introduction_to_separation_processes

7/27/2019 introduction_to_separation_processes

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Chapter 1. Separation Processes

2012. 1


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Energy Consumption /.

/.

: enantiomerically pure components

Softenon : (R-enantiomer), (S-enantiomer)

Aspartame : (S, S) , (R, R) Limonen : (S), (R)


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Separations

Separations Enrichment

Concentration

Purification

Refining

Isolation

Separations are important to chemist andchemical engineers Chemist : Small scale (Analytical separation methods)

Chemical Engineers : Economical, large scale methods


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Industrial Chemical Processes

Natural raw material

Plant or animal matter

Chemical intermediate

Chemicals of commerce

Waste products

Feed

Batchwise

Continuous

Semicontinuous

Mode of Operation

Key Operation

Reaction

Separation

Auxiliary Operation

Heat / Work

Mixing, Dividing

Size reduction

Operation


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Hypothetical vs. Industrial Processes

Simple ,hypotheticalprocess is not possible

Impurities in the feed

Side Reactions

Separation processes areimportant in real industrialapplication

5


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Mechanism of Separation

Mixing : Spontaneous, natural process

Separation : Not spontaneous process

Require energy (heat / work)

Question : Why ?


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General Separation Technique

Separation by Phase Creation Energy (heat/work) ,

Separation by Phase Addition 3 (MSA : Mass Separating Agent)

Separation by Barrier Barrier (membrane)

Separation by Solid Agent ,

Separation by Force Field or Gradient ,, ,


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Classification of Separation Techniques

8

Barrier

Force fieldor gradient

Feed

Phase 1

Phase 2

(i) By Phase Creation

Feed

Phase 1

Phase 2

Feed

Phase 1

Phase 2

Feed

Phase 1

Phase 2

Feed

Phase 1

Phase 2

(ii) By Phase Addition

(iii ) By Barrier

(iV) By Solid Agent (Vi) By Force Field or Gradient

MSA

Mass SeparatingAgent


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Driving Force of Separation :Gradient of Concentration

Rate of Separation : how fast ? Governed bymass transfer

Extent of Separation : how far ?

Limited bythermodynamics

Properties of ImportanceMolecular Properties Thermodynamic and Transport Properties

Molecular Weight

Van der Waals Volume

Van der Waals Area

Molecular Shape (Accentric Factor)

Dipole Moment

Polarizability

Dielectric Constant

Electric Charge

Radius of Gyration

Vapor Pressure

Solubility

Adsorptivity

Diffusivity

9

Handbooks

Journals

Electronic Databases

Commercial Process Simulators


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Separation By Phase Addition or Creation -1

1

V/L

V

L

V/L

V

L

Partial Condensation or Vaporization Flash Vaporization

(Heat Transfer) (Pressure Reduction)

ESA

(Energy-Separating Agent)


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Separation By Phase Addition or Creation - 2

1

V/L

L

L

Distillation

(Heat transfer (ESA) or sometimes work transfer)

When the volatility difference

among species are not sufficiently

large

Most widely used industrial

separation technique

Multiple contact between counter

current flow of V/L in trays (stages) .

Rectifying section

Stripping section

Condenser

Reboiler

Reflux

Reboil


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Distillation Tower

1


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13

V/L

L

L

Azeotropic Distillation

Liquid entrainer (MSA)

and Heat Transfer (ESA)

Recycle MSA

Makeup MSA

Recovery of acetic acid from water

using n-butyl acetate


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1

MSA (L)

L1

L2

L1

LiquidLiquid Extraction

Liquid solvent(MSA)

Recovery of Aromatics

MSA2 (L)

L

L

L

Liquid-Liquid Extraction

(Two Solvent)

Use of Propane and Cresylic acid as solvents to separate

paraffins from aromatics and naphthenes

MSA1 (L)


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1

Drying Evaporation Crystallization Desublimation

V (V)

L/(S) S

V

L

(V)

L L

S

V

S

LV

Removal of water from PVCEvaporationof water from

Water + Urea

Crystallization op-Xylenefrom m-Xylene

Recovery ofphthalic anhydride

Heat transfer (ESA)

Heat transfer (ESA) Heat transfer (ESA) Heat transfer (ESA)


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Crystallizer

1


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1

Leaching (Liquid-Solid Extraction) Foam Fractionation

S

MSA (L)

S

L

L

MSA (g)

L (foam)

V

L

Extraction of sugar using hot water

Liquid Solvent

Recovery of detergent from water soln.

Gas Bubbles (MSA)

Detergent tend torise with gas bubble


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Separation by barrier

Use of microporous / nonporousmembrane as semipermeable

barriers

Membranes Natural fibers

Synthetic polymers Ceramics

Metals

Liquid films

Fabrications Flat sheets

Hollow fibers Spiral-wound sheets

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Separation by barrier - 2

2

Microfiltration Ultrafilration Pervaporation

L

L

L

L

V

Microporous membrane Microporous membrane Nonporous membrane

Pressure gradient Pressure Gradient Pressure Gradient

Separation of whey from

cheese

Separation of azeotropic

mixtures

L

L

L

Removal of bacterial

From drinking water

L

0.02-10 mm 1 20 nm

solventsolvent gas (evaporation)


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Separation by barrier - 3

2

Gas permeationLiquid Membrane

V

V

V

V/L

V/L

Nonporous membraneLiquid membrane

Pressure Gradient Pressure Gradient

Hydrogen enrichment Removal of hydrogen sulfide

V/L

gas

Gas mixture

Liquid layer


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Liquid Membrane

2


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Separation by solid agent

Solid mass separating agent

Granular material or packing

Saturation Periodical regeneration required

Batchwise or semicontinuous operation

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Molecular sieve Silica gel

pore


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2

Adsorption Chromatography Ion Exchange

Solid Adsorbent Solid adsorbent or liquid

Adsorbent on solid support

Resin with ion-active sites

Separation of xylene isomers

and ethylbenzene

Demineralization of water

Purification of

p-xylene

V/L

V/L

V/L V/L

V/L

L

L

L


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Adsorption Adsorbent

Activated carbon

Aluminum oxide

Silica gel

Zeolite adsorbents (Molecularsieve)

Adsorption / Regeneration

Regeneration methods Thermal Swing (TSA)

Pressure Swing (PSA)

Inert purge stripping Displacement desorption

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Hydrogen PSA Units


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Separation by external field or gradient

Separation operation Initial or Feed Phase Force field or gradient Industrial Example

Centrifugation Vapor Centrifugal force Separation of Uranium

isotope

Thermal diffusion Vapor or liquid Thermal gradient Separation of chlorine

isotope

Electrolysis Liquid Electrical force field Concentration of

heavy water

Electrodialysis Liquid Electrical force field

and membrane

Desalinization of sea

water

Electrophoresis Liquid Electrical force field Recovery of

hemicelluose

Field-flow

fractionaltion

Liquid Laminar flow in force

field

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Centrifugation

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Electrodialysis

2


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Electrophoresis ()

2

Using different migration velocities of charged colloidal orsuspended species in a electrical field

Application : Biochemicals

Fi ld Fl S ti


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Field Flow SeparationField Flow Fractionation (FFF)

3

Micromolecular andcolloidal materials


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Component Recoveries and Product Purity

Separation process

No reaction

Continuous and steady state

i : 1 ~ C Number of Components

p : 1~ NProduct phases

F : feed

)()1()3()2()1(

1

)()(

...N

i

N

iiii

N

p

p

i

F

i nnnnnnn

31


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Example Hydrocarbon Recovery Plant

3

Purpose :Production of polymers

- PP- PB.

S li F i d S li R i


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Split Fraction and Split Ratio

Split fraction ( 0 1)

Split ratio ( 0 very large value)

)(

,

)1(

,

, F

ki

ki

ki

n

nSF

)1( ,

,

)2(

,

)1(,

,

ki

ki

ki

ki

ki

SF

SF

n

nSR

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i : component

k : separator

(F) : feed

(1) : f ir st product (ex: top product)

(2) : second product (ex : bottom product)

i product /feed

i top / bottom


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Separation Power

)1/()1(

/

/

/)2()1(

)2()1(

,

ji

ji

j

i

jj

iiji

SFSF

SFSF

SR

SR

CC

CCSP

Key-component split Column SP

Separation Power

nC4H10 / iC5H12 C1 137.1

C3H8/iC4H10 C2 7103

iC4H10/nC4H10 C3 377.6

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S l i f ibl S i


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Selection of Feasible Separation

Selection of a best separation processes Selection among a number of feasible candidates

Two or more operations may be the best

Important Factors that influence the selectionof feasible separation operations

Feed conditions

Product conditions

Property differences

Characteristics of separation3

F h I fl h S l i f F ibl


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Factors that Influence the Selection of FeasibleSeparation Operation

Feed condition Compositions

Flow rate

Temperature

Pressure

Phase state

Product conditions Required purities of products

Temperatures

Pressures

Phase states

Property differences Molecular

Thermodynamic

Transport

Characteristics of separationoperation

Ease of scale-upEase of staging

T, P, Phase-state requirements

Physical size limiation

Energy requirement

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Most important

Can be altered by pump,

Compressor, heat exchangers,

Technological and Use Maturity of Separation


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Technological and Use Maturity of SeparationProcesses

3

SeparationBy Barrier

Separation bySolid agent

Creation of Addition ofSecond Phase Cheap

Expensive


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