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ChELE Review > Unit Operations > Flashcards

Unit Operations Flashcards

1
Q

Principal type of gas-solid separator employing centrifugal force

A

Cyclone

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2
Q

Evaporation is sometimes called ____

A

Water distillation

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3
Q

The total amount of evaporation an evaporator is capable of producing per unit time

A

Capacity

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4
Q

When the pressure of an evaporation chamber is decreased, the boiling point of the solution inside the chamber will _____

A

Decrease

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5
Q

The temperature driving force in an evaporator is determined as the difference between the condensing steam temperature and _____

A

Boiling point of the solution

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6
Q

In country where capital is scarce and energy cost is low, it is appropriate to install a ______ effect evaporator

A

Single

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7
Q

It is the deposition and growth on body walls, and especially on heating surfaces, of a material undergoing an irreversible chemical reaction in the evaporator

A

Scaling

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8
Q

It is the formation of deposits other than salt or scale and may be due to corrosion. It is caused by poor material of construction

A

Fouling

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9
Q

Slow cooling produces ____ crystals, and fast cooling produces ____ crystals

A

Large, small

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10
Q

The process by which crystalline bodies are created within a supersaturated fluid

A

Nucleation

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11
Q

The ability of a substance to crystallize into different crystalline forms

A

Polymorphism

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12
Q

Major stage of a crystallization process, and consists of the addition of new atoms, ions, or polymer strings into the characteristic arrangement of the crystalline lattice

A

Crystal growth

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13
Q

Technique widely employed to provide preformed templates on which new molecules can converge to form crystals

A

Seeding

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14
Q

When a solution is cooled to produce a supersaturated solution, the heat that must be removed is the sum of the ______ necessary to cool the solution and the heat of crystallization

A

Sensible heat content

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15
Q

During sensible cooling, relative humidity _____

A

Increases

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16
Q

Removal of all moisture from a wet solid requires _____

A

Perfectly dry air

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17
Q

Portion of water that cannot be removed by the air in its contact

A

Equilibrium moisture content

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18
Q

Moisture contained by a substance in excess of the equilibrium moisture

A

Free moisture

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19
Q

Drying method employed for heat sensitive materials such as pharmaceuticals and food stuff

A

Freeze drying or lyophilization

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20
Q

Detergent solution is dried to a powder in a _____

A

Spray dryer

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21
Q

Calcium ammonium nitrate fertilizer is dried using a _____

A

Rotary dryer

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22
Q

Feed characteristics for forward feed evaporation

A

Hot

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23
Q

Feed characteristics for backward feed evaporation

A

Heat sensitive, viscous

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24
Q

Feed characteristics for parallel feed evaporation

A

High feed rate

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25
Q

Advantage of parallel feed evaporation

A

Prevents salting or precipitation of solids

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26
Q

Suitable evaporator for concentration of foaming liquid

A

Long tube evaporator

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27
Q

Unit operation in which a soluble component is removed from an inert solid by a solvent which preferentially dissolves the soluble matter

A

Leaching

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28
Q

Unit operation by which soluble components of a liquid mixture are dissolved in a liquid immiscible with the insoluble component

A

Solvent extraction

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29
Q

Common leaching solvent in the vegetable oil industry

A

Hexane

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30
Q

In a counter-current extractor, extraction efficiency ____ with increasing axial mixing

A

Decreases

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31
Q

Extractor used for extraction of oil from oilseed

A

Bollman extractor

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32
Q

Extractor used in mineral processing to extract metals (e.g., Au and U) from their ores

A

Pachuca Tank

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33
Q

Extractor used to treat radioactive nuclear waste

A

Pulsed column extractor

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34
Q

Liquid-liquid extraction is based on the differences in _____

A

solubility

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35
Q

Single large washing is _____ effective than repeated small washing

A

Less

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36
Q

Why should the solvent used in liquid extraction not have a high latent heat of vaporization?

A

Recovery cost by distillation is high

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37
Q

Liquid-liquid extraction is preferred when extracting solvent is _____

A

cheap and abundantly available

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38
Q

TRUE or FALSE: In a counter-current liquid extractor, only one of the liquids may be pumped at any desired rate

A

True

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39
Q

It is comprised of a thin bed of substances with high porosity used in a mixer-settler liquid-liquid extraction column to increase the bubble size of the entering settler and to increase the settling rate of the bubbles.

A

Coalescer

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40
Q

Extraction equipment which best handles antibiotics

A

Podbielniak extractor

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41
Q

The relative volatility of most ideal binary solutions is _____ affected by temperature

A

greatly

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42
Q

Increasing the operating pressure of a distillation column makes separation ____

A

Difficult

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43
Q

Distillation technique used to avoid thermal decomposition of a component

A

Steam distillation

44
Q

In steam distillation, the amount of steam required per unit quantity of distillate is reduced by ____ temperature, and ____ total pressure.

A

Increasing temperature, decreasing total pressure

45
Q

Cooled liquid stream returned to the column to a cool plate or stage

A

Reflux

46
Q

The pressure in a distilling column decreases from ____ to _____

A

Bottom to top

47
Q

The temperature in a distilling column decreases from ____ to _____

A

Bottom to top

48
Q

In a distillation column, the heat removed in the cooler ____ with increasing reflux ratio

A

Increases

49
Q

Fenske equation is applicable when

A

Relative volatility is constant

50
Q

Design calculation for multiple component distillation

A

Fenske-Underwood-Gilliland (tray-to-tray calculations)

51
Q

Distillation technique wherein solvent is added to alter the relative volatility of the mixture

A

Extractive distillation

52
Q

Distillation technique employed to separate a constant boiling mixture

A

Azeotropic distillation

53
Q

Material passing one screening surface and retained on a subsequent surface

A

Intermediate material

54
Q

Indicates the number of holes per linear inch

A

Mesh number

55
Q

TRUE or FALSE: The Ponchon-Savarit method is more accurate than McCabe-Thiele method to determine the number of theoretical stages required for the separation of non-ideal binary systems by distillation

A

True

56
Q

TRUE or FALSE: In Ponchon-Savarit method, the stripping and rectifying operating lines are vertical at total reflux

A

True

57
Q

TRUE or FALSE: Dehydration of ethyl alcohol is most economically done by molecular distillation at very high vacuum

A

False

58
Q

For an azeotropic mixture, the equilibrium liquid composition is ____ the vapor composition

A

Equal

59
Q

Size measurement expression for coarse particles

A

cm, in, mm

60
Q

Size measurement expression for ultrafine particles

A

surface area per unit mass

61
Q

Size measurement expression for fine particles

A

mesh

62
Q

Size measurement expression for very fine particles

A

microns

63
Q

Property of a material to resist indentation or scratches

A

Hardness

64
Q

Mohs Hardness Scale

A

Soft: talc, gypsum, calcite
Intermediate: fluorite, apatite, feldspar
Hard: quartz, topaz, corundum, diamond

65
Q

Moisture content of coarse solids

A

< 3-4%

66
Q

Moisture content of fine solids

A

> 50%

67
Q

Reduction ratio (R = Df/Dp) for coarse solids

A

R = 5 to 7

68
Q

Reduction ratio (R = Df/Dp) for fine solids

A

R ≈ 100

69
Q

Measure of rate of grinding of materials in a particular mill

A

Grindability

70
Q

Equipment for coarse size reduction

A

Hard: jaw crusher, gyratory crusher
Soft: squirrel cage disintegrator, hammer mill

71
Q

Equipment for intermediate size reduction

A

Cone crusher, crushing rolls, roller crusher

72
Q

Equipment for fine size reduction

A

Ball mill, tube mill, pebble mill, rod mill

73
Q

Mechanism for coarse size reduction

A

Compression

74
Q

Mechanism for fine size reduction

A

Impaction

75
Q

Mechanism for very fine size reduction

A

Attrition

76
Q

Mechanism for shaped size reduction

A

Cutting

77
Q

Equipment for ultrafine size reduction

A

Fluid energy mill

78
Q

The operating speed of a ball mill should be _____ than the critical speed

A

Less

79
Q

The critical speed of a ball mill is dependent on

A

Radius of mill (D) and ball (d)

80
Q

Operation by which solids are separated from liquids due to the difference in densities

A

Sedimentation

81
Q

Forces acting on a particle settling in fluid

A

Gravitational or centrifugal, buoyant, and drag forces

82
Q

Used to increase the porosity of the cake during filtration

A

Filter aid

83
Q

Cake porosity is ____ at the filter medium

A

Minimum

84
Q

In gas absorption, one solute is being absorbed while the rest of the components are assumed to be ____, and the liquid is _____

A

non-soluble, non-volatile

85
Q

Ideal conditions in a gas absorber

A

low T, high P

86
Q

Ideal conditions in a stripping column

A

high T, low P

87
Q

The operating velocity in a packed tower is usually ____ the flooding velocity

A

Half

88
Q

Types of membrane modules

A

Plate and frame
Tubular
Spiral-wound
Capillary
Hollow-fiber

89
Q

Membrane configuration with low surface area per volume, used in flat and plate modules

A

Flat

90
Q

Membrane configuration with high surface per volume; feed is preferably inside the membrane

A

Tubular

91
Q

Fraction of stream that passes through a membrane

A

Permeate

92
Q

Fraction retained in the membrane

A

Retentate

93
Q

Usual flow arrangement for plate and frame module membranes

A

Perpendicular/cross flow

94
Q

Selective flow by a fluid

A

Channeling

95
Q

Instrument to prevent channeling in membrane separation

A

Stop disk

96
Q

Advantages of plate and frame module

A

Easy to clean, easy to replace, high work pressure, for high viscosity liquids

97
Q

Disadvantage of plate and frame module

A

Small area to volume ratio

98
Q

Advantages of spiral-wound module

A

High packing density, easy and inexpensive

99
Q

Disadvantages of spiral-wound module

A

Difficult to clean, high pressure drop, only for pure media

100
Q

Advantages of tubular modules

A

Resistant to fouling, easy to clean

101
Q

Disadvantages of tubular modules

A

Low packing density, expensive

102
Q

Applications of tubular modules

A

Reverse osmosis, ultrafiltration

103
Q

Type of module with the highest packing density (30,000 m²/m³)

A

Hollow-fiber module

104
Q

Advantages of hollow-fiber module

A

High packing density, low cost

105
Q

Disadvantages of hollow-fiber module

A

high fouling, high pressure drop

ChELE Review (12 decks)

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