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Liquid Membranes

Membrane

Phase 1

Phase 2

2

Types of LM

Immobilised (ILM) or Supported (SLM)

Emulsion (ELM)Organic liquid & surfactant

Receiving phase

Porous support

liquid

Volumetric or Bulk (VLM)

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Facilitated TransportA

A

Facilitated transport

Diffusive transport

A

A

AC

4

Carrier Mediated TransportMobile Carrier Fixed Carrier

10-5-10-7

Diffusivities (cm2/s)

10-6-10-8 >10-7

Mobile Gel Fixed

5

A

A

AC

BCB

B

Types of FT…

ReactionA+C<=>AC

Uncoupled A

A

AC

Coupled

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A

A

AC

BCB

B

Coupled configurations

AACA

BB

B

Counter coupled transport

ReactionA+CB<=>AC+B

Co-coupled transport

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FT Mechanism

M+

H+

M+HC

MC H+

Source phase LM Strip phase

1) Carrier reacts with solute

2) The complexed carrier diffuses across the membrane

3) Because the adjacent solution is dilute, the solute carrier reaction is reversed, releasing solute

4) The carrier returns across the membrane

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FT: fast reaction case Carrier-solute Complex reaction:

fA

fAACfA

AA KkC

CcKk

L

DC

L

kDJ

,

,, 1

Flux of solute A:

Flux due to diffusion

Flux due to complexation

ACCA

fA

A

CC

k,

0,

CA

AC

CC

CK

0,

0,

K...equilibrium constant

k...distribution coefficient

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Limiting cases

Fickean diffusion

Diffusion of the

complex

Total Flux

Fickean Flux

Damkolher number

Intermediate Region

5.0

2

Dt

CA,0>>CAC,0

CAC,0>>CA,0

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PlanarFlat

Laboratory

Hollow Fiber Industry

Spiral wound

SLM Geometry

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Comparing Flat Sheet Hollow Fiber

Feed and strip solutions mix directly and the integrity of separation is lost.

Small leaks do not seriously affect the performance

If the membrane liquid is contaminated, it can be easily be replenished.

The pressure drop in fibre bundles is larger

Can be fabricated easily in the lab

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Solvent loss

Carrier loss

Liquid flows

evaporationdisolutionlarge p

Irreversible side reactions

Solvent condensation

SLM Problems

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Stabilization techniques

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Classical Fields of Applications Facilitated transport of gases

OxigenCarbon DioxideCarbon MonoxideHydrogen SulfideOlefinsNitric OxideSensor development

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... more Applications

Immobilized Liquid MembranesMetal ion separations

Control of heavy metals pollutantsRecovery of: copper, uranium and cobalt

Separation of fermentation productsAcetic and citric acid

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...and more

Emulsion Liquid MembranesMetal ion extractionAmino acid extractionRemoval of species without chemical carriers

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Hollow fiber membrane-based enzyme-facilitated separation

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Emulsifier

Fresh emulsion

SettlerPurified Water

Mixer

Wastewater

Inner Phase

Recovered components

of the LM

Addition of LM components

Emulsion reflux

Inner PhasePurification using ELM

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Balance of using LM Benefits

High fluxes Very selective separations Ions can be concentrated Expensive extractants can be used

Major Limitations Rupture Long term stability