This set of Air Pollution Control Multiple Choice Questions & Answers (MCQs) focuses on “Gaseous Pollutants – Control of Nitrogen Oxides – Set 3”.
1. To what value can the nitrogen oxide concentration in flue gases be reduced when calcium hydroxide is used as an absorption medium?
a) 200 ppm
b) 150 ppm
c) 100 ppm
d) 50 ppm
View Answer
Explanation: Using calcium hydroxide as an absorption medium reduces the nitrogen oxide emissions to 200 ppm. Ammonia liquor absorbent reduces the concentration to 100 ppm or so. Both these absorbents recover the oxides as fertilisers.
2. Which of the following can be used as an adsorbent to recover NO and NO2?
a) Alkalised alumina
b) Manganese oxide
c) Activated alumina
d) Zeolites
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Explanation: Among the given options, manganese oxide is the only adsorbent commonly used for nitrogen oxide removal. Other adsorbents are silica gel, activated carbon, molecular sieves. Metal oxides like alkalised ferric oxide are also very potent.
3. Why is activated carbon not a very viable adsorbent for the adsorption of nitrogen oxides?
a) It cannot handle high concentrations
b) Its selectivity is low
c) Efficiency reduces in the presence of other compounds
d) Regeneration is difficult
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Explanation: Activated carbon, although an efficient adsorbent, is not very viable for the capture of nitrogen oxides. It is because the presence of oxygen reduces the absorption of nitrogen oxides. This limitation makes it unsuitable.
4. Which adsorbent is advantageous for the adsorption of nitric acid tail gases?
a) Activated carbon
b) Alkalised ferric oxide
c) Manganese oxide
d) Molecular sieves
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Explanation: Molecular sieves are viable for the adsorption of the tail gases of nitric acid production. The setup commonly used runs two batch adsorbers: one does adsorption, the other regenerated adsorbent. The emissions contain about 50 ppm of nitrogen oxides.
5. Most adsorbents have low efficiencies for the adsorption of nitrogen oxides at high concentrations.
a) True
b) False
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Explanation: Most adsorbents have low efficiencies for the adsorption of nitrogen oxides at typical concentrations in the flue gas. Typical nitrogen oxide concentrations in the flue gas are very low. Therefore, the given statement is false.
6. What is the disadvantage of using molecular sieves for the adsorption of nitric acid tail gases?
a) Selectivity is low
b) Concentration of nitrogen oxides is too low
c) Space requirement is high
d) Operating costs are high
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Explanation: Explanation: The main disadvantage of using molecular sieves is that they have low selectivity for nitrogen oxide adsorption. This limitation results in the simultaneous adsorption of water vapour and low collection efficiency of the target.
7. Which is the most promising adsorbent of nitrogen oxide?
a) Ferrous salt
b) Molecular sieves
c) Activated carbon
d) Alkalised alumina
View Answer
Explanation: Ferrous salts are promising adsorbents of nitrogen oxides. The best adsorbents are those that are easily regenerated and that have a high selectivity for nitrogen oxides. Molecular sieves have low selectivity.
8. Which catalyst is used for the catalytic decomposition of NO?
a) Aluminium oxide
b) Chromium (III) oxide
c) Ferric oxide
d) No catalyst is efficient
View Answer
Explanation: The decomposition of nitric oxide is very slow, so slow that heterogenous catalysts are unable to speed up the reaction. Although many such catalysts exist, they are unusable at moderate temperatures.
9. Why is catalytic reduction preferred over the catalytic decomposition of nitric oxide?
a) Efficiency is low
b) Decomposition is low
c) Reduction has higher efficiency
d) The operating cost is low
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Explanation: The decomposition of NO is very slow. Additionally, the flue gases contain reducing agents. These reasons make the catalytic reduction viable over the catalytic decomposition of nitric oxide. The catalysts used for this purpose are palladium and platinum.
10. Which of the following is not a commercial catalyst used for the catalytic reduction of nitrogen oxide?
a) Supported palladium
b) Supported platinum
c) Fe-chromite
d) Cr-promoted Fe-oxide
View Answer
Explanation: Among the given options only supported palladium is not used as a commercial catalyst. Noble metal catalysts can get very expensive for bulk reduction, therefore commercial alternatives are preferred.
Sanfoundry Global Education & Learning Series – Air Pollution Control.
To practice all areas of Air Pollution Control, here is complete set of 1000+ Multiple Choice Questions and Answers.
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