...........................................................
1.
Consider distribution of the solute (A) in two partially miscible solvents B (carrier) and S (solvent). What is the selectivity at the plait point? a.
Zero b.
One c.
Below one but above zero d.
Very large
2.
Which of the following point is/are applicable for the mixer-settler type of equipments for liquid-liquid extraction? a.
They occupy large floor space b.
They require large solvent inventories c.
They provide high stage efficiencies d.
All of the above
3.
Four solvents have been identified for the extraction of a solute from an aqueous solution. The interfacial tension values in unit of N/m corresponding to these solvents are given below. Which solvent appears to be most suitable for use? a.
0.003 b.
0.01 c.
0.05 d.
0.07
4.
An ideal countercurrent mixer-settler cascade containing six stages removes 95% of the solute from the feed. One of the mixers has developed a mechanical problem and is by-passed. For the same percentage removal of the solute from the feed, the solvent rate should be a.
Increased b.
Decreased c.
Kept constant d.
Any of the above
5.
A solution of solute (A) in diluent (B) is mixed with a solvent (S). The component (B) is slightly soluble in (S).
The resulting raffinate will be a.
Rich in S, poor in B, rich in A b.
Poor in S, rich in B, poor in A c.
Rich in S, poor in B, poor in A d.
Rich in S, rich in B, rich in A
6.
The distribution coefficient of solute A between two mutually immiscible liquids B (carrier) and S (solvent) is
𝐾 = 𝑦
𝐴 = 0.75
. What is the slope of the tie-line in the
𝑋
𝐴 right triangular phase diagram if the mass fraction of the solute in the solvent phase is 𝑦
𝐴 a.
Zero
= 0.1
? b.
Infinity c.
-27 d.
-12
7.
An ideal single stage extraction process is used to treat
100 mol/s of an aqueous feed solution. The solute concentration in this solution is to be reduced from 0.5 mol% to 0.1 mol%. A pure solvent S is used. To reduce the solvent requirement by half for the same separation, a.
Add one more ideal co-current stage b.
Use another pure solvent whose partition coefficient is twice of that of S c.
Use solvent S containing 0.02 mole fraction of the solute d.
Double the resistance time of the solvent S in the container
8.
In a liquid-liquid extraction process the extraction solvent has no selectivity when the ratio of the two components in the extract solvent phase to that in the feed solvent phase is a.
Zero b.
One c.
Two d.
Infinity
9.
In a single stage extraction process, 10 Kg of pure solvent S is mixed with 30 Kg of feed F containing A at a mass fraction of 0.2. The mixture splits into an extract phase E and a raffinate phase R, containing A at a mass fraction of 0.5 and 0.05 respectively. The total mass of the extract phase is (Kg) a.
6.69 b.
8.89 c.
10 d.
12
10.
The following mass and solute concentrations are given for an ideal single-stage extraction system:
1

Feed is 500 Kg with solute at 40 mass%. Solvent is 400
Kg (pure). Extract is 550 Kg with solute at 33 mass%.
What is the distribution coefficient (or partition ratio) of the solute at this condition? a.
0.52 b.
2.15 c.
6.24 d.
8.41
1.
A binary liquid mixture of acetone (25% by mass) and water is fed to a countercurrent multistage extraction column using pure methylisobutyl ketone as a solvent. The feed to solvent ratio is maintained at 2.
Analysis of the exit raffinate stream shows 3% by mass of acetone. Equilibrium data at 25-26 0 C and 1 atm is found in Geankoplis, Appendix A.3-25. (x
A
-axis up to 0.35 mass fraction and placed at the upper 1/3 of the graphing paper will suffice to put all relevant data in the right triangular coordinates in the same graph) a.
What is the rich extract composition? b.
How many ideal stages are required? c.
If the feed is 100lb/hr, what is the rich extract flow rate? d.
If the feed is 100lb/hr, what is the % acetone recovered? e.
If the feed is doubled from 100lb/hr to 200 lb/hr with all other variables remain the same, which of the following statements is true? i.
The % acetone recovered will increase ii.
The number of ideal stages will increase iii.
The solvent flow rate will double iv.
The rich extract flow rate will be halved
2.
A stream of wastewater containing 2% benzoic acid is to be extracted with benzene in order to remove 95% of the solute. Wastewater enters a multistage countercurrent cascade at a rate of 2000 Kg/hr. If water and benzene are assumed to be mutually immiscible and the distribution coefficient is where 𝑥
𝐴
and 𝑦
𝐴 𝑦
𝐴 = 0.6
𝑥
𝐴
are the mass fraction of the solute in water and benzene phases respectively, calculate the following: a.
The minimum rate of benzene required for countercurrent separation of the mixture. b.
The number of stages required if 1.5 times the minimum solvent is used.
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I.
1.
B
2.
D
3.
D
4.
A
5.
B
6.
C
7.
B
8.
B
9.
B
10.
C
II.
1.
a.
... b.
4.4 c.
76.11 lb/hr d.
91.33% e.
Iii
2.
a.
3128 Kg/hr b.
5.6 stages
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