membrane separation

Question 1

On what basis does membrane separation separate by?

Answer 1

Molecular weight / size
Membrane acts as a barrier

Question 2

Where might membrane separation be used?

Answer 2

-Finely dispersed solids, especially compressible, highly viscous, gelatinous, or those with a density close to water
-Low molecular weight, non-volatile organics/pharmaceuticals and dissolved salts
-Biological materials that are sensitive to physical and chemical environment

Question 3

What are the advantages of using membranes

Answer 3

-Operation at ambient temperature
-Relatively low capital and running costs
-Low cost of modular construction

Question 4

Which membrane separation processes are driven by pressure?

Answer 4

-Microfiltration
-Ultrafiltration
-Nanofiltration
-Reverse osmosis

Question 5

What are natural membranes made from?

Answer 5

Cellulose

Question 6

What is the membrane made from in pressure driven separation

Answer 6

Synthetic polymers -polymeric materials e,g, polyamide

Question 7

Why are synthetic polymers used as membranes

Answer 7

-They have improved chemical stability
-Have better resistance to microbial degradation (moulding)
than the natural cellulose membranes
-Narrower pore size distribution

Question 8

What are the key features of a membrane which characterise it for application?

Answer 8

-Pore structure (determined using microscopy)
- Permeability of membrane to fluids (determined using bubble point or permeability methods)
-Maximum pore size and pore size distribution
-Nominal molecular weight cut off - linked to solute rejection factor

Question 9

Approximately what pressure and velocity is used in microfiltration separation

Answer 9

velocity: 1-8m/s
pressure: 1-5 bar

Question 10

Examples of applications of microfiltration?

Answer 10

-Biomass separation
-Sterile filtration
-Fermentation

-Used for dewatering suspensions ot solid concs. that are difficult to handle or control by other separations

Question 11

What effects the rate of membrane permeation

Answer 11

-Membrane fouling
-The materials being processed
-The cross flow velocity
-The applied pressure

Question 12

Approximately what particle size is separated with microfiltration

Answer 12

10 - 0.1 micrometres (10e-6)

Question 13

Approximately what particle size is separated with ultrafiltration?

Answer 13

<5 nanometres

Question 14

Approximately what particle size is separated with reverse osmosis?

Answer 14

< 1 nanometres

Question 15

How does an increase in cross flow velocity affect membrane separation variables?

Answer 15

-Mass transfer coefficient, hD,increases
-Membrane permeation flux, J, increases
-Causes increase in both laminar and turbulent flow

Question 16

How does a decrease in channel height affect membrane separation variables?

Answer 16

-Mass transfer coefficient, hD, increases
-Membrane permeation flux, J, increases
-Causes increase in both laminar and turbulent flow

Question 17

How does an increase in channel length affect membrane separation variables?

Answer 17

-Mass transfer coefficient, hD, decreases in laminar flow
-Due to an increased build up layer/fouling

Question 18

What effects if a solution will pass through a membrane

Answer 18

-if it is sufficiently small to pass through a pore
-If it doesn’t significantly interact with the membrane
-If it doesn’t interact with other larger solutes