week 4

Question 1

Distillation method used for low volume high value products

Answer 1

batch distillation

Question 2

Two types of batch distillation

Answer 2

1. Differential distillation
2. Batch rectification

Question 3

Batch rectification has two modes of operation

Answer 3

• constant product composition
• constant reflux ratio

Question 4

As material is withdrawn, the MVC composition becomes smaller

Answer 4

Constant Product Composition

Question 5

To maintain a constant product composition, the reflux ratio must be ____ as the composition of the MVC decreases

Answer 5

Increased

Question 6

To maintain a constant product composition, the _____ must be increased as the composition of the MVC decreases

Answer 6

Reflux ratio

Question 7

Material balance of constant product composition

Answer 7

𝑆1𝑥𝑠1 − 𝑆2𝑥𝑠2 = 𝐷𝑏𝑥𝑑

S1 = mols in still initially
S2 = mols I’m still after
xs1 = mol frac of MVC in still initially
xs2 = mol frac of MVC in still after

Question 8

Equation for amount of product obtained in constant product composition

Answer 8

𝑆1 − 𝑆2 = 𝐷𝑏
S1 = mols in still initially
S2 = mols I’m still after

Question 9

MVC

Answer 9

Most volatile component

Question 10

If a column is operated at _____, the composition of MVC will continuously fall

Answer 10

Constant reflux

Question 11

If a column is operated at constant reflux, the composition of MVC will continuously ___

Answer 11

Fall

Question 12

Constant product composition reflux ratio equation

Answer 12

dLb/dDb

Question 13

Most expensive type of tray arrangement

Answer 13

Bubble cap trays

Question 14

Tray arrangements from highest relative cost to lowest

Answer 14

1. Bubble-cap
2. Valve
3. Sieve (lowest)

Question 15

Tray arrangements from highest pressure drop to lowest pressure drop

Answer 15

1. Bubble cap (highest)
2. Valve
3. Sieve (lowest)

Question 16

Which tray arrangement has the lowest efficiency?

Answer 16

Sieve tray

Question 17

Which tray arrangement has the lowest vapour capacity?

Answer 17

bubble cap trays

Question 18

3 Tray arrangements

Answer 18

• Sieve trays
• Valve trays
• Bubble cap trays

Question 19

Typical turndown ratio of a sieve tray

Answer 19

2

Question 20

Typical turndown ratio of a valve tray

Answer 20

4

Question 21

Typical turndown ratio of a bubble cap tray

Answer 21

5

Question 22

indicates the range of flow that is able to be measured with acceptable accuracy

Answer 22

Turndown ratio

https://en.wikipedia.org/wiki/Turndown_ratio

Question 23

3 types of reboilers

Answer 23

• Kettle type reboiler
• Vertical thermosyphon reboiler (reboiler liquid withdrawn from bottom sump)
• Vertical thermosyphon-type reboiler (reboiler liquid withdrawn from bottom tray downcomer)

Question 24

Possible vapour liquid flow regimes for a contacting tray

Answer 24

1. Spray
2. Froth
3. Emulsion
4. Bubble
5. Cellular foam

Question 25

Overall Column Efficiency equation

Answer 25

E = number of ideal stages/actual number of stages x 100 ## Footnote Values of E tend to vary between 30-100%

Question 26

Factors affecting column efficiency

Answer 26

1. Kinetics slow as you near equilibrium 2. Factors related to plate design

Question 27

measures performance of a single tray by considering the composition of the vapour phase as it enters and leaves a given tray

Answer 27

Murphree Efficiency ## Footnote https://neutrium.net/equipment/distillation-tray-efficiency/

Question 28

Murphree efficiency equation

Answer 28

(yn - yn-1)/(ye - yn) ## Footnote yn = vapour mol fraction on plate n yn-1 = vapour mol fraction on plate n-1 ye = vapour mol fraction that is in equilibrium with the liquid mol fraction

Question 29

For a single plate, the vapour leaving is in equilibrium with the liquid leaving, and the ratio of that actual composition achieved to that which could occur if equilibrium between yn and xn were achieved is known as...

Answer 29

Murphree plate efficiency

Question 30

Shown by the lowest point on the total cost line

Answer 30

min total cost

Question 31

McCable Thiele Plots with a single side stream have

Answer 31

2 top operating lines with slope Ls/Vs and Ln/Vn

Question 32

McCable Thiele Plot for a distillation column with two feeds has...

Answer 32

An operating line per section (3) A q line per feed (2)

Question 33

Overall column efficiency

Answer 33

E = (number of ideal plates/ actual number of stages) * 100

Question 34

Factors related this are

Answer 34

1. Kinetics slow as you near equilibrium 2. Factors related to plate design