DAEHAN HWAHAKHWOEJEE
(Journal of the Korean Chemical Society) Vol. 20, No. 5, 19
花
Printed in Republic bf Korea
촉매반응에 의한 연탄 연소가스로부터 일산화탄소의 제거 (제
1보) 鄭基鎬•李源國
한국과학원 화학 및 화학공학과
(1975. 11. 14 접수)
Removal of Carbon Monoxide from Anthracite Flue Gas by Catalytic Oxidation (I)
Ki Ho Chung and Won Kook Lee Korea Advanced Institute of Science, Seoul, Korea
(Received Nov. 14, 1975)
요 약.
연탄 연소가스중의 일산화탄소와 산소 사이의 반응을 몇가지 촉매에 대해 조사했다. 이 산화망간, 산화 동 및 그 혼합촉매를 사용하였으며, 그 실효반응 온도(elective reaction temper- ature) 는 각각 다음과 같다. 즉, MnC)2 단독촉매 및 30 % MnO2-70 % CuO 혼합촉매 는 250 °C, 60는 450 °C, 50 % MnO2-50 % CuO는 200 °C, 70 % MnO厂
30 % CuO는 180 °C였다. 실효반응 온도 이 하에서 일산화탄소의 산화율은 일산화 탄소의 농도가 증가함에 따라 감소하는 경 향을 보였 으며, 실효반응 온도 이상에서는 변화가 없었다.반응기 내 체재시간은 0.9〜1.8초의 범위 내에서는 일산화탄소 산화반응에 조금도 영향을 주지 않았다.
ABSTRACT. On the condition of adequate air supply, complete removal of carbon monoxide occurred above 650 °C. Using catalysts, the oxidation of carbon monoxide occurred at lower tempe
ratures ；on both MnO2 and 30 % MnO2 - 70 % CuO at 250 °C, on CuO at 450 °C, on 50 % MnO 2- 50 % CuO at 200 °C, and on 70 % MnO2 - 30 % CuO at 180 °C.
Manganese dioxide (/>-type) showed higher activity than cupric oxide (n-type) and a catalyst consisting of 60 % MnO2 -40 % CuO had the highest activity of all the MnO2-CuO mixture.
Over the range of transitional temperature, carbon monoxide removal efficiency decreased linearly with increasing inlet carbon monoxide concentration while temperature was fixed.
Residence time of gases in the catalytic reactor, in the range of 0.9 to 1. 8 seconds, gave no effect on carbon monoxide conversion.
INTRODUCTION
Carbon monoxide seems to be the most ubi
quitous pollutant gas in the world today. Parti
cularly in Korea, most of the population are threatened by this gas from using anthracite briquette for their heating system as the principal fuel materials.
—431
一
432 鄭基鎬•李源國
The main component of the anthracite is car
bon, 1 and carbon monoxide, as well as carbon dioxide, is produced primarily during combustion of the anthracite. 2,3
There have been many investigations on the carbo교 monoxide pollution. Morterra and Low4 investigated the chemisorption o£ carbon mono
xide on reactive silica, and Hofer and his co
workers5 determined the characteristics of several catalysts f。호 the oxidation of ethylene and carbon monoxide. For practical purpose, the catalytic muffler was developed to oxidize residual com
bustible matter which was discharged from the automobile engine. 6
In Korea, many workers have been investi- 잉ating on controlling carbon monoxide gas libe
rated from anthracite briquette.7,9 An efficient carbon monoxide detector and alarm system were developed by Kim et. al.10 Lee et. al.11 studied the several catalysts on burning of Korean anthracite, and effective combustion devices were also developed.12,13 Hwang and Son14 found that the combustion rate was rapid in the environment of proper moisture than dry.
Carbon monoxide can be removed by a selec
tive oxidation to carbon dioxide, by catalytic reaction with hydrogen to hydrocarbons, by absorption in cuprous salt solutions or by reaction with steam on a catah'st to carbon dioxide and hydrogen, but oxidation method will be the most convenient to the heating system used in this country. Carbon monoxide is oxidized con
tinuously to carbon dioxide over the temperature of 650°C.15 For pollution control, however, oxidation at rather lower temperature is required, and highly selective catalysts that will convert carbon monoxide to carbon dioxide are a great demand.
It is obvious that 力一type or n-type metal ox거es play an important catalytic role on the oxidation of carbon monoxide alone. 16~19 The
mechanism of the catalytic oxidation of carbon monox너e was investigated by many workers,20^22 and MnOz (/»-type) showed a high catalytic activity on carbon monoxide oxidation, however, CuO (n-type) rather mild activity.16,17 The addition of foreign ions (such as Cu2+) into the manganese dioxide lattice might modify the concentration and distribution of holes and electrons by suitable changes of the Fermi level of the semi-conductor23.
In this experiment, catalytic activities of ma
nganese dioxide and admixtures with cupric oxide were investigated for the oxidation of carbon monoxide contained in the anthracite flue gas.
EXPERIMENTAL METHOD
Experiment was carried out by using a small catalytic reactor (2. 5cm I. D. and 30cm long) which was made of Vycor glass. A s사lematic diagram of the catalytic reactor is illustrated in Fig. 1.
The reactor was heated electrically, and con
trolled by a variable transformer. Temperature in the catalytic reactor was measured by a pyrometer with alumel-chromel thermocouple.
-
——
- 트 w o ——
Journal of the Korean Chemistry Society
433
Fire brick surrounded the reactor was used as a insulator, and inlet gas was introduced from the top of the reactor. Vycor glass chips were filled at the lower side of the reactor to support cata
lyst and 30cc of catalyst was followed on it.
Fig. 2 shows a thematic diagram of the equipment set-up. From the anthracite furnace to the suction pump, a gas line was built with 4 mm glass tube. Gas could be passed through it with the aid of suction pump. Gas flow rate was checked with a rotameter, and a manometer was employed to show the pressure drop between entrance and exit of the reactor. The gas trap was made of alternate layers of silica gel, cal
cium chloride, calcium oxide and sodium hy
droxide, which removed water vapor, hydrogen sulfide and sulfur dioxide, respectively.
Samples of gas were collected respecting from the gas line at the place of inlet and outlet the reactor, and analyzed by the method of iodine pentoxide24 and by a gas chromatography.25
Cupric oxide and manganese dioxide used as catalysts in this experiment were a brand of
Japan Wago pure Chemical Industries and were reagent grade. Several powder mixtures of these two materials were knealed with distilled water and pelleted to 3 mm X 3 mm cylindrical shape under the pressure of about 200 psi. Then these pellets were heated at the temperature of 500° C for 2 hours. Then these products were kept in the sealed bottle so as not to adsorb any un wanted components from the air.
RESULTS AND DISCUSSION
While burning the anthracite, temperature above burning area reached to 850〜900 °C at maximum. It showed no effect in carbon mono
xide conversion by varying the gas flow rate from 1,000 to 2,000 cc/min or the residence time in the reactor from 1.8 to 0.9 second.
These showed that this range of residence time would be sufficient for the oxidation of carbon monoxide in the catalyst bed, so that the effect of surface area in catalysts used could be negli
gible for overall reaction in this experiment. In general, for a given catalyst, the greater the
鄭基鎬•李源國 434
amount cf surface available to the reacting gas, the better conversion can be obtained.
About 20,000 ppm of carbon monoxide was liberated on dry basis when the burning was not in good condition. Anthracite Rue gas ccntaincd about 1 to 2 volume percent of CO, in general, 8 to 9% cf CO2, 15% O2, 75% N2 and a trace
(less than 0. 04%) cf H2 on dry basis. A trace of sulfur oxides, hydregen sulfide and hydrocar
bons were predicted, but not detectable. Instru
ment used was Varian Aerograph cf model 202 with TCD, and the column involved 90% of molecular sieve 5A and 10% of molecular sieve 13X.
The effect of temperalure on the percent con
version of carbon monoxide is presented in Fig.
4 to 8 for each catalyst, and in Fig. 3 without catalyst. When catalyst was not used, carbon monoxide oxidation was started at about 4-50 °C but the reaction rate was very slow. Over 650
°C. carbon monoxide was oxidized continuously (Fig, 3). Both MnO2 and 30 % MnO2 - 70 % CuO oxidized carbon monoxide completely at 250 °C, CuO at 450 °C, 50 % MnO2-50 % CuO at 200 CC, and 70 % MnO2-30 % CuO at 180° C.
MnO2 Cotype) showed better activity than CuO (n-t^-pe), and the former had some catalytic activity even at room temperature. Inteipolation in Fig. 9 indicated that the 60% MnO2 - 40 弓 CuO as the best catalyst of all the MnO2~C：j.O system.
The effective reaction temperatures of the catalysts used in 나］
诅
expariment were somewhat higher than the reaction of pure carbon monoxide with oxygen. These results seemed to ba from the difference in catalyst preparation p:x>
cedure26 in each cases and/or the interaction of the foreign gases in the inlet gas mixture during reaction. Inlet gas used here might be a mixture of 0
务
N2, CO2, CO, H2O, H2 and a trace ofIOO ^.00 300. 400 5OC 600 Reaction terr^p ,CC
Fig. 5. Effect of temperature on carbon monoxide conversion (with CuO).
Fig- 3. Effect of temperature on carbon r財mow，：。 conversion (without catalyst).
Fig. 4. Effect or temperature on carbon monoxide
■ conversion (with MnO2).
恥思.6. E任ect of temperature on carbon monoxide conversion (with 30% MnO2-70 % CuO).
Journal of the Korean Chemistry Society
촉매반응에 의한 연탄연소가스르부더 일산화단土의 제거 （제 1 느; 435
Fig. 7. E任ect of temperature on carbon monoxide conversion (with 50 % MnO2~50 % CuO).
Fig. 8. Effect of temperature on carbon monoxide conversion (with 70 % MnC)2~30 % CuO).
SOZ, H2S and hydrocarbons. It was shown22 that oxygen and moist air a任ected the semi
conductivity of cuprous oxide at room temper
ature.
The initial step of the reaction of carbon monoxide oxidation on MnO2 may be the pro
duction of positive holes in MnO2 lattice by the excess of oxygen. The progressive mechanism of the carbon monoxide oxidation on the MnO2 may be represented；
(1) 102 ——> O\ds + ©, adsorption of O2 (2) CO +
㊉
——> CO^ds， adsorption of CO (3) CC广ads+OLds—>CO+acl3-O~atis, reactionstep (4) CO^ads-O_ads-^CO2, desorption step
Where ® represents the positive hole, CO+ads is the carbon monoxida molecule adsorbed in the
Vol. 20, No. 5, 1976
vacancy and Oaas~ is th은 oxygen atom dissaved in the active site. Oxygen was always adsorbed as a negatively charged species, giving rise the enhancement of conductivity to />-type oxide.
As © is dissipated because of combining carbon monoxide with © and COads++Oads--- >
COadJ-OadsL oxygen in the 흥as mixture have to bs dissolved in MnO2 lattice in order to fill up the Oads- consumed. From this viewpoint, production rate of COads+-Oads- is dependent upon the number of positive hole, and consequently COads*-°ad
厂
—부CO2 is depended mainly upon§。2——>0涵
厂
+㊉
.It was already proved27 that 4O2—>Oad「+㊉
was the rate determining step in the catalytic oxidation of carbon monoxide, and the partial pressure of the oxygen showed severe effect on this reactionn and that carbon monoxide affected rather mildly than the oxygen.The introduction of Cu2+ to MnOo lattice might increase the number of positive hole and
436 鄭基鎬,李源國 60
1000 2000 3000 4000 5000 6000 7000 8000 9000 Inlet CO concentraiion,ppm
Fig. io. Effect of CO concentration on removal e伍ciency with CuO at temperature of 300 °C.
the reaction on the admixtures with CuO would begin on the condition of higher concentration of positive hole than M11O2 alone. Parravano23 and many other workers22 showed the influence of doping the lower or higher-valence ions to the p-type semi-conductor. But exact mechanism of the catalytic reaction in this experiment was not cleared at this stage, and the mechanism 'will be reported in future study.
In Fig. 10, the effect of inlet carbon monoxide concentration on carbon monoxide conversion was depicted for the reaction on CuO at 300°C.
With enough oxygen, carbon monoxide conver sion was affected severely by the inlet carbon monoxide concentration in the transitional tem
perature, but negligible above the effective reaction temperature. During experiment, inlet carbon monoxide concentration was controlled to minimize its effect on carbon monoxide con
version.
Pressure drop between reactor entrance and -exit showed 3 mmHzO. In the actual application, the catalysts, M11O2 or admixtures with CuO, can be employed by making a shape of hone
comb or wire screens to remove carbon mono
xide from the flue gas of the domestic anthracite briquette. The honeycomb unit has the advan
tages of low pressure drop, good distribution of gas to the entire catalyst surface, ease of handl ing, high volumetric e伍ciency, and thermal stability.
CONCLUSION
On the condition of adequate air supply, com plete removal of carbon monoxide occurred above 650 °C. Using catalysts, the oxidation of carbon monoxide occurred at lower temperatures;
on both MnO2 and 30 % MT1O2 - 70 % CuO at 250 °C, on CuO at 450 °C, on 50 % M11O2-50
% CuO at 200 °C, and on 70 % MnO2-30 % CuO at 180 °C.
Manganese dioxide (ZType) showed higher activity than cupric oxide (n-type) and a catalyst consisting of 60 % MnO2 - 40 % CuO had 바此 highest activity of all ,the MnO2-CuO system.
Over the range of transitional temperature, carbon monoxide removal efficiency decreased linearly with increasing inlet carbon monoxide
촉매반응에 의한 연탄연소가스로부터 일산화탄소의 제거 （제 1보） 437 concentration while temperature was fixed.
Residence time of gases in the catalytic re
actor, in the range of 0. 9 to L 응 seconds, gave no effect on carbon monoxide conversion.
These catalysts can be practically used to remove comparative amount of carbon monoxide from the anthracite flue ga옹 with a 옹hape of honeycomb or wire screen catalyst bed and placing on the anthracite briquette.
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Vol. 20, No. 5, 1976
