Membranes 1-3 Flashcards
(27 cards)
What are 3 applications of membranes
Desalination, haemodialysis, and separations of proteins
Why has there been growing demand?
There is a demand for low energy, environmentally friendly solutions
(i.e alternative to distillation)
what is the significance of catalytic membranes
A membrane can be both catalysing a reaction and removing the product to effectively shift the equilibrium and produce a higher yield
What is a membrane fabrication technique
Wet or dry
describe a symmetric membrane
no variation along the thickness of the membrane
Describe an asymmetric membrane
at least two bands of differing porous networks
What are the 5 steps in the Hollow fibre manufacture process
- Homogeneous dope is transferred to a metal container (5 bar)
- Dope is extruded through spinneret with included bore fluid to make the fibre hollow
- Hollow fibre is passed through a water bath to complete the phase inversion process
- second water bath for extra washing
- Left in water for a couple of days to ensure washing
Definition of Chemisorption
Adsorption which involves valence forces of those operating in chemical compounds
Definition of Physisorption
Adsorption which uses intermolecular forces like van der Waals (irreversible) no significant change in electron orbitals
Why use membranes
Allows simultaneous concentration and purification
Large concentrations can be treated with high energy efficiency (no phase change, or steam source)
What are some applications of gas separation membranes
- Separation of hydrogen from argon and methane in ammonia plants
- Production of nitrogen from air
- separation of CO2 from methane in natural gas operations
What is membrane selectivity
A measure of the ability to separate 2 gases A and B. It is the ratio of the permeabilities A and B
11 Advantages of gas separation membranes
- Low cost
- Unattended operation
- Good space efficiency
- Ease of scale up (however no economy of scale)
- Minimal associated hardware
- No moving parts
- Ease of installation
- Flexibility
- Low utility requirements
- Low environmental impact
- Reliability
What is a critical problem in ultra and micro filtration
Fouling
What is a challenge in gas separation membranes
Creating a defect free layer (only 1 defect per square meter is enough to destroy the efficiency)
What are 4 techniques to prepare organic membranes
Sintering
Stretching
Track etching
Phase inversion
What are 3 techniques used to make inorganic membranes
Sintering
Sol - Gel process
Anodic oxidation
How is track etching achieved?
Highly concentrated KOH with KmnO4 additives maintained at 85C
What is the sol gel process
Hydrolysis of a metal oxide in a solution followed by drying to a rigid oxide material
Describe wet phase inversion
It is the conversion of a liquid to a solid usually by a solvent which is removed from the solution leaving behind a solid stricture
What are some issues with polymer membranes
Polymers can not withstand high temperatures or aggressive chemical environments
What three types of membranes are used in gas separation
Flat (plate and frame)
Hollow fibre
Spiral wound
What is an advantage of flat membranes
Easy to fabricate
What are flat membranes mainly used for
Experimental use
