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7/27/2019 Separation Techniques Involving Equilibration
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Separation techniques
involving equilibration
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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
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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)
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Partial condensation or vaporization
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2. Flash vaporization
Partial vaporization by reducing the pressure ofthe feed.
Principle of separation: difference in volatilities Created phase: vapor Separating agent: pressure reduction
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Flash vaporization
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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)
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Boilup
Reflux
Rectifying
Stripping
Condenser
Reboiler
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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)
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Extractive Distillation
Solvent
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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
Created or added phase: vapor and liquid
Separating agent: liquid absorbent (MSA) andheat transfer (ESA)
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Reboiled absorption
Absorbent
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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)
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Absorption
Absorbent
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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)
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Stripping
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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
Created or added phase: vapor and liquid
Separating agent: stripping vapor (MSA) andheat transfer (ESA)
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Refluxed Stripping
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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)
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Reboiled Stripping
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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
Created or added phase: vapor and liquid
Separating agent: liquid entrainer (MSA) andheat transfer (ESA)
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Azeotropic Distillation
( i ) + MSA
( j )
( MSA + i )
azeotrope
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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)
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Liquid-liquid extraction
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Liquid-liquid extraction (two solvent)
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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)
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Drying
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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
Separating agent: heat transfer (ESA)
V
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Evaporation
V
14 Crystallization
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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
Separating agent: heat transfer (ESA)
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Crystallization
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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)
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Desublimation
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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)
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Leaching (liquid-solid extraction)
Solvent
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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)
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Foam fractionation
Gas