Exam 1

Question 1

Heavy key
Light key

Answer 1

1. Heaviest component in top product
2. Lightest component in bottom product

Question 2

Distillation columns
1. Direct sequence
2. Indirect sequence

Answer 2

1. Removes the lightest component (most volatile) first
   (Reboiler sequencing down)
2. Removes the heaviest component (least volatile) in each column (distillate sequencing down)

Question 3

Why separate hazardous/ corrosive substance first

Answer 3

Removing them needs expensive materials and removing them first minimises the use of expensive materials. It minimises potential exposure

Question 4

Key parameters needed for distillation column

Answer 4

Plates or Packing
Number of stages
Reflux ratio
Column diameter

Question 5

Consequences of having a distillation column with low reflux ratio

Answer 5

Little contact between vapour and liquid
Poor separation
More stages required
High capital cost

Question 6

Implications/ limitation s of using empirical correlations for design of distillation columns

Answer 6

The correlations were probably from scaled down version of a column in a lab which is not representative of the full scale
They also have limitations of the type of column/ tray/ packing for which they are appropriate

Question 7

How does fluid surface tension and viscosity affect distillation column efficiency

Answer 7

Bubble size - hence surface area
Rising/ settling velocity hence vapour/ liquid contact time
Diffusivity hence mass transfer
Flow regime ( froth, spray)

Question 8

Isotherm graphs recap and VLE graph

Question 9

Question 1j equation

Answer 9

overall gas-phase mass transfer resistance formula from the two-film theory. It shows that the total resistance to mass transfer is the sum of resistances in the gas film and the liquid film (converted to gas-phase units using Henry’s law).

Question 10

When is flash distillation used

Answer 10

Big difference in relative volatilities of components
Example MeOH/ water from outlet of MeOH synthesis reactor

Question 11

Hysterisis

Answer 11

Amount of adsorbate on the adsorbent is different for the apportion and desorption isotherms at the same pressure

Question 12

Continuation of hysteresis

Answer 12

Adsorption Path: When the adsorbate is introduced to the adsorbent, it adsorbs onto the surface, and the adsorption isotherm is traced.
• Desorption Path: When the adsorbate is removed (for example, by decreasing pressure or concentration), the desorption follows a different path, leading to a different amount of adsorbate being desorbed compared to what was adsorbed.

This difference creates a hysteresis loop between the adsorption and desorption curves.