Ultrafiltration Flashcards
What is ultrafiltration?
Ultrafiltration is used to separate a mixture of different molecular weight proteins.
What can be retained and what can move through the membrane?
It can retain suspended particles, microorganisms, fats and proteins.
Carbohydrates, minerals and acids and water can move through the membrane.
Why is the osmotic pressure usually very low and negligible?
the concentration of the large molecules is usually small
in moles/litre
What is the driving force?
The driving force is the differential pressure
How does the concentration polarization increase?
As the solute is rejected by the membrane and accumulates at the surface of the membrane. As the concentration of the solute is increases , the concentration polarization increases which is more severe than RO, due to the size of the molecules.
What does increasing the pressure drop do?
- give a higher convective transport of the solute to the membrane.
Further increasing the pressure drop,
- increases the value of cs to a limiting concentration
where the accumulation solute forms a semisolid gel where cs = cg.
What is gel polarization?
The trans-membrane pressure is large enough to form a gel layer on the membrane surface
Where membrane permeation rate is limited by back diffusion of the solute from the membrane surface to feed.
What is the flux limited by?
The flux is limited by the concentration polarization.
how do you achieve a higher flux rate?
The more dilute protein concentration
Does ultrafiltration steady state flux increase or decrease with increasing size of macromolecules?
As C1 decreases, Nw will increases, as shown by this equation!
Nw/density = k_c ln (c_g/c_l)
In order to increase the ultrafiltration solvent flux:
- The crossflow of the fluid past the membrane can be used to sweep away part of the polarized layer, by increasing the mass transfer coefficient
- Higher velocities can also be used to increase turbulence (will carry away the CP layer) and increase the mass transfer coefficient.
