This set of Air Pollution Control Multiple Choice Questions & Answers (MCQs) focuses on “Control of Gaseous Emissions – Set 2”.
1. What is the alternative to the absorption of gaseous emissions?
a) Adsorption
b) Combustion
c) Incineration
d) Catalytic oxidation
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Explanation: Adsorption is a popular alternative to the absorption process. In adsorption, the gas gets attached to the surface of solid particles. The other combustion processes come into play when the recovered materials have no further use in the industry.
2. How are adsorbed gases desorbed from the solid surface in physical adsorption?
a) Catalytic oxidation
b) Pressure increase
c) Temperature reduction
d) Chemical reaction
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Explanation: In physical adsorption, the gas condenses on the surface of the adsorber solid. To desorb the gas, either the pressure is reduced, or the temperature is increased. This process shows that physical adsorption is reversible.
3. Which adsorption method is the primary mechanism of adsorption in air pollutant control?
a) Both chemisorption and physical adsorption
b) Chemisorption
c) Physical adsorption
d) Adsorption is avoided
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Explanation: Although viable for catalyst study, chemisorption is not the primary mode of adsorption for air pollutant capture. On the other hand, physical adsorption is reversible and an easy choice for the control of emissions.
4. Where do adsorbers find the most application?
a) Sulphur dioxide control
b) Nitrogen dioxide control
c) Smoke control
d) Odour control
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Explanation: Nitrogen dioxide and sulphur dioxide are removed in absorbers. Smoke is particulate matter, so its removal occurs in particulate collectors. Adsorption is used for odour and colour removal, where a small quantity of pollutants are present in a large volume of gas.
5. How are valuable organic substances collected from emission streams?
a) Adsorbers
b) Absorbers
c) Catalytic oxidation
d) Cyclones
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Explanation: Adsorbers are used to collect pollutants that are present in small quantities in large quantities of gas. Such valuable organics are collected by adsorbers that would otherwise not be collected by scrubbers.
6. Which of the following is a factor upon which the rate of adsorption does not depend?
a) Adsorbent surface area
b) Volume of adsorbent used
c) Porosity of the adsorbent
d) Temperature of operation
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Explanation: Except for the volume of adsorbent used, all the listed options affect the rate of adsorption. The porosity of the adsorbent controls how much of the gas or liquid is adsorbed onto its surface. Other factors include the chemical nature of the adsorbent and the concentration of the material around the adsorbent.
7. Why are adsorber design significantly dependent on empirical methods?
a) The environmental factors
b) Porosity of adsorbents is variable
c) Adsorption rate
d) Surface area of adsorbents is variable
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Explanation: The main reason for the dependence of adsorber design upon empirical analysis is the adsorption rate. The process occurs in different stages, and it is difficult to determine the rate-controlling stage. Thus, the need for empirical analysis exists.
8. Which adsorbent is used for the removal of odours?
a) Activated carbon
b) Silica gel
c) Molecular sieves
d) Activated Alumina
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Explanation: Out of the given options, only activated carbon is used for the recovery of odour. Activated carbon can also be used to remove trace impurities and the purification of industrial gases. Other listed adsorbents have niche applications.
9. What are molecular sieves used to adsorb in adsorbers?
a) Odour
b) Selective adsorption of carbon dioxide
c) Gas purification
d) Removing trace impurities
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Explanation: Molecular sieves are used for selective adsorption. This process is done to recover gases like carbon dioxide, ammonia, hydrogen sulphide, and sulphur dioxide. Activated carbon removes the other listed impurities.
10. When is the exhaustion point of the adsorber reached?
a) At the breakthrough point
b) Before the breakthrough point
c) After the breakthrough point
d) Too little information
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Explanation: The exhaustion point of the adsorber is reached after the breakthrough point. At the exhaustion point, the outlet concentration of the pollutants is equal to the inlet concentration. At this state, no pollutant recovery occurs and that the bed has been exhausted.
11. When is the adsorbent regenerated?
a) When outlet and inlet pollutant concentration are equal
b) Somewhere between the exhaustion and breakthrough points
c) At the exhaustion point
d) When it reaches the breakthrough point
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Explanation: The adsorbent is regenerated when the bed reaches the breakthrough point. This point is reached when the breakthrough curve (S-shaped) begins to rise rapidly. It is too late to regenerate the bed at the exhaustion point.
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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