Membrane Separation Flashcards
Define a Membrane
A membrane is a semi-permeable barrier that allow selective exchange between two regions
Define Biological membranes
- Complex, highly specific
- Use ACTIVE TRANSPORT
Define Synthetic membranes
- Less complex & (energy) efficient
- Use generally PASSIVE TRANSPORT
- higher chem & mech STABILITY
What is the difference between Isotropic and Anisotropic membranes
Isotropic membranes have uniform composition and physical nature across the membrane where as Anisotropic do NOT
Define Flux & units
Flux is the amount of fluid permeate passing through the membrane [volume/area/time] OR [ms-1]
Define Selectivity
Selectivity is the ability of a membrane to separate out components
Define Permeability
Permeability is the measure of the rate at which a comp. is transported
@ constant conc, temp, pressure & electric field
What are the factors for Performance of a membrane
(4 for membranes & 3 for comp.)
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.
Membrane Applications and how it works
Dialysis
- Filters WASTE from blood
- For kidney failure
Desalination
- Uses REVERSE OSMOSIS (+ nanofilt.)
- Filters SALT ions = drinking water
What can membranes filter
- Microbes
- Macromolecules
- Pharmaceuticals
- Unwanted ions
Membrane Advantages
(4)
- Continuous & Batch
- Low ENERGY consumption
- Easy SCALE UP
- AMBIENT temp
Membrane Limitations (5)
- Fouling
- Low LIFETIMES
- Low SELECTIVITY
- Low FLUX
- LINEAR scale up
Membranes divide the Feed into the ________ and _________
Membranes divide the Feed into the PERMEATE and RENTATE
Selectivity, expressed as retention:
R = Cf - Cp / Cf
What happens is membrane rejects solute
Cp = 0 ( no permeate conc)
therefore R = 1, perfect separation
Define Asymmetric membrane Structure
Asymmetric membranes have:
- a THIN, DENSE top layer
-> determines transport rate
- & a THICK, POROUS sub layer
-> for support
Permeation rate is _________ proportional to thickness of barrier layer
Permeation rate is INVERSELY proportional to thickness of barrier layer
Asymmetric membranes have a higher __________ ____ than Symmetric membranes of similar thickness
Asymmetric membranes have a higher PERMEATION RATE than Symmetric membranes of similar thickness
Arrange Filtration types based on highest pore size to lowest:
Nano-filtration, Ultra-filtration, Reverse osmosis, Micro-filtration.
Micro-filtration < Ultra-filtration < Nano-filtration < Reverse Osmosis
Bacteria & particles < Macromolecules < divalent ions < Monovalent ions
Define Microfiltration & Applications (2)
Microfiltration removes particles, bacterial cells and spores
Application: Pharmaceutical production, Water treatment
Define Ultrafiltration & Applications (3)
Ultrafiltration removes macromolecules e.g. proteins and carbs.
Application: Food products, Water treatment, Pharmaceutical production
Define Reverse Osmosis & Application (1)
Reverse Osmosis removes SALTS
Application: produce DRINKING WATER
Porous vs Non - porous membranes
Non - porous is gas separations (RO)
Porous is fluid separations (Micro/Ultrafiltration/RO)
Define Sintering
Compress powder then HEAT at HIGH temp
- For MICROfiltration
- Low POROSITY
Define Stretching
MECHANICAL STRESS applied to film and small ruptures occur
- For ULTRAfiltration
- use only CRYSTALLINE POLYMERIC material
- High POROSITY
Define Track Etching
High ENERGY particle RADIATION applied perpendicular to FILM
-> create tracks
Immerse in ACID BATH and polymer etched away along tracks = pores
- For ULTRAfiltration
Define Phase Inversion
Changes POLYMER from LIQ –> SOLID
- For NANOfiltration & RO
Define Solvent Evaportaion (Phase Inversion)
- Polymer dissolved in solvent
- Cast on support
- Solvent evaporates under N2 stream
