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Separation Processes > Week 3 > Flashcards

Week 3 Flashcards

1
Q

3 types of distillation

A
  • Differential distillation
  • Flash/equilibrium distillation
  • Recification
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2
Q

Type of distillation the Rayleigh equation relates to

A

Differential distillation

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3
Q

Simple one step distillation process

A

flash distillation

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4
Q

Overall flash distillation balance

A

F = V + L

F = feed, V = top, L = bottom

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5
Q

In a continuous rectification process, temperature ________ as you go up the column

A

increases

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6
Q

In a continuous rectification process, temperature increases as you go ____ the column

A

up

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7
Q

The fractionating column is mounted on a large reboiler or still which holds the charge. The charge is boiled and the vapour evolved passes up the column, is condensed and partially returned as reflux

A

Differential distillation

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8
Q

Differential distillation: as the vapour passes ____ the column, it becomes increasingly rich in the more volatile component.

A

up

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9
Q

Differential distillation: as the vapour passes up the column, it becomes ________ rich in the more volatile component.

A

increasingly

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10
Q

Differential distillation: as the vapour passes up the column, it becomes increasingly rich in the ____ volatile component.

A

more

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11
Q

Differential distillation: charge remaining the still becomes ________rich in the less volatile component

A

increasingly

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12
Q

Differential distillation: charge remaining the still becomes increasingly rich in the ____ volatile component

A

less

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13
Q

In this distillation method, the composition of the distillate falls below the specification and the distillation is stopped

A

Differential distillation/ batch distillation

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14
Q

flash distillation

Assuming a binary system

A

y = F/V z - x(F/V - 1)

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15
Q

Rich in more volatile components

A

Distillate

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16
Q

Rich is less volatile components

A

Bottoms

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17
Q

Vapour flows up, liquid flows down.
Vapour and liquid are brough into contact on plates or packing.
Some of the condensate is returned to the column to provide liquid flow above the feed point.
Some of the liquid at the base of the column is vapourised to provide vapour flow.
In the section below the feed, the more volatile components are stripped out.
Above the feed the concentration of the more volatile components is increased.

A

Continuous rectification

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18
Q

Section below the feed where the more volatile component is stripped out

A

stripping section

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19
Q

Above the feed where the concentration of the more volatile component is increased

A

enrichment/ rectifiying section

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20
Q

theoretical plate

A

a distillation column plate such that the vapour leaving the plate is in equilibrium with the liquid on and leaving the plate

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21
Q

heat entering a plate =

A

heat leaving a plate + losses + heat of mixing

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22
Q

If component A is more volatile

A

Yn > Yn-1
Xn+1>Xn

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23
Q

Mass balance for plate n
Continuous rectification

A

Vn-1 + Ln+1 = Vn + Ln

24
Q

Component balance for the more volatile component

A

Vn-1 Yn-1 + Ln+1 Xn+1 = VnYn + LnYn

25
Q

Requires you to perform two mass balances on the column

A

Lewis Sorel Method

1) Balance around the top of the column
2) Balance around the bottom of the column

26
Q

Lewis Sorel top of column overall balance

A

Vn = Ln+1 + D

27
Q

Lewis Sorel bottom of column overall balance

A

Lm+1 = Vm + W

28
Q

Lewis Sorel top of column component balance

A

yn = (Ln+1/Vn) (Xn+1) + (D/V) Xd

29
Q

where feed is introduced into the column

A

feed plate

30
Q

Lewis Sorel top of column slope

A

Lm/Vm

31
Q

Lewis Sorel bottom of column slope

A

Ln/Vn

32
Q

McCabe Thiele method simplfying assumptions

A
  1. Constant molar heat of vapourisation
  2. No heat losses
  3. No heat of mixing
33
Q

q value equation

A

heat to vapourise 1 mol of feed/ mol latent heat of the feed

34
Q

Feed at boiling point q value

A

q = 1

35
Q

Cold feed as liquor q value

A

q > 1

36
Q

Party vapour q value

A

0 < q < 1

37
Q

Saturated vapour q value

A

q = 0

38
Q

Superheated q value

A

q < 0

39
Q

Diagram plotted for McCabe Thiele method

A

xy plot

40
Q

The points the top operating line in McCabe-Thiele plot goes through

A

(xD, xD) (0, DxD/Vn)

41
Q

q line slope

A

q/q-1

42
Q

The points the q-line line in McCabe-Thiele plot goes through

A

(xw, xw)

43
Q

The points the bottom operating line in McCabe-Thiele plot goes through

A

(xw, xw) and intersection of top operatng line and the q-line

44
Q

the total number of steps on the McCabe Thiele graph is equal to

A

number of theoretical pates required for the separation

45
Q

Reflux ratio equation

A

Ln/D

46
Q

McCabe Thiele equation for top operating line in terms of reflux ratio

A

R/R+1 xn+1 + xd/R+1

47
Q

Occurs when all the distillate is returned to the column and no product is withdrawn

A

total reflux

48
Q

occurs when the top operating line coincides with the y=x line

McCable Thiele

A

total reflux

49
Q

occurs when both the q line and the top operating line intersect the equilibrium line at the same point (pinch point)

McCable Thiele

A

condition of minimum reflux

50
Q

The two things that intersect at pinch point

Minimum reflux condition

A

q-line
top operating line

51
Q

Any ____ in R above this Rmin value will produce a workable column

A

increase

52
Q

If the q-line is vertical then it can be shown that the slope of the operating line is:

A

Rmin = xd - yf/ yf - xf

53
Q

If the q-line is horizontal then it can be shown that the slope of the operating line is:

A

Rmin = xd - xf/xf - xc

54
Q

Differential mass balance equation

A

Rayleigh equation

55
Q
  • Relative volatility is constant
  • lets you find R min for the system
  • you do not need to use graph to find R min with this method
A

Underwood equation

56
Q
  • Relative volatility is constant
  • Way to calculate the minimum number of stages needed operating under the condition of total reflux
  • actual number of stages > number of stages determined in this method
A

Fenske Equation

Separation Processes (6 decks)

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