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ARC > DAY 2 QUIZ > Flashcards

DAY 2 QUIZ Flashcards

1
Q

At a temperature of 366.4 K, the vapor pressures of n-hexane and octane are 1480 and 278 mmHg, respectively. Assume the hexane-octane system obeys Raoult’s law and the total pressure is 1 atm. Calculate the equilibrium vapor composition (in mole fraction) of the more volatile component.

A. 0.94
B. 0.54
C. 0.78
D. 0.25

A

C. 0.78

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2
Q

The ratio of the solubility of stearic acid per unit volume of n-heptane to that in 97.5% acetic acid is 4.95. How many extractions of a 10 ml solution of stearic acid in 97.5% acetic acid with successive 10 ml portions of n-heptane are needed to reduce the residual stearic acid content of the acetic acid layer to less than 0.5 percent of its original value?

A. 2
B. 1
C. 3
D. 4

A

C. 3

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3
Q

Lambanog (coconut vodka) comes from the fermented sap of the coconut tree. This is then distilled to make the drink more potent. It is clear, colorless spirit, with a neutral taste, potent kick, and a finish with a hint of sweetness. A batch differential distillation is made upon a 25 kg mixture of ethanol-water containing 7% weight alcohol. How many kg of distillate must be collected so that it will have an ethanol content of 30% weight? Assume that the relative volatility of the mixture is equal to 12.

A. 9 kg
B. 8 kg
C. 2 kg
D. 5 kg

A

D. 5 kg

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4
Q

The reflux to a distillation column is 100 moles/hr, when the overhead product rate is 50 moles/hr. The reflux ratio is

A. 150
B. 0.5
C. 50
D. 2

A

D. 2

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5
Q

Entrainer used in azeotropic distillation should

A. have high latent heat of vaporization.
B. have high viscosity to provide high tray efficiency.
C. form a new azeotrope of low relative volatility with one of the constituents of the mixture.
D. form a low boiling azeotrope with one of the constituents of the mixture.

A

D. form a low boiling azeotrope with one of the constituents of the mixture.

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6
Q

An ideal single stage extraction process is used to treat 100 mol/s of an organic 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 S* whose partition coefficient is twice that of S
C. double the residence time of the solvent S in the contactor
D. use solvent S containing 0.02 mole fraction of the solute

A

B. use another pure solvent S* whose partition coefficient is twice that of S

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7
Q

Tray spacing in a distillation column of dia 10-12 ft. used in petroleum refinery may be around __________ inches.

A. 5
B. 100
C. 30
D. 60

A

C. 30

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8
Q

The charge to a simple batch still consists of an equimolar mixture of hexane and heptane. If the relative volatility of hexane to heptane is 2.0 and 50% of hexane has vaporized, what is the mole fraction of heptane in the total distillate?

A. 0.15
B. 0.43
C. 0.29
D. 0.37

A

D. 0.37

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9
Q

Ten kg of a solid containing 45% of soluble material were treated with 15 kg of a solvent containing the same solute at 2% concentration in a vessel under constant agitation. After a long time, the solution and the solid were separated by pressing. The solid analyzed 0.8 kg of solvent per kg of inert solid. The extract quantity obtained in kg was therefore

A. 15.1
B. 14.8
C. 13.7
D. 16.9

A

A. 15.1

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10
Q

A binary distillation column is operating with a mixed feed containing 20 mol% vapor. If the feed quality is changed to 80 mol% vapor, the change in the slope of the q-line is

A. 0.85
B. 1.50
C. 2.25
D. 3.75

A

D. 3.75

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11
Q

A counter current multiple contact extraction system is to treat 50 tons/hr of wet beets with fresh water as the solvent. The beets have the following analysis: Components Mass fraction water 0.48 pulp 0.40 sugar 0.12 The strong solution leaving the system is to contain 0.15 mass fraction sugar, 97% of the sugar in the sliced beets is to be recovered. Determine the number of extraction cells required, assuming equilibrium between the underflow and overflow in each cell if each ton of dry pulp retains 3 tons of solution.

A. 16
B. 17
C. 15
D. 14

A

A. 16

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12
Q

Repeat if each ton of dry pulp retains 3 tons of solvent.

A. 14
B. 16
C. 17
D. 15

A

C. 17

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13
Q

The orebody of the Union Miniere du Haut-Katanga in the Belgian Congo is composed of malachite, CuCO3 Cu(OH)2 and gangue. Copper is extracted by crushing the ore to -20 mesh, agitating with a dilute solution of sulfuric acid, followed by multiple-contact countercurrent washing to wash the gangue free of the copper-bearing solution. The rich solution from the washing system is treated for removal of dissolved iron and aluminum and then sent to the electrolytic cells for precipitation of the copper. The dilute acid solution from the cells is recycled to the agitators for treatment of more raw ore. The counter current washing operation uses Dorr thickeners for the recovery of the rich solution. The slurry from the agitators, with the copper in the solution as copper sulfate, is fed to the thickeners at the rate of 300 tons per hour. According to operating records, the underflow from each thickener retains 1.22 tons of solution per ton of gangue, and the streams have the following compositions in mass percent. Determine the number of equilibrium stages.

               Feed to            Strong          Underflow
               Thickener,       Solution       Leaving the
                     %	 ,                  %	               System, % CuSO4	         6.10	                6.69	                1.0 Gangue	       14.92	               -                     	99 Water	           78.98	           93.91                  99

A. 3
B. 5
C. 4
D. 6

A

C. 4

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14
Q

Which of the following mixtures does not form an azeotrope at atmosheric pressure?

A. Water-alcohol
B. None of these
C. Methyl alcohol-acetone
D. Butyl acetate-water

A

B. None of these

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15
Q

In case of liquid-liquid binary diffusion, diffusivity of one constituent into another is not dependent on the

A. temperature and pressure
B. nature of the constituents
C. concentration
D. None of these

A

D. None of these

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16
Q

An example of elutioh is

A. recovery of vegetable oils from seeds.
B. separation of uranium oxide from its ore by H2SO4 in a Pachuca tank.
C. dissolution of tannin out of tree barks by water. D. separation of sugar from sugar beet by hot water.

A

B. separation of uranium oxide from its ore by H2SO4 in a Pachuca tank.

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17
Q

Large scale usage of flash distillation is practiced in

A. petroleum refinning
B. soap manufacturing
C. polymerization industry
D. ammonia synthesis plant

A

A. petroleum refinning

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18
Q

In an operating distillation column, the

A. driving force for the liquid flow is its specific weight.
B. vapors and liquids are at their dew point and bubble point respectively
C. driving force for the vapor flow is the pressure drop, as the pressure decreases gradually from the bottom to the top of the column.
D. highest temperature is encountered at the top of the column.

A

C. driving force for the vapor flow is the pressure drop, as the pressure decreases gradually from the bottom to the top of the column.

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19
Q

In case of steam distillation, the steam leaving the liquid is not completely saturated with distillate vapor, because

A. saturated steam is used for steam distillation.
B. total pressure is less.
C. mixing of steam with the material being vaporised is not so intimate as to result in equilibrium condition.
D. temperature is less.

A

C. mixing of steam with the material being vaporised is not so intimate as to result in equilibrium condition.

20
Q

For a binary mixture distillation process, the degree of freedom is 2. However, if the pressure is fixed in this process, the number of independent variables in this process will be

A. 1
B. 3
C. 0
D. 2

A

A. 1

21
Q

__________ is used as an ‘entrainer’ for the separation of acetic acid-water mixture by distillation.

A. Hexane
B. Furfural
C. Benzol
D. Butyl acetate

A

D. Butyl acetate

22
Q

For water-ethanol system, the minimum reflux ratio

A. is computed from the slope of the upper operating line that is tangent to the equilibrium curve.
B. cannot be computed.
C. is the optimum reflux ratio.
D. is computed from the intercept of the operating line.

A

A. is computed from the slope of the upper operating line that is tangent to the equilibrium curve.

23
Q

If Rm is the minimum reflux ratio, the optimum reflux ratio may be around __________ Rm.

A. 2.5 to 3
B. 3 to 4
C. 1.2 to 1.5
D. 5

A

C. 1.2 to 1.5

24
Q

Solvent used in extractive distillation

A. does not alter the relative volatility of the original components.
B. forms a high boiling azeotrope.
C. forms a low boiling azeotrope.
D. is of low volatility.

A

C. forms a low boiling azeotrope.

25
Q

Hydrogenation of oil is carried out in a/an __________ in Vanaspati manufacturing plant.

A. agitated vessel
B. sieve tray column
C. bubble cap column
D. packed tower

A
26
Q

To get high tray efficiency

A. time of contact between the two phases should be less.
B. interfacial surface between liquid and gas phase should be large.
C. liquid entrainment should be severe.
D. gas velocity should be very low.

A

B. interfacial surface between liquid and gas phase should be large.

27
Q

With increase in temperature, the rate of leaching increases, because the

A. viscosity of solvent decreases.
B. none of these
C. diffusivity of solute increases.
D. thermal conductivity of solute increases.

A

C. diffusivity of solute increases

28
Q

For ethanol-water system, the lowering of distillate quality from 95% to 92% will cause __________ plate requirement.

A. major decrease in the number of
B. None of these
C. no change in theoretical
D. marginal decrease in the number of

A

D. marginal decrease in the number of

29
Q

An aqueous solution of methanol is to be distilled in a tray column. High pressure steam is available as a source of heat. For a given reflux ratio and overhead composition, two options are being explored; (i) a reboiler is used and (ii) no reboiler is used but steam is fed directly to the bottom of the column. As compared to option (i), in option (ii)

A. less number of trays are required.
B. composition of the residue remains unchanged.
C. more number of trays are required but the residue composition remains unchanged.
D. more number of trays are required and the residue composition is more dilute in methanol.

A

A. less number of trays are required.

30
Q

What is the reflux ratio at total reflux ?

A. Data insufficient
B. Zero
C. Unity
D. Infinity

A

D. Infinity

31
Q

If the solubilities of different components (in a liquid-liquid extraction system) increase with rise in temperature, then the temperature above which they dissolve completely is known as the critical solution temperature (CST or consolute temperature). If solubilities increase with decrease in temperature, then CST is the temperature below which they dissolve completely. If a binary system has no critical solution temperature, it implies that

A. the system comprises of an azeotrope.
B. the system comprises of miscible liquids.
C. the system comprises of partially mis-cible liquids. the system comprises of partially miscible liquids.
D. on heating, a vapor phase will appear ; while on cooling, a solid phase will appear.

A

D. on heating, a vapor phase will appear ; while on cooling, a solid phase will appear.

32
Q

The fixed cost of a distillation column at minimum reflux ratio is

A. infinite
B. none of these
C. optimum
D. minimum

A

A. infinite

33
Q

In case of an ideal solution, the total vapor pressure varies __________ with the composition expressed as mole fraction,

A. linearly
B. None of these
C. exponentially
D. inversely

A

A. linearly

34
Q

In a binary distillation column, if the feed contains 40 mole % vapor, the q line will have a slope of

A. 0.6
B. -0.6
C. -1.5
D. 1.5

A

C. -1.5

35
Q

In most of the mechanically agitated liquid-liquid extractors, baffles or horizontal compartmental plates are provided, which helps in

A. All of these
B. increasing the rate of extraction.
C. maintaining the concentration difference between the two phases.
D. reducing the axial mixing.

A

A. All of these

36
Q

Which of the following applies to a feed at dew point?

A. 0 < f < 1
B. f = 1
C. f > 1
D. f = 0

A

B. f = 1

37
Q

With decrease in the throughput (compared with the design capacity) for a bubble cap distillation column, its efficiency

A. decreases
B. increases
C. may increase or decrease ; depends on individual design
D. remains same

A

B. increases

38
Q

The operation involved when the soluble material is largely on the surface of an insoluble solid and is merely washed off by the solvent is called

A. elutriation or elution
B. none of these
C. decoction
D. percolation

A

A. elutriation or elution

39
Q

In distillation columns, the number of bubble caps per tray primarily depends upon the

A. feed composition.
B. allowable liquid velocity.
C. allowable gas velocity.
D. allowable gas and liquid velocities.

A

D. allowable gas and liquid velocities.

40
Q

Which of the following liquid-vapor contacting devices provides maximum contact surface area for a particular duty ?

A. Wetted wall column
B. Sieve plate column
C. Randomly packed column
D. Bubble cap column

A

A. Wetted wall column

41
Q

Which of the following is not a continuous leaching equipment?

A. Pachuka tank
B. Bollman extractor
C. Kennedy extractor
D. Hydrocyclones

A

A. Pachuka tank

42
Q

Large scale usage of flash distillation is practiced in

A. polymerization industry
B. soap manufacturing
C. ammonia synthesis plant
D. petroleum refinning

A

D. petroleum refinning

43
Q

High pressure at the bottom of a distillation tower handling heat sensitive materials results in

A. increased relative volatility.
B. very efficient operation.
C. erosion of the tower.
D. thermal decomposition of bottoms.

A

D. thermal decomposition of bottoms.

44
Q

For a binary mixture with low relative volatility, continuous rectification to get pure products will require

A. less number of trays
B. low reflux ratio
C. high reflux ratio
D. small cross-section column

A

C. high reflux ratio

45
Q

columns are used for liquid dispersion in a continuous gas phase.

A. Bubble cap
B. Pulse
C. Packed
D. Sieve plate

A

C. Packed

ARC (9 decks)

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