GOVERNMENT ENGINEERING COLLEGE, BHARUCH

Department -Chemical Engineering (7th sem.)

SUBJECT : New Separation TechniquesTOPIC : Reverse Osmosis(R.O.)

OVERVIEW

Different types of Membrane separation techniques

Concept of osmosis

Reverse Osmosis

Different type of membrane

Types of membrane module

Advantage & Disadvantage of RO

Application of RO

Different type of membrane process

OSMOSIS:FUNDAMENTAL Osmosis is a natural phenomenon that

provides water to all animal and vegetable

cells to support life.

Water moves from a high concentration of

water to a low concentration of water

across a semi-permeable membrane.

This means that water can cross a

selectively permeable membrane from a

dilute solution (less dissolved in it) to a

concentrated solution.

OSMOSIS: WHAT IS IT?

A semi-permeable membrane is a

membrane which will allow only

certain molecules or ions to pass

through

Osmosis is very important in biology

as it provides the primary means by

which water is transported in and out

of cells.

REVERSE OSMOSIS:WHAT IS IT? RO is a form of filtration using osmosis in reverse Water passes from a

more concentrated solution to a less concentrated solution.

To accomplish this a force or pressure must be applied RO requires 1 psi

of pressure for every 100 ppm of TDS.

RO is used to remove dissolved solids from water but it can also improve

taste, odor & color of water.

RO membranes have the capability to remove particles as small as ions

i.e. magnesium ions or sodium ions.

RO membrane will reject most compounds based largely on size

Dissolved ions, such as salts, carry an electric charge and will also be

rejected by membrane.

REVERSE OSMOSIS:HOW IT WORKS

Feed water flows into RO unit with the force of line pressure Water is forced

through membrane by cross flow filtration.

Cross flow filtration is most commonly used in RO as it allows membrane to

continually clean itself Membrane then either rejects or repels contaminants.

Two exit streams generated: waste & product stream

Waste stream consists of: A concentrate (reject) stream which carries

contaminants (compounds too large to pass through membrane)

Permeate stream consists of: Product water which has been forced through

the membrane & is virtually free of TDS.

Reverse Osmosis Fundamentals:

REJECT WATER: Portion of feed water which did not pass through membrane; carries

impurities to drain.

MODULE: Combination of spiral round membrane element & pressure vessel.

FEED WATER: Main flow of impure water to be treated.

PRODUCT WATER: Portion of feed water which passes through membrane as

permeate.

(1)Asymmetric membrane : This type of membranes have a thin(-100 nm) permselective skin

layer support on a more porous sublayer of the same polymer.

Dense skin layer determines the fluxes and selectivites of membrane ,whereas the porous sublayer serves only as a mechanical support for the skin layer . its block the passage of quite small solute molecules.

RO Membrane:

(2)Thin film composite membrane:

TFC membranes are intolerant to

chlorine– will cause deterioration

of membrane.

Must use a carbon pre-filter for

TFC membranes.

TFC membranes have a much

higher rejection rate of many

chemicals than CTA membranes.

Carbon pre filters are vital in the

life of this membrane & must be

changed regularly.

Membrane material and modules

Although reverse osmosis membrane have been formed and tested using a large number of different material.

Two types of membrane material

(1)cellulosic acetate(2) Aromatic Polyamide

(1)Cellulose acetate membranes

Cellulose acetate has a higher flux and a smaller area of membrane is therefore required. It is also resistant to small concentrations of free chlorine and may therefore be kept free of bacteria and also produce a product with residual chlorine in it to prevent subsequent re-growth.

The polyamide membrane can be used at a higher temperature (35 oC) than cellulose acetate (30 oC), it cannot tolerate chlorine but is not attacked by bacteria whereas some bacteria which can occur in surface water in woodlands actually destroy cellulose acetate. Finally, polyamides can be used over a much wider pH range (4-11) than cellulose acetate (4-7.5)

(2)Polyamide membranes

MEMBRANE MODULES

TYPES OF MEMBRANE MODULE

The permeate from each pair of membranes can be visually observed in the plastic tubing coming from each support plate.

A gasket is used to transform the flat plate into a long tortuous narrow channel.

Replacement of membranes on site is relatively easy.

PLATE AND FRAME MODULE

SPIRAL-WOUND MODULE

Particles hang-up in the mesh network, resulting in cleaning problem.

This makes it difficult to process feeds containing suspended particles. Spiral-wound modules work best on relatively clean feed streams with a minimum of suspended matter

TUBULAR MODULE Tubular membranes are not self-supporting

membranes. They are located on the inside

of a tube, made of a special kind of material.

This material is the supporting layer for the

membrane.

Because the location of tubular membranes

is inside a tube, the flow in a tubular

membrane is usually inside out. The main

cause for this is that the attachment of the

membrane to the supporting layer is very

weak.

HOLLOW FIBRE MODULE:

A bundle of hollow fibers are mounted in a pressure vessel and open end of u shaped fibers is plotted into head plate.

In a hollow fiber module the permeate water flow per unit area of membrane is low and therefore concentration polarization is not high at the membrane surface .

The net result is that hollow fibre units operate in a non-tubulent and laminar flow regime.

COMP. OF VARIOUS MODULES

Parameters that affect RO Pressure: The water flux is a function of the pressure differential between

the applied hydrostatic pressure and the osmotic pressure across the membrane. Passage of water increased with increased in applied pressure, assuming osmotic pressure constant. Solute rejection rises with pressure , since solvent flux increase and solute diffusion doesn’t.

Temperature: solvent flux increases with increase in temperature since viscosity decrease.

Solute concentration : flux declines with increasing solute concentration because of increase is osmotic pressure difference. At low feed velocity past the membrane , solute is ploarized at the membrane.

Membrane packing density :This is expression of unit area of membrane , which can be placed per unit volume of pressure vessels.

Recovery factor: The consideration of recovery factor of actually represents Plant capacity. Feed water stream velocity:The hydraulics of reverse osmosis system are

such that velocities in the range of 1.2 to 76.2 cm/s are common.

ADVANTAGES RO performs a separation without a phase change.

RO system are compact and space requirement are less space other desalting system. EX.-distillation.

Simultaneous separation and concentration of both inorganic and organic compounds are possible using RO process.

RO eliminates 95% to 99% of total dissolved solids(TDS),reverse osmosis is the best technology today for getting clean water free of contaminants.

Today RO system provides such diverse uses as drinking water , rinse ,ice making to so many industries that uses it.

DISADVANTAGES The small pores of the membrane block particles of large

molecules but pesticides and chlorine are molecularly smaller then water can pass through. This is the why carbon filter must be used as supplement to the RO process because it can remove chlorine in the water.

As most minerals like iron , magnesium , calcium and solution are

larger in size than water molecules , semi permeable prevents

them from passing on to other side.so water actually gets de-

mineralized.

The systems needs professional for cleaning.

Applications for Reverse Osmosis Systems

The ideal applications for RO water filtration equipment include:

Boiler Feed Water Ion Exchange Pre-treatment Beverage Production Safe Drinking Water Spot Free Product Rinse

THANK YOU

MAYUR GAMI

120140105008HARDIK SUTARIYA

120140105019

PARVEJ CHAVDA120140105046

AJAY KAMALIYA110140105042

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