1. “Membrane Separation Process”
ERT 313 :
BIOSEPARATION ENGINEERING
“Membrane Separation Process”
By; Mrs Hafiza Binti Shukor
ERT 313/4 BIOSEPARATION ENGINEERING
SEM 2 (2010/2011)
By; Mrs Hafiza Binti Shukor

2. Students should be able to;
ANALYZE the separation of gases and liquids using membranes.
ANALYZE Microfiltration, Ultrafiltration, Reverse-Osmosis and Nanofiltration, membrane configurations and mode of operations.
CALCULATE and ANALYZE membrane permeability, concentration polarization and membrane fouling.
DEVELOP basic design of membrane unit.
ERT 313/4 BIOSEPARATION ENGINEERING
SEM 2 (2010/2011)

3. ERT 313/4 BIOSEPARATION ENGINEERING
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WHAT IS A MEMBRANE?
Membranes are materials which have voids in them, letting some molecules pass more conveniently than some other molecules.
A semi-permeable membrane is a VERY THIN film that allows some types of matter to pass through while leaving others behind

4. WHAT IS A MEMBRANE? Retentate Membrane Permeate Feed
ERT 313/4 BIOSEPARATION ENGINEERING
SEM 2 (2010/2011)
WHAT IS A MEMBRANE?
Feed
Retentate
Permeate
Membrane

5. HOW SEPARATION OCCURS DRIVING FORCES
ERT 313/4 BIOSEPARATION ENGINEERING
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HOW SEPARATION OCCURS
Difference in permeabilities through a membrane:
Difference in size,
Affinity to the membrane,
Charge, etc.
DRIVING FORCES
Pressure difference,
Concentration difference,
Voltage difference, etc.

6. ADVANTAGES DISADVANTAGES
ERT 313/4 BIOSEPARATION ENGINEERING
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ADVANTAGES
Continuous separation
Low energy requirement
Meet various separation demands
DISADVANTAGES
Fouling
Service periods

7. ERT 313/4 BIOSEPARATION ENGINEERING
SEM 2 (2010/2011)
Membrane material
•Membranes may be composed of natural (e.g modified natural cellulose polymers ) or synthetic polymers (plastic materials) or inorganic ceramic materials
be good film formers,
manage high permeate flows,
have high selectivity,
have good chemical and bacteriological resistance,
be resistant to detergents and disinfectants,
be inexpensive.

8. Membrane filtration applications
ERT 313/4 BIOSEPARATION ENGINEERING
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Membrane filtration applications
•Reverse osmosis (RO)
Concentration of solution by removal of water
•Nanofiltration (NF)
Concentration of organic components by removal of part of monovalent ions like sodium and chlorine (partial demineralisation)
•Ultrafiltration (UF)
Concentration of large and macro molecules
•Microfiltration (MF)
Removal of bacteria, separation of macromolecules

9. OSMOSIS REVERSE OSMOSIS
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OSMOSIS
Pure water flows from a dilute solution through a semipermeable membrane (water permeation only) to a higher concentrated solution
Rise in volume to equilibrate the pressure (osmotic pressure)
REVERSE OSMOSIS
•If pressure greater than the osmotic pressure is applied to the high concentration the direction of water flow through the membrane can be reversed.
Osmotic pressure- P required to equalize the solvent activities if pure solvent is on one side of membrane

10. ERT 313/4 BIOSEPARATION ENGINEERING
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REVERSE OSMOSIS
only remove some suspended materials larger than 1 micron
the process eliminates the dissolved solids, bacteria, viruses and other germs contained in the water
only water molecules allowed to pass via very big pressure
almost all membranes are made polymers, cellulosic acetate and matic polyamide types rated at 96%-99+% NaCl rejection

11. REVERSE OSMOSIS extensive applications:
ERT 313/4 BIOSEPARATION ENGINEERING
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REVERSE OSMOSIS
extensive applications:
Prepare pure water from dilute aqueous solutions
Purify organic solvent
potable water from sea or brackish water
ultrapure water for food processing and electronic industries
water for chemical, pulp & paper industry

12. ERT 313/4 BIOSEPARATION ENGINEERING
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MICROFILTRATION
Is a filtration process which removes contaminants from a fluid (liquid & gas) by passage through a microporous membrane

13. MICROFILTRATION a sterile filtration with pores 0.1-10.0 microns
ERT 313/4 BIOSEPARATION ENGINEERING
SEM 2 (2010/2011)
MICROFILTRATION
a sterile filtration with pores microns
micro-organisms cannot pass through them
operated at low pressure differences
used to filter particles.

14. MICROFILTRATION wide array of applications:
ERT 313/4 BIOSEPARATION ENGINEERING
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MICROFILTRATION
wide array of applications:
sterile water for pharmaceutical industry
food & beverages
chemical industry
microelectronics industry
fermentation
laboratory/analytical uses

15. ERT 313/4 BIOSEPARATION ENGINEERING
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ULTRAFILTRATION
Is a variety of membrane filtration in which hydrostatic pressure forces a liquid against a semi permeable membrane.
Suspended solids and solutes of high molecular weight are retained, while water and low molecular weight solutes pass through the membrane.
This separation process is used in industry and research for purifying and concentrating macromolecular ( Da) solutions, especially protein solutions.

16. ULTRAFILTRATION has smaller pores than microfiltration membranes
ERT 313/4 BIOSEPARATION ENGINEERING
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ULTRAFILTRATION
has smaller pores than microfiltration membranes
driving force → pressure differential (2-10 bars to bars)
used to separate species with pore sizes Å ( microns)
Can be obtained down to a a molecular weight cutoff (MWCO) level of 1000 Daltons (Da) and up to as high as Da.
assymmetric; the pores are small
Assymmetric - membrane in which the pore size and structure vary from one side of the membrane to the other

17. ULTRAFILTRATION wide range of applications :
ERT 313/4 BIOSEPARATION ENGINEERING
SEM 2 (2010/2011)
ULTRAFILTRATION
wide range of applications :
oil emulsion waste treatment
treatment of whey in dairy industries
concentration of biological macromolecules
electrocoat paint recovery
concentration of textile sizing
concentration of heat sensitive proteins for food additives

18. ERT 313/4 BIOSEPARATION ENGINEERING
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NANOFILTRATION
Relatively recent membrane filtration process used most often with low total dissolved solids water such as surface water and fresh groundwater, with the purpose of softening (polyvalent cation removal) and removal of disinfection by-product precursors such as natural organic matter and synthetic organic matter.

19. NANOFILTRATION Range between UF and RO membranes
ERT 313/4 BIOSEPARATION ENGINEERING
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NANOFILTRATION
Range between UF and RO membranes
the mass transfer mechanism is diffusion & separate small molecules from the solution (assymmetric)
cellulosic acetate and aromatic polyamide type membranes (salt rejections; 95% for divalent salts to 40% for monovalent salts)
can typically operate at higher recoveries; conserving total water usage due to a lower concentrate stream flow rate.

20. NANOFILTRATION typical applications:
ERT 313/4 BIOSEPARATION ENGINEERING
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NANOFILTRATION
typical applications:
desalination of food, dairy and beverage products or byproducts
partial desalination of whey, UF permeate or retentate as required
desalination of dyes and optical brighteners
purification of spent clean-in-place (CIP) chemicals
color reduction or manipulation of food products
concentration of food, dairy and beverage products or byproducts
fermentation byproduct concentration

21. ERT 313/4 BIOSEPARATION ENGINEERING
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22. ERT 313/4 BIOSEPARATION ENGINEERING
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SUMMARY

23. Membrane Configurations / modules
ERT 313/4 BIOSEPARATION ENGINEERING
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Membrane Configurations / modules
This refers to the packing of the membrane in the module so that it can be installed in the system.
Common configurations include:
Plate and frame
Tubular
Spirally wound
Hollow fine fibre

24. Flat membranes Mainly used to fabricate and used
ERT 313/4 BIOSEPARATION ENGINEERING
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Flat membranes
Mainly used to fabricate and used
In some cases modules are stacked together like a multilayer sandwich or plate-and-frame filter press
Three basic structures are commonly uses for membranes: - homogeneous (no significant variation in pore diameter from the filtering surface to the other side)
- asymmetric (has a thin layer next to the filtering surface that has very pores)
- composite (containing very small pores next to the filtering surface)

25. ERT 313/4 BIOSEPARATION ENGINEERING
SEM 2 (2010/2011)
Plate and frame design
•Membrane sandwiched between membrane support plates which are arranged in stacks similar to a plate heat exchanger
•Typically polymers (e.g polyethersulfone) with polypropylene or polyolefin support
•UF (<1 to 1000 kDaMWCO)
•MF (0.1 to 0.16 um diameter)

26. Plate and frame membrane systems
ERT 313/4 BIOSEPARATION ENGINEERING
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Plate and frame membrane systems

27. waste water system ERT 313/4 BIOSEPARATION ENGINEERING
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waste water system

28. Spiral wound membranes
ERT 313/4 BIOSEPARATION ENGINEERING
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Spiral wound membranes
Constructed from flat sheet membranes separated by spacer screens
Consists of a sandwich of four sheets wrapped around a central core of a perforated collecting tube
The four sheets consist of a
i) top sheet of an open separator grid for feed channel
ii) a membrane
iii) a porous felt backing for the permeate channel
iv) another membrane
The feed solution is fed into one end of the module and flows through the separator screens along the surface of the membranes
The retentate is the collected in the other end of the module
The permeate spirals radially inward, eventually to be collected through a central tube

29. Spiral-wound elements and assembly
ERT 313/4 BIOSEPARATION ENGINEERING
SEM 2 (2010/2011)
Spiral-wound elements and assembly

30. spiral-wound membrane - cross section
ERT 313/4 BIOSEPARATION ENGINEERING
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spiral-wound membrane - cross section

31. 3. Hollow-fiber membranes
ERT 313/4 BIOSEPARATION ENGINEERING
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3. Hollow-fiber membranes
The membranes are in the shape of very-small-diameter hollow fibers
Typically, the high-pressure feed enters the shell side at one end and leaves at the other end
The hollow fibers are closed at one end of the tube bundles
The permeate solution inside the fibers flows countercurrent to the shell-side flow and is collected in a chamber where the open ends of the fibers terminate
Then the permeate exits the device
Hollow-fiber separator assembly.

32. Comparison of membrane module
ERT 313/4 BIOSEPARATION ENGINEERING
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Comparison of membrane module

33. Comparison of membrane module
ERT 313/4 BIOSEPARATION ENGINEERING
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Comparison of membrane module

34. Flux Equation for Reverse Osmosis
ERT 313/4 BIOSEPARATION ENGINEERING
SEM 2 (2010/2011)
1. Osmotic pressure of solutions
Experimental data shows that the osmotic pressure π of a solution is proportional to the concentration of the solute and temperature T
Van’t Hoff originally showed that the relationship is similar to that for pressure of an ideal gas
For example, for dilute water solutions,
If a solute exists as two or more ions in solution, n represents the total number of ions
For more concentrated solutions, Eq. (1) is modified using the osmotic coefficient Φ, which is the ratio of the actual osmotic pressure π to the ideal π calculated from the equation
n: number of kg mol of solute,
Vm: volume of pure solvent water in m3
associated with n kg mol of solute,
R: gas law constant x 10-3 m3·atm/kg mol·K,
T: temperature in K.
(1)

35. Example 1 Calculate the osmotic pressure of a solution containing
ERT 313/4 BIOSEPARATION ENGINEERING
SEM 2 (2010/2011)
Calculate the osmotic pressure of a solution containing
0.10 g mol NaCl/1000 g H20 at 25°C.
Solution:
The density of water = kg/m3 and then, n = 2 x 0.10 x 10-3 =
2.00 x 10-4 kg mol (NaCl gives two ions). Also, the volume of the
pure solvent water Vm = 1.00 kg/(997.0 kg/m3). Substituting into
Eq. (1),
This compares with the experimental value in Table 1 of 4.56 atm.

36. ERT 313/4 BIOSEPARATION ENGINEERING
SEM 2 (2010/2011)
Example 1
TABLE 1. Osmotic Pressure of Various Aqueous Solutions at 25°C

37. Flux Equation for Reverse Osmosis
ERT 313/4 BIOSEPARATION ENGINEERING
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2. Diffusion-type models
For the diffusion of the solvent through the membrane,
Nw is the solvent (water) flux in kg/s·m2;
Pw the solvent membrane permeability, kg solvent/s·m·atm;
Lm the membrane thickness, m;
Aw the solvent permeability constant, kg solvent/s·m2·atm;
ΔP = P1 - P2 (hydrostatic pressure difference with P1 pressure exerted on feed and P2 on product solution), atm;
Δπ = π1 - π2 (osmotic pressure of feed solution - osmotic pressure of product solution), atm.
(2)
(3)

38. Flux Equation for Reverse Osmosis
ERT 313/4 BIOSEPARATION ENGINEERING
SEM 2 (2010/2011)
Flux Equation for Reverse Osmosis
For the diffusion of the solute through a membrane, an approximation for the flux of the solute is
Ns is the solute (salt) flux in kg solute/s·m2;
Ds the diffusivity of solute in membrane, m2/s;
Ks = cm/c (distribution coefficient), concentration of solute in membrane/concentration of solute in solution;
As is the solute permeability constant, m/s;
c1 the solute concentration in upstream or feed (concentrate) solution, kg solute/m3;
c2 the solute concentration in downstream or product (permeate) solution, kg solute/m3.
The distribution coefficient Ks is approximately constant over the membrane.
(4)
(5)

39. Flux Equation for Reverse Osmosis
ERT 313/4 BIOSEPARATION ENGINEERING
SEM 2 (2010/2011)
Making a material balance at steady state for the solute, the solute diffusing through the membrane must equal the amount of solute is leaving in the downstream or product ( permeate) solution:
where cw2 is the concentration of solvent in stream 2 (permeate), kg solvent/m3. If the stream 2 is dilute in solute, cw2 is approximately the density of the solvent.
In reverse osmosis, the solute rejection R is defined as the ration concentration difference across the membrane divided by the bulk concentration on the feed or concentrate side (fraction of solute remaining in the feed stream):
(6)
(7)

40. Flux Equation for Reverse Osmosis
ERT 313/4 BIOSEPARATION ENGINEERING
SEM 2 (2010/2011)
Flux Equation for Reverse Osmosis
This can be related to the flux equation as follows, by first substituting Eq. (2) and (4) into (6) to eliminate Nw and Ns in Eq. (6)
Then, solving for c2/c1 and substituting this result to Eq. (7)
(8)
where B is in atm-1
(9)

41. Example 2 Experiments at 25°C were performed to determine the
ERT 313/4 BIOSEPARATION ENGINEERING
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Experiments at 25°C were performed to determine the
permeabilities of a cellulose acetate membrane. The laboratory
test section shown in Fig. 3 has membrane area A = 2.00 x 10-3
m2. The inlet feed solution concentration of NaCl is c1 = 10.0kg
NaCl/m3 solution (10.0 g NaCI/L, ρ1 = 1004 kg solution/m3). The
water recovery is assumed low so that the concentration c1 in the
entering feed solution flowing past the membrane and the
concentration of the exit feed solution are essentially equal. The
product solution contains c2 = 0.39 kg NaCl/m3 solution (ρ2 = 997
kg solution/m3) and its measured flow rate is 1.92 x 10-8 m3
solution/s. A pressure differential of 5514 kPa (54.42 atm) is used.
Calculate the permeability constants of the membrane and the
solute rejection R.
FIGURE 3. Process flow diagram
of experimental reverse-osmosis
laboratory unit.

42. Example 2
ERT 313/4 BIOSEPARATION ENGINEERING
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Solution:
Since c2 is very low (dilute solution), the value of c2 can
be assumed as the density of water (Table 1), or cw2 =
997 kg solvent/m3. To convert the product flow rate to
water flux, Nw, using an area of 2.00 x 10-3 m2,
Substituting into Eq. (6),

43. Example 2 To determine the osmotic pressures from Table 1, the
ERT 313/4 BIOSEPARATION ENGINEERING
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To determine the osmotic pressures from Table 1, the
concentrations are converted as follows. For c1, 10 kg NaCl is in
1004 kg solution/m3 (ρ1 = 1004). Then, 1004 – 10 = 994
kg H2O in 1 m3 solution. Hence, in the feed solution, where the
molecular weight of NaCl = 58.45, (10.00 X 1000)/ (994 x 58.45) =
g mol NaC1/kg H2O. From Table 1, π1 = 7.80 atm by linear
interpolation. Substituting into Eq. (1), the predicted = 8.39 atm,
which is higher than the experimental value. For the product
solution, = kg H2O. Hence, (0.39 x 1000)/(996.6
x 58.45) = g mol NaCl/kg H2O. From Table 1, π2 = 0.32
atm. Then, Δπ = π1 - π2 = = 7.48 atm and ΔP =
54.42 atm.
Substituting into Eq. (2),

44. Example 2 Solving, (Pw/Lm) = A = 2.039 x 10-4 kg solvent/s • m2• atm.
ERT 313/4 BIOSEPARATION ENGINEERING
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Solving, (Pw/Lm) = A = x 10-4 kg solvent/s • m2• atm.
Substituting into Eq. (4),
Solving, (DsKs/Lm) = As = x m/s.
To calculate the solute rejection R by substituting into Eq. (7),
Also, substituting into Eq. (9) and then Eq. (8),

45. Factors affecting membrane performance
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Factors affecting membrane performance
Concentration polarisation
Differential solute conc between membrane surface and bulk stream
Reversibly affected by operation parameters
Fouling
Formation of deposits
Irreversibly affected by operation parameters

46. Concentration Polarization in Reverse- Osmosis Diffusion Model
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In desalination, localized concentrations of solute build up at the point where the solvent leaves the solution and enters the membrane
The solute accumulates in a relatively stable boundary layer next to the membrane
Concentration polarization, β, is defined as the ratio of the salt concentration at the membrane surface to the salt concentration in the bulk feed stream c1
Concentration polarization causes the water flux to decrease, since the osmotic pressure π1 increases as the boundary layer concentration increases.
Also, Solute concentration increases at the boundary
Hence, often the ΔP must be increased to compensate, which results in higher power costs

47. 2 types membrane fouling
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2 types membrane fouling
Surface (temporary) fouling
•Foulant appears an evenly deposited layer on the membrane surface
•Can be easily removed by cleaning solution
•Permeation rate of membrane can be regenerated by cleaning
•Most common type of fouling in UF plant
•Most studies dealt with this type of fouling
Pore (permanent) fouling
Particulate matter diffuses into the membrane
•Could be caused by the poor quality of the cleaning water
•Flux cannot be regenerated by cleaning
•Determines the lifetime of the membrane
•Received much less attention in literature

48. Implications of membrane fouling
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Implications of membrane fouling
•More energy consumption
•Duration of continuous operation without need for cleaning
•Membrane durability
•Properties and quality of concentrate
•Overall economy of the membrane process

49. Glossary •Feed The solution to be concentrated or fractionated •Flux
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Glossary
•Feed
The solution to be concentrated or fractionated
•Flux
The rate of extraction of permeate measured in litres per square meter of membrane surface per hour (L/m2/h)
•Membrane fouling
Deposition of solids on the membrane, irreversible during processing

50. •The filtrate, the liquid passing through the membrane
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Permeate
•The filtrate, the liquid passing through the membrane
Retentate
•The concentrate, the retained liquid
Transmembrane pressure
•Pressure gradient between the upstream (retentate side) and downstream (permeate side)
•Average pressure at the inlet and outlet of the equipment

51. ERT 313/4 BIOSEPARATION ENGINEERING
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The End