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# Separation Processes MCQ’s – McCabe-Thiele Graphical Method for Trayed Towers

1 - Question

What is the goal of distillation?

a) To produce a distillate rich in light key and the bottoms product rich in high key

b) To produce a distillate rich in high key and the bottoms product rich in light key

c) To produce a distillate rich in light key and the bottoms product rich in light key

d) To produce a distillate rich in high key and the bottoms product rich in high key

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Answer: aExplanation: The goal of distillation is to produce a distillate rich in light key and the bottoms product rich in high key.

2 - Question

What is meant by light key (LK)?

a) A feed that contains less volatile components

b) A feed that has less mass

c) A feed that has higher concentration of less molecular weight solute

d) A feed that contains more volatile components

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Answer: dExplanation: Light key is the feed that contains more volatile components.

3 - Question

What is meant by high key (HK)?

a) A feed that contains less volatile components

b) A feed that has less mass

c) A feed that has higher concentration of less molecular weight solute

d) A feed that contains more volatile components

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Answer: aExplanation: High key is the feed that contains less volatile components.

4 - Question

If LK=1 and HK=2, what is the formula for α 1,2 ?

a) α 1,2 =K1/K2

b) α 1,2 =K1*K2

c) α 1,2 =K1-K2

d) α 1,2 =K1+K2

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Answer: aExplanation: To find out whether the separation is possible or not α 1,2 values are used whose formula is α 1,2 =K1/K2.

5 - Question

For what value of α1,2 ,the separation cannot be achieved?

a) 0.8

b) 1.2

c) 1.3

d) 1.8

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Answer: aExplanation: For α1,2 = 0.8, the separation cannot be achieved since its value has to be greater than 1.Thus by further increasing pressure, separation cannot be achieved.

6 - Question

What is the formula for distillation rate according to mcCabe-thiele’s method?

a) D= F(z F – x B )/(x D + x B )

b) D= F(z F – x B)/(x D /x B )

c) D= F(z F – x D )/(x D – x B )

d) D= F(z F – x B )/(x D – x B )

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Answer: dExplanation: D= F(z F – x B )/(x D – x B ) is the correct equation where D is the distillation rate, F is the total feed rate, z F is the mole fraction of LK in feed, x D , x B are mole fractions of LK in distillate and bottom.

7 - Question

What is the distillation rate if feed rate is 4moles/s and mole fraction of LK in feed is 0.7, and mole fraction of LK in distillate and bottom is 0.5, 0.4?

a) 8moles/s

b) 12moles/s

c) 16moles/s

d) 20moles/s

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Answer: bExplanation: Since D= F(z F – x B )/(x D – x B ), D=4*(0.7-0.4)(0.5- 0.4)=12.

8 - Question

What is the distillation rate if feed rate is 20moles/s and mole fraction of LK in feed is 0.8, and mole fraction of LK in distillate and bottom is 0.5, 0.4?

a) 80moles/s

b) 12moles/s

c) 16moles/s

d) 20moles/s

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Answer: aExplanation: Since D= F(z F – x B )/(x D – x B ), D=20*(0.8-0.4)(0.5- 0.4)=80.

9 - Question

What is the distillation rate if feed rate is 9moles/s and mole fraction of LK in feed is 0.7, and mole fraction of LK in distillate and bottom is 0.5, 0.3?

a) 45moles/s

b) 16moles/s

c) 18moles/s

d) 20moles/s

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Answer: cExplanation: Since D= F(z F – x B )/(x D – x B ), D=9*(0.7-0.3)(0.5- 0.3)=18.

10 - Question

What is the distillation rate if feed rate is 31moles/s and mole fraction of LK in feed is 0.9, and mole fraction of LK in distillate and bottom is 0.6, 0.4?

a) 23moles/s

b) 26moles/s

c) 28moles/s

d) 31moles/s

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Answer: dExplanation: Since D= F(z F – x B )/(x D – x B ), D=31*(0.9-0.4)(0.6- 0.4)=12.