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Multiple choice question for engineering

Set 1

1. The mixture can be made homogeneous azeotropic mixture using a _________
a) Stabilizer
b) Entrainer
c) Surfactant
d) Two columns

View Answer

Answer: b [Reason:] An entrainer is used to make a mixture Homogeneous Azeotropic mixture.

2. How many columns are used in Homogeneous azeotropic distillation?
a) Two or three
b) Minimum five
c) Only one
d) Minimum 10

View Answer

Answer: a [Reason:] Two or three columns are used in homogeneous azeotropic distillation.

3. What other operations are included in homogeneous azeotropic distillation?
a) Crystallization
b) Fractional crystallization
c) Solvent extraction
d) Decantation

View Answer

Answer: c [Reason:] Solvent extraction is used in homogenous azeotropic distillation.

4. For an entrainer E, the components A and B must lie in :
a) Same distillation region
b) Different distillation region
c) On convergence point
d) On tie line

View Answer

Answer: a [Reason:] For an entrainer E, the components A and B must lie in Same distillation region.

5. Which of the following must be a saddle?
a) Component A
b) Component B
c) Component A and component B
d) Component A or Component B

View Answer

Answer: d [Reason:] Component A or B must be a saddle but not both.

6. The distillation boundaries for hypothetical ternary systems are shown as:
a) Curved lines
b) Straight lines
c) Stars
d) Triangle

View Answer

Answer: b [Reason:] The distillation boundaries for hypothetical ternary systems are shown as straight lines.

7. When a distillation boundary is curved, it may be crossed provided that the distillate and bottoms lie on:
a) Different side of boundary
b) Opposite sides of boundary
c) On the boundary
d) Same side of boundary

View Answer

Answer: d [Reason:] When a distillation boundary is curved, it may be crossed provided that the distillate and bottoms lie on same side of boundary.

8. The maps suitable for a sequence that includes homogeneous azeotropic distillation are classifies in:
a) 2 groups
b) 3 groups
c) 4 groups
d) 5 groups

View Answer

Answer: d [Reason:] The maps suitable for a sequence that includes homogeneous azeotropic distillation are classifies in 5 groups.

9. In the residue-curve map, the lowest boiling component is at :
a) Bottom left vertex
b) Bottom right vertex
c) At the centroid
d) At the top vertex

View Answer

Answer: d [Reason:] In the residue-curve map, the lowest boiling component is at the top vertex.

10. In the residue-curve map, the intermediate boiling component is at:
a) Bottom left vertex
b) Bottom right vertex
c) At the centroid
d) At the top vertex

View Answer

Answer: a [Reason:] In the residue-curve map, the intermediate boiling component is at the bottom left vertex.

11. In the residue-curve map, the intermediate boiling component is at:
a) Bottom left vertex
b) Bottom right vertex
c) At the centroid
d) At the top vertex

View Answer

Answer: b [Reason:] In the residue-curve map, the intermediate boiling component is at the bottom right vertex.

Set 2

1. When is the pressure swing distillation used?
a) When the binary azeotrope changes composition by 5mol% over a moderate range of pressure
b) When the binary azeotrope changes composition by 10mol% over a moderate range of pressure
c) When the binary azeotrope changes composition by 2mol% over a moderate range of pressure
d) When the binary azeotrope changes composition by 0.5mol% over a moderate range of pressure

View Answer

Answer: a [Reason:] Pressure swing distillation is used when a binary azeotrope disappears or changes composition by 5mol% over a moderate range of pressure.

2. What is done in pressure swing distillation?
a) Two columns in series at same pressure
b) Two columns in parallel at same pressure
c) Two columns in series at different pressures
d) Two columns in parallel at different pressures

View Answer

Answer: c [Reason:] Pressure swing distillations using two ordinary columns in series operating at different pressures.

3. Which of the following is an application of pressure swing distillation?
a) Tetrahydrofuran-water mixture
b) Hydrochloric acid-methanol mixture
c) Tetrahydrofuran-methanol mixture
d) Hydrochloric acid- tetrahydrofuran mixture

View Answer

Answer: a [Reason:] The minimum boiling azeotrope of Tetrahydrofuran-water mixture is separated by pressure swing distillation.

4. Formic acid-water mixture is separated using:
a) Salt distillation
b) Extractive distillation
c) Differential distillation
d) Pressure swing distillation

View Answer

Answer: d [Reason:] Formic acid-water mixture is separated using Pressure swing distillation.

5. Hydrochloric acid-water mixture is separated using:
a) Salt distillation
b) Extractive distillation
c) Differential distillation
d) Pressure swing distillation

View Answer

Answer: d [Reason:] Hydrochloric acid-water mixture is separated using Pressure swing distillation.

6. Why is recycle ratio a key design factor?
a) Low cost of gas compression
b) High cost of gas compression
c) High equipment cost
d) High gas cost

View Answer

Answer: b [Reason:] Due to the high cost of gas compression, the recycle ratio is key design factor.

7. What does recycle ratio depends on?
a) Variation of azeotropic composition with column pressure
b) Variation of pressure with composition
c) Cost of gas compression
d) Efficiency of instrument

View Answer

Answer: a [Reason:] The recycle ratio depends on Variation of azeotropic composition with column pressure.

8. In the separation of ethanol-water the feed is __________ in ethanol than azeotrope.
a) Less rich
b) More rich
c) Less clear
d) More clear

View Answer

Answer: a [Reason:] In the separation of ethanol-water the feed is less rich in ethanol than azeotrope.

9. For pressure swing distillation, due to high cost of gas compression, __________ is akey factor.
a) Efficiency
b) Feed
c) Yield
d) Recycle ratio

View Answer

Answer: d [Reason:] Recycle ratio is the key factor due to high cost of gas compression.

10. Why is pressure swing distillation costly?
a) High cost of gas compression
b) High cost of equipment
c) High cost of columns
d) Less yield

View Answer

Answer: a [Reason:] Due to high cost of gas compression, the separation technique is costly.

Set 3

1. What does reactive distillation denote?
a) Distillation after reaction
b) Reaction after distillation
c) Reaction along with distillation
d) Automatic distillation by reaction

View Answer

Answer: c [Reason:] Reactive distillation denotes simultaneous reaction and distillation.

2. What are similar to reactive entrainers?
a) Reactive absorbents
b) Reactive adsorbents
c) Reactive sublimers
d) Reactive evaporators

View Answer

Answer: a [Reason:] Reactive absorbents are similar to reactive entrainers and they are widely practiced.

3. What is meant by sweetening of natural gas?
a) Removal of H2S
b) Removal of H2O and CO2
c) Removal of H2S and CO2
d) Removal of H2O and CO

View Answer

Answer: c [Reason:] Sweetening of natural gas means removal of H2S and CO2 by addition of reactive absorbents.

4. What reactive absorents are added for sweetening of natural gas?
a) Triethanol amines
b) Ethyl alchol
c) Monoethanol amine
d) Ethanol

View Answer

Answer: c [Reason:] Monoethanol amine is added for the removal of H2S and CO2 that sweetens the natural gas.

5. Reactive distillation is carried out when the reaction occurs in:
a) Solid phase
b) Gaseous phase
c) Solid or gaseous phase
d) Liquid phase

View Answer

Answer: d [Reason:] Reactive distillation is carried out only when the reaction occurs in liquid phase in presence or absence of homogeneous catalyst.

6. What is the relation between reaction rate and distillation rate for reactive distillation?
a) Reaction rate is more
b) Distillation rate is more
c) It depends on the components
d) Both are equal

View Answer

Answer: d [Reason:] The feasible temperature for the reaction and distillation are the same. Hence the reaction rate and distillation rates are same.

7. Why a large reactant excess not required for high conversion?
a) Because conversion is very high already
b) Conversion is driven by temperature
c) Conversion is driven by pressure
d) If one or more products can be distilled out, there is a high conversion

View Answer

Answer: d [Reason:] If one or more products can be distilled out then the reaction proceeds to completion. Hence a large reactant excess is not required.

8. Which of the following is an application of reactive distillation?
a) Avoiding undesirable reactions
b) Avoiding temperature rise
c) Separation of gases
d) Separation of solids

View Answer

Answer: a [Reason:] Avoiding undesirable reactions is an application of reactive distillation.

9. Which of the following is not a commercial application of reactive distillation?
a) Esterification of acetic acid with ethanol
b) Reaction of formaldehyde and methanol
c) Reaction of isobutene and methanol
d) Oxidation of ethyl alcohol

View Answer

Answer: d [Reason:] Since oxidation of alcohols involves gaseous phase, it cannot be used for reactive distillation.

10. For the reaction A< – -> R where A is more volatile, why does it require close examination?
a) Reaction is very exothermic
b) Reverse reaction may occur when equilibrium is reached
c) Reaction cannot occur if a certain barrier of temperature is crossed
d) Reaction may not occur if the reactants get mixed

View Answer

Answer: b [Reason:] At a certain point in the column, equilibrium may be attained. If the reaction is allowed to carry on further the reverse reaction may take place. Hence a close examination is required.

Set 4

1. What is the disadvantage of using water in distillation of acetone and methanol?
a) Purity is not much
b) Acetone is less pure
c) Large amount of water required
d) Large amount of yields not possible

View Answer

Answer: c [Reason:] Large amount of water is required to alter the value of alpha hence it is a disadvantage.

2. The water vapor pressure and purity of acetone can be increased using?
a) Large amount of water
b) Metal oxides in water
c) Minerals dissolved in water
d) Using an inorganic-salt solution

View Answer

Answer: d [Reason:] By using an inorganic-salt solution the vapor pressure of water can be increased.

3. Which salt decreases the volatility of water, and has a strong affinity for methanol?
a) Sodium chloride
b) Calcium chlorate
c) Calcium chloride
d) Potassium iodide

View Answer

Answer: c [Reason:] Calcium chloride decreases the volatility of water, and has a strong affinity for methanol.

4. Which salt solution in glycerol is not used to separate ethanol from water?
a) Calcium chloride
b) Zinc chloride
c) Potassium carbonate
d) Ferric sulphate

View Answer

Answer: d [Reason:] Ferric sulphate cannot be used to separate ethanol and water.

5. The salt which must be soluble in reflux is recovered by __________ and _________
a) Evaporation and crystallization
b) Decantation and settling
c) Evaporation and distillation
d) Distillation and fractional crystallization

View Answer

Answer: a [Reason:] The salt which must be soluble in reflux is recovered by Evaporation and crystallization.

6. Which is the most important problem in salt distillation?
a) Pollution
b) Corrosion
c) Not cost efficient
d) Requires large quantity of salts

View Answer

Answer: b [Reason:] Corrosion is the most important problem in salt distillation. Hence a stainless steel vessel is used.

7. _______ of potassium acetate can eliminate ethanol-water azeotrope.
a) Large concentrations
b) Low concentrations
c) Large amount
d) Small amounts

View Answer

Answer: b [Reason:] Low concentrations of potassium acetate can eliminate ethanol-water azeotrope.

8. In the column, the presence of dissolved salt my increase __________
a) Yield
b) Efficiency
c) Foaming
d) Residence time

View Answer

Answer: c [Reason:] In the column, the presence of dissolved salt my increase Foaming.

9. Why is the possibility of clogging and plugging unlikely?
a) Because salt is in solid state
b) Because the concentration of water increases down the column
c) Because the concentration of water decreases down the column
d) Because the concentration of methanol increases.

View Answer

Answer: The possibility of clogging and plugging unlikely because the concentration of less volatile component like water increases down the column and thus it can dissolve salt.

10. Salt distillation can be applied to organic compounds that have little capacity of dissolving inorganic salts by using organic salts called?
a) Hydrotopes
b) Hygrotopes
c) Hydrostattic materials
d) Hydrating materials

View Answer

Answer: a [Reason:] Salt distillation can be applied to organic compounds that have little capacity of dissolving inorganic salts by using organic salts called Hydrotopes. Example: Alali and alkaline salts of sulphonates of toluene.

Set 5

1. Find the expression for peak capacitor voltage in case of a current commutated chopper circuit.
a) Io √(L/C)
b) Vs + √(L/C)
c) Vs + Io √(L/C)
d) Zero

View Answer

Answer: c [Reason:] 1/2 CVc2 = 1/2 LIo2 Vc = Io √(L/C) Vc (peak) = Vs + Io √(L/C).

2. Identify the below given chopper circuit.
tough-power-electronics-questions-q2
a) Type D chopper
b) Type C chopper with commutating capacitor
c) Load commutated step-down chopper
d) Voltage commutated step-up chopper

View Answer

Answer: c [Reason:] Load commutated chopper uses 4 SCRs and one commuting capacitor. As there is no L in the circuit, it is a step down chopper.

3. In the below given commutated chopper circuit, __ and __ SCRs act together in pairs.
tough-power-electronics-questions-q2
a) T1-T2, T3-T4
b) T1-T3, T2-T4
c) T1-T4, T2-T4
d) T1, T2

View Answer

Answer: a [Reason:] T1-T2 and T3-T4 act together as one pair for conducting the load current alternately.

4. When T1 and T2 are conducting, which components act as the commutating components?
tough-power-electronics-questions-q2
a) T3 and T4
b) All the SCRs
c) T3, T4 and C
d) T3, T4, C and FD

View Answer

Answer: c [Reason:] Commutating components are the one which will help the main SCRs T1 and T2 in this case turn off safely. FD is not a commutating component, it only freewheels the current during inductive loads.

5. What is the voltage across the load when T1 and T2 are gated after charging the capacitor to Vs?
tough-power-electronics-questions-q2
a) Vs
b) 0
c) 2Vs
d) Vs + Ldi/dt

View Answer

Answer: c [Reason:] The main SCRs T1 and T2 are conducting, and the path is Vs –T1 – C – T2 – Load. Hence, Vo = Vs + (capacitor voltage). As the capacitor is already charged to a voltage Vs. Vo = 2Vs.

6. What is the expression for design of commutation capacitance in case of a load commutated chopper circuit?
a) (I x Ton)/Vs
b) Cannot be determined
c) (I x Ton)/2Vs
d) (I x T)/Vs

View Answer

Answer: c [Reason:] Total change in the voltage is 2xVs in time Ton. I = C x (2Vs/ Ton) C = (IxTon)/2Vs.

7. Which type of commutating circuit will have highest switching losses for same rating of all the components?
a) current commutated chopper
b) voltage commutated chopper
c) load commutated chopper
d) forced commutated chopper

View Answer

Answer: c [Reason:] Load commutated choppers have 4 SCRs which require frequent turning on and turning off which increases the switching losses.

8. The speed of a separately excited dc motor is controlled below base speed by using a type-A SCR based chopper. The supply voltage is 220 V dc and the armature resistance is 0.5 Ω. Calculate the minimum value of firing angle if the motor drives a constant torque load requiring an average armature current of 30 A.
a) 1/2
b) 3/44
c) 59/46
d) 7/12

View Answer

Answer: b [Reason:] For a motor, Vo = E + Ir The minimum possible speed = 0. This gives the motor counter emf E = 0. Therefore, Vo = αVs = Ir α x 220 = 30 x 0.5 α = 15/220 = 3/44.

9. For the step down chopper shown in the figure below, Vs = 100 V and the duty cycle of the switch is 0.8. The load is sufficiently inductive so that the load current is ripple free. The average current through the diode (D) under steady state is
tough-power-electronics-questions-q9
a) 2 A
b) 1.6 A
c) 8 A
d) 6.4 A

View Answer

Answer: b [Reason:] The diode is active only during Toff. If Ton = 0.8 then Toff = 0.2 Output voltage Vo = 0.8 x 100 = 80 V When D is active during Toff, consider inductor as a short circuit thus, Id = (VoxToff)/R = 80 x 0.2/10 = 1.6 A.

10. A chopper circuit is fed from an input voltage of 20 V delivers a power of 16 watts. If the chopper efficiency is 80 %, then find the value of input current.
a) 0.64 A
b) 1 A
c) 0.8 A
d) 1.25 A

View Answer

Answer: b [Reason:] 0.8 = ouput/input Input power = 16/0.8 16/0.8 = V x I V = 20 V. Hence, I = 1 A.