inception final

8/17/2019 Inception Final

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LIQUID-LIQUID

EXTRACTION –

CONTINUOUS CONEQUIPMENT


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EXTRACTIOPRINCIPLE


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Feed phase contains a component, i, which is to be removed.

Addition of a second phase (solvent phase) which is immiscible with fcomponent i is soluble in both phases.

Some of component i (solute) is transferred from the feed phase to the solve

extraction the feed and solvent phases are called the raffinate (R) and extrespectively.

Normally one of the two phases is an organic phase while the other is an aqueo

Under equilibrium conditions the distribution of solute i over the two phase by the distribution law.

After the extraction the two phases can be separated because of their immiscib

Component i is then separated from the extract phase by a technique such asthe solvent is regenerated.

Further extractions may be carried out to remove more component i.

Liquid liquid extraction can also be used to remove a component from an or

adding an aqueous phase.


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-

CONTACT

Stage 1 Stage 2


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Stage 1 Stage 2

CROS


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COUNTE

CURRENT F

Stage 1 Stage 2


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PHASE DIAGR

B

A S

P

%A

%S

%B

A mixture of overall compositiinto two phases – E & R. R phaequilibrium with E phase

R/E = line ME/line MR

E

M


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CHOICE OFSOLVENT

Factors to be considered:

SelectivityDistribution coefficientInsolubility of solventRecoverability of solute from solventDensity difference between liquid phasesInterfacial tension

Chemical reactivityCostViscosity, vapour pressureFlammability, toxicity


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PACKE

TOWE


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Considering , a case ofarranged for light liquid

The void space of the pfilled with the continuouwhich flows downwards

The remainder of the v

with droplets of light liqlower distributor , whichheavy liquid and coalesc

bulk layer, forming an in


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The nature of the liquid flow in such towers require that the choice of packing adispersed – phase distributor be given careful attention .

If the dispersed liquid preferentially wets the packing, it will pass through in rivuletsas droplets , and the interfacial area produced will be small. For this reason packing showetted by the continuous phase.

Usually, ceramics are wet by aqueous liquids and carbon and plastics by organic liquidsThe packing should be sufficiently small, no greater than one-eighth of the tower diam

density to be fully developed.

Where the material of the packing support is not wet by the dispersed droplets and theoutside the packing, the drops will have difficulty in entering the packaging and prematu


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DESIGN O

EQUIPME


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The change in concentration with height of either liquid as it passes throughdiffernetial , the height of the tower is expressed not in number of stages but in units.

Although the raffinate is flowing downwards as if it were denser, in some instancor extract, phase will be denser and will enter at the top. In the either case, in what1 will always represent the end of the tower where the raffinate enters and the extsubscript 2 will indicate where extract enters and raffinate leaves.

Expect in special cases, the transfer of solute usually results in change of mutuacontacted liquids, so that in general all components of the systems transfer from other. The F- type mass-transfer coefficients are capable pf handling this problem.


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In reality, we know so little about the mass transfer coefficients that the interface expressioFor practical reasons , it is usually necessary to deal with overall coefficients and the transfer


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MECHANICALLY

AGITATED EXTRAC


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Mechanically-agitated columns can be divided into 2 main classes mechanical motion patterns:

Rotary-agitated columns

Reciprocating or vibrating-plate columns

Examples of rotary-agitated columns include:Scheibel columns, rotating disk cOldshue-Rushton Columns, Kuhni columns, etc. An example of the reciproctheKarr columns.

Because of the mechanical advantages of rotary agitation, most modern extracmethod. Mechanical agitation helps improve the formation of new dropleinterfacial turbulence, resulting in greater efficiency.These extractors are typically proprietary devices for which complete design prpublicly available.


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In this system, horused as agitating elem

are mounted on a cesupported shaft.

Mounted on the cooffset against the agithe stator rings, who

is greater than the agdiameter.

This device uses thaction of the rapidly inter-disperse the ph


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CENTRIFUG

EXTRACTO


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Centrifugal extractor—also known as acentrifugal co

Principle:-

Uses the rotation of the rotor inside acentrifuge to mix twoimmiscible liquids outside the separate the liquids in the field of gravity inside the rotor. This way, a centrifugal extractor continuousextraction from one liquid phase into another liquid phase .

Process Description:-

Two immiscible liquids of different densities are fed to the separate inlets and are rapidly annular space between the spinning rotor and stationary housing. The mixed phases are directed toward the centre of the rotor by radial vanes in the housiAs the liquids enter the central opening of the rotor, they are accelerated toward the wall.The mixed phases are rapidly accelerated to rotor speed and separation begins as the liquupward. A system of weirs at the top of the rotor allow each phase to exit the rotor where it landsand exits the stage.

https://en.wikipedia.org/wiki/Centrifugehttps://en.wikipedia.org/wiki/Miscibilityhttps://en.wikipedia.org/wiki/Liquid-liquid_extractionhttps://en.wikipedia.org/wiki/Liquid-liquid_extractionhttps://en.wikipedia.org/wiki/Miscibilityhttps://en.wikipedia.org/wiki/Centrifuge


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CONTACT

Phases flow through the equipment in continuous intimate cont

without repeated physical separation and recontacting

Operation should be either semi-batch or steadystate

Equilibrium between two phases at any position in the equip

established.


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CONTACT EXTRAC

Countercurrent flow is produced due to difference in densities ofLight liquid enters at the bottom and heavy at the top

Rate for only one liquid can be controlled

If flow rate of second liquid is increased, flooding may take place

Cross section area should large enough to prevent flooding

Method used depends on the stage efficiency

Used only when stage efficiency is low


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APPL

Recovery of tightly hydrogen-bonded organics from water; such as formaformic acid and acetic acid

Removal of high boiling organics from wastewater; such as phenol, anilinnitrated aromatics

Essential oil extraction; such as pharmaceuticals, flavors, fragrances and

Biofuels and chemicals produced by biological processes such as fermentalgae often require liquid-liquid extraction (LLE) as the first step in recovpurification


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