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Dynamic NO adsorption characteristics of iron-treated activated carbon fibers
ooo44981/87 53.00+0.00 PwymonJournals Ltd.
~nnoaphvic hironmrnrVol.21.NO.9. pp.2053-2055, 1987. Prinwdin Gut Britrin.
SHORT COMMUNICATION DYNAMIC NO ADSORPTION CHARACTERISTICS OF IRON-TREATED ‘ACTIVATED CARBON FIBERS KATSUMI KANEKO,
Department
SUMIOOZEKI and
KATSUYA INOUYE
of Chemistry, Faculty of Science, Chiba University,
Yayoicho,
Chiba-shi 260, Japan
(First received 12 March 1986 and received for publication 6 March 1987) Abstract-The breakthrough curve for NO adsorption on the activated carbon fibers treated in iron salt solutions was determined. They can adsorb much more NO than granular activated carbon by a factor of more than 10 from a Rowing 300 ppm NO-N, mixed gas at 1OOCand 20 ml min- the most effective one of the iron-treated carbon fibers of 0.2 g is able to reduce the NO concentration from 300 ppm to 30 ppm. These adsorbents can adsorb the same amount of NO from even a 300 ppm NO-500 ppm SO1-10% CO,-10% HrO-1 % Os-N2 mixed gas.
‘;
,F;ey word index: NO, adsorption, FeOOH, atmospheric pollutant, carbon fiber.
The concentration of NO in the atmospheric environment does not decrease in spite of various efforts; rather, it is gradually increasing in the urban atmosphere according to reports by Munger et al. (1983k Georgii (1984)and Murano (1985). As the waste gases from automobiles mainly lead to these increases of NO concentration, a concise, cheap and effective method to remove NO from the exhausted gas must be established in order to protect our environment. A recent study by Sexton and Wesolowski (1985)showed that not only outdoor, but also indoor pollution, even in non-industrial environments, is dangerous for our health. The method for removing the indoor NO should be easier and less complicated. Adsorption of NO on solids should be helpful in developing such a new method for NO removal, if there is a good adsorbent for NO. Ermenc (1956) produced a recovery system of dilute NO by use of a silica gel as a catalyst for oxidation of NO to NO,. Ganz (1958) renorted that activated carbons (AC) are the m&t active for ‘NG of several practical adsorbents, but their adsorption capacity for NO is much smaller than that for SOs. Later Joitheet al. (1972)and Urano et al. (1978)confirmed that AC, silica gels and zeolites are less effective for NO. Hence it is expected that a new adsorbent for a new fixation mechanism for NO will be found. Kaneko and lnouye have obtained a promising candidate, the iron-treated activated carbon fibers (ACF) which have much greater adsorption capacity and rate for NO than the generally used granular AC and are simultaneously effective for NO and SOs from static adsorption measurements, and Kaneko (1987) has reported that cx-FeOOH dispersed ACF shows a chemisorption-assisted micropore filling of NO. These authors have also found that NO,adsorption activity of aFeGGH dispersed ACF is enhanced by heat treatment above 3OO*Cin nacuo. Furthermore, ACFcan take the form of a felt of great practical value. We used cellulose-based ACF (ACF-CEL), PAN-based ACF (ACF-PAN) made from polyacrylonitrile and kynolbasedACF(ACF-KNL). ACF-PAN has nitrogen atoms in the carbon chains (the percentage of nitrogen/carbon = 6-73 and ACF-KNL is prepared from phenol resin. Three kinds of the treatments were made: a-ACF: ACF was treated in 0.6 M ferric sulfate solution at 30°C and pH 13 for 6 h.
a-ACF(ox): The ACF pre-oxidized in 6 M HNOs at 100°C for 20 min was treated in a similar way to the a-ACF. /I-ACF: ACF was treated in 0.2 M ferric chloride solution at 100°C and pH 2 for 4 h. The amounts of Fe deposited on the ACF determined by chemical titration are summarized in Table 1. The dynamic NO adsorption characteristics of these samples were measured by use of a flow system with a 300 ppm NO-N, mixed gas at the velocity of 20 ml min- ’ and 100°C. Also the NO adsorption characteristics of the iron-tats ACF-CEL samples from the mixed gas of 3OOppm NO-SOOppm SO,-10% CO,-10% HrO-1% Or-N2 were examined. The flow adsorption apparatus is composed of a tedlar bag, an adsorption cell, flow meters and sampling system, as shown in Fig. 1. Prior to the adsorption measurement, samples were dried at 100°C in an Ns stream of 20 ml min-’ for 60 min. Thechange in the NOconcentration of the gas through the sample layer of 0.2 g during 60 min (I 50 min for part of samples) was determined by calorimetry with naphthylethylenediamine; the NO gas in the 25 ml gas sampled from the adsorption system was oxidized with a 1% 03-Or mixed gas so that it dissolved in water in the form of NO;, then the absorbance of the solution after the reaction of naphthylethylenediamine and the products of NO; formed by Zn powder with sulfani~mide were determined with the use ofa 545 nm light. The specific surface am S, ofsamples was obtained by a f-plot analysis (Broelchoff and L&en, 1970) of nitrogen adsorption isotherms at - 196°C. The S, values are listed in Table I. Figure Zshows breakthrough curves for NOadsorption on iron-treated ACF-CEL from the 3OOppm NO-N1 gas at IOV’C. In this system &treatment is very eflective for removal of NO. The fi-ACF-CEL can reduce the NO co~nt~t~on from 300 ppm to 30 ppm and its b~kthrou~ time is much larger than the o&et ACF-CEL. o-or-Treatment did not improve the dynamic adsorption characteristics, although it markedly enhanced the static NO adsorption activity reported in an earlier paper (Kaneko. 1987). a-Treatment slightly improved the dynamic adsorption characteristics. Figure 3 shows breakthrough curves for NO adsorption on irontreated ACF-PAN. Both o-ox- and &treatments produced remarkably elhcient adsorbent for NO; they can lower the NO concentration to less than I00 ppm and a-ox- and /I-
2054
Short Communication Table 1. Amounts of NO adsorbed for 60 min and iron deposited and specific surface area ACF-PAN None
5, (m’g-‘) NO (mg g- ‘) Fe (wt %) S (m*g-‘) x 0 (mg g-‘)
u-Treatment
J-Treatment
Fe W %)
a-ox-Treatment
S (m’g-‘) r-R) (mgg-r) Fe (wt %) S (m*g-‘) x 0 (mg g‘ ‘)
ACF-CEL
870 0.05 4 810 0.05 4 880 1.0 2 400 1.3
1400 0.1 4 1490 0.7 5 1650 1.7 5 605 0.1
ACF-KNL 1500 11 1500 2 1320 0.5 5 860 0.8
The amounts of NO adsorbed for coal-based AC, coconut shell AC, silica gel and MS-13X are 0.1, 0.06, < 0.05 and -c 0.05 mg g- ‘, respectively.
Silica gels N2 Time
IminI
Fig. 1. Flow adsorption apparatus. Fig. 3. Breakthrough curves for NO adsorption on iron-treated ACF-PAN at 100°C.
ly.-.-.*
300
z 5
200
a -ox-ACF-CEL
? B
a -ox-ACF-KNL
s E e I00 E c? s u
0’
a -OX -ACF-PAN s ” I
I
20 Time
I
I
40
I
I
60
(min)
Fig. 2. Breakthrough curves for NO aosorption on iron-treated ACF-CEL at 100°C.
ACF-PAN are not saturated with NO within @min. In particular,a-ox-ACF-PAN can continue toadsorbalmost the same amount of NO after 60 min as after 10min. The breakthrough curves of a-ox-treated ACF sampks are shown
OI
Time
imin)
4. Breakthrough curves NO adsorption on a-ox-treated ACF of g and AC-NUT 0.5 g.
in Fig. 4. Their adsorption characteristics are very ditTerent from one another, though all a-ox-treated ACF can remove much more NO from the diluted NO-N2 mixed gas than coconut shell AC. The breakthrough curve of a-ox-ACF-
2055
Short Communication
200 6 5 c e 0
E:: 100 5 0.
o
NO-N2
a
NO-S02-CO*-H20-O2
I
I
I
I
I
30
60
90
120
150
Time
IminI
Fig. 5. Breakthrough curves for NO adsorption of/3-ACF-CEL and AC-NUT from the 300 ppm NO-N2 and 300 ppm NO-500 ppm SOI-lO% CO1-10% H@-I % 01-N, at 100”.
PAN is placed at the lowest position and almost parallel with the abscissa in Fig. 4. a-ox-ACF-PAN has the best adsorption characteristics, namely, the greatest adsorption rate and capacity of these four samples. a-ox-ACF-KNL is also effective in removing NO. Theadsorption amountscalculated from the breakthrough curves within 60 min are summarized in Table 1. The amounts of NO adsorbed on /3-ACF-CEL, aox-ACF-PAN and a-ox-ACF-KNL are greater than those of AC, silica gels and teolites by a factor of over 10, because the iron-treated ACF with a longer breakthrough time than 60 min should be able to adsorb more NO than the values in Table I. Figure 5 shows the breakthrough curves of /?-ACF-CEL and AC-NUT from the 300 ppm N&N2 and 300ppm NO-500 ppm SO1-10% CO,-10% H&l %0,-N, mixed gases durmg I50 min. The data indicate that the-coexistence of SO*, COz, Hz0 and Ox in the 300 ppm NO-N, mixed gas does not damage the NO adsorbability of the g-ACF-CEL. The NO adsorbability of g-ACF-CEL during I50 min is much better than that of AC-NUT: the amount of NO adsorption of /?-ACF-CEL is over lOOtimes larger than that of the AC-NUT, comparing the adsorption amounts per unit weight of the adsorbents. Also the NO adsorbability of aACFCELdoes not decline despite the presence of SO1, CO,, Hz0 and Oz. In conclusion the iron-treated ACF exhibits favourable dynamic NO adsorption characteristics. These treated ACF give us the possibility that the residual NO from exhaust gases can be removed by a simple adsorption method, although further examination of these adsorbents from the viewpoint of chemical engineering is required before their practical use.
Acknowledgcmenrs-This work was supported by the Environmental Science Project (R36-1) of the Ministry of Education, Japanese Government. The assistance of Mr T. Funamoto in measurements of NO adsorption from the multi*mponent mixed gas is appreciated.
REFERENCES
Broekhoff J. C. P. and Linsen B. G. (1970) Studies on pore systems in adsorbents and catalysts. In Physical and Chemical Aspects o/ Adsorbenrs and Catalysts (Edited by Linsen B. G.) Chapt. I. Academic Press, New York. Ermenc E. D. (1956) Wisconsin process system for recovery of diluted oxides of nitrogen. them. Ening Prog. 488-492. Ganz S. N. (I 958) Adsorption of NO on solid adsorbents. Zh. Prikl. K&m. 3i, l38-‘140. Georgii H. W. (1984) Atmospheric pollution by SO1 and oxidants. In Polluranrs and Their Ecoroxicological
publication). Kaneko K. and Inouye K. (1987b) Erect of heat treatment in uacuo on the NO adsorption activity of a-FeOOH dispersed activated carbon fibers. Carbon (in press). Munger J. W.. Jacob D. J., Waldman J. M. and Hoffmann M. R. (1983) Fog water chemistry in an urban atmosphere. J. geophys. Res. 88, 5109-5121. Murano K. (1985) Behavior of acidic pollutants produced by photochemical Environmental Science Project (B-248-R-l l-8), Japan, Chapt. 5. Sexton K. and Wesolowski J. J. (1985) indoor air quality. Enoir. Sci. Technol. 19, 305-309. Urano K., Tanigawa N., Masuda T. and Kobayashi Y. (1978) Oxidation adsorption of nitrogen monoxide on activated carbon. Nippon Kagaku Kaishi 303-308.
~nnoaphvic hironmrnrVol.21.NO.9. pp.2053-2055, 1987. Prinwdin Gut Britrin.
SHORT COMMUNICATION DYNAMIC NO ADSORPTION CHARACTERISTICS OF IRON-TREATED ‘ACTIVATED CARBON FIBERS KATSUMI KANEKO,
Department
SUMIOOZEKI and
KATSUYA INOUYE
of Chemistry, Faculty of Science, Chiba University,
Yayoicho,
Chiba-shi 260, Japan
(First received 12 March 1986 and received for publication 6 March 1987) Abstract-The breakthrough curve for NO adsorption on the activated carbon fibers treated in iron salt solutions was determined. They can adsorb much more NO than granular activated carbon by a factor of more than 10 from a Rowing 300 ppm NO-N, mixed gas at 1OOCand 20 ml min- the most effective one of the iron-treated carbon fibers of 0.2 g is able to reduce the NO concentration from 300 ppm to 30 ppm. These adsorbents can adsorb the same amount of NO from even a 300 ppm NO-500 ppm SO1-10% CO,-10% HrO-1 % Os-N2 mixed gas.
‘;
,F;ey word index: NO, adsorption, FeOOH, atmospheric pollutant, carbon fiber.
The concentration of NO in the atmospheric environment does not decrease in spite of various efforts; rather, it is gradually increasing in the urban atmosphere according to reports by Munger et al. (1983k Georgii (1984)and Murano (1985). As the waste gases from automobiles mainly lead to these increases of NO concentration, a concise, cheap and effective method to remove NO from the exhausted gas must be established in order to protect our environment. A recent study by Sexton and Wesolowski (1985)showed that not only outdoor, but also indoor pollution, even in non-industrial environments, is dangerous for our health. The method for removing the indoor NO should be easier and less complicated. Adsorption of NO on solids should be helpful in developing such a new method for NO removal, if there is a good adsorbent for NO. Ermenc (1956) produced a recovery system of dilute NO by use of a silica gel as a catalyst for oxidation of NO to NO,. Ganz (1958) renorted that activated carbons (AC) are the m&t active for ‘NG of several practical adsorbents, but their adsorption capacity for NO is much smaller than that for SOs. Later Joitheet al. (1972)and Urano et al. (1978)confirmed that AC, silica gels and zeolites are less effective for NO. Hence it is expected that a new adsorbent for a new fixation mechanism for NO will be found. Kaneko and lnouye have obtained a promising candidate, the iron-treated activated carbon fibers (ACF) which have much greater adsorption capacity and rate for NO than the generally used granular AC and are simultaneously effective for NO and SOs from static adsorption measurements, and Kaneko (1987) has reported that cx-FeOOH dispersed ACF shows a chemisorption-assisted micropore filling of NO. These authors have also found that NO,adsorption activity of aFeGGH dispersed ACF is enhanced by heat treatment above 3OO*Cin nacuo. Furthermore, ACFcan take the form of a felt of great practical value. We used cellulose-based ACF (ACF-CEL), PAN-based ACF (ACF-PAN) made from polyacrylonitrile and kynolbasedACF(ACF-KNL). ACF-PAN has nitrogen atoms in the carbon chains (the percentage of nitrogen/carbon = 6-73 and ACF-KNL is prepared from phenol resin. Three kinds of the treatments were made: a-ACF: ACF was treated in 0.6 M ferric sulfate solution at 30°C and pH 13 for 6 h.
a-ACF(ox): The ACF pre-oxidized in 6 M HNOs at 100°C for 20 min was treated in a similar way to the a-ACF. /I-ACF: ACF was treated in 0.2 M ferric chloride solution at 100°C and pH 2 for 4 h. The amounts of Fe deposited on the ACF determined by chemical titration are summarized in Table 1. The dynamic NO adsorption characteristics of these samples were measured by use of a flow system with a 300 ppm NO-N, mixed gas at the velocity of 20 ml min- ’ and 100°C. Also the NO adsorption characteristics of the iron-tats ACF-CEL samples from the mixed gas of 3OOppm NO-SOOppm SO,-10% CO,-10% HrO-1% Or-N2 were examined. The flow adsorption apparatus is composed of a tedlar bag, an adsorption cell, flow meters and sampling system, as shown in Fig. 1. Prior to the adsorption measurement, samples were dried at 100°C in an Ns stream of 20 ml min-’ for 60 min. Thechange in the NOconcentration of the gas through the sample layer of 0.2 g during 60 min (I 50 min for part of samples) was determined by calorimetry with naphthylethylenediamine; the NO gas in the 25 ml gas sampled from the adsorption system was oxidized with a 1% 03-Or mixed gas so that it dissolved in water in the form of NO;, then the absorbance of the solution after the reaction of naphthylethylenediamine and the products of NO; formed by Zn powder with sulfani~mide were determined with the use ofa 545 nm light. The specific surface am S, ofsamples was obtained by a f-plot analysis (Broelchoff and L&en, 1970) of nitrogen adsorption isotherms at - 196°C. The S, values are listed in Table I. Figure Zshows breakthrough curves for NOadsorption on iron-treated ACF-CEL from the 3OOppm NO-N1 gas at IOV’C. In this system &treatment is very eflective for removal of NO. The fi-ACF-CEL can reduce the NO co~nt~t~on from 300 ppm to 30 ppm and its b~kthrou~ time is much larger than the o&et ACF-CEL. o-or-Treatment did not improve the dynamic adsorption characteristics, although it markedly enhanced the static NO adsorption activity reported in an earlier paper (Kaneko. 1987). a-Treatment slightly improved the dynamic adsorption characteristics. Figure 3 shows breakthrough curves for NO adsorption on irontreated ACF-PAN. Both o-ox- and &treatments produced remarkably elhcient adsorbent for NO; they can lower the NO concentration to less than I00 ppm and a-ox- and /I-
2054
Short Communication Table 1. Amounts of NO adsorbed for 60 min and iron deposited and specific surface area ACF-PAN None
5, (m’g-‘) NO (mg g- ‘) Fe (wt %) S (m*g-‘) x 0 (mg g-‘)
u-Treatment
J-Treatment
Fe W %)
a-ox-Treatment
S (m’g-‘) r-R) (mgg-r) Fe (wt %) S (m*g-‘) x 0 (mg g‘ ‘)
ACF-CEL
870 0.05 4 810 0.05 4 880 1.0 2 400 1.3
1400 0.1 4 1490 0.7 5 1650 1.7 5 605 0.1
ACF-KNL 1500 11 1500 2 1320 0.5 5 860 0.8
The amounts of NO adsorbed for coal-based AC, coconut shell AC, silica gel and MS-13X are 0.1, 0.06, < 0.05 and -c 0.05 mg g- ‘, respectively.
Silica gels N2 Time
IminI
Fig. 1. Flow adsorption apparatus. Fig. 3. Breakthrough curves for NO adsorption on iron-treated ACF-PAN at 100°C.
ly.-.-.*
300
z 5
200
a -ox-ACF-CEL
? B
a -ox-ACF-KNL
s E e I00 E c? s u
0’
a -OX -ACF-PAN s ” I
I
20 Time
I
I
40
I
I
60
(min)
Fig. 2. Breakthrough curves for NO aosorption on iron-treated ACF-CEL at 100°C.
ACF-PAN are not saturated with NO within @min. In particular,a-ox-ACF-PAN can continue toadsorbalmost the same amount of NO after 60 min as after 10min. The breakthrough curves of a-ox-treated ACF sampks are shown
OI
Time
imin)
4. Breakthrough curves NO adsorption on a-ox-treated ACF of g and AC-NUT 0.5 g.
in Fig. 4. Their adsorption characteristics are very ditTerent from one another, though all a-ox-treated ACF can remove much more NO from the diluted NO-N2 mixed gas than coconut shell AC. The breakthrough curve of a-ox-ACF-
2055
Short Communication
200 6 5 c e 0
E:: 100 5 0.
o
NO-N2
a
NO-S02-CO*-H20-O2
I
I
I
I
I
30
60
90
120
150
Time
IminI
Fig. 5. Breakthrough curves for NO adsorption of/3-ACF-CEL and AC-NUT from the 300 ppm NO-N2 and 300 ppm NO-500 ppm SOI-lO% CO1-10% H@-I % 01-N, at 100”.
PAN is placed at the lowest position and almost parallel with the abscissa in Fig. 4. a-ox-ACF-PAN has the best adsorption characteristics, namely, the greatest adsorption rate and capacity of these four samples. a-ox-ACF-KNL is also effective in removing NO. Theadsorption amountscalculated from the breakthrough curves within 60 min are summarized in Table 1. The amounts of NO adsorbed on /3-ACF-CEL, aox-ACF-PAN and a-ox-ACF-KNL are greater than those of AC, silica gels and teolites by a factor of over 10, because the iron-treated ACF with a longer breakthrough time than 60 min should be able to adsorb more NO than the values in Table I. Figure 5 shows the breakthrough curves of /?-ACF-CEL and AC-NUT from the 300 ppm N&N2 and 300ppm NO-500 ppm SO1-10% CO,-10% H&l %0,-N, mixed gases durmg I50 min. The data indicate that the-coexistence of SO*, COz, Hz0 and Ox in the 300 ppm NO-N, mixed gas does not damage the NO adsorbability of the g-ACF-CEL. The NO adsorbability of g-ACF-CEL during I50 min is much better than that of AC-NUT: the amount of NO adsorption of /?-ACF-CEL is over lOOtimes larger than that of the AC-NUT, comparing the adsorption amounts per unit weight of the adsorbents. Also the NO adsorbability of aACFCELdoes not decline despite the presence of SO1, CO,, Hz0 and Oz. In conclusion the iron-treated ACF exhibits favourable dynamic NO adsorption characteristics. These treated ACF give us the possibility that the residual NO from exhaust gases can be removed by a simple adsorption method, although further examination of these adsorbents from the viewpoint of chemical engineering is required before their practical use.
Acknowledgcmenrs-This work was supported by the Environmental Science Project (R36-1) of the Ministry of Education, Japanese Government. The assistance of Mr T. Funamoto in measurements of NO adsorption from the multi*mponent mixed gas is appreciated.
REFERENCES
Broekhoff J. C. P. and Linsen B. G. (1970) Studies on pore systems in adsorbents and catalysts. In Physical and Chemical Aspects o/ Adsorbenrs and Catalysts (Edited by Linsen B. G.) Chapt. I. Academic Press, New York. Ermenc E. D. (1956) Wisconsin process system for recovery of diluted oxides of nitrogen. them. Ening Prog. 488-492. Ganz S. N. (I 958) Adsorption of NO on solid adsorbents. Zh. Prikl. K&m. 3i, l38-‘140. Georgii H. W. (1984) Atmospheric pollution by SO1 and oxidants. In Polluranrs and Their Ecoroxicological
publication). Kaneko K. and Inouye K. (1987b) Erect of heat treatment in uacuo on the NO adsorption activity of a-FeOOH dispersed activated carbon fibers. Carbon (in press). Munger J. W.. Jacob D. J., Waldman J. M. and Hoffmann M. R. (1983) Fog water chemistry in an urban atmosphere. J. geophys. Res. 88, 5109-5121. Murano K. (1985) Behavior of acidic pollutants produced by photochemical Environmental Science Project (B-248-R-l l-8), Japan, Chapt. 5. Sexton K. and Wesolowski J. J. (1985) indoor air quality. Enoir. Sci. Technol. 19, 305-309. Urano K., Tanigawa N., Masuda T. and Kobayashi Y. (1978) Oxidation adsorption of nitrogen monoxide on activated carbon. Nippon Kagaku Kaishi 303-308.