ULTRAFILTRATION -

It is a cross-flow separation process. Here liquid flow tangentially long the membrane surface, thereby producing two streams.

1) The stream of liquid that comes through the membrane is called permeate(pass into every part).

2) The other liquid stream is called concentrate.

It is a separation process using membrane with pore size in the range of 0.01- 0.1 micron & it is normally operated in the pressure range of 15-50 psig (Pound per square inch gage)

In cross-flow separation, therefore, the membrane itself does not act as a collector of ions, molecules or colloids but it act as a barrier to these species.

It will remove high molecular weight substances like colloidal materials, organic & inorganic polymeric molecules. It will not remove low molecular weight organic & ions like Na, Ca, Mg, & $So_{4}$. Because the osmotic pressure differential across the membrane surface is negligible.

Low applied pressures are sufficient to achieve high flux rates from ultra- filtration membrane. (Flux- is defined as the amount of permeate produced per unit area of membrane surface per unit time.) It is expressed as GFD(Gallons per square foot per day). Ultra-filtration membrane can have extremely high fluxes, but in most practical applications the flux varies between 50-200 GED at an operating pressure of about 50 psig,

Reverse osmosis only produces between 10-30 GFD at 200-400 psig

Industrial applications-

1. It is used to separate suspended solid from solution.

2. Paint recovery in the automotive industry.

3. It is widely used in the fractionation of milk, whey & in protein fractionation & protein isolation

4. Removal of colloids.

5. Also used in power, food, pharmaceutical, biotechnology & semiconductor industries.