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Civil Law > Distillation > Flashcards

Distillation Flashcards

1
Q

When to use:
Flash Distillation

A

Have a large difference in boiling point

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2
Q

When to use:
Steam Distillation

A

*Avoid thermal decomposition of a component.
*When one component to be distilled has an unusually high normal boiling temperature.
*High boiling component immiscible in water

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3
Q

When to use:
Differential / Rayleigh Distillation

A

Experimentation on relative volatilities

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4
Q

When to use:
Simple Continuous Distillation

A

*Components have a low relative volatility.
*No reflux used

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5
Q

When to use:
Fractional Distillation

A

*Components have a low relative volatility.

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6
Q

Condenser

A

used to extract heat from the vapor leaving the topmost stage to produce the low-boiling enriched distillate.

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7
Q

Reboiler

A

inject heat to the liquid leaving the most bottom stage to produce the low-boiling stripped bottoms product.

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8
Q

Factors Affecting Distillation

A
  1. Method used
  2. Feed conditions (q, x, y, relative volatility)
  3. Reflux Ratio, R
  4. Number of Stages, N
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9
Q

When is dew point and bubble point the same?

A

Dew point and bubble point are the same for pure substances

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10
Q

How the following affects Distillation:
1. Method used
2. Feed conditions (q, x, y, relative volatility)
3. Reflux Ratio, R
4. Number of Stages, N

A
  1. Method used
  2. Feed conditions (q, x, y, relative volatility)
    q =
    x =
  3. Reflux Ratio, R
    higher R, lower N
  4. Number of Stages, N
    Lower N needs higher R
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11
Q

Data Needed for:
Flash Distillation

A

*Feed:
Flowrate
Composition
Temperature
Pressure
*P,drum < crit P,mix

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12
Q

Flash Distillation

A

*Pump - Heater - Valve - Flash Drum
*The fluid is pressurized and heated and is then passed through a throttling valve or nozzle into the flash drum

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13
Q

Distillation used in petroleum refining

A

Flash distillation

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14
Q

Demister

A

Entrainment Eliminator
* Employed to prevent liquid droplets from being entrained in the vapor

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15
Q

Ponchon - Savarit Method

A

Distillation graphical method
* Heat effects and heats of solution is not negligible anymore.

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16
Q

Constant molar overflow

A

For each stage
*vapor in = liquid out

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17
Q

Gilliland equation

A

Estimate the number of equilibrium stages in a distillation column.

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18
Q

Fenske equation

A

Used to calculate the N,min for separation of binary feed stream by a fractionation column at R,max

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19
Q

Fenske-Underwood-Gilliland Method

A

Multicomponent shortcut methods for design approximation of simple distillation
*Combines Fenske, Underwood and Gilliland equations

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20
Q

Underwood Equation

A

Apply when some of the components do not appear in either the distillate or the bottom products at minimum reflux

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21
Q

Differentiate Fenske vs Underwood vs Gilliland Equations

A

Fenske - N,min
Underwood - R,min
Gilliland - Actual R and N

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22
Q

Enriching Section

A

Upper section of distillation column

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23
Q

Striping Section

A

Lower section of distillation column

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24
Q

q

A

fraction of saturated liquid in feed

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25
Q

f

A

fraction of saturated vapor in feed

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26
Q

Pinch point

A

Intersection of feed line and equilibrium curve
When N = infinite,and R,min

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27
Q

How __ Affects Distillation:
Pressure

A

High P:
* decreases relative volatility - More stages
* increase viscosity = decrease/increase diameter of distillation column @ low/high pressure distillation
* decreases flooding velocity = increase distillation column area required
High P allows separation of

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28
Q

How __ Affects Distillation:
Feed Temperature

A

Higher T = lower reboiler power consumption = higher condenser power consumption

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29
Q

How __ Affects Distillation:
Vacuum

A

Lower P = Lower T required
*Used to separate high boiling mixtures
*Thermal sensitive feed

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30
Q

Extractive Distillation

A
  • 3rd Component: solvent (has low volatility)
    *more liquid product than azeotropic
    *introduce a solvent to relative volatilities by changing the intermolecular interactions of the components within the mixture.
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31
Q

Azeotropic Distillation

A
  • 3rd Component: Entrainer (Mass separating agent) (forms low boiling azeotrope.)
    *Forms azeotrope AFTER adding 3rd component
    *More vapor than extractive
  • More complicated distillation
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32
Q

Azeotropic distillation is employed to separate ___

A

constant boiling mixture.

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33
Q

Constant Molar Overflow

A
  • To achieve 4 eq, 4 unknowns
    *Molar flow rates of the vapor and liquid phase within a column section are presumed not to change from one stage to another.

V,n = V,n+1
L,n-1 = L,n

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34
Q

When to use:
Open Steam Distillation

A

*Used when one of the components is water.
*Instead of a reboiler, steam is used to sustain the countercurrent effect.

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35
Q

Flooding

A

Excessive accumulation of liquid inside the column

36
Q

Jet Flooding

A

Froth of liquid-vapour mixture touches the next above tray

37
Q

Downcomer Flooding

A

Liquid level in downcomer on any tray rises above the weir

38
Q

Causes of Flooding

A
  1. Clogged tray perforation
  2. High vapor velocity = High vaporization rate of reboiler
39
Q

Preventing Flooding

A

1.Decrease feed rate
2. Decrease reflux rate
3. Decrease reboiler duty

40
Q

Foaming

A

Expansion of liquid due to passage of vapour or gas.

41
Q

Weeping / Dumping

A

*Caused by low vapour flow
*Liquid in tray WEEPS down the packing
*Pressure exerted by the vapour is insufficient to hold up the liquid on the tray

42
Q

Priming

A

*Foam height on plate reaches next plate
*Reduces separation efficacy

43
Q

Why N,min is impossible?

A

N,min needs very large condenser (infinite reflux)

44
Q

Why R,min is impossible?

A

R,min needs infinite stages

45
Q

Feed Factors Affecting Distillation

A

CLASH

*Close boiling liquids
*Low boiling liquids
*Azeotropic mixtures
*Scaling and Fouling
*Heat sensitive liquids

46
Q

DISTILLATION Design Considerations

A

*Tray Performance
*Jet Flooding
*Operating pressure
*Mass Loading

47
Q

COLUMN TYPES:
Packed Columns

A

ADVANTAGES
*When high number of theoretical stages are required
*When Small diameter is required (liquid distribution concerns)
*Vacuum distillation
*Lower cost and pressure drop
*For foaming, corrosive, heat sensitive and high viscosity
*Large surface area

DISADVANTAGES
*Does not high turnover ratio
*Can’t remove side products

48
Q

COLUMN TYPES:
Plate / Tray Columns

A

ADVANTAGES
*Wide range of gas and liquid flow rates
*Can have side products
*High solids content / fouling while HIGH DIAMETER

DISADVANTAGES
*Easier fouling and solids cleanup
*More expensive

49
Q

Reflux Ratio

A

Reflux Amount / Distillate Amount

50
Q

Why is there __ in Distillation?
*Reflux
*Boil up

A

*Reflux
-to provide a steady stream of liquid to contact with vapor
-to maintain temperature and pressure profile accross the column
*Boiler
–to provide a steady stream of vapor to contact with liquid

51
Q

Why azeotropes are hard to distill?

A

Even how much you boil the liquid mixture, its composition is equal to its vapor.
Separation becomes impossible

52
Q

Total reflux in a distillation operation requires minimum ____

A

number of plates

53
Q

In distillation, overhead product contains ____

A

any number of components

54
Q

With increase in pressure, the relative volatility for a binary system ____

A

decreases.

55
Q

McCabe Thiele vs Ponchon Savarit

A

*McCabe Thiele
-Ideal binary

*Ponchon-Savarit
-Non ideal binary mixture
-Appreciable heat of solution and mixture

56
Q

Packed towers are preferred over plate towers because it gives ___ pressure drop and ___ hold up

A

low pressure drop and low hold up.

57
Q

Weeping in a distillation column results due to ____

A

results due to very low gas velocity.

58
Q

Plate towers are preferred to packed towers, when ____ because ____

A

*WHEN large temperature changes are involved
*BECAUSE packing may be crushed due to thermal expansion/ contraction of the components of the equipment

59
Q

Channeling

A

*Due to low liquid flowrate, and no liquid distributor
*Liquid tends to flow in column wall (if not distributed well)

60
Q

Channeling in a packed tower results from the ___

A

*maldistribution of liquid
*non-uniformity of packing

61
Q

Inside the distillation column, pressure drop is the ___

A

driving force for the vapour flow

62
Q

Operating velocity in a packed tower is usually __________ the flooding velocity.

A

half

63
Q

Solvent used in extractive distillation
____

A

forms a low boiling azeotrope.

64
Q

Channeling is prevented by ____

A

liquid distributor

65
Q

Temperature from of distillation column from bottom to top ___

A

decreases

66
Q

Azeotropes obey Raoult’s Law at ____

A

at all temperatures

67
Q

___ vapor fraction of feed ____ reflux ratio

A

increases ; increases

68
Q

Channeling is caused by __

A

low tray efficiency

69
Q

Petroleum Fractions

A

LiGa Na KaDa FueL
1. LPG
2. Gasoline
3. Naphtha
4. Kerosene
5. Diesel
6. Fuel Oil
7. Lubricating Oil

70
Q

When to Use:
Random or Structured Packing

A

*Random: high liquid loading > 49 m3/hr/m2
*Structured: low liquid loading < 49 m3/hr/m2

71
Q

When is LLE used over Distillation?

A

*Heat sensitive feed
*High latent heat of vaporization
*Separation applications that would not be cost-effective, or even possible, with distillation

72
Q

Distillation to obtain methanol

A

Destructive Distillation of coal

73
Q

Sweetening and its Importance

A

*Remove dihydrogen sulfide and mercaptans
*Improve color, odor and oxygen stability

74
Q

Slope of rectifying line is unity if the reflux ratio is ___

A

Infinite

75
Q

DECREASING the distillation tower temperature ___ top product purity and ___ bottom product purity

A

Decrease T
= Decrease top and bottom purity

76
Q

Increasing condenser and reboiler duty will ____ top purity and ____ bottom purity, respectively

A

Increased duty =
increased top and bottom purity

77
Q

Flooding can be recognized by ____

A

significant reduction of product quality

78
Q

Dew and Bubble Point Pressures

A

*Dew Point
Pdew = sum (xi * Psat)

*Bubble Point
Pbbl = 1/[sum (yi/Psat)]

79
Q

Assumptions of McCabe-Thiele Method

A
  1. dH,vaporization equal for all components
  2. dH,mix and sensible enthalpy negligible
  3. Equal pressure throughout column
  4. No heat loss
80
Q

Distillation Limiting Conditions

A

*R,min –> N = infinite
*N,min –> R = infinite or D = 0 and V=L
*Relative Volatility, a = infinite –> N = 1

81
Q

When to use LLE over Distillation?

A
  1. High latent heat of vaporization
  2. Forms azeotrope
  3. Close-boiling and Close-melting mixture
  4. Heat sensitive
  5. Recovery of small concentrations of desired
82
Q

Advantage / Disadvantage:
* Bubble-Cap
* Valve Tray
* Sieve Tray

A
  • Sieve Tray
    + Cheapest
    + Fouling liquids
    + Easiest to clean
  • Very low turndown
  • Valve Tray
    +Higher turndown than sieve tray
    +Most economical for fluids with solids
  • Bubble-Cap
    +Suited for either low or high flow rates.
    -Fouling and polymer-forming liquds
    -Expensive
83
Q

Packing

A

*Increase surface area for contact between liquid and vapor phases
*Tortuous path to increase residence time
*Made of metal, ceramics, plastics or glass

84
Q

Turndown Ratio

A

[Max vapor velocity] / [Vapor velocity on offset of weeping]

85
Q

When to use:
* Plate Columns
* Packed Columns

A
  • Plate Columns
  • Large diameter
  • Side products required
  • Solid content and fouling
  • High turndown ratio is required
  • Packed Columns
  • Corrosive, fouling and foaming liquids
  • Small diameters
  • Low liquid flowrates

Civil Law (31 decks)

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