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SEPARATION PROCESS II

ADVANCE SEPARATION

PROCESS

ION EXCHANGE 1

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Topics :

Definition Operation Mode

Application

Resin Exchange Capacity

Equilibrium Relations

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DEFINITION

A reversible chemical reaction

where an ion from an aqueous phase

is exchanged for a similarly chargedion attached to an immobile solid

phase (resin)

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INDUSTRIAL APPLICATIONS

-Water softening

-Recovery of antibiotics/vitamin from

fermentation broth

-Decolourisation of sugar

-Wastewater removal of N,

heavy metal &

total dissolved solids

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Water Softening

Hardness in water, caused by calcium and magnesiumions, which form insoluble compounds, is removed by ion

exchange.

Ca

2+

+ Na2R

CaR + 2 Na

+

(12.4-1)(solution) (solid) (solid) (solution)

The water is filtered through an artificial zeolite (ion

exchange resin), such as Permutite, and the sodium in

the zeolite replaces the undesirable ions that are in thewater.

When the zeolite is saturated with these metallic ions, it

is washed with salt solution, which restores the sodium.

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Demineralisation

Removal of total dissolved solids

Uses both anionic and cationic resins

Acid

regenerant

Alkali

regenerantStorage tank

Degasifier

Cation

exchangerAnion

exchanger

treated water

H2O

HCO3

Ca Mg Na

Cl

H

ClHCO3

raw water

demineralisedwater

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OPERATION MODE

Batch

Resin is stirred with solution to be treated

in a reactor until the reaction is complete.

Spent resin is removed by settling. Regenerated and reused.

Continuous

Exchanged material is placed in a bed orpacked column.

Solution to be treated is passed through it.

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Operation Mode

(Similar to adsorption)

a) Continuous countercurrent: packed bed

C

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Design Considerations

Fixed-Bed Ion-Exchange Columns

- Rate depends on

Mass transfer ions from bulk to particle

surface

Diffusion in the pores of solid to surface

Exchange of ions at the surface

Diffusion of the exchange ion back to the

bulk solution

O i M d

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Operation Mode

a) Continuous countercurrent: fluidized-bed

ION EXCHANGE RESIN

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ION EXCHANGE RESIN

Natural occurring resin zeolites

Synthetic resins Strong-acid cation (SAC)

Weak-acid cation (WAC)

Strong-base anion (SBA) Weak-base anion (WBA)

Heavy-metal selective

chelating resins

P ti f th ti i

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Properties of synthetic resins

Type of resin CharacteristicsStrong-acid cation resins

(SAC)

Behave like strong acid

Highly ionised

Acid form (R-SO3H)

Salt form (R-SO3Na)

Weak-acid cation resins (WAC) Have weak-acid functional group (-COOH)

Strong-base anion resins

(SBA)

Highly ionised

Have strong-base functional group (OH)

Weak-base anion resins (WBA) Have weak based functional group

Heavy-metal selective

chelating resins

Similar to weak-acid cation

But have a high degree of selectivity for

heavy-metal cations.

Functional group EDTA

R-EDTA-Na

SYNTHETIC ION EXCHANGE RESIN

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SYNTHETIC ION EXCHANGE RESIN

Made from styrene and divinylbenzene.

Important properties Exchange capacity

Particle size

Stability

E h it (EC)

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Exchange capacity (EC)

Definition:

Quantity of an exchangeable ion that can betaken up.

Can be expressed as

Volume based

equivalent/L or meq/L (N) Weight based eq/kg or meq/g

Synthetic: 210 eq/kg, zeolite: 0.050.1 eq/kg

R

VC0EC V= throughput volume at stoichiometriccapacity

C0= initial concentration in meq/L

R = amount of resin in kg or L

E h it (EC)

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EC for resin

Expressed in terms of grams CaCO3 percubic meter of resin

Or grams equivalent per cubic meter of

resin

Unit conversion

Exchange capacity (EC)

333

3

3 m/CaCOg50m

eq/CaCOg50eq1

m

eq1

/

L

meq

valencyMW

Lmg

valencymolarity

Resin particle size

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Resin particle size

Important with respect to the

Hydraulics of the ion-exchange column

Kinetics of ion-exchange

Rate of exchange 1/dp2Particle

diameter

Stability

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Stability

Important for performance of the resin

Parameters:

Excessive osmotic swelling and shrinking

Chemical degradation

Structural changes caused by physicalstresses

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