MEMBRANE SEPARATION Flashcards
Produced by casting a film from a solution of polymer and solvent and immersing the cast film in a nonsolvent for the polymer
phase inversion
this type of membrane have broadly similar pore structure and chemical composition. many of the early membranes of this type were based on cellulose
isotropic
Other term for asymmetrical membranes
anisotropic
(one side of the membrane possesses a thin layer of thin polymer
Most popular anisotropic membrane
polysulfone
Another term for nylon and is also another common membrane polymer
polyamide
External factors affecting membrane performance
concentration polarization
fouling
Accumulation of solute at the membrane surface
concn polarization
long term and frequently irreversible deterioration of flux
Fouling
Strategies to reduce flux declining
pretreatment of feed
frequent cleaning
careful selection of membrane
cross filtration
Mass transfer coefficient in the analyses of concn polarization can be found using
Sherwood number
It is four times the flow area over channel perimeter
hydraulic diameter
driving force for Dialysis
concentration difference
Driving force for pervaporation
partial pressure difference
Mechanism of electrodialysis
ion migration
Flux across the membrane is proportional to applied force which is equal to
applied pressure minus osmotic pressure
It is essentially a sterile filtration and it most closely resembles conventional particle filtration in that it separates larger structures
Microfiltration
Commonly used membrane in Microfiltration
Polypropylene
PTFE( polytetrafluoroethylen)
At lab scale, microfiltration is applied in what mode
dead end mode
Employed in situations where it is desired to separate low molecular weight solutes from high molecular weight solutes
ultrafiltration
Frequently used to characterize Ultrafiltration membranes
Nominal molecular weight cutoff (NMWCO)
Artificial kidneys used for haemodialysis is an example of
Dialysis
Membrane process where separation is accompanied by a phase change
Pervaporation
Membrane separation where a gas mixture is pressurized on one side of the membrane and a low pressure is maintained on the permeate side
Gas separation
