Membrane separation or osmotic separation Theory and ppt for Advance Separation Techniques.

1. Presented by :
Abhi Panchal
Ahir Mayur
Ayush Singh
Sagar Bhanderi
Bhoot Abhay
MEMBRANE SEPARATION
S. N. PATEL INSTITUTE OF TECHNOLOGY
AND
RESEARCH CENTRE

2. CONTENT
 INTRODUCTION
 REVERSE OSMOSIS
 DIALYSIS
 ELECTRODIALYSIS

3. INTRODUCTION
 A membrane is a selective barrier that permits the separation of
certain species in a fluid by combination of sieving and diffusion
mechanisms.
 Membranes can separate particles and molecules and over a wide
particle size range and molecular weights.

6. REVERSE OSMOSIS
 Reverse osmosis (RO) is a water purification technology that uses
a semi permeable membrane to remove larger particles from drinking
water.
 In reverse osmosis, an applied pressure is used to overcome osmotic
pressure, a colligative property, that is driven by chemical potential,
a thermodynamic parameter.
 Reverse osmosis can remove many types of molecules and ions from
solution, including bacteria, and is used in both industrial processes
and the production of portable water.
 The result is that the solute is retained on the pressurized side of the
membrane and the pure solvent is allowed to pass to the other side.

7. Cntd.
 In the normal osmosis process, the solvent naturally moves from
an area of low solute concentration (high water potential),
through a membrane, to an area of high solute concentration
(low water potential).
 The movement of a pure solvent is driven to reduce the free
energy of the system by equalizing solute concentrations on each
side of a membrane, generating osmotic pressure.
 Applying an external pressure to reverse the natural flow of pure
solvent. Thus, is reverse osmosis.

8. PROCESS
 Osmosis is a natural process. When two liquids with different
concentrations of a solute are separated by a semi permeable
membrane, the fluid has a tendency to move from low to high
solute concentrations for chemical potential equilibrium.
 Formally, reverse osmosis is the process of forcing a solvent
from a region of high solute concentration through a semi
permeable membrane to a region of low solute concentration by
applying a pressure in excess of the osmotic pressure.
 The largest and most important application of reverse osmosis is
the separation of pure water from seawater and brackish waters.

10. DIALYSIS
 A process for selectively removing low mol. wt. solutes from
solution by allowing them to diffuse into a region of lower
concentration through thin porous membranes.
 There is little or no pressure difference across the membrane and
the flux of each solute is proportional to the concentration
difference.
 Solutes of high mol. wt. are mostly retained in the feed solution,
because their diffusivity is low and because diffusion in small
pores is greatly hindered when the molecules are almost as large
as the pores.
 Uses thin porous membranes

11. PRINCIPLE
 Dialysis works on the principles of the diffusion of solutes
and ultra filtration of fluid across a semi-permeable membrane.
 Diffusion is a property of substances in water; substances in
water tend to move from an area of high concentration to an area
of low concentration.

12. ELECTRODIALYSIS
 Electro dialysis (ED) is used to transport salt ions from
one solution through ion-exchange membranes to another
solution under the influence of an applied electric
potential difference.
 This is done in a configuration called an electrodialysis cell. The
cell consists of a feed (dilute) compartment and a concentrate
(brine) compartment formed by an anion exchange membrane
and a cation exchange membrane placed between two electrodes.
 In almost all practical electrodialysis processes, multiple
electrodialysis cells are arranged into a configuration called an
electrodialysis stack, with alternating anion and cation exchange
membranes forming the multiple electrodialysis cells.

13. Cntd.
 Electro dialysis processes are different than distillation techniques
and other membrane based processes (such as reverse
osmosis(RO)) in that dissolved species are moved away from the
feed stream rather than the reverse.
 Because the quantity of dissolved species in the feed stream is far
less than that of the fluid, electrodialysis offers the practical
advantage of much higher feed recovery in many applications.
 Electro dialysis reversal(EDR) is an advanced electrodialysis
process which utilizes a flow and polarity reversal to de-scale
membrane surfaces and enable high concentration operation.

16. At the anode small amounts of oxygen gas are generated:
 Electrode reactions:
Small amounts of hydrogen gas are generated at the cathode:
2 22e 2H O H (g) 2OH 
  
2 2
-
2
H O 2H 1/ 2O (g)
(also possible 2Cl Cl (g) 2e )


 
 

17. Thank you