Membrane Separation

Question 1

Define a Membrane

Answer 1

A membrane is a semi-permeable barrier that allow selective exchange between two regions

Question 2

Define Biological membranes

Answer 2

• Complex, highly specific
• Use ACTIVE TRANSPORT

Question 3

Define Synthetic membranes

Answer 3

• Less complex & (energy) efficient
• Use generally PASSIVE TRANSPORT
• higher chem & mech STABILITY

Question 4

What is the difference between Isotropic and Anisotropic membranes

Answer 4

Isotropic membranes have uniform composition and physical nature across the membrane where as Anisotropic do NOT

Question 5

Define Flux & units

Answer 5

Flux is the amount of fluid permeate passing through the membrane [volume/area/time] OR [ms-1]

Question 6

Define Selectivity

Answer 6

Selectivity is the ability of a membrane to separate out components

Question 7

Define Permeability

Answer 7

Permeability is the measure of the rate at which a comp. is transported
@ constant conc, temp, pressure & electric field

Question 8

What are the factors for Performance of a membrane
(4 for membranes & 3 for comp.)

Answer 8

Permeability determined by:
- Structure of membrane, (tortuosity/ pore no.
& size)
- Chem comp., (hydrophobic/phillic)
- Electrical charge of membrane
- DRIVING FORCE applied (conc dif.)
- size/chem nature/electric charge of comp.

Question 9

Membrane Applications and how it works

Answer 9

Dialysis
- Filters WASTE from blood
- For kidney failure
Desalination
- Uses REVERSE OSMOSIS (+ nanofilt.)
- Filters SALT ions = drinking water

Question 10

What can membranes filter

Answer 10

• Microbes
• Macromolecules
• Pharmaceuticals
• Unwanted ions

Question 11

Membrane Advantages
(4)

Answer 11

• Continuous & Batch
• Low ENERGY consumption
• Easy SCALE UP
• AMBIENT temp

Question 12

Membrane Limitations (5)

Answer 12

• Fouling
• Low LIFETIMES
• Low SELECTIVITY
• Low FLUX
• LINEAR scale up

Question 13

Membranes divide the Feed into the ________ and _________

Answer 13

Membranes divide the Feed into the PERMEATE and RENTATE

Question 14

Selectivity, expressed as retention:
R = Cf - Cp / Cf
What happens is membrane rejects solute

Answer 14

Cp = 0 ( no permeate conc)
therefore R = 1, perfect separation

Question 15

Define Asymmetric membrane Structure

Answer 15

Asymmetric membranes have:
- a THIN, DENSE top layer
-> determines transport rate
- & a THICK, POROUS sub layer
-> for support

Question 16

Permeation rate is _________ proportional to thickness of barrier layer

Answer 16

Permeation rate is INVERSELY proportional to thickness of barrier layer

Question 17

Asymmetric membranes have a higher __________ ____ than Symmetric membranes of similar thickness

Answer 17

Asymmetric membranes have a higher PERMEATION RATE than Symmetric membranes of similar thickness

Question 18

Arrange Filtration types based on highest pore size to lowest:
Nano-filtration, Ultra-filtration, Reverse osmosis, Micro-filtration.

Answer 18

Micro-filtration < Ultra-filtration < Nano-filtration < Reverse Osmosis

Bacteria & particles < Macromolecules < divalent ions < Monovalent ions

Question 19

Define Microfiltration & Applications (2)

Answer 19

Microfiltration removes particles, bacterial cells and spores
Application: Pharmaceutical production, Water treatment

Question 20

Define Ultrafiltration & Applications (3)

Answer 20

Ultrafiltration removes macromolecules e.g. proteins and carbs.
Application: Food products, Water treatment, Pharmaceutical production

Question 21

Define Reverse Osmosis & Application (1)

Answer 21

Reverse Osmosis removes SALTS
Application: produce DRINKING WATER

Question 22

Porous vs Non - porous membranes

Answer 22

Non - porous is gas separations (RO)
Porous is fluid separations (Micro/Ultrafiltration/RO)

Question 23

Define Sintering

Answer 23

Compress powder then HEAT at HIGH temp
- For MICROfiltration
- Low POROSITY

Question 24

Define Stretching

Answer 24

MECHANICAL STRESS applied to film and small ruptures occur
- For ULTRAfiltration
- use only CRYSTALLINE POLYMERIC material
- High POROSITY

Question 25

Define Track Etching

Answer 25

High ENERGY particle RADIATION applied perpendicular to FILM
-> create tracks
Immerse in ACID BATH and polymer etched away along tracks = pores
- For ULTRAfiltration

Question 26

Define Phase Inversion

Answer 26

Changes POLYMER from LIQ –> SOLID
- For NANOfiltration & RO

Question 27

Define Solvent Evaportaion (Phase Inversion)

Answer 27

1. Polymer dissolved in solvent
2. Cast on support
3. Solvent evaporates under N2 stream