This document summarizes key concepts in membrane separation processes used in food engineering applications. It defines membrane separation as selectively separating materials through a semi-permeable barrier based on molecule size and properties. It then discusses membrane transport mechanisms and important membrane properties like permeability and retention. Finally, it provides examples of membrane processes and materials commonly used in food industries like dairy, fruit juice, sugar, and brewing.

1. Course No & Title : FPE 806- Advances in Food Engineering Unit Operations
Course Teacher : Dr. Venkatachalapathy
Associate Professor and Head
Presented by,
Priyadarshini S R
1st Ph.D (FPE)
ID. No :-2017894608
IICPT, Thanjavur

2. Membrane separation is a technology which selectively separates
materials through a semi permeable barrier and the separation
occurs by the membrane controlling the rate of movement of
molecules between two liquid phases, two gas phases, or a liquid and
gas phases.

3. Permeation:
• Dissolution of permeating molecules in the membrane
• Diffusion of dissolved molecules
• Desorption of penetrant molecules to the downstream side.
Knudsen diffusion (d/λ < 0.2):
Single gaseous molecules diffuse under rarefied conditions so that the
mean free path is longer than the pore diameter.
Molecular diffusion (d/λ > 20):
Viscous flow through the pores of ultrafiltration and microfiltration.

4. 𝜋 ∝
1
𝑀 𝑤
𝜋 ∝ C
Hence , 𝜋 =
𝑅𝑇𝐶
𝑀 𝑤
The above equation is vant hoff’s equation for dilute solutions

5. This property indicates the extent of separation of a membrane
with respect to the solute concentration in the feed. Thus,
observed retention is defined as,

6. Real retention is a constant that defines the partition of the
solute concentration across the membrane, i.e., between the
membrane-solution interface and the permeate side. The definition
indicates the true separation efficiency of the solute by the
membrane.
Here,
Cm = solute concentration in membrane solution interface
For complete solute retention, Rr = 1.0

7. The molecular weight at 90% solute retention indicates roughly the
molecular weight cut off of the membrane.

8. • This parameter shows how porous the membrane is.
• If Lp is more, then the membrane is more porous
Mathematically, Lp is defined as,
Lp=
𝐽 𝑜
∆𝑃
unit :
𝑚
𝑃𝑎.𝑠
where,
𝐽 𝑜 - pure water flux
ΔP - transmembrane pressure drop

9. • First generation membrane processes
– Microfiltration (MF)
– Ultrafiltration (UF)
– Nanofiltration (NF)
– Hyper filtration (HF) /Reverse osmosis (RO)
– Electro dialysis (ED)
• Second generation membrane processes
– Gas separation (GS)
– Pervaporation (PV)
– Membrane Distillation (MD)

11. Sl.No Materials Membrane separation
process
1. Polypropylene Microfiltration (MF)
2. Polysulfone Ultrafiltration(UF),Gas
separation (GS)
3. Polyamide Gas separation, Reverse
osmosis (RO)
4. Polyacrylonitrile Ultrafiltration
5. Cellulose MF, UF and RO

12. In the ED process a semi-permeable barrier allows passage of either
positively charged ions (cations) or negatively charged ions (anions)
while excluding passage of ions of the opposite charge. These semi-
permeable barriers are commonly known as ion-exchange, ion-
selective or electrodialysis membranes.

13. • Used for separation of gas mixtures.
• Separation of gases is due to their different solubility and
diffusivity in the polymer membranes.
• Rate of permeation:
– Proportional to pressure differential across the membrane,
solubility of gas in the membrane, diffusivity of gas through
membrane.
– Inversely proportional to the membrane thickness.
• Driving force: Concentration difference.
• Pore size: < 1 nm.
• Ex: Separation of Carbondioxide from natural gas

14. • Separation of miscible liquids
• Liquid is maintained at atmospheric pressure on the feed side of
the membrane, and permeate is removed as a vapour because of a
low vapour pressure existing on the permeate side.
• Differs from all other membrane processes because of the phase
change of the permeate.
• Transport is effected by maintaining a vapour pressure gradient
across the membrane.
• Membranes used: Zeolite and Poly Dimetyl Siloxane

15. Three steps sequence:
– Selective sorption of one of the components of the liquid
into the membrane on the feed side
– Selective diffusion of this component across the membrane
– Evaporation, as permeate vapour, into the partial vacuum
applied to the underside of the membrane

16. • Is a process in which two
liquid or solutions at
different temperatures are
separated by a porous
hydrophobic membrane.
• The liquid/solution must not
wet the membrane otherwise
the pores will be filled for
capillary force.
• Membrane distillation is a
type of low temperature,
reduced pressure distillation

17. Feed
H2O
T1
Permeate
H2O
T2
Air/vapour
Hydrophobic
porous membrane
T1>T2
Liquid water Liquid water
Schematic representation:
Such transport occur in a
sequence of three steps:
Evaporation on the high-
temperature side.
Transport of vapour
molecules through the pores
of the hydrophobic porous
membrane.
Condensation on the low-
temperature side.
 It is one of the membrane processes in which the membrane is not
directly involved in separation the only function of the membrane is
to act as a barrier between the twos phases. Selectivity is
completely determined by the vapour liquid equilibrium involves. This
means that the component with the highest partial pressure will
show the highest permeation rate.

18. • The membrane module and its support usually called as “module”
• Modules are assembled and can be easily integrated as a
separation system
Functions
• To accommodate large membrane areas in small volume
• Should withstand pressure required by the separation and cross
flow velocities to maintain a clean membrane surface area
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19. • Also called plate and frame module
• Consists of a series of alternate ribbed plates and hollow spaces
with membrane placed on either side of each plate and acts as
flow channel
• The upstream leaves as the retenate and is enriched in non-
permeate
• Permeates is collected from channels in support plates and
leaves enriched in the most permeate component
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20. • Advantage - Easy to clean and replace membranes
• Disadvantage - Low membrane area per volume
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21. 11/1/2017 22

22. • Most commonly used configuration in food industry particularly
for RO and UF
• Extension of the flat plate configuration
• Feed passes through membrane that is spirally wound around the
porous tube
• Membrane feed spacer and permeate spacer are glued on three
sides and terminates at its fourth side into the porous pipe
collects the permeate
• This module is wrapped into a spiral and placed in a cylinder
shell
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23. Advantages :
o High surface area available with low space requirement
o Turbulent flow is enhanced by the spacers
Disadvantages
o Low membrane area per volume
o Difficult to clean and sanitize
o It may become expensive for high pressure because extra high-
pressure shells must be purchased
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24. 11/1/2017 25

25. • Similar to tube in shell heat exchanger
• A cylindrical membrane and a support system is housed inside a
large tube in a tubular system
• Feed solution is pumped into the tube through one end and
forced in the radial direction through the porous pipe and the
membrane
• Relatively easy to clean and replace
• Disadvantage is relatively low membrane surface area
• Expensive and high operating cost
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27. • 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
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28. Membrane
module
Membrane
area/unit vol.
(m2 m-3 )
Membrane
costs
Control of
Fouling
Application
Plate & frame
Module
400 - 800 medium good MF, UF, RO,
ED
Spiral-wound
module
800 - 1200 low good UF, RO, GS
Tubular
module
20 - 100 very high very good MF, UF, RO
Capillary
module
600 - 1200 low very good UF, MF,
Hollow fiber
module
2000 - 5000 very low very poor RO, GS

29. It is a process where solute or particles deposit onto a membrane
surface or into membrane pores in a way that degrades the
membrane's performance.

30. Accumulation of solute particles over the membrane surface is
defined as concentration polarization. It has the following effects
i. Increase in osmotic pressure of the solution.
ii. Formation of gel over the membrane surface.
iii. Increases the viscosity of the solution.
iv. Solute enters into the pores and pores are blocked partially or
completely.

31. Major Foulants
• Organic materials
• Biological growth
• Colloidal and suspended
particles
• Soluble salts
• Membrane properties
• Solution properties
• Operating conditions
Influential factors

32. 1. Pre-treatment of the feed solution
2. Membrane
properties
3. Module and process conditions
4. Cleaning
a. Reducing concentration
polarisation
a1. Increasing flux velocity
a2. Using low flux membranes
a. Narrow pore size distribution
b. Hydrophilic membranes
a. Heat treatment
b. pH adjustament
c. Addition of complexing agents
d. Chlorination
e. Adsorption onto active carbon
a. Hydraulic cleaning
b. Mechanical cleaning
c. Chemical cleaning

33. – No specific chemical knowledge is needed for operation
– No Complex instrumentation
– Basic concept is simple to understand
– Separation can be carried out continuously
– Membrane processes can easily be combined with other
separation processes
– Separation can be carried out under mild conditions
– Membrane properties are variable and can be adjusted
– Greater design flexibility in designing systems
– Clean technology with operational ease

34. – Membranes are relatively expensive
– Certain solvents, colloidal solids, especially graphite and
other residues can quickly and permanently destroy the
membrane surfaces
– Oil emulsions are not "chemically separated," so secondary oil
recovery can be difficult.
– Synthetics are not effectively treated by this method
– Biofouling/membrane fouling;
– Low membrane lifetime;
– Generally low selectivity

35. • Development and advancement of Nano-materials for effective
membrane strength and separations.
• Over-coming the problem of Membrane Fouling.
• To design membranes for high selectivity.

36. Food industries Applications References
Dairy industry whey processing Mohammad et al.,
2012
bacteria can be removed from skim milk using a commercial
MF process called Bactocatch®
Tetra Laval,
Lund, Sweeden
As with RO, it can be used for the preconcentration of milk or
whey (by the
removal of water and minerals) mainly to reduce
transportation costs or energy requirements before the
evaporation process
Munir, 2006
Fruit and vegetable
juices (clarification
and concentration of
fruit juice)
use of immobilized pectinases on UF membrane has been
proposed as a method to allow the reuse of enzymes while
controlling membrane fouling during clarification processes
Giorno & Drioli,
2000
Sugar refining
(concentration,
clarification,
and purification)
RO has been used for the concentration of maple syrup,
resulting in more than 30% reduction in processing costs
Munir, 2006
Vegetable oils
processing
UF has been successfully applied to obtain soy protein isolates
(i.e. 60–65% of proteins) from the defatted soybean meal or
“cake”
Ladhe & Krishna
Kumar, 2010

37. Food industries Applications References
Brewing and
wine industry
MF is used for the separation of wort
following the
mashing step, for rough beer clarification
and for cold sterilization
Daufin
et al., 2001
Electrodialysis removal of calcium from milk
and lactic acid from whey, the control of
sugar/acid ratio
in wine, the pH control of fruit juices and
fermentation
reactors, and the purification of bioactive
peptides
Brennan & Grandison,
2012
Pervaporation used to concentrate fruit
juices, alcohol in fermentation broth,
dealcoholization of
alcoholic beverages (i.e. final product of
0.5% v/v of
ethanol), and recovery and concentration
of aroma compounds
Karlsson & Tragardh,
1996