1. MEMBRANE
SEPARATION
MEMBRANE PROCESSES

2. PRESSURE DRIVEN MEMBRANE PROCESS
Various pressure-driven membrane process can be used to :
1. Concentrate
2. Purify a dilute (aqueous or non aqueous)
THE PARTICLE OR MOLECULAR SIZE AND CHEMICAL PROPERTIES of solute DETERMINE :
Structure of membrane
1. Pore size
2. Pore size distribution
PORE SIZE

3. Various PROCESS CAN BE DISTINGUISH RELATED TO THE PARTICLE SIZE OF THE SOLUTE AND CONSEQUENTLY TO MEMBRANE STRUCTURE :

4. Various PROCESS CAN BE DISTINGUISH RELATED TO THE PARTICLE SIZE OF THE SOLUTE AND CONSEQUENTLY TO MEMBRANE STRUCTURE :

5. MICROFILTRATION
Is the membrane process which most closely resembles conventional coarse filtration.
10 – 0,05 m
Pore size:
Suitable for retaining suspensions and emulsions
The Darcy’s Law :
Where the permeability constant A contains structural factors such as the porosity and pore size (pore size distribution)
For laminar convective flows through a porous systems :
Where r is the pore radius, Δx is the membrane thickness, η is he dynamic viscosity and is the tortuosity factor ehich is unity in the case of cylindrical pores.

6. MEMBRANE FOR MICROFILTRATION
Can be prepared from organic materials (polymers) and inorganic (ceramics, metals, glasses)
Various techniques can be employed :
1. Sintering
2. Stretching
3. Track - etching
4. Phase inversion
Frequently, inorganic membranes are used instead of polymeric membranes because of their outstanding chemical and thermal resistances.
POROSITIES AND PORE SIZE DISTRIBUTION
Process
Porosity
Pore size distribution
Sintering
Low / medium
Narrow / wide
Stretching
Medium / high
Track-etching
Low
Narrow
Phase inversion
High

7. Polytetrafluoroethylene (PTFE) Poly(vinylidene fluoride) (PVDF)
These various techniques allow to prepare microfiltration membranes from virtually all kinds of materials of which polymers and ceramics are the most important.
Polytetrafluoroethylene (PTFE)
Poly(vinylidene fluoride) (PVDF)
Polyproylene (PP)
Polyethylene (PE)
HYDROPHOBIC POLYMERIC MEMBRANES
Cellulase esters
Polycarbonate (PC)
Aliphatic polyamide (PA)
Polyetheretherketone (PEEK)
HYDROPHILIC POLYMERIC MEMBRANES
Alumina (Al2O3)
Zirconia (ZrO2)
Titania (TiO2)
Silicium carbide (SiC)
CERAMIC MEMBRANES

8. MAIN PROBLEMS of MICROFILTRATION
Deposition of solute inside the pores of membrane or membrane surface
Concentration polarization and fouling
FLUX DECLINE
NEED
Careful control over the mode of process operation
NEED
Must be cleaned periodically

9. TWO MODES OF FILTRATION:
DEAD END FILTRATION
The feed flow is perpendicular to the membrane surface, so that the retained particles accumulate and form a type of a cake layer at the membrane surface. The thickness of the cake increases with filtration times and consequently the permeation rate decreases with increasing cake layer thickness
CROSS FLOW FILTRATION
The feed flow is along the membrane surface, so that part of the retained solutes accumulate

10. INDUSTRIAL APPLICATIONS
Cold sterilization of beverages and pharmaceutical
Cell harvesting
Clarification of fruit juice, wine and beer
Ultrapure water in the semiconductor industry
Metal recovery as colloidal oxides or hydroxides
Waste-water treatment
Continuous fermentation
Separation of oil-water emulsions

11. Summary Of Microfiltration
Membranes :
(a)Symmetric porous
Thickness :
10 – 150 um
Pore sizes :
0,05 – 10 um
Driving force :
Pressure (< 2 bar)
Separation principles :
Sieving mechanism
Membrane material :
Polymeric, and ceramic
Main application :
Analytical applications
Sterilization (food, pharmaceutical)
Ultrapure water (semiconductor)
Clarification (beverages)
Cell harvesting and membrane bioreactor (biotechnology)
Water treatment

12. 0,05 m – 1 NM ULTRAFILTRATION
Is a membrane process whose nature lies between nanofiltration and microfiltration
0,05 m – 1 NM
Pore size:
UF is typically used to retain macromolecules and colloids from a solution. UF and MF can both be consider as porous membrane where rejection is determined by the size and shape of the solutes relatives to the pore size in the membrane and where the transport of solvent is directly proportional to the applied pressure.
In fact both UF and MF involve similar membrane processes based on the same separation principle. However, an important difference is that UF membrane have an asymmetric structure with a much denser top layer (small pore size and lower surface porosity) and consequently a much higher hydrodynamic resistance.

13. MEMBRANE FOR ULTRAFILTRATION
Most of UF membrane used commercially these day are prepared from :
POLYMERIC MEMBRANES
Polytetrafluoroethylene (PTFE)
Poly(vinylidene fluoride) (PVDF)
Polyacrylonitrile
Polyimide
Polyetheretherketone
Aliphatic polyamides
Cellulosics
BY PHASE INVERSION PROCESS
INORGANIC (CERAMIC)
Alumina (Al2O3)
Zirconia (ZrO2)
SOL GEL TECHNIQUE

14. APPLICATIONS Recovery of whey proteins
Recovery of potato starch and proteins
Concentration of egg product
Clarification of fruit juices and alcoholic beverages 1
FOOD AND DAIRY INDUSTRY 2
PHARMACEUTICAL INDUSTRY 3
METALLURGY
CHEMICAL INDUSTRY 4
TEXTILE INDUSTRY 5 6
LEATHER INDUSTRY 7
PAPER INDUSTRY

15. Summary Of Ultrafiltration
Membranes :
Asymmetric porous
Thickness :
150 um (or monolithic for some ceramics)
Pore sizes :
1– 100 nm
Driving force :
Pressure (1-10 bar)
Separation principles :
Sieving mechanism
Membrane material :
Polymeric (PS, Polyacrylonitrile)
Ceramic (zirconium oxide, aluminum oxide)
Main application :
Dairy (milk, whey, cheese making)
Food (potato starch and protein)
Metallurgy (oil-water emulsion, electropaint recovery)
Textile (indigo)
Pharmaceutical (enzymes, antibiotics, pyrogens)
Automotive (electropaint)
Water treatment

16. REVERSE OSMOSIS AND NANOFILTRATION
RO and NF are used when low molecular weight solutes such as inorganic salts or small organic mocules such as glucose, and sucrose have to be separated from solvent.
PRINCIPE OF REVERSE OSMOSIS
FORCE
The membrane is permeable to the solvent (water) but not to the solute (salt). In order to allow water to pass through the membrane, the applied pressure must be higher than the osmotic pressure.
Salt solution
Membrane
“Complete barrier to dissolved salt”
Pure water

17. The pressure used in reverse osmosis range from 20 – 100 bar and in nanofiltration from about 10 – 20 bar, which much higher than those used in ultrafiltration
Both process are considered as one process since the basic principles are the same.
NF membranes are the same as RO membranes only the network structure is more open.
Comparison of retention characteristic between nanofiltration (NF) and reverse osmosis (RO) are listened :
Solute RO NF
Monovalent ions (Na, K, Cl, NO3)
>98%
<50%
Bivalent ions (Ca, Mg, SO4, CO3)
>99%
>90%
Bacteria and viruses
<99%
Micro solutes (Mw >100)
>50%
Micro solutes (Mw < 100)
0-99%
0-50%

18. MEMBRANES FOR RO AND NF
The flux is approximately inversely proportional to the membrane thickness and for this reason most reverse osmosis membranes have an asymmetric structure with a thin dense toplayer (thickness ≤ 1um) supported by a porous sublayer (thickness 50 – 150 um)
The resistance towards transport being determined mainly by the dense toplayer.
An asymmetric membrane structure can be distinguished: (i) integral asymmetric membranes, and (ii) composite membranes.

19. Integral Asymmetric Membranes
Both toplayer and sublayer consists of the same material. These membrane are prepare by phase inversion technique. The polymeric material from which the membrane it to be prepared is soluble in a solvent or a solvent mixture. 1
cellulose esters. This materials are very suitable for desalination because of their high permeability towards water in combination with a (very) low solubility towards salt.
An important class of asymmetric membranes are : 2
Aromatic polyamides. These material also show high selectivities towards salts but their water flux is somewhat lower. 3
Polybenzimidazoles, polybenzimidazolones, polyamidedehydrazide, and polyimides

20. Composite Membranes
The second type of structure frequently used in RO while most of the NF membrane are in fact composite membrane.
In such membranes the top layer and sublayer are composed of different polymeric materials so that each layer can be optimized separately.
The first stage is the are preparation of the porous sublayer. Important criteria for this sublayer are surface porosity and pore size distribution and asymmetric ultrafiltration membranes are often used. Different methods have been employed for placing a thin dense layer on top of this sublayer :
dip coating
Interfacial polymerization
Plasma polymerization

21. APPLICATION RO
purification water, desalination of brackish and seawater to produce potable water
Production of ultrapure water for the semiconductor industry
Concentration step particularly in the food industry ( concentration of fruit juice)
Galvanic industry (concentration of waste stream)
Dairy industry (concentration of milk to prior cheese manufacture) NF
When a high retention is required for NaCl with high feed concentrations reverse osmosis reverse osmosis is the preferred process. In other cases with much lower concentrations, divalent ions and micro solutes with molecular weight nanofiltration is the preferred process. Since the water permeability is (much) higher in nanofiltration the capital cost for a certain application will be lower.

22. Summary Of Nanofiltration
Membranes :
Composite
Thickness :
Sublayer : 150 um
Toplayer : 1 um
Pore sizes :
< 2 nm
Driving force :
Pressure (10 – 25 bar)
Separation principles :
Solution – diffusion
Membrane material :
Polyamide (interfacial polymerisation)
Main application :
Desalination of brackish and seawater
Removal of micropollutents
Water softening
Wastewater treatment
Retention of dyes (textile industry)

23. Summary Of Reverse Osmosis
Membranes :
Asymmetric or composite
Thickness :
Sublayer : 10 um
Toplayer : 1 um
Pore sizes :
< 2 nm
Driving force :
Pressure : brackish water (15 – 25 bar)
seawater (40 – 80 bar)
Separation principles :
Solution-diffusion
Membrane material :
Cellulose triacetate, aromatic polyamide, polyamide and poly(ether urea) (interfacial polymerization)
Main application :
Desalination of brackish and seawater
Production of ultrapure water (electronic industry)
Concentration of food juice and sugars (food industry) and the concentration of milk dairy industry)

24. Microfiltration
Ultrafiltration
Nanofiltration / reverse osmosis
Separation of particles
Separation of macromolecules (bacteria, yeasts)
Separation of low MW solute (salt, glucose, lactose, micropollutant)
Osmotic pressure negligible
Osmotic pressure high
(1-25 bar)
Applied pressure low (< 2bar)
Applied pressure low (1-10 bar)
Applied pressure high (10-60 bar)
Symmetric structure
Asymmetric structure
Thickness of separating layer:
Symmetric structure : um
Asymmetric structure :1 um
Thickness of actual separating layer : 0,1-1,0 um
Thickness of actual separating layer : 0,1 – 1 um
Separation based on particle size
Separation based on differences in solubility and diffusivity