.H. Kim, Y.H. Chin, G.G. Muntean, A. Yezeretz, N.W. Currier, W.S. Epling, H.Y. Chen, H. Hess, C.H.F. Peden, Relationship of Pt particle size to the NOx storage performance of thermally aged Pt/BaO/Al2O3 lean NOx trap catalysts, Ind. Eng. Chem. Res. 45 (26) (2006) 8815–8821. [4] International Marine Organization, . [5] S. Kasaoka, E. Sasaoka, M. Funahara, S. Nakajima, Process Development for DryType Simultaneous Removal of Sulfur Oxides and Nitrogen Oxides, KAGAKU KOGAKU RONBUNSHU, 1982, vol. 8, no. 4, pp. 459–463 (in Japanese). [6] H. Nishioka, K. Yoshida, T. Asanuma, T. Fuukuma, Development of clean diesel NOx after-treatment system with sulfur trap catalyst, SAE Int. J. Fuels Lubric. 3 (1) (2010) 30–36. [7] B. Rubio, M.T. Izquierdo, Influence of low-rank coal char properties on their SO2 removal capacity from flue gases: 1. Non-activated chars, Carbon 35 (1997) 1005–1011. [8] N. Karatepe, I. Orbak, Y. Reha, A. Özyu˘guran, Sulfur dioxide adsorption by activated carbons having different textural and chemical properties, Fuel 87 (2008) 3207–3215. [9] P. Davini, The effect of certain metallic derivatives on the adsorption of sulphur dioxide on active carbon, Carbon 39 (2001) 419–424. [10] H.H. Tseng, M.Y. Wey, C.H. Fu, Carbon materials as catalyst supports for SO2 oxidation, catalytic activity of CuO/AC, Carbon 41 (2003) 139–149.
Y. Osaka et al. / Separation and Purification Technology 150 (2015) 80–85 [11] J.R. Ma, Z.Y. Liu, Q.Y. Liu, S.J. Guo, Z.G. Huang, Y. Xiao, SO2 NO removal from flue gas over V2O5/AC at lower temperatures: role of V2O5 on SO2 removal, Fuel Process. Technol. 89 (2008) 242–248. [12] J.X. Guo, J. Liang, Y.H. Chu, H.Q. Yin, Y.Q. Chen, Influence of Ni species of Ni/AC catalyst on its desulfurization performance at low temperature, Chin. J. Catal. 31 (2010) 278–282. [13] Q.Y. Fan, G.J. Xiu, C.Y. Hao, S.M. Chao, Y.H. Qiang, The influence of Mn species on the SO2 removal of Mn-based activated carbon catalysts, Appl. Surf. Sci. 282 (2013) 425–431. [14] T. Kitou, Y. Osaka, N. Kobayashi, A. Matsuyama, Basic study on the on-board removing low concentration SO2 under the high space velocity conditions, J. Japan Soc. Energy Resour. 31 (4) (2010) 214–221.
85
[15] Y. Osaka, M. Mmamiya, N. Kobayashi, A. Matsuyama, The basic study on the absorption of thin sulfur dioxide from diesel exhausted gas, in: Proceedings of 8th world congress of chemical engineering, 2009. [16] Y. Osaka, S. Kurahara, N. Kobayashi, M. Hasatani, A. Matsuyama, Study on the SO2 absorption behavior of composite materials for DeSOx filter from diesel exhaust, Heat Transfer Eng. 35(13) (2014) (in press). [17] M. Ishida, C.Y. Wen, Reaction rate of sulfur dioxide with particles containing calcium oxide, Environ. Sci. Technol. 7 (8) (1973) 703–708. [18] Robert H. Borgwardt, Richard D. Harvey, Properties of carbonate rocks related to sulfur dioxide reactivity, Environ. Sci. Technol. 6 (4) (1972) 350–360.
