L9 - Ion Exchange

8/10/2019 L9 - Ion Exchange

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Ion Exchange (IEX) Processwith focus on organic matter removal

CHBE 373 October 28th , 2014


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Water analysis

What needs to be removed from water?

Organics

Taste & odor compoundsSynthetic organic chemicals

Pesticides, herbicides and etc.

Natural Organic Matter (NOM)

Inorganics

Hardness (Ca+2 , Mg+2)Alkalinity (CO3

-, HCO3-2)

Salts (Na+, K+, Cl-, NO3-)

Scale forming chemicals (SiO2)

ionic : + & - charge

nonionic: no charge !

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Courtesy of Franois de Dardel, (dardel.info)

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IEX Applications

Water Treatment (softening, NOM removal)

Food Industry (sugar extraction)

Chemical Industry (metal extraction)

Pharmaceutical Industry (drug purification)

Other Applications

Mining

Analytical chromatography

http://www.seesgroup.com

http://www.nwce.co.uk

http://www.simontechnicalservices.com.au

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How IEX works ?

Exchange of the ions on the resin structure with the ones

present in the solutionCourtesy of Franois de Dardel, (dardel.info)

Counter ion

Ca+2

NO3-

Ca+2 + 2 Na-R Ca-R2 + 2 Na+

Cation IEX Anion IEX

NO3- + Cl-R NO3-R+ Cl

-

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How IEX works ?

Courtesy of ORICA

Courtesy of Lewatit

Cation +

Anion -

resin resinAdsorption

Regeneration

Removal mechanisms: Ionic exchange of negatively charged NOM

Adsorption of NOM

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Resin Structure

Polystyrene Polyacrylic

DVB


Gel Macroporous

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Resin Types

Remove hardness/alkalinity and other cations

Weakly Acidic Cation Exchange Resins (-COOH)

Strongly Acidic Cation Exchange Resins (-HSO3- )

Remove anions (NO3-, SO4

-2, HCO3-) and organics

Weakly Basic Anion Exchange Resins (-N(CH3)2)

Strongly Basic Anion Exchange resins (-N(CH3)3 OH)

o Type I (trimethyl amine)

o Type II (dimethyl ethanol amine)

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organics are typically

negatively charged


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Capacity

Exchange capacity (eq/L)

The number of ion exchange sites

Operating capacity (useful capacity)

The number of ion exchange sites where exchange has really

taken place during the loading run.

Operating capacity < Total capacity

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Operating capacity depends on:

Concentration and type of ions to be adsorbed

Service flow rate

Temperature

Type, concentration and quantity of regenerant

Type of regeneration process (co-flow, reverse flow)

Bed depth (reverse flow regeneration only)

Particle size of the ion exchange resins

Performance data and computer programs

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The typical operating capacity of a weak base anion

exchange resin is 70 to 90 % of the total capacity.

The typical operating capacity of SAC and SBA resins is about

40 to 60 % of their total capacity.

Resin type Total Capacity OperatingCapacity

WAC 3.7- 4.5 1-3.5

SAC 1.7-2.2 0.6-1.7

WBA 1.1-1.7 0.8-1.3SBA 0.9-1.4 0.4-0.9


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Throughput

Volume produced until the cartridge has to be replaced

Salinity of the feed water

Volume of resin in the cartridge

Type of resin used

Quality and efficiency of the off-site regeneration process

Endpoint (conductivity at which the unit is considered

exhausted)

With good resins and good regeneration, the throughput can be

approximately calculated as:Throughput [L] = 500 (Resin volume [L]) / (Salinity [meq/L])

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Water Softening

Remove hardness mainly Ca+2 and Mg+2

Strongly acidic cation exchange resin in Na+

form

Applications

Domestic and industrial water boilers

Laundries, Dish washer

Soft drink plants

Treated water quality

Residual hardness < 0.02 meq/L (1 mg/L as CaCO3) with

reverse flow regeneration

Regeneration: brine (NaCl as a 10 % solution)15


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Degasification

2 R-H + Ca (HCO3)2 R2-Ca+2 H+ + 2 HCO3

-

H+ + HCO3CO2 + H2O

(CO2 solubility @ 25 : 1.5 g/L)

Reduce the ionic load thus regenerant

CO2 residual 10 mg/L

A Liquicel membrane degasifier


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http://www.liquicel.com/http://www.liquicel.com/


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Degasifier


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Degasifier

Atmospheric degasser (bicarbonate + CO2

< 0.6

meq/L)

Forced draft degasser

Thermal degasser, (O2-CO2) Vacuum degasser, (1-5 kPa, O2-CO2)

Membrane degasser

Small size, for RO permeates with low pH and high

free CO2, small demineralization systems

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Water Dealkalization

Remove bicarbonate and temporary associated hardnessWeakly acidic cation exchange resin in H+ form

Applications

Beverages, Soft drink plants, municipal water

Treated water quality

Endpoint at 10 % of the raw water alkalinity

Contains CO2 which requires degasifier

Regeneration: Acid (preferably HCl at 5 % concentration)

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Water Demineralization

Remove all forms of ions from water CIX (H+) - AIX (OH-)

Treated water contains only traces of sodium and silica

Applications

Beverages, soft drink plants, municipal water

Treated water quality (lower than RO or Distillation)

Conductivity: 0.2 to 1 S/cm

Residual silica 5 to 50 g/L

Regeneration: strong acid and caustic soda

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Water Demineralization

Water for high pressure boilers

Rinse water used in electronic devices

Water for batteries

Water for laboratories


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Natural Organic Matter (NOM)

Negatively charged molecules (OH-, COOH-)

Wide range of molecular sizes

Measured as Dissolved Organic Carbon (DOC), UV254http://www.tut.fi

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Conventional Drinking Water TreatmentPlant

IEX

IEX

IEX

IEX can positively improve the performance of

entire treatment as well as individual units

http://www.gopixpic.com

Use of chemicals

Large footprint, Sludge

Clogging

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IEX as pre-treatment

Coagulation

Complimentary role

Lower coagulant dose

Lower pH adjustment

Better settling and dewatering characteristics of flocs

Disinfection-Oxidation

Lower chlorine dosage

DBPs precursor removal

Reduced fouling and plugging

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can remove hardness, alkalinity, and organics (NOM)

if they can be removed prior to adding coagulant (less

coagulant will be needed)

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Configurations

MIEX Process

SIX Process

Conventional Packed bed

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Operational aspect

Column Operation


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Operational aspect

Batch (well-mixed)

Courtesy of ORICA, www.miexresin.com 27


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Regeneration


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Regeneration

Co-flow regeneration

Reverse exchange (displacement

of low affinity with high affinity

ions)

Requires large excess of solution

to fully regenerate

Leakage in the next run

Counter-flow regeneration

Higher reg. Efficiency, lower reg.

quantity

Lower elution leakage

Lower resin inventory

Improved water quality

Hard to keep the resin bed

consolidated

Resin mixing

Purity of the regenerantCourtesy of Franois de Dardel, (dardel.info)

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Regenerant

NaCl (10% ) or NaOH (4%) for SBA

WBA, NaOH, NH3, bicarbonate

HCl for nitrate removal

De-alkalization WAC , HCl, H2SO4 (0.7%)

Demineralization (SAC)

o HCl (5%), efficient no precipitation

o H2SO4 (0.7-6%), cheaper and easier to store , less efficient,

potential for precipitation

o HNO3, exothermic reaction, dangerous, not recommended

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Brine reuse

Reduction of regenerant salt disposal and waste

requirements

Biological denitrification (sludge blanket reactors, 96%)

Sulphate reduction (62%)

GAC and or NF(contaminants ellimination)

Capacitive deionization (CDI)

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Column test : Breakthrough Curve

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Batch test : Jar Test

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Bottle point experiments

1. Constant concentration Vary adsorbent

2. Constant adsorbent Vary concentration

A

Measure initial C

Mix solution and adsorbents continuously

B

Measure C vs. t till equilibrium

Equilibrium : no further change in C vs. t

C

Measure residual C i.e., Ceq Construct q vs. Ceq for steps 1 and or 2

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Kinetics of IEX

m An+ +n Bm+ m An+ + n Bm+

nm

mn

nm

mn

BABA

BA

K

.

.

KAB : equilibrium constant (Thermodynamic) , selectivity coefficient

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qB

cA

qA

cB

Solid phaseLiquid phase

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Kinetics of IEX

n

BqBc

m

AcAqBAK

, A : substance adsorbed (mg/g) at equilibrium (solid phase concentration)

= ( )

0 : initial concentration of substance in the solution (mg/L)

, c : equilibrium concentration of substance in the solution (mg/L)

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m : resin mass (g)

V : solution volume (L)

@ Equilibrium & using [1]

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Kinetics of IEX

nmn

A

Am

A

ABA

C

Q

Y

X

X

YK

1

1

B

B

A

A

A

B

X

Y

X

Y

Separation factor: indicate ion

exchange preference

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3

Q : total exchange capacity of the IEX resin (eq/L)

C : total ionic concentration in the solution (eq/L)XA : fraction of A specie in solution

YA : fraction of A specie in solid phase, Note : =

=

, =

+ = 1 , + = 1

Considering above and eqn. [2]


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Kinetics of IEX

What does higher KAB mean ?

What does KA

B

=1 mean?

What does =1 mean?

Chen et al., 2006

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FractionofA

insolidphase,

YA

,

Fraction of A in liquid phase , XA ,

FractionofB

insolidphase,

YB

,

0

0.2

0.4

0.6

0.8

1


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Clifford , 1999


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IEX Calculations - IsothermsDegree of ion uptake depends on chemical and physical properties of the resin and

the solution chemistry

Equilibrium (sorption isotherm)

What is an isotherm ?

Langmuir theoretical isotherm

: substance adsorbed (mg/g) at equilibrium (solid phase concentration)

= ( )

0 : initial concentration of substance in the solution (mg/L)

: equilibrium concentration of substance in the solution (mg/L)

Langmuir constant (related to heat of adsorption)

: maximum sorption capacity

e

e

e Cb

Cbqq

.1

..max

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m : resin mass (g)

V : solution volume (L)


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Linearized Langmuir equation

e

ee

Cb

Cbqq

.1

..max

1

=

1

+

1

.

1

1

1

.

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q

C

Favorable : 1/n < 1

Linear : 1/n = 1

Unfavorable : 1/n > 1

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Chemical Equivalence


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An amount of material that will release or react with an Avogadro's number of

electrical charges (i.e., 1 mol) on molecules like OH-, H+ and or electrons.

The equivalent weight of an element is its gram atomic weight divided by its valence

Acid : the amount of the acid that donates one mole of H+ in reactions with bases

Base : the amount of the base that will react with one mole of H+

=

, where n is the number of H+, OH- , # of valence

= ()

1 mol H3PO4 = 3 equivalents H3PO41 mol H3PO4 = 98 grams H3PO4 ; 1 equivalent H3PO4 = 32 grams H3PO41 eq H2SO4 = 49.04 g H2SO4

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Calculate the #eq of Ca(OH)2 in 6.32 g of Ca(OH)2

=MW

=

4.9

= 37.05

Using the formula:

# . 2 =

=

6.32

37.05= 0.171 .

Substances react with each other in stoichiometric, or chemically equivalent,

proportions

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Think-pair-share

Strong base anion exchange is used to remove nitrate from the water with

following characteristics

Resin capacity = 2 eq/L

Selectivity for nitrate = 5

Maximum volume of water that can be treated if 15 L of resin is used?

ion Conc. mg/L ion Conc. mg/L

Ca+2 30 Cl- 106.5

Mg+2 24.30 SO4

-2 0

Na+ 49.9 NO3- 150

Blue baby syndrome

L9 - Ion Exchange

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