Membranes Flashcards
7 critical roles membranes have in the purification process
Sterile filtration Virus removal Clarification Initial harvest Protein concentration Buffer exchange Protein purification
6 Advantages of membranes
- Processing is efficient (even at low temperatures)
- Concentration and purification achieved in one step
- Mechanical and chemical stress is minimised
- Selectivity is good
- No phase change ( good for energy costs)
- Scale up is easy (Batch or Continuous)
5 Disadvantages of membranes
Concentration polarisation Membrane fouling Particle interactions (aggregation) Low membrane lifetime Not high resolution fractionation for protein purification
4 Process classifications
Micro, Ultra, Nano filtration and Reverse osmosis
Sketch the membrane process
Slide 8 Membranes part 1
What 3 parameters can be used to define the performance of a membrane
Flux
Selectivity
Permeability
What is the meaning of flux (in relation to membranes)
give units
The amount of permeate passing through the membrane.
Divided by the cross sectional area of the membrane
(mol, kg)/m2 s
Define Selectivity
The ability of a membrane to separate out components
Define Permeability
The measure of the rate at which a component is transported through the membrane at constant concentration, pressure, temperature, electric field.
What are 3 less common but important membrane properties
Mechanical stability
Temperature stability
Chemical resistance
What is selectivity expressed in terms of?
Retention or rejection
What are 2 operational parameters commonly used with membranes
Flow rate and driving force
- Flow rate often defined with respect to the flux or permeation
- Driving force can be mass, volume, heat or electrical flux
What is the generic equation for driving force?
What 4 different types of flux are there?
Name their corresponding laws
Name the parameters for A and dX for Each
J = -A(dX/dx)
- Mass (Fick’s) D (diffusion) dC (concentration)
- Volumetric (Darcy’s) L (permeability coef) dP (Pressure)
- Thermal (Fourier’s) Lambda (thermal diffusivity) T (temperature)
- Electrical (Ohm’s) 1/R (Electrical conductivity) E (Electric potential)
What are the 4 classifications of membranes
- Structure (symmetric, Asymmetric)
- Configuration (Flat, tubular, hollow fibre)
- Material (organic, inorganic)
- Surface charge (positive, negative, neutral)
Describe an asymmetric membrane structure
One that can see two distinct structures in the cross section. One thin dense layer and a supporting layer below
