Separation Techniques Involving Equilibration

7/27/2019 Separation Techniques Involving Equilibration

1/37

Separation techniques

involving equilibration


2/37

Feed: homogeneous, single phase solution (gas,liquid or solid)

A second phase must be developed or added:

Energy separating agent ESA (heat transfer,

shaft work, reduced pressure) Mass separating agent MSA ( partially

immiscible or completely miscible)

Contact of fluid phases intimate mixing tomaximize mass transfer rates disengagingphases through gravity or application of force


3/37

1. Partial condensation, partial

vaporization Feed mixture: species that differ widely in

their tendency to vaporize or condense.

Heat removed to partially condense a vaporfeed and heat added to partially vaporizeliquid feed.

Principle of separation: difference in volatilities Created phase: liquid and/or vapor Separating agent: heat (ESA)


4/37

Partial condensation or vaporization


5/37

2. Flash vaporization

Partial vaporization by reducing the pressure ofthe feed.

Principle of separation: difference in volatilities Created phase: vapor Separating agent: pressure reduction


6/37

Flash vaporization


7/37

3. Distillation

If volatility differences are not sufficiently largesingle partial vaporization or condensation step isnot sufficient multiple stages

Principle of separation: difference in volatilities

Created or added phase: vapor and liquid

Separating agent: heat (work) transfer (ESA)


8/37Distillation

Boilup

Reflux

Rectifying

Stripping

Condenser

Reboiler


9/37

4. Extractive Distillation

If volatility differences are so small as tonecessitate use of more than 100 trays.

Principle of separation: difference in volatilities Created or added phase: vapor and liquid

Separating agent: liquid solvent (MSA) and heat

transfer (ESA)


10/37

Extractive Distillation

Solvent


11/37

5. Reboiled Absorption

If condensation of vapor leaving the top of thedistillation column is not easily accomplished byheat transfer, a liquid MSA called an absorbentmay be introduced to the top tray in place of reflux

Principle of separation: difference in volatilities,preferential solubility


Separating agent: liquid absorbent (MSA) andheat transfer (ESA)


12/37

Reboiled absorption

Absorbent


13/37

6. Absorption

If the feed is all vapor and the stripping sectionof the column is not needed to achieve thedesired separation.

Usually does not require an ESA, conducted atambient temperature and high pressure.

Principle of separation: preferential solubility Created or added phase: liquid

Separating agent: liquid absorbent (MSA)


14/37

Absorption

Absorbent


15/37

7. Stripping

The inverse of absorption. A liquid mixture is

separated by contacting liquid feed with astripping agent ( a vapor).

Eliminates the need to reboil the liquid at the

bottom of the column. Important if the liquid isnot thermally stable.

Principle of separation: difference in

volatilities Created or added phase: vapor

Separating agent: stripping vapor (MSA)


16/37

Stripping


17/37

8. Refluxed Stripping

It is employed if simple stripping is not sufficientto achieve the desired separation and contactingtrays are needed above the feed tray.

Principle of separation: difference involatilities


Separating agent: stripping vapor (MSA) andheat transfer (ESA)


18/37

Refluxed Stripping


19/37

9. Reboiled Stripping

If the bottoms product from a stripper isthermally stable, it may be reboiled withoutusing an MSA

Principle of separation: difference involatilities

Created or added phase: vapor

Separating agent: heat transfer (ESA)


20/37

Reboiled Stripping


21/37

10. Azeotropic Distillation

For constant boiling mixtures, separation by

distillation is not possible. An entrainer (MSA) isused which forms a heterogoneous minimum boilingazeotrope with one of the components in themixture.

Principle of separation: boiling point differencescaused by formation of a heterogeneousazeotropic mixture


Separating agent: liquid entrainer (MSA) andheat transfer (ESA)


22/37

Azeotropic Distillation

( i ) + MSA

( j )

( MSA + i )

azeotrope


23/37

11. Liquid-liquid extraction

Used when distillation is impractical.i. The mixture to be separated is heat

sensitive,

ii. Volatility differences are much too small

Principle of separation: different solubilities

of different species in the two liquid phases

Created or added phase: liquid

Separating agent: liquid solvent (MSA)


24/37

Liquid-liquid extraction


25/37

Liquid-liquid extraction (two solvent)


26/37

12. Drying of solids

Many chemicals are processed wet but sold in

dry, solid forms. Drying is used to removeliquid from a solid by vaporizing the liquid.

Principle of separation: evaporation of water

Created or added phase: Vapor

Separating agent: gas (MSA) and/or heattransfer (ESA)


27/37

Drying


28/37

13. Evaporation

The transfer of volatile components of a liquid into

a gas by volatilization caused by heat transfer.Major applications are humidification, airconditioning, flash cooling, concentration ofaqueous solutions.

Principle of separation: difference in volatilities(vapor pressure)

Created or added phase: vapor


V


29/37

Evaporation

V

14 Crystallization


30/37

14. Crystallization

Desired product is finely divided solid.

Solution crystallization: The mixture is cooled and/or thesolvent is evaporated to cause crystallization.

Melt crystallization: Two or more soluble species, in theabsence of a solvent, are separated by partial freezing.

Zone melting (refining): Reverse of melt crystallization. Usedfor removing impurity solids in metals by moving a molten zoneslowly through an ingot.

Principle of separation: difference in freezing tendencies;

preferential participation in crystal structure.

Created or added phase: solid (and vapor). Liquid in zonemelting



31/37

Crystallization


32/37

15. Sublimation-Desublimation

Sublimation: Transfer of a substance from solid

into gaseous without going through liquid stateunder high vacuum. Used for removal of avolatile compound from an essentially nonvolatileone.

Principle of separation: sublimation of water -preferential participation in crystal structure

Created or added phase: solid Separating agent: heat transfer (ESA)


33/37

Desublimation


34/37

16. Leaching (Liquid-solid extraction)

Diffusion of the solute out of the solid and intothe liquid solvent is mostly the controlling step.

Principle of separation : preferential solubility

Created or added phase: liquid

Separating agent: liquid solvent (MSA)


35/37

Leaching (liquid-solid extraction)

Solvent


36/37

17. Foam fractionation

Two-phase adsorptive bubble separationmethod. Surface active material collects atbubble surfaces and leave in the foam product.

Principle of separation : tendency ofsurfactant molecules to accumulate at gas-liquidinterface and rise with air bubbles

Created or added phase: gas

Separating agent: gas bubbles (MSA)


37/37

Foam fractionation

Gas

Separation Techniques Involving Equilibration

Documents

Transcript of Separation Techniques Involving Equilibration