Week 3

Question 1

3 types of distillation

Answer 1

• Differential distillation
• Flash/equilibrium distillation
• Recification

Question 2

Type of distillation the Rayleigh equation relates to

Answer 2

Differential distillation

Question 3

Simple one step distillation process

Answer 3

flash distillation

Question 4

Overall flash distillation balance

Answer 4

F = V + L

F = feed, V = top, L = bottom

Question 5

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

Answer 5

increases

Question 6

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

Answer 6

up

Question 7

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

Answer 7

Differential distillation

Question 8

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

Answer 8

up

Question 9

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

Answer 9

increasingly

Question 10

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

Answer 10

more

Question 11

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

Answer 11

increasingly

Question 12

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

Answer 12

less

Question 13

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

Answer 13

Differential distillation/ batch distillation

Question 14

flash distillation

Assuming a binary system

Answer 14

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

Question 15

Rich in more volatile components

Answer 15

Distillate

Question 16

Rich is less volatile components

Answer 16

Bottoms

Question 17

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.

Answer 17

Continuous rectification

Question 18

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

Answer 18

stripping section

Question 19

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

Answer 19

enrichment/ rectifiying section

Question 20

theoretical plate

Answer 20

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

Question 21

heat entering a plate =

Answer 21

heat leaving a plate + losses + heat of mixing

Question 22

If component A is more volatile

Answer 22

Yn > Yn-1
Xn+1>Xn

Question 23

Mass balance for plate n
Continuous rectification

Answer 23

Vn-1 + Ln+1 = Vn + Ln

Question 24

Component balance for the more volatile component

Answer 24

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

Question 25

Requires you to perform two mass balances on the column

Answer 25

Lewis Sorel Method ## Footnote 1) Balance around the top of the column 2) Balance around the bottom of the column

Question 26

Lewis Sorel top of column overall balance

Answer 26

Vn = Ln+1 + D

Question 27

Lewis Sorel bottom of column overall balance

Answer 27

Lm+1 = Vm + W

Question 28

Lewis Sorel top of column component balance

Answer 28

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

Question 29

where feed is introduced into the column

Answer 29

feed plate

Question 30

Lewis Sorel top of column slope

Answer 30

Lm/Vm

Question 31

Lewis Sorel bottom of column slope

Answer 31

Ln/Vn

Question 32

McCabe Thiele method simplfying assumptions

Answer 32

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

Question 33

q value equation

Answer 33

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

Question 34

Feed at boiling point q value

Answer 34

q = 1

Question 35

Cold feed as liquor q value

Answer 35

q > 1

Question 36

Party vapour q value

Answer 36

0 < q < 1

Question 37

Saturated vapour q value

Answer 37

q = 0

Question 38

Superheated q value

Answer 38

q < 0

Question 39

Diagram plotted for McCabe Thiele method

Answer 39

xy plot

Question 40

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

Answer 40

(xD, xD) (0, **D**xD/**V**n)

Question 41

q line slope

Answer 41

q/q-1

Question 42

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

Answer 42

(xw, xw)

Question 43

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

Answer 43

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

Question 44

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

Answer 44

number of theoretical pates required for the separation

Question 45

Reflux ratio equation

Answer 45

Ln/D

Question 46

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

Answer 46

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

Question 47

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

Answer 47

total reflux

Question 48

occurs when the top operating line coincides with the y=x line ## Footnote McCable Thiele

Answer 48

total reflux

Question 49

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

Answer 49

condition of minimum reflux

Question 50

The two things that intersect at pinch point ## Footnote Minimum reflux condition

Answer 50

q-line top operating line

Question 51

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

Answer 51

increase

Question 52

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

Answer 52

Rmin = xd - yf/ yf - xf

Question 53

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

Answer 53

Rmin = xd - xf/xf - xc

Question 54

Differential mass balance equation

Answer 54

Rayleigh equation

Question 55

- 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

Answer 55

Underwood equation

Question 56

- 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

Answer 56

Fenske Equation