MEMBRANE SEPARATION

Presented by : Abhi PanchalAhir MayurAyush SinghSagar BhanderiBhoot AbhayMEMBRANE SEPARATION

S. N. PATEL INSTITUTE OF TECHNOLOGY AND RESEARCH CENTRE

CONTENTINTRODUCTIONREVERSE OSMOSISDIALYSISELECTRODIALYSIS

INTRODUCTIONA 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.

REVERSE OSMOSIS

Reverse osmosis(RO) is a water purification technology that uses asemi permeable membraneto remove larger particles from drinking water. In reverse osmosis, an applied pressure is used to overcomeosmotic pressure, acolligative property, that is driven bychemical potential, athermodynamicparameter. Reverse osmosis can remove many types of moleculesandionsfrom solution, including bacteria, and is used in both industrial processes and the production of portable water. The result is that thesoluteis retained on the pressurized side of the membrane and the puresolventis allowed to pass to the other side.

Cntd.In the normalosmosisprocess, 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.

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 andbrackish waters.

DIALYSISA 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

PRINCIPLEDialysis works on the principles of thediffusionof solutes andultra filtrationof fluid across asemi-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.

ELECTRODIALYSISElectro dialysis(ED) is used to transportsaltionsfrom onesolutionthroughion-exchangemembranes to another solution under the influence of an appliedelectric potentialdifference. 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 ananionexchange membrane and acationexchange membrane placed between twoelectrodes. 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.

Cntd.Electro dialysis processes are different thandistillationtechniques and other membrane based processes (such asreverse 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.

At the anode small amounts of oxygen gas are generated:Electrode reactions: Small amounts of hydrogen gas are generated at the cathode:

Thank you